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The geologic and paleoceanographic evolution of the Serranilla Basin, Northern Nicaragua Rise, Caribbean Sea

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Title:
The geologic and paleoceanographic evolution of the Serranilla Basin, Northern Nicaragua Rise, Caribbean Sea
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x, 212 leaves : ill. ; 29 cm.
Language:
English
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Duncan, David S.
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University of South Florida
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Tampa, Florida
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Subjects / Keywords:
Geology, Stratigraphic -- Serranilla Basin -- Nicaragua   ( lcsh )
Paleoceanography -- Nicaragua -- Serranilla Basin   ( lcsh )
Plate tectonics -- Caribbean Sea   ( lcsh )
Dissertations, Academic -- Marine Science -- Doctoral -- USF   ( fts )

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General Note:
Includes vita. Thesis (Ph. D.)--University of South Florida, 1997. Includes bibliographical references (leaves 175-183).

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University of South Florida
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University of South Florida
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aleph - 024207112
oclc - 38197323
usfldc doi - F51-00201
usfldc handle - f51.201
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SFS0040011:00001


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THE GEOLOGIC AND PALEOCEANOGRAPHIC EVOLUTION OF THE SERRANILLA BASIN: NORTHERN NICARAGUA RISE, CARIBBEAN SEA by DAVIDS. DUNCAN A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Marine Science University of South Florida August 1997 Major Professor: Albert C. Hine, Ph.D.

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Graduate School University of South Florida Tampa, Florida Ph.D. Dissertation This i s to certify that the Ph.D. Dissertation of DAVIDS. DUNCAN with a major in Marine Science has been approved by the Examining Committee on June 13, 1997 as satisfactory for the dissertation requirement for the Doctor of Philosophy degree Examining Committee: Major Professor: Albert C. Hine, Ph.D. Member: AndreW. Droxler, Ph. D. Member: Pamela Hallock-Muller, Ph.D. Member: David F. Naar, Ph.D. Member: Terrence M. Quinn Ph.D.

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TABLE OF CONTENTS LIST OFT ABLES m LIST OF FIGURES IV ABSTRACT Vlll CHAPTER 1. GEOLOGIC AND PALEOCEANOGRAPHIC SETTING 1 General Introduction 1 Tectonic Setting 5 Oceanographic Setting 13 CHAPTER 2 TECTONIC CONTROLS ON SERRANILLA BASIN EVOLUTION: A SEQUENCE STRATIGRAPHIC APPROACH 17 Introduction 17 Previous Studies 20 n Age Control 22 Results 25 Bathymetry 25 Deep Structure 28 Dredge Hauls 32 Sequence Stratigraphic Analysis 37 Sequence A 37 Seismic Stratigraphy 37 Structure 43 Sequence B 48 Seismic Stratigraphy 48 Structure 56 Sequence C 56 Seismic Stratigraphy 56 Structure 65 Sequence D and E 65 Seismic Stratigraphy 65 Discussion 75 Seismic Reflectors and Sequence Boundaries 75 Tectonic Contro l s on Sequence Formation 80 Serranilla Basin Geologic Evolution 86 Oligocene? to Early Miocene 87 Early to Late Miocene 90 Late Miocene to Present 93 Conclusions 96

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CHAPTER 3. LATE QUATERNARY SEDIMENTARY AND PALEOCEANOGRAPHIC EVOLUTION OF THE SERRANllLA BASIN 97 Introduction 97 Methods 104 Results 107 Modem Sedimentation Patterns 1 07 Detailed Core Analysis 121 Isotope Stratigraphy 129 Age/depth 129 Sediment Components 136 Discussion 153 Controls on Modem Sedimentation Patterns 153 Echo Character Type ill 153 Echo Character Type llA 156 Echo Character Type Im 162 Echo Character Type illC 163 Echo Character Type IllA 163 Quaternary Cyclicity 164 Neritic Production: Sea Level and Dissolution 164 Planktonic Production: Nutrients and Current Winnowing 167 Non-Carbonate Input: Dilution and Sources 169 Causes of Quaternary Cyclicity 170 Conclusions 173 REFERENCES 175 APPENDICES 184 Appendix I. Core Descriptions 185 Appendix II. Geochemical Data 196 VITA End Page ll

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LIST OF TABLES Table 2.1. Seismic units identified in this study with interpreted ages and seismic boundary and facies characteristics 41 Table 3 .1. A compilation of echo character types from several studies 109 Table 3.2. Piston core sites depths and information on turbidite content 119 Table 3.3 Sediment components and their origin 165 ll1

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LIST OF FIGURES Figure 1.1. Map showing the entire northern Nicaragua Rise (NNR) in the Caribbean Sea 3 Figure 1 2. Campanian (80 Ma) reconstruction showing the location of the NNR with respect to the Greater Antilles Arc, Yucatan, and Chortis Block 6 Figure 1.3. A NW-SE cross -section through the crust from the Yucatan Basin to the Colombian Basin from A to A' as s hown in Figure 1 9 Figure 1.4. Four industry wells across the NNR showing depth, age and lithology obtained in exploratory wells 12 Figure 1 5. Idealized model of breakup of carbonate megabank showing orienttation of strike-slip faults and location of the Cayman Trough 14 Figure 1.6. Direction and magnitude of the currents in the Caribbean 15 Figure 2.1. Location map for seismic data set used in this study 23 Figure 2 .2. Bathymetry of the Serranilla Basin using 100 m contour intervals ba se d on 3 5 kHz and sing le channel, high-resolution data 24 Figure 2.3. Comparison of seismic data from the Serranilla Basin with data used in the Pedro Basin to obtain chronostratigraphic control 27 Figure 2.4. Line drawing of UTIG processed MCS data crossing the Serranilla Basin 30 Figure 2.5 Detail of processed UTIG MCS data crossing the PFZ 31 Figure 2.6. Line drawing s of industry MCS data used to help define the deep structure of the Serranilla Basin 34 Figure 2 7 Representative thin sections from dredge haul 31 and 3 7 35 Figure 2.8. Seismic location of dredge 37 showing ambiguity in tying into se ismic sequence 36 Figure 2 .9. Dredge haul site 22, along the flank of a mound on the seafloor 38 Figure 2.10. Dredge haul site 24 on the eastern flank of Hunapu Bank 39 Figure 2.11. Dredge haul location 38 along the base of the Serranilla Bank 40 IV

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Figure 2 .12. Single-channel seismic data showing sequence boundary R 1, interpreted here based on the lateral onlap terminations of overlying reflectors 42 Figure 2.13. Structure/contour map to sequence boundary R1 45 Figure 2.14. Line drawing and processed, single-channel data for line 21 47 Figure 2.15. Processed single-channel seismic line 12 with interpretation 50 Figure 2.16. Seismic facies map for unit B l of sequence B 51 Figure 2.17. Seismic facies map for unit B.2 of sequence B 52 Figure 2.18. Seismic facies map for unit B.3 of sequence B 53 Figure 2.19. Sediment isopach map of sequence B show ing the depositional patterns 55 Figure 2.20 Proce sse d si ngle-channel seismic line 15 with interpretation showing the marginal buildup identified in the struc ture/contour map 58 Figure 2.21. Structure/contour map to sequence boundary R2 60 Figure 2 22. Processed single-channel seismic date (line 20) with interpretation 62 Figure 2.23. Seismic facies map of unit C.l of sequence C 63 Figure 2.24. Seismic facies map of unit C.2 of sequence C 64 Figure 2.25. Map s howing fault locations interpreted from the seismic data 66 Figure 2 26. Sediment i sopach map for seq uence C 68 Figure 2.27 Line drawing of single-channel se ismic line 8 70 Figure 2.28. Structure/contour map to sequence boundary R3 72 Figure 2.29. Seismic facies map of sequence D 73 Figure 2.30. Seismic facies map of sequence E 74 Figure 2.31 Sediment isopach map of combined sequences D and E 77 Figure 2.32 Processed single-channel seismic line 9 and interpretation 79 Figure 2 .33. Compilation of tectonic events in different areas along the NCPBZ and the NNR 82 v

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Figure 20340 Map showing location of significant fault zones along the NCPBZ and their relationship to the study area 85 Figure 20350 Oligocene ?/ear ly Miocene reconstruction of the Serranilla Basin showing isolated basins surrounded by marginal buildups 89 Figure 2 0360 Middle to late Miocene reconstruction showing the emergent reef?margin along the western basin 92 Figure 20370 Late Miocene-early Pliocene reconstruction showing the drowning and step-back along the western portion of the basin 95 Figure 3 010 Shows the southern hemisphere circulation and the source of a portion of the waters that enter the Caribbean 101 Figure 3020 Shows a north-south cross-section through the Atlant ic Ocean indicating circulation patterns, with depth, during modem ( interglacial) and glacial times 102 Figure 3030 Basemap s howing 3 05kHz coverage and piston core loc atio n s for the Serranilla Bas in 105 Figure 3.4 0 Echo character type m from 3 05kHz data 111 Figure 3050 Echo character type IIA from 305kHz data 112 Figure 3060 Echo character type IIB from 305kHz data 113 Figure 3 0 7 0 Echo character type illA fro m 3 05 kHz data 114 Figure 3080 Echo character type illC from 305kHz data 115 Figure 3 0 9 0 Echo character map based on distribution of 3 05kHz echo character types 117 Figure 30100 Piston core location s s howing turbidite frequency 120 Figure 3 0110 Piston core 27 sedimentological and isotopic data versus depth based on a 10 em samp ling interval down the entire core 123 Figure 30120 Piston core 35 sedimento logical and isotopic data versus depth based on a 10 em sampl ing interval down the entire core 125 Figure 30130 Piston core data for V18-357 126 Figure 30140 Carbonate mineralogy of cores 35 and 27 based on X ray diffraction analysis of the fine fraction ( <63 J.Lm) 128 Figure 3 0150 The SPECMAP oxygen isotope curve, isotope stage picks, and the age estimates for each of the isotope stages (from Imbrie et alo, 1984) 131 vi

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Figure 3.16. Oxygen isotope stratigraphy for core 27 and 35 133 Figure 3.17. Age/depth plot for core 27 134 Figure 3.18. Age/depth plot for core 35 135 Figure 3.19. Percent coarse (A) and fine (B) fraction curves versus age downcore 138 Figure 3.20. Percent fine aragonite (A) and percent fine Mg-calcite (B) to bulk se diment versus age 141 Figure 3.21. Percent fine calcite (A) and percent non -carbo nate (B) to bulk se diment versus age 143 Figure 3.22 Bulk accumulation rates of both cores versus age 145 Figure 3.23. Accumulation rate curves for the coarse (A) and fine (B) fraction of each core versus age 14 7 Figure 3.24. Fine aragonite (A) and fine Mg-calcite (B) accumulation rate for each core versus age 150 Figure 3.25. Fine calcite (A) and non carbonate (B) accumulation rate for each core versus age 152 Figure 3.26. Echo character map based on 3.5 kHz echo character types of Damuth and Hayes ( 1977) and Mullins et al. ( 1979) 155 Figure 3 27 Core transect #1 from northwest to southeast in the eastern portion of the basin 158 Figure 3.28. Core transect #2 from west to east in the southern portion of the basin 161 Vll

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THE GEOLOGIC AND PALEOCEANOGRAPHIC EVOLUTION OF THE SERRANILLA BASIN : NORTHERN NICARAGUA RISE, CARIBBEAN SEA by DAVIDS. DUNCAN An Ab s tract Of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Marine Science University of South Florida August 1997 Major Professor : Albert C. Hine, Ph. D. viii

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The Serranilla Basin lies at the western end of the northern Nicaragua Rise, which is composed of a series of carbonate banks separated by basins and seaways that stretch from Jamaica to the Nicaragua/Honduras coast in the Caribbean. The geologic and paleoceanographic development of the basin has been affected by its location. Not only does the northern Nicaragua Rise lie along the active Northern Caribbean Plate Boundary, it represents an important 'gateway' to global thermohaline circulation. Because of this, the basin provides an opportunity to investigate the geologic evolution in a sequence stratigraphic framework with respect to possible tectonic controls, and also to study the basin's role in recording the paleoceanographic evolution of the Caribbean during the late Quaternary. Single-channel, high-resolution seismic data were calibrated to rock dredges and ODP Site 1000, to define the sequence stratigraphy that constitutes the early Miocene to Quaternary infilling of the basin. Five seismic sequences were identified within the Serranilla Basin. The two lower sequences (A and B) are interpreted as neritic and shallow peri platform deposits infilling three distinct basins that make up the early to late Miocene Serranilla Basin. The three upper sequences (C through E) are interpreted as periplatform and pelagic deposits interspersed with turbidites, and in some areas, megabreccias. Faulting is prevalent in sequences A through C in the central basin and becomes progressively younger toward the south, disrupting the sea floor in places and perhaps indicating renewed activity along the Pedro Fracture Zone, although there are no teleseismic (large magnitude) earthquakes recorded from this area. The timing of sequence boundary formation has been correlated to tectonic activity along the Northern Caribbean Plate Boundary and the Central American Seaway. Although a direct genetic relationship is not proven, regional tectonic changes are considered more IX

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important than eustatic sea-level changes in controlling depositional sequence formation in the Serranilla Basin. Piston cores were taken in the basin to investigate the late Quaternary paleoceanographic evolution in this part of the Caribbean. Throughout the l ate Quaternary, turbidite deposition makes up a significant portion of the sediments infilling the Serranilla Basin. These turbidites infill against the predominant Caribbean Current direction, indicating that other factors (e.g., seasonal reversals in surface currents due to storms, or tectonic activity) play a role in turbidite deposition. This differs from other basins studied along the northern Nicaragua Rise and the Bahamas. Glacial and interglacial deposition are controlled by differing paleoceanographic factor s during the l ate Quaternary. Glacial deposition is controlled by 1) current-winnowing of sediments related to strengthening of currents, perhaps due to increased trade winds and 2) increased dilution by non-carbonate inputs, most likely from South America and brought in by these same currents. Interglacial deposition is controlled by 1) sea level flooding of shallow banks, resulting in increased neritic production and export to the basin, 2) dis so lution of metastable carbonates and 3) increased nutrients due to upwelling providing for increased productivity. Overall, the periplatform sediments indicate a longterm (500 ky to present) increase in currents and decrease in carbonate dissolution in this part of the Caribbean and support a link between Southern Ocean circulation and North Atlantic Deep Water formation. Abstract Major Professor: Albert C. Hine, Ph.D Professor, Department of Marine Science Date Approved : >/i/f + X

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CHAPTER 1 GEOLOGIC AND PALEOCEANOGRAPHIC SETTING General Introduction The northern Nicaragua Rise (NNR) consists of a series of carbonate banks (20-50 m deep), separated by basins and seaways (200-1500 m deep), that extend from Jamaica to the Central American continental shelf in the western Caribbean Sea (Fig 1.1 ). Bounded on the north by the Cayman Trough, an oceanic basin formed by s eatloor spreading, these ba si n s lie within the Northern Caribbean Plate Boundary Zone (NCPBZ), a 200 -250 km wide deformation zone, which separates the Caribbean plate from the North American plate (Mann et al 1990). The Serranilla Basin is the westernmost of the basins segmenting the NNR. The Serranilla Basin is a flat-floored, semi-circular bathymetric depression (about 100 x 100 km; 1100-1200 m deep) bounded to the north and west by carbonate banks and s hallow s eaways (Diriangen and Rosalind channels) The Pedro Fracture Zone separates the Serranilla Basin from the southern Nicaragua Rise, which in tum is separated from the Colombia Basin to the south by the Hess Escarpment (Fig. 1.1 ). The Serranilla Basin lies in an area of the Caribbean that is poorly understood from a geologic perspective. However this basin is important in understanding the tectonic and paleoceanographic evolution of the region. The NNR plays an oceanic gateway role in the global thermohaline circulation system, allowing warm, saline equatorial waters to be tran s ported northward into t he Gulf of Mexico, and eventually to the North Atlantic

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2

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Figure I. I. Map showing the northern Nicaragua Rise (NNR) in the Caribbean Sea The Serranilla Basin is identified in the square. Locations of faults identified along the NCPBZ are shown The location of UTIG lines 10 and 11 are shown, as well as ODP Site 1000 used for seismic chronostratigraphic correlations. Contour interval is 1000 meters with the exception of the 100 meter isobath showing the carbonate banks (shaded) along the NNR. The cross section in Figure 1.3 is indicated by A-A'

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Miskito Bank l 5 N 500 kilometers s s w so w 1s w

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Understanding the structural controls and early evolution of the Serranilla Basin may help con s train the timing of the onset of oceanic thermohaline circulation during the Cenozoic Tectonically the NNR as a whole, and the Serranilla Basin in particular should provide geologic evidence of the complex s trike-slip movement that characterizes the NCPBZ. Understanding the response of carbonate basins along the NNR to a changing tectonic regime may provide insight into other analogous plate boundary depositional settings. Furthermore, the development of carbonate sequences within this deep-basin setting may bring into question the view that eustatic sea-level change is solely responsible for sequence boundary formation (Vail et al., 1977; Posamentier et al., 1988; Sarg, 1988). On a different scale the study of the Quaternary paleoceanography of the Serranilla B as in has the possibility of improving our understanding of global climate variability. In addition to the basin's role as a gateway, the sediments themselves may provide, through their depositional patterns and geochemical signatures, a means of identifying oceanographic changes in the past. In fact, the paleoceanographic importance of the Serranilla Basin sediments may be as a recorder of global circulation changes related to glacial/interglacial variability. The main goal of this study is to define the geologic and paleoceanographic evolution of the Serranilla Basin and tie this evolution into a larger regional and global context. Several specific objectives are: 1) develop a sequence stratigraphic framework based on single-channel, high resolution seismic data, which may be used to address the controls (eustatic tectonic, climatic, and biologic) on the structure and infilling of the basin 2) correlate the seismic data with nearby Ocean Drilling Program (ODP) Site 1000 and rock dredges of known age from within the basin, to constrain the timing of sequence deposition Relate the stratigraphy to events along the NCPBZ 3) investigate the late Quaternary paleoceanography and sedimentation patterns with a series of piston cores taken at different depths within the basin Determine any regional or 4

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global linkages by comparing geochemical and sedimentological parameters within the Serranilla Basin with other similar records. Tectonic Setting The plate tectonic evolution of the Caribbean is much debated and as yet, not well understood. Since Molnar and Sykes (1969) helped define the boundaries of the Caribbean plate using earthquake hypocenters, numerous studies have focused on the origin and evolution of the plate, as well as the islands and bathymetry that make up the plate borders. The Decade of North American Geology volume on the Caribbean region lists thirteen different models for the evolution of the Caribbean area (Pindell and Barrett, 1990). At present, the most widely accepted model proposes that the Caribbean plate originated in the Pacific, as part of the Farallon plate (Pindell and Barrett, 1990). During the separation of the North and South America, the early Farallon/Caribbean plate began a progressive eastward drift into this opening (Freeland and Dietz, 1972; Malfait and Dinkelman, 1972; Sykes et al., 1982; Pindell et al., 1988; Ross and Scotese 1988; Pindell and Barrett, 1990). The theory that the Caribbean Plate originated in the Pacific has received recent support from paleogeographic studies based on fossil Radiolaria (Pindell 1990; Montgomery et al., 1994a, 1994b ). The capture of this portion of the Farallon Plate is believed to have occurred during the Late Cretaceous (Campanian, 80 Ma) as the North and South American Plates overode the Farallon Plate (Pindell and Barrett, 1990) (Fig. 1.2). Other lines of evidence have been cited to support a Pacific origin for the Caribbean plate. Despite isolated basins within the Caribbean showing magnetic anomalies (Grenada Basin Yucatan Cayman Trough) there is no evidence of seafloor spreading magnetic anomalie s in the deep Caribbean to account for an in situ formation of a plate (Duncan and Hargraves, 1984; Burke, 1988; Case et al., 1990). Any magnetic anomalies are believed to 5

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Mexico I \ Atlantic I Ocean I /\ \ l. \. "\ Bahamas '-.: , .......... ___ -Anomaly 34 Spread ing Center Car ibbean :oceanic : South America : : Campanian about 80 rna Figure 1.2. Campanian (80 Ma) reconstruction s howing the location of the NNR with respect to the Greater Antilles Arc Yucatan, and Chortis Block. The NNR is believed to repre sen t islandarc type crust. V's represent areas of active volcanism, while subduction zones are marked with dark triangles pointing in the subduction direction Modified after Burke ( 1988) and Case et al. ( 1990).

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be covered under the well-known seismic horizon, Horizon B, which has been identified within the Colombian and Venezuelan basins as Late Cretaceous basalt overlying pelagic sediments (Donnelly et al., 1990). This Late Cretaceous basalt resembles oceanic basalt plateaus identified in the western Pacific (e.g Ontong Java Plateau), and may represent off-ridge volcanism as the Farallon/Caribbean plate passed over the Galapagos hotspot prior to its passage into the present Caribbean (Duncan and Hargraves, 1984 ). The initiation of volcanism at the hotspot matches well the age of Horizon 'B' basalts (100-75 Ma) The details of the development of the NNR along the northern plate boundary is perhaps the least understood aspect of Caribbean tectonic reconstructions. These reconstructions of the northern plate boundary generally depict the NNR as part of an island-arc originating in the East Pacific during the Cretaceous (Pindell and Barrett, 1990). Reconstructions of Burke ( 1988) and Pindell and Barrett ( 1990) show the location of the NNR during the Late Cretaceous (Fig. 1.2). Perfit and Heezen ( 1978) argue that this island-arc formed during the Laramide Orogeny (Maastricthian) based on petrographic, radiometric, and paleontologic data There is no evidence for pre-Cretaceous rocks along the NNR (Pindell and Barrett, 1990). Based on gravimetric (Bowin, 1976), magnetic and seismic refraction surveys (Ewing eta!., 1960; Edgar et al., 1971), a model for the crust underlying the NNR has been developed by Case et al. (1990) (Fig 1.3). This model indicates crustal thickness of about 25 km underlying the NNR, making it intermediate between normal oceanic and continental crust, which is compatible with an island-arc origin Throughout the Paleocene to early Eocene, structural deformation and rifting was widespread along the NNR and on Jamaica (Holcombe et al., 1990) Mann and Burke ( 1984) li s t sixteen Cenozoic rifts forming in the northern Caribbean beginning with the olde s t Paleogene Wagwater Trough on Jamaica, and getting progressively younger 7

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8

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Figure 1.3. A NW-SE cros s s ection through the crust from the Yucatan Ba s in to the Co l ombia n Basin from A to A' as shown in Figure 1. Seismic ve locities are indicated and ar e ba se d on the work of Ewing et al. (1960), and Edgar et al. (1971). Note the int e rmediate nature of the crust underlyin g the NNR perhaps indicatin g an island-arc origin.

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E .... o. .!:! C':! A C':! .... 3: C':! uo Cl) tt +N. Am. Plate Mantle Peridotite D Cla s tic sedimentary strata c 0 0 .... E "' u eNic a ragua C':! C':! Colombian tt u
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westward. They infer three pre-Oligocene rifts west of Jamaica along the NNR based on bathymetry, which would include the Serranilla Basin. Another important component in the tectonic history of the area at this time is the formation of the Cayman Trough (Fig 1 .1). Early studies found evidence for seafloor spreading based on bathymetric and seismic reflection data (Holcombe et al., 1973) Later, with the use of magnetic anomalies and heat-flow data, Rosencrantz and ScJater (1986) determined that the onset of seafloor spreading within the Cayman Trough began during the earl y to middle Eocene ( Rosencrantz et al., 1988). Beginning in the middle Eocene, s ubsidence and submergence of Jamaica and the NNR occurred, virtually excluding terrigenous sediment sources (Holcombe et al., 1990) Exploratory industry oil wells along the NNR penetrate to depths of >4 km, with most bottoming out at -2 km. A cross section along the NNR shows thick sections of carbonates unconformably over conglomerates or igneous basement (Arden, 1975) (Fig. 1.4 ). In Jamaica, where the geologic column is better defmed, these carbonates make up the Paleogene Yell ow Limestone and the Neogene White Limestone. Some of these carbonates are of exceptional purity (e g White Limestone Jamaica;< 2% terrigenou s) (Horsfield a nd Roobol, 1974; Arden, 1975). Partly due to the lack of terrigenous depo sition during this time the late Eocene to middle Miocene is believed to be a time of tectonic quiescence in Jamaic a, perha p s related to strikesl ip movement farther to the north a long the Oriente Trans form Fault (Arden, 1975). Final emergence of Jamaica and southward ti ltin g of the entire NNR is thought to have occurred during the middle Miocene in response to major lateral movement along the Cayman Trough (Arden, 1975) The pre se nt geometry and spreading rates of the Cayman Trough appear to be a post-early Miocene phenomena based on reinterpretation of magnetic lineations (Rosencrantz, 1995). There is evidence for continuing fault-movement and tilting o f Jamaica and the NNR throughout much of the Neogene ( Robin son, 1971 ; Horsfield, 1975; Mann et al., 1990; Leroy et al., 1996) 10

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11

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Figure 1.4 Four industry wells across the NNR showing depth age and lithology obtained in exploratory wells ( Holcombe et al., 1990). Volcanic basement occurs at approximately the same depth in all wells.

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Q) s:: Q) (.) 0 Q) s:: Q) Colombia Berta -1 16 13' N 82 04' w 27 (.) -------------0 u.l T.D 2265 ft 1:::::::::1 Limestone Fossiliferous Limestone D_olomitic -L1mes t one I I Siltstone t-..-.-.-.-.-.-A Claystone ---Occidental Miskito -1 14 52.4' N 81 41.2' w Q) s:: Q) (.) 0 17 Andesite r x x x x1 ......... ,.. "' ,.. "' "' 1 Diorite Granodiorite -??-??--. .,..... --)()() Mobil Turquesa -I 0 c c u u o.S? 0 TU I I '}1 I I Occidental Pedro Bank -I 16 56 .2' N no 48' w 16 Q) s:: Q) (.) 0 u.l Q) ....... '"0 '"0 ...... lll..l .. Ll .l 1 7 77 7 7 7 7 7 ---A--.................. T D 2021 ft / Serrnnilla /......,. ...._ / Bank (' ,.I 'v-

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Two alternate theorie s invoke t he NCPBZ tectonic s for the formation of the present bathymetry of alt ernat ing s h a llow banks a nd seaways along the NNR. Drexl e r et al. ( 1989; 1 992) propose th a t the NNR was a car bonate megabank from the late Eocene throu g h mjdd1e Miocene, a nd subsequent seg mentation and foundering led to the present day physiography and oceanographic circulation (Fig. 1.5) A mjddle Miocene jump of l eft l ate ral s tri ke-s lip displacement alon g the northern Oriente Transform Fault t o the more so uthern Enriquillo-Plantain Garden Fault zo ne i s belie ved to be the mechanism responsible for th e onset of thi s seg mentation (Drexler et al. 1992b) (Fig 1.5) Thi s cor r e late s well the f in a l e m erge nce a nd tilting of Jamaica during the late mjddle Miocene ( Ro se ncr a nt z and M an n 199 1 ). This differ s from the Mann and Burke (19 8 4) hypothe s is, that argu es for progressively younger rifting, from eas t to west, along the rise, beginning in the Paleocene. The passage of the Caribbean plate around a continental promontory (Yucatan) a t an oblique angle, with s ub se quent wrench f a ultin g, i s belie ve d to b e the m ec h anis m responsible for the se troughs (Mann and Burke, 1984). Oceanographic Setting The Serranilla Basin lies in th e tropical Caribbean, with normal oceanic s urfa ce wate r sali nities a nd s urface temperatures ra nging f rom 26-29 C. Surface currents throu g h t he Serranilla Basi n are a component of the Caribbean Current, which i s an extension of the Guiana Current that e nter s the eastern Caribbean through various pa sses in the Le sse r Antilles (Fig. 1.6) (Wust, 1964 ). The b a nk s and sea way s of the NNR act as a gateway for t h e Caribbean Current to pass through th e Yuc ata n Channel into the Gulf of M ex ico a nd l a t er join w ith the Gulf Stream ( Wu st, 1 964 ). The waters that make up the Caribbean Curre nt are highly st ratified down to about 1200 m and thi s i s related to th e sill depth s that 13

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Core 27 Oxygen isotope stratigraphy 2 0 12 3 4 5 6 7 9 10 II 12 13 -1. 5 llj s.s ILl? \" 'rv/1 J\ X ;; AJ. oo I 335 0 S.2 5.4 6\;N.o 7_ y \ r:o 0 0 6.3 6.S 7.4 8 0 10.0 42 8j 8 .6 0.5 6.4 6 6 8 2 u u 13.11 v.r 4 12.2 v 100 200 300 400 500 600 Depth in core (em) 700 800 900 1000 11 00 Core 35 Oxygen isotope stratigraphy -2.0 12 3 4 5 6 7 8 9 s.s -1.5 1 1 -1.0 c: 9.1 ::1 2 0 (.) -0.5 WIJ'' 0 S.l 00 .0 rt:> 0.0 2.2 6 3 7 .4 83 4 .2 u u 0 5 u u u 1.0 X v 100 200 300 400 500 600 700 800 900 1000 Depth in core (em) 133

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Early Oligocene Middle Miocene Late Middle/Late Miocene Swan Is land Transform F a ult Oriente Transform Fault Enriqui ll o-P i antain Garden Fault Zone Cir cumtroplc:ai Cu rrent Clrcumtroplc:a l C u rrent SIT OFf EPGFZ c::J -Nort hern Nicaragua Rise S hall ow Carbonate Bank O cea ni c Crust Figu r e 1 .6 Id ea li zed m o d e l of breakup of carbo nat e megabank s h owing orie n tatio n of s t rikes li p fault s and the l ocatio n of th e Cayman Troug h. The propose d mechanism for segmentation and foun d e rin g of the megabank i s the mig r ation of left-lateral st rik e-s lip fro m the Oriente Transform Fault to t h e Pl a nt a in G a rd en Enriquillo Fault Zo n e (D r ox l e r et a l. 1 992) 14

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25 20 -VI 1s to 85. 80" --Florida Current <20 em/sec 75 70 65 20-41 em/sec 41-61 em/sec 61-82 em/sec >82 em/sec .April Greater Antilles Windward Jamaica Passage Caribbean Current <330--Ane gada Pass age 1950m Jungfem II ... 0 Lesser eJ> Antilles \ 0 Figure 1.6 Direction and magnitude of the currents in the Caribbean Modified from Wust (1964) and Gordon (1967).

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control entry into the Caribbean from the Atlantic (Gordon, 1967). Below about 1800 m, the deep Caribbean is nearly homogenous. It has been estimated that volume transport through the Caribbean is approximately 30 Sv (1 Sv = 106m3 s-1), two-thirds corning through the Lesser Antilles and one-third through the Windward Passage (Kinder et al., 1985). Flow velocities have been calculated and are predicted to decrease with depth. Measured surface currents average 61-82 em/sec during the spring and 42-61 em/sec during the fall (Gordon, 1967) (Fig. 1.6). In the western Caribbean, surface velocities increase up to 80 em/sec (Kinder et al., 1985). Measurements taken in the Bawihka Channel and over the banks of the NNR indicate velocities may reach over 100 em/sec (Triffleman et al., 1992). Although seasonal storms may temporarily alter surface circulation patterns, the dominant control on surface currents is the Northeast Trade Winds, which are consistent, year-round, at between 5-10 rnls (Hastenrath and Lamb, 1977). The deeper stratified layers of Subtropical Underwater (100200 m depth) and Antarctic Intermediate Water (600-800 m depth) average 30-40 em/sec and -15 em/sec respectively (Gordon, 1967). 16

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CHAPTER 2 TECTONIC CONTROLS ON SERRANILLA BASIN EVOLUTION: A SEQUENCE STRATIGRAPHIC APPROACH Introduction The banks, basins and seaways that make up the Serranilla Basin carbonate system lie within the tectonically active Northern Caribbean Plate Boundary Zone (NCPBZ) (Mann et al 1990). This plate boundary is characterized by sinistral strike-slip movement of the Caribbean Plate past the North American Plate (Molnar and Sykes, 1969 ; Sykes et al., 1988, Pindell and Barrett, 1990). The Serranilla Basin system is bounded to the north by the Cayman Trough, an area of active seafloor spreading, and to the south by the Pedro Fracture Zone (Fig 1.1). The active tectonic setting of the Serranilla Basin system makes it unique when compared to other well-studied carbonate systems. For instance, the northern Bahamas Platform, probably the most intensively studied of all carbonate systems, represents a tectonically stable environment (Sheridan et al., 1988) Although believed to have originally formed along a transform fa ult, the present geometry and structure of Great Bahama Bank can be attributed to a passive tectonic setting. Aggradation and progradation of the bank margins are dominant controls on the evolving structure of the platform. In their study based mainly on seismic data, Eberli and Ginsburg ( 1989) have documented the Cenozoic progradation and infllling of two seaways th a t have allowed the present Great Bahama Bank to coalesce from three separate banks. 17

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The southern Baham as, on the other hand is currently undergoing collision with Hispaniola, and represents an active tectonic regime (Mullins et al., 1991 ) Drowning and 30 km of backstep of the Mouchoir Bank h as occurred during the late Miocene-early Pliocene as a result of collisional tectonics (Mullins et al., 1991; 1992). The drowning in this case is attributed to tectonic tilting and increased subsidence. The Serranilla B asi n system differs from these two modern analogs in that it developed within a strike-s lip tectonic setting. Two other modem analogs deserve mention because they have been used by Handford and Loucks ( 1995) in their compilation of important carbonate platforms, to illustrate sequence stratigrap hic principles. These analogs are Belize and the northeast Yucatan Peninsula. Both occur along transform margins, a tectonic setting similar to the Serranilla Basin, but each is attached to a continent providing a source for sil iciclastic s ediments. The Serranilla Basin is essentially detached, representing a nearly complete carbonate system at present. The most obvious ancient analog for carbonate systems in an active tectonic setting wou ld be the Tethyan carbonate platforms of the late Mesozoic and ear ly Cenozoic. Bosellini ( 1989) s ummar izes the tectonics and geologic evolution of the Tethyan carbonates, pointing out that many exhibit tectonic retreat and/or demi se by drowning He concl ude s that aggradation and progradation are the general rule for Tethyan platforms, and when this pattern is disturbed, tectonic s, s ubaerial exposure, or environmental degradation must be the cause (Bosellini, 1989). Two types of drowning are postulated: anoxic drowning, which is related to unfavorable water conditions and starved drowning, which involves tectonic collapse. Tectonic co llapse is often associated with megabreccia deposition at the base of the platform (Bosellini, 1989) Again, the main difference between these Tethyan analogs and the Serranilla Basin system is the tectonic setting: collisional versus strike-slip. 18

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The use of sequence stratigraphic concepts to study the structural development of carbonate systems is not a new idea Sarg ( 1988) laid out the original ground rules for a pplying this methodology to carbonates, and this was later expanded on by Handford and Loucks (1993). The underlying assumption of these sequence stratigraphic schemes is that eustasy plays the dominant role in controlling sequence architecture. This assumption has been argued against in a general sense (Watts, 1982 ; Miall, 1992), as well as in the carbonate realm (Schlager, 1992; Hunt and Tucker, 1993; Pratt and Smewing, 1993). Other proposed controls on the sequence architecture include variations in current intensity or location (Pinet and Popenoe, 1985; Mullins et al., 1987), tectonic tilting or block faulting (Simo, 1989; Underhill, 1991), or specifically in the carbonate setting, changes in the oceanic environment that may induce platform drowning or alter sedimentation patterns (Schlager, 1992; Pratt and Smewing, 1993). The application of sequence stratigraphic techniques to the Serranilla Basin is s ignificant for several reasons. First, as Sarg ( 1988) points out, basinal chalks are not considered in the development of his models. In fact, nearly all sequence stratigraphic studies of carbonates focus on the platform/shelf to slope transitions, with little detail paid to the b as in (see studies in Loucks and Sarg 1993) The Serranilla Basin averages about 1200 m deep at present and based on initial seismic interpretations, has maintained at least 700-800 m of relief throughout its history. Secondly and perhaps most importantly, the role of tectonics has not been fully studied in sequence stratigraphic investigations of carbonate systems. Loucks and Handford (1993) conclude their introduction to AAPG Memoir 57. Carbonate Sequence Stratigraphy with the following: Most studies have not adequately addressed tectonic influences on platform development. Thus, we lack information on how stratal geometries differ between quiescent and tectonically active areas, and we have insufficient criteria to 19

PAGE 36

dis tingui s h relative influences of tect o nic pr ocesses and eus t as y in the tJf s equence bound a ries Thus, to s ummari ze, the S e rranilla Ba sin c arb o n ate s y s t e m r epre se n ts a unlqoo tec tonic s etting within which to investigate the co ntr o l s o n structure a n d infiJHng, By s equ e nce stratigraphic principles, alternative s t o eu s t as y a s a drivin g f o r ce behind the se quence architecture may be better explored F inally, a n under s tandin g of t he evoJulitJn (Jf thi s we s ternmo s t ba s in of the NNR will provid e in s ight int o the significance of thi$ area a n o c eanic gatew a y, and its role in the on se t o f the mod e m glo b a l t her m ohaline ci radatloo sy s tem Previous Studie s Present re s earch a long the NCPBZ ha s focu se d ma i nly o n the end a&llte C a yman Trough including ons hore and o ffs h o re s tudi es of Jamaica ( Man n et at. 19$5; M ann a nd Burke 199 0; Glaser and Droxler 1993; Le roy et al. 1996 ). ( Heubeck et al., 1991; Calais et al., 1 9 92; Pren t i ce e t al. I 993 ; CaJa is and Mttcia de L e pinay 1995 ; Mann et al. 1995; Russ o and Villasen o r 1 99 5 ) and CllDibxa1 (Calai s and Mercier de Lepinay 199 1). Litt l e i s know n concerning the of the deeper basin s that make up th e w es tern NNR. specifically abe Sernmilla BaM>nn . Pr e viou s work in thi s area of the NNR incl ud e sei smi c studies of the sB:nallow Channel west of the Serrani lla Basin and the D iriangen Channel ro the DOII1b Jiijmxe ett ;allL 1992 1994 ). The Bawihka Channel s tud y i dentified three seismjc sequences m llnii.P r e s olution s ingle-channel se i s mic ( S CS ) dat a Within these S"eq1llleDir.'eS. se\"e1r.llll seii.'Wlliic f a ci es were ident i fied. The d eepes t s equ e nc e (A) is c haracterized b}q J!IWil'<4l!lll.dl l a minated reflecto rs, c ut in man y p laces by numerous higb-3DllgDe. f:alllll]tls.. '1J'be 20

PAGE 37

deepest sequence (A) was mapped at a depth range of 375 to 500 m below the seafloor. The sequence boundary shows erosional truncation and marks the tops of the high-angle faulting. This sequence was mapped beneath the channel throughout the study area (Hine et al., 1994). Sequences B and C are less widespread within the channel and are identified by their style of reflector termination. The upper sequence boundaries varied in depth, but were generally shallower than about 300m below seafloor. The seismic facies that make up these sequences are diverse and include mounded structures, prograding clinoforms, and chaotic lenses For the most part, these units represent Quaternary infill of the channel (Hine et al., 1994) The deeper geologic history of the Bawihka Channel was obtained through interpretation of MCS data, revealing a broad basin of early Eocene age bound by ramps (Hine et al., 1994, their Fig. 6.). Rimmed margins developed from early Eocene through the middle Miocene. Since mid-Miocene, the eastern side of the channel has prograded 30 km to the west while the western side has been essentially aggradational The same three sequences have been identified to the northeast in the Diriangen Channel (Hine et al., 1992). Similar seismic facies have been identified within the upper sequences and high-angle faulting is present to the top of sequence A. A unique characteristic of Diriangen Channel appears to be its infilling by large debris flows or megabreccias These extensive 'megabreccias' appear as acoustically chaotic units within the upper two sequences, and as massive debris flow deposits on the present channel floor. The se have been tied to the active tectonics within this area and represent, along with sa ndy, bank-derived turbidites, the primary infill of the seaway. The seismic data (single-channel, airgun data) from the Hine et al. ( 1992) study represents approximately 0.5 seconds of penetration, whereas the data set collected for the present study penetrates to over 1 second within the basin. For this reason, the units identified in the channels are thought to represent just the uppermost units within the basin. 21

PAGE 38

Methods Several research cruises were conducted along the NNR ( CH0587 ; CH0388; CH0492); the most recent wa s during 1992 aboard the R!V Cape Hatteras Approximately 1 100 trackline kilometer s of 3.5 kHz and single-channel, high resolution seismic airgun data were collected in the Serranilla Basin. An 80 cu. in. GI airgun with bubble-pulse s uppression was used as a seismic source. The data were digitally recorded using ELICS and MASSCOMP software and processed using ELICS and PROMAX systems. In addition, four multi-channel seismic (MCS) lines were obtained from the University of Texas, Institute for Geophysics, to help define the deep structure of the basin. Finally, industry MCS data was consulted to help constrain the bank-to-basin transitions (Fig. 2.1). All depths for isopach and structure were determined using a seismic velocity of 2,000 rnl s as determined by Ewing et al. ( 1960) for the NNR. This velocity represents a goo d average for these sediments based on the recent work at ODP Site 1000, in the adjacent Pedro Basin (A.D Cunningham, 1996, pers. comm.) Five dredge haul s were obtained within the Serranilla Basin to help con s train lithology and timing of depo s itional sequences (Fig. 2.2). Twelve thin sections of specific rocks from the s e dredge s were analyzed and photographed. Age Control Age control for this study is obtained from three sources; industry wells drilled along the NNR (general age) (Fig. 1.4 ), biostratigraphic ages associated with dredged material (Fig. 2.2), and correlation to ODP Site 1000 in the adjacent Pedro channel (Fig 2.1, for location). Analy s i s of thin sections have yielded biostrati g raphic ages for two of th e sa mples although their utility in tyin g into seismic sequences is limited (Fig. 2.2). Ages were obtained based on identification of benthic foraminifera by E. Robin so n, 22

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16. 00' 1s 30' \ \ UTIGiine 10 \ \ Seismic dala UTI G p rocessed 0 1 0 2 0 30 40 s o 60 70 80 KILOMETERS 90 100 ODP Site 1000 14 s2 00' s1 30' s1 00' so 30' so oo 79 30' Figure 2.1. Location map for the seismic data set used in this study. Locations of figures within the text are indicated Also ODP site 1000 is mapped with respect to the s eismic line s within the adjacent Pedro Basin 23

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Possible sediment pathways Dredge locations J lu i 40 50 l 7 o so 90 KILOMETT.RS stoo soJo' sooo Figure 2.2. Bathymetry of the Serranilla Basin using 100m contour intervals based on 3.5 kHz and single-channel, high-resolution data. This bathymetry indicates several previously unmapped submerged banks within the basin (tentatively named Hunapu, Xbalanque, and Tlaloc banks, respectively). Hunapu Bank was previously mapped as an extension of Serranilla Bank but it is in fact, isolated within the basin. Dredge haul locations are indicated with age control where determined. Ages are primarily based on biostratigraphic evidence (E. Robinson, pers. comm.). Also inferred sediment pathways are indicated from scalloped margins into the deeper basin via submarine canyons. 24 79 30'

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University of the West Indies, Jamaica. A third age obtained from previous work in the Rosalind Channel is also tied into the seismic network, and this confirms Pliocene age for sequence D (A.C. Hine, unpubl. data). The age control from the ODP site provides the best framework within which to place the sequences identified in this study. Seismic lines from the Serranilla Basin do not tie directly into the Pedro Basin because of poor resolution in the intervening seaway, and therefore the jump corre lati ons are based upon matching of seismic facies patterns and reflector characteristics (Fig. 2.3). However, as both data sets were collected on the same crui s e, and similar seismic units have been interpreted, the correlations seem reasonable (A.D. Cunningham, pers comm. 1996) Results Bath y metry The Serranilla Basin represents a poorly mapped bathymetric region along the NNR. This study presents the bathymetry contoured from 3.5 kHz and single-channel, high-re s olution seismic data collected during research cruises in 1987, 1988, and 1992 (Fig 2 2) The bathymetry of Serranilla Bank was adapted from Triffleman et al. (1992) while the detai l s of the Bawhika and Diriangen channels were taken from Hine et al (1992; 1994). The main features identified during this survey that were previously undescribed, include three submerged platforms south of Serranilla Bank Dredge hauls on the two northern banks (tentatively named Hunapu and Xbalanque banks) obtained carbonate grainstones and these have been interpreted as 'drowned' carbonate banks The southern bank (tentatively named Tlaloc bank) has not been dredged. The shallow seaways to the north of the basin have been mapped in detail. The Diriangen channel has been previously described (Hine et al., 1992), although the 25

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26

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Figure 2 3 Comparison of seismic data from the Serranilla Basin with the data used in the Pedro Ba s in to obtain chronostr a tigraphic control. Seismic units were identified aboard ODP Leg 165 at site 1000 by A.D. Cunningham and A W. Droxler. Lithologic description i s f rom the general preliminary lithologic logs released through ODP (Sigurdsson et al., 1996 ) Age s o f lithologic boundaries are given in bold at the right of the lithologic column. Sei s mic boundary ages are inferred from the s e lithologic boundary ages

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N -...) 2000 Serranilla Basin Sequences .. ,iiiiJ,,,..;r. .. __ CH9204-12 Leg 165 ODP Site 1000 Pedro Channel (1996) Litholog;ic Age Description Umts Miocene volcanic episode associated with Tertiary Igneous Province in Central America Peak @ 19 rna 7 m/106 years thick volcanic ash fallout lOOm Turbidite-free sequence with few volcanic ash layers Volcanic ash layers common throughout 200m Uniform micritic biogenic ooze 300m 400m SOOm Volcanic ash layers common throughout Some turbidites common in lower portion of unit Lower carbonate content ; detrital clays and quartz reach maximum Uniform micritic biogenic ooze similar to lb turbiditefree Abrupt chalk to Limestone transiti o n High carbonate content 600 m Fluctuating carbonate content highest abundance of volcanic ash layers and turbidites

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transition into the basin from the s haJJow seaway is first s hown in this bathymetry (Fig. 2.2). The Diriangen channel drops abruptly into the basin, in contr as t to the Rosalind Channel, which is deeper and shows a gradual shallowing to the north. The channel connecting Serranilla and Pedro Basi n stays relatively deep, shaJJowing to onJy about 800 mas it trends northward into the Pedro Basin (Fig. 2.2). The Serranilla Bas in itself is a relatively flat-floored, circular depression ranging from ll 00-1300 m deep. The southern boundary of the basin can be approximated by the 1500 m i so bath, which also marks the beginning of the rugged seafloor representing the Pedro Fracture Zone Beyond this lies the southern Nicaragua Rise and the 4 km deep Colombia Basin Two canyons hav e been mapped cutting across this boundary into the deeper water to the south. The first, just south of the Serranilla Bank (see loc a tion on Fig. 2.2), appears to connect the scalloped bank margin with the deep basin. The canyon system in thi s area may provide the conduit for rapid removal of shallow-water material into the deep basin facilitating the loss from the bank The second mapped canyon (Fig. 2.2) is located in the southwestern portion of the basin and may al s o represent a pathway for se diments moving from the Bawihka Bank into the deeper areas to the southeast although no data are available to confirm if movement of sediments i s occurring at present. Deep Structure The deep s tructure of the b as in h as been interpr ete d based on four multi -c hannel seismic (MCS ) lines obtained f rom both the University of Texas, Institute of Geophysics and propri etary source s (Fig. 2.1). These data are included as a foundation on which to place the res ult s of this s tudy. Interpretation and timing of the deep s tructural elements are tenuous, based solely on these line s and publi s hed well-log data within the area Further 28

PAGE 46

deep seismic studies, such as that of Bowland et al. ( 1993) for the Columbia Basin, are needed to complete the early geologic history in this part of the NNR. A north to south transect (Fig. 2.1, for loc atio n) from the Cayman Trough to the Hess Escarpment gives a general indication of the deep structure of the NNR (Fig. 2.4 ). The NNR i s a prominent area of s hallower bathymetry with relatively little seismic penetration. This in part, is due to the nature of the sediments/rocks underlying the NNR, which, from well-data, have been shown to be almost exclusively limestones from Eocene through at l east middle Miocene (Arden 1975 ; Caceres-Avila et al., 1984; Holcombe et al., 1990) Further south, the seaway (Rosalind Channel) to basin transition is indicated by a gentle grad i e nt, as s hown in the bathymetry (Fig 2.2). Seismic penetration is deeper into the basin sediments, and seismic basement is indicated in the interpreted sections (Fig. 2.4). The basement is block -fa ulted at the southern boundary of the Serranilla Basin in the area of the Pedro Fracture Zone (Fig. 2.5). This block -fa ulted area separates the NNR from the low e r or southern Nicaragua Ri se ( SNR) A relatively thick sedimentary section (compared to the top s of the NNR) continues to the south as the bathymetry deepens The Hess Escarpment marks the boundary of the SNR, and i s b elieve d to be a zone of left lateral fault displacement during the eastward movement of the Caribbean plate between North and South America (Pindell and Barrett 1990). The Serranilla Bas in itself shows relatively little deep structure based on these lines Faulting i s evident within the Rosali nd Channel (Fig. 2.4), although the transition into the bas in is not conclusive with respect to fault control. The so uthern boundary however, appears to be controlled by block-faulting in the area of the Pedro Fracture Zone A s will be shown later, thi s block faulting may have controlled the location and extent of the early basin margin. 29

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NW UTIG line 10 southeast I -2-3-4 -5-6-I 00 kilometers NW UTIG line 11 southeast-----r a mp margin ?? -100 ldlomet e rs_ Southern Nicaragua Rise SE -basement SE Colombia B as in Figure 2.4. Line drawings of UTIG proce sse d MCS data crossing the Serranill a Ba s in Lines were obtained uninterpr e ted from E. Ro s encrantz, UTIG Note the general physiography of the NNR, how the Pedro Fracture Zone separates the NNR from the SNR, and the block faulted nature of thi s boundary. See Figure 2.1 for location of profiles.

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w ,__. UTIG Line 11 Southeast rJj "'d 0 u II I (].) rJj (].) a 2 ault Block (].) > 3 4 0 Figure 2.5 Detail of processed UTIG MCS data crossing the PFZ. Fault blocks are labeled and dark lines indicate interpreted faults. I

PAGE 49

The industry MCS data shows the bank to basin transitions for the Diriangen Channel and Bawihka Bank (Fig. 2.1 for location), indicating possible fault control at these transitions (Fig. 2 6). Line 210 shows evidence of normal faulting at the bank/basin transition. Seismic basement appears to have tilted, down-dropping to the north and rising within the basin. Line 200 crosses the basin obliquely from west to east traversing the top of Bawihka Bank and ends within the Pedro Fracture Zone Again, some faulting is indicated on Bawihka Bank and also at the margin The same tilted basement structure is crossed within the basin and there is a zone of faulting east of this structure. Faulting of basement is indicated at the approach of the Pedro Fracture Zone as well, although not as clearly evident as the block faulting on the UTIG line (Fig. 2.6). Dredge Hauls Five dredge hauls were taken in the Serranilla Basin in an attempt to identify the lithology and constrain the timing of the seismic sequences in this study (Fig 2.2 for locations). Dredge haul locations were chosen in an attempt to sample specific seismic units outcropping on the seafloor. Of the five dredge hauls obtained, only two have yielded biostratigraphic age data: site 37 and site 31 (Fig. 2.2). Both are predominately pelagic chalks and/or limestones, showing abundant microfossils (foraminifera pteropods) in a micritic matrix (Fig. 2.7) Unfortunately, there are seismic data at only one of these sites (site 37), and these data do not allow for unequivocal seismic correlation to the dredge haul location therefore these ages cannot be tied directly into a seismic sequence (Fig. 2.8). The following general descriptions and site locations for the remaining three sites have no biostratigraphic age estimates, and are given to show the similarity in rock type at each location. 32

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33

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Figure 2.6. Line drawings of industry MCS data used to help define the deep structure of the Serranilla Basin. Both lines indicate deep-seated faulting at the step-down from the s hall ow seaway and banktop into the Serranilla Basin. The deep penetration of these data also allow for the interpretation of continous parallel reflectors below tho se identified in the high resolution se i smic data set for the present study.

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Q) 8 ...... ..... ......... Q) > Line 21 0 Channel --1 2o kilometers ---5 A _ -2o kilometers Serranilla Basin Hunapu Bank sout heast

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Dredge Site 31 Dredge Site 37 Figure 2 7 Representative thin sections from dredge haul sites 31 and 37. The thin section from site 31 is primarily micrite with some pelagic microfossils. The thin sec tion from s ite 37 has a higher percentage of microfossils and also s hows a darkening near the edge of the slide caused by ferromanganese precipitation (A. D. Cunningham, pers. comm.) 35

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VJ 0\ w :.-. _ ... """.:. -.. s -(].) > C'd rJJ b s S::: 1000 ms I 0 Dredge Site 37 Line 15 (mid-Miocene or younger rocks) 1500 ms E Figure 2.8. Seismic location of dredge 37 showing the ambiguity in tying into a seismic sequence. An age of mid-Miocene or younger was determined (E. Robinson, pers. comm.) but it is not possible to constrain the sequence stratigraphy with these data.

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Site 22 is an isolated high in the east-central portion of the basin (Fig. 2 9). Rocks obtained at thi s site ranged from friable chalks to bored, phosphatized, chalky limestones, with a predominately pelagic microfossil composition (molluscs, forams) and micritic matrix. Site 24 occurs on the eastern side of Hunapu Bank, along the Pedro Fracture Zone. The rocks obtained here are poorly to moderately lithified, porous grainstones composed of foraminifera, molluscs (many pteropods) and echinoderm and sponge fragments with some micrite (Fig. 2.1 0). Finally, site 38 is located at the edge of Serranilla Bank. Rocks obtained in this dredge haul range from poorly lithified mudballs' to bored, lithified grainstones. The 'mudballs' contain mostly pelagic microfossils in a micritic matrix while the grainstones contain more open pore space with larger molluscs and some sponge spicules (Fig. 2.11). Sequence Stratigraphic Analysis Five seismic sequences were mapped within the Serranilla Basin (Table 1) using established sequence stratigraphic methods (Vail et al., 1977; Van Wagoner et al 1988). The earlier definition of sequence boundary has been used in this study to avoid any genetic connotations (e.g., eustatic sea -le vel sequences). Structure and isopach maps were created to identify changing depositional patterns within the basin and possible structural controls Seismic facies were also mapped using esta bli shed techniques (Sangree and Widmier, 1978; Fontaine et al., 1987). Ages of the sequences are estimated from a jump correlation to ODP Site 1000 and dredge hauls (Fig. 2.3). Sequence A S e ismic Stratigraphy The upper boundary of Sequence A marks the deepest sequence boundary (R1) identified in this study. It is characterized by onlap of overlying units at the basin margins and structural highs within the basin (Fig 2 .12). The folded 37

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C/) ""d = 0 () (!) C/) ...... -' = ...... (!) s ...... ...... -(!) ::> C'j b ;;:..... C'j I 0 w E Dredge Site 22 Line 18 Figure 2 9 Dredge haul site 22 along the flank of small mound on the seafloor. The thin section shows predominately pelagic microfossils, and it is difficult to determine if the lower unit within the mound was obtained This site h as no significant age diagnostic microfossils. 38

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w Dredge Site 24 Line 22 E Figure 2.1 0 Dredge haul site 24 on the eastern flank of Hunapu Bank. Pelagic, as well as so me neritic microfo ss il s are pres e nt indicating that sediments along this s lope represent transported materials or drowned Hunapu Bank is exporting neritic microfossils itself. No age data were obtained for the se samples. 39

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w Dredge Site 38 Line 15 E Figure 2 11. Dredge haul location 38 along the base of the Serranilla Bank Again, the thin section shows primarily pelagic microfo s sil s in a micrite matrix No age data were obtained 40

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Table 1. Seismic units identified in this study with interpreted ages and seismic boundaryand facies characteristics. Seismic Interpreted Thickness Basal Boundary Seismic Interpretation unit age Character facies E Quaternary0-125 ms low to high amp low-amp, continuous pelagic and periplatform depostion alternating Late Pliocene avg 100-125 ms continuous to discontinou s, some with turbidite s R4 transparent D Late Pliocene50-200 ms pelagic and periplatform depo s tion alternating Late Miocene avg 100 ms high-amp continuous low-amp continuous with turbidites and some evidence of megabreccia R3 deposition +:-..... 2 high-amp continuous low-amp continuous pelagic and peri platform depostion alternating c -Late Miocene 50-400 ms very high above to discontinuous ; with turbidites, neritic depo sti on at base of unit. 1 avg 150-250 ms bank margins high-amp continuous Carbonate buildups (reefs?) in margin areas R2 in buildup s of this s equence 3 75-200 m s high-amp, continuous peri platform deposition grading into neritic shallower to eli' -Late Miocene-variable, refer to depo sits with depth in the sequence B 2 Early Miocene 50-200 ms high-amp continuous facies map s High amp, continuous sections may also be affected by to discontinuous 1--volcaniclastic depo sitio n occurring throughout the 1 50-400 ms variable we s tern Caribbean at this time R1 Early Miocene-Below the depth of seis mic penetration Po ss ible neritic deposits A NA NA NA associated with the early carbonate megabank along Older theNNR

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Line 18 east---...., 1.5 r::/J "'d 0 0 (.) r::/J 0 ....-1 2.5 s ....-1 ;> c\j 10 kilometers ::>-. c\j 1.5 I 0 2 0 2.5 Fig ure 2.12. Single-channel se i s mic dat a s howing se quence boundary R 1 interpret e d her e based on the lateral onlap terminations of overlying reflectors. The three di s tinct units in sequence B can be see n here. The high-amplitude chaotic nature of se qu e nce A i s also di s played Folding is possibly related to deeper block-faulting. 42

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strata of sequence A may overlie the fault block illustrated in the line drawing of industry MCS of Figure 2.6. If so, this deeper structure plays a part in the onlap defining sequence boundary R 1. Below sequence boundary R 1, seismic character is generally chaotic, although some high amplitude, continuous reflectors are present. These deeper reflectors although not traceable throughout the basin, agree with deep (MCS) data that show high-amplitude, continuous reflectors below the R1 sequence boundary overlying a deeper chaotic unit (see Fig 2.6) Therefore, sequence A most likely represents an early phase of development within the carbonate basin itself. Sequence A is interpreted to be deeper than the 700 m drilled at ODP Site 1000 and is interpreted as pre-Miocene and/or early Miocene. Structure Sequence boundary R1 is traceable throughout the basin, displaying a high-amplitude, continuous reflector character. The structure map to R1 shows the early Serranilla Basin is made up of three distinct basins, labeled 1, 2, and 3 (Fig. 2.13). Two basins occur to the west of the Hunapu Bank and are separated by a structural high. This structural high may be a product of continued block-faulting occurring syn -depositionally to sequence A. This folding occurs prior to the deposition of sequence B as indicated by the onlap onto these highs (Fig 2.12) East of these basins, a relatively shallow, northeast -southwest trending structural high marks the boundary with the Pedro Fracture Zone. This structural high may represent an early eastern bank margin To the southeast of this bank margin is a third basin. Here the structure appears more irregular, and deeper than the central portion of the basin. Evidence of biock -faulting can be seen (Fig. 2.14) along the most southeastern portion of the seismic grid, although it is not possible to determine the exact orientation or timing of these faults. 43

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Figure 2.13. Structure/contour map to sequence boundary Rl. Contours are at 100m interval s ba se d on a 2000 m/s s eismic velocity. Three basins are identified and labeled as 1 3 A structura l high se parate s basin 1 from 2, and a northeast-southwest trending slope separa te s these basins from bas in 3. Double arrow indicates northeast-southwest trending s tructur a l hig h (early bank margin). The modern banks are shown for orientation.

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Bank cModern banks s hown using 1530' 1:::100 m bathym e tric contour 0 10 20 30 40 50 60 70 80 90 100 kilometers ""-\ ,_ lll 810J O

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46

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Figure 2. 14 Processed, single-channel seismic data and line drawing for line 21. The block faulting can be seen and seq uence boundaries are indicated where deposition fills the intervening depressions (grabens?)

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2 3 Line 21 north 2 -lOkilometers -3 fault block -fault block 4L_ ______________________________________________________

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Sequence B Seismic Stratigraphy. Sequence B can be subdivided into three units (Rl, Rl, And R3) based on seismic facies characteristics and mappable high-amplitude basal boundaries (Fig 2.15). The deepest, unit B.l, is characterized throughout much of the basin by a variable to high-amplitude discontinuous seismic facies while the structural high in the center of the basin shows high amplitude, parallel, continuous character (Fig. 2.16) The so utheast has high-amplitude, but chaotic reflection character, as do the areas near the present-day Ro sal ind and Serranilla Banks. Unit B 1 is interpreted as early to middle Miocene ba se d on its correlation to ODP Site 1000 (Fig 2 3) Unit B.2 overlies B.1 displaying similar seismic facies characteristics (Fig. 2.17). The ba sal boundary of B .2 is a high amplitude, continuous reflector and is correlated throughout the entire basin. This basal boundary also correlates with a chalk to limestone transition in ODP Site 1000 and is interpreted to be middle Miocene in age based on this correlation (Fig. 2.3). Note the area of continuous, high-amplitude parallel character in the center of the basin i s more widespread and the so uthern extent of the ba si n s how s more variable character ( Fig. 2.17). In overlying Unit B.3 the high-amplitude parallel se i smic facies reaches it s greatest extent, encompassing the entire center of the basin, as well as portions of the southern boundary (Fig. 2.18). The thickness of Sequence B varies in th e basin, thinning near the stru ctural highs along the Pedro Fracture Zone ( <3 00 m), and thickening along the west-central portion of the ba s in (Fig. 2.19). This seq uence appears to infill the southern s tructural low (basin 2) and a lin ear north-south trough off the present-day Bawihka Bank perhap s due to fault block s controlling the accommodation in thi s area. Comparatively littl e infilling ( <300 m) of the northern structural basin (basin 1) occurs during the depo si tion of Sequence B, and this also may be due to the und e rlying structure isolating this basin from neritic sources to the west (location of present day Bawihka Bank). 48

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49

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Figure 2.15. Processed single-channe l seismic line 12 with interpretation. Note the faulting in s equences B and C. These faults are prevalent throughout these units in the center of the basin. The three se parate units (B l B2 B3) of sequence Bare demon s trated here s howing the continuous high-amplitude, parallel seismic facies character.

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tr) 0 C'l C'l spuoJgs ll! gUJ!llgABJl ABM-OM.L 50

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1630' kilometers t6 oo ts3o' lll -tsoo / ,.r-Seismic Facies Key . Chaotic relatively high = : ... : amplitude Low-amplit u de, discontin u ous D Variab le, high-a m plitude, mainly discontinuous H i gh-amplitude, continuo u s, parallel Low-a m plit u de, con t i nuous Chaotic (deb r is n ow?) 1430' stJO stoo so JO so oo 79 30' Figure 2 16. Seismic facies map for unit B I of sequence B. 51

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-ts oo Seismic Facies Key Low-amplitude, D Variable, high-amplitude, discontinuous mainly discontinuous High-amplitude, continuous parallel Low-amplitude, continuous Chaotic (debris n ow?) 14 30' stJo' stoo soJo' sooo 79 30' Figure 2.17. Seismic facies map for u nit B.2 of sequence B. 52

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16oo 15 30' 1soo "';_,./ ll Seismic Facies Key High-amplitude, continuous parallel ............ .I ,.. "' ,.. Low-amplitude, discontinuous D Variable, high-amplitude, mainl y disco ntinu ous ( Chaotic (debris now ?) I4 30'..L..--------......I..--------.....J---------.L...--------...I 8 1 30' s1oo so3o sooo 79 30' Figure 2 .18. Seismic facies map for unit B 3 of sequence B. The most notable feature i s the increasing area of continuous high-amplitude, parallel s eismic facies as one moves upward in sequence B. 53

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Figure 2 19 Sediment isopach map of sequence B showing the depositional patterns. Contour s are in 100m intervals. The thickest deposition occurs along the western side of the basin. This deposition may be related to infilling of the southern basin (basin 2). The deposition tends to parallel the western bank developing along this margin of the basin (see Fig 2.13).

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Bawihka Bank Diriangen \ Rosalind Bank Bank ,. Dir iangen Channel I J ) 4'oo 3 00 :11 odern banks s hown using A 100m bathymetric contour \ 3oo 3oo D epoce nter 400 '-'2' 81 00' Serranilla Bank 3

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Structure. Sequence boundary R2 is correlated throughout the basin and marks the top of many bank margin areas that were later drowned and back -stepped. Sequence boundary R2 is characterized by onlap of overlying units in these areas of margin back-step (Fig. 2.20). The bank margin represented here isolates a small basin to the west. This small back-margin basin does not appear further south however, and may be related to the underlying fault -block structure identified here in Line 210 of the industrial MCS data (Fig. 2.6). The structure of the eastern bank margin has changed, subsiding in the south, but persisting in a NE-SW orientation to the east of the northern basin (basin 1) (Fig. 2.21). The upper units of Sequence B (B 1 and B2) can be seen overlying this subsided southern bank margin as flat-lying reflectors (Fig 2.22). Here also, the beginning of the steep NESW striking slope can be seen (indicated by debris flows in the upper sequences) The structure southeast of this slope (basin 3) remains deep. Faulting is prevalent within all of sequence B units. Most faults appear to begin in lower sequence B, although some reach deeper, and nearly all pass into the upper sequences (Fig 2 15). Nearly all of sequence B is represented by relatively flat-lying, continuous reflectors, which differs from the folding seen in sequence A These units were later cut by the faulting Therefore, the deposition of sequence B may represent a time of tectonic quiescence, postulated for Jamaica and the NNR during the early to middle Miocene (Arden, 1975). Sequence C Seismic Stratigraphy. Sequence C, subdivided into two units, represents a fundamental change in seismic facies within the basin from predominately high-amplitude to low-amplitude reflector character. This change occurs progressively, from lower sequence C (unit C.1) (Fig. 2.23), which has isolated high-amplitude areas, to upper sequence C (unit C.2) (Fig. 2.24), which is almost entirely low amplitude. The high-56

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Figure 2.20. Processed single-channel seismic line with interpretation showing the marginal buildup identified in the structure/contour map. Onlap termination of the overlying reflectors mark R2 as a sequence boundary. The present-day basin margin occurs approximately 25 km to the west, indicating backstep and/or drowning of this marginal buildup.

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"' ..... Cl.) rJ:J ..... ro Cl.) s 0 ] 0 if) (1) lr1 0 V) 0 C'i C'i 58

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Figure 2 .21. Structure/contour map to sequence boundary R2. Traveltimes have been coverted to meters using a 2000 rn/s seismic velocity. 100m contour intervals show the beginning of a bank-margin buildup along the western portion of the basin. A small back margin basin is also present in the northwest.

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back-margin bas in ft \i,JOO Modern banks shown using 15o 30' 100 m bathymetric contour .1 I marginal 1 100 m contour interval buildup 81 30' 81'

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Figure 2.22. Processed single-channel seismic data (line 20) with interpretation. Sequences D and E are identified showing their low-amplitude seismic character.The debris flow/slump is shaded marking the transition from the 1100-1200 m deep ba':lin down into the area affected by the Pedro fracture zone. An older bank margin is can be seen at this tran s ition.

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Line 20 Southeast (/) "'0 2.5 1:: 0 u ll) (/) 1:: ll) s 3.0 ...... ll) ;:> ...... ;:;..... I 0

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Seismic Facies Key High-amplitud e, continuous, parallel Low-amplitude, discontinuous D Variable, high-amplitude, mainly d iscontinuous C haotic (debris now ?) 1430' Figure 2.23. Seismic facies map of unit C.l of sequence C. Sequence C marks the tr a n s ition from high-amplitude facies to low amplitude facies within the ba sin. The transition i s progressive because unit C.l has areas of high-amplitude and variable facies. 63

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Seismic Facies Key E3 High-amplitude, continuous parallel Low-amplitude, discontinuous Low-amplitude D Variable, high-amplitude, mainly discontinuous Chaotic (debris flow?) 14 30'..1....--------......l.---------l...---------...l...--------...J 81 30' 81 00' 80 30' 80 00' Figure 2.24. Seismic facies map of unit C.2 of seq u ence C. Sequence C m a rks a transition from high-amplitude to low-amplitude facies within the basin. Unit C.2 is nearly completely low amplitude. Note the chaotic (debris flow?) facies in the northeastern portion of the basin. This cou ld mark the beginning of megabreccia deposition related to catastroph ic demise of the shallow banks. 64

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amplitude areas of unit C.l correspond in the north, to bank-margin buildups and sediment infilling the northern basin (1). In the south, high-amplitude chaotic facies mark the transition downslope into the deeper southeast basin and may represent slope failure and/or debris flows in this area (Fig 2.22). In the middle portion of the basin, faulting occurs throughout this sequence (Figs. 2.15 and 2.25). These are high-angle faults ( -75 degrees to vertical), similar to those described by Hine et al. (1992; 1994) in the seaways to the north and west. With the exception of the southernmost basin, these faults terminate at R3, marking the end of activity within the basin Sequence C occurs as a thick depositional unit in the northern basin (1), infilling the previous low (Fig. 2.26). The infilling may be related to backstepping of a bank-margin structural high to the east, as seen in the seismic data (Fig. 2.27), or a change in the source of sediments from the western bank-margin to the northern margin. More isolated depocenters occur in the southeast infilling graben-like features, and the northwest, where the small back-margin basin infills (Fig. 2 26). Structure. The structure contour map of sequence boundary R3 is similar to the modern bathymetry of the Serranilla Basin (Fig. 2.28). Infilling of both the southern and northern structural lows has smoothed the basin bathymetry creating the nearly flat-floored basin observed today. Backstepping of the marginal buildup south of the Diriangen Bank has occurred with basin margin retreat of nearly 25 km (Fig. 2.28). Sequence D and E Seismic Stratigraphy. Sequences D and E (Fig. 2.22) represent low-amplitude, continuous facies, with isolated areas of variable, to chaotic facies which may represent 'megabreccia' type debris flow deposits (Fig 2.29 and 2.30). This chaotic facies was 65

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Bawihka Bank Rosalind Bank Faults become you n ge r to the southeast ... .. .... ... ... .................. MCS data e Basement fau l ting + Faults above ba sement to Miocene This study Faulting in sequences A-C early Miocene-Pliocene (coul d go d eepe r ) .& Fau l ting reaching recent sediments w i t h seafloor displacement 0 I 0 20 30 40 50 kilometers 14 30' -1---==========+============+============+==========-..J Figure 2.25. Map show ing fault locations interpreted from the seismic data D ee p ba sement fau lt ing i s seen along th e margins of the ba s in, perh a p s implying a genetic relationship. Faulting of sequences A-C occurs in the middle of the ba sin, while seafloor disruption, i ndic at ing rece nt fault activity, occurs in the so uth of th e ba sin. 66

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Figure 2.26. Sediment isopach map for sequence C. Note the depocenters occur in the northern basin south of Rosalind Bank, and in the southeast, in an area of block-faulted bathymetry. Isopach thickness in 100 m contour interval.

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iriangen \ Rosalind Bank Bank '. Diriangen Channel Modern banks shown using 100 m bathymetric contour / / / / 100 / / Depocenter s Serranilla Bank 81 30

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Line 8 North --2 0 2.5 tr.J ""d 0 () Q) tl:l 3 0 Q) s -..) ...... 0 -Q) > C\:1 """ ...... :>... C\:1 I 0 I -. --.I 'V ,'-' ............_ J -------10 kilometers -I ---4

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Figure 2.28 Structure/contour map t o seq uence boundary R3. Tra velt ime i s co n verted t o depth u s in g a 2000 rn/s se i s mic ve locity Th e basins s tructur e contours are s imil ar to the pre sen t day bat h yme try an d s tructure. Backstepping of the northwestern margin has occurred to it s present position along the Bawihka Bank and Diri angen Channel.

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back-step of margin ,Qoo) 1100 1,100 0 10 20 30 40 50 60 70 80 90 100 kilometers Serranilla Bank Location of Hun apu Bank (no se i s mic data)

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1 6 00' 15 30' 15 00' Seismic Facies Key High-amplitud e, con tinuou s, parallel Low-amplitude, discontinuous Low -am plitude 0 10 20 30 40 50 kilom e ter s D Variabl e, high-amplitud e, m a inl y disco ntinuous Chaotic (debris n ow?) 1 4 30'..&....--------.....L.----------l---------.L....--------..J 8 1 30' 8 1 00' 80 30' 80 00' 79 30' Figure 2 .29. Seismic facies m ap of seq u e n ce D. Nearly all l ow-amplit ud e con tinuou s to di sco n tinuou s with i so l a ted areas of chaotic seis mic facies. The northw es t ern portion s how s c haoti c facies that m ay ind i cate m egabreccia d epos ition and bank demi se. 73

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Seismic Facies Key High-amplitude, continuous, parallel Low-amplitude, discontinuou s D Variable, high-amplitude, mainly discontinuous C haotic (debris now ?) 81 30' 8100' 80 30' 8000' 79 30' Figure 2.30. Sei s mic facies map of sequence E. Nearly all low -a mplitude continuous to discontinuous with isolated areas of chaotic seismic facies. Note the two i so lated areas of chaotic character. Thes e may represent megabreccia deposition originating from the drowned Hunapu Bank, or perhaps even the Serranilla Bank. 74

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identified throughout the s h allow seaways to the north (Hine et al., 1992 ), but is much le ss common in the ba si n. The thickest deposition of sequences D and E (>300 m) occurs to the northeast in the basin but isolated depocenters still persist to the northwest and southeast, inftlling the back-margin basin and the graben features, respectively (Fig. 2.31). Lin e 9, in the southern basin, shows the only faulting of seq uence s D and E within the entire basin (Fig. 2.32). These faults have evidence of seafloor disruption and indicate relatively rec en t tectonic activity. Discussion Seismic Reflectors and Sequence Boundaries The interpretation of seis mic data relies on an understandin g of the geophysical and geoc hemical controls that create seismic reflections, which are ultimately the result of acoustic impedance contrasts within the rocks and/or sediments. Acoustic impedance i s the product of velocity of the propagating waves times the density of the material it is passing through (Sheriff, 1977). Most reflections are interference composites of variations in the acoustic impedance over a s hort distance within a sedi mentary col umn ( Sheriff, 1977). Mayer (1979) has found this to be true for deep equatorial Pa cific carbonates, and pointed out that the fine-scale acoustic stratigraphy is nearly completely controlled by the saturated bulk density of the sed iment, or its inverse, porosity with velocity changes being minor. Mayer ( 1979) adds that changes in the percent calcium carbonate content of the sedime nts corre lates very well with sa turated bulk density Mayer (1979) inve stiga ted only the upper ten meters of seafloor sediments. It is reasonable to assume however, based on the veloc ity/d e n sity dependence of acoustic impedance, that porosity may also play an important role with increa se d depth in carbonate sediments. Other factors that may control c hange s in porosity and hence, acoustic impedance in carbonates, include changes in grain 75

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Figure 2.31. Sediment isopach map of combined sequences D and E. The thickest area of deposition occurs in the northern portion of the basin with isolated depocenters located in the central and eastern portion near the PFZ. 100 m contour interval.

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100 0 I 0 20 30 40 50 60 70 80 90 100 ki l o m eters l 100 0100? 200 i so l a ted Qoo 8130' 8100'

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Figure 2.32. Processed single-channel seismic line 9 and interpretation. The faulting along this so uth ernmost line disrupts the seafloor indicating recent tectonic activity. This is the only area in the basin where faulting cuts seq uences D and E. Note the canyon in the central portion of the seismic line, which may be a conduit for s hallow sediments into the deeper southern Nicaragua Rise. See Figure 2 1 for location of Line 9.

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I.s

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size, dissolution or winnowing, productivity, and diagenetic alteration (ooze to chalk to limestone changes). In the Serranilla Basin, only one reflector is definitively tied into a major porosity change. This is the basal boundary of unit B.2, which marks an abrupt chalk to limestone transition, based on correlation to ODP Site 1000 (Sigurdsson et al., 1996). Interestingly, this reflector is not a sequence boundary Sequence boundaries in seismic data, as originally defined by Vail and Mitchum (1977), are recognized as surfaces of lapout (onlap, downlap, and toplap) or erosional truncation. This original definition implies no genetic connotation (see Van Wagoner et al., 1988), and as previously stated, has been used in this study. The sequence boundaries identified in this study do not fit neatly into carbonate sequence stratigraphic models as explained at the outset, and an alternative interpretation to eustatic sea level controlling their timing and formation is proposed. Tectonic controls on sequence formation The sequence stratigraphic framework within the Serranilla Basin appears to correlate well with the timing of tectonic events along the NCPBZ (Fig. 2.33). However, the actual formation of depositional sequences requires a mechanism for creating the lapout geometry that is used to define the sequence boundaries. In the case of siliciclastic sequence models, eustatic sea-levellowstands are shown to control depositional patterns that create the sequence boundaries through erosional truncation or lapout. In the Serranilla Basin, sedimentary transport plays a role, as will be demonstrated, but changes in productivity, water chemistry, and even tectonic tilting of fault blocks may play a role in the formation of these depositional sequences. Sequence boundary R1 is the deepest identified in this study (separating sequences A and B). It is characterized by structural highs within the basin that exhibit onlap of 80

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Figure 2.33. Compilation of tectonic events in different areas along the NCPBZ and the NNR. The sequence stratigraphic interpretation from this study is plotted at the left along with the Exxon sea level curve (Haq et al 1988). References for the tectonic studies are given at the bottom left of the diagram. There are two different groups (Mann group and Calais and Mercier de Lepinay group) investigating the tectonic events of the Greater Antille s Each particular study refers to some tectonic episode however the cause of the episode may not be the same (e.g., the timing proposed for the collision of Hispaniola with the Bahamas differs between groups).

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00 N Thi s Study Central Am e rica Cayman Trough J amaica Greater Anti ll es Inden tation of southern His paniola b y B eata --Ridge9 -----+-o Restricted surface a. 'f ilii R3 water exchange e _Hispaniola collision ____________ ------------0 ---withBahamas7 div e rgen ce2 g c 1 Initial faunal g R2 . C o llision of Panama u with Sou th America/ (:Q 8 Spread i ng ha l f r ate -ltOmfiVy r Uplift o-;-----Swan Islands 4 Sp readi ng renew el after ridge jump and l e n gthening o f sp r eading center 3.4 Seq uence A 1 S pread ing stops --I ---R -------spr eading half-rate e.erences _1 6 mnV r ----I )KelloggandVega,l995 1y 2) Keller e t al. 1989 II 4 ) R osencrantz and Mann, 1991 5) Arden, 1975 6) Mann et al., 1990 7) Calais and Mercier de Lepi n ay 1995 8) deZoeien and Mann 1 995 9 ) H e ubeck and M ann, 1991 10) Mann et al., 1 995 Ini tia l ope nin g an d rifting of Cayman Trough 3 IJ)l!aq I+----.Initiation o f f olding Onset of movement a l ong d 1'f al Enriquillo Piaintain Garden t San up 1 onl gFZ F Zo J eptremnona ault ne m ama 1ca 6 be d r estmm m 8 n 8 9 Uplift o f B lue Mountains o f and ______ Collision of Hi spanio la __ to the south 5 with the Bahamas 10 Collisionof t southern Cuba with B ahamas (20 ma)? isp nnio l a with Centr a l Hispanio l a 9 of sou thwest 1 ---: Tec:tonic _I_-----i_-:::i Quessence I !l l South Yucatan/Cuba mic rop l ate s h ifted ------------,+. i Initi a l collison of Collision of Cuba _ .Hispani o l a -with Bah 1 7 with Bah amas 8 II) ij Ca lais and Me r cier de Lepinay tim i ng of Mann grou p timi n g tectonic eve n ts of tectonic events

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overlying reflectors (Fig. 2.12). The formation of this boundary (R1) and the deposition of sequence B may be tied to the early Miocene reorganization of the NCPBZ, perhaps initiated by the collision of southern Cuba with the Bahama platform and the southern jump in strike-slip motion between Cuba and Hispaniola (Pindell and Barrett, 1990; Calais and Mercier de Lepinay, 1995) Renewal of spreading within the Cayman Trough also occurred at this time, as well as uplift of the Swan Islands, north of the NNR (Rosencrantz et al ., 1988; Rosencrantz and Mann, 1991). This reorganization may account for movement along the Pedro Fracture Zone and accelerated subsidence and/or segmentation and back -stepping of the bank margin in this location (Fig 2 22 shows drowned bank margin) There are several possibilities for the formation of sequence boundary Rl. It could be that increased turbidites within the basin, due to tectonic uplift, onlap previous structural highs Underhill (1991) has pointed out that sedimentary processes associated with submarine fans may create downlap and onlap, unrelated to sea-level changes. The core log description from ODP Site 1000 indicates increased turbidites in the lower units (Sigurdsson et al., 1996). Another possibility, also highlighted by Underhill (1991) (his Figure 13), is block-faulting and subsequent onlap onto the footwall. Onlap onto the s tructural highs within the Serranilla Basin may be rel a ted to block-faulting associated with the reorganization of the NCPBZ during the early Miocene (Rosencrantz et al. 1988; Rosencrantz and Mann, 1991) A third possibility could be increased ash deposits associated with increased volcanism in Central America during the early Miocene (Sigurdsson et al., 1996). These deposits are present at ODP Site 1000 and the units identified within sequence B (units 1 2 and 3) may be a seismic response to this increase in ash deposits. The units identified within sequence B are not separate sequences however, and therefore it is unlikely that increased ash falls actually created the reflector configuration necessary to define a sequence boundary. The top of sequence B (R2) marks a fundamental change in the Serranilla Basin depositional character. Marginal highs are abandoned due to back-step and the basin 83

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margins move north and west. Correlation to ODP Site 1000 indicates this boundary is late Miocene Two tectonic events may be responsible for step-back and drowning of the bank margins and formation of sequence boundary R2. First, the continued collision of the Greater Antilles (Hispaniola at this time) with the Bahama Platform shifts the location of strike-slip movement along the NCPBZ further southward, from the Oriente Transform fault to the Enriquillo-Plantain Garden fault zone. The Enriquillo-Plantain Garden can be tied to the NNR through the Duanvale and Walton Fault zones (Rosencrantz and Mann, 1991; Calais and Mercier de Lepinay, 1995) (Fig 2.34). This reorganization may have led to foundering and segmentation along the NNR, opening seaways and increasing oceanic current transport (Droxler et al., 1992) Secondly, the closure of the Central American Seaway began during the late Miocene restricting flow and causing upwelling in the western Caribbean (Keller et al., 1989; Kellogg, 1995). It has been demonstrated that increased trophic resources are detrimental to coral reefs along the western NNR today (Hallock and Elrod, 1988; Hallock et al., 1988). Late Miocene drowning and step-back of these marginal highs may in fact indicate the initiation of conditions unfavorable for reef development in this area. There is no evidence indicating fault control or debris flow deposits in the seismics and this supports the idea that a change in oceanic environment (excessive trophic resources) caused the drowning. Sequence boundary R2 is most easily identified by the onlap of overlying sediments onto the high-amplitude, continuous reflector that marks the top of the drowned bank margins (Fig 2 20). This type of drowning unconformity resembles the classic sequence boundary but does not occur due to a sea-level lowstand, but in fact, during a relative rise or highstand of sea level (Schlager, 1989). Therefore, sequence boundary R2 marks a major change in sedimentation within the basin, is a major sequence boundary, yet most likely was caused by tectonic events increasing the vigor of oceanic circulation and hence, upwelling across the NNR. 84

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20 N Jamaica 15 N / / / Hess Escarpment / Serranilla Basin / / / / / / / / / / / 70o W I) Cayman spreading center 2) Swan Island fault zone 3) Walton fault zone 4) Duan vale fault zo ne 5) Oriente fault zone 6) Enriquillo-Plantain Garden fault zo n e 7) Septentrional fault z one 8) South Jamai ca fault zo ne Figure 2.34. Map showing locations of significant fault zones along the NCPBZ and their relationship to the study area.

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Sequence boundary R3 correlates to an increase in carbonate mass accumulation rates at ODP Site 1000 ( 4.2-4 1 Ma), and it has been suggested that this is a downstream consequence of the tectonic closure of the Central American Seaway (Sigurdsson et al. 1996). Continued closure of the Central American Seaway and increased current transport to the north may have induced further upwelling and hence productivity. Sequence D, overlying R3, shows the first evidence of 'megabreccia' deposition, and this mass wasting may play a role in creating the onlap that defmes R3 as a sequence boundary. In fact, sequence boundary R4, the final sequence boundary identified in this study may have similar origins. Sequence boundary R4 correlates with a Pliocene tectonic adjustment and southward shift in the strike-slip motion identified along the eastern NCPBZ at 2 rna (Calais and Mercier de Lepinay, 1995). Uplift of the Cordillera Septentrional in northern Hispaniola and cessation of subsidence in the Windward Passage occurs at this time (Calais and Mercier de Lepinay, 1995) (Fig. 2.34 for locations). This southern shifting of the strike-slip motion in Hispaniola may have played a part in the renewed initiation of movement along the Pedro Fracture Zone. Evidence from within the Serranilla Basin indicates the youngest faulting, actually breaching the seafloor, is occurring closest to the Pedro Fracture Zone (Fig. 2.25). Serranilla Basin geologic evolution The sedimentary infilling of the Serranilla Basin is controlled to a large extent by the structure and geometry within the basin, which creates the depocenters for the various sedimentary sources (e g., pelagic neritic, ashfalls) 'Megabreccia' deposition, which has been documented in Diriangen Channel to the north (Hine et al ., 1994), does not appear as a major component of deposition in the early infilling of the SerraniUa Basin Pelagic, periplatform, and early neritic deposition with intermittent volcanic input appears to 86

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dominate. Only in the upper two units is there evidence for 'megabreccia' deposition and mass wasting of the bank margins Based on seismic facies interpretation and lithology obtained from dredges and ODP Site 1000, three different styles of deposition account for the sedimentary evolution of the Serranilla Basin These are 1) early neritic and peri platform deposition, punctuated by intermittent ash falls in sequences A and B, 2) pelagic and periplatform deposition during upper sequence Band sequence C, and 3) pelagic deposition with 'megabreccias' and turbidites in sequences D and E. Oligocene ? to Early Miocene Bas ed on UTIG (MCS) and industry data, the early structure of the Serranilla Basin can be approximated (Fig 2.35 ). Along the west faulting is indicated in the seismic data, with a basin located between the Bawihka Bank edge and the tilted block (Fig. 2.35). As mentioned, this early structure may have controlled the deposition of overlying sequ ences by providing accommodation, but also may have isolated other structural lows (e.g., basin 1) from sediment sources. The northern boundary of the basin was a structural high a nd may have been a continuous carbonate bank across this part of the NNR. Deep MCS data indicate a possible ramp margin bordering the basin in the north at this time. The southeastern margin of the basin was a buildup parallel to the Pedro Fracture Zone. Thi s structural high fronted the early basins (1 and 2) and may have been related to possible transtension/transpression and block-faulting along the Pedro Fracture Zone Deep basement faulting is only seen in a few loc a tions other than the Pedro Fracture Zone (Fig. 2.25). Based on deep MCS data, dredge hauls and exploratory industry wells along the NNR, it is possible to speculate an Eocene Oligocene origin for the Serranilla B as in The dredge from site 31 is made up predominately of micritic, pelagic ooze (see Fig. 2.7), supporting a basin setting at this location in the Oligocene. The tectonics of the NCPBZ at 87

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Figure 2.35 Oligocene?/early Miocene reconstruction of the Serranilla Basin showing isolated ba s ins surrounded by marginal buildups. The area to the southeast is dominated by the Pedro fracture zone and associated block-faulting which later developed a carbonate margin. At this time the basin is already present indicating possible origin during the late Eocene/Oligocene. This does not rule out a continuous carbonate bank in the area of the present day Ro sal ind and Diriangen Banks.

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Oligocene?-Early Miocene Reconstructi tilted block Deep ba s in/pelagic Shallow ca rbonate bank/neritic Periplatfonn deposit s Pedro frac tur e zo n e / (Po ss ible extension) ? / / / / / / /

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this tim e included collision of n o rthwe s tern Cub a with the Bah ama pl atfo rm and the ear ly openin g stages of the Cayman Trough (Rosencrantz et al., 1988; Calais and Mercier de Lepinay, 1995). The Pedro Fracture Zone may have been an area of tectonic adjustment and possible transtension and block-faulting following the collision of the Greater Antilles with the Bahamas. This block-faulting i s also likely responsible for the locations of the basins west of the Pedro Fracture Zone within the Serranilla Basin proper. A more complete grid of MCS data within the basin would likely verify this block-faulted origin. Early t o Late Miocene During the deposition of sequence A, syndepostional folding may have been occurring (e.g., Fig. 2.12), but sequence B appears as flat-lying reflectors most likely depo s ited during a time of little tectonic activity within the basin The deposition during the middle Miocene i s concentrated along the western m arg in of th e ba s in ( Fig. 2.19). Thi s d eposi tion is du e mainly to the aggradation of a bank (reef?) margin here located approximately atop the early Miocene tilted block (Fig. 2.36). This bank margin also provided the sediments that created the reef?-front fill, adding to deposition in this area of the basin. Concurrently, th e structu ral high along the Pedro fracture zone beg an to subside at it s so uthern end. This may have played a part in the depositional pattern observed here. With the removal (subsidence, backstepping) of the marginal high, infilling and bank margin g rowth was able to occur further west (Fig. 2.36). The seismi c facies (Fig 2.16-2.18) show increasingly high amplitude, parallel character and may be interpreted as neritic and bank derived ( turbidite s) deposition during this time. Another factor leading to this seismic character, from evidence in ODP Site 1000 may be the increase in volcanic ash l ayers associated with the Mio cene volcanic episode i n Central America, as previou s ly mentioned The episode, peakin g at about 19 Ma 90

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9 1

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Figure 2.36. Middle to late Miocene reconstruction showing the reef?margin along the western basin. This isolates a small back-margin basin. Backstepping of a portion of the bank-margin along the Pedro fracture zone has occurred and possible reef?margin growth occurs north of this. Basin 2 has been completely infilled at this time.

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MiddleLate Miocene Reconstruction ? Depositional pathways Deep b as in/pelagic Shallow carbonate bank/neritic t-:-j Reef? margins Pedro fracture zon e Periplatfonn deposits Drowned backstepped margin

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(Sigurdsson et al., 1996), produced extensive ash deposits, and changes in the porosity and carbonate content most likely had an effect on the seismic facies character. Late Miocene to Present The structure defining the modem Serranilla Basin was essentially complete by the late Miocene (Fig. 2.37). Infilling of back-margin lows occurred accounting for much of the deposition of sequences C and D. The seismic facies are interpreted as pelagic and periplatform deposition alternating with turbidites and isolated areas of debris flow deposition (e.g Fig. 2.22). Additionally, the fault activity within these upper sequences shows spatial and temporal variability. As previously shown, faulting within the central portion of the basin encompasses sequences A through C (Fig. 2.25). Detailed mapping of faults throughout the entire basin indicates that fault activity becomes progressively younger and more prevalent moving from north to s outh. In fact, the southernmost basin (seismic line 9) s hows evidence of seafloor disruption related to faulting of sequences D and E, in addition to the deeper units (Fig 2.32). Although not recorded on maps showing the seismicity of the region (Molnar and Sykes, 1969), faulting of the seafloor may indicate renewed activity along the PFZ in the south. The cause of this renewed activity could conceivably be tied to continued tectonic readjustment of the NCPBZ and collisional tectonics to the east. Mann et al. ( 1995) have developed an elegant model which shows that, through time, tran s fer of slivers of land from the Caribbean to North American Plate has occurred along the NCPBZ due to oblique collisional tectonics. Concomitant to this transfer of territory, the zone of active left -lateral strike-slip movement moves further south into the Caribbean Plate (see Mann et al., 1995; their Fig. 36). Recent fault activity along the Pedro Fracture Zone would support this model. Sequences D and E display the only seismic facies evidence comparable to the 'megabreccia' deposition identified within the northern seaways (Fig. 2.29 and 2.30) 93

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Figure 2.37. Late Miocene-early Pliocene reconstruction showing the drowning and step back along the western portion of the basin. The new bank margin is indicated. Backstep off the so uthern edge of Serranilla Bank has occurred leaving the remant (Hunapu Bank) reef? margin. Infilling of the northern ( 1) basin is occurring at this time. Arrows indicated possible depositional pathways.

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\0 Ul Late MioceneEarly Pliocene Reconstruction Depositional pathways Deep bas in/pelagic Shallow carbonate bank Periplatfonn deposits Drowned backstepped margin r:-:.; Reef? margins ; ; L ate Miocene bank margin ; Pedro fracture zone; ; ; ; ;

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(Hine et al., 1992). Most notably, the seaway separating the Serranilla Basin from the Pedro Channel exhibits chaotic 'megabreccia' type seismic character (Fig. 2.29). These deposits most likely originate on the adjacent banks. Isolated chaotic facies within the center of the basin may indicate debris flow deposition from the 'drowned' Hunapu Bank to the southeast, or may be part of larger debris flows originating from the Serranilla Bank that have not been fully defined due to limits on seismic control (Fig. 2.30). If these deposits do originate on the Serranilla Bank, over 50 km separates them from their source The occurrence of these deposits solely in the post-Miocene sequences of the basin supports the proposal ofHine et al. (1992) regarding the shallow seaways to the north. They propose a combination of the seismic activity and high-amplitude sea-level fluctuations associated with post-Miocene northern hemisphere glacial cycles as the driving force behind these deposits. The youngest unit identified, sequence E, is interpreted as pelagic and periplatform deposition intermixed with turbidites based on 3.5 kHz, single-channel seismics and piston cores The following chapter will further investigate the sedimentary processes that are responsible for the upper part of sequence E deposition In addition, mineralogical and geochemical variations within the sediments over the past half-million years will be investigated in relation to changing paleoceanographic and climatic conditions. Conclusions The following conclusions are based on interpretation of the structural and depositional evolution of the Serranilla Basin in a sequence stratigraphic framework. 1) Five seismic sequences were identified within the Serranilla Basin ranging in age from early Miocene to present. The lower sequences (A and B) are interpreted as neritic and shallow peri platform deposits associated with the early structural development of the Serranilla Basin. The early basin margin fronted the the PFZ to the southeast and three 96

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distinct basins were identified Additionally, these units may contain a record of volcanic activity in Central America. The upper sequences (C through E) are interpreted as deeper peri platform and pelagic deposits interspersed with turbidites and, in localized areas, megabreccias. These sequences infill the structural lows, creating a predominately flat floored basin. Faulting within these sequences becomes progressively younger toward the south and indicate renewed activity along the PFZ. 2) Seismic evidence indicates that the Serranilla B asin w as not part of a carbonate 'megabank' during the early Miocene to present. Most likely, thi s portion of the NNR consisted of isolated basins fronted by structurally-controlled marginal highs Ba sed on limited deep MCS data, the initial formation of the Serranilla Basin occurred prior to the Miocene 3) Sequence boundaries identified within the basin can be correlated to tectonic activity along the NCPBZ and the Central American Seaway. Sequence boundary Rl correlates to renewed spreading along the Cayman Trough and poss ible movement along the Pedro Fracture Zone. Sequence boundary R2 correlates with the jump in strike-slip movement from the Oriente to the Enriquillo-Plantain Garden Fault Zone and the initial c lo sing of the Central American Seaway. A fundamental change in basin infilling occurs at this time A direct genetic relationship has not been proved, but regional tectonic changes must be con sidered an important factor in controlling depositional se quences of the bas in. 97

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Introduction CHAPTER 3 LATE QUATERNARY SEDIMENTARY AND PALEOCEANOGRAPHIC EVOLUTION OF THE SERRANILLA BASIN The Serranill a Basin is the westernmost basin along the NNR and i s the final 'gateway' the Caribbean Current passes through before joining the northward flow of surface waters that eventually join the Gulf Stream (Wust, 1964; Gordon, 1967) (Fig. 1 .6). The Caribbean Current potentially has two important effects on the late Quaternary evolution of the Serranilla Basin. First it may play a role in the se diment distribution patterns within the Serranilla Basin through current winnowin g, nutrient upwelling, and by affecting the location and frequency of turbidites shed during sea -level highstands. In the Bahamas, Mullins et al (1979) has mapped the sediment distribution patterns in Northwest Providence Channel using 3.5 kHz echo character patterns, and ba s ed on these data, inferred possible controls on sediment distribution Using this methodology, large areas may be mapped without the need for closely spaced bottom sampli n g ( Damuth, 1975 ; Damuth and Hayes, 1977). By ground-truthing echo-character types in key locations with piston cores, infilling patterns and the role of surface and deep currents may be determined in the Serranilla Basin In addition, much of the work done in modem carbonate basin s ettings has focused on the connection between the shallow banks ( neritic) and the adjacent basin or 98

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peri platform environments (Schlager and Chermak, 1979; Boardman et al., 1986; Wilber et al., 1990; Glaser and Drexler, 1991 ; Schlager et al., 1994). This connection, for the most part is represented by turbidite deposition often tied to 'highstand shedding' off the carbonate platforms (Lynts et al. 1973; Schlager and Chermak, 1979; Drexler et al., 1983; Drexler and Schlager, 1985; Glaser and Drexler, 1991; Schlager et al 1994) The Serranilla Basin differs from the other basins along the NNR (e.g Pedro and Walton Basins; Fig. 1 .1) because of the downstream location of the shallow banks with respect to the prevailing surface currents (the Caribbean Current) (Fig. 1.6) In fact, it also differs from Bahamian basins in this respect. Most studies of turbidite deposition infer that the prevailing surface currents control the volume and location of turbidites deposited during sealevel highstands (Kier and Pilkey, 1971; Glaser and Drexler 1991; Schwartz, 1996). The Serranilla Basin represents an opportunity to test this idea and determine if factors other than the prevailing currents affect turbidite deposition. In the Walton Basin, northeast of the Serranilla Basin, Glaser and Drexler (1993) have pointed out the importance of the Caribbean Current and partial seafloor dissolution of metastable carbonates as two important factors controlling late Quaternary stratigraphy. Two other factors; namely, input of siliciclastic sediments and input of pelagic and bank top carbonates, round out their list of controls on deposition (Glaser and Drexler, 1993). The Serranilla Basin differs from the Walton Basin in its distance from a source of siliciclastic sediments (Walton Basin is adjacent to Jamaica) Also, as pointed out above the Serranilla Basin is essentially upstream from the surrounding shallow banks, in contrast to the Walton Basin, which lies directly between the Pedro Bank and Jamaica (Fig. 1.1, for location). These two differences may affect the controls on late Quaternary sedimentation within the Serranilla Basin. Therefore, an objective of this study is to identify the factors (currents, dissolution, siliciclastic input, etc ) that control glacial and interglacial sedimentation within the basin, and determine which are most significant in controlling the late Quaternary stratigraphy. 99

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The second effect of the Caribbean Current involves paleoceanographic changes. The modern Caribbean Current is a portion of the surface return flow of the global thermohaline circulation system, which originates in the Indian Ocean and is brought north by the Benguela and Guiana Currents (Fig. 3 1) (Gordon et al., 1992; Haddad and Droxler, 1996). An important component of this return flow is corrosive, low [CO/"] Antarctic Intermediate Water (AAIW), entrained into the Caribbean with the sub thermocline water of these currents (Fig 3.2) (Gordon et al., 1992; Haddad and Droxler, 1996). Metastable carbonates (aragonite and Mg-calcite) are sensitive recorders of the presence or absence of AAIW in the Caribbean during the late Quaternary (Glaser and Droxler, 1993; Haddad and Droxler, 1996) and may provide a paleoceanographic record linked to glo bal circulation events from the Serranilla Basin A comparison between the NNR and Bahamian metastable carbonate dissolution rates highlights the importance of this AAIW in controlling peri platform sediment accumulation (Droxler et al., 1991; Glaser and Droxler, 1993). Haddad and Droxler (1991) point out that shallower than 1200 meters the Atlantic and Caribbean CaC03 preservation history is in phase (both show dissolution during glacial stages), while below that depth they are out of phase (Caribbean shows CaC03 dissolution during interglacials). Global circulation patterns that direct the flow of more corrosive AAIW into the Caribbean at this depth are the primary cause of this poor carbonate preservation This circulation also provides inter-hemisphere heat and salt exchange from the South to the North Atlantic ocean and this may pre-condition the Atlantic for NADW formation (Gordon et al., 1992). The effects of peri platform dissolution in the Caribbean may therefore be used to infer global paleoclimatic changes. Finally, long-term (525 ka to present) changes in paleoceanographic factors (increased currents and decreased nutrients) have been identified in the adjacent Pedro Basin based on detailed analyse s of geochemical and mineralogical components of peri platform sediments (Schwartz, 1996). Additionally, Schwartz ( 1996 ) has interpreted 100

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........ 0 ........ A B 30"W o _, Figure 3.1. A) Shows the Southern Ocean circulation and the source of a portion of the waters that enter the Caribbean. Numbers indicate Sverdrups of volume transport (1 Sv = 106 m3s 1 ). Shallow waters are indicated by solid lines, AAIW is indicated by dashed lines (from Gordon et al., 1992). B) Shows a simplified global pathway for AAIW as part of the global thermohaline circulation system. Small arrows indicate surface flow patterns. The heavy line represents AAIW flow (from Haddad and Drexler, 1996).

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5 sso 40 20. Modern Atlantic Circulation o Latitude Gla c ial Atlantic Circulation o 20 Latitude 40 60 N 10 Figure 3.2 Shows a north-south cross-section through the Atlantic ocean indicating circulation pattern s with depth, during modem (int erg lacial ) and glacial times (Haddad and Droxler, 1996) The small box indicates waters that would enter the Caribbean over the 1600-1800 meter s ill depth These include a portion of entrained AAIW during interglacial s (mo d em), but this water mass i s absent in the Caribbean during glacials. 102

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the Mid-Brunhes (525-185 ka) as a time of mild (less severe glacials) glacial/interglacial cycles, while the Late-Brunhes (185 ka to present) is characterized by more drastic climatic shifts Several studies find similar long-term trends globally (Raymo et al 1993 ; Rodell 1993). Droxler et al. (1988) in the Bahamas, Farrell and Prell (1991) in the Pacific, and Droxler et al. (1990) and Bassinot et al. (1994) in the Indian Ocean, have all found evidence suggesting an increase in calcite preservation since the Mid-Brunhes dissolution cycle' centered at about 400 ka. Separate evidence, using a1 3C in the deep sea suggests that NADW formation has varied through time, and that the Mid-Brunhes is a time of stronger NADW formation during both glacials and interglacials perhaps suggesting milder climate extremes (Raymo et al. 1990; Rodell, 1993) Drawing on the framework of Quaternary investigations outlined above, the goals of this research are to develop a sedimentary, paleoclimatic and paleoceanographic history for the late Quaternary Serranilla Basin and tie these into the regional/global paleoceanography. The main objectives will include ; 1) Map the sediment distribution patterns within the Serranilla Basin and tie these patterns into controls (neritic and pelagic inputs, current direction/intensity). Also, to investigate the relationship between the turbidite frequency as determined from piston cores, and turbidite provenance, with relation to the Caribbean Current. 2) Identify the factors (neritic/pelagic/siliciclastic input, dissolution, current winnowing, sea-level) that control glacial and interglacial sedimentation within the basin and determine which are more significant in controlling the late Quaternary stratigraphy of the Serranilla Basin. 3) Compare and contrast the findings of similar studies in the Walton and Pedro Basin with results from the Serranilla Basin Differences in proximity to terrigenous sources, westward intensification of the Caribbean Current, and differences in the locations 103

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of shallow banks with respect to these factors, may affect the signature of late Quaternary sediments. 4) Identify any long-term trends in sediment characteristics which may indicate fluctuations in current strength, nutrients, or preservation of carbonates, and tie these into possible regional or global causes. Methods Approximately 1100 trackline kilometers of 3.5 kHz seismic data were collected within the Serranilla Basin aboard the RN Cape Hatteras in April and May of 1992 (Fig 3.3). These were collected using a hull-mounted seismic source which was in continuous operation during other types of data collection The 3 5 kHz data were used to construct echo character maps of the bottom sediments based on the scheme of Damuth and Hayes (1977) and Mullins et al. (1979). Ten piston cores were also collected within the basin (Fig 3.3) Core sites were selected using the seismic data in an attempt to sample thick, continuous deposits that might be isolated from turbidite activity. These cores were taken in water depths ranging from 888 to 1785 m and the lengths of core retrieved varied from 6 to over 11m. Some of these cores have been used to corroborate sediment interpretations derived from echo character. Cores were cut into 1.5 meter sections aboard ship and kept in cold storage during the remainder of the cruise. Splitting and core description was conducted at Rice University All ten cores were described with particular attention paid to bioturbation and turbidite occurrence and frequency (Appendix I) The two longest cores 27 (1126 em) and 35 (1045 em), were chosen for further sub-sampling and analyses based on their general lack of turbidites, and their different depths (27; 1210 meters; 35; 888 meters). Sub-sampling was conducted downcore at 10 em intervals Each subsample was immediately weighed to determine the wet weight, and then dried in an oven for at least 48 104

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Diriangen Bank Figure 3.3. Basemap showing 3.5 kHz coverage and piston core locations for the Serranilla Basin. Location of core VlS-357 is also shown. Bathymetry is based on 3.5 kHz data (see chapter 2 for details). 105

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hours and weighed again (dry weight) Standard grain size analyses were conducted on each sub-sample, separating the mud from the sand ( 63 J..Lm wet sieve) and these size fractions were weighed to determine relative proportions The fine fraction ( <63 J..Lm) was analyzed for carbo nate content using the carbonate bomb method. The pressure of C02 released by dissolving the carbonate in HCl was compared to a 100% CaC03 standard dissolved in HCl to determine total percent carbonate (for details see Droxler, 1984, Droxler et al., 1988) Carbonate mineralogy of the fine fraction was determined through X-ray diffraction analysis. The analyses were carried out on a Scintag XDS 2000 X-ray diffractometer at 40 KV and 35 Ma with a 2-theta angle from 26 to 31 at a rate of 2 I minute. The areas under the curves for the calcite, high-Mg calcite (>4 mole% MgC03 ) and aragonite were estimated using peak-fitting and peak area algorithims that are part of the Scintag software In core 35, peak areas values of high-Mg calcite were distinct enough for the peak area software to identify and calculate these values Core 27 however, did not have a distinct high-Mg calcite peak below the upper 5 meters of core and the peak area was set to 0.00 for high-Mg calcite for these samples This did not affect the aragonite values, as these are based on total area of both the calcite and high-Mg calcite peaks, only the calcite to high-Mg calcite percentages. Reproducibility for this methodology has been reported as a maximum discrepancy of 9% between measured values of calci te and high-Mg calcite (Droxler et al., 1988) Aragonite percentages have been calculated with an accuracy of 5% or better from a calibration curve (Droxler, 1984; Droxler et al., 1988) The coarse fraction (>63 J..Lm) was analyzed for microfossil content with special attention paid to developing an initial Globorotalia menardii complex zonation based on presence or absence of G. menardii and G tumida (Ericson and Wollin, 1968). Oxygen isotope stratigraphy was developed using Globigerinoides sacculifer, a planktonic foraminifera. This surface-dwelling foraminifera (0 -50 meters) was chosen for this study based on initial studies with other foraminifera (Orbulina universa and G 106

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mennardii) and its use in other Caribbean basin studies (Prell, 1978; Glaser and Drox1er, 1993; Haddad and Droxler, 1996 ; Schwartz, 1996). The 355-425 J..Lm fraction was separated from the remainder of the coarse sample and 6-20 hand-picked specimens of G. sacculifer were obtained. These were sent to the University of Michigan Stable Isotope Laboratory for oxygen and carbon isotope analyses. The resulting curves were compared to the SPECMAP stack (Imbrie et al., 1984) to help develop an age/depth model within the basin. Results Modern Sedimentation Patterns Modem sediments infilling the Bawihka and Diriangen Channels have been previously studied and described using dredge hauls, single-channel seismic and 3.5 kHz data (Hine et al., 1992; Hine et al. 1994). Based on 3.5 kHz profiles, echo character maps were constructed for Bahwika Channel and three dominant echo character types were identified (Hine et al., 1994). Type 1 are described as flat-lying, mostly prolonged bottom echo with a single sub-bottom reflector and have been interpreted as winnowed partially cemented sands. Type 2 are mounded, rugged textures with both small and large overlapping hyperbolic diffractions and have been interpreted as debris-flow deposits and displaced blocks. The final echo character, Type 3, is described as a sharp bottom reflector with numerous continuous/semicontinuous subbottom reflections and this is interpreted to be turbidites and/or winnowed sands. The classification of these reflector types does not follow the scheme of Damuth and Hayes ( 1977) and Mullins et al. ( 1979) who identify three main types with several sub-classes (Table 3.1). These are: type I (A and B), distinct reflectors; type II (A and B), indistinct reflectors; and type III (A thru F), hyperbolic reflectors. Mullins et al. (1979) identify type IIIG and type IV, a combination of type lA and type liB, in the Bahamas and although these were not found in the Serranilla Basin 107

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Table 3 .1. A compilation of echo character types from several studies. The echo character types u se d in the Bawihka Channel are also listed, although Type 2 is difficult to match with a particular type from the earlier studies. Not all echo character types were found in the Serranilla Bas in and the column on the far right lists those identified.

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Echo C haracter Damuth and Mulli ns et at. Hine etal Schlager and. Identified i n Description Hayes ( 1 977) ( 1979) (199 4 ) C hermak (1979) this study (from Damuth and Hayes, 1977) Brazilian coast Bahamas* Bawihka Channel TOTO SerranillaBasin Sharp continu o u s w/ no s ub -Type !A Type IA N/A N/A N/A bottom reflectors Sharp continuous w/ n ume rous T ype IB Type IB Type3 Basin Interior TypeiB parallel sub-bottoms Semi prolonged w/ intermittent TypellA TypellA Type 1 Basin Margin? Type ITA parall el sub-bottoms Very prolong ed w/ no s ub -Type llB Type llB N/A Bas in Margin Type llB bottoms Large irregular hyperbola e w/ Type IDA Type IDA N/A Gullied Slope TypelllA varyi n g vertex e l evations Regular single h yperbo l ae w/ Type lliB Type lliB N/A N/A varyi ng vert i ces and co nformabl e N/A s ub-bottoms Regular overlapping h yperbolae w/ TypeffiC TypeffiC Type 2? Gullied Slope? T ype me varyi ng vertex elevations Regular overlapping hyperbolae w/ TypelllD Type IllD Type 2? N/A N/A ve rtices tangent to the sea flo o r Type IIID h yperbo l ae w/ inter -Type lliE Type lliE mitten! zo n es of 18 echoes N/A N/A N/A Irregular single h yperbo lae w/ T ype lliF Type lliF N/A N/A N/A non -confo rmable sub bottom s Regular di s crete or s l ight l y over-Type fiG l apping hyperbolae w/ eq u al vertex N/A Type 2? N/A N/A e l evations and no sub-botto m s* Type lA overlying Type liB N /A T ype IV N/A N/A N/A

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Schlager and Chermak (1979) are included in Table 3.1 although their classification scheme is minimal. Five echo character types were identified within the Serranilla Basin (Figs. 3.43.8). Each echo character type has been described using the above terminology of Damuth and Hayes (1977) and Mullins et al. (1979). Echo character type m represents a distinct seafloor reflector with a single, distinct, continuous sub-bottom reflector (Fig. 3.4). This echo character i s mapped along the southern margin of the basin and interfingers with echo character type ITA southeast of the Pedro Fracture Zone (Fig. 3.9). Echo character type IIA is an indistinct echo character response, with semi prolonged bottom echoes (Fig. 3.5). It is the predominant echo character type within the Serranilla Bas in, covering much of the central and eastern portion of the basin. It is also mapped at the entrances into the Diriangen and Pedro Channel and it interfingers with type ITA in the deeper southeast portion of the basin (Fig. 3.9). A similar echo type, echo character type Im, also shows an indistinct re sponse with no s ub bottom reflector s (Fig. 3.6). This echo character typ e i s predominately located in the northern part of the basin at the entrance into the Rosalind and Diriangen channels, respectively (Fig. 3 9). It i s also mapped off the s outheastern tip of Bawihka Bank and on the slope of the Pedro Fracture Zone. The final two echo character types, type lliA and me, are hyperbolic reflector s (Fig. 3 7 and 3.8). Echo character type lliA occurs proximal to the bank margins. Isolated patches of type IDA are found off Hunapu bank and to the south along the Pedro Fracture Zone (Fig 3.9) Tighter 3.5 kH z coverage along the Pedro Fracture Zone may s how mor e extensive type lliA echo character parallel to the ba se of s lope. Ec ho c haracter type illC is marked by regular overlapping hyperbo l ae with subtle variation in elevation above the s eafloor (Fig. 3 8). This echo character type lie s exclusively in a circular area in the western portion of the ba si n (Fig. 3.9). 110

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w E Echo Character Type ffi PC20 . --------------------" ---:-r ---------. __ -16Y5 0 1 . I ,, . !' .. i Kilometers 2 3 --'-----1687 5 m 4 5 Figure 3.4 Echo character type ill from 3.5 kHz data Location of this is shown in Figure 3 3 This echo character shows a distinct seafloor return with a sing le continuou s sub-bottom reflector

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E Echo Character Type IIA . . ...... . : . . I ,t. : .. :,. : ... ." . , 0 1 . ' . 2 3 4 Kilometers .. 5 w Figure 3.5. Echo character type IIA from 3.5 kHz data See Figure 3.3 for location. Echo character type IIA from 1150 meters water depth, shows an indistinct bottom reflector respon s e with semi -pr olonged s ub-bottom echos.

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w E Echo Character Type liB I. l ; : I : o ...... 0 1 2 3 4 5 Kilometers Figure 3.6. Echo character type liB from 3.5 kHz data. See Figure 3.3 for location. Echo character type liD, from 1150 m waters depth, shows an indistinct seafloor re s ponse with no continuous sub-bottom reflector s.

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N s Echo Type IliA m Kilometers Figure 3.7. Echo character type IliA from 3.5 kHz data. See Figure 3.3 for location. Echo type IliA, obtained in 975 m water depth, s how s both smal l and large, irre g ular ove rlappin g hyperboli c diffractions.

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E w Echo Character Type IIIC 0 1 2 3 4 5 Kilometers Figure 3.8. Echo character type IIIC from 3.5 kHz data. See Figure 3.3 for location. This echo character type, from 1150 meters water depth, exhibits regular overlapping hyperbolic diffractions that show very little variation in e l evation above the seafloor.

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116

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Figure 3.9. Echo character map based on distribution of 3.5 kHz echo character types Piston core locations are also included. Descriptions of each echo character type are given. Echo character types are based on the work of Damuth and Hayes ( 1977) and Mullin s et al. (1979).

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Pauem D -Ec h o Charac ter T ype* De scri pti o n IB IIA liB III A IIIC Continu ous, s harp bo n o m ec h oes with continuous, sharp, paralle l s ub -bott om r eflec t ors Semi prolonged bo n o m ec h oes w ith int e rm itte nt zones of semipro l onged disco ntinu ous oarnllel sub-bouom reflectors Prolonged bo n om ec h oes with n o s ub-bottom reflectors Large, irr egu l ar over la pp in g hy perbo lae with widely varying vertex eleva ti o n s above th e sea floor Regular overlapping h ype rbol ae w ith varying e l evatio n s above th e sen floor and no s ub-bouom r eflectors Based on Damuth and H ayes ( 1977) and Mullins e t nl. ( 1979) 117

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Another source of information on sedimentary patterns and provenance within the basin is turbidite location and frequency as indicated in the piston cores (Table 3.2) Turbidites are identified within piston cores as coarser sequences, often lighter colored than the surrounding sediments with distinct basal contacts, and often fining-upwards. Samples from turbidites in piston cores from the adjacent Pedro Basin indicate sediments of neritic and shallow-water affinity (pers comm. J. Schwartz). Hence, provenance (shallow banks) has been interpreted based on core locations and predominant current direction. As discussed previously the Caribbean Current flows northwestward through the Serranilla Basin and adjacent seaways (Wust, 1964). It is worth noting however, that seasonal storms produce reversals in the surface-current flow from northwestward to southeastward (Hallock et al., 1988). How these excursions from the norm may affect sediment transport will be discussed later. The piston cores are divided into three groups ; cores with essentially no turbidite activity (cores 20,28,34,35), cores with intermittent turbidite activity (cores 21, 26, 27), and cores that are characterized as having substantial turbidites (cores 19 25, 33) (Fig. 3 10). The details of turbidite frequency and turbidite versus total sediment are given in Table 3 2 In general, the further from the shallow banks, the less turbidite deposition occurs within the core, core 28 being an end-member example (Fig 3.10). Notable exceptions to this general rule are cores 34 and 35, which are located on a sediment high between the Diriangen and Rosalind channels As shown in the bathymetry, this area is shallower than the surrounding seafloor, and may account for their lack of turbidites. Core 25 is also exceptional in that it shows substantial turbidite activity at nearly 70 kilometers from the nearest shallow water bank. Possible reasons for this will be addressed in a following section. 118

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Table 3 2 P is ton core sites, depth s and i nformation on turbidite content. core # LAT LON Length (em) #sect depth (m) Tim of core* total % T** 19 15. 518 -79 911 694 5 1577 1.01 9 10 20 15.416 -80 079 604 4 1548 0 .00 0.00 21 15. 573 -80 188 601 4 1123 0 .8 3 7 10 25 15. 251 80.413 720 5 1228 1.67 3 0 30 26 15 233 -80.357 799 6 1204 0 .63 2.50 27 15 234 -80 357 1126 8 1210 0 27 0 .90 28 15 068 80 046 612 4 1785 0.00 0 .00 33 15 783 80 261 776 6 115 3 1.30 32.50 34 15.785 80.732 833 6 891 0 1 2 2.00 35 15.784 -80.731 1045 7 888 0 00 0 .00 Turbidit es pe r meter of core. Totals number of distinct turbidit e interval s divided by total core length. **Total percenta g e of core made up of turbidite depo s its. Thicknes s of total turbidite horizon s divided by core len g th.

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16 00' 15 00' Uule or no turbid ite s (< 0.20 turbidites/meters of core) A Intenniue nt turbidites (0.21.0 turbidites/meters of core) Substan t ia l tur bidites (>1.0 turbidites/meters of core) w a ; a ; t ;o t Figure 3.1 0. Piston core lo ca tions showing turbidite frequency. Turbidite frequency is determined by number of distinct turbidite events divided by the entire length of the core This provides a minimum frequency of occurrence. Core 27 and 35 were used for detailed analysis. 120

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Depth in core (em) z Menardii Zones ()18o curve 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 30 v Piston Core 27 % carbonate mud 40 50 60 70 80 90 20 I I I I I I I I I I I %total mud 40 60 Bottom of core ()13C curve 80 100 1.0 1.5 2.0 2.5 3.0

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Figure 3.12. Piston core 35 sedimentological and isotopic data versus depth based on a 10 em sampling interval down the entire core. Core 365 is 1045 em long. Menardii zones are shown for approximate ages. Percent total carbonate of the fine fracton and percent mud of bulk s ediment were determined for each sub-sample and are shown here. Both the oxygen and carbon isotope curves are also given. Isotope values are relative to the PDB standard.

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Piston Core 35 Menardii Depth in core (em) z Bottom of core Zones alSo curve % carbonate mud % total mud a13c curve X v 1.0 o.s 0 0 -0.5 -1. 0 1.5 -2.0 so 60 70 80 90 20 40 60 80 100 1.0 t.S 2 0 2.5 3 0 I I I I I I I I I I I I _____ .J_l_ ___ I I I I I I I I I I I I I I ------'----

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70 %total 60 car b o n a t e 50 40 25 20 %aragonite 15 (to total car b. ) 10 5 0 V 18 3 57 (Serranilla Basin; Prell and Hays, 1976) Isotope stages 0 100 200 D epth (e m ) 6.3 300 400 Overa ll Sed. rate 2.08 cm/ky Figure 3.13. P iston core data for Vl8-357 New oxygen isotope stages were c h osen based on the SPECMAP stack (Imbrie et al., 1984). This choice for age/depth gives a sedime n tation rate of 2.08 crn/ky. Percent total carbonate a n d p ercent aragonite are also shown. 126

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Figure 3 .14. Carbonate mineralogy for cores 35 and 27 based on X -ray diffraction analysis of the fine fraction ( <63 flm). Selected samples were chosen to identify patterns based on oxygen isotope curves. Note that core 27 shows no discemable Mg calcite below 480 em.

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Core 35 Core 27 carbonate mineralogy (%) carbonate mineralogy (%) (fine fraction) (fine fraction) 0 10 20 30 40 50 60 70 80 90 100 0 w w 60 m w 90 100 Depth in Depth in core (em) core (em) 100 100 200 200 300 300 400 Aragonite 400 D Mg-calcite 500 500 D Calcite 600 600 700 700 800 800 900 900 1000 1000 bottom of core @ 1045 em 1100 bottom of core @ 1126 em

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chronostratigraphy hence, menardii zonation is also plotted and provides an estimate of age downcore (Ericson and Wollin, 1968)(Fig 3.11 and 3.12). Isotope stratigraphy Age/depth An age/depth model was developed for core 27 and 35 based on the SPECMAP oxygen isotope curve and menardii complex zones (Ericson and Wollin, 1968; Imbrie et al ., 1984). Ages assigned to isotope events for the SPECMAP curve are shown in Figure 3.15. Correlation of oxygen isotope stages for core 27 and 35 are straightforward, based on pattern matching (Fig. 3.16). The beginnings of interglacials are easily matched as there is an abrupt decrease in d180 values. The ends of interglacials are slightly more problematic as the transition into a glacial stage is never abrupt, and often occurs over an extended depth range within the cores. Therefore, matching of individual events in stages 6, 8 and 10 is less straightforward, and these picks may affect estimated sedimentation rates and mass accumul a tion rates. Additionally, through stage 6.5, menardii zones are also used One questionable data point occurs in core 27, where stage 11.1 appears as a much more negative isotopic spike than in the SPECMAP curve. The adjacent isotope stages (9,10 and 12) match well however, so the choice for 11.1 is maintained. Based on these age/depth relationships, variation in sedimentation rates can be seen downcore (Fig. 3.17 and 3.18). In core 27, lowest sedimentation rates occur during stages 1-3 stage 6, 10 and 12 (1.15-2.98 cm/ky)(Fig. 3.17). Stage 4 also shows a flat slope, but it is not resolved within the 10 em sampling interval due to low overall sedimentation rates In general, sedimentation rates alternate with isotopic stages, with the exception of stage 8 Odd numbered isotopic stages, or interglacials, show higher sedimentation rates than glacial stages. The high sedimentation rate in stage 8 may be related to the choice of isotope peaks 8 5 and 8.6. If, in fact, the sedimentation rate of stage 8 is low, as in stage s 6, 10 and 12 stages 8.5 and 8 6 would need to be shifted to the left. Assuming the 8/9 129

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Figure 3.15 The SPECMAP oxygen isotope curve, isotope stage picks, and the age es timate s for each of the i s otope stages (from Imbrie et al., 1984) The age/depth model developed for core 27 and 35 are based on these isotope stage age estimates.

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Figure 3.15. The SPECMAP oxygen isotope curve, isotope stage picks, and the age estimates for each of the isotope stages (from Imbrie et al., 1984) The age/depth model developed for core 27 and 35 are based on these isotope stage age estimates.

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SPECMAP curve (Imbrie et at, 1984) -2 5 -1.5 0.5 a I so 0.5 1.5 2 5 0 100 200 300 400 500 ....... VJ ....... Age (ky) SPECMAP SPECMAP SPECMAP SPECMAP 1.1 6 5.5 122 8.0 245 11.1 368 2.0 12 6.0 128 8.2 249 11.2 375 2 2 19 6 2 135 8 3 257 11.3 405 3 0 24 6 3 146 8 4 269 12.0 423 3 1 28 6.4 151 8 5 287 12.2 434 3.3 53 6 5 171 8.6 299 12.31 443 4 0 59 6 6 183 9.0 303 12.33 461 4.2 65 7 0 186 9 1 310 12.4 471 5 0 71 7.1 194 9 2 320 13.0 478 5 1 80 7 2 205 9.3 331 13.11 481 5 2 87 7.3 216 10.0 339 5.3 99 7.4 228 10. 2 341 5.4 107 7.5 238 11.0 362

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Figure 3.16. Oxygen isotope stratigraphy for core 27 and core 35. Isotope stages are chosen based on pattern matching downcore with the SPECMAP oxygen isotope curve (Fig. 3 .15). Dark shading shows interglacial s tages, light shading shows glacials, with the exception of s tage 3, which is included as part of glacial stages 2 and 4. The menardii zo nation i s also included and has been u s ed to help refine choices for isotope s tages 5 and 6.4/6. 5.

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Core 27 1200 3 4 5 6 7 8 9 10 lt 1100 1000 900 800 Depth in 700 Average core (em) 600 Sed rate 500 Stage (crnfky) 1-3 1.15 400 4 not resolved 300 5 2.28 200 6 1.93 7 2.22 100 8 2.95 0 9 2.80 10 2.17 11 3.28 12 12 2.00 10 8 Avg sed. rate Sed rate 6 crn!ky 4 2.28 crnlky 2 0 0 100 200 300 400 500 Age (ky) Figure 3.17. Age/depth plot for core 27. Upper part of figure shows age (horizontal axis) versus depth in core. Steeper parts of the curve represent higher sedimentaion rates. The lower part of the figure shows age versus sedimentation rate. The highest sedimentation rates occur at the ends of interglacials (11, 9 and 7). The average sedimentaton rate for each stage is shown at the right. Overall average sedimen t ation rate for the entire core is also shown. 134

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Figure 3.18. Age/depth plot for core 35 Upper part of figure shows age (horizontal axis) versus depth in core. Steeper parts of the curve represent higher sedimentaion rates. The lower part of the figure shows age versus sedimentation rate. The highest sedimentation rates occur at both the beginning and ends of interglacials. The high sedimentation rates at the beginning of interglacials may be related to flooding of the nearby banks The average sedimentaton rate for each stage is shown at the right. Overall average sedimentation rate for the entire core is also determined. 135

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boundary would then occur at 595 em depth downcore, this would change sedimentation rate s for stage 8 and stage 9 to 2.43 crnlky and 3.64 crnlkyr, respectively. Additional nannofos s il biostratigraphy may be needed to better place these isotopic stages. Therefore, in this study, the original placement of isotope peaks will be used as this is the best match to the SPECMAP curve. The average sedimentation rate for the entire core 27 is 2.28 crn!ky. This is similar to the deep core Vl8-357, which shows an average sedimentation rate of 2.02 crn!ky ba se d on a revised age/depth relationship (Prell and Hays, 1976; Glaser and Droxler, unpub. data ) (Fig 3.13). Core 35 has a slightly higher overall sedimentation rate at 3.23 crnlky, but this is not unexpected, as core 35 lies closer to the carbonate banks and this additional neritic source (Fig. 3.18). Core 35 also shows the alternating high and low sedimentation during interglacial/glacial stages. In detail, core 35 has low sedimentation rates during stages 1-3 and stage 6. Odd stages 5, 7, and 9 show high sedimentation rates, as well as glacial stage 8. Again, stage 4 is difficult to resolve, but in this core appears to show a high sedimentation rate as well. Both cores (27 and 35 ) tend to agree with the general pattern observed in s edimentation rates in the adjoining Pedro Basin, high during interglacials and low during glacials (Schwartz, 1996). Noticably, both ba s ins show the lowe s t sedimentation rates during stages 1-3. Sediment Compon e nts Variation in the percent coarse and fine fraction (inverse curves) have been plotted downcore (Fig. 3.19A, B). The coarse fraction is made up of both planktonic and benthic foraminifera and pteropod s. In general, the percent coar se fraction increases during interglacials and decreases during glacials. Core 35 shows a deviation from this during s tage 5, when the coarse fraction decrease s during the middle of this stage but remains high at the beginning and end. Core 27 reaches a coarse fraction minimum in glacial stage 8 with 136

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Figure 3 19 Percent coarse (A) and fine (B) fraction curves versus age downcore. Core 35 i s s hown as the dotted line, core 27 is solid. Interglacial stages are shaded for reference One a nomalous peak occurs at the stage 11110 boundary. See text for details.

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A P e r c ent coar s e fra c tion 10 11 12 13 5 0 40 Q) 0 (.) 30 20 1 0 0 0 50 100 1 50 200 250 300 350 400 450 500 A g e (ky) B P e r ce nt fin e fractio n 5 6 7 12 13 80 7 0 60 50 40 --core 2 7 (12 1 0 meters dt!f.th ) ,._ .... .. co re 3 5 (888 m e t ers deJ1b) 0 50 100 150 200 250 300 350 400 450 500 A g e (ky) 1 38

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slightly increasing glacial values during stage 6 and 2-4. The fine fraction percentages (Fig 3 .19B) are the inverse of the coarse fraction and in general show high values during glacial stages. One value of note on these curves occurs during the beginning of stage 10 A dramatic coarse spike (increased coarse percent) occurs at this time Visual examination of these grains indicate that they are in fact, aggregates of finer-grained material, or what Schwartz (1996) has termed 'cohesive grains'. These represent the only 'cohesive grains' identified in the cores and their origin is unclear The mineral components that make up the fine fraction of the sediments have also been determined at a 20 em sampling interval in core 27 and selected glacial/interglacial samples for core 35 These have been plotted with respect to relative percents. Percent fine fraction aragonite shows a strong glacial/interglacial variability, with high values occurring during interglacials in both cores (Fig. 3.20A). Overall, Core 35 shows higher values than core 27, although this is to be expected based on recent work on high-stand shedding of neritic carbonates (Boardman et al., 1986 ; Drexler et al., 1988; Glaser and Drexler, 1993 ; Schlager et al., 1994) (Fig. 3 20A). The fine fraction Mg-calcite curve however does not show a recognizable glacial/ interglacial variability (Fig. 3.20B). Core 35 again has higher values than core 27, peaking during stage 6 and declining gradually through stage 1 The deeper core 27 shows no discernable Mg-calcite prior to late stage 8, a peak at stage 6, and an increasing trend from stage 6 through stage 1. The fme fraction calcite curve also lacks a distinct glacial/interglacial variability in both cores (Fig. 3 21A) In core 27 it reaches a maximum at the beginning of stage 9 and shows an overall decrease through stage 1. Core 35, although lower in total percent than core 27, follows the same overall trend from stage 9 through stage 1. Variations in the fine fraction non-carbonate component do show a degree of cyclicity with higher values occurring during glacials (Fig. 3.21B). This pattern is most prominent in core 27 although the same general pattern can be observed in both cores. The 139

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Figure 3.20. Percent fine aragonite (A) and percent fine Mg-calcite (B) to bulk sediment versus age. Selected samples (see appendix ll) were analyzed downcore to determine trends. (A) Percent fine aragonite shows strong glacial/interglacial variability in core 35, less s trong in core 27. Generally increasing trend in percent fine aragonite from stage 10 to stage 1. (B) Mg-calcite curves show no strong glacial/interglacial correlation. Mg-calcite is absent in core 27 prior to stage 8.

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Percent fine aragonite (to bulk sediment) A 0 50 100 150 200 250 300 350 400 450 500 Age (ky) B Percent fine Mg calcite (to bulk se dim e nt) 12 3 (1210 me rr rs depth) ........... core 3 5 (888 meter s depth) 5 / i /\ { \ I \ \4 \/ v v 0 5 0 100 150 200 250 300 350 400 450 500 Age (ky) 141

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Figure 3.2 1 Percent fine calcite (A) and percent non-carbonate (B) to bulk sediment versus age. Selected samples were analyzed downcore to determine trends. (A) Percent fine calcite does n ot s how glacial/interglacial variability but does display a long -term trend in toward lower fine calcite percent ages. (B) Percent non-carbonate shows fairly well-developed g lacial/intergl ac ial cyclicity with higher percentages during the glacial stages in both cores.

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50 20 10 Percent fi n e calcite (to bulk sedimen t ) A --core 27 (1210 met e r s d ep th ) ............... core 35 (888 met ers depth) 0 60 50 ...... 40 0 .D @ (.) Q 30 0 s:: 20 10 0 0 50 1 00 150 200 250 300 350 400 Age (ky) B P e rcent fine non-carbonate ( t o bulk se dim e nt ) s i i ., : '.,) 6 --core 27 (1210 d epth) ... ............ co r e 3 5 (888 m eters depth) 50 100 150 200 250 300 350 400 Age (ky) 143 450 500 450 500

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maximum values in core 27 occur during stages 6 and 4 (nearly 50%), with a matching maximum in core 35 during stage 6 (-30% ). The mineralogy of the fine non-carbonate fraction was not determined in this study, but estimates obtained from an idealized sample in the Pedro Basin indicate 25% chlorite, 25% kaolinite, 25% smectite, and 25% quartz (Schwartz, 1996) Mass accumulation rates are another measure of sediment deposition and are based on sedimentation rates and dry bulk density of the sediments. Mass accumulation rates for this study have been determined based on the formulas outlined in Schwartz ( 1996) and Backman et al. (1988). Mass acccumulation rate of component (g/cm2ky) =dry bulk density of component (g/cm3 ) *sedimentation rate (cmlky) These values are highly dependent on sedimentation rates, which in tum are dependent on the isotope stratigraphy chosen for the core The overall bulk sediment mass accumulation rate for both cores in shown in Figure 3.22. Core 27 shows positive spikes in bulk sediment accumulation at the ends of stages 13,11, 9 and 7, reaching nearly 10 g/cm2ky, with generally lower bulk sediment accumulation during stage 5 These spikes in accumulation are synchronous with high sedimentation rates at the end of each interglacial. Generally low accumulation rates occur during glacial stages. Core 35 shows multiple high accumulation spikes in stages 9, 7 and 5, with lows during the glacial stages Stage 5 in core 35 shows noticab1y higher bulk sediment accumulation than stage 5 in core 27. Breaking bulk accumulation into the coarse (>63 J..Lm) component and fine ( <63 J..Lm) component lends some insight into the differences between the cores (Fig. 3.23A, B). The coarse fraction accumulation rate of core 35 shows a peak at the end of stage 9, at the beginning and end of stage 7, and during stage 5.3 and 5.1 (Fig. 3.23A). These rates, with the exception of those at the end of stage 7, are all greater than in core 27 Accumulation rates in core 27 peak only at the ends of interglacial stages 13 through 7, with a smaller peak during the transition from stage 6 to 5 The accumulation rate for the fine fraction of 144

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Bulk mass accumulation rate 12 13 2.5 0 50 100 150 200 250 300 350 400 450 500 Age (ky) Figure 3.22. Bulk accumulation rates of both cores versus age. Note the accumulation rate scale, as different components in ensuing figures will have a di fferent vertical scale. Core 27 shows generally high bulk accumulation rates at the ends of stage 13, 11, 9 and 7, with generally low accumulation rates during the glacials. Core 35 shows high bulk accumulation rate s at the beginning and end of each interglacial with the exception of s tage 5 where three peaks are present.

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Figure 3.23. Accumulation rate curves for the coarse (A) and fine (B) fraction of each core versus age. A si milar pattern exists between this record in the core 27 record and the bulk accumulation rate curve (high at the end of interglacials with the exception of stage 5). Core 35 again s how s high accumulation rates at both the beginning and end of interglacials.

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A Coarse f r actio n accum ulati o n r a t e >. C'l 3 s u Ob '-' B !':! c: .52 'ill 2 "5 s ;:l u u <( Age (ky) B Fine fractio n acc u mu lation rate >. C'l 6 s u ....... .!::) .... c: 4 0 3 s ;:l u u <( 2 Age (ky) 147

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core 27 (Fig. 3.23A) is greater than core 35 at the ends of the interglacials This early and late interglacial spike in core 35 is maintained in other sediment components and differs from core 27, which only displays a late interglacial peale The fine fraction ( <63 J.Lm) can be broken down into its components ; namely fine ara gonite, fine Mg-calcite, fine calcite and fine non-carbonate (Fig 3.24 and 3 25). Overall, core 35 shows greater mass accumulation rates for aragonite and Mg-calcite than core 27 (Fig. 3.24A, B). Core 35 also demonstrates the same cyclicity as shown in bulk and coarse/fine accumulation rates for this core In core 35 each interglacial (stage 9 and 7) s hows a peak at the beginning and end and stage 5 shows multiple peaks matching stages 5.5, 5.3, and 5.1, respectively (Fig. 3.24A, B) The fine aragonite accumulation rate in core 27 is generally low ( < 0.5 g/cm2ky) with small peaks at the end of s tage 9 and the s t age 817 and 6/5 transitions (Fig. 3.24A). The fme Mg-calcite accumulation rate for core 35 matches its aragonite counterpart, although with slightly lower values (<1 g/cm2ky vs -2 g/cm2ky) (Fig. 3.24B). The fine Mg-calcite accumulation rate values for core 27 are uniformly low (<0.25 g/cm2ky), with only slight peaks at the stage 817 and stage 6/5 transition Older than stage 8 no Mg-calcite was detected, as previously mentioned. In contrast to aragonite and Mg-calcite, the fine calcite accumulation rate in core 27 is generally equal to, or greater than core 35 (Fig. 3.25A). Core 27 shows the same pattern in fine calcite accumulation as it does for coarse fraction accumulation rate The high a ccumulation rate peaks ( 3-4 g/cm2ky) occur at the ends of interglacial st ages ( 13, 11, 9, 7 ) with generally lowe r values during stage 5 (Fig 3.25A ) Core 35 shows generally low fine calcite accumulation rates (<1 g/cm2ky) with the only prominent peak (nearly 2 g/cm2ky) occurring at the end of stage 9 (Fig. 3.25A). The fine non-carbonate accumulation rates of core 27 (Fig. 3 25B) match well with the fine calcite accumulation rates (Fig. 3 25A) Values of up to 4.0 g/cm2ky occur at the ends of stage 11 and stage 7, although peaks also mark the ends of stage 13 and 9. The fine 148

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Figure 3.24. Fine aragonite (A) and fine mg-calcite (B) accumulation rate for each core versus age Core 35 shows a high fine aragonite accumulation rate versus core 27, with peaks occurring at both the beginning and end of interglacials Core 27 shows smaller peaks during the interglacials at different times within Fine aragonite accumulation rates are low in both cores during glacials In core 35 the fine Mg-calcite trends match the aragonite trends No trend is apparent in core 27 and fine Mg-calcite is absent below stage 8

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A Fine aragonite accumulation rate 1 2-4 5 6 7 8 9 13 core 27 (12 i 0 meters d e f.th) ....... core 35 (88S m eters N E ib "-" "' .... c 0 '::l "' 3 E :::> 0 0 < N E 2.5 2 1.5 0 5 0 0 75 .... c 0 '::l "' 0 5 :::> 0 .'i: 0.25 0 50 100 1 50 200 250 300 350 Age (ky) B Fine mg -ca lcite accumulation rate 0 5 6 --core 27 (1210 me ers depth) ............... core 35 (888 mete rs depth) j \ [ \ AI\ 1\ A! v I l \ j ; \j .......... I ...... : 50 100 1 50 7 8 9 10 I 200 250 300 350 Age (ky) 150 400 450 500 11 12 13 400 450 500

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Figure 3.25. Fine calcite (A) and non-carbonate (B) accumulation rates for each core versus age. (A) Core 27 shows the higher fine calcite accumulation rates of the two cores, with peaks occurring at the ends of interglacial13, 11, 9, and 7. Core 35 shows smaller peaks during the interglacials Both cores show lower accumulaton rates during glacials. (B) The non-carbonate accumulation rate is similar for both cores with high rates during interglacials and low rates during glacials The highest peaks occur in core 27 at the end of stage 11, 9, and 7.

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;>, ('l E 3 u 2 e 1::: 2 0 a "' "3 E ::s u u <: Q 2 ('l E 1.5 e 1::: 0 "3 E ::s u u <: 0 5 A 0 50 100 B 0 50 100 Fine calcite accumulation rate 150 200 250 300 350 400 450 500 Age (ky) Fine non-carbonate accumulation rate 150 200 250 300 350 400 450 500 Age (ky) 152

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non-carbonate accumulation rates for core 35 (Fig. 3.25B) essentially show the same pattern as fine aragonite or fine Mg-calcite for the same core (Fig. 3.24A, B). The high peaks of core 35 occur in stage 9 and stage 7 at the beginning and end of the interglacial, while stage 5 contains three peaks ; at the 6/5 transition, at stage 5.3 and 5.1. Although high sedimentation rates at the ends of interglacial s (Fig. 3.17 and 3.18) tend to create these mass accumulation rate peaks, the percentage of fine non-carbonate sediment to total bulk sediment is greater during glacials (Fig. 3.21) Discussion Controls on Modern Sedimentation Patterns Interpretation of sedimentary patterns based on echo character can be compared to the work on periplatform sediments in the Bahamas (Mullins et al., 1979 ; Schlager and Chermak, 1979) and corroborated by piston core data. The five echo character types are interpreted to represent different depositional environments and/or sediment types (Fig. 3.26). Echo Chara c ter Type IB Echo character type IB represents the deposits furthest from the bank margins, they are least likely to include turbidite deposition and are interpreted as pelagic muds. Corroboration with core data (cores 20 and 28) indicates no turbidites and predominately forarn/nannofossil ooze (Appendix I). This echo characte r type is controlled by biogenic (pelagic) input and proximity to the shallow carbonate banks. It s hould be pointed out that both of these cores were taken sout heast of the Pedro Fracture Zone, which may present a barrier to turbidite deposition in these areas as the rim is s lightly shallower than the basin to the west. Core 19, which is also located on the deep-water side of the Pedro Fracture Zone does contain turbidites, and this will be addres se d in the following paragraphs. 153

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Figure 3 26. Echo character map based on 3.5 kHz echo character types of Damuth and Haye s ( 1977) and Mullins et al. ( 1979). Interpretations of each echo character type with respect to sediment characteristics and controls is given. Core locations, some of which were used in grou nd-truthin g the echo character types are also shown. Core transect # 1 and core tran sect #2 are given.

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Pattern D A Echo Characte r Type* I nterpretatio n Pelagic muds L imit ed turbidites d u e to di stance from banks. Deposits in deeper IB basin and at di s tance f r om bank s IIA Pelagic muds interbedded w ith tur bid i t e deposits These depo sits make up the majori t y of basinal sed im ents. liB Coarser-grained, c urrent wi nn owed sed im ents; c oarse offbank, cora l gal sands. Deposits found i n channe l s and proximal to banks Ili A Rugged bottom topography, bank-edge canyons and megabreccia deposits. Occur proximal to banktops. IIIC Current controlled/e r oded bottom features. Sea floor bedforms created by north westward flowing Caribbean Current Based on D amuth and Hayes ( 1 977) and Mullin s et al. ( 1 979) 155

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Echo Character T ype IIA The majority of the basin is made up of echo c haracter type IIA. Cores 2 1 and 33 in the central portion of the basin, core 25, near the Pedro Fracture Zone in t he so uth ern part of the basin, and core 19, were sa mpled in this echo character type, and show alterna tin g pelagics and turbidite depo s ition (Append ix I). A closer examination of the extent of echo character type IIA reveals that in fact, the intermixed turbidite /pelagic deposition occurs predominately in the central and eastern portion of the bas in although thin bands occur along Bawihka Bank and at the e ntrance of Diriangen Channel. Core 33, which shows the highest ratio of turbidite to total sediment (-33%), lie s off the lee ward side of the Serranilla Bank with r espec t to the northwestward flowing Caribbean Current. The provenance of turbidites in core 21 and cores 25-27 is more problematical, however. The lower percentage of turbidites in core 21 (-8 %; Table 3.2) may be explained by its s li g ht so uthwe stwar d position relative to the Serranilla Bank, although Core 21 was taken only about 25 kilometers di s tanc e from the Serranilla Bank. Another interpretation may involve sediments mobilized from the 'drowned' ( <400 meters) Hunapu Bank. This interpretation would require s ediment production on this bank during low s tands of sea lev e l providing for a sce nario in which the 'carbonate factory' is turned on during g l acia l s and sed im e nt export as turbidites occurs during g l acials This is the opposite of that found in the Bahamas, i.e., more turbidite s during interglacials (Drox l er and Schlager, 1985; Haak and Schlager, 1989) A final interpret at i o n for co r e 21, which can also be applied to cores 25-27, i s that t h e provenance for these turbidites is actually the banks to the northwest in a downcurrent pos iti on with respect to the Caribbean Current. Core transect 1 (Fi g 3.27) s how s cores 33, 21 and 20, a so utheastward transect from Ro sa lind Bank across the Pedro Fractur e Zone. The frequency and total percentage of turbidites in the cores decrease with distance from Ro s alind Bank.This may indicate t h at seaso nal reversal s in th e surface currents caused by 156

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15 7

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Figure 3.27. Core transect #1 from northwest to southeast in the eastern portion of the basin (See Figure 3.26 for exact locations). Tra n sect #1 shows decreased turbidite frequency a n d percent of core, from northwest to sout he ast.

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....... VI 00 1153 meters 1123 meters 100 100 200 200 300 300 400 400 500 500 600 700 Core 33 NW Core Transect # 1 SE D no sample turbidites carbonate ooze bioturbated ooze 0 10 I kilometers

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storms, etc., plays a role providing and 'setting up' banktop sediments, to later be transferred to the basin in the form of turbidites. A look at core transect 2, which contains cores 25-27 and 28 shows a decrease in frequency and total percentage of turbidites from northwest to southeast as well (Fig. 3.28). Based on bathymetry, there is no neritic source that could account for provenance in an upstream direction with respect to the Caribbean Current. The Hunapu Bank is the closest source to the northeast, but cores 26 and 27 are closer than core 25, and both contain fewer turbidites than core 25. The only other alternatives are the shallow banks to the north and northwest. Bawihka Bank is closest, at about 70 kilometers distance, and therefore seems the likely source Again, this implies that the provenance of these turbidites is downstream with respect to the direction of the predominant currents A final core exhibiting alternating pelagics and turbidites (echo character type IIA) is core 19, located directly south of Serranilla Bank. Core 19 is about 9% turbidite sediments (Table 3.2) and the provenance for these deposits is either the deep ( -900 meters) Xbalanque Bank, or, more likely, the downcurrent Serranilla Bank. A close look at bathymetry reveals that core 19 is located at the base of a canyon system that ties directly into the scalloped margin of the Serranilla Bank, which would not only provide a neritic source, but a conduit as well (Fig. 2.2). Thus it appears that the turbidites of echo character type ITA are infilling the Serranilla Basin against the predominant Caribbean Current direction. This differs from interpretations in the Walton Basin to the northeast, where the Caribbean Current play s a dominant role in the transfer of neritic material to the deeper basin (Glaser and Droxler 1993). The frequency of turbidites in Pedro Basin however, is essentially the same upcurrent and downcurrent of Pedro Bank (Schwartz, J., pers comm., 1996) so factors other than predominant current direction appear to control turbidite distribution along the western NNR. 159

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160

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Figure 3.28. Core transect #2 from west to east in t h e southern portion of the basin (see Figure 3 26 for l ocations). Transect #2 shows decreased tu r bidite frequency and percentage of turbidite in the core from east to west.

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100 200 300 NW Core Transect #2 core 27 40 kilometers carbonate ooze bioturbated ooze 0 10 I kilometers 161 SE

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Echo Character Type JIB Echo character type liB occurs predominately in the north off Rosalind and Diriangen Banks, and in Rosalind Channel. This echo character type is interpreted as coarser-grained current-winnowed sediments and possible neritic deposits, based on the interpretation of Mullins et al. ( 1979) in the Bahamas. The closest piston core samples to this echo character type are core 34 and 35, which were taken on a sedimentary high off the tip of Diriangen bank. These cores are predominately peri platform ooze, lacking turbidites and due to their position on a bathymetric high, they may not accurately reflect echo character type liB sediments. Their visual description matches very well with core 27, which is predominately periplatform ooze. The average mud percentage, however, is lower in core 35 than in core 27 (63% vs 70%, respectively), perhaps supporting current induced winnowing of the core 35 sediments Echo character liB also occurs off the southeastern tip of Bawihka Bank, and these sediments are interpreted as current-winnowed, or possibly even neritic sands (Fig 3.26). If Bawihka Bank is the source of the turbidites in cores 25-27, then echo type liB near the Bawihka Bank may represent the coarse-grained, proximal portion of offbank transport Alternatively, or perhaps in addition, these deposits may be current-winnowed, as has been suggested further north near Rosalind Channel in cores 34 and 35 Although Glaser and Droxler (1993) found cores at less than 600 meters that showed the effects of current-winnowing during glacials in the Walton Basin, the type liB sediments lie in depths from less than 600 to 1200 meters of water. There is evidence, however, from deep areas (>1200 meters) of the Caribbean for current-winnowing of sediments, so winnowing at these depths is not unreasonable (Prell, 1977). Additionally, Gordon (1967) calculates geostrophic currents in the western Caribbean down to depths of 1200 meters. Unfortunately, no core samples are available to corroborate this interpretation. 162

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Echo Character Type IIIC Directly north of echo type IIB in the western Serranilla Basin lies echo character type IIIC, which is also interpreted to be strongly current-controlled (Fig. 3.26). This echo character type, based on correlation with the Bahamas, is interpreted as seafloor bedforms created by the northwesterly flowing Caribbean Current as it impinges on the margin of Bawihka Bank. In the Bahamas, echo character type IDC is interpreted to be formed by the bottom-flowing waters of the Florida Current (Mullins et al., 1979). Evidence from the deeper Colombia Basin indicates that bottom currents are active across much of the sea floor, but intensify near the Hess Escarpment (Fig. 1.1 ), creating current ripples and even erosional scour (Prell 1977). It is not unreasonable to suggest bottom current intensification related to restriction and shallowing in the Serranilla Basin. Based on these echo character types, it appears clear that the Caribbean Current does play a role in modifying the depositional environments in the Serranilla Basin. Although not considered a direct control on turbidite deposition, the Caribbean Current winnows, creates bedforms, and possibly even scours and erodes sediments, most notably in the western part of the basin and the shallow channels to the north. Echo Character Type II/A Nearly all of the bank-to-basin transitions are dominated by echo character type IliA. These areas ar e interpreted as rugged bottom topography bank-edge canyons and in some area s debris flows. Two locations along the Pedro Fracture Zone show evidence of downslope movement of blocks based on 3 5 kHz crossings, but tighter seismic coverage may indicate that the entire Pedro Fracture Zone is lined with these debris flows on its eastern slope. The absence of echo character type IliA at distance from the banks indicates that megabreccia deposition, although important in the shallower channels to the north (Hine et al., 1992), is not a major control on infilling of the basin. 163

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Quaternary Cyclicity The periplatform sediments of the Serranilla Basin record Quaternary cycles in their geochemical and sedimentological character, as in Pedro and Walton Basin (Glaser and Droxler, 1993; Schwartz, 1996). In this section, an attempt at determining the controls on Quaternary cycles based on each of the different sediment components, will be made. Each of the components can be used as a proxy for one or more oceanographic factors (Table 3 3). For instance the oxygen isotope curve downcore has been established as a proxy for sea-level change and also geologic time, when tuned to orbital variations (Imbrie et al., 1984 ) This listing (Table 3.3) follows the tabulation of Schwartz (1996) used in the adjacent Pedro Basin. A cursory review of Table 3.3 highlights some important controlling factors; pelagic and neritic production, dissolution, input of non-carbonates, and oceanic currents. It is not an accident that these factors were determined to be the main controls on periplatform sedimentation in the Walton Basin (Glaser and Droxler, 1993). The relative importance of each of these factors will be interpreted for the Serranilla Basin and differences between the Walton and Pedro Basins will be noted Neritic Production: Sea Level and Dissolution Within a basin in the vicinity of neritic carbonate banks, the most reliable indicators of sea level change, notwithstanding the ()180 curve, are fine aragonite and Mg-calcite in the periplatform sediments (Kier and Pilkey, 1971; Droxler, et al., 1983; Boardman et al., 1986). Both of these components are produced in shallow waters (bank-top production) and exported to the periplatform environment during sea-level highstands (Droxler and Schlager, 1985; Boardman et al., 1986 ; Glaser and Droxler 1991; Schlager et al 1994) Both cores from the Serranilla Basin record the glacial/interglacial cyclicity in fine aragonite, with core 35 exhibiting higher percentages (Fig 3 20) The highest percentages occur at the onset of the interglacials indicating an increase in production and export when 164

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Table 3.3 Sediment compone n ts and th ei r origin (after Schwartz, 1996) S edim ent Ori g in P roxy f or C ontr o l s c o mpon e nt Coarse Fraction Pe l agic; planktonic Nutrien t s Prod u c t ion, forams pteropo d s preservation Globorotallid P l anktonic forams; Sout h ern Ocean C u rrent co n trolled species G. mena r dii a n d G. Influence introduction into tum ida tropical Atlantic from Indian Ocean Fine arago n ite Neritic production; Sea level; nutrie n ts; H alimeda i ndica t e percent and mass mainly green algae, disso lu t i on euphotic benthic accumulatio n rate Halimeda species production; aragonite metasta b le, dissolves at intermediate dept h s Fine cal cite percen t Pelagic ; mainly Winnowi n g Current s t rength and mass coccoli thophores accumu l ation rate No n carbona t e Eolian i n put, Input ; winnowing Continenta l percent a n d mass Fluvia l input weathering ; riverine accumula t ion rate t ransport by curre n ts ru n-off Fi n e mg-calcite Neritic produc t io n ; D isso lu tion; sea Mg-calcite percent and mass mainly calcareous level metastable disso l ves accum u lation rate algae at intermediate depths, relative l y small i nput Oxygen iso t ope G. sacculifer Sea l evel, time Isotopic values composition of sea water; temperature salinit 165

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sea level initially overtops the banks. Boardman et al. ( 1986) explains the slight decrease during continued high-stand conditions as an autocyclic response of carbonate platforms to growth of bank margin barriers, restricted circulation and tidal flat progradation Mass accumulation rates of fine aragonite are about 5 times higher during interglacials than glacials in the Serranilla Basin (Fig 3.24) and peaks generally occur at the beginning of interglacials as well. This contrasts with the Pedro Basin where fine aragonite accumulation rates generally increased near the end of interglacials prior to stage 5 (Schwartz, 1996) Schwartz ( 1996) interprets other factors such as current strength, nutrients and dissolution as possible modifying controls Based on fine aragonite percentage and mass accumulation rate in the Serranilla Basin, sea level appears to be the main control on late Quaternary cyclicity. Overall trends in fme aragonite percentage of core 27 indicate a slight increase from a low centered on stage 10 to the Holocene (Fig. 3 20). This long-term trend may be the result of increased nutrients, decreased dissolution, or both. At present Halimeda growth is abundant on the banktops bounding the Serranilla Basin and has been grab-sampled and dredged in the shal low seaways to the north (Hallock et al., 1988; Hine et al. 1988; Triffleman et al. 1992) A transect from east to west along the NNR indicates a change from coral-algal communities in the east (Jamaica and Pedro Bank) to sponge-algal dominated communities in the west (Serranilla, Bawihka, Rosalind Banks) (Hallock et al., 1988 ; Triffleman, et al., 1992). This change in communities has been tied to a nutrient gradient from east to west (Hallock and Elrod 1988; Hallock et al ., 1988) Hence, the long-term increase in fine aragonite percent may indicate a long-term increase in nutrients favoring green algae production over coral production on the banks surrounding the Serranilla Basin. This differs from the Pedro Basin where a long-term decrease in nutrients has been interpreted (Schwartz, 1996). An alternative explanation for the long-term increase in fine aragonite percent may be related to decreased dissolution. Schwartz ( 1996) suggests a dissolution maximum at 166

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400 ky ago in the Pedro Basin, with increased preservation since that time. He adds that this matches the well-documented 'mid-Brunhes dissolution interval' in other ocean basins (Droxler et al., 1988, 1990; Farrell and Prell, 1989; Bassinot et a l. 1994). The long-term trend in the Serranilla Basin may be a manifestation of this global phenomena. It is not clear what causes this long-term cyclicity but changes in Ca2+ to the oceans and climate-induced changes in carbon cycling among reservoirs has been suggested (Droxler et al.,1990; Bassinot et al., 1994). Mg-calcite variations are not as straightforward as the fine aragonite (Fig. 3 20B). They do not follow aragonite patterns but instead, actually show the greatest percent during stage 6, a glacial stage (Fig. 3.20B). This peak is evident in both cores indicating increased preservation, or a source of fine Mg-calcite during the glacial stage, perhaps fine Mg-calcite cement coating particles It is unclear which of these two accounts for the peale The mass accumulation rate of Mgcalcite does show a n increase during interglacial stages in core 35 (Fig. 3.24B), but no pattern is evident in the deeper core. The deeper core is devoid of Mgcalcite prior to stage 8, perhaps indicating complete dissolution prior to this time. Mg calcite preservation has been deemed important in determining dissolution indices in the Bahamas and Walton Basin (Haddad and Droxler, 1996) and it appears that in the Serranilla Basin, prior to stage 8, dissolution was more active. Planktonic Production: Nutrients and Current Winnowing The coarse fraction of the peri platform sediments is made up of two components; planktonic foraminifera and pteropods. Pteropods being aragonitic, are subject to dissolution. Planktonic foraminifera on the other hand, are calcitic, and at the depths of the Serranilla Basin, are essentially unaffected by dissolution. In addition coarse fraction components are not thought to be removed by current winnowing. Because of this, planktonic foraminifera have been used as a proxy for nutrients in the Pedro Basin (Schwartz, 1996). Glaser and Droxler (1993) in the Walton Basin have suggested that 167

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variations in the coarse fraction are controlled by production, dilution by fine bank-derived or siliciclastic inputs, and removal of fines by current winnowing. Based on visual estimates, pteropods generally make up a small fraction of the coarse sediments relative to planktonic foraminifera so have not been included in the following discussion. Therefore, variations in the coarse fraction will be assumed to represent variations attributed to planktonic foraminifera in relation to other controls. The shallow core 35 does not show a clear glacial/interglacial cyclicity in percent coarse fraction (Fig. 3.19A) The lowest values correspond with glacials but stage 5 3 also shows low percentages. This record may reflect dilution during stage 5.3 by fine bank-top carbonates. This is reasonable, as stage 5.3 shows the highest mass accumulation rate of fine aragonite and fine Mg-calcite (Fig. 3 24A, B) A slight overall increase in coarse percent occurs from stage 6 to the present. Core 27 shows a better glacial/interglacial cyclicity with high coarse fraction percents occurring during interglacials The amplitude between glacial and interglacial values tends to decrease from stage 8 to stage 1. Mass accumulation rates for both cores show a high degree of cyclicity with peaks occurring during interglacials As a proxy for nutrients, these data match previous studies in the area (Prell and Hays, 1976; Glaser and Droxler, 1993; Schwartz, 1996). Higher nutrients during interglacials account for higher coarse fraction percents and mass accumulation rates. This agrees with observations of Prell and Hays (1976) in the Columbia Basin and Glaser and Droxler (1993) in the Walton Basin, who both suggest that there is intrusion of low nutrient, low-productivity, Sargasso Sea-type water during glacials. Schwartz (1996) argues that during the late-Brunhes (stages 1-6) North Atlantic gyre migration (intrusion of Sargasso Sea water) accounts for decreased nutrients during glacials in the Pedro Basin but prior to stage 6, other factors controlled surface water nutrients. Data from the Serranilla Basin do not rule out other factors but the glacial/interglacial cyclicity in coarse fraction hence nutrients, appears to be maintained back through stage 13 (Fig 3.23A). loR

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Fine planktonic production is produced by coccolithophores (fine calcite) which release coccoliths and may be used as a proxy for current winnowing due to their resistance to dissolution and fme grain size. Although production may also play a part, coccolithophores are adapted to low nutrients. In general the percent fme calcite shows no glacial/interglacial cyclicity in either core This may argue for no strong glacial/interglacial cyclicity in currents Mass accumulation rates peak at the ends of stage 13, 11, 9 and 7 in the deeper core 27. This matches the coarse mass accumulation rate in that core, and may be an overprint of nutrient flux. The clearest trend in percent fme calcite however is the general overall decrease from early stage 9 to stage 1 in both the deep and shallow cores. Schwartz (1996) interprets sluggish currents during the mid-Brunhes but does suggest increased current activity during the late-Brunhes. This overall general decrease in fine calcite may indicate an increasing current regime in the Serranilla Basin, as well. Non-carbonate Input: Dilution and Sources A final component in the peri platform sediments that may affect percentages and mass accumulation rates is the fine non-carbonate. This includes both eolian dust (quartz, clay minerals) (Boardman et al. 1995) and non-carbonate brought into the basin through riverine input and transported by currents (Prell 1978). Non-carbonate percentages in the Serranilla Basin show a clear glacial/interglacial cyclicity with higher values during glacials (Fig 3.21B). This agrees with work in the Colombia Basin, where Prell (1978) concluded that dilution by non-carbonates was the main control on carbonate percentage s He further adds that an increase in terrigenous influx occur s due to rapid erosion of the continental shelf and aridity on the South American continent during glacials (Prell 1978) This contrasts slightly with the Walton Basin where s hallow cores collected near the Jamaican coast indicate higher interglacial non-carbonate percentages, but deeper core s follow the same pattern as the Colombia Basin (Glaser and Droxler, 1993). 169

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It is interesting to compare the non-carbonate percentages downcore with the mass accumulation rates. As noted, non-carbonate percentages are greatest during glacials but the highest mass accumulation rates occur during interglacials (Fig. 3 25B) More specifically the highest rates occur at the ends of interglacials in core 27 and both the beginning and end of interglacials in core 35. Schwartz (1996) has noted the similarity in mass accumulation rates of fine calcite, planktonic foraminifera and non-carbonate in the Pedro Basin and s uggested that this similarity may be the result of non-carbonates being tied to nutrient inputs. Another explanation, both in the Pedro and Serranilla Basin, may be that these high mass accumulation rate peak s are an artifact of the age/depth model chosen for each core ( Fig 3 16) (Schwartz 1996). A long-term trend in non-carbonate percentage can be seen in core 27, where stages 2-4 and 6 show higher percentages than the previous stages. The increased percentage of non-carbonate during the late-Brunhes may be related to the general decrease in fine calcite, which is interpreted as current strengthening. If the source of these non-carbonate s ediments is riverine input from South America as Prell (1978) suggests, perhaps increased current transport is the main control on these patterns. The fact that core 27 in deeper water clo ser to the South American coast shows systematically higher non-carbonate percentages than core 35 (Fig. 3 21B) may support the current controlled source for these non carbonate sediments. C a uses of Quat e rnary C y clicity Based on the records discussed above two long-term paleoceanographic trends have been interpreted in the Serranilla Basin Since stage 10 there has been a general decrease in dissolution and a general increase in current strength. These same trends have been identified in the Pedro Basin (Schwartz, 1996). A long-term nutrient trend is not as clear in the Serranilla Basin as in the Pedro Basin Although in general the percent coar s e fraction has increased in the lon g -term ( Fig. 3 19A), it is more prevalent in the s hallower 170

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core 35, where coarse mass accumulation rates also show an increase in stage 5 (Fig. 3 23A). This may support stronger current intensity in combination with nutrient increase due to upwelling or a nutrient increase so lel y due to flooding of the shallow banks. A long term nutrient decrease has been identified in the Pedro Basin, however, attributed to intrusion of low-nutrient, Sargasso Sea-type waters during more intense glacials (Schwartz, 1996). This contradiction in nutrient trends between basins may lie in local upwelling and bank geometry, and as yet, is unresolved. The larger causes of these long term trends can be tied to intermediate water mass and circulation changes within the Caribbean which ultimately reflect global changes in NADW production, AAIW entrainment into the Caribbean, and increased trade wind intensity, as discussed below Globorotallid species have been used in the tropical Atlantic and Caribbean as s tratigraphic tool because of their absence during certain glacials during the late Quaternary (Ericson and Wollin, 1968). Repopulation of the tropical Atlantic and Caribbean occurs from the Indian Ocean where Globorotallid sp. have a continuous history, by the surface return flow of the thermohaline circulation system ( Gordon et al., 1992; Jones, G.A., in press). Today, this thermohaline return flow also entrains the more corrosive, [CO/-] poor Antarctic Intermediate Water with le ss corrosive upper NADW into the Caribbean It has been s uggested by Gordon et al. (1992) that this surface return flow may actually pre-condition the North Atlantic for NADW formation by tran s ferring heat and sal t from the Indian into the North Atlantic Ocean. Through these interhemispheric oceanic connections, Schwartz ( 1996) has tied Globorotallid presence in the Pedro Basin with formation of NADW His data indicate a strong correlation between the Globorotallid abundance with the NADW production curve of Raymo et al. ( 1990). In addition, H a ddad and Droxler ( 1996) have tied composite dis so lution index (CDI) values in the Walton Ba s in with NADW formation ; more di sso lution due to AAIW entrainment occurs during times of strong NADW formation (interglacia l s). Furthermore studies of ()13C within the deep ocean basins has shown that 171

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NADW formation has varied through the Quaternary, with the mid-Brunhes being a time of relatively stronger NADW formation during both glacials and interglacials, with stages 7, 9, and 11 showing unusually warm interglacial conditions (Raymo et al., 1990 ; Hodell, 1993). This pattern has been described by Schwartz (1996) in the Pedro Basin as relatively mild mid-Brunhes (525-185 ka) glacial/interglacial variability and more severe late-Brunhes climate variability. Droxler et al. (1991), and more recently Haddad and Droxler (1996), have studied water column chemistry and periplatform surface sediments in the Bahamas and Walton Basin, and determined that glacial/interglacial changes in intermediate water chemistry related to changes in global circulation account for changes in metastable carbonate preservation. More specifically they conclude that during interglacials, entrainment of corrosive, C03 2 --poor AAIW into the Caribbean, promotes dissolution of these metastable carbonates. Hence, the long-term fine aragonite record of core 27 (depth 1210 meters) which shows an overall decrease in intermediate dissolution in the Serranilla Basin may be tied to an overall decrease in NADW formation, or shutdown of the thermohaline circulation system during the most recent glacials. The general presence of Globorotallid species in the Serranilla Basin during stages 7 through 12 and absence during glacial stages 2-4 and 6, also supports this idea of continuous NADW formation during the mid Brunhes, and intense glacials during the late Brunhes The long-term trend showing increasing current strength in the Serranilla Basin can also be tied to this increased glacial severity since stage 6. Prell and others (1976) have concluded that glacial temperature and faunal gradients in the tropical Atlantic were greater during the last glacial maximum than today, arguing for more intense trade winds and circulation. They also point out that compression of the North and South Atlantic tropical gyres would add to increased current velocities during glacials Evidence for increased trade winds during glacials is also found in peri platform sediments of the Bahamas, which indicate higher eolian components from Africa during glacials (Boardman et al., 1995). 172

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The periplatform record in the Serranilla Basin shows similar patterns to those found in the adjacent Pedro Basin. Slight differences in the locations of the cores with respect to the shallow banks may account for differences in nutrient inputs and the effects of the Caribbean Current on turbidite distribution The Walton Basin, furthest east along the NNR, shows the increased influence of Jamaica on the non-carbonate input, but overall, matches Serranilla Basin depositional controls Conclusions The following conclusions are based on the modem sedimentation patterns and the Quaternary cyclicity observed within the peri platform sediments of the Serranilla Basin. 1) Turbidites make up a significant portion of the sediments infilling the basin, but megabreccia deposition, which is common in the seaways to north, is relatively unimportant as a modem depositional system. The turbidites infill against the predominant Caribbean Current direction and although not a direct control on turbidite depostion, does modify the modem sediment distribution. The western Serranilla Basin shows evidence of current -winnowing and current -controlled/eroded bedforms. 2) Interglacial periplatform deposition is controlled by several factors: ( a) sea-level rise and subsequent flooding of the shallow banks, which increased neritic production and export to the basin, (b) dissolution of these metastable carbonates due to entrainment of corrosive AAIW into the Caribbean Basin and (c) increased nutrients, which enhance surface productivity, as shown in bulk and coarse fraction mass accumulation rates. 3) Glacial periplatform deposition is controlled by (a) increased current-winnowing due to increased trade winds,tropical circulation patterns, and constriction in seaways due to lowered sea-level, and (b) increased dilution by non-carbonate inputs brought in by currents and eolian sources. 173

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4) Late Quaternary cyclicity of periplatform sediments indicates a long-term (stage 10 to present) increase in current velocity and decrease in dis solution in the Serranilla Basin. Evidence indicates the late Brunhes (stage 1-6 ) is dominated by more severe climate changes between g lacials and interglacials, while the mid-Brunhes (stages 7-13) represents milder glacial/interg l acial cycles. This agrees with findings in the P edro Basin, as well as global ocean patterns 5) The causes of late Quaternary cyclicity in the Serranilla Basin are related to global paleoclimatic and paleoceanographic factors; namely NADW formation and strength, entrainment of AAIW into the Caribbean which affects intermediate water chemistry, and variab ly compressed climatic belts which directly affect trade wind velocities, surface currents and tropical Atlantic circulation intensity. Evidence in the Serranilla B asi n supports a link between Southern Ocean circulation and NADW production and their controls on glacial/ interglacial cyclicity. 174

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REFERENCES Arden, D.D., Jr., 1975, Geology of Jamaica and the Nicaragua Rise, in Nairn A E M. and Stehli, F G., eds., The Ocean Basins and Margins, v 3, The Gulf of Mexico and the Caribbean: Plenum P r ess, New York, NY, p 617-661. Arden D D., Jr. 1969 Geologic history of the Nicaraguan Rise : Trans. Gulf Coast Assoc. Geol. Soc v 19, p 295-309 Backman J., Duncan, R.A., et.al., 1988, Explanatory notes in Barbu, E M., ed. Proc. of the O D.P., Initial Reports, v. 115 p. 17-42 Bassinot, F.C., Beaufort, L., Vincent, E Labeyrie, L.D., Rostek, F ., Muller, P J Quidelleur, X., and Lancelot, Y 1994, Coarse fraction fluctuations in pelagic carbonate sediments from the tropical Indian Ocean: a 1,500 kyr record of carbonate dissolution: Paleoceanography, v. 9, p. 579-600 Boardman, M.R McCartney R.F ., and Eaton, M R., 1995 Bahamian paleosols : origin, relation to paleoclimate, and stratigraphic significance in Curran, H A., and White B., eds., Terrestrial and Shallow Marine Geology of the Bahamas and Bermuda: Boulder, CO, GSA Special Paper 300 p. 33-54 Boardman M.R., Neumann, A.C., Baker, P.A., Dulin, L.A., Kenter R.J., Hunter, G E, and Kiefer, K B 1986, Banktop responses to Quaternary fluctuations in sea level recorded in periplatform sediments : Geology, v 14, p. 28-31. Bosellini A., 1989, Dynamics of Tethyan carbonate platforms, in, Crevallo P D Wilson, J.L. Sarg, J.F and Read, J.F., eds Controls on Carbonate Platform and Basin Development: SEPM Spec Pub. no 44. p 3-14. Bowin, C., 1976, Caribbean gravity field and plate tectonics: Geol. Soc Am. Spec Paper 169, 79 p .. Bowland, C.L., 1993 Depositional history of the western Colombian Basin, Caribbean Sea, revealed by seismic stratigraphy: Bull. Geol. Soc. Am., v 105, p 13211345. Brunner C.A., 1984, Evidence for increased volume transport of the Florida Current in the Pliocene and Pleistocene: Marine Geology, v. 54 p. 223-235. Burke K., 1988, Tectonic evolution of the Caribbean: Ann Rev. Earth Planet. Sci., v 16, p. 201-230. Cacere s Avila, F., Tappmeyer, D.M Aves H.S Gillett, M. and Klenk, C.D., 1984, Recent studie s of basins are encouraging for future exploration in Honduras: Oil a nd Gas Journal, p 139-149. 175

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APPENDICES 184

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Appendix I Core Descriptions 185

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100 200 300 Piston Core 019 b rown muddy pter opod/foram ooze uniform, possibly disturbed during cori n g mottle d It brown, muddy pteropodlforam ooze (burrow fill) dark brown, carbonate mud w/pteropod s and forams turbidite, I t brown-tan, foram ooze/hash brown muddy foram ooze turb i dite, I t brown. med foram ooze/ hash brown grading down to tan. muddy foram ooze white foram ooze gray to tan, muddy foram ooze turbidite, I t tan. med coarse foram ooze, dk gray at bottom brown gray muddy pteropodlf oram ooze It brown slightly mottled, burrowed pteropod/foram carbonate mud turbidite: white to g ray med. coarse foram ooze tan muddy foram ooze turbidite: tan. fine-med foram ooze at top: dk gray. blue coarse foram ooze I t gray. foram carbonate mud, mottled mottled It gray/dk gray. burrowed mudd y foram ooze w/pteropods small white turbidite. white, muddy foram ooze It gray/dk gray m ottled. burrowed muddy pteropod foram ooze gray. slig h tly mottled. ptero/foram carbonate mud turbidite. gray. muddy coarse pteropodlforam ooze

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Appendix I. (co ntinued ) Ocm-....,......,.-,.-, 100 200 300 TTTTT TTTTT 400 __J,,!T-.!,.T _;TU Piston Core 020 mud (creamy brown wl li ght m ott l es) Mud (mott led-bioturbation) mud (co l or tran siti on) light m o ttl es mud {lighter mottl e s) grayish h orizo n blackis h h orizon bottom 6 em of core di s turbed mud (mottled s l ight biot u rbation)

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App e nd ix I. (co ntinued) Piston Core 021 Ocm mud slightly grayish t inge 400 possib l e thin turbidite color tansition mud ( light mottles bioturbation) m u d more bioturbated tu rbidi t e 100 turbid i te d a r ke r zo n e @ 94-98 e m 500 mud s l igh t mottling. b i oturbation m u d s l ight m o tt ling t u rbidi te, gray horizon followed by ye ll ow h orizo n distinc t gray @ bottom mud, s l ight mott li ng 200 mud grayish tinge 600 bottom of core ragged pro b able turbi d ite, sharp bottom contact m ud smallligtht col o red n ecks. elongated??

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Appe n dix I. (co n tinued) Piston Core 025 Ocm turbidite 400 mud (st ructural crack @ 17 em) mud wlbrown gray mottling turbidite mud w/ gray to slightly gray coloration 100 500 turbidite (creamy white) mud grading into turbidite turbidite ( di sturbed) 200 mud w/ dk gray flecks and pat c he s black patch @ 225 em 600 bioturbation turbidit e (wrute ) mud mottled and bio turbated 300 700 turbidite (w hiti sh gray w/dk gray pat c hes) mud (dk yellow layer over thin gray l ayer a t bottom) turbidite ( tannish white with greenish pat c hes) mud w/gray patch es very coarse lay e r 400 800 mud (grey h orizon @ 403 em) turbidi t e ( greeni s h backg round ) mud (gray w/ fleck s and h orizons som e bioturb a t io n) turbidite mud w/ dark gray h orizons turbidit e mud w/ rare gray patches mud w/ s light mottling and bioturbation turbidite ( black @ top and bottom, yellow colo rin g ) mud w / gree n h orizo n s @ 677 e m bla c ki s h h o riz ons @ 6 85 mottled and bioturbated turbidit e w/gray layer @ bottom

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Appendix I. (continued) Piston Core 026 turbidite mud mud mott l ed wlbioturbation turbidite mud mottled wlbiotu r bation black specks @ I 62 I 63 em mud trans i tion to grayish horizons @ I 69I 73 gray layer@ 2 1 0-2 1 I e m light h orizo n @ 217 em mud mottled with s light bioturbation turbidit e mud mottled with bioturbation turbidite w/dark gray zones mud w/very sligh t mottling and b io turbati o n mud w/dark mottl es, rare black flecks, bioturbati o n mud w/very slight mottling and bioturbati o n col o r tran sitio n @ 464 em turbidite mud w/ slight mottling color transition @ 563 em slightly coarser @ 598-600 e m turb idite? whiter p atch @ 603-605 em mud w/ rare black flecks mud dark/ t ough possib le miss in g secti o n ? mud w/rare b lack flecks, patches, h o rizons, bioturba ti on mud. mottled and bioturbated mud oran gish color around edges disturbed bottom

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Appendix I. ( continu e d ) Piston Core 027 V t o p @ 5 em (compactio n ?) 400 tan-brown sandy ooz e 800 T T 812-838 em brown ooze 13 e m coarse l ighter color zone, possible blac k specks @ 416 e m T TTTT 818-820 em b la c k spec k turbidit e t r a n s i tion from ligh t brown to gray-ta n ooze TTTTT 0-34 em san d y bro wn ooze .,..,..,..,..,. .,..,..,..,..,. t u r bidi t e, light e r brown, milky brown .,..,..,..,..,. 449-451 em ligh t e r whitish tan l ayer TTTTT .,..,. .,..,. 40-68 em brown sand ooze, some mottlin g T T T TTTTT TT T TTTTT (dista l t u rb idi t e?) .,..,..,..,..,. black spec k s in ooze @ 68 e m .,..,..,..,..,. TTTTT o liv e t an ooze, l ighte r coarse r .,..,..,..,..,. TTTTT .,..,..,..,..,. t owar d bottom .,..,..,..,..,. .,..,..,..,..,. gray ish brow n oo z e TTTTT TTTTT 500 TTTTT 900 TTTTT TTTTT tan-brown sa nd y ooze, so m e m ottling TTTTT .,..,..,..,..,. TTITT TT TTT .,..,..,..,..,. .,..,. .,..,. TTTTT TTTTT TTTTT TTf TTTTT TTTTT TT T 555 -560 em blot chy whi t e and gray TTTTT TTTTT whitis h l aye r @ 154 e m TT TT inclu s i ons ( m o ttling) TTTTT TTTTT TTTTT TTT T TTTTT TTTTT TTTTT It tan s andy ooze TTTTT TTTTT TTTTT 200 TTT TT TTtT t an brown sand y ooze, some mottling TTTTT 982-1036 e m o li ve to tan ooze some TT TT 600 TTTTT 1000 TTTTT TT T mottling, whi t e and black i s h spec ks TT TT TTTTT TT T T T T 5 e m missing TTTTT TTTTT 1037-1041 e m dk gray m ott l ed T T T TTTTT TTTTT (biotu rbated?) TTTTT TTTTT 1053 em d k b lack s pot TTTTT TTTTT 667 em dk bla c k spec k 1041-1064 em ol i ve t a n m o tt led ooze TTTTT TTTTT 300 mott l es of l i g hter col o r TTTTT TTTTT TTTTT TTTTT 1 064-1086 em l ig ht e r tan ooz e T TTTT tan-brown sandy ooze TTTTT 685-72 0 em sa nd y gray tan ooze 1086-1101 em d k o li v e ooze TTTT T 700 TTTTT tra n s it ion t o darker fin e r ooze 1100 TTTTT TTTTT 1 101114 2 em ta n olive sa n dy ooze TTT TT TTTTT TTTTT l ighte r colo red laye r @ 321 e m TTTTT black spec k ( p yrite?) @ 732 em TTTTT TTTT T TTTTT TTET 720-779 e m t a n g reen ooz e, finer than above TTTTT TT TT TTTTT 345-376 e m grayish m ottling i n ooze TT TT 758765 em w h i t e m ot tling TTTTT TTT T 779 812 e m da r ker o li ve bro wn ooze TTTTT TTf 784 7 8 6 em g ra y black mottlin g TTTTT TT T 799-802 e m dk black spec k TTTTT TT TT 800 1200

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Appe n d i x I (co ntinu e d ) Piston Core 028 0-65 em brown, muddy coarse n a n no/p t e r opod foram ooze 65 -70 em b rown muddy. very coarse foram pteropod l aye r 701 48 em mo ttled, lt brown ta n mu ddy nan n olpterol foram ooze 148-258 em sl i ght l y monied tanl ight brow n muddy na n nolforam ooze 258-279 em It tan muddy nannolforam ooze 279-302 e m It brown foramlnan n o ooze I 0 e m sec t ion m i ss ing 3 1 2-405 em u niform, t an I t brow n foramlna nn o ooze 400 -...-;T:-r:;"T r;! 500 600 700 TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTTT TTTT T TTTTT TTTTT TTTTT TTTTT TTTTT T T T 800-....._____, 405-445 em It tan-gray muddy foramlnanno ooze 445-460 em t an-It brow n foraml n anno ooze 460-490 em gray muddy n anno/foram ooze 490-493 em t an muddy foramlnan n o ooze 493-496 em It tan muddy f oraml n anno ooze 496-506 em tan m u ddy foramlnan n o ooze 506-530 em I t tan-gray mud dy nan n olforam ooze 530-555 em t a n foramlnan n o ooze 555-515 em It tan gray muddy nan nolforam ooze 515-606 em t an foramlnanno ooze

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,..... \0 w Appendix I. (continued) roughly 0.5 m mis s ing based from top based on gravity core A .W. Droxler Piston Core 033 0 em 1 t t t 1 0-8 em disturbed sediment, tan color 8-22 em slightly darker creamy brown nanno/foram ooze 22-46 em creamy brown uniform color nanno/foram ooze 46-61 em turbidite sequence calcareous ash, light cream color 61-73 em turb idite sequence a few pteropods storm cloud gray wlbottom I em grading to blacki s h gray foram ooze 73-95 em uniform sickly gray nanno/foram ooze w/pteropods 100 __ j 95-115 32cm foram ooze_, lklt gray pos s ible bioturbation 115-1 em umform s1c y gray nanno ooze 132-154 em lighter tannish gray w/dark gray mottles .,... T nanno/foram ooze l T T 1154-164 em uniform s ickly gray nanno ooze 7 em section missing 163199 em green gray grading down to It gray mottled w/dark gray muddy nanno/foram ooze 200 11 r 1 turbidite green coarse foram ooze at b a sed fining upward to white carbonate mud mottled gray (It and d a rk) muddy nanno/foram ooze turbidite It gray muddy foram ooze grading up into white 400 large turbidite sequence chalky white gray 393-420 em (foram as h) darker coarser (uniform lighter gray) w/forams halimeda micromollusk, pteropods 420-470 em 5 em section missing base of turbidite coarse ptero/foram ooze dk gray grading dwon to tan/gray foram/nanno ooze 482-500 em 500 I!':Oa!'" turbidite white very coarse ptero/foram ooze at base fining upw ar d to gray very fine foram ooze h as h ; contain s halimeda 600 and bryozoan frags T T T 537 570 em gray ptero/for a m/nanno ooze j: T: T: Tl570-580 em gray w/dk gray black speck muddy ptero/ foram ooze 580-600 em gray ptero/foram/nanno ooze carb mud turbidite ; white very coarse calcareous hash (w/h a limed a, mollusk, pteropods, forams) fining up to white fine hash 617-650 em mottled It gray/dk gray muddy nanno/ptero foram ooze 650-667 em gray slightly muddy very coarse foram/ptero ooze 657-667 em gray ptero/foram/nanno ooze turbidite ; gray ptero/foram ooze at base fining up to white carbonate mud 300 ca rbonate mud 700 400-..liiCI!iZ!i:ili mottled gray grading down to tan, muddy nanno/foram pteropod ooze 393-317 em sickly gray coarse foram/pteropod ooze @ 337 em nanno ooze 317-366 em turbidite 366-375 em c halky gray whithe top 2 em are grayi s h purple 375-393 em uniform sickly gray nanno ooze 800 ___, __, 695-747 em mottled It gray/dk gray muddy nanno/ptero foram ooze turbidite; white c a rb mud green gray nanno ooze/ carbonate mud

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Appendix I. (continued) Piston Core 034 0 em -...,..,.....,......,,..., 0-39 em It brown muddy nanno/ptero 100 200 foram ooze disturbed sediments possible turbidite? 58 -102 em It gray, g reen gray mottled muddy f orarnl nanno pt ero ooze I 02-154 e m g reen gray/It gray mottled SOO w/dk gray b l obs, muddy nanno/ptero foram 1541 96 em g r een/gray/It gray nanno/ptero foram ooze 1 98-205 e m It gray w/dk gray mottles, muddy pterol n anno/fora m ooze 205-208 em green is h muddy ooze 600 208-222 em gray w/green gray mott les muddy ooze 10 e m section missing 232-387 em mott led It gray/g r ee n gray/ dk gray muddy w/ dk gray blebs ; oannolptero fora m ooze 700 80 0 435-437 em brown gray sandy mud pte r o/ n anno/forarn ooze 437-489 e m brown/gray w/dk g ray b l e b s muddy ooze 489-540 em gray gree n muddy w /dk 900 gray bleb s ooze funky b lack s tuf f @ 573 e m 540-686 em ligth gray dk gray m ott l e d w/dk gray b lack blebs w/greeni s h areas 1000 of mottling ooze funky black stuff @ 603 em black @ 699 em 686-742 em m ottled It gray/dk gray muddy nanno/pte r olforam ooze 1100 7 4 2-76 6 e m m ott l e d I t gray lkd gr a y w/dk gray to black blebs ooze black @ 761 em 766-767 em sand mud, It gray ooze black @ 795 em 767-836 em mottled It gray/ dk gray ooze

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Appendix I. (continued) Piston Core 035 Ocm T T 0-2 em brown tan sandy ooze 400 T T T 418-426 em black spots 800 T T 743-847 e m gray green ooze .,..,..,..,..,. .,..,..,..,..,. more olive i n color .,..,..,..,..,. coarser than borrom .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 2-32 em coarser olive gray sandy ooze w/ .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. alremaring bands of tannish yellow mud .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 32-44 em lighler ran sandy ooze .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. whirish mauling @ 859 e m .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 44-117 em ran 10 It olive sandy ooze .,..,..,..,..,. 426-540 em ran/olive sandy ooze withprer o .,..,..,..,..,. 847-904 black speck s more .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. b lack flecks throughoul .,..,..,..,..,. olive color, clayey with less sand 100 .,..,..,..,..,. 500 .,..,..,..,..,. 900 .,..,..,..,..,. .,..,..,..,..,. 102-105 em coarser preropod secrion .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 117-212 em ran 10 lr olive ooze grades down .,..,..,..,..,. .,..,..,..,..,. 904-1027 e m gray g reen sandy ooze .,..,..,..,..,. 10 o live s eaf oam g reen .,..,..,..,..,. 540-580 em grad es imo m ore ran gray color .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 190 e m g reen mud layer .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,." .,..,..,..,..,. .,..,..,..,..,. 991 em black srreak across core 200 .,..,..,..,..,. 600 .,..,..,..,..,. 1000 .,..,..,..,..,. .,..,..,..,..,. 209-211 em green mud lay er .,..,..,..,..,. 580-647 e m gray ran sand y foram ooze .,..,..,..,..,. 1 011-1015 e m black srreaks across .,..,..,..,..,. .,..,..,..,..,. wlblack flecks throughour .,..,..,..,..,. core .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 212-270 e m abrupl change ro tannish gray .,..,..,..,..,. .,..,. .,..,. .,..,..,..,..,. sandy ooze coarser ar bouom o f section .,..,..,..,..,. .,..,..,..,..,. 1027-1054 e m sandy tan ooze, much .,..,..,..,..,. .,..,..,..,..,. black mortling .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. .,..,..,..,..,. 688 em black spor .,..,..,..,..,. 270-344 em grayis h olive sandy ooze w /small .,..,..,..,..,. TTTTT black flecks TTTTT 300 TTTTT 700 TTTTT 647-734 em gray green ooze TTTTT TTTTT 1100 TTTTT TTTTT TTT TT TTTTT TTTTT 355 em grayis h spol _T,..T.., TTTTT 9 e m secri o n missing TTTTT 344-426 em changes 1 0 a more tan olive ooze 'T'T'T TTTTT w/large prer opods visible TTTTT TTTTT TTTTT TTTTT TTTTT 749-774 em black spots aboul 4 em apart TTTTT grayish spor @ 392 em TTTTT TTTTT 400 800 1200

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Appendix II Geochemical Data 196

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....... \0 -..) CH9204-027 (Core 27) Depth (em age (ky) sed rate 6 6 1.00 11 1 9 0 .38 21 28 1.11 31 34.25 1.60 41 40.5 1 .60 51 46.75 1 .60 61 53 1.60 71 65 0 .83 81 71 1.67 91 80 1 11 101 83.5 2 .86 111 87 2 .86 121 90 3 .33 131 93 3 .33 141 96 3 .33 151 99 3 .33 161 107 1.25 171 114. 5 1 .33 181 122 1.33 191 124 5 .00 201 126 5 .00 211 128 5 .00 223 135 1.71 233 140. 5 1 .82 243 146 1.82 253 151 2 .00 263 157.67 1 .50 273 164.34 1.50 283 171 1.50 293 183 0.83 Wet wt Dry wt 19.892 11.814 15.701 9 .162 18.235 10.541 18.491 10.805 19.361 11.46 19.537 11.4 72 18.321 10.392 15. 841 8.976 15.271 8.466 14.694 8.059 16.17 9 .106 15.805 9 .085 16.472 9.451 16.274 9.189 16.2 9 .309 16.795 9 .942 16.744 9.666 14.819 8.274 17.039 9 .645 17.752 10.207 15.588 9.182 17. 041 10.195 11.817 6 .99 14.649 8.581 14.265 8.334 14.141 8.165 14.38 8.141 14.362 8.125 13.901 8 061 14.217 8 .479 Fine Carbonate Mineralogy %fine %coarse a18o %CaC03 % Araq % MqCalc %Calcite Dry Bulk Den 59 38 -1.07 70 37 16 47 0 .97 61 35 0.72 54 70 27 0 .08 56 24 1 9 57 0.92 65 31 0.43 59 72 25 0 11 58 21 09 71 0.96 72 25 0 .19 66 80 17 0.05 39 24 18 58 0.90 77 1 9 0.16 46 73 20 -0.45 49 23 17 60 0 .87 67 29 -0.47 56 64 33 -0.47 61 29 11 60 0.89 64 32 -0.20 61 68 29 -0.24 52 28 12 60 0 91 65 31 -0.32 63 62 35 -0.45 68 24 09 67 0 .92 61 36 -0.48 72 63 34 -0.30 60 34 08 58 0 .92 61 32 -0.78 58 55 42 -1.14 61 35 08 58 0 .89 57 40 -0.76 68 63 33 0 .93 72 38 10 52 0 .96 81 16 -0.02 57 76 20 0 .68 60 15 00 85 0 .96 81 15 0.42 52 83 14 0 .20 50 13 00 87 0 .94 82 14 0 .56 48 85 11 0.44 38 19 25 56 0.89 81 15 0.15 43 73 24 0.13 48 16 00 84 0 .93 71 26 0.40 61

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Appendix II. (continued) CH9204 027 (Core 27) I Fine Carbonate Mineralogy Depth (em age (ky) sed rate Wet wt Dry wt %fine %coarse Cl180 %CaC03 % Araq % MqCalc %Calcite Drv Bulk Den 303 184 10.00 15.118 9 .065 70 27 0 .36 60 1 1 00 89 0 .98 313 185 10.00 15.399 9 181 77 20 0 .16 53 323 186 10.00 15.116 8.967 75 22 0 .05 54 10 00 90 0 .96 333 188.67 3 .75 15.592 9 .158 69 28 -0.13 59 343 191 .34 3.75 15.797 9 .288 65 32 -0.33 61 22 09 69 0 .95 353 194 3 .76 16.001 9.437 64 33 -0.55 55 363 199.5 1 .82 15.962 9 .778 54 43 -0.45 72 31 06 63 1.02 373 205 1 .82 16.209 9 .804 65 32 -0.30 66 384 208.67 3 .00 17.027 10.297 61 35 0 .38 65 28 11 60 1.00 394 212.34 2 .72 15. 371 8 .948 53 43 -0.30 70 -404 216 2.73 16.66 9 .89 62 35 -0.67 72 32 06 62 0.97 \0 00 414 222 1 .67 16.65 9 .989 79 18 -0.32 53 424 228 1.67 16.832 9.956 66 31 -0.03 57 18 08 74 0 .96 434 233 2.00 18.253 10.933 58 39 -0.23 59 444 238 2 .00 18.959 11.815 54 43 -0.43 71 36 05 59 1 .04 454 245 1.43 16.297 9.66 50 47 -0.41 71 464 247 5 .00 18.725 11.417 72 25 -0.27 74 28 11 61 1 01 474 249 5 .00 15.996 9 .643 76 21 0 .47 64 484 257 1 .25 17.102 10.386 75 22 0 .44 62 14 00 86 1 .00 494 261 2 .50 18.719 11 481 70 27 0 .50 64 504 265 2 .50 16.384 9 .734 68 29 0.66 69 10 00 90 0 .96 5 1 4 269 2.50 18.737 11.443 76 21 0 .69 71 524 275 1 .67 18.523 11.13 79 18 0.18 59 12 00 88 0 .98 535 281 1 .83 15.689 9.212 88 09 0.27 48 545 287 1 .67 17.587 10.294 85 12 -0.08 53 13 00 87 0 .94 555 290 3 .33 17. 891 10.533 77 20 -0.02 57 565 293 3.33 16.699 9.717 73 24 0.11 62 15 00 85 0.93 575 296 3 .33 17.992 10.53 64 33 0.07 72 585 299 3 .33 17.566 10.43 52 45 0.24 73 21 00 79 0 .96 595 301 5 .00 16.516 9 921 75 22 -0.10 67

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....... \0 \0 Appendix II. (continued) CH9204-027 (Core 27) Depth (em age (ky) sed rate 605 303 5.00 615 304.167 8.57 625 305.334 8.57 635 306. 501 8 .57 645 307.668 8.57 655 308.835 8.57 665 310 8.58 675 314. 2 2.38 686 318.4 2.62 696 322.6 2.38 706 326. 8 2.38 716 331 2.38 726 335 2.50 736 339 2.50 746 341 5 .00 756 348 1.43 766 355 1.43 776 362 1.43 786 363 10.00 796 364 10.00 806 365 10.00 816 366 10.00 826 367 10.00 836 368 10.00 846 375 1.43 856 377.73 3.66 866 380.46 3.66 876 383.19 3.66 886 385.92 3.66 896 388.65 3 .66 Wet wt Dry wt 17.68 10.576 18.33 10.841 18.634 10.959 18.262 11.039 19.261 11.86 20.213 12.374 19.794 11.794 19.363 11.767 17.089 10.217 20.095 12.084 17.125 10.436 16.63 10.166 17.574 10.734 18.094 10.888 19.115 11.189 17.944 10.598 17.448 10. 401 17.618 10.413 14.987 6.609 15.673 8.282 16.99 9 .909 18.51 10. 991 17.244 10.266 17.52 10.683 15.579 9.572 14.79 8.606 16.015 9 .518 17.338 10.294 16.636 9.854 14.572 8 .322 Fine Carbonate Mineralogy %fine %coarse a18o %CaC03 % Arag % MgCalc %Calcite Dry Bulk Den 80 17 0 .23 63 20 00 80 0.97 71 26 0.09 69 74 23 -0.42 67 13 00 87 0.95 74 23 -0.18 72 73 24 -0.18 75 23 00 77 1 .02 75 22 -0.38 75 79 1 8 -0.74 65 22 00 78 0.97 70 27 -0.46 71 61 35 -0.18 75 16 00 84 0 .98 64 33 -0.46 77 71 26 -0.44 79 15 00 85 1 01 76 21 -0.76 80 83 14 0.19 70 00 00 100 1.01 84 13 0.75 55 80 17 0.77 51 12 00 88 0.94 80 18 0 .68 61 80 17 0.75 62 07 00 93 0 .97 82 15 0.49 64 45 50 0 .04 41 00 00 100 0.62 74 23 0 .11 46 83 14 0.66 48 1 2 00 88 0 .93 84 14 -0.04 52 78 20 0 .32 51 06 00 94 0 .96 78 20 -1.26 56 73 24 0.06 65 04 00 96 1.02 82 14 -0.31 58 69 28 -0.11 67 12 00 88 0 .97 66 31 -0.38 65 74 23 -0.42 61 17 00 83 0.96 67 29 -0.58 59 L___ ------------------

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Appendix II. (continued) CH9204-027 (Core 27) Fine Carbonate Mineraloav Depth (em aqe (ky) sed rate Wet wt Drv wt %fine %coarse a180 %CaC03 % Araa % MaCalc %Calcite Drv Bulk Den 906 391 .38 3 .66 17.144 10.023 69 28 -1.19 65 19 00 81 0 .94 916 394.11 3 .66 14.509 8.581 61 36 -0.70 66 926 396.84 3.66 16.271 8.964 44 52 -1.30 61 19 00 81 0.86 936 399.57 3.66 14.962 8.332 48 48 -0.87 71 946 402. 3 3.66 17.987 10.381 53 44 -1.33 73 30 00 70 0 .92 956 405 3.70 18. 1 07 10.525 52 45 -1.48 73 966 414 1.11 16.48 9.698 65 32 0.02 72 12 00 88 0.95 N 8 976 423 1.11 19.455 11.505 66 31 0.09 71 986 428. 5 1 .82 17.735 11 125 83 14 0.02 55 1 1 00 89 1.05 996 434 1 .82 20.23 12.29 75 22 0.79 55 1006 439.4 1.85 20.348 12.302 72 25 0.69 56 14 00 86 0.99 1016 444.8 1.85 20.35 12. 291 75 22 0.55 53 1026 450.2 1 .85 20.671 12.546 79 18 0.41 62 08 00 92 1.00 1036 455. 6 1 .85 20.708 13.088 75 23 0.24 72 1046 461 1.85 19.232 11.38 84 13 0.01 46 12 00 88 0.96 1056 466 2.00 17.821 10.865 80 18 0.23 54 1066 471 2.00 19.679 12.016 78 20 0.48 63 07 00 93 1.00 1076 474.5 2.86 17.042 10.206 83 15 -0.24 55 1086 478 2 .86 19.393 11.762 70 28 -0.45 52 15 00 85 0.99 1096 479. 5 6 .67 18.601 11.266 69 28 -0.59 52 1106 481 6.67 17.542 10.895 70 27 -0.61 62 23 00 77 1.04 1116 18.873 11.902 67 31 -0.45 71 1126 19.713 12.564 67 30 -0.28 72 16 00 84 1.08 1131 20.168 12.946 66 32 -0.39 73 I

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N 0 Appendix II. (continued) CH9204-027 (Core 27) Total Fine Sediment Content Depth (em) Age (ky) % Araq % MqCalc %Calcite 6 6 26 11 33 11 19 21 28 13 11 32 31 34.25 41 40. 5 12 05 41 51 46.75 61 53 09 07 23 71 65 81 71 11 08 29 91 80 101 83. 5 18 07 37 111 87 121 90 1 5 06 31 131 93 141 96 16 06 46 151 99 161 107 21 05 35 171 114. 5 181 122 21 05 35 1 91 124 201 126 27 07 37 211 128 223 135 08 00 44 233 140. 5 243 146 06 00 44 253 151 263 157.67 07 09 21 273 164.34 Accumulation Rates % Non-Carb Bulk Ace Fine Ace Coarse Ace Araq Ace Mq-Calc Ace Calc Ace Non-Carb Ace 30 0 .97 0 .57 0.36 0 .15 0 .06 0.19 0 .17 44 1 .03 0.72 0.27 0 .10 0 .08 0 .23 0 .32 42 1.53 1 .10 0 .39 0 .13 0 .06 0.45 0.46 61 1.43 1.15 0.24 0.10 0 .08 0 .26 0 .70 51 1 .46 1 .06 0.29 0 .12 0.09 0 31 0.54 39 2 .53 1 .62 0 .83 0 .29 0 11 0 .60 0 .63 48 3.04 2.06 0 .89 0 .30 0 .13 0.64 0 .99 32 3 .05 1 .88 1 .07 0 31 0 .12 0 .86 0.60 40 1 .15 0 .72 0.40 0.15 0 .03 0 .25 0 .29 39 1.19 0 .65 0.51 0 .14 0 .03 0.23 0 .25 28 4.78 3 01 1.59 0.82 0 21 1 .12 0 .86 48 1 .65 1 .25 0 .33 0.09 0.00 0 .55 0 .60 50 1. 71 1.42 0 .23 0.09 0.00 0 .62 0 71 62 1 .34 1 .14 0 .15 0 .08 0.11 0 .24 0 71

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N 0 N Appendix II. (continued) CH9204-027 (Core 27) Total Fine Sediment Content Depth (em) Age (ky) % Arag % MgCalc %Calcite 283 171 08 00 40 293 183 303 184 06 00 54 313 185 323 186 05 00 48 333 188.67 343 191.34 1 3 05 42 353 194 363 199.5 23 04 45 373 205 384 208.67 20 08 42 394 212.34 404 216 23 04 45 414 222 424 228 10 04 42 434 233 444 238 25 04 42 454 245 464 247 21 08 45 474 249 484 257 09 00 53 494 261 504 265 07 00 62 514 269 524 275 07 00 52 535 281 545 287 07 00 46 555 290 565 293 08 00 49 Accumulation % Non-Carb Bulk Ace Fine Ace Coarse Ace Arag Ace Mq-Calc Ace Calc Ace Non-Carb Ace 52 1 .39 1 .02 0.33 0 .08 0.00 0.41 0 .53 40 9 .78 6 .82 2 .65 0.44 0 .00 3 .67 2 .72 46 9.60 7 .23 2.11 0.39 0.00 3 .50 3 .34 39 3.55 2 .30 1 .14 0.31 0.12 0 .97 0.90 28 1.85 1.00 0 .79 0.23 0 .04 0 .45 0 .28 30 2 .99 1 .83 1.04 0 .36 0 .15 0 .77 0.55 28 2 .64 1.63 0 .92 0 .37 0.06 0 .73 0.46 43 1.60 1.06 0.49 0 .11 0.05 0.45 0.46 29 2 .09 1 .13 0 .90 0 .28 0 .04 0.47 0.33 26 5 .04 3.62 1 .27 0.76 0 .28 1.62 0.95 38 1 .25 0.94 0.27 0.08 0 .00 0 .50 0 .36 31 2.41 1.63 0 .70 0 .12 0.00 1.02 0 .50 41 1 .63 1.29 0.30 0 .09 0.00 0 .67 0 .52 47 1 .57 1.33 0.19 0.09 0 .00 0.61 0 .62 43 3 11 2 .26 0 .76 0 .19 0 .00 1.1 0 0.96

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N 0 (j.) Appendix II. (continued) CH9204-027 (Core 27) Total Fine Sediment Content Depth (em) Age (ky) % Ar1!f} %MgCalc %Calcite 575 296 585 299 15 00 57 595 301 605 303 14 00 54 615 304.167 625 305.334 09 00 59 635 306.501 645 307.668 17 00 55 655 308.835 665 310 16 00 59 675 314. 2 686 318. 4 12 00 63 696 322.6 706 326. 8 11 00 67 716 331 726 335 00 00 70 736 339 746 341 06 00 45 756 348 766 355 04 00 58 776 362 786 363 00 00 41 796 364 806 365 06 00 42 816 366 826 367 03 00 48 836 368 846 375 03 00 63 856 377.73 Accumulation Rates %Non-Garb Bulk Ace Fine Ace Coarse Ace Araq Ace Mq-Calc Ace Calc Ace Non-Garb Ace 28 3.21 1.68 1.44 0 .25 0 .00 0.95 0.48 33 4.87 3.91 0.84 0.53 0 .00 2 .10 1.27 31 8 .13 6 .02 1.85 0 .55 0 .00 3 .58 1.89 28 8.76 6 .40 2.13 1.06 0.00 3 .52 1.82 25 8.31 6.57 1.52 1 .07 0 .00 3.85 1 .64 25 2 .56 1 .57 0.89 0 .19 0 .00 0.98 0.40 21 2.39 1.69 0 .62 0.19 0.00 1.14 0 .36 30 2.52 2 .08 0 .36 0 .00 0.00 1.45 0.63 49 4 .70 3 .76 0 .80 0.24 0.00 1 .69 1.83 38 1.38 1 11 0.23 0.05 0.00 0.64 0.42 59 6.19 2 .78 3.10 0 .00 0.00 1.14 1 .64 52 9.34 7 .78 1 31 0.47 0.00 3.27 4.04 49 9.64 7.48 1 .92 0.23 0.00 3.61 3 .63 35 1.46 1 .06 0 .34 0.03 0.00 0 .66 0.37

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Appendix II. (cont i nued) CH9204-027 (Core 27) Total Fine Sediment Content Accumulation Rate,s Depth (em) Age (ky) % Arag % MgCalc %Calcite % Non-Carb Bulk Ace Fine Ace Coarse Ace Arag Ace Mg-Calc Ace Calc Ace Non-Carb Ace 866 380.46 08 00 58 33 3 .54 2.42 0 .99 0 .20 0.00 1.42 0 81 876 383.19 886 385.92 1 1 00 50 39 3 .52 2 .60 0 .80 0 .28 0.00 1 .31 1.02 896 388.65 906 391.38 12 00 53 35 3.45 2 .36 0 .97 0 .29 0 .00 1 .25 0.83 916 394. 11 926 396.84 12 00 49 39 3 .14 1 .37 1 .65 0 .16 0 .00 0 .67 0 .54 936 399.57 946 402.3 22 00 51 27 3 .38 1 .79 1.47 0.40 0 .00 0 91 0.48 N 956 405 966 414 09 00 64 28 1 .05 0.68 0.34 0 .06 0 .00 0.43 0 .19 976 423 986 428. 5 06 00 49 45 1 .92 1 .59 0 .27 0 .10 0 .00 0 .78 0 71 996 434 1006 439.4 08 00 48 44 1.84 1 .32 0 .46 0 .10 0 .00 0 .63 0.58 1016 444. 8 1026 450. 2 05 00 58 38 1 .84 1 .46 0 .34 0 .07 0 .00 0 .84 0.55 1036 455. 6 1046 461 05 00 41 54 1 .77 1.49 0 .24 0 .08 0.00 0 61 0.80 1056 466 1066 471 04 00 58 37 2 01 1.57 0 .39 0.07 0 .00 0 91 0 .59 1076 474.5 1086 478 08 00 44 48 2 .84 1 .98 0 .80 0.15 0 .00 0.88 0 .95 1096 479.5 1106 481 6.9 4.86 1.88 0 .69 0 .00 2 .32 1 .84 1116 1126 1131

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N 0 Ul Appendix II. (continued) CH9204 035 (Core 3f Depth (em) Age (ky) a1ao 2 6 -1.55 12 19 -0.06 22 28 -0.36 32 40.5 -0.15 42 53 -0.51 52 56 -0. 11 62 59 -0.09 72 62 0 .11 82 65 0 .18 92 67 -0.33 102 69 -0.46 112 71 -0.39 126 72.8 -0.67 136 74.6 -0.56 146 76.4 -0.94 156 78. 2 -0.91 166 80 -1.00 176 83. 5 -0.91 186 87 -0.48 196 88.33 -0.69 206 89.66 -1.01 216 90.99 -0.99 226 92.32 -0.92 236 93.65 -1.00 246 94.98 -0.90 256 96. 3 1 -0.99 266 97.64 -0.88 276 99 -1.30 286 102.29 -0.90 Sed rate Wet wt .33 12.700 .77 14.532 1 11 14.283 .80 13.130 .80 16.313 3 .33 14.448 3 .33 14.939 3.33 15.017 3.33 13.789 5 .00 16.055 5 .00 13.946 5 .00 11.700 7.78 12.295 5.56 14.506 5 .56 14.559 5.56 15.340 5 .56 15.106 2.86 15.377 2.86 15.756 7.52 12.726 7 .52 14.177 7 .52 15.184 7 .52 15.498 7 .52 14.864 7 .52 14.225 7 .52 16.285 7.52 16.346 7 .35 15.176 3.04 16.366 I Fine Carbonate Mineralogy Dry wt %fi ne %coarse %CaC03 % Arag % Mg-Calc %Calcite Dry Bulk Den 7 .349 46 48 83 59 12 29 0 .94 8 .292 49 46 64 37 25 39 0.91 8.468 56 41 72 38 23 39 0.96 7.495 58 38 69 39 18 43 0 91 9.291 52 45 68 36 20 44 0.90 8.598 58 38 65 8 .922 62 34 60 8 .925 56 40 61 35 32 33 0.97 8.003 53 44 60 39 29 32 0 .93 9.595 43 53 63 8 .922 35 52 61 38 23 39 1 .14 6 .952 45 51 60 6 .978 46 50 69 8.498 51 44 74 8.653 52 44 79 8.740 50 45 76 8.838 56 39 77 51 22 27 0.95 9.021 54 41 63 9 .252 75 21 74 47 22 31 0 .95 7 .235 72 24 74 8.194 73 23 73 8.796 71 26 77 9.124 67 30 79 8.989 66 30 78 53 1 8 29 1 .00 8.469 68 29 79 10.178 79 18 68 10.071 69 28 78 9 .357 62 33 79 56 21 23 1.04 9.717 66 31 75 -L_

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N 0 0\ Appendix II. (continued) CH9204-035 (Core 3Ei) Depth (em) Age (ky) a1ao 296 105.58 -1 11 306 108.87 -1 .15 316 112.16 -1.20 326 115.45 -1.40 336 118.74 -1.37 346 122 -1.66 356 124 -1.48 366 126 -1.35 376 128 -0.93 386 130.33 0 .29 396 132.66 0 .37 406 135 0 .43 416 138.67 0 .32 426 142.34 0 .47 436 146 0 .06 446 151 0 .57 456 154.33 0.30 466 157.66 0 .19 476 160.99 -0.01 486 164.32 0 .02 496 167.65 -0.20 506 171 -0.31 516 177 -0.26 526 183 0 .31 536 184.5 -0.24 546 186 -0.53 556 187. 6 -0.71 566 189. 2 -1.03 576 190. 8 -1.10 587 192. 4 -0.86 Sed rate 3 .04 3.04 3.04 3 .04 3 .04 3 .07 5.00 5 .00 5 .00 4.29 4 .29 4 .27 2.72 2 .72 2 .73 2.00 3.00 3.00 3 .00 3 .00 3.00 2 .99 1 .67 1.67 6 .67 6 .67 6 .25 6 .25 6.25 6 .88 I Fine Carbonate Mineralogy Wet wt Drv wt %fine %coarse %GaC03 %Arag % Mg Calc %Calcite Dry Bulk Den 16.206 9.671 69 27 73 14.637 8.462 48 48 72 15.785 9.071 40 56 78 61 16 24 0 .92 17.765 10.368 40 55 75 18.819 11 .524 64 33 82 18.410 11 .294 66 31 85 61 16 22 1 .02 19.602 12.458 73 24 87 18.322 11.374 73 24 78 55 20 25 1 .04 18.669 11 167 74 24 64 17.758 10.595 67 30 61 16.515 9 .602 62 35 65 15.853 9.443 72 26 63 29 27 44 0 .97 19.902 1 1 .810 80 18 64 19.937 12.145 75 21 63 16.414 9.916 78 16 58 24 36 40 1 .00 17.583 10.552 78 19 58 25 38 37 0 .98 17.692 10. 381 73 24 54 I 17.236 10.174 61 36 64 16.853 9.479 52 45 56 19.413 10.953 71 26 65 18.269 10.498 66 31 62 16.103 9 .323 58 39 65 32 18 50 0 .93 21.085 12.516 69 29 63 17.613 10.465 68 29 64 35 18 46 0 .97 15.804 9.391 57 41 65 18.377 10.952 66 32 73 18.014 10. 961 58 38 72 50 23 27 1 01 17.506 10.324 63 35 77 21.060 13.206 68 29 67 49 25 26 1 .06 17.847 11.090 62 34 79

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Appendix II. (continued) CH9204-035 (Core 3 i) Fine Carbonate Mineralogy Depth (em) Age (ky) d180 Sed rate Wet wt Dry wt % f i ne %coarse %GaC03 % Arag % Mg-Calc %Calcite Dry Bulk Den 598 194 -1.28 6.87 18.129 11 .302 67 30 85 609 198 -0.87 2 .75 18.457 11 .484 60 37 86 620 202 -1 .11 2.75 19.847 12.615 72 25 77 630 205 -0.70 3 .33 17.540 10.871 58 39 77 50 19 31 1 .04 640 210. 5 -0.95 1 .82 19.720 12.186 62 35 86 650 216 -1.18 1 .82 15.182 8.590 57 38 72 59 11 30 0 .90 660 218.4 1 .05 4 .17 16.657 10.085 63 33 77 670 220. 8 -1.02 4.17 17.557 10.628 59 38 84 680 223.2 -0.99 4 .17 17.986 10.840 61 36 81 690 225. 6 -0.71 4 .17 17.687 10.636 70 27 66 700 228 -0.02 4.17 15.480 9 .293 74 24 66 40 18 42 0.98 -..) 710 229.67 -0.37 5 .99 14.059 8 .370 67 30 70 720 231.34 -0.29 5.99 15.968 9.448 63 34 71 730 233. 01 -0.88 5 .99 17.994 10.801 59 38 78 56 14 30 0 .99 741 234.68 -0.70 6 .59 18.411 11 .975 63 33 84 751 236.35 -0. 91 5.99 16.327 10.178 59 35 81 761 238 -1.08 6.06 20.007 12.390 54 43 82 58 13 29 1.04 771 241. 5 -0.56 2 .86 18.706 11.400 65 31 72 38 13 48 1 .01 781 245 0 .28 2 .86 17.879 10.716 60 37 73 32 12 56 0 .98 791 247 0 .33 5 .00 15.399 9 .187 56 41 69 801 249 0.42 5 .00 16.243 9 .733 60 36 71 I 811 257 0 .29 1 .25 16.981 9 .859 54 43 72 821 259. 4 0 .32 4.17 16.850 10.000 63 34 71 I 831 261.8 0.48 4.17 16.560 9 .905 63 34 72 I 841 264.2 0 .50 4.17 16.989 10.205 76 21 64 851 266.6 0 .38 4 .17 16.479 9.942 81 17 64 861 269 0 .52 4 .17 17.712 10.679 83 1 5 70 I 34 10 56 0 .99 871 272 0 .03 3 .33 16.966 10.406 76 21 70 881 275 -0.12 3 .33 19.531 11.885 74 24 72 891 278 -0.13 3 .33 15.219 8 .849 54 42 76 I 47 06 47 0 .94

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N 0 00 Appendix II. (continued) CH9204-035 (Core 3! Depth (em) Age (ky) a1ao 901 281 -0.38 911 284 -0.34 921 287 -0.50 931 299 0.29 941 300.57 0.23 951 302.14 -0.23 961 303. 71 0 11 971 305.28 -0.46 981 306.85 -0.51 991 308.42 -0.37 1001 310 -0.71 1011 -0.21 1021 0 .02 1031 0 .11 Sed rate 3 .33 3 .33 3 .33 .83 6.37 6 .37 6 .37 6 .37 6 .37 6.37 6.33 Fine Carbonate Mineralogy Wet wt Dry wt %fine %coarse %CaC03 % Arag % Mg-Calc %Calcite Bulk Den 14.185 8.448 62 35 80 16.725 9.934 60 36 79 17. 511 10.319 64 33 75 45 1 0 45 0.96 15.162 9.236 68 29 72 34 09 57 1 .01 17.741 10.811 66 31 69 15.185 9.112 73 24 70 39 08 53 0 .98 18.700 11 .597 69 28 79 17.958 10.237 60 35 76 19.694 12.071 72 25 82 16.649 9.461 61 35 84 19.172 11 .602 71 26 80 50 11 39 1.00 19.450 11 0 961 69 28 75 17.899 11.023 67 30 68 I 10.689 6 .717 62 34 75 45 07 48 1.06

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N 0 \0 Appendix ll.{continued) CH9204-035 {Core 35) I I Total Fine Sediment Content Depth {em Age {ky) % Arao % Mo-Calc %Calci te 2 6 48.64 9 .63 24.31 12 19 23.60 15.73 24.83 22 28 27.17 16.88 28.37 32 40. 5 26.80 12.63 29.74 42 53 24.58 13.49 29. 71 52 56 62 59 72 62 21.51 19.39 20.39 82 65 23.29 17.22 19.18 92 67 102 69 23.28 14.23 23. 71 112 71 126 72. 8 136 74.6 146 76.4 156 78. 2 166 80 39.40 17.08 20.73 176 83. 5 186 87 34.82 16.63 22.87 196 88.33 206 89.66 216 90.99 226 92.32 236 93.65 41.33 13.95 22.65 246 94.98 256 96.31 266 97.64 276 99 44.79 16.47 18.04 286 102.29 Accumulation Rate % Non-Carb Bulk Ace Fine Ace Coarse Ace Arag Ace Mg-Calc Ace Calc Ace Non-Carb Ace 17.42 0 .31 0 .14 0 .15 0.07 0.01 0 .03 0.02 35.84 0.70 0 .35 0 .32 0.08 0 .05 0 .09 0 .12 27.58 1 .07 0 .60 0 .44 0.16 0.10 0 .17 0 .17 30.83 0 .73 0.42 0 .28 0 11 0 .05 0.12 0.13 32.22 0 .72 0 .37 0 .32 0 .09 0 .05 0 .11 0 .12 38.71 3 .23 1.82 1.29 0.39 0.35 0 .37 0.70 40.31 3 .11 1.64 1 .35 0 .38 0 .28 0.31 0 .66 38.77 5 .70 1.98 2 .94 0.46 0.28 0.47 0 .77 22.79 5.28 2.94 2.08 1 .16 0 .50 0 .61 0.67 25.69 2 .72 2 .05 0.57 0 71 0 .34 0.47 0 .53 22.07 7 .51 4 .98 2.29 2 .06 0 .69 1 .13 1.1 0 20.70 7 .63 4 .72 2 .55 2 .11 0 .78 0 .85 0 .98 1

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Appendix ll.(continued) CH9204-035 (Core 35) I I Total Fine Sediment Content Accumulation Depth (em AQe (ky) % AraQ % MQ-Calc %Calcite %Non-Garb Bulk Ace Fine Ace Coarse Ace AraQ Ace MQ-Calc Ace Calc Ace Non-Garb Ace 296 105.58 306 108.87 47.25 12.14 18.32 22.28 2.80 1 .12 1.56 0.53 0.14 0 .21 0 .25 316 112.16 326 115.45 336 118.74 52.26 13.81 18.99 14.93 3.14 2 .07 0 .98 1.08 0 .29 0.39 0 31 346 122 356 124 42.57 15.72 19.36 22.35 5.21 3.81 1.27 1.62 0 .60 0.74 0 .85 366 126 376 128 386 130.33 N 396 132.66 18.23 17.27 27.54 36.96 4 .14 2 .98 1.06 0.54 0 .51 0 .82 1.10 ,_. 0 406 135 416 138.67 426 142.34 14. 01 20.69 22.91 42.39 2 .73 2.14 0 .45 0 .30 0.44 0 .49 0 .91 436 146 14.33 21.77 21.54 42.36 1 .96 1 .53 0.38 0.22 0 .33 0 .33 0.65 446 151 456 154.33 466 157.66 476 160.99 486 164.32 496 167.65 21.05 11.48 32.85 34.62 2 .76 1 .60 1 .09 0.34 0 .18 0 .53 0 5 _L_ 506 171 516 177 22.44 11.78 29.57 36.21 1 .61 1.09 0.47 0.25 0.13 0 .32 0.40 526 183 536 184. 5 546 186 36.26 16.46 19.68 27.61 6.30 3 .68 2.41 1.34 0.61 0 .72 1.02 556 187. 6 566 189. 2 32.57 17.05 17.50 32.88 6 .61 4.51 1 .93 1.47 0.77 0 .79 1.48 576 190. 8 587 192.4

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N ...... ........ Appendix ll.(continued) 8H9204-035 (Core 35) I I Total Fine Sediment Content )epth (em Age (ky) % Arag % Mg-Calc %Calcite 598 194 609 198 620 202 38.49 15.08 23.83 630 205 640 210.5 42.48 8.00 21.87 650 216 660 218.4 670 220. 8 680 223.2 690 225.6 26.34 12.11 27.36 700 228 710 229.67 720 231.34 43.23 10.92 23.37 730 233. 01 741 234.68 751 236.35 47.17 10.38 24.05 761 238 27.58 9.68 35.05 771 241. 5 23.13 8 .73 41 .29 781 245 791 247 801 249 811 257 821 259. 4 831 261.8 841 264. 2 851 266. 6 23.73 7 .02 38.92 861 269 871 272 881 275 35.56 4.28 35.95 891 278 Accumulation % Non Carb Bulk Ace Fine Ace Coarse Ace Araq Ace Mq-Calc Ace Calc Ace Non-Carb Ace 22.60 3.46 2 .00 1.37 0 .77 0.30 0.48 0.45 27.65 1 .63 0 .94 0.63 0.40 0 .08 0 21 0 .26 34.19 4 .09 3 .02 0 .96 0 .80 0 .37 0 .83 1.03 22.49 5.90 3 .49 2.24 1 51 0.38 0 81 0 .78 18.40 6.30 3 .38 2 71 1.59 0 .35 0 81 0.62 27.68 2 .89 1 .88 0 .90 0 .52 0.18 0.66 0 .52 26.85 2 .80 1 .68 1 .04 0.39 0 .15 0 .69 0.45 30.32 4 .12 3.41 0.60 0.81 0 .24 1 .33 1 .03 24.21 3.13 1 .69 1.31 0.60 0 .07 0.61 0.41

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Appendix l l. (continued) CH9204-035 (Core 35) I I Total Fine Sediment Content Accumulation Rate Depth (em Age (ky) % Arag % Mg-Calc %Calcite % Non-Carb Bulk Ace Fine Ace Coarse Ace Arag Ace Mg Calc Ace Calc Ace Non-Carb Ace 901 281 911 284 34.00 7.68 33.65 24.67 3 .19 2 .03 1.04 0 .69 0.16 0.68 0 .50 921 287 24.90 6 .25 41 .16 27.68 0 .84 0 .57 0.24 0 .14 0 .04 0.24 0 .16 931 299 941 300.57 26.89 5 .49 37.13 30.49 6.27 4 .55 1.50 1 .22 0 .25 1.69 1.39 951 302.14 961 303.71 971 305.28 981 306.85 991 308.42 40.19 8.51 31.16 20.14 6 .33 4 .51 1 .63 1 81 0.38 1 .40 0 91 N 1001 310 -N 1011 1021 33.67 5 .08 36.43 24.82 1031 --

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VITA David Duncan received a Bachelor's Degree in Geology from Michigan State University in 1985 and a Master's Degree in Marine Science from the University of South Florida in 1993. He began teaching at Eckerd College in the Marine Science Program in 1995 and is currently a Visiting Assistant Professor of Marine Science at Eckerd. While in the Ph.D. program at the University of South Florida, Mr. Duncan completed over two months of oceanographic research at sea. He has presented his work at national meetings including the Geological Society of America and the 1st SEPM Congress on Sedimentary Geology In 1995 he was the recipient of the Robert M. Garrels Fellowship at the University of South Florida.