Reassessing the aminostratigraphy of eolianites on San Salvador Island, Bahamas

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Reassessing the aminostratigraphy of eolianites on San Salvador Island, Bahamas

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Title:
Reassessing the aminostratigraphy of eolianites on San Salvador Island, Bahamas
Creator:
Purcell, Noreen Anne Buster
Place of Publication:
Tampa, Florida
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University of South Florida
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English
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ix, 85 leaves : ill. ; 29 cm. + 1 computer disk (3 1/2 in.)

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Subjects / Keywords:
Racemization ( lcsh )
Amino acids ( lcsh )
Geology, Stratigraphic -- Quaternary ( lcsh )
Geology -- San Salvador (Bahamas) ( lcsh )
Dissertations, Academic -- Geology -- Masters -- USF ( FTS )

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General Note:
Thesis (M.S.)--University of South Florida, 2000. Includes bibliographical references (leaves 72-75).

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University of South Florida
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Universtity of South Florida
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027470334 ( ALEPH )
45827570 ( OCLC )
F51-00153 ( USFLDC DOI )
f51.153 ( USFLDC Handle )

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REASSESSING THE AMINOSTRATIGRAPHY OF EOLIANITES ON SAN SALVADOR ISLAND BAHAMAS by "' NOREEN ANNE BUSTER PURCELL A thesis submitted in partial fulfillment of the requirements for the degre e of Master of Science Department of Geology College of Arts and Sciences University of South Florida May2000 Major Professor : Eric A. Oches Ph.D.

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Office of Graduate Studies University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of NOREEN ANNE BUSTER PURCELL with a major in Geology has been approved for the thesis requirement on April 20 2000 for the Master of Science degree Examining Committee: Major Professor: Eric A. Oches, Ph. D. Member: H.L. Vacher_Ph.D...

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To Jessie, my dog and companion, who was by my side a lmost all the way through school. I miss you

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Acknowledgements I would like to thank my advisor Rick Oches for all of his support throughout my graduate school years His help with my thesis has been wonderful and his knowledge is amazing I have known Len Vacher for years now, and I could not have made it through school without him. His support and advice was immeasurable and I will remember him forever for everything. I would also like to thank Skip Davis for always encouraging me to do what he knew I could, knowing I just needed a push to get there. I will always be grateful to Mark Stewart for his continued assistance and encouragement. I thank the University of South Florida Research and Creative Scholarship Program for financial support that provided a trip to San Salvador Island and laboratory materials to complete this project. In addition, I thank Mr. Kenneth Buchan, Director of the Bahamian Field Station, who took great care of us while in San Salvador. In addition I would like to thank my parents for all their support and love beginning the day I was born I would have never made it this far without you. I would like to thank my dear friends Sandy, Becky and Kristen for being there for me during all different periods of my life in graduate school, some good, some bad thank you for believing in me. I am grateful to Steve who worked in the lab with me, and helped with my samples, kept the analyzer running and helped keep me sane Mary and Nancy always took care of me, no matter what trouble I got into and words can not even express my feelings for them. Last, but certainly not least, I thank my dear husband Scott, who never let me give up on myself and was always there to dance with and cry to you are my soul.

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TABLE OF CONTENTS LIST OF TABLES .. ... . . ......... . .. . .. .. .............................. ... . ........... . .. . . . .. . ............ i ii LIST OF FIGURES .... .... ..... .. . ... . .. ... ... . ... . .. ......... ... ........ ... ..... .... ... ... ..... ... ... .. iv ABSTRACT ............ .... .... . ... ...... . ... ......... .... .... . ....... ... ... ....... .............. ....... .......... vii Reassessing the Aminostratigraphy of San Salvador Island, Bahamas INTRODUCTION ............. .... ..... ... ... .... ..... .... . .... . ....... ............ ...... .. . ... . ... 1 Eolianites ..... ..... ............... ..... .... ....... ........ .... ..... ... . .... .... ... ... ...... ... 3 Geologic Setting ........ . . ... .... ... ... ...... ...... .... .... ... ....... .. .... ... ...... . ........ 6 Str a tigraphic Backround ............. . .......... . ... . . .......................... . ... ...... 9 Bahamas Stratigraphy and Aminostratigraphy ...... .... .... . .... . . ........ ... 12 Amino Acid Geochronolog y .............. ......... .... . ......... .. .... ... .... ... ...... 16 METHODS ...... . .... ...... . ..... .... .. . .. ................. .... .. ......... .... .... ... . ........... ... ..... 19 Field Sampling ....... .... .. ....... ......... ....... ......... ........... ..... . . ..... ... . ..... 19 Laboratory Procedures .... . ... . .... ........... . ... ............... .... .. ........ . . ...... 24 General ..... ....... ... ... . .......... .... .... .... ............... .............. ... ... .. 24 Sample Analysis ... ............ ........ ... ............ .. . ........ ... . . . ........ ... 25 AMINO ACID RACEMIZATION DATA ..... ... . .. ....... . ..... ...... .... . . . .... ........ 26 North Point and Hanna Bay .... ... ..... .. . .. .................................. ... ... ...... 35 Intra-dune variability in amino acid racemization measurements .... ........ ... .. . ... ... .. ..... .... .......... ........ .. ... . ........... 35 Intra-unit variab i lity in amino ac id racemization measurements .. . ... ..... ... ...... ... .... ..... ......... ... .. ...... .. . . ....... ... 3 8 Distance below surfac e ...... ........ ..................... .... ... ... 48 Int e r unit variability in amin o acid rac e m i z a tion ..... ...... ... .... .. measur e ments . .. .... . . . . ..................................... ....................... 48 Other Sample Locat i ons .... .. .... ..... ............. ....... ... ........ .... .... .... ... .... . 52 North Point Rice Bay ........ ......... .......... ... ............. ...... .... . . ....... 52 Cockburn Town ....... ... . ......... .......... . ........ . .... ... .. ....... .. . .... 52 Watling's Quarry .............. ... .... ... ......... ..... ...... ... ...... ........ ... .... 55 DISCUSSION ...... .......... ..... ....... ........ ... .... .. ... ... . ........ ... ... .... .... . . ............... 57 Intra-dune Variab i lity . ..... .............. ... ... ... .... ... . .... .... ...... ......... . . .. . 57 Intra unit Variability ... .... .. ..... ..... .... ... . ... .... . ............ .... .... .... . ... ......... 58

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Inter-unit Variability ..... ... .. ............ ..... ... ... ......... .. . .. ...... ... .... ............ 59 Aminostratigraphic Column .. .... .. ..... . .. ... .. .... ... ...... .. ...... ............ . ... ... 67 CONCLUSIONS ... ..... .... ... ... .... ..... . ... ........... .. . .......... .. ... .. .......... . . . .......... 70 Future Research .......... . .. ... ... ...... ...... .... ... ..... ............. .. . ........ ... .. . ... 71 REFERENCES ...... .... ....... ... ... .. . ..... .. ... .. .... ... . ..... .. . .. . .. . .... ... .. ........................... 72 APPENDICES .... . ... . .... . ... . ... ........... ..... .... ... ... ....... . ..... .... ... . ... .... ....... .. ... ... ........... 77 Appendix A : Field Sample Numbers and Locations .. ........ .. ......... ............... 78 Appendix B : Methods ... ..... .... .. ....... ....... ... ... . .... .......... .... .. ... ...... ......... ... 82 Labora t ory Procedures .... . ..... ... .. ........ . ............. ... .. 82 Hydrolysis .... .... .......... . . .. ........ ..... .................. 83 Rehydration . ...... .... . .... . . .... . .... . ....... . ... ........ 83 Sample Analysis ....... .... . ....... .... ... . . .... ......... ... 84 Appendix C: Rec i pes ....... .... .... ....... ..... .... .. .... . . ....... .... .... ....... ..... .... . .... ..... 85 Appendix D : FAL Sample Numbers and Amino Acid Racemization Data .... ..... .......... ... .. .... ........... .......... .... . .... . .. . .. .............. 86 11

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List ofTables Table 1. Summary of estimated radiometric ages on San Salvador Island, Bahamas ........ ............... ............. ... . ........... ........................... ....... ..... ... ... . 13 Table 1. (Continued) .. ....... ....... ......... ......... ..... ..... . .... . ...................... ........... . ....... 14 Table 2. Results of amino acid analysis of samples from uncontested stratigraphic units on San Salvador Island Bahamas ......... ....................... 30 Tabl e 3 Results of amino acid analysis of subsamples from North Point dune# 8 ........................... .... ..... . .... .................. .... ............ ........... . ........... ... 37 Table 4 Results of amino acid analysis of subsamples from Hanna Bay dune# 3 .................. ..................... ........ .... .... .... .... ... ......... .... . ...... .............. 40 Table 5 Results of amino acid analysis of subsamples from ten dunes at North Point. ..... ..... . .............. .... ....... ....... .................................................. 45 Table 6. Results of amino acid analysis of subsamples from five dunes at Hanna Bay ............. ..... .... .... ..... ............................................ . ...... . ........... 47 1ll

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List of Figures Figure 1. Map of the Bahamian islands including San Salvador Island, Bahamas (after Curran and White 1995) ..... ... ... ..... ..... ........... ............. ....... ....... .. 7 Figure 2. Map of San Salvador Island, Bahamas .... ... ............... ... . .... ...... ... ........ ... ... 8 Figure 3a. Stratigraphic column of Carew and Mylroie (1985, 1995a) ....... .... ......... ... 10 Figure 3b. Stratigraphic column ofHearty and Kindler (1993) ...... .................... .......... 10 Figure 4 Eolianite complex at North Point, San Salvador Island Bahamas, with dunes numbered and separated as shown by vertical lines ................ . 20 Figure 5. Eolianite outcrop at Hanna Bay .......... .... ............ ....... .............. ........... ..... 21 Figure 6. Looking north on west coast of San Salvador Island Bahamas, at the Cockburn Town Reef and associated facies .... .... ............... ................ ..... 22 Figure 7. East facing outcrop at Watling's Quarry, San Salvador Island, Bahamas ................. ................ ............... .................. ................................ .... 23 Fig ure 8 Mean DIL values of seven amino acids measured in whole rock subsamples collected from several localities on San Salvador Island Bahamas ................ ..................... ......... ........................................................ 27 Figure 9. Relative concentrations ofL and D isomers of all sample locations on San Salvador Island, Bahamas .... ......... ...... ... ...... ... ... .............. .... ........ 28 Figure 10 Histograms ofDIL data from North Point for four amino acid pairs .......... 31 Figure 10 (Continued) ................ ........... ...................................... ...... ... ... ...... ... ...... ..... 32 Figure 11. Histograms ofDIL data from Hanna Bay for four amino acid pairs ........... 33 Figure 11. (Continued) ..................................... .... ................ ....................................... 34 Figure 12. Five samples were taken from a single continuous layer within dune# 8 at North Point indicated by the line through samples F-G-B-H-1 above ..... ........... ....... ............................................................ ... . 35 l V

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Figure 13. Plots of four DIL amino acid values measured in subsamples collected from dune# 8 at North Point (see Figure 12 for position of each sample) ........ ....... .... .... ......... ............... ............. .......... ..... ... ... ........ 36 Figure 14 Three samples were taken from a single continuous layer within dune# 3 at Hanna Bay ..... ....... ........ ....... ...... ..... ...... ... ...... .... ................ ........ 38 Figure 15. Plots of four DIL amino acid values measured in samples collected from dune# 3 Hanna Bay (see Figure 14 for position of each sample) ..... 39 F igure 16. D i agram showing individual dunes within the fossil dune complex at North Point. .... ....... ............. ... ........................ ........ .... ... ............................ 41 F i gure 17 Diagram showing individual dunes within the fossil dune complex at Hanna Bay ..... ........ .................................. ... ........... .... .. ........ .................... 42 Figur e 18 The mean DIL values of four amino acids are plotted for ten North Point fossil dunes to examine the variati o n across the dune complex ..... ........ .... .. .... .................................................................... ... 44 Figure 19 The mean DIL values of four amino ac i ds are plotted for five Hanna Bay f o ssil dunes to examine the variation across the dune complex .... .......... ....... .... ................................... ........................ ........... 46 Figure 20. Three samples were taken vertically on each dune at North Point to determine i f high e r effective d i agenetic temperatures near the surface had impacted the uppermost samples .............. ..... .. .... ..................... 49 Figure 21. Three samples were taken vertically on each dune at Hann a Bay to determine if higher effective diagenet i c temperatures near the surface had impacted the uppermost samples ..... ..... .. .................................. 50 Figure 22. The m e an DIL values of four amino acids for subsamples ofboth North Point and Hanna Bay fossil dune complexes .. .... ...... ................... ...... 51 Figure 23. DIL values of four amino acids are plotted for subsamples from North Point Rice Bay fossil dunes to e x am ine the variat ion across the dune complex ....... ...... .... .. ...................................................... ............. ...... ... 53 Figure 24. DIL values of four amino acids are plotted for subsamples from Cockburn Town to examine the variation across exposure ........ ......... .. .. .. .. 54 Figure 25. DIL values of four amino acids are plotted for subsamples from Watling's Quarry to examine the variation abov e and below a paleosol. .......... ... ... ..... ..... ..... ..... ..... .............................. .... ........... ......... 56 v

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Figure 26. The mean DIL values for Aspartic Acid, Glutamic Acid and Valine of all subsamples for all sample locations plotted against Alloisoleucine/Isoleucine ............................ .......... .. ... .... ... ........ ...... ....... ... 60 Figure 27. The mean DIL values of four amino acids for all sample locations on San Salvador Island addressed in this study ........................................... 61 Figure 28. Aminostratigraphic column and its relationship to the two stratigraphic columns previously published for San Salvador Island, Bahamas ......................... ................................................................. 68 Vl

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REASSESSING THE AMINOSTRATIGRAPHY OF EOLIANITES ON SAN SALVADOR ISLAND, BAHAMAS by NOREEN ANNE BUSTER PURCELL An Abstract of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida May 2000 Major Professor: Eric A. Oches, Ph.D Vll

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By analyzing numerous samples from different eolianite outcrops, this study assesses the suitability of "whole rock" samples in the aminostratigraphic subdivision of Middle to Late-Quaternary eolianite units on San Salvador Island. Principle questions in this study address whether DIL ratios can be used to resolve details of deposition within a single dune, between dunes, and between different units Using reverse-phase high performance liquid chromatography this study measured DIL ratios of multiple amino acids, including Aspartic Acid, Glutamic Acid, Valine, and Alloisoleucine!Isoleucine (Ali) in order to test conflicting previous aminostratigraphic interpretations which were based on a limited number of All values alone. Aspartic Acid DIL ratios offer the best resolution in the samples At Watling's Quarry (30 samples), there is a trend of increasing A/I ratio with depth, but the data do not distinguish between the upper and lower units, which are separated by a distinct paleosol. However, Aspartic Acid DIL values from the same samples suggest separate stratigraphic units This study also analyzed 115 samples from the eolianites at North Point and 52 samples from Hanna Bay in order to evaluate intra-unit variability and test the resolution of amino acid geochronology These sediments have been previously radiocarbon dated at approximately 5300 yr B.P. and 3400 yr B.P., respectively (Carew and Mylroie, 1987). While radiometric ages and physical stratigraphic relationships indicate that each unit was deposited during a slightly different Holocene sea level, no distinction could be made between DIL values from the two eolianite complexes. Amino acid racemization data are not able to resolve the relatively short period of time separating them Vlll

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Three distinct aminostratigraphic groups, from this study, correlate with the Rice Bay, Grotto Beach, and Owl's Hole Formations, as defmed by the two published stratigraphic columns for San Salvador Island Our resulting aminostratigraphy of San Salvador Island, using several pairs of amino acids, demonstrates that amino acid racemization data should be used cautiously, yet can be used successfully when accompanied with a physical stratigraphic interpretation to determine the interglacial geochronological history of eolianite islands. Abstract Approved: ______ ...:....__...::....._ _____ Major Professor: Eric A. Oches, Ph.D. Assistant Professor, Department of Geology Date IX

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REASSESSING THE AMINOSTRATIGRAPHY OF EOLIANITES ON SAN SALVADOR ISLAND, BAHAMAS INTRODUCTION Using amino acid racemization data measured on whole rock samples this study investigates the reliability of amino acid geochronology in distinguishing stratigraphic units on San Salvador Island Bahamas San Salvador has been the center of concentrated work in several disciplines of geology including stratigraphy and geochronology. Although the physical stratigraphy and numerical ages of several l i thostrat i graphic units are widely agreed upon, there are some units whose ages are still in question (c f., Carew and Mylroie 1994, 1995a 1995c ; Hearty and Kindler, 1993, 1994) Amino acid geochronology has previously been used on San Salvador to address questions regarding the ages and stratigraphic correlations of sedimentary units, but the resolution of the method remains controversial (c.f. Hearty and Kindler 1993 1994 ; Mirecki et al. 1993 ; Carew and Mylroie, 1987, 1994, 1995c) "Whole rock" (carbonate sediments consisting ofbioclasts, ooids and pellets) samples were analyzed in this study to evaluate the suitability of this material for amino acid geochronological applicat i ons. This study also addresses the variability of amino acid racemization data and temporal 1

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and stratigraphic resolution of the method on a finer scale than has previously been attempted by others on San Salvador Island This study focuses principally on sites of uncontested age and stratigraphic position to assess whether the amino acid racemization signature can be used reliably as a method of chronostratigraphic analysis Specific objectives of this study are : 1) to evaluate temporal and spatial variability in amino acid racemization data measured in samples collected within and between individual lithostratigraphic units on San Salvador Island, using 'whole rock" samples, 2) to better understand the resolution and limitations of the method when dealing with potentially heterogeneous carbonate sediment samples, 3) to evaluate the utility of measuring D/L values of mult iple amino acids in aminostratigraphic and amino acid geochronologic investigations of Bahamian geology . Amino acid D/L values depend principally on the age of a sample, its diagenetic temperature history, and the taxonomy of constituent particles of carbonate sediment. Samples were analyzed from different uncontested lithologic units to evaluate the effect of time on D/L ratios Samples were also collected from different distances below the surface within a deposit of uniform age in order to assess the effects of near-surface heating on racemization rates 2

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Eolianites Eolianites, or lithified carbonate dunes, comprise much of the subaerially exposed bedrock in the Bahamas Carbonate dune deposition is dependent upon the rate of adjacent shallow-marine carbonate production, and minimal terrigenous input. Favorable conditions for deposition of coastal eolianites include warm water for abundant calcium carbonate production and prevailing on-shore winds for transportation of the sediment (McKee and Ward, 1983) In the Bahamas, for example, the majority oflarger eolianite deposits are located along the shelf margin where the winds are easterly and the sediment source is substantial (McKee and Ward, 1983). The carbonate constituent particles of eolianites can include skeletal and coral fragments, foraminifera, ooids, pellets, calcareous-algal fragments, and some cryptocrystalline grains (Mackenzie, 1964 : McKee and Ward, 1983). Eolianite particles are typically fineto medium-grained sand. Larger and/or smaller particles may be present, depending upon source, transport distance and depositional energy of the particular location. Grains are normally well sorted to very well sorted for the same reasons as above, yet also are affected by location. While overall sorting is good and sometimes excellent, interlayer sorting is only fair to good (Mackenzie, 1964) Eolianite particles are generally well rounded, as the particles have undergone both wave and wind abrasion. Sphericity is dependent upon the constituents but can complete the full range of shapes, including prolate, bladed, equant and disc shaped. Color, although not always used as a primary characteristic, can serve as a diagnostic criterion of constituents while studying eolianites. Mackenzie (1964) described the eolianites on Bermuda as dull-white 3

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to pinkish-white as found on fresh surfaces while they weather to gray This is also characteristic ofthe eolianites of the Bahamian islands. The lithology of eolianite complexes can aid in distinguishing one stratigraphic unit from another, because carbonate depositional source areas are dynamic and reflect changing geologic processes. For example, oolitic particles can dominate an eolianite ridge that later may be buried by or be found laterally adjacent to a primarily skeletal grainstone eolianite package. These differing facies associations can also stratigraphically intertongue with lagoon, beach or nearshore deposits where they can conceivably display a good example ofWather's Law (McKee and Ward, 1983) Lithological contacts or boundaries may be distinguished in either a regressive or transgressive sequence with paleosols (when found) and epikarst features representing times of extended exposure as they are in the Bahamas (Carew and Mylroie 1995a) Lithologic correlation of units can be achieved, but may not fully represent the depositional history as eolianite growth may not be continuous and is sometimes aerially sporadic or patchy in nature along the coastline (Carew and Mylroie, 1995a) The preservation potential of both depositional systems and environments is dependent upon four main factors : sea level, sediment supply, lithification, and tectonics. Diagenesis also plays a key role in carbonate sedimentation Eolianites are subaerially exposed during deposition and subsequent cementation of the sediment occurs rapidly due to the percolation of meteoric water (Dravis, 1996). The architecture of eolianites is distinctly well preserved due to the rapid cementation of the sediment. Eolianites are characterized by large-scale trough cross beds (Reading, 1978) This depositional environment has an obvious hierarchy compared 4

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to the other depos i tional environments within the system itself (nearshore and reefal deposits) due to the various scales of bounding surfaces present. Paleosols may represent first-orde r bounding surfaces as these represent a prolonged time of erosion and or nondeposition ofthe predominant carbonate material (Brookfield 1984). Second -order bounding surfaces may be placed between depositional sequences of forset and three dimensional trough cross-strata, which are large-scale features of these dunes (Brookfield 1984) Other medium to large-scale cross strata associated with eolianites, include wedgeand tabular-planar along with horizontal bedding (McKee and Ward, 1983) Grainflow and grainfalllenses can be found within the dunes and they also can be separated as medium to small-scale strata (Rice and Loope, 1991) Reactivation surfaces (third-order bounding surfaces) are prevalent and represent times of migration ofboth larger and smaller strata (Brookfield, 1984) By the depositional nature and position of eolianites within the shallow-shelf system it is obvious that sea-level fluctuations play a s ignificant role in periods of erosion and deposition Lithological comparisons between units can be accomplished and the formal stratigraphic nomenclature has been applied to these deposits. In addition, other stratigraphic methods are able to place a temporal relationship between strata The stratigraphic methods used to interpret the carbonate dune depositional environment and its relation to accompanying facies (beach, nearshore, and reef) are plentiful. For a complete geologic record, one must attempt to use any and every m e thod available Fortunately, eolianites allow for the alliance of s e v e ral separate stratigraphic methods, each one contributing additional information to the geologic record. 5

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Geologic Setting San Salvador Island, is located on the Grand Bahama Bank (Figures 1 and 2) This bank is an extensive carbonate platform (1400 km from north to south) with islands rising to elevations of up to 30 meters, from shallow depths typically no more than 10 meters (Curran, 1989a; Carew and Mylroie, 1995a) San Salvador is located along the southeast margin of the Bahamian archipelago, and its eastern boundary is the Atlantic Ocean. The Bahamian Islands are tectonically stable, although they are slowly subsiding at a rate of one to two meters per 100,000 years during at least the last 300,000 years, due to continued cooling of the oceanic crust (Carew and Mylroie, 1995b). The stability of these islands provides a location where evidence of the geologic past is preserved without significant tectonic modification The interior of San Salvador is characterized by arcuate carbonate ridges of eolianites and both fresh and saltwater lakes (Curran 1989a). Geologic exposures are plentiful along the perimeter of the island and provide a detailed picture of various Pleistocene and Holocene depositional environments. Fossilized reef and nearshore environments can be seen in exposures near Cockburn Town and elsewhere on the island. Eolianite complexes are numerous on San Salvador and are responsible for the highest elevations on the island. The existence of Cockburn Town fossilized reef and its associated nearshore and eolianite facies, located on the western side of San Salvador, and the huge eolianite complexes of North Point and Hanna Bay provide insight into the island's Mid to Late Quaternary sea-level history. The deposits at Cockburn Town show evidence of a regressive sedimentary sequence that has been interpreted through UraniumThorium 6

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....;) FLORIDA . 0 9 o' Sal \.Bank . . ooo "\ .. ... ,Oo ..... baco : LITTLE B,tj .:..: -: ,' .' I I THE BAHAMA I SLANDS I .. ; .. 'f-J't: I I -t-o G t aod 'i30hemo 15 . : .. '".\! ">< ..... ' . . '1>,..... '5o 0 100 mi. I I I .. Ids. G') ::c m )> '00 ....... ..... , ' Eieuthera -z,. ,.. ..., BeHy o . .. ,Is. '(> Ids ) / p \ \ _./_ ... .: . \ : '% ( . '. I f 0 100km Bat hymetr i c conlours i n fathoms 0 0.(\' ""'1-\ -.... ; tij w ; : I , ':<: :\' i . ,-, C'a( f !', < ;. -,\ '%>. ... : r,.;..,__5 Sal"do' Is . ., ... ... "i.. i .14[ . 'b. ----,., ... < \ 0) .. --' ,,..,_ ,2 .,, ,' . .. ..... . 9 .... ...... 'l".. ': :. ..,Tongveol ; -.J'. 'R\.lin' 'I the O< . , G eat : .. samana Cay 1" . r I ,,,_,_ .... , 24 O <)"N .... 'o o -r.--1-;. . ,p E'"ma s Lo .:.,, ,; Is. -v .... . ..... ,.-..__ ,Cr ooked 'co / l.._, : } .. ';Plana Ca y s ,.. A,' .... ; ... > ' ' ; , ,_ Is i >-'( f \ "ci' )-' ,_ 1 \ '; .-,\ckHos _, .. ;;:, ,,, \ --, .. ...... . .. "'<:J '.' .......... ""' .., '!A.. ... . .:.., C>i"' '/ ,.." -:;; .... ,' .... ..... .. .. .. .-' .. ,, ._ "'" Grea l ,., / !C/ '," .. ---'ho, .. .. Figure 1. Map of the Bahamian islands including San Sal v ador Island (after Curran and White, 1995).

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Cockburn li Watlings 0 Legend N Primary Roods NReefs Beaches D Tidal C reek Lake s and Ponds 2 0 2 4Miles I Robinson, Matthew C. and Davis, R Lourence.l999 San Salvador I sland GIS Database. University o f New Haven & Bahamian Field S t ation. Figure 2. Map of San Salvador Island, Bahamas. Field s ite s addressed in this study are labeled and indicated by arrows (after Robinson and Davis, 1999). 8

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radiometric dates where the oldest coral was dated at 130.75 1.5 ky B.P., and the youngest coral was dated at 119.2 1.5 ky B.P. (Curran et al., 1989). The steeply dipping eolianite forset beds located at North Point were deposited during a time when sea level was lower than present. The forsets of the Hanna Bay eolianites dip at an angle corresponding to a sea level closer to that of today (Carew and Mylroie, 1995a; Hearty and Kindler, 1993) These are but a few examples on San Salvador that allow correlation of depositional environments with past sea levels. The relative times at which these facies were deposited have been inferred through physical stratigraphic relationships (Carew and Mylroie, 1985, 1995a; Hearty and Kindler, 1993, 1994). Numerical ages have been determined through the use ofU-series dating and carbon-14 dating (Carew and Mylroie, 1987, 1995a) Amino acid racemization data previously have been calibrated to these numerical ages (Hearty and Kindler 1993 1994; Mirecki et al., 1993 ; Carew and Mylroie, 1985, 1987). Stratigraphic Backround The stratigraphy of San Salvador Island, Bahamas has been highly debated for years, and somewhat different subdivisions of lithologic units have been proposed (Figures 3a, b) (Carew and Mylroie 1985, 1987, 1995a, c; Hearty and Kindler 1993, 1994). An additional stratigraphic column was presented by Titus (1987) Other researchers, including Curran and White (1989b, 1995), Curran (1989a), and Mirecki et al. (1993) have contributed to our knowledge of the geology of San Salvador. Both Carew and Mylroie (1995a) and Hearty and Kindler (1993) have employed sequence stratigraphy to describe deposition of carbonate dunes beach and nearshore facies, and 9

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-0 f>HY SICAL O f BAHAM#\ H ..... -...........:'-.. .......... ........... ........... 0 .._. _........ HANNA BAY ............... __ L ____ ... MEMBER ......... RICE BAY 0 -..:. -::--:::_. . c ,'. E NORTH POINT FORMATION N .. ' . MEMBER ' ' E ... ..... : ................... -:-.........' -.................... .... .... -.::::. ........_ '- [, COCKBURN .....,"-......_.......,.... TOWN P [;;/_y //d///}, GROTTO MEMOER BEACH .. FORMATION T 0 '/: FRENCH BAY C ////% MEMBER E "') ./.: N E OWL S HOLE FOIIMAT10N --F igur e 3 a S tratigra p hic co lumn of Carew and Mylro ie ( 1 985 1995a) PAUOSOL PALt.oSO L P ALEOSOL PAL&OSOL RICE BAY FORMATION (Holoce n e ) ALMGREEN CAY FORMATION (Late Sangamonian) GROTTO BEACH FORMATION (Sangamonian) FORTUNE HILL FORMATION ( M id-P !.Istoc eM) OWL'S HOLE FORMATION ( M idPielstocene ) East Bay Mb. Hanna Bay Mb North Point Mb. UpperMb. LowerMb Fernandez Bay Mb. Cockburn Town Mb. French Bay Mb. Figure 3b Stratigraphic column of H earty a n d Kindle r (1993)

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reef complexes and they have contributed to the understanding of the overall depositional history throughout the Holocene and Pleistocene epochs The stratigraphic column proposed by Carew and Mylroie (1985, 1987, 1995a) includes units belonging to both the Holocene and Pleistocene epochs (Figure 3a). The Rice Bay Formation comprises the entire Holocene of San Salvador and is divided into the North Point Member and Hanna Bay Member. The Pleistocene units are divided into the Grotto Beach Formation and the Owl's Hole Formation. The Owl's Hole Formation is thought to include the oldest rocks on the island (Carew and Mylroie 1985, 1995a ; Hearty and Kindler, 1993) The Cockburn Town Member is the younger of the two units included in the Grotto Beach Formation and is underlain by the French Bay Member. The three formations that Carew and Mylroie (1985, 1987, 1995a) have described within their physical stratigraphic column are separated from each other by well developed paleosols. This stratigraphic scheme has evolved through analysis of physical stratigraphic relationships petrology, paleomagnetics, existence of paleosols Uraniwn/Thorium ages radiocarbon dating and amino acid racemization geochronology, to create both a stratigraphic column and a proposed depositional history of San Salvador Island (Carew and Mylroie 1985, 1987 1995a). Hearty and Kindler (1993) have also proposed a stratigraphic column for deposits found on San Salvador (Figure 3b ). Add i tional formations and members distinguish their column from that proposed by Carew and Mylroie (1985, 1995a) The Holocene Rice Bay Formation is divided from oldest to youngest into the North Point Member, the Hanna Bay Member and the East Bay Member (Hearty and Kindler 1993) The Almgreen Cay Formation is the uppermost Pleistocene unit and is separated into the 11

PAGE 25

Upper and Lower Members. The Grotto Beach Formation is divided from bottom to top i nto the French Bay Member, the Cockburn Town Member and the Fernandez Bay Member The Fortune Hill Formation and the underlying Owl's Hole Formation are Middle Pleistocene Each formation is separated by a paleosol. Hearty and Kindler (1993) have also proposed a morphostratigraphic model and an aminostratigraphic framework for San Salvador Island Their stratigraphic column is based on field relationships petrology, petrography, geomorphology, morphostratigraphy and calibration of amino acid racemization data with radiometric ages (Hearty and Kindler 1993) Radiometric ages for several locations on San Salvador have been published in the past two decades (Curran et al., 1989; Chen et al., 1991; Carew and Mylroie, 1987) These ages are summarized in Table 1 to provide additional information about the stratigraphic relationships of the units on San Salvador Island, Bahamas Bahamas Stratigraphy and Aminostratigraphy Aminostratigraphy is not considered as a formal method of stratigraphic subdivision of rock units by the North American Commission on Stratigraphic Nomenclature (1983), but amino acid racemization data have been used to suggest relative ages for carbonate dune deposits in other locations (Hearty et al. 1992; Belperio et al. 1995 ; Price, 1999) Hearty and Kindler (1994 1995 and 1997) and Carew and Mylroie (1985, 1987) and Mirecki et al. (1993) have used amino acid ratios in the Bahamas to correlate and estimate ages of carbonate deposition. 12

PAGE 26

Table I. Sununary of Estimated Radiometric Ages on San Sa l vador Island, Bahamas Unit Material Dated Uffh C14 Lab# Reference Sandy Hook bulk rock 1990 Andersen and Boardman (1989) (modern) Hanna Bay whol e rock 3470 80 Carew and Mylroie (198 7) Member North Point whole r ock 5345 125 Member Carew and Mylroie ( 1 987) whole r ock 5360 110 Carew and Mylroie (1987) bulk rock 5360 110 Colby and Boardman ( 1989) bulk rock 5435 125 Colby and Boardman ( 1 989) bulk rock 5670 1 60 Col by and Boardman ( 1989) bulk rock 6000 100 Colb y and Boardma n (1989) bulk rock 6190 150 Colby and Boardma n (1989) Cockburn Town D strigosa (rubble) 171 15 1619A Carew and Mylroie (1987) Member Diploria sp 126 1654C Carew and Mylroie (1987) Diploria sp 124 16748 Carew and Mylroie (1987) Monastrea annularis 120.0 1.4 I Curran et al ( 1989) M. annularis 120.5 1.4 2 Curra n et al (1989) Diploria strigosa 122.1 1.2 3 C urran e t a! ( 1989) D c/ivosa 1 21.8.3 4 Curran eta! ( 1989) M annularis 122.7 1.3 5 Curran et al ( 1 989) D c/ivosa 128. 7 1.2 6 Curran e t a! ( 1989) Acropor a cervicornis 124.2 2 7 C urra n e t a l (1989) D. strigosa 119.2 1.5 8 Curran et al (1989) A palma/a 121.2 1.4 9 Curran et al (1989) A .palmata 122. 5 1.5 10 C urran e t al ( 1989) A .palmata 130.75 1.5 II Curran et al (1989) A. palma/a 124.6 1.3 1 2 Curran e t a! ( 1 989) A.palmata 123. 7 1.6 13 Curran e t al (1989) A cervicornis 124.7 1.5 14 Curran et a l (1989) D. s trigosa 126.3 1.2 1 5 Curran e t al ( 1989) M a nnularis 127. 1 2 1 1 6 Curran et al (19 89) M. annularis 119. 9 1.4 I C h e n et a l (1991) M. annularis 122. 0 1.5 2 C h e n et al (1991) D. s trigosa 123.6 1.2 3 C h e n et al (1991) D clivosa 123.3 1.3 4 C h e n et a l (1991) M. annulari s 1 24.2 1.3 5 C h e n eta! (1991) M. mmularis 122. 3 1.0 6 C h e n et al (1991) D clivosa 130. 4 1.1 7 Chen e t al ( 1 99 1 ) A cervicornis 125. 3 0 8 C h e n e t al (1991) D clivosa 53.7 0.4 9A C h e n et al (1991) D clivosa 107.8 1.3 9B C h e n eta) (1991) D strigosa 1 2 0 7 1.5 10 C h e n e t al (1991) A .palmata 122. 7 1.4 II C hen e t a ) (1991) A .palmata 124.0 1.6 1 2 Chen e t al (1991) A.palmata 132. 6 1.3 13 Chen e t al ( 1 991) A.pa/mata 125.5 1.4 14 Chen et a l (199 1 ) A pa/mata 123. 8 1.7 1 5 Chen et al (1991) A palmata 125.3 1.7 1 6 C h e n e t al (1991) A .palmat a 126. 1 1.3 17 Chen et al (1991) A. cervicornis 126. 3 1.5 18 Chen et al (1991) D s trigosa 127. 9 1.2 19 Chen et al (1991) M annularis 127.3 1.0 20 Chen e ta! ( 1 99 1 ) M. annularis 128.5 1.0 2 1 C hen et al (1991) M. annularis 127.21.5 22 C h e n e t a l (1991) (continued) Note : All sum marized data (including ages, terms and genus/species) is represen ted as i s found in individual references. 13

PAGE 27

Table 1. (continued) Unit Material Dated Uffh C14 Lab# Reference Other locations on San Salvador Island, Bahamas Sue Point reef M annularis 122. 9 1.9 23 Chen et a1 (1991) M annularis 122. 1 1.4 24 Chen et a1 (1991) D strigosa 122. 4 1.6 25 Chen e t at (1991) M annularis 135 1619C Carew and Mylroie (1987) Quarry Point A.palmata 145 12 16198 Carew and Mylroie (1987) Pigeon Cr. M atuiUiaris 146 10 1654e Carew and Mylroie (1987) Quarry A Diploria sp. 140 1654i Carew and Mylroie (1987) Gulf Diploria sp. 115 1654b Carew and Mylroie (I 987) Holiday Tract (T Hanna) Diploria sp \03 1654f Carew and Mylroie (I 987) Storr's Lake M annularis 125 1654g Carew and Mylroie (1987) M annularis 123 1654h Carew and Mylroie (1987) Hall's Landing Diploria sp 120 1654d Carew and Mylroie ( 1987) Crab Cay M annularis 135 1674a Carew and Mylroie (1987) Snow Bay whole rock 3300 5 0 Car e w and Mylroie ( 1987) Slngerbar Point whole rock 3040 90 Carew and Mylroie (1987) Barker's Point whole rock 420 Carew and Mylroie (1987) Note : All s ummarized data (including ages, terms and genus/species) is represented as is found in individual re ference s. 14

PAGE 28

The reliability of amino acid racemization as a dating tool has been questioned in previous work done on San Salvador Carew et al. (1985) formally assigned the Dixon Hill strata as a member of the Grotto Beach Formation based on results of amino acid racemization analysis. The amino acid data, calibrated with radiometric age estimates, gave an age of85,000 years BP for the Dixon Hill Member (Carew and Mylroie, 1985). With increased knowledge of the regional geology, sea-level history, and cave development, Carew and Mylroie (1992) decided that an age of85,000 years BP was unlikely for the Dixon Hill strata. After further study of the physical stratigraphic relationships, they removed the Dixon Hill Member from their published stratigraphic column, because it did not constitute a distinct member (Carew et al., 1992; John Mylroie, personal communication, 2000). Hearty and Kindler published their stratigraphic column in 1993 and have used evidence from their morphostratigraphic model and amino acid racemization analysis to add additional formations to the stratigraphy of San Salvador Hearty and Kindler also used amino acid racemization data from several islands to aid in their stratigraphic interpretations (Hearty and Kindler, 1993, 1995 and 1997). In order to test Hearty and Kindler's stratigraphic model, Mirecki et al. (1993) did a blind study using amino acid racemization data from Cerion shells from San Salvador. They completed their study to evaluate the precision of amino acid racemization data and the ability of this technique to resolve the additional units proposed by Hearty and Kindler (1993) (Mirecki et al., 1993; Carew and Mylroie, 1994) 15

PAGE 29

Amino Acid Geochronology The Bahamian islands are composed of carbonate sediment of both organic and inorganic origin Marine organisms produce amino acids as part of the organic templates upon which they construct a carbonate shell. Encased within the crystalline structure, the amino acids undergo the biochemical process of racemization, which can be used as a geochronological tool (Miller and Brigham Grette, 1989). Amino acids are characterized by their L and Disomers (levorotatory and dextrorotatory) which rotate plane-polarized light in opposite directions Living organisms create L amino acids, which invert to D amino acids after death (Miller and Brigham-Grette, 1989). When amino acids have a single, central (or chiral) carbon atom about which stereomeric inversion takes place, then the Dand L-forms are simple mirror images of each other and are called enantiomers In a few amino acids, two central carbon atoms are present, and inversion occurs about the ex-carbon This results in two structurally distinct amino acids, or diasteromers (McCoy, 1987) The reaction ofL-to D-amino acids is reversible Both time and temperature influence the rate of the reaction When the reaction reaches equilibrium, the system is considered racemic (Mi tterer, 1993) The enantiomer system is fully racemized when the equilibrium ratio ofD: L amino acids of 1.0 is reached. In the case of diastereomers the process is termed epimerization, and the equil i brium ratio is 1 3 (Miller and Brigham-Grette 1989) Aminostratigraphy involves the use ofDIL ratios or Alloisoleucine/Isoleucine (All) ratios to aid in the understanding of both the temporal and spatial relationships recorded in the stratigraphic record Because the DIL or Ali ratios increase with time, they can be used as a relative dating tool. The rate of racemization is also strongly 16

PAGE 30

controlled by temperature and will increase with increased temperature and decrease if the shell is exposed to low temperatures When DIL ratios are used to correlate or differentiate sedimentary units, the method is termed aminostratigraphy Although increased time and temperature result in increased racemization and a higher DIL ratio, other factors can also complicate interpretation (Mitterer and Kriausakul, 1989). Taxonomy, for example, can affect the rate of racemization. Racemization is partly a function of the position of the amino acids bound within a protein chain or in the free (unbound) state (Bada 1985). Different organisms combine amino acids in different arrangements, resulting in varying racemization rates (Miller and Brigham-Grette, 1989) Therefore taxonomic identification and the use of mono generic samples is important. Leaching and contamination of amino acids must also be considered and addressed during preparation of samples and interpretation of results (Mitterer, 1993) Amino acid racemization (AAR) can be an employed as a tool to determine the relative and, with independent calibration, numeric geologic ages of a region (Mitterer and Kriausakul, 1989). However, care must be taken to acknowledge and identify the inherent complexities associated with AAR. A difference in temperature is not considered to be a factor in this investigation because San Salvador is relatively small and samples from across the island have experienced similar post-depositional temperature histories This study uses 11Whole rock" carbonate samples which consist ofbioclasts, ooids and pellets Because several different organisms may be represented in these whole rock samples, taxonomic variation is a complexity that must be accounted for in assessing results of whole rock sample amino acid analysis When whole rock samples from 17

PAGE 31

different stratigraphic units have the same taxonomic constituent particle composition, the differences in racemization will be a function of age differences However, when the compositions are not the same, the differences in racemization may reflect both taxonomic and time variables The variability of mean values of several amino acid DIL values and rates of racemization of whole rock samples and their stratigraphic relationships will be addressed specifically within this study of San Salvador Island, Bahamas. 18

PAGE 32

METHODS Field Sampling Field sites were chosen on the basis of literature reviews of San Salvador Island and through personal communication with researchers familiar with the area. Samples were collected from eolianite complexes around the island. The North Point and Hanna Bay Members of the Rice Bay Formation are two stratigraphic units whose ages are uncontested These two units where chosen for the purpose of carrying out detailed sampling, both vertically and horizontally, across the eolianite complexes. Detailed sampling of these preserved dunes is used in evaluating variations in DIL ratios within a single stratigraphic unit or between two units that are close in age. The eolianite complex at North Point (NP ; Figures 2 and 4) is approximately 1/2 mile long where it separates Graham's Harbor to the west from Rice Bay to the east. The fossil dune complex at Hanna Bay (HB; Figures 2 and 5) faces the open Atlantic Ocean to the east. A total of 115 subsamples was analyzed from the west-facing side of the fossil dune complex at North Point. A total of 52 subsamples was analyzed from Hanna Bay. Five field samples were taken from a single layer within dune #8 at North Point and three samples were taken in the same manner from dune #3 at Hanna Bay. Each field sample was split into three subsamples to further evaluate intra-sample variability. At the same time, additional samples were taken from the top portion of each dune and the lower portion of each dune to compare with the individual layer and also to determine if surface temperature had an affect on the amino acid ratios Sampling at North Point and Hanna Bay provides an opportunity to evaluate the importance of time and taxonomy in 19

PAGE 33

whole rock amino acid racemization At both type localities for North Po int and Hanna Bay Members, dunes were numbered according to their apices and separated where two adjacent dune faces overlapped (Figures 2, 4 and 5) Samples were taken on the exposed dunes and positions measured with respect to distance below present day surface (Appendix A) The samples taken closest to the apex of each dune were done so at a distance from the surface of at least 1 meter to reduce the effect of increased effective diagenetic temperature (Wehmiller, 1977) near the surface. A minimum of three samples (labeled A, B and C) was taken vertically from each dune w ith sample A consistently located at the top. Although the uppermost samples in each dune were taken at a distance below surface, this method of field sampling may determine ifD/L ratios reflect any variation due to increased temperature near the surface In a geologic time reference these dunes were deposited rapidly and any significant temperature effect upon AAR would if at all, affect only the 20

PAGE 34

outcrop at Bay were following the same scheme as at North Point. Dunes are not separated on photo due to oblique angle of photo uppermost material. Within two dunes at North Point and Hanna Bay more detailed sets of samples were collected to aid in the understanding of intra-dune and intra-unit AAR variability. Outcrops of the eolianites bordering Rice Bay are located between the exposures of North Point and Hanna Bay (Figure 2). Samples were taken from the outcrops bordering the southern shoreline of Rice Bay North Point Rice Bay (NPRB) A total of 23 subsamples was analyzed from this location Another uncontested site that was sampled was the type locality of the Cockburn Town Member (CBT) of the Grotto Beach Formation (Figure 6) The Cockburn Town fossilized reef and associated facies are located on the west side of San Salvador Island directly west of Cockburn Town (Figure 2) The eolianite sediments occur within a regressive sequence west of Cockburn Town (Figure 2) (Curran and White, 1985) These sites were located in the field using the map of Curran and White (1985) Twenty-two 21

PAGE 35

subsamples were collected and analyzed that were believed to be eolianite facies, although there is the possibility that some beach facies material was also included (corals and shell samples are not included in this data set) (Appendix A) .._,vJ"-u,; north on west coast at Cockburn Town Reef and associated facies Arrow indicates back s ide of eolianite location sampled in this study. Samples were also collected at Watling's Quarry (WQ) Watling's Quarry i s located in the southeastern portion of the island (Figures 2 and 7). Two paleosols were noted, one at the surface ofthe outcrop and one approximately 1/3 of the way up from the base of the exposure. This eastward facing outcrop was sampled between the upper and lower paleosol (Upper Watling's Quarry; UWQ) and also below the lower paleosol (Lower Watling's Quarry; LWQ) A total of 15 subsamples was analyzed from Upper Watling's Quarry, and a total of 15 subsamples was analyzed from Lower Watling's Quarry Samples 1 and 3a,b,c,d were taken below the lowest paleosol and samples 4 through 8 were taken between the paleosols The samples taken at Sandy Hook (SH) (Figure 2) on the southeastern corner of the island were collected to get a "modern" sample, as the dunes there are in the process of being formed These samples were taken as a test case to compare ratios from this 22

PAGE 36

site to other sample locations and to see if sediment recycling along the coast is reflected in amino acid racemization values The samples taken at Sandy Hook Road (SHR) (Figure 2) were of unknown age and stratigraphic position to this author, and the samples offer an opportunity to test the ability to stratigraphically correlate using amino acid racemization data. Sandy Hook Road samples came from a roadcut on the northern side of the road leading to Sandy Hook (above) (Figure 2) outcrop at lower paleosol is indicated by the arrow and field sample locations are numbered. Photographs were taken of each sample site and at all sites in this study Distance (meters) from the surface was measured for most samples (Appendix A) Samples were collected placed in labeled sample bags for further analysis at the Amino Acid Geochronology Lab at the University of South Florida, Tampa 23

PAGE 37

Laboratory Procedures General Laboratory procedures for preparation, hydrolysis and analysis using reverse phase high performance liquid chromatography (RP-HPLC) closely followed those detailed by Kaufinan and Manley (1998). All field samples were given a University of South Florida Amino Acid Geochronology Lab (FAL) number Field samples were divided into subsamples generally three subsamples per field sample to check for intra-sample reproducibility Each subsample was considered independent of each other during analys i s because one chunk of whole rock is heterogeneous Better representation of the full range of values at each unit was accomplished by treating each subsample individually Because the field samples were split i nto subsamples, the remainder of the text will address the subsamples unless reference to the location of field samples is apparent. For example field sample 98-NP-3A refers to sample "A" (uppermost) taken from North Point dune# 3 This sample was divided into three subsamples Several pretreatment preparation procedures were tested to determine the optimal cleaning procedure and hydrolysis time needed for well-defined peak height and areas on chromatograms. The pretreatment preparation procedure began with repeated sonication in ultrapure water When samples were clean, they were dried, weighed and hydrolyzed under N2 for 6 hours in a llOo C oven. Samples were then dried in a vacuum desiccator, rehydrated, and placed in HPLC vials to be analyzed 24

PAGE 38

Sample Analysis Whole rock samples were analyzed using a Hewlett Packard 1100 reverse-phase liquid chromatograph following the methods ofKaufinan and Manley (1998) The main advantage for using reverse-phase chromatography (RPC) is the ability to separate at least nine pairs of amino acids into their D-and L-isomers (Kaufinan and Manley, 1998) combined with relative ease of sample preparation compared with gas chromatography For ease of explanation of amino acid ratios throughout the following text, the term DIL will be used to refer to both enantiomeric (DIL) and diastereomeric (e g., Ali) ratios Daily calibration of the University of South Florida Amino Acid Geochronology Lab instrument with a laboratory sample standard (ILC) (Wehmiller, 1984) was conducted to monitor internal reproducibility. For further description oflaboratory and analytical methods, see Appendix B and C. 25

PAGE 39

AMINO ACID RACEMIZATION DATA A total of262 subsamples was analyzed from San Salvador Island using RP-HPLC Previous amino acid racemization stud i es on San Salvador Island used only Alloisoleucine!Isoleucine (All) values that represented a limited number of samples Reverse-phase chromatography allowed for the comparison of several amino acid pairs, and DIL ratios were calculated using peak height values (Appendix D) Seven amino acids for which DIL ratios were calculated are shown graphically in Figure 8 and are listed in Appendix E The amino acids Phenylalanine, Alanine and Serine were not chosen for further study because the chromatogram peaks for either the D or L isomers were not consistently resolved for all analyzer runs DIL Aspartic Acid, D/L Glutamic Acid, and DIL Valine values were chosen for study because they consistently had well defined peak resolution Alloisoleucine!Isoleucine values were chosen for the same reasons, and also because this has been the only amino acid pair previously used for amino acid racemization studies on San Salvador Island Mean DIL values, and (sample) standard deviations were calculated for individual sample locations (e g North Point, Hanna Bay, etc.) and for individual sample numbers (e g., North Point 3A). Concentrations ofD and L enantiomers of Aspartic Acid for all subsamples and sample locations were plotted to determine if there were any laboratory preparation errors or if excessive leaching had affected any samples (Figure 9) No data were rejected in this study on the basis of anomalous concentrations. For some subsamples, the chromatographic resolution was consistently poor and those points were not included in data analysis (Appendix D) 26

PAGE 40

N ......:) 1 0 0.9 f/) 0 8 0 .. cu 0 7 0:: 0.6 0.5 '-0 ..J 0.4 l c 0.3 0.2 0 1 0.0 0 Seven Amino Acid Pairs --+-NI -Aspartic Acid -.Alanine A cid ---*-Phenylalanine -.-Serine .... .:>j.._--Valine 1 2 3 4 5 6 Samp l e Locat i ons 7 8 9 Figure 8 Mean D/L values of seven amino acids measured in whole rock subsamples collected from several localities on San Salvador Is l and, Bahamas Locations are shown on Fig 2, 1 =Sandy Hook beach (SH) 2 =Hanna Bay (HB) 3 =North Point (NP), 4 = North Point Rice Bay (NPRB) 5 = Cockburn Town (CBT) 6 =Uppe r Watling's Quarry (UWQ) 7 =Lower Watling's Quarry (L WQ) and 8 =Sandy Hook Road (SHR) All localities have been described previo usly (e.g., Carew and Mylroie 1995 ; Hearty and Kindler, 1993 ) except Sand y Hook (modem beach sediment) and Sandy Hook Road

PAGE 41

2 5 2 -o u < 1 5 u ;:: "' Q. :l ..J a 0 .5 0 0 8 -o 0. 6 u < .2 E 0.4 6 ..J a 0 2 0 Relative Co n centrat ions o f 0 and L isomers vs. Sample Locations 0 .4 I E x planatio n T c u 0 3 I L -isomer :;, 1 .!! D -Is o mer 0 ... .. II II c 0 2 u :;, I 0 .. I I :g 0.1 I I = I I I < I I ;t; I I = I ::a;: 0 V:- T 0.2 ...,.-T _t .1. -'-I -,--0 1 I I I I _1_ I T = :X: I :;a;: 0 # a V:-
PAGE 42

The mean values of relative concentrations ofD and L isomers were plotted (Figure 9) for each amino acid pair at each sample location The relative concentration is consistent when comparing the D isomers to the L isomers for each location The data suggest that relative concentrations decrease with increase age of the sample material. To assess the distribution of data, histograms of all samples from North Point for all four amino acid pairs were plotted (Figures 1 Oa,b,c,d). The D/L Aspartic data from North Point are distributed symmetrically about the mean value and appear to be normally distributed, although appropriate statistical tests were not applied to confirm normality. Other D/L data show less uniform distribution of data about the mean. Histograms were also plotted for the data from Hanna Bay (Figures lla, b, c,d) and perform similar to the samples from North Point. Hanna Bay D/L Aspartic Acid is the one set of samples which is not as uniformly distributed as shown with the lack of data within the 0.26 and 0 27 bin, but it may still be considered a normal distribution with further statistical tests. In the following sections, AAR data from individual units are presented, and each sample location is discussed and then compared to other appropriate sample locations The large number of subsamples analyzed in this study aid in the understanding of the amount of variability found within units and between units of different ages North Point and Hanna Bay make up the largest sets of samples and are addressed together and in more detail than other locations, because these field sites allowed for more comprehensive sampling and their ages are not contested Table 2 summarizes results of amino acid analyses for all subsamples at all localities studied in this investigation. 29

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w 0 R F I 0 C R EM A B T A I Yo N F 0 G B R REM 0AA T C T T H I 0 0 N OWL'S HOLE FORMATION I DIL Aspartic Acid I I Alloisoleucinellsoleucine I I DIL Glutamic Acid I J DIL Valine J Mean sd # %CV Mean :1: sd # % C V Mean :1: s d # %CV Mean :1: sd # %CV Sampled Units SANDY HOOK (modem beach) 0 .204 m2 (7) 6 0 043:1: 010 (7) 23 0.142 ;I; 038 (7) 27 0 046:1: 006 (7) 13 HANNA BAY o .262 m6 (52) 6 0 070:1: 008 (SO) II 0 .168:1:. 023 (52) 14 0 073 :1: 007 (52) I 0 NORTH POINT 0 247 ;I; 015 (liS) 6 0 .065:1: 0 I 0 (110) IS 0 .161 022 (liS) 14 0 073:1: 006 (113 ) 8 NORTH POINT RICE BAY 0.260 ;I; .010 (23) 4 0 .059:1:. 010 (22) 17 0 144:1:021 (23) IS 0 070:1: 010 (2 3 ) 14 COCKBURN TOWN 0 480 ;I; 027 (22) 6 0 .276:1:. 02 0 (22) 7 0 287:1: 046 (22) I 7 0 261 :1:. 016 (22) 8 UPPER WA TLINGS 0 433:1: 016 ( IS) 7 0 .303:1:. 047 (IS) 17 0 .288:1:. 046 (IS ) 17 0 277:1:.039 (IS) 14 QUARRY LOWER WATLINGS QUARRY 0 .658:1:. 040 (IS) 6 0 .449:1:. 069 (15) 16 0.439 :1: 059 (15) 14 0.429:1: 078 (IS) 19 SANDY HOOK ROAD 0 .476 012 (6) 2 0 .371 :1:.011 (6) 3 0 409:1: 016 (6) 5 0 331 :1:. 013 (6) 3 Table 2 Results of amino acid analysis of samples from uncontested stratigraphic units on San Salvador Island, Bahamas (mean sd) = mean value one standard deviation; (#) = number of subsamples analyzed; (%CY) = coefficient of variation unknown aged unit analyzed to test aminostratigraphic column

PAGE 44

..... Q) ..c E ::I z (a) 1/) Q) 0.. E ns 1/) ..c ::I 1/) ._ 0 ..... Q) ..c E ::I z (b) 40 30 20 10 40 30 20 10 NORTH POINT D/L Aspartic Acid Alloisoleucine/lsoleucine Figure 10. Histograms of data from North Point for four amino acid pair s. a) D / L Aspartic Acid, b) Alloisoleucinellsoleucine c) DIL Glutamic Acid, and d) DIL Valine Star indicates the mean value for each data set. (continued) 31

PAGE 45

Ill Q) 30 a. 20 E ro Ill ..0 :J Ill .... Q) ..0 E 10 :J z (c) Ill Q) a. E ro Ill ..0 :J Ill .._ 0 .... Q) ..0 E :J z (d) 0 -t-80 60 40 2 0 Figure 10 continued NORTH POINT 0/L Glutamic Acid 0/L Valine 32

PAGE 46

Ill C1l a. E 20 16 l}l 12 .0 ;:, Ill til 8 .0 E ;:, z 4 0 (a) 25 20 Ill C1l a. E <11 15 Ill .0 ;:, Ill ..... 0 '-10 C1l .0 E ::J z 5 (b) 0 HANNA BAY D/L Aspartic Acid Alloisoleuc i nellsoleuc ine Figure 11. Histograms of data from Hanna Bay for four amino acid pairs. a) DIL Aspartic Acid, b) Alloisoleucine/Isoleucine, c) DIL Glutamic Acid, and d) DIL Valine Star indicates the mean value for each data set. (continued) 33

PAGE 47

Ill Q) a. E ('CI Ill ..c :J Ill 0 .... E :J z (c) Ill Q) a. E ('CI Ill ..c :J Ill -0 .... Q) ..c E :J z (d) 16 12 8 4 0 ---+--30 20 10 Figure 11. (continued) HANNA BAY 0/L Glutamic Acid 0/L Valine 34

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North Point and Hanna Bay The North Point and Hanna Bay subsamples are examined to evaluate amino acid racemization variability within and between lithostratigraphic units Three levels (degrees) of variability in North Point and Hanna Bay are examined and include : 1) variability within a single fossil dune at each location, 2) the amount of variability measured among the ten dunes at North Po i nt and, separately, the five dunes at Hanna Bay, and 3) the comparison of North Point with Hanna Bay and with other sample locations Intra-dune Variability in Amino Acid Racemization Measurements The eighth dune of the North Point complex and the third dune at Hanna Bay were chosen in the field to test small-scale intra-unit variability of amino acid racemization values Figur e 12 shows the locations where each field sample was taken on the outcrop, while Figure 13 graphically illustrates the D/L values for all subsamples from North Point dune #8 and data are summari z ed in Table 3 Figu r e 12 + N E D 5 meters Five samples were taken from a single continuous l a yer within dune #8 at North Point indicated b y the line through samples F G-B-H 1 above Each field sample was divid e d into three subsamples for analysis Samples were also collected and analyzed from the upper and lower portions of the dune (samples A and D-E, respectively) to compare vertical and lateral variability in amino acid racemization within a s ingle g e omorphic feature 35

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0.4 0.3 "0 c::; < loo 0.2 Q. "' < Q 0.1 0 0.4 0.3 "0 c::; < s 0.2 :I G g 0.1 0 North Point Dune # 8 - + T --+ + -T A B C D E F G H I (3) (2) (3) (2) (2) (2) (3) (3) (3) .J_ + ....... + -+- I A B C D E F G H I (3) (2) (3) (2) (2) (2) (3) (3) (3) c c::; :I 0 "' Gl c c::; :I 0 "' : < .5 -; 0.4 0 3 0.2 0.1 0 0.4 0.3 > 0.2 g 0.1 0 -r-+ ++++++A B C D E F G H I (3) (2) (3) (2) (2) (2) (2) (2) (2) ++++++ .......... + A B C D E F G H I (3) (2) (3) (2) (2) (2) (3) (2) (2) Figure 13. Plots of four DIL amino acid values mea sured in subsamples collected from dune# 8 at North Point (see Figure 12 for position of each samp le) Horizontal line s indicate the mean value of sam ples at the sample location. Numbers in parentheses are the numb ers of subsamples analyzed for each field location. Mean values, stan dard deviation and number of samples analyzed are in Table 5 36

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Vol -.....) Table 3. Results of amino acid analysis of subsamples from North Point dune# 8 Field # ID FAL# #sub AspAsp-SO %CV AllA/I-SD samples Mean Mean 98-NP-8A A 0153 3 0 243 0 015 6 0 070 0 009 98-NP-8B B 0138 2 0 226 0.002 1 0 067 0.012 98-NP 8C c 0168 3 0 249 0 007 3 0.066 0.005 98-NP-8D D 0182 2 0 241 0.017 7 0 053 0.002 98-NP-8E E 0183 2 0 234 0.004 2 0.059 0.001 98-NP-8F F 0184 2 0.227 0 021 9 0.059 0.004 98-NP-80 G 0185 3 0 237 0 011 4 0 048 0.005 98-NP -8H H 0186 3 0 257 0 015 6 0 050 0 007 98-NP-81 I 0187 3 0.267 0 011 4 0 055 0 004 (ID) = Identification letter given to sample set; (F AL #) = University of South Florida Amino Acid Geochronology Lab; (SD) = one standard deviation; (%CV) = coefficient of variation 0/oCV GluGlu-SD %CV ValVal-SD %CV Mean Mean 13 0.177 0 017 9 0 077 0 004 6 18 0.160 0 005 3 0 079 0.008 10 7 0.162 0 027 17 0 072 0 002 3 3 0.133 0.028 21 0.061 0 005 7 2 0 155 0.002 1 0.066 0.002 3 6 0.141 0.005 3 0 077 0 004 5 10 0 142 0.025 18 0 067 0 001 1 14 0 134 0.028 21 0 070 0 001 2 8 0.127 0 033 26 0 074 0.006 8

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--+ N A D ....._____, -..... __ B c E 5 meters Figure 14 Three samples were taken from a single continuous layer within dune #3 at Hanna Bay. Each field sample was di v ided into three subsamples for analysis Samples were collected and analyzed from the upper and lower portions of the dune to compare vertical variability in amino acid racemization within a single geomorphic feature Figures 14 and 15 display the same information for dune #3 at Hanna Bay. Data are summarized in Tables 3 and 4 for North Point and Hanna Bay, respectively. Both sets of intra-dune data (NP and HB) for each of the four amino acids show overlap in DIL results between field samples and do not suggest a trend in deposition. On this smaller scale and for North Point dune #8 and for Hanna Bay dune #3 DIL Aspartic Acid %CV values (%CV = coefficient of variation = standard deviation/mean x 1 00) are overall the lowest, followed by DIL Valine, All, with DIL Glutamic Acid showing the highest variability. The coefficient of variation is used to aid in comparison between amino acid pair values because it is a relative measure of dispersion and expresses the sample standard deviation in terms of the sample mean. Intra-unit Variability in Amino Acid Racemization Measurements Figures 16 and 17 depict individual dunes and their respective DIL mean values, standard deviation and number of subsamples analyzed for North Point and Hanna Bay, 38

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'C u < u = c. "' < 'C u < e :! = (3 Q Ha nn a Bay D une # 3 0 4 0.4 0 3 = 0.3 u -r- ..... = ...... 0 "' 0 2 c 0.2 u = 0 "' : 0.1 < 0 1 ..... _,_ ..L ..... 0 0 A B c D E A B c D E (3) (3) (3) (2) (2) (2) (3) ( 3) ( 2) ( 2 ) 0.4 0 4 0 3 0 3 5 0.2 > 0 2 T ....L T Q 0.1 0 1 + + ....-..... ... 0 0 A B c D E A B c D E (3) (3) (3) (2) (2) ( 3 ) ( 3 ) (3) (2 ) (2) Figure 15. Plots of four OIL amino acid values measured in subsamples c olle c ted from dune # 3 Hanna Bay (see Figure 14 for position of each sample) Horizontal lines indicate the mean value of samples at the sample l ocation Numbers in parentheses are the numbers of subsarnples analyzed for each fie l d location Mean values standard deviation and number of samples analyzed are in Table 6 39

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0 Table 4. Results of amino acid analysis of subsamples from Hanna Bay dune # 3. Field # ID FAL # #sub AspAsp-SD %CV A/1-A/I-SD samples Mean Mean 98-HB-3A A 0158 3 0.275 0 019 7 0 .069 0 001 98-HB-3B B 0143 3 0 258 0.010 4 0 073 0.009 98-HB 3C c 0173 3 0.275 0 009 3 0.073 0 008 98-HB-30 D 0188 2 0.255 0 .034 13 0.061 0.012 98 HB-3E E 0189 2 0.247 0 012 5 0.069 0.001 (ID) = Identification letter given to sample set; (F AL #) = University of South Florida Amino Acid Geochronology Lab; (SD) = one standard deviation; (%CV) = coefficient of variation %CV Glu Glu-SD %CV ValVal-SD %CV Mean Mean 2 0 161 0 .010 6 0.073 0.008 11 12 0 183 0 .020 11 0 077 0.006 8 12 0 173 0 035 21 0.074 0.004 6 20 0 .131 0 040 31 0.061 0 002 3 2 0 173 0 018 10 0.070 0 013 18

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.;:.. ....... N 0 163 0 024
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__. N #5 #5 #5 #5 HANNA BAY #4 #3 #2 0 258 0 013 (9) 0 263 0 012 (8) 0.264 0 018 (13) 0/L Aspartic Acid #4 #2 0 066 0 009 (9) 0 073 0 008 (7) 0.070 0 008 (12) Alloisoleucine/lsoleucine #4 #2 0 166 0 024 (9) 0 173 0 017 (8) #4 0 166 0.02 7 (13) 0/L Glutamic Acid #2 0 074 0 004 (8) 0 072 0.008 (13) 0/L Valine #1 Fi g ure 17 Diagram showing individual dunes within the fossil dune complex at Hanna Bay. Mean and standard deviations of OIL values for four amino acids are shown; the number in parentheses indicates the number of subsamples prepared and analyzed for each dune 42

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respectively At first glance of the North Point dunes (Figure 16}, there appears to be somewhat of a decreasing trend from dune #1 (south) to dune# 10 (north}, especially for D/L Aspartic Acid and D/L Valine Looking only at the means of the five Halllla Bay dunes (Figure 17), there appears to be a decreasing trend from dune #1 (north) to dune #5 (south) However, the amount of variability within each dune appears to be greater than the variability due to the apparent trend. The mean D/L values for the ten North Point dunes and the five Halllla Bay dunes were plotted for each amino acid pair to show the variation across the dune complex (Figures 18 and 19). Tables 5 and 6 show the mean D/L values standard deviations and coefficient of variation for individual dunes of North Point and Halllla Bay. Initially, when looking at the graphs from North Point and Halllla Bay, one may notice the "straight lines" of data plotting for each of the four amino acids Although this low variability as a unit will help when comparing one dune complex to another, it is not the question addressed for these particular graphs. The question is whether or not one dune can be resolved from another dune using this method. The scatter for the data points for each dune overlap for each of the four amino acid pairs In addition, D/L Aspartic Acid and D/L Valine display the least variation within the North Point dune complex while D/L Glutamic shows intermediate variability, and Ali gives the highest variability DIL Aspartic Acid and DIL Valine are also the least variable amino acid pairs for the dunes at Halllla Bay, while NI and D/L Glutamic show decreasing variability, respectively. Amino acid pairs showing the least variability and the least amount of scatter of the data, may be more sensitive to deciphering depositional histories. 43

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0.4 :2 0 3 (,) < (,) :e 0.2 nJ c. Ill < ..J -c 0 1 0 0.4 "C 0 3 u < .!::! E 0 .2 nJ :::::1 (5 ..J 0.1 c 0 North Point Dunes 0.4 Q) c u :::::1 0.3 Q) III T I 0 I I I I Il .!!! Q) c 0 2 '(> :::::1 Q) 0 Ill 0 1 : I I I II:t::IIII :;;: 0 10 9 8 7 6 5 4 3 2 1 10 9 8 7 6 5 4 3 2 1 0.4 0 3 Q) .= c; 0.2 II III > -,I I I I _t ..J -c 0 1 I:t.::.:Ixxix=-==-= 0 10 9 8 7 6 5 4 3 2 1 1098765432 Figure 18. The mean DIL values of four amino acids are plotted for ten North Point fossil dunes to examine the variation across the dune complex Error 1 bars show one standard deviation X-axis shows numbered dunes from North Point, as shown in Figure 4. 44

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VI Table 5 Results of amino acid analysis of subsamples from ten dunes at North Point. Field # ID FAL # #sub AspAsp-SD %CV All-A/I-SD %CV samples Mean Mean 98-NP 10 10 0155 9 0.234 0.012 5 0.059 0 009 98-NP-9 98-NP-8 98-NP-7 98-NP-6 98-NP-5 98-NP-4 98-NP-3 98-NP-2 98-NP-1 9 0154 8 0.252 O.o15 6 0 073 0 .006 8 0153 23 0 244 0.016 7 0.059 0 009 7 0152 9 0 244 0.009 4 0 066 0.012 6 0151 9 0.244 0 009 4 0.064 0 007 5 0150 9 0 247 0.011 4 0.067 0 007 4 0149 9 0 250 0.009 4 0 072 0.012 3 0148 21 0 248 O.o15 6 0 062 0 006 2 0147 9 0 258 0.023 9 0 070 0 007 1 0146 9 0.254 0 012 5 0 063 0.012 (ID) = Identification letter given to sample set ; (F AL #) = University of South Florida Amino Acid Geochronology Lab; (SD) = one standard deviation ; (%CV) = coefficient of variation 15 8 15 17 11 10 16 10 10 19 GluGlu-sD %CV ValVal-SD %CV Mean Mean 0.163 0.023 14 0 069 0 008 12 0.171 0 024 14 0 079 0.007 8 0 148 0 025 17 0 071 0 006 9 0.167 0.022 13 0 073 0.008 10 0.172 0 019 11 0 073 0 005 7 0 167 0 .016 10 0 .074 0.005 6 0.166 0.018 11 0 .074 0.008 11 0 153 0 .024 16 0 071 0 004 6 0.171 0 014 8 0 074 0 004 5 0 169 0.014 8 0.078 0 003 4

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Hanna Bay Dunes 0.4 0.4 Cl) c "CJ 0 3 u c::; :I 0.3 ca: -,-I I I I ..t 0 u Cl) :e ::::: 0 2 Cl) ns c 0 2 c. c::; Cl) ca: :I Cl) ..J 0 0 1 c Cl) 0 1 : I I I I ;;: 0 0 5 4 3 2 1 5 4 3 2 0.4 0.4 "CJ 0 3 0.3 c::; ca: Cl) (.) c E 0.2 ns 0 2 ns I I > -I I I :I ..J C) c ..J 0 1 0 1 c I :a: I :8: 0 0 5 4 3 2 1 5 4 3 2 Figure 19. The mean D/L values of four amino acids are plotted for five Hanna Bay fossil dunes to examine the variation across the dune complex. Error bars show one standard deviation. X axis s hows numbered dunes from Hanna Bay Figure 5 46 I 1 I 1

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-.) Tabl e 6 Results of amino acid analysis of sub samples from five dunes at Hanna Bay. Field # 98-HB-5A 98-HB-4A 98-HB -3A 98-HB -2A 98-HB-1A ID FAL # #sub Asp-Asp-SD %CV All-A/I-SD samples Mean Mean 5 0160 13 0.254 0.012 5 0 070 0 006 4 0159 9 0 258 0 013 5 0 066 0 009 3 0158 13 0.264 O.oi8 7 0 070 0 008 2 0157 8 0 263 0 012 0 0 073 0 008 1 0156 9 0 276 0.018 7 0 075 0 007 (ID) =Identification letter given to sample set ; (F AL #) = University of South Flori d a Amino Acid Geochrono logy Lab; (SD) =one standard d eviation; (%CV) =coefficient of variation %CV G luGlu-SD %CV Val-Val-SD %CV Mean Mean 8 0.163 0 022 13 0 070 0 007 10 13 0.166 0 024 14 0 070 0.003 5 11 0.166 0 027 17 0.072 0 008 1 1 10 0 173 0 017 10 0 074 0 004 5 10 0.176 0 024 13 0 .079 0 006 8

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Distance below surface Care was taken at each outcrop to take samples from a distance of greater than one meter below the surface to avoid the surface heating effect on amino acid racemization. It was unknown, at these locations, if one meter was enough to avoid this effect. DIL values measured in samples A, B, and C from each dune at North Point and Hanna Bay were plotted for the four amino acid pairs to compare the data from different distances below surface (Figures 20 and 21) For each location on the dune (A, B or C) data from three subsamples were averaged and compared with the same location on the other dunes. Inter-unit Variability in Amino Acid Racemization Measurements The complete data sets for North Point and Hanna Bay (Table 2) include comparisons of the mean values for each unit, standard deviation, and %CV to each other and to other lithostratigrahic units. For North Point, the mean D/L Aspartic Acid values show 6% CV, which is the lowest, and the All CV value of 15% is the highest for all four pairs of amino acids (Table 2). Also from Table 2, the mean DIL Aspartic Acid values for Hanna Bay show the lowest variability (6%), while D/L Glutamic Acid shows the highest variability (14%). Figure 22 shows both North Point and Hanna Bay data together The graph shows an overlap of the two locations where the mean DIL Aspartic Acid value of all samples from North Point is 0.247 0 015 (n = 115) and Hanna Bay samples have a mean value of0.262 0 016 (n =52). D/L Valine, D/L Glutamic and A/I also show overlap between the two units (Table 2) Figure 22 also suggests an inversion 48

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0 4 "C 0 3 c:; ct u :e 0 .2 ca c. Cl) ct ....1 c 0 1 0 0.4 :2 0 3 u ct 2 E .!! 0 2 :l C) ....1 a 0 1 0 Figu r e 20. No rt h Point Du n es To Com p are D i stance below Surface : A 8 a n d C 0.4 A Q) 8 5 0 .3 u ... c :l Q) 0 Cl) :::: Q) c 0 2 u :l Q) 0 Cl) : 0 1 0 1 0 9 8 7 6 5 4 3 2 1 1 0 9 8 7 6 5 4 3 2 1 0.4 0 3 Q) 5 0 2 ....1 a 0 1 0 10 9 8 7 6 5 4 3 2 1 10 9 8 7 6 5 4 3 2 1 Three samples were taken vertically on each dune at North Point to determine if higher effective diagenetic temperatures near the surface had impacted the uppermost samples. In the fie l d, sample A was taken at about one meter depth; sample B was taken from the middle of the dune face and samp l e C was taken from near the bottom of the exposure. Numbers II 0 correspond to the ten fossi l dunes from North Point. Lines connecting the samples are only present to show trends along the exposure 49

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H a nna Bay Dunes To Co m pare Distance below S u rface : A B and C 0.4 0.4 A Q) B 0.3 c 'tS '(j 0 3 c '(j :;, ... Q) < 0 (,) E Q) Ill 0 2 c 0 2 Q, '(j en < ..J -c :;, Q) 0 en 0 1 : 0 1 C( I 1 0 0 5 4 3 2 1 5 4 3 2 1 0.4 0.4 Figure 2 1 Three samples were taken vertically on each dune at Hanna Bay to determine if higher effective diagenetic temperatures near the surface had impacted the uppermost samples. In the fie ld, samp l e A was taken at about one meter depth ; samp l e B wa s taken from the midd l e of the dune face and sample C was taken from near the bottom of the exposure Numbers 1-5 correspond to the five fossil dunes from Hanna Bay Lines connecting the samples are only present to show trends along the expo s ure. 50

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North Po i n t a n d Ha n na Bay 0 .4 0.4 G) 5 "0 0 3 CJ u ::s 0 3 G) < I I 0 CJ Ill :e ::::: 0 2 G) ., c 0 2 c. u Ill < ::s G) ..J 0 0 1 Q Ill 0 1 : I I < 0 0 NP HB N P HB 0.4 0.4 "0 0 3 0.3 u < G) ,g 5 E 0 .2 Ci 0 .2 ., I > -I ::s ..J 8 -Q _, 0.1 0 1 Q :J.: I 0 0 N P H B NP HB Figure 22 The mean O IL values of four amino acids for the total n umber of subsamples from North Poin t and Hanna Bay fossil dune co m plexes Error bars at one standard deviation. 51

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of the mean ratios compared to the radiometric ages 5345 125 and 3470 80 yr B.P for North Point and Hanna Bay, respectively (Table 1) Other Sample Locations North Point Rice Bay Samples taken from this location come from the same unit as North Point. The individual measurements and their mean are shown in Figure 23 for four amino acid DIL values. The mean DIL values and standard deviation for samples from North Point Rice Bay are in Table 2. As observed at North Point and Hanna Bay, individual dune units cannot be distinguished from each other on the basis of D/L values. Cockburn Town Mean DIL values with their associated standard deviation for this location are shown in Table 2 and individual DIL results and their mean are plotted in Figure 24. Comparing data at each Cockburn Town sampling site, the samples at Cockburn Town graphically show a larger variation between samples than other locations (e.g., between Hanna Bay and North Point) However, the coefficient of variation about the mean of all CBT samples is low for all amino acid pairs except D/L Glutamic Acid (Table 2 and Figure 24) In this case the outcrop was not split into separate dunes because the eolianite outcrop was patchy Therefore, intra-unit variability is not as apparently meaningful as with the previous locations mentioned 52

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'0 u c( u "' a. II) c( Q '0 u c( u e s ::s c; ...I a North Point Rice Bay 0.4 0 4 G) c 0 3 u 0 3 :I G) t t 0 til 0 2 'i c 0 2 u :I G) 0 0 1 til 0 1 : t < 0 0 NPRB1 NPRB2 NPRB3 NPRB1 NPRB2 NPRB3 (8) (6) (9) (8) (6) (8) 0.4 0 .4 0 3 0 3 G) .: 0 2 iii > 0 2 t 1 ...I a 0.1 0 1 t 0 0 NPRB1 NPRB2 NPRB3 NPRB1 NPRB2 NPRB3 (8) (6) (9) (8) (6) (9) Figure 23. D/L values offour amino acids are plotted for subsamples from North Point Rice Bay fossil dunes to examine the variation across the dune complex Horizontal lines ind ica te the mean value of samples at the sample loc a tion Numbers in parenth e ses are the numbers of subsamples analyzed for each field location 53

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, u < u a 1/) < u < u e J! :I Ci ..J a Cockburn Town 0 6 0 6 ... t 41 i c: u :I 0.4 CD 0 0 4 1/) 'i c: t .... u T t .. :I 0 2 CD 0 0 2 1/) :2 < 0 0 0.6 0.4 0 2 0 CBT1 CBT6 CBT9 CBT10 CBT11 CBT1 CBT6 CBT9 CBT10 CBT11 (9) (3) (3) (5) (2) (9) (3) (3) (5) (2) 0 6 0.4 CD t I .E t ..J t ... T T a 0 2 0 CBT1 CBT6 CBT9 CBT10 CBT11 CBT1 CBT6 CBT9 CBT10 CBT11 (9) (3) (3) (5) (2) (9) (3) (3) (5) (2) Figure 24. D/L values of four amino acids are plotted for subsamples from Cockburn Town to examine the variation across exposure. Additional samples were collected but were not analyzed becau s e they were not eolianite material (Appendix A) Horizontal lines indicate the mean value of samples at the sample location Numbers in par e nthe ses are the numbers of subsampl es anal yzed for each field location 54

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Watling's Quarry All subsamples from above and below the paleosol are plotted for Watling's Quarry (Figure 25). A difference can be seen when comparing DIL Aspartic Acid with the other three amino acid pairs. The DIL Aspartic Acid values cluster into two distinct groups: Lower and Upper Watling's Quarry Subsamples from location #1 seem to separate into a "third cluster" on the graph These subsamples are consistently higher than the other two clusters for each of the four amino acid pairs. This grouping consists of one field sample (3 subsamples), which is not enough data to justify separating it aminostratigraphically from other samples taken from below the paleosol. The "third cluster" is therefore, grouped with samples 3A, 3B, 3C and 3D and considered Lower Watling's Quarry. In addition, four samples (3A, 3B, 3C, and 3D) were taken vertically below the paleosol that divides Upper and Lower Watling's Quarry, to evaluate whether surface temperature had an effect on amino acid racemization (Figure 7). In this case, 3D was the lowest sample and 3A was closest to the paleosol. DIL Aspartic Acid shows a tight grouping with ratios increasing slightly with distance from paleosol. The other three amino acid pairs are more variable and show no trends in the data from top to bottom (Figure 25) Sample 3A was taken as close to below the paleosol as possible while trying to obtain a clean' sample (no paleosol material). Exposure to surface temperature did not seem to affect the uppermost sample differently from those lower in the section (Figure 25). More samples need to be analyzed to make concrete conclusions about surface temperature effects 55

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0. 8 'C 0 6 u 4( u :e 0.4 [ Cll 4( ...J a 0 2 0 0 8 'C u 0 6 4( u e !! 0 4 :I a ...J a 0 2 0 Watling s Quarry 0 8 ... Ql t c T u j 0.6 ... Ql 0 .!!! ..!. .!. .l .. .!. Gi + T T c 0.4 'U T ... ... :I .. Gl 0 Cll 0 2 T :2 C( 0 3A 3 B 3C 3D 4 5 6 7 8 1 3A 3B 3C 3D 4 5 6 7 8 (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) 0 8 0 6 .l ... Gl .E ... T .. iV > 0.4 ... T ...J .. ... a t ... T ... 0 2 0 1 3A 3B 3C 3D 4 5 6 7 8 1 3A 3B 3C 3D 4 5 6 7 8 (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) (3) Figure 25 DIL values offour amino acids a r e plotted for s u bsamples from Watling's Quarry to examine the variation above and below a paleosol. Horizontal lines indicate the mean val u e of samp l es at the sample location. Numbers in parentheses are the numbers of subsamples analyzed for each field location 56

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DISCUSSION The main question addressed in this study is whether D/L amino acid ratios measured by RPHPLC can be used to resolve details of the depositional history of San Salvador eoliantes Previous aminostratigraphic investigations have relied on a limited number of samples, typically 2-3 per unit. This investigation, however, makes use of a larger data set, especially when looking specifically at intra-unit variability in D/L values The evaluation of temporal and spatial variability in amino acid racemization data measured on whole rock field samples collected within and between individual lithostratigraphic units on San Salvador Island, Bahamas will aid in the assessment of aminostratigraphic resolution. The way to assess variability in the data is by looking at the scatter of D/L values within and between different stratigraphic units Aspartic Acid DIL values show the least variability throughout all groups of samples At all three levels of variability-intra-dune, intra-unit and inter-unit -DIL Aspartic Acid values are consistently less variable than D/L Glutamic Acid D/L Valine and All. D/L Valine valu e s also show low variability, but are sometimes not as sensitive to temporal differences as D/L Aspartic Acid D/L Glutamic Acid and All ratios have a tendency to show more of a gradual change in values through units where younger strata are separated from older strata by a distinct paleosol. Intra-dune Variability The amount ofvariability seen at the intra-dune level is important in terms of the stratigraphic resolution that amino acid racemization measurements may offer. Because 57

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of rapid cementation of carbonate dunes, individual layers of deposition within a dune can be seen in the field. First, comparing the scatter in the data of subsamples from each field sample, there was no trend or difference between the values obtained from the individual layer compared to the upper and lower portions of the same dune for either North Point or Hanna Bay (Figures 12-15) The scatter in the data, even in the D/L Aspartic Acid values, was too large to see a trend or resolve depositional history on this small of a scale Second, amino acid racemization measurements on the subsamples (A B and C) taken vertically from both dune complexes at North Point and Hanna Bay showed that surface temperature did not affect the uppermost samples of each dune (Figures 20 and 21 ). The scatter in the data from the uppermost sample was interspersed with the samples taken from both the middle and the bottom of the dune outcrop. In this case, either the effect of effective diagenetic temperature (Wehmiller, 1977) is negligible, or a distance of one meter below the surface is enough to remove this effect. The variability of the data on an intra-dune scale showed that amino acid racemization cannot resolve individual layers within a single dune. In addition amino acid racemization cannot resolve a vertical depositional history within a single dune Intra-unit Variability Understanding the uncertainties accompanied with amino acid racemization data within a lithostratigraphic unit can further aid in proposing constraints of the method All of the following sample locations are compared at one standard deviation from the mean D/L value for each amino acid at each location. 58

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The Hanna Bay and North Point eolianite outcrops sampled in this study correspond physically to the Hanna Bay Member and the North Point Member, respectively, of the Rice Bay Formation in both published stratigraphic columns for San Salvador Regardless of which amino acid pair is used to determine variability, the overlap in scatter of the DIL data points at each location indicates that amino acid racemization data cannot distinguish one dune from another (Figures 18 and 19). The three dunes from the North Point Rice Bay location, which are also from the North Point Member, exhibit these same results (Figure 23). Inter-unit Variability Understanding the variability between different lithostratigraphic units is imperative when using amino acid racemization data as a geochronological tool. The amount of variability within an individual unit contributes to the ability to separate different units using DIL ratios. Graphs of DIL Aspartic Acid, DIL Glutamic Acid and DIL Valine against Ali values for each sample location, show that the ratios covary (Figure 26). This figure also shows the similarities at North Point, North Point Rice Bay and Hanna Bay. Amino acid racemization data from the eight sample locations, shown separately for each of the four amino acids, illustrates the relationship of the lithostratigraphic units addressed in this study (Figure 27). Three aminogroups can be separated when all the data are compared, with the exception of Sandy Hook Road (SHR), which will be addressed later in this section. DIL Aspartic Acid shows the greatest separation and seems to have the ability to resolve the groups more obviously 59

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'0 '() lft-1 ..J c 0 2 0 0 2 0.4 0.6 0 0.2 0 4 0 6 Allo is oleucine/lsoleuc in e Allo is oleuclne/lsoleuclne Figure 26. The mean D/L values for Aspartic Acid, Glutamic Acid and Valine of all subsamples for all sample locations plotted against Alloisoleucine / lsoleucine Mean values are shown with one standard deviation both vertically and horizontally 60

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0 8 'C u 0 6 c( u :e IV 0.4 Q. II) c( ....J c 0 2 0 0 8 'C Cj 0 6 c( u e 0 4 .s 8 ....J 0 0 2 0 Sample Locations 0 8 Cll I c 'Cj 0 6 Cll 0 =-= II II) I 'ai c 0.4 u =-= II I=-:I Cll 0 =-= II) 0.2 : < =-= =-= =-= ::a:: 0 N P NPR B HB S H SHR LWQUWQ C B T N P NPR B HB SH SHR LWQ UWQ C B T 0 8 0 .6 Cll II .E I ii 0.4 > II ....J ::.: c 0 2 ..... --,-I -=-=--0 NP NPRB H B S H SHR LWQUWQ CBT NP NPRB HB SH SHR LWQUWQCBT Figure 27. The m ean DIL va l ues of four amino acids for all samp l e l ocations on San Salvador Islan d addressed in this study Error bars show one standard deviation Figures 10 and 11 display the distributions for North Point and Hanna Bay 61

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The first group of amino acid racemization data includes North Point, North Point Rice Bay, Hanna Bay and Sandy Hook. The overlap, or scatter, between North Point, North Point Rice Bay and Hanna Bay (Figure 27) does not allow for the locations to be separated given this information alone Because a clear distinction cannot be made between these sites, an unknown sample (NP or HB) could not be assigned to the correct unit on the basis of measured DIL values. On this small of a scale of comparison other tests should be performed to possibly better resolve two units of such similar age. Another complicating feature of the data from both North Point and Hanna Bay is the apparent inversion of ratios with respect to independent age estimates and stratigraphic evidence DIL Aspartic Acid shows this inversion with values of0.247 0.015 and 0.262 0.016 for North Point and Hanna Bay, respectively. Alloisoleucine/Isoleucine and DIL Glutamic Acid ratios for NP and HB are also inverted, while DIL Valine values are almost equal (Table 2). Carbon-14 age estimates recorded for North Point and Hanna Bay are 5345 125 and 3470 80 yr B P., respectively (Carew and Mylroie, 1987) (Table 1). Fortunately the physical stratigraphic relationships at these two locations show the differences in dipping strata, which may correlate with different sea-level positions (Carew and Mylroie, 1985, 1995a). The North Point beds dip at an angle that suggests a lower sea level than today, and Carew and Mylroie (1985, 1995a) propose that the beds at Hanna Bay dip at an angle that suggests deposition took place at a sea level closer to that of today IfD/L ratios alone are used to distinguish two or more stratigraphic units, then the higher the ratio, the older the samples. And, if time was the only contributing factor to the overall amino acid ratio and physical stratigraphic 62

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relationships are not apparent, then misinterpretations may be made using this AAR data set alone If the physical stratigraphy is blurred there may be an incorr ect evaluation of the aminostratigraphy. Even when the mean values with standard deviations are significantly different (with no overlap), a difference in taxonomic composition or a temperature difference may lead to misinterpretations However, given the limited geographic ext ent of the sampling region it is unlikely that North Point and Hanna Bay samples were subjected to different post-depositional temperature histories One must then consider either time or taxonomy as the cause of inversion of ratios A constituent particle analysis followed with a chromatographic analysis for taxonomy was not completed as part of this study. Hearty and Kindler (1993) performed a constituent particle analysis for North Point and Hanna Bay. They found the c onstituent particles at North Point were mostly pellets and ooids and that bioclasts were the main constituent at Hanna Bay. The differences in composition at these two locations were noted during sample preparation for this study In addition given the physical stratigraphic relationships at North Point and Hanna Bay, it is probably differences in the taxonomic signature of these two units which are responsible for the in v ersion in amino acid ratios The results found from the samples taken at North Point and Hanna Bay contributed to our comprehension of the stratigraphic constraints of amino acid racemi z ation. Understanding all the factors that affect amino acid racemization two units that are close in age should not be considered as different using AAR data as the only method of interpretation 63

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Given the above comparisons, it is not surprising that the comparison of samples from Hanna Bay and North Point Rice Bay are also inconclusive when trying to distinguish these two units of similar age The mean DIL Aspartic Acid values of Hanna Bay and North Point Rice Bay are 0.262 0.016 and 0.260 0 010, respectively (Table 2 and Figure 27). The ratios of Hanna Bay and North Point Rice Bay may have a common source area and the methods of transportation (wind, wave and current) were probably somewhat similar. The differences or similarities in the data suggest that constituent particle heterogeneity of these dunes may contribute to the inability of amino acid racemization data to resolve these units of similar age The mean values for Sandy Hook are not as low as one may expect from a 'modem' deposit (Figure 27) and it is grouped with NP, NPRB and HB. The sediment that is being deposited in these carbonate dunes probably includes reworking of older sediment. Boardman et al. (1987) suggest that significant erosion of eolianite complexes greatly contributes to the "modem" sediment signature of nearshore environments and estimated carbon-14 ages from Sandy Hook and Snow Bay support this argument (Table 1) If older sediments (fossil organisms) are being reworked with modem (alive or recently dead organisms), this may also contribute to the difficulty in separating deposits of similar age using AAR. The second grouping includes samples from Cockburn Town and Upper Watling's Quarry (Figure 27) The first group can be distinguished from the second group unequivocally on the basis of AAR data. The published stratigraphic columns place the Cockburn Town deposits within the Cockburn Town Member of the Grotto Beach Formation. However Hearty and Kindler place the deposits at Upper Watling's Quarry 64

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within their French Bay Member and Carew and Mylroie more generally classify this outcrop as belonging to the Grotto Beach Formation (Figures 3a and b). These two units physically belong to the same formation, and, because of this, the mean DIL values with standard deviation for these two sample locations overlap for all but one amino acid pair (Table 2 and Figure 27). For this study, there is not enough evidence to conclude anything except that they were deposited within the same interglacial period The mean values and standard deviation, of Cockburn Town and Upper Watling's Quarry show no overlap with samples from Lower Watling's Quarry The physical stratigraphic differences between these units are uncontested among different research groups It has been shown, with the second grouping, that Cockburn Town and Upper Watling's Quarry cannot be separated on the basis of amino acid racemization data. Therefore, for ease of explanation, the following discussion regarding separation of the third aminogroup will include only the comparison between Upper Watling's Quarry and Lower Watling's Quarry. Watling's Quarry was separated into Upper Watling's Quarry and Lower Watling's Quarry because a paleosol divides the outcrop. According to both published stratigraphic columns, these units (above and below the paleosol) belong to two different formations. DIL Aspartic Acid values for Watling's Quarry cluster into two groups corresponding to the field evidence in which a paleosol separates the two units. The other three amino acid pairs show a gradual increase in values with distance from the surface. A vague distinction can be made between the two units using DIL Valine ratios 65

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however, no amino acid pair resolves the two units better than DIL Aspartic Acid IfNI values were used alone, the amount of time required to form a distinct paleosol would not be apparent and may be overlooked When the mean and standard deviation were calculated for all Upper Watling's Quarry samples and from all Lower Watling's Quarry samples for all four amino acid pairs, the two units can be easily distinguished from one another (Figure 25) Throughout this study, the mean values ofDIL Aspartic Acid have shown the least variability and DIL Glutamic Acid has shown consistently higher variability The mean values of both amino acid pairs for these units (DIL Aspartic Acid UWQ = 0.433 016 and LWQ = 0 658 .040 ; DIL Glutamic Acid UWQ = 0 288 046 and LWQ = 0.439 059) are distinct, and even with the largest amount of scatter, the two units can be separated using AAR {Table 2 and Figures 27). Sandy Hook Road was chosen as a sample location of unknown age to determine if amino acid racemization could consistently place this outcrop into a stratigraphic position D / L Aspartic Acid values from Cockburn Town overlap with those at Sandy Hook Road (Figure 27) Although DIL Glutamic Acid is highly variable, it should be noted that DIL Glutamic Acid values of Sandy Hook Road overlap with those at Lower Watling's Quarry. DIL Aspartic Acid is the only amino acid pair that places Sandy Hook Road unequivocally within the Grotto Beach Formation (Figure 27) Two years after the samples were taken at Sandy Hook Road, and after all sample analysis was complete, i t was discovered that the SHR of this study is the same location as "The Gulf' in Carew and Mylroie's field observations (John Mylroie, personal communication, 2000) Carew and Mylroie (1985, 1995a) consider the eolianite deposits 66

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at "The Gulf' as regressive-phase eolianites which at The Gulf' overstep a fossilized reef. They place the eolianites at the The Gulf' into the Cockburn Town Member of the Grotto Beach Formation Therefore it is apparent that DIL Aspartic Acid is the only amino acid pair that agrees with the physical stratigraphy of Carew and Mylroie More samples at this location, along with a more in-depth look at taxonomy, would certainly help achieve a more complete understanding of where this site belongs in the aminostratigraphic column The three aminogroups seen on Figure 27 correlate to the Rice Bay Formation, the Grotto Beach Formation and the Owl's Hole Formation, respectively. These three formations are included in both published stratigraphic columns. It has been shown that amino acid racemization can resolve units deposited in different interglacial periods and that DIL Aspartic Acid illustrates the lowest variability of all four amino acid pairs The three ani.inogroups were placed in stratigraphic order in an aminostratigraphic column for this study Aminostratigrapbic Column An aminostratigraphic column was constructed from the four pairs of average amino acid ratios and is compared to the two previously published stratigraphic columns for San Salvador in Figure 28 and Table 2 All amino acid pairs appear to cluster into three DIL groups (aminogroups) The three groups contain samples taken to compare inter and intra-unit variability of amino acid racemization values The samples taken from North Point, North Point Rice Bay and Hanna Bay cluster into the youngest of the three groups for all the amino acid pairs. Samples taken from Upper Watling s Quarry 67

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R F I 0 CR EM A BT A I Yo N F 0 G B R REM 0AA TCT THI 0 0 N OWL'S HOLE FORMATION Sampled Units SANDY HOOK (modem beach} HANNA BAY NORTH POINT NORTH POINT RICE BAY COCKBURN TOWN UPP.bK WATilNGS QUARRY LOWER WATilNGS QUARRY SANDY HOOK ROAD Carew & Mylroi e (1995) R F HANNA I 0 BAY CR MB EM A NORTH B T POINT A I MB Yo N G R F 00 COCKBURN T R TOWN TM MB OA BT E I not broken Ao intomb eN I< RENCH H BAY OWL'S HOLE NO MBS FORMATION *** units not samp led or not correlated with other units Hearty & Kindl er (1993) EASTBAYMI R F I 0 JlAN'llll\ CR BAY EM MB A B T A I NORTHPOIN Yo MB N ALMGREEN UPPER MB CAY FORMATION LOWERMB G FERNANDEZ R F BAY 00 MB TR TM COCKBURN OA TOWN MB B T E I Ao FRENCH eN BAY MB H FORTUNE HILL NOMBS FORMATION OWL'S HOLE NOMBS FORMATION Figure 28 Arninostratig r aphic col umn and i t s re l ations h ip to the two stratigrap h ic columns previous l y p ub lished for San Sa l vador Island Bahamas Sa n dy Hook R oad was an unknown age d unit ana l yzed t o tes t the aminostratigraphic column. The only correlatio n that can be made using AAR i s th a t the sample l ocation is Mid-P l eistoce n e in age. 68

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and Cockburn Town cluster into the second group. Lower Watling's Quany samples cluster into the oldest group. Comparing the %CV, DIL Glutamic Acid and Alloisoleucinellsoleucine have the highest overall intra-unit variability DIL Aspartic Acid shows the lowest intra-unit variability D/L Valine shows moderate variability when compared to the other amino acid pairs (Table 2). The aminostratigraphic column (Table 2) that was constructed from this study does not differ from the previously published stratigraphic columns The sample locations that were analyzed were placed on the stratigraphic column for ease of comparison with the other columns The sample locations that diagrammatically correlate with members of the other stratigraphic columns do not mean that they are subdivided into members for this study. In fact, the only stratigraphic interpretations that can be determined by amino acid racemization of whole rock samples are that the sample locations cluster into three groups. These groups correlate with the three formations published by Carew and Mylroie (1985, 1995a) (Figures 3a and 28) and Hearty and Kindler (1993) (Figures 3b and 28). It should be mentioned that the additional two formations within Hearty and Kindler's (1993) stratigraphic column (Almgreen Cay Formation and Fortune Hill Formation) and the additional members (Figures 3b and 28) were not sampled and, therefore, are not directly addressed in this study. 69

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CONCLUSIONS The following conclusions have been reached and are proposed as constraints to using amino acid racemization analysis of whole rock eolianite deposits: 1 "Whole rock" analysis using AAR cannot resolve the depositional history of a single dune nor can the method resolve trends in deposition of an entire dune complex Intra-unit variability in AAR data exceeds the temporal resolution of the method. 2 The amino acid data from NP HB, and NPRB suggest that the composit i onal (taxonomic) heterogeneity within these fossil dune complexes is a more significant influence on DIL values than real differences in age between units In this case, inter-unit variability in AAR data exceeds the temporal resolution ofthe method when comparing Holocene units that are only a couple thousand years different in age 3 Amino acid racemization can be used on "whole rock" samples regardless of constituent particle composition if the lithostratigraphic units were deposited during the last three interglacial periods for which eolianites have been identified on San Salvador In this case the age differences are more signifi c ant than compositional variation between units. 4. DIL Aspartic Acid shows the highest degree of laboratory reproducibility the least amount of variation within a sample, and therefore the highest sensitivity to age and compositional characteristics of "whole rock" samples from San Salvador Island Overall, DIL Glutamic Acid displays the lowest degree of precision for the "whole rock" samples. The resulting aminostratigraphy of San Salvador Island using several pairs of amino acids, demonstrates that amino acid racem i zation data should be used cautiously yet can be used successfully while accompanied with a physical stratigraphic interpretation to determine the interglacial geochronological history of eolianite islands 70

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Future Research The more that is known about the depositional environment of a whole rock carbonate sample, the environment the sample is subjected to through time, and the biochemical composition of the organisms themselves, can only help interpret amino acid ratios The use of whole rock samples in an analysis of the kind described in this investigation provides us with a measure ofthe 'average' of all the racemization and epirnerization rates of the constituents in each unit. This 'average' is advantageous when using eolianite material, as the sediment is abraded, made up of sand-sized particles, and large shells are not common. Therefore, taxonomic identification of constituent particles is difficult. However, a general knowledge of the constituent particles in each unit would be helpful when the amino acid ratios from different lithostratigraphic units are being interpreted using amino acid racemization. The type of cement (aragonite, low-Mg or high-Mg calcite) and the process ofleaching and recrystallization may also add to the complex nature of amino acid racemization (Schroeder and Bada, 1976). Future work should include a detailed constituent particle analysis plus an analysis of cements. This study was concerned primarily with the variation of whole rock values within and between units. To attempt to separate two units of similar age, a detailed study focused fully on all aspects that could affect a ratio should be completed, where all the factors are calculated into the final reported ratio. Even if all of the above factors are considered, the resolving power of amino acid racemization may not be good enough to separate the units which are less than a few thousand years different in age. 71

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REFERENCES Anderson C B., and Boardman, M R., 1989. The Depositional Evolution of Snow Bay, San Salvador. In : J.E. Mylroie (Editor), Proceedings ofthe 4th Symposium on the Geology of the Bahamas. CCFL Bahamian Field Station, Fort Lauderdale, Florida, p. 7-22 Bada, J.L. 1985 Racemization of Amino Acids. In : G.C Barrett (Editor), Chemistry and Biochemistry of the Amino Acids Chapman and Hall, London p 399-414 Belperio, A P ., Murray-Wallace C V., and Cann, J.H., 1995. The last interglacial shoreline in southern Australia; morphostratigraphic variations in a temperate carbonate setting. Quaternary International 26 : 7-19. Boardman, M R., Carew, J.L., and Mylroie, J.E 1987 Holocene Deposition of Transgressive Sand on San Salvador, Bahamas Geological Society of America Abstracts with Programs, 19(7) : 593 Brookfield M E 1984 Eolian Sands. In: R.G. Walker, (Editor), Facies Models, second edition Geological Association of Canada Publications, Toronto Ontario p. 91104 Carew, J L. and Mylroie, J.E., 1985 The Pleistocene and Holocene stratigraphy of San Salvador Island Bahamas with regerence to marine and terrestrial lithofacies at French Bay. In : H.A Curran (Editor), Pleistocene and Holocene carbonate environments on San Salvador Island, Bahamas Geological Society of America, Orlando Annual Meeting Field Trip Guidebook, Ft. Lauderdale Florida CCFL Bahamian Field Station pp 11-61. Carew, J .L. and Mylroie, J.E 1987. A Refmed Geochronology for San Salvador Island Bahamas. In: H.A. Curran (Editor) Proceedings of the 3rd Symposium on the Geology of the Bahamas CCFL Bahamian Field Station, Fort Lauderdale, Florida, p 35-44 Carew J.L. Mylroie, J E., and Sealey N.E., 1992 Field Guide to sites of geological interest, Western New Providence Island, Bahamas. Field Trip Guidebook Proceedings of the 6th Symposium on the Geology of the Bahamas. CCFL Bahamian Field Station, Fort Lauderdale, Florida, p 1-23 Carew J L. and Mylroie, J.E., 1994 Discussion of: Hearty, P.J. and Kindler, P 1993 New Perspectives on Bahamian Geology: San Salvador Island, Bahamas Journal of Coastal Research, 9, 577-594. Journal of Coastal Research, 10(4): 1087 1094 72

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Carew, J L. and Mylroie, J.E 1995a. Depositional model and stratigraphy for the Quaternary geology of the Bahama Islands In H.A. Curran and B. White (Editors), Terrestrial and Shallow Marine Geology of the Bahamas and Bermuda. Geological Society of America Special Paper 300, p. 5-32. Carew, J.L. and Mylroie, J E., 1995b. Quaternary Tectonic Stability of the Bahamian Archipelago : Evidence from Fossil Coral Reefs and Flank Margin Caves. Quaternary Science Reviews, 44 : 145-153 Carew, J.L. and Mylroie, J.E. 1995c Rejoinder to: Hearty, P J and Kindler, P 1994 Reply Straw Men, Glass Houses, Apples and Oranges: A Response to Carew and Mylroie's Comment on Hearty and Kindler (1993). Journal of Coastal Research, 10(4) 1095-1105 Journal of Coastal Research, 11(1) : 256-260. Chen, J.H., Curran, H.A., White, B., and Wasserburg G J., 1991. Precise chronology of the last interglacial period : 234U-230 Th data from fossil coral reefs in the Bahamas Colby, N D. and Boardman, M R., 1989. Depositional Evolution of a Windward, High Energy Carbonate Lagoon San Salvador, Bahamas. In: J E Mylroie (Editor), Proceedings of the 41 h Symposium on the Geology of the Bahamas CCFL Bahamian Field Station, Fort Lauderdale, Florida, p. 95-105 Curran, H.A., 1989a. Introduction to the geology of the Bahamas and San Salvador Island, with an overflight guide In: H.A. Curran (Editor), Pleistocene and Holocene Carbonate Environments on San Salvador Island, Bahamas Geological Society of America, Annual Meeting Field Trip Guidebook, Field Trip #2. CCFL Bahamian Field Station, Fort Lauderdale, Florida, pp. 1-15 Curran, H.A and White, B., 1989b. The Cockburn Town fossil coral reefofSan Salvador Island, Bahamas In: H A. Curran (Editor), Pleistocene and Holocene Carbonate Environments on San Salvador Island, Bahamas Geological Society of America, Annual Meeting Field Trip Guidebook, Field Trip #2 CCFL Bahamian Field Station, Fort Lauderdale Florida, pp. 95-120 Curran, H A., White, B., Chen, J.H and Wasserburg G.J. 1989. Comparative Morphologic Analysis and Geochronology for the Development and Decline of Two Pleistocene Coral Reefs, San Salvador and Great Inagua Islands, Bahamas. In: J E Mylroie (Editor), Proceedings of the 41h Symposium on the Geology of the Bahamas CCFL Bahamian Field Station Fort Lauderdale, Florida, p 107-117. Curran, H .A. and White, B. 1995. Introduction : Bahamas Geology. In H.A Curran and B. White (Editors), Terrestrial and Shallow Marine Geology of the Bahamas and Bermuda Geological Society of America Special Paper 300, pp 1-3. 73

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Dravis, J.J., 1996. Rapidity of freshwater cementationimplications for carbonate diagenesis and sequence stratigraphy. Sedimentary Geology, 107: 1-10. Hearty, P.J., Vacher, H.L., and Mitterer, R.M., 1992. Aminostratigraphy and ages of Pleistocene limestones of Bermuda Geological Society of America Bulletin, 104: 471-480. Hearty, P.J and Kindler, P., 1993. New Perspectives on Bahamian Geology: San Salvador Island, Bahamas. Journal of Coastal Research, 9(2): 577-594. Hearty, P J and Kindler, P 1994. Straw Men, Glass Houses, Apples and Oranges : A Response to Carew and Mylroie's Comment on Hearty and Kindler (1993) Journal of Coastal Research, 10(4) : 1095-1105. Hearty, P J and Kindler, P 1995 Sea-level highstand chronology from stable carbonate platforms (Bermuda and Bahamas) Journal of Coastal Research, 11(3): 675-689 Hearty, P.J and Kindler, P., 1997 The Stratigraphy and Surficial Geology ofNew Providence and Surrounding Islands, Bahamas. Journal of Coastal Research, 13(3) : 798-812 Kaufman, D S. and Manley, W F 1998 A New Procedure for Determining DL Amino Acid Ratios in Fossils using Reverse Phase Liquid Chromatography Quaternary Geochronology, 17: 987-1000. Mackenzie, F T., 1964. Bermuda Pleistocene Eolianites and Paleowinds. Sedimentology, 3: 52-64. McCoy, W.D, 1987. The Precision of Amino Acid Geochronology and Paleothermometry. Quaternary Science Reviews, 6:43-57 McKee, E D and Ward, W.C., 1983 Eolian Environment. In: P.A Scholle, D.G. Bebout, and C H Moore, (Editors), Carbonate Depositional Environments AAPG Memoir 33. AAPG Publications, Tulsa, Oklahoma, p 131 170 Miller, G.H. and Brigham-Grette, J., 1989. Amino Acid Geochronology: Resolution and Precision in Carbonate Fossils. Quaternary International, 1: 111-128. Mirecki, J E Carew, J.L., and Mylroie J.E 1993 Precision of Amino Acid Enantiomeric Data from Fossiliferous Late Quaternary Eolianites San Salvador Island, The Bahamas In : B. White (Editor), Proceedings of the 61h Symposium on the Geology of the Bahamas CCFL Bahamian Field Station, Fort Lauderdale, Florida pp. 95-101. 74

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Mitterer R.M and Kriausakul N 1989 Calculations of Amino Acid Racemizat ion Ages Based on Apparent Parabolic Kinetics Quaternary Science Reviews 8 : 353-357 Mitterer, R.M 1993. The Diagenesis of Proteins and Amino Acids in Fossil Shells In: M H Engel and S A Macko (Editors) Organic Geochemistry Plenum Press, New York, pp. 739-753 Mylroie J.E. 2000. Personal communication. SEGSA Meeting Charleston South Carolina. Price D M ., 1999. Faci e s architecture of a last interglacial barrier ; a model for Quaternary barrier development from the Coorong to Mount Gamb ier coastal plain southeastern Austral ia Marine G e ology 158(1-4): 177-195 Reading H G. ( Editor), 1978 Sedimentary Environments and Fac i es Blackwell S c ientific Publications Oxford England 557 p. Rice J.A. and Loope D.R. 1991. Wind-reworked carbonates Permo Pennsylvanian of Arizona and Nevada GSA Bulletin 103 : 254-267. Schroeder R.A and Bada, J.L. 1976 A r eview of the geochemical applications of the amino acid racemi z ation reaction Earth-Science Reviews 12(4) : 347-391. Titus R., 1987. Geomorphology, Stratigraphy, and the Quaternary history of San Salvador. In: Curran H A., (Editor) Proceedings ofthe 3rd Symposium on the Geology of the Bahamas. CCFL Bahamian Field Station, Fort Lauderdale Florida pp. 155-164 Wehmiller J F. 1977 Amino acid studies of the Del Mar, California midden site: Apparent rate constants ground t emperature m odels and chronological implicat i ons Earth and Planetary Scienc e Letters, 37: 184-196 Wehmiller J.F ., 1984. Relative and absolute dating of Quaternary mollusks with amino acid racemization : Evaluation application, questions In: W C. Mahaney, (Editor), Quaternary Dating Methods, Elsevier, Amsterdam pp. 171-193 75

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Appendices 76

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Append ix A: F i eld Sampl e Numbers and Loc a tions F i e ld Sample # Material Dis t an ce b elo w sur fa ce COMMEN T S ( m e t e r s) NORTH POIN T 98-NP-IA w hole rock 1.3 A is always top closest to surface 98-NP-IB whole rock 2 5 98-NP-1C whole rock 2.9 98-NP 2A whol e rock 0 5 98-NP-2B whol e rock 1 .4 98-NP -2C w h o l e rock 2.5 98 -NP3A whol e rock 0 7 98-NP 3B whol e rock 2 3 98-NP-3C whol e rock 3.6 98-NP-30 whol e rock 5.1 98-NP -3E w h o l e r ock 6.2 98-N P -3F whol e rock 5 1 Horizontal Distance (m ) 98-NP-30 whole rock 5 1 F toG 4.5 98-NP-3H whole rock 5 1 GtoD S 7 98-NP-3 1 whole r oc k 5.1 DtoH 3 3 Hto l 4 1 9 8 -N P -4A whole rock 1.7 98-NP4 B whole rock 2 .9 98-NP-4C w h o l e rock 4 7 98-NP-5A w h o l e rock 2 98-NP-58 w hole rock 3.2 98-NP5C w hole rock 6 1 98-N P6A w hole rock 1.6 98-NP-68 w hole rock 3. 1 98-NP-6C w h o l e rock 4 6 98-NP-7A whol e rock 4 98-NP-78 whol e rock 5 2 98-NP-7C whol e rock 7. 1 98-NP-8A whole rock 1.5 98-NP SB whol e rock 1.9 98 NP-8C whol e rock 3 9 98 -NP-80 whol e rock 5 6 98-N P -8E whole rock 6. 7 98 -N P-8F whol e rock 5 4 Horizontal Distance (m) 98-NP-80 w hole r ock 3.6 F toG m 2 9 98 NP-8 H whole rock 2 8 GtoH 10.7 98 -N P-8 1 whole rock 3 5 H to l 6 6 98-NP-9A whole rock 1.6 98-NP-9B whole rock 3.3 98 NP-9C whole rock 6. 5 98-NP-IOA whole rock I 98-NPIOB whole rock 2 4 98-NP -IOC w hole r ock 5 1 7 7

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Appendix A: (Continued) Field Sample# Material Distance below surface COMMENTS (meters) NORTH POINT RICE BAY 98-NPRB-lA wholeroelc 2 .0-3. 0 98-NPRB-IB whole rock 3 2 98-NPRB-IC whole rock 4 8 98-NPRB-2A whole rock I Only 2 sample s because section is vertically thin here 98-NPRB-2B whole rock 2 8 98-NPRB-3A whole rock I 98-NPRB -38 whole rock 4 98-NPRB-3C whole rock 6 HANNA BAY 98-H8-IA whole rock 1.2 98-H8-18 whole rock J 98-H8-IC whole rock 4 2 98-HB-2A whole rock 2 8 98-H8-28 wbolerock 5 1 98-H8-2C whole rock 6 6 98 -HB-3A whole rock 2 98 -H8-38 whole rock 3 .8 98-H8-3C whole rock 5.4 98-H8-30 w h o l e rock 6 9 98-HB-3E whole rock 8.5 98-H8-4A whole rock 2 5 98-H8-48 whole rock 4 9 98-H8-4C whole rock 6.8 98-H8-5A whole rock I 98-H8-58 whole rock 2 5 98-H8-5C whole rock 4 98-H8-50 whole rock 5 2 98-H8-5E whole rock 6 7 COCKBURN TOWN 98 -C8T-IA whole rock 1.5 In this case A,B,and Care horiz. South ro North along dock ourerop 98-C8T-18 whole rock 1.5 98-C8T-IC whole rock 1.5 78

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Appendix A: (Contin u ed) Field Sample # Material Distance below surface COMMENTS ( m eters) 98-C8T-2 hash Not analyzed shell hash 98-C8T-3 co121 &ass Not analyzed-eo12l frass 98-C8T-4 co121 &ass Not analyzed -eo12l frass 98-C8T-5 paleosol Not analyzed paleosol and vegemorpbs 98-C8T-6 whole rock 3 2 98-C8T-7 bash 1.5 Not analyzed too shelly 98-C8T-8 bash 2 3 Not analyzed too shelly 98-C8T-9 whole rock random eolianite, if that, on the way to new marina quarry 98-C8T-10A whole rock 0 7 98-C8T-108 whole rock 1.2 98-C8T-11 whole rock 1.9 was JOe but changed blc thinlc it is a beach facies WATLINGS QUARRY 98-WQ-1A whole rock 0.8 below lost 98-WQ-18 whole rock 0 7 below 98-WQ2 whole rock 0 1 98-WQ-3A whole rock 0.1 below 98-WQ-38 whole rock 0 5 below 98-WQ-3C whole rock 0 8 below 98-WQ -30 whole rock 1.1 below 98-WQ-4 whole rock 3 above lowest 98-WQ-5 whole rock pa leosol and98-WQ-6 whole rock generally 98-WQ-7A gastropods generally Not anlyzed -gastropods 98 WQ-78 whole rock generally 98-WQ-8 whole rock generally GROTTO BEACH 98 G8-1A whole rock -2 sampl es taken horiz. along same bed? they arc beach, maybe stonn layer 98-G8-18 whole rock -2 NA 79

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Appendix A: (Continued) Field Sample# Material Distance below surface COMMENTS {meters) 98-08-IC whole rock -2 NA 98-10 whole rock NA 98G8-2A whole rock NA 98-08-28 NA 98G8C NA 98G8-3A Not analyud lost 98G8-4A whole rock NA 98-08-48 whole rock NA 98-GB-4C whole rock NA OWL'S HOLE 98-0HBOTIOM NotAnalyud 98-0H MIDDLE Not Analy:tcd 98-0HTOP Not Analy:tcd 98-0H Not Analy:tcd SANDY modem example of eolianite newest ridge among numerous older HOOK ridges inland from beach 98-SHIA whole rock 98-SHIB whole rock 98-SH-IC whole rock SANDY On road right near "The Gull" HOOK ROAD 98-SHR-IA whole rock 1.9 98-SHRIB whole rock 2 5 98-SHRIC whole rock 2 5 80

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Appendix B : Methods METHODS Laboratory Procedures Laboratory procedures for preparation hydrolysis and liquid chromatography closely followed those detailed by Kaufinan and Manley (1998) All whole rock samples used for AAR data where manually broken into blocks weighing approximately 30 grams and placed in individual snap cap vials. All samples were given a University of South Florida Amino Acid Geochronology Lab (FAL) number The samples were cleaned using a sonicator and several baths of ultrapure water The samples were sonicated at periods of 3-4 minutes repeating with fresh ultrapure water until the water was clear North Point and Hanna Bay samples were placed on several layers of kim wipes, labeled, covered with kimwipes, and then placed in drawers to dry All other samples were left in their open snap cap vials in the laminar flow hood covered by a large kimwipe until dry. The suites of samples were allowed to dry at least 72 hours to ensure accurate weights. Individual samples were then weighed as they were split into three subsamples (labeled AH, BH, and CH) for total acid hydrolysate analysis. The subsamples weighed between 20 and 25 mg and the weights reported were to 0 .01 milligram Weighed subsamples were placed (F AL number subsample letter and weight) in labeled glass vials. Extra sample material was also labeled and placed in an archive vial. 81

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Appendix B (Continued) Hydrolysis Samples intended for total acid hydrolysate analysis were dissolved in cold 7N HCL. The amount of 7N HCL was calculated using the weight of the sample multiplied by .02 and then multiplied by 1000 to get microliters ofHCL (1 ml HCL per 50 mg of material) (Miller and Brigham-Grette, 1989) Samples vials were then flushed with nitrogen and placed in a 110 C oven for 6 hours After cooling, all samples were placed in a vacuum desiccator until completely dry(-10 hours). Rehydration Samples numbered FAL 0131AH,BH,CH0139 AH,BH,CH along with FAL 0140AH,Bw0141 AH,BH were rehydrated with "0 02X" rehydrating solution for "normal"samples (Kaufman and Manley, 1998) (see recipes-Appendix C) This solution was added to the sample vial in a ratio of 1ml solution per 50 mg of sample material. To increase concentration (and therefore peak resolution on the chromatograph), the above proportion was changed to 1 ml rehydration solution per 1 00 mg of sample material C'0.01X" rehydrating solution for frees) (Kaufman and Manley, 1998) (Appendix C) for samples numbered FAL 0140CH0145CH and FAL 0146AH,BH,CH0248 AH,BH,CH. Rehydrated samples were thoroughly mixed and pi petted into labeled HPLC vials for analysis using an Hewlett-Packard HP 1100 liquid chromatograph 82

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Appendix B (Continued) Sample Analysis The Hewlett Packard HP 1100 allows samples to be analyzed using reverse-phase chromatography (pre-column derativization) Three mobile phases (A, B, and C) where introduced to the column using gradients and temperature setting followed from Kaufinan and Manley (1998). Mobil Phase A, was made daily (Appendix C) Mobile Phase B was HPLC grade Methanol and Mobile Phase C was HPLC grade Acetonitrile. The auto injector mixed each sample and the sample was introduced between a sandwich of a derivatizing reagent (o Phthaldialdehyde (OPA) and potassium borate buffer (Kaufinan and Manley, 1998) (Appendix C) to insure complete reaction with sample and to maximize fluorescence detection. This mixture was then injected onto the column Heights of peaks are in luminescence units and areas under detected amino acid peaks are automatically integrated. The amino acid L-HomoArginine was added to each sample in known quantity in order to calculate concentrations of individual amino acids. 83

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Appendix C: Recipes RECIPES (directly from Kaufman and Manley 1998) "0. 02X" Rehydration Solution for "normal" samples (0.02mVmg) 0 01 M HCL plus 0 .030 mM L-HomoArganine plus 0.77 mM Na azide measure 500 ml H 2 0 in volumetric flask pour into 500 ml glass bottle add 0.84 ml of6 M HCL (or 0 714 ml of7 M HCL) add 3.37 mg L-HomoArganine (or 3.33 ml of 4 5 mM L-hArg) add 25 mg sodium azide "0.01 X" Rehydrating Solution for Frees (0.01 0 .01 M HCL plus 0.060 mM L-HomoArganine plus 0 77 mM Na azide measure 500 ml H20 in volumetric flask pour into 500 ml glass bottle add 0 .84 ml of6 M HCL (or 0 714 ml of7 M HCL) add 6 .74 mg L-HomoArganine (or 6 66 ml of 4.5 mM L-hArg) add 25 mg sodium azide Deriyatizing Reagent (OPA/IBLC) Measure and mix in 4 ml vial : 99.4 mg IBLC (260mM) 45 6 mg OPA (170 mM) in 2.0 ml1 M potass ium borate buffer of pH 10.4 use touch mixer to dissolve (takes time); holding the vial in the sonicator works well ; mark and fill vials with micro inserts about half full and place in freezer. 1M Potassium borate buffer measure 500 ml H20 with volumetric flask; pour into beaker add 30.9 g of Boric acid pellets (H3B03); use stirrer add potassium hydroxide (KOH) crystals to bring to pH 10.4 (ca. 23-24 g) add a few drops of buffer preservative Mobile Phase A 23.0 mM sodium acetate plus 1 54 mM sodium azide solution measure 1000 ml H20 in dedicated volumetric flask pour into 1500 ml beaker add 3 .13 g trihydrous sodium acetate (or 1.89 g anhydrous sodium acetate) add 10 mg sodium azide (to prohibit bacterial growth) use magnetic stirrer; adjust to pH of 6 0 by adding several drops of 10% acetic acid ; pour into mobile phase bottle 84

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Appendix D: F AL Sample Numbers and Amino Acid Racemization Data 85


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