CLASTIC SEDIMENTS IN CAVES – IMPERFECT RECORDERS OF PROCESSES IN KARST


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CLASTIC SEDIMENTS IN CAVES – IMPERFECT RECORDERS OF PROCESSES IN KARST

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CLASTIC SEDIMENTS IN CAVES – IMPERFECT RECORDERS OF PROCESSES IN KARST
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Acta Carsologica
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Sasowsky, Ira D.
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Clastic Sediments ( local )
Paleoclimate ( local )
Sedimentology ( local )
Stratigraphy ( local )
Dating ( local )
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serial ( sobekcm )

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Clastic sediments have played an important role in deciphering geologic history and processes since the inception of the discipline. Early studies of caves applied stratigraphic principles to karst deposits. The majority of cave deposits are breakdown and alluvium. The alluvial materials have been successfully investigated to determine ages of caves, landscape evolution, paleoenvironmental conditions, and paleobiota. Rapid stage changes and the possibility of pipe-full flow make cave deposits different than surface deposits. This and other factors present difficulties with interpreting the cave record, but extended preservation is afforded by the “roofing” of deposits. Dating by magnetism or isotopes has been successful in many locations. Caves can be expected to persist for 10 Ma in a single erosive cycle; most cave sediments should be no older than this.
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Acta Carsologica, Vol. 36, no. 1 (2007-04-01).

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C LASTIC SEDIMENTS IN CAVES IMPERFECT RECORDERS OF PROCESSES IN KARST K LASTIfNI SEDIMENTI V JAMAH NEPOPOLNI ZAPIS KRAKIH PROCESOV Ira D. S ASO W SK Y 1 Izvleek UDK 552.517:551.7 Ira D. Sasowsky Klastini sedimenti v jamah – nepopolni za pis krakih procesov be od nekdaj so klastini sedimenti pomembno orodje pri raz biranju geoloke zgodovine. V zgodnjih tudijah so uporabili naela stratigraje tudi pri raziskovanju jamskih sedimentov . Glavnino jamskih sedimentov sestavljajo podori in aluvij. Ra ziskave aluvija so se uspeno izkazale pri dataciji jam, doloanju razvoja povrja, paleookolja in paleontologije. Zaradi monega tlanega toka in hitrih sprememb stanj, so jamski sedimenti drugani od povrinskih. To, poleg ostalih dejavnikov, pred stavlja teave pri interpretaciji zapisov, ki jih hranijo jame. Po drugi strani pa je obstojnost jamskih sedimentov dalja zaradi zavetja, ki jim ga nudi jama. Po vsem svetu poznamo tevilne uspene datacije jamskih sedimentov z magnetizmom ali izo topi. Jame znotraj erozijskega cikla vzdrijo do10 milijonov let, zato naj jamski sedimenti ne bi bili znatno stareji. K ljune besede: klastini sedimenti, paleoklima, sedimen tologija, stratigraja, datiranje. 1 Orce for Terrestrial Records of Environmental Change, Department of Geology and Environmental Science, University of Ak ron, Akron, OH 44325-4101, USA. Received/Prejeto: 24.01.2007 COBISS: 1.01 TIME in KARST, POSTOJNA 2007, 143 Abstract UDC 552.517:551.7 Ira D. Sasowsky: Clastic sediments in caves – imperfect re corders of processes in karst Clastic sediments have played an important role in deciphering geologic history and processes since the inception of the disci pline. Early studies of caves applied stratigraphic principles to karst deposits. e majority of cave deposits are breakdown and alluvium. e alluvial materials have been successfully investi gated to determine ages of caves, landscape evolution, paleoen vironmental conditions, and paleobiota. Rapid stage changes and the possibility of pipe-full ow make cave deposits dierent than surface deposits. is and other factors present dirculties with interpreting the cave record, but extended preservation is aorded by the “roong” of deposits. Dating by magnetism or isotopes has been successful in many locations. Caves can be expected to persist for 10 Ma in a single erosive cycle; most cave sediments should be no older than this. Key words: clastic sediments, paleoclimate, sedimentology, stratigraphy, dating. I NTRODUCTION Geology is undeniably a science of history, and since the earliest practice of the discipline, that history has been revealed in clastic sedimentary deposits. W illiam Smith, for example, created maps of the sedimentary rocks in England in the late 1700’s, and established a relative chro nology of their deposition using stratigraphic position and fossils. It has been natural, therefore, that karst scien tists examine clastic deposits in caves, in order to explore geologic time. In doing so, they are in large part applying the same principles and techniques developed by classi cal stratigraphers. An early example of this was a study by Kukla and Loek (1958) examining the processes of cave sediment deposition and preservation. In the present day, work such as that by Granger et al. (2001) and Polyak et. al. (1998) builds upon those classical techniques and ap plies laboratory methods to develop absolute chronolo -

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TIME in KARST – 2007 144 gies. ese chronologies in turn have allowed insight to such processes as river incision, water-table lowering, and landscape/climate linkages. is paper is a brief evaluation of clastic sediments as they apply to deciphering historical processes and events in karst terrane. Advantages and problems of working with these unique deposits are presented. For purposes of this paper, the “age” of a given cave sediment refers to the time of deposition of the material in the cave. M ATERIALS AND PROCESSES e processes that result in clastic sedimentation in caves are quite varied. Reviews and details including classi cation of deposits are presented in several texts (W hite, 1988; Ford and W illiams, 1989; Sasowsky and Mylroie, 2004). A perspective is given here. A useful broad-level classication is genetic, and based upon whether the clastic material originated within the cave (autogenic) or was carried in from the surface (allogenic). e former class is mainly bedrock breakdown (incasion), but encompasses ne grained sediments sourced from insoluble residue during phre atic enlargement, collapse of secondary mineralization (speleothems), and so forth. Allogenic sediments include alluvium, windblown material, animal feces, fossil mat ter, till, etc. In practice, the most commonly occurring materi als by far are bedrock breakdown and alluvium. Conse quently, autogenic cave sediments are mainly limestone. Allogenic sediments are usually resistant siliciclastics, because carbonates do not typically persist in the uvial environment. ere is no satisfying overall term for the clastic de posits found in caves. e word “soil” has been applied to the ne grained deposits, but this is a misnomer by most denitions, and is not recommended. Cave ll and cave earth have also been used. Regolith seems applica ble in spirit, but, because this material does not strictly “.form(s) the surface of the land ....” (Jackson, 1997) some may object to such usage. B REAKDO W N e collapse of cave bedrock walls and ceilings results in material that is angular, and ranges in size from sand to boulders. It is possible many times to visually t larger blocks to their point of origin on the adjacent cave walls and ceilings. e process of breakdown is not a common occurrence on human timescales. Only a few cases of present-day natural failure have been documented. For example, in Mammoth Cave, Kentucky only one large col lapse was noted in 189 years of mining and tourism (May et al. , 2005). However, on geologic timescales, the proc ess is pervasive and evident in most caves. Failures occur along existing planes of weakness (joints, faults, bedding planes). Causes of collapse can include removal of under lying support (particularly loss of buoyancy caused by the transition from phreatic to vadose conditions), removal of overlying arch support, cryoclastism (wedging by ice), and secondary mineral wedging (W hite and W hite, 2003). Triggering by earthquakes has also been observed, for example in Sistem Zeleke Jame-Karlovica (personal communication, F. Drole). Davies (1951) published an early analysis of expected collapse parameters in the cave environment. is was expanded on by W hite (1988, p. 232) to evaluate stability of ceilings relative to limestone bed thickness. Greater spans can be maintained by thick er beds. Jameson (1991) provides a comprehensive over view and classication of breakdown. Breakdown is frequently most prolic at 1) the intersections of cave passages, presumably due to the greater span lengths present at such points, and 2) where the cave is close to the surface, due to lack of thinning of the span and resulting decreased competency. In evalua tions of causes for passage terminations (W hite, 1960) it was noted that many cave passages ended in breakdown blockage (referred to by explorers as “terminal break down”). Although pervasive, breakdown has not found sig nicant utility for deciphering earth history in karst ter ranes. A LLUVIUM Alluvium enters caves by sinking stream, and occasion ally by colluvial mechanisms. e transport processes are for the most part similar to those in surface chan nels. e full range of sediment sizes are seen, structures such as cross-bedding and pebble imbrications develop, and cut-and-ll stratigraphy is possible. However, there are two important dierences exhibited for stream ow in caves when compared to most surface channels. First, channel width is severely constrained by bedrock walls. is promotes rapid stage increase during ooding, akin to that of slot canyons in surface streams (Fig. 1). Second, I RA D. S ASO W SK Y

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TIME in KARST – 2007 145 because the channel is roofed over, it is possible to have conned (pipe-full) rather than open channel ow. Tak en in conjunction, the results of these two conditions are the likelihood of high ow velocities, and the possibil ity of upwards phreatic ow. A striking example of rapid Fig. 1: Subterranean stream channels are typically narrow, and have no oodplain (a). is leads to rapid stage changes. Similar conditions in the surface environment are only seen in slot canyons such as the V irgin River, Utah, USA (b). stage change is seen in Hlloch, Switzerland, where rises of 250 m in a single ood have been recorded (W ildberger and Preiswerk, 1997; Jeannin, 2001). Cases of phreatic lis are seen in many cave systems. In Castleguard Cave (Rocky Moun tains, Canada) a seasonally active li of 9 m is observed (Schroeder and Ford, 1983). In that situation wellrounded cobbles are accumulated at the base, where they reside until communition reduces them sur ciently to allow transport up the li tube. e composition of the allu vium reects the source of the ma terial, as well as some other factors. It is interesting to note that a high proportion of clay sized material found in cave alluvium is actually ne-grained silica, not a clay min eral (W hite, 1988). e residuum found on the surface of many karst terranes frequently contains high amounts of clay and chert. e clay results from insoluble residues of the weathered limestone. e chert behaves in a very persistent way, being found throughout cave passages. I NFORMATION REVEALED In the investigation of clastic sedimentary deposits, either cave related or not, answers are sought to such questions as: How old? W hat was the paleoenvironment? W hat was the ow direction? W hat organisms were present? ese in turn allow an understanding of geologic history, environments of deposition, past climates, and potential for sedimentary deposits to act as mineral and fuel res ervoirs. In the case of cave studies, it is primarily the rst question which has been addressed. Caves can only be numerically dated by the deposits that they hold, and this age is usually reported as a minimum value. Alluvial materials are considered superior to speleothems in this undertaking, because they are emplaced much earlier in the existence of the cave. Once a date has been obtained, subsequent inferences such as rates of river incision, de nudation, and so forth, can then be made based upon the relation of the cave to the landscape. Dating has been accomplished by radiocarbon, magnetism, and cosmo genic isotopes. Paleoenvironmental information is revealed through studies of sedimentary structures and sequences, as well as via analyses of clay mineralogy and environmental magnetism. Paleohydrology can be deduced using tra ditional stratigraphic indicators such as cross-bedding, pebble imbrication, etc. Fossil deposits of organisms are actually rather rare within caves – most cave depsits are barren of these materials. Signicant deposits are known, though, and many excavations made in caves (particu larly in the entrance facies) serve as irreplaceable records of terrestrial fauna. C LASTIC SEDIMENTS IN CAVES IMPERFECT RECORDERS OF PROCESSES IN KARST

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TIME in KARST – 2007 146 L IMITS ON TIMESCALE Caves are erosional landforms, which have a limited pe riod of existence. Excluding those caves which have been subjected to burial, this places a practical limit on their duration as potential recorders of nearby processes. In any case, the cave sediments can be no older than the cave they are emplaced in (Sasowsky, 1998). erefore, the ultimate limit on preservation of sediments within a cave is the persistence (lifetime) of the cave in the envi ronment. In most limestone terranes epigenetic processes occur, with dissolution taking place both at the surface (forming pavements, dolines, etc.) and in the subsur face (forming caves). As base level lowers, denudation of the upland surfaces is also occurring and uppermost caves are eventually breached and destroyed. In certain settings examples of various states of decay can be seen in the landscape, and the sedimentary lls of breached (unroofed) caves may even be observed (e.g. uteri, 2004). In settings such as the Appalachian Valley and Ridge, hundreds of meters of carbonate have been de nuded from anticlinal valleys (W hite, 1988), and one may imagine extensive systems of caves which have been obliterated with no remaining trace. Bounds on the expected lifetime of an epigene cave may be evaluated by considering the two main control ling factors: initial depth of formation and rate of land surface lowering (denudation, Fig. 2). Although caves may form at any depth, a practical limit of 300 m is rea sonable, and the majority of caves are much shallower (Milanovic, 1981). Note that this “depth” is not correla tive to the frequently reported mapped depth of caves, which refers to the maximum vertical extent of survey. In the context of the present evaluation, depth is the posi tion below surface (thickness of overlying rock) at a given point in the cave. Denudation rates can be quite variable, and tend to correlate with rainfall (W hite, 1988, p. 218). Envelopes of expected cave persistence can be construct ed (Fig. 2) using these 2 parameters. Based upon this cal culation, epigene caves would usually exist in the erosive environment for up to 10 Ma. In practice, dating has not yet resulted in identica tion of caves this old within the present erosional cycle. Paleomagnetic dating has been used back to 4.4 Ma (Cave of the W inds, Colorado, USA; Luiszer, 1994). Cosmogen ic isotope dating has documented cave sediments as old as 5.7 (.1) Ma (Bone Cave, Tennessee, USA; Anthony and Granger, 2004). e absence of older values may be a consequence of limitations of dating methods, or reect the relative dearth of older caves in the environment, or both. e challenges of paleomagnetic dating include ab sence of ne-grained sediments, lack of uninterrupted sedimentation, and uncertainties of correlation with the global magnetic polarity scale. Cos mogenic dating is constrained by the absence of quartzose sediments, un certainties in parent isotope values, and the cost/eort of analyses. If consideration is extended beyond the present erosional cycle, lled and buried caves (paleokarst) are found in the rock record. Such materials have been recognized in many places, and the lls described in some detail (e.g. Loucks, 1999). Interest has been strong in the con text of exploration for minerals or petroleum. ese deposits also rep resent a potential trove of informa tion on far past hydrologic and en vironmental conditions because of their capacity to preserve. Fig. 2: eoretical persistence of caves in an erosional environment. e length of time that a given cave will exist depends upon the initial depth of formation (position on y-axis) and the denudation rate (slope of line). Gray regions envelope a range of reasonable denudation pathways for two examples. In case A, a cave formed at 200 m depth, the expected lifetime is 2.5 to 10 M a. For a cave formed at 100 m depth (case B), the lifetime is reduced to 1.25 to 5 M a. Solid sloping lines are the average denudation rate, 69 m/M a, for 33 major drainage basins (calculated from data in Summereld and H ulton, 1994). I RA D. S ASO W SK Y

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TIME in KARST – 2007 147 R ESOLUTION , CONTINUIT Y, AND VERACIT Y Stratigraphers have traditionally examined marine or paralic sediments because of their resolution, continuity, and veracity. Compared to terrestrial deposits, marine/ paralic strata are much more laterally and vertically ex tensive, they are of economic interest, and they potential ly function as continuous recorders for long periods of time. Terrestrial deposits are of interest though, particu larly because they contain information about the on-con tinent setting. W ithin the terrestrial environment lacus trine deposits and uvial terraces have seen the greatest attention as recorders of Cenozoic paleo-conditions. Lakes probably represent the highest quality records in the terrestrial environment – their environment many times is one of high preservation potential. Lacustrine deposits can be sampled by coring; duplication of cores can serve as a quality control; accumulation rates can be rapid; sediment properties are well tied to local environ mental conditions; and spatial variability is usually well understood. Terraces tend to preserve a partial record of the uvial environment, depending upon regional upli or down-cutting of the stream. In comparison, most caves contain spatially irregu lar deposits that can be aected by factors such as plug ging of swallets, extreme ow events, and back-ooding. Hydrologic complexity is common (Bosk et al. , 2003), even more so than surface uvial environments. Analysis of the paleohydrology of the depositional setting through cave passage morphometry is usually necessary, and may be quite time consuming if detailed maps are not avail able. Stratigraphic sections may be discontinuous, and require compilation. Caves are dircult sampling loca tions, due to logistics, remoteness, lack of light, and con straints on sampling equipment transport. Nevertheless, the cave environment is one that pro vides some advantages in recording the history of a re gion. e greatest advantage is that of potential preserva tion. Because caves are “roofed over” deposits are likely to be protected (at least on intermediate time scales), from Fig. 3: Comparison of sedimentary records from Lake B aikal, Russia (3 columns on le), and Cave of the Winds, USA (3 columns on right). B aikal data used with permission from King and Peck, 2001. Cave of the Winds data used with permission from Luiszer, 1994. C LASTIC SEDIMENTS IN CAVES IMPERFECT RECORDERS OF PROCESSES IN KARST

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TIME in KARST – 2007 148 surcial erosion. is is particularly germane for the u vial deposits. W eathering and erosion of surface uvial terraces is commonplace. In the cave, such materials may sit undisturbed for years. For example, in Xanadu Cave, Tennessee, USA, a pristine, non-indurated uvial deposit that is greater than 780 ka was sampled (Sasowsky, et al. , Fig. 4: Episodic inlling and removal of sediments is commonly observed in caves. In this section of Windy M outh Cave (West V irginia, USA) a diamict was almost completely removed aer being covered with owstone. e conduit is presently dry. 1995). Although rare, in exceptional settings the quality of the cave re cord may approach that of lakes (Fig. 3). Conditions amenable to this are stable recharge conguration, dif fuse recharge, minimal variation of discharge, and deep circulation. In Figure 3 two exceptional records are compared. e Lake Baikal record was constructed from cores taken on watercra. In that setting, about 40 m of sediment accumulate in 1 Ma. In contrast, at Cave of the W inds the accumulation rate is slower by more than an order or magnitude. In many settings caves appear to undergo episodic lling and exca vation (Fig. 4). In certain cases this may be locally controlled by cata strophic storms (e.g. Doehring and Vierbuchen 1971). However, the presence of broadly similar depos its/incisions within many caves in a region supports the idea that cave clastic materials reect regional paleoclimatic conditions. ese deposits hold much information that will be revealed with continued advances in conceptual frameworks and improved labo ratory methods. R EFERENCES Anthony, D.M. & D.E. Granger, 2004: A Late Tertiary origin for multilevel caves along the western escarp ment of the Cumberland Plateau, Tennessee and Kentucky, established by cosmogenic 26 Al and 10 Be. Journal of Cave and Karst Studies, v. 66, no. 2, p. 46-55. Bosk , P., P. Pruner, & J. Kadlec, 2003: Magnetostratigra phy of cave sediments: Application and limits. Stu dia Geophysica et Geodaetica, v. 47, p. 301-330. Davies, W . E., 1951: Mechanics of cavern breakdown. National Speleological Society Bulletin, v. 13, p. 3643. Doehring, D.O. & R.C. Vierbuchen, 1971: Cave Develop ment during a catastrophic storm in the Great Val ley of Virginia. Science, v. 174, no. 4016, p. 13271329. Ford, D.C. & P.W . W illiams, 1989: Karst geomorphology and hydrology. Unwin Hyman, London, 601 p. Granger, D.E., D. Fabel, D. & A.N. Palmer, 2001: Plio cene–Pleistocene incision of the Green River, Ken tucky, determined from radioactive decay of cosmo genic 26 Al and 10 Be in Mammoth Cave sediments. Geological Society of America Bulletin, v. 113; no. 7, p. 825-836. Jackson, J.A. (ed.), 1997: Glossary of geology. 4 th ed., American Geological Institute, Falls Church, Vir ginia, 769 p. Jameson, R.A., 1991: Concept and classication of cave breakdown: An analysis of patterns of collapse in Friars Hole Cave System, W est Virginia: In, Kast ning, E.H. and Kastning, K.M. (eds.), Appalachian Karst. National Speleological Society, Huntsville, Alabama, USA, p. 35-44. Jeannin, P.-Y ., 2001: Modeling ow in phreatic and epi phreatic karst conduits in the Hlloch cave (Muo tatal, Switzerland). W ater Resources Research, v. 37, no. 2 , p. 191-200. I RA D. S ASO W SK Y

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TIME in KARST – 2007 149 King, J. & J. Peck, 2001: Use of paleomagnetism in studies of lake sediments: In: Last, W .M. & J.P. Smol, (eds.), Tracking environmental change using lake sedi ments” Volume 1: Basin analysis, coring and chron ological techniques. Kluwer Academic Publishers, Dordrecht, p. 371-389. Kukla, J. & V. Loek, 1958: K promlematice vyzkumu jeskynnich vyplni (To the problems of investigation of the cave deposits). feskoslovensy Kras, v. 11, p. 19-83. Loucks, R.G., 1999: Paleocave carbonate reservoirs: Ori gins, burial-depth modications, spatial complexity, and reservoir implications. AAPG Bulletin, v. 83; no. 11; p. 1795-1834. Luiszer, F. G., 1994: Speleogenesis of Cave of the W inds, Manitou Springs, Colorado: In Sasowsky, I. D., and Palmer, M. V. (eds.) Breakthroughs in karst geomi crobiology and redox geochemistry (Special Publi cation 1). Charles Town, W est Virginia, Karst W a ters Institute, p. 91-109. May, M.T., K.W . Kuehn, C.G. Groves, C.G., & J. Meiman, 2005: Karst geomorphology and environmental concerns of the Mammoth Cave region, Kentucky. American Institute of Professional Geologists 2005 Annual Meeting Guidebook, Lexington, Kentucky, 44 p. Milanovic, P. T., 1981: Karst Hydrogeology (translated from the Y ugoslavian by J. J. Buhac). W ater Re sources Publications, Littleton, Colorado, 434 p. Polyak, V.J., W .C. McIntosh, N. Gven, N., & P. Proven cio, 1998: Age and origin of Carlsbad Cavern and related caves from 40 Ar/ 39 Ar of alunite. Science, v. 279, no. 5358, p. 1919 1922 Sasowsky, I.D., 1998: Determining the age of what is not there. Science, v. 279, no. 5358, p. 1874 Sasowsky, I. D. & J.W . Mylroie (eds.), 2004: Studies of cave sediments: Physical and chemical recorders of climate change. Kluwer Academic/Plenum Pub lishers, New Y ork, 329 p. Sasowsky, I. D., W .B. W hite, & V.A. Schmidt, 1995: Deter mination of stream incision rate in the Appalachian Plateaus by using cave-sediment magnetostratigra phy. Geology, v. 23, no. 5, p. 415-418. Schroeder, J. & D.C. Ford, 1983: Clastic sediments in Cas tleguard Cave, Columbia iceelds, Canada. Arctic and Alpine Research, v. 15, no. 4, p. 451-461. Summereld, M. A., & N.J. Hulton, 1994: Natural con trols of uvial denudation rates in major world drainage basins. Journal of Geophysical Research, v. 99(B7), p. 13,871,884. uteri, F., 2004: Cave sediments and denuded caverns in the Laki Ravnik, classical Karst of Slovenia: In: Sasowsky, I.D. and Mylroie, J.W . (eds.), Studies of cave sediments: Physical and chemical recorders of climate change. Kluwer Academic/Plenum Pub lishers, New Y ork, p. 123-134. W hite, W . B., 1960: Termination of passages in Appala chian Caves as evidence for a shallow phreatic ori gin. Bulletin of the National Speleological Society, v. 22, no. 1, p. 43-53. W hite, W .B., 1988: Geomorphology and hydrology of karst terranes. Oxford University Press, 464 p. W hite, W .B. & E.L. W hite, 2003: Gypsum wedging and cavern breakdown: Studies in the Mammoth Cave System Kentucky. Journal of Cave and Karst Stud ies, v. 65, no. 1, p. 43-52. W ildberger, A. & C. Preiswerk, 1997: Karst and caves of Switzerland. SpeleoProjects, Basil, Switzerland, 208 p. C LASTIC SEDIMENTS IN CAVES IMPERFECT RECORDERS OF PROCESSES IN KARST


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