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32 páginas.- 3 figuras.- 2 tablas.- 260 referencias, Nearly half a century ago, two papers postulated the likelihood of lunar lava tube caves using mathematical models. Today, armed with an array of orbiting and fly-by satellites and survey instrumentation, we have now acquired cave data across our solar system-including the identification of potential cave entrances on the Moon, Mars, and at least nine other planetary bodies. These discoveries gave rise to the study of planetary caves. To help advance this field, we leveraged the expertise of an interdisciplinary group to identify a strategy to explore caves beyond Earth. Focusing primarily on astrobiology, the cave environment, geology, robotics, instrumentation, and human exploration, our goal was to produce a framework to guide this subdiscipline through at least the next decade. To do this, we first assembled a list of 198 science and engineering questions. Then, through a series of social surveys, 114 scientists and engineers winnowed down the list to the top 53 highest priority questions. This exercise resulted in identifying emerging and crucial research areas that require robust development to ultimately support a robotic mission to a planetary cave-principally the Moon and/or Mars. With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable. Subsequently, we will be positioned to robotically examine lunar caves and search for evidence of life within Martian caves; in turn, this will set the stage for human exploration and potential habitation of both the lunar and Martian subsurface., The following funding sources are recognized for supporting several of the contributing authors: Human Frontiers Science Program grant #RGY0066/2018 (for AAB), NASA Innovative Advanced Concepts Grant #80HQTR19C0034 (HJ, UYW, and WLW), and European Research Council, ERC Consolidator Grant #818602 (AGF), the Spanish Ministry of Science and Innovation (project PID2019-108672RJ-I00) and the "Ramon y Cajal" post-doctoral contract (grant #RYC2019-026885-I (AZM)), and Contract #80NM0018D0004 between the Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration (AA, MJM, KU, and LK).

Limestone boulders on top of pedestals reminiscent of karrentische occurring in glaciated karst were found and studied on the karstic part of Guam, Mariana Islands. Field, petrographic and XRD examination showed that these features form as a boulder falls from a cliff on limestone ground and protects it from surface lowering that affects the surroundings. Consequently, a pedestal forms and its height is a direct measurement of the denudation amount since the boulder fell. Since their formation and occurrence on karstic terrain closely resembles karrentische but the placement of boulders differs from the “classic” karrentische, we refer to them as tropical karrentische.The investigated karrentische on Guam are essentialy also a consequence of reef formation during MIS 5e interglacial period and denudation during glacial period. Hence, we investigated the denudation rate using tropical karrentische in combination with sea-level notches and fossil reef terraces which provided palaeosurface elevation and time constraint for denudation onset, respectively.The accuracy of the field evidence was tested by theoretical calculations. We calculated the denudation from the a) runoff of the measured CaCO3 solute amount in the vadose water and b) the maximum possible denudation as if the system in the given conditions was at equilibrium.Field evidence indicates an average denudation rate of ~40-70 mm/ka since the Last Interglacial (MIS 5e) sea-level maximum drawdown, ~125-116 ka ago. Theoretical denudation considering the modern solute runoff would be ~110 mm/ka, while the maximum possible rates can be up to 150 mm/ka, which is in line with the karrentisch-deduced estimate, since only a portion of the theoretical estimates translate into actual denudation.The results of this research show that tropical karrentisch can be a very valuable denudation indicator in coastal tropical settings and can probably be extended to non-tropical areas where time and palaeosurface can be constrained. Additionally, the deduced relatively high denudation rates also have implications on palaeo sea-level reconstructions based on elevated reef terraces that are prone to denudation.

2 páginas.- 1 figura.- 16 referencias, To the Editor — 2021 is the International Year of Caves and Karst. To honour this occasion, we wish to emphasize the vast potential embodied in planetary subsurfaces. While researchers have pondered the possibility of extraterrestrial caves for more than 50 years, we have now entered the incipient phase of planetary caves exploration....

Research on planetary caves requires cross-planetary-body investigations spanning multiple disciplines, including geology, climatology, astrobiology, robotics, human exploration and operations. The community determined that a roadmap was needed to establish a common framework for planetary cave research. This white paper is our initial conception

Karst landscapes form where solutional removal of bedrock is the dominant process in landform development. Subsurface solution conduits are best studied as cave systems, forms produced during part of the karst hydrologic cycle. The general public poorly understands karst landforms and processes, as evidenced by its opinion of cave conduits and its use of land in karst areas. Karst forms can be classified by their position and function in a hydrological regime, i.e. part of the terrestrial, fluvial component of the hydrologic cycle. Karst topography results from solutional sculpturing of bedrock initiated when this soluble material enters the domain of the hydrologic cycle. Karst landforms and cave systems can develop on a variety of scales from a few meters to many kilometers in magnitude. The observation of passage size, flow markings, sediments and size and orientation of abandoned upper levels can help unravel the geomorphic history of a karst area.

Pores in the Seroe Domi Formation on Curacao contain large quantities of clay minerals, organic material, and protodolomite or very high-magnesium calcite (VHMC) crystals. Transmission electron microscopy (TEM) applied to bio-sectioned rock samples showed the in situ relationship between the organic material, clay minerals, and VHMC. Dumbbells, consisting of two globular bodies connected by a narrow waist, ~20 mm in length and 5–8 mm wide, characterize the organic masses. The dumbbells are coated by clay minerals. VHMC crystals grew from nucleation points within microbial films and sheaths that surround the dumbbells. DNA extraction for 16 s rRNA gene analysis revealed the presence of sulfate- and sulfur-reducing bacteria, a variety of marine cyanophytes, bacteridetes, and proteobacteria, plus freshwater cyanophytes within the rock samples. This study provides evidence from a new field locality for the microbial nucleation and growth of VHMC associated with clay minerals, and the in situ appearance of microbial dumbbells associated with dolomite. Additionally, this study is the first to reveal the internal structure of these dumbbell features indicating that they are organic in origin with crystalline material in the surrounding sheath.

Rodrigues Island is located in the western Indian Ocean ~600 km east of Mauritius, at 19°42′S and 63°24′E, a volcanic island with a small overlay of Quaternary eolian limestones, an area of 108 km2, elongated ENE to WSW, 18 km long and 6.5 km wide, maximum elevation of 396 m. The last volcanic activity was 1.3 ma, and only one lava tube is known. The eolian calcarenites are restricted to a narrow segmented band on the east coast, and two larger patches, Plaine Caverne and Plaine Corail, on the south coast. No subtidal carbonate facies are known, and no flank margin caves are known, indicating that platform subsidence has been in excess of 5 m/100 ka to bring such features from the MIS 5e +6 m sea-level highstand below modern sea level. The eastern eolianite outcrops contain rectangular incisions similar to the bokas found in the Netherlands Antilles, as a large volcanic rock watershed traverses a thin coastal limestone outcrop. The southern calcarenite exposures each contain large epigene cave passages developed by surface catchment from volcanic rocks. The Plaine Corail caves are abandoned by streams today, are segmented and modified by collapse and contain massive calcite speleothems, evidence of an eolianite age of perhaps 1 ma or more. Plaine Caverne contains two long, linear stream caves, mostly intact. Mauritius has flank margin caves, subtidal facies above modern sea level, and abundant lava tubes (volcanic activity as recent as 26 ka), consistent with thermal inflation now long ended on subsiding Rodrigues.

12 páginas.- 9 figuras.- 6 tablas.- 90 referencias, San Salvador (Bahamas) is a carbonate island with dozens of flank margin caves formed in the phreatic zone by fresh seawater mixing within the freshwater lens. These caves have no direct connection with the sea, and form at or close to the tidally influenced fluctuating water table. After sea-level fall, in their subaerial parts caves are enlarged mainly by rock dissolution and by erosion close to the water level, condensation-corrosion and breakdown processes. For understanding the geomorphological features observed in these caves and how they are related to light attenuation, we investigated three sampling sites in the tidally influenced zone of Lighthouse Cave, which has been re-invaded by seawater during the Holocene sea-level highstand. A freshwater lens no longer exists within or adjacent to the cave. Rock samples were collected above and below the internal lake shores close to the entrance, and in the twilight and dark zones of this cave. Light and electron microscopy examinations were conducted for detecting microbial cells, as well as bioconstruction and bioweathering features. In addition, a high precision laser scanner was used for characterising sample microtopography. Our data showed that the microtopography and geomorphology of the lake shore samples (cave entrance) are dominated by bioweathering, whereas the samples of the twilight and dark zones are controlled by a combination of both bioweathering and bioconstructive processes depending on light availability. Bioconstructive structures, such as semi-planar lamination, at the fluctuating water level of the Lighthouse Cave show that dissolution due to water mixing of sea and freshwater in the Holocene is no longer the most important speleogenetic process. We propose that the geomorphological evolution is strongly influenced by the degree of rock diagenesis more than the initial mechanism of speleogenesis., the support from the CEECIND/01147/2017 contract funded by Fundação para a Ciência e a Tecnologia (Portugal). Funding was also provided by the Spanish project MINECO CGL2016-75590-P with ERDF funds.

Mylroie, J.; Lace, M.; Albury, N., and Mylroie, J., 2020. Flank margin caves and the position of mid- to late Pleistocene sea level in the Bahamas. Journal of Coastal Research, 36(2), 249–260. Coconut Creek (Florida), ISSN 0749-0208.The Bahamian Archipelago has abundant fossil coral reefs and related subtidal deposits as evidence of the last interglacial (marine isotope stage [MIS] 5e) sea-level highstand; evidence of earlier highstands from the mid-Pleistocene is limited and controversial (excepting Mayaguana Island). Data from flank margin cave elevations, used as a sea-level proxy, were initially interpreted to demonstrate an MIS 5e origin derived from ∼60 mapped caves across the archipelago. A new analysis of cave morphologies and distribution has now produced 363 maps of flank margin caves, demonstrating for the first time that 26 caves with associated elevations between +8 and +24 m above modern sea level are found spanning the northwest to the southeast boundaries of the archipelago. Flank margin caves are the primary remaining evidence of past sea-level position, because almost all mid-Pleistocene subtidal deposits, and related sea-level indicators such as subtidal facies, sea caves, and bioerosion notches, have been removed by karst denudation. Cave elevations up to 24 m (above sea level) indicate that prior assumptions as to the rate of subsidence of the Bahama Banks at 1–2 m per 100 ka may not be correct. The activity of MIS 5e was recent enough, and its subtidal deposits voluminous enough, to survive to the present, along with the majority of flank margin caves formed at that time. Karst denudation may have created sufficient mass loss that isostatic subsidence stopped, or was possibly reversed, as has been demonstrated for the Florida peninsula. If true, then mid-Pleistocene flank margin caves may not represent eustatic sea-level position at the time of speleogenesis.

The glacially deranged karst topography of the Helderberg Plateau, central New York, contains glaciolacustrine lithofacies deposited at the end of the Wisconsin glaciation. Eight pre-glacial caves (Barrack Zourie Cave, McFail's Cave, Howe Caverns, Secret Caverns, Bensons Cave, Gage Caverns, Schoharie Caverns, and Caboose Cave), containing a unique sediment section, are located within the footprint of Glacial Lake Schoharie, Schoharie County. The lithofacies consist of three individual facies, stratigraphically uniform, with the middle facies in sharp contact with the facies directly above and below. This assemblage displays a similar stratigraphic sequence from bottom to top: tan/white to light-grey, very thinly bedded, silts and clays, rich in calcite, overlain by poorly sorted, matrix-supported gravels, in turn overlain by dark- brown very thinly bedded silts and clays. A post-glacial cave within the lake's footprint (Westfall Spring Cave) and a nearby pre-glacial cave outside the footprint (Knox Cave) were found to lack these lithofacies. The tan/white to light-grey sediment facies is interpreted to be a glacial rock flour deposited under stagnant lake conditions that limited fine-grained calcite particle dissolution. The overlying gravel facies were emplaced during lake termination and reestablishment of turbulent epigenic flow in the eight stream caves. The more recent dark-brown facies is perhaps soil-loss deposition following European settlement. Initial interpretations hypothesized that the deposits were laid down under ice-cover conditions, but similar deposits were not found in other glaciated cave settings in New York. The results presented here explain why the unusual tan/white and light-grey glaciolacustrine facies are not found in other caves in the glaciated central New York region, as those areas were not subject to inundation by glacial lake water.

Modification of the mixing zone model to include microbial processes that promote dolomitization explains many of the petrographic, isotopic, and outcrop observations found on Isla de Mona. Large flank margin caves at the contact between the Isla de Mona Dolomite and the capping Lirio Limestone formed during prolonged, likely episodic, periods with a stable lens position. These periods would produce a stable halocline. The halocline is hypothesized to be the zone of dolomitization in the microbial mixing zone model. Collection of organics at the density interface of the halocline coupled with sulfate reduction by sulfate-reducing bacteria would establish a geochemical environment that promotes dolomitization of the precursor limestone. This microbial community and geochemical environment would overcome the kinetic and thermodynamic barriers associated with the previous mixing zone model.

Barbados is a small island located on the crest of an accretionary prism at the eastern edge of the Caribbean Sea. Dolomite occurs in relatively small amounts in Pleistocene carbonates and in the underlying Oligocene–Miocene chalk, which also contains a few small caves, distinctive authigenic calcites, and oil that ascended through a dense networks of fractures. The stable isotopes of calcites form a positive trend, while those of the dolomites form a negative trend. Dolomite δ18O values range from about +1 to +8‰ PDB, and δ13C values range from about +2 to −25‰ PDB. Sr-isotope ratios range from 0.7079 to 0.7094, which corresponds to a secular range from the Oligocene to the Holocene. The data presented in this study support the notion that the Barbados accretionary wedge has undergone a prolonged history of compression with concomitant expulsion of fluids that varied through time and space. At times these fluids were diluted relative to seawater and also undersaturated with respect to calcite, which resulted in limited dissolution along fractures and in their immediate vicinity. At other times the expelled pore fluids were prone to limited dolomitization, forming pods of dolomite. At yet other times the expelled fluids formed calcite as interstitial cements and around submarine points of exit in what appears to be “cold seeps” with calculated temperatures as low as +4 °C. The expelled fluids were chemically slightly modified seawater that contained thermogenic methane. Calculated temperatures of dolomitization range between +4 and +25 °C, which suggest fluid expulsion from sub-sea depths of zero to about –650 m. A temperature of +4 °C is the lowest ever determined for dolomite formation. The Sr-isotope data suggest that the hypogene fluids were expelled episodically between about 8 and 2 My ago. This study provides support for the hypothesis that dolomitization can result from fluid expulsion in an accretionary prism setting. However, the volumes of dolomite formed in Barbados are small and probably are similarly small in most other accretionary prism settings. Thus, regionally extensive, pervasive dolomitization is not to be expected from the dolomitizing process identified here. If elevated to the status of a model, dolomitization via fluid expulsion from an accretionary prism would be comparable in importance to the mixing zone model of dolomitization.

Taborosi, D.; Jenson, J.W., and Mylroie, J.E., 2013. Field observations of coastal discharge from an uplifted carbonate island aquifer, northern Guam, Mariana Islands: a descriptive geomorphic and hydrogeologic perspective. Understanding the hydrogeologic properties of carbonate island aquifers requires a conceptual framework within which specific and local properties, especially quantitative phenomena, can be placed and evaluated. In this paper, we present observations and hypotheses for such a qualitative conceptual model based on more than a decade of field studies in Guam. Fieldwork has shown that coastal groundwater discharge features can be usefully classified in terms of their geomorphic context and distinctive, readily observable characteristics: beach seeps and springs, reef seeps and springs, fracture springs, and cave springs. Seeps and springs on beaches and reefs are associated with matrix porosity and diffuse flow or are fed by fissures buried under sediment. Concentrated discharges...

Fieldwork in the Bahamian Archipelago in the 1970s and 1980s identified a new cave type, the flank margin cave, as macroscopic dissolutional voids developed in the margin of a freshwater lens, under the flank of the enclosing landmass. These voids are produced by three conditions that exist at the lens margin: mixing dissolution, organic decay horizons, and the increase in freshwater flow rate. The water flow enters flank margin caves as diffuse flow and exits as diffuse flow, a flow regime that produces dissolutional sculpture lacking turbulent flow features, such as asymmetric scallops. The caves are tied to sea level, which controls the freshwater lens position, and as such are excellent indicators of past sea-level position. The caves form without entrances and become accessible only after subaerial erosion has breached their ceilings or walls. Flank margin caves initiate as individual globular dissolutional voids that then intersect as the voids enlarge, increasing cave size in a sudden stepwise manner. As cave development is restricted to the lens margin, the largest flank margin caves acquire a linear shape as voids interconnect parallel to the lens margin. Flank margin caves are hypogene caves based on their diffuse, slow-flow regimes, because the dissolutional aggressiveness is generated below the surface by mixing, and the ascending marine water following the base of the lens to the site of dissolution at the lens margin. Because these caves form rapidly at shallow depths, there is a debate as to their hypogene classification, but they meet all criteria for hypogene speleogenesis.

We present bulk average Sr and Mg data for 13 speleothems from different locations in the western equatorial Pacific (Guam, Solomon Islands, and Vanuatu). These data plot on a single straight line in a graph of ln(Sr/Ca) vs ln(Mg/Ca) with a slope of ~ 0.9. A 22,000 year record of Sr and Mg in one of these samples from Guam also plots with the same slope, suggesting that the process partitioning Mg and Sr within the Guam speleothem is the same as the one that partitions Mg and Sr between the different Pacific speleothems. We rule out temperature, growth rate, detrital phases, and sea-spray as likely mechanisms for this correlation. We construct mathematical models of limestone diagenesis and show that this cannot explain the slope of the correlation. Our favoured explanation for the correlation is calcite/water interaction in the form of prior calcite precipitation (PCP) and/or incongruent calcite dissolution (ICD). We present a formal mathematical model of PCP and prove that the slope of a graph of ln(Sr/Ca) and ln(Mg/Ca) is given by Kd Sr − 1 Kd Mg − 1 . A similar equation is derived for ICD in a companion paper ( Sinclair, 2011 ). Using published values for KdSr and KdMg, this slope is calculated to be ~ 0.88, in excellent agreement with our observations. Because the slope is independent of solution and host-limestone composition it can be used to diagnose calcite–water interaction in individual cave water studies where host rock composition is unknown, or in speleothems for which no field drip water data or host-rock geochemistry exists. Approximately half of published drip and speleothem Mg + Sr studies plot within error of this slope. We hypothesize that the overall trend in our Pacific speleothem data results from the individual dripwater systems evolving from a roughly similar initial rock composition set by late Quaternary reef limestone. In the Guam speleothem, the broad peak in Mg and Sr centred on the early–mid Holocene reflects a change in hydrology (rainfall), with the most likely scenario being that dry conditions prevailed on Guam at this time.

Sealevel curves are best developed on tectonically stable coastlines, like San Salvador, where eolianites preserve transgressive and regressive phases associated with Quaternary high seastands, while reef facies mark the highstands. At 11 locations around San Salvador, terrestrial molluscs ( Cerion ) from the eolianites, lagoonal bivalves ( Codakia ), and corals from the highstand deposits were dated by ESR. Volumetrically averaged sedimentary dose rates were calculated from sedimentary geochemistry and time-averaged cosmic dose rates from each sample’s current and past geologic contexts. Rice Bay Formation corals dated at 3.9 ± 0.3 to 7.1 ± 0.4 ka (OIS 1). Minimum ages for the Cockburn Town Member’s regressive phase ranged from 49 ± 6 to 75 ± 8 ka, correlating with OIS 3–4. Codakia dates showed that an OIS 5a sealevel approached modern levels at 91–78 ka. In situ corals from the Cockburn Town Reef averaged from 127 ± 6 to 138 ± 10 ka, correlating well with OIS 5e. Ages from the Reef’s rubble zones hint that some coral reefs grew as early as OIS 7, but were likely reworked during OIS 5. San Salvador preserves deposits from three mid to late Quaternary highstands above, and as many as three that closely approach, modern sealevel.

Anchialine caves in coastal locations develop in two ways: by pseudokarst processes that form talus caves, sea caves, tafoni, fissure caves and lava tubes, and by karst dissolutional processes that form stream caves, flank margin caves, and blue holes. Pseudokarst caves are of minor importance in anchialine cave habitat development, with some lava tubes being notable exceptions. Dissolution caves provide the most extensive, variable, and long-term environments for anchialine habitats. The Carbonate Island Karst Model (CIKM) allows dissolutional cave development in carbonate coasts to be understood as the interplay between freshwater and marine water mixing, sea-level change, rock maturity, and interaction with adjacent non-carbonate rocks. Glacioeustatic sea-level changes of the Quaternary have moved all coastal anchialine cave environments repeatedly through a vertical range of over 100 m, and modern anchialine environments could not develop at their current elevations until ~4,000 years ago when sea level reached its present position. Blue holes form by a variety of mechanisms, but the most common is upward stoping and collapse from deep dissolutional voids. As a result, they provide vertical connection between different levels of horizontal cave development produced by a variety of earlier sea-level positions. Blue holes are overprinted by successive sea-level fluctuations; each sea-level event adds complexity to the habitats within blue holes and the cave systems they connect. Blue holes can reach depths below the deepest glacioeustatic sea-level lowstand, and thereby provide a refugia for anchialine species when cave passages above are drained by Quaternary sea-level fall. Blue holes represent the most significant anchialine cave environment in the world, and may provide clues to anchialine cave species colonization and speciation events.

2 Abstract: Abaco Island, Bahamas, contains a large number of conical hills that strongly resemble cone karst, a dissolutional landform associated with karst processes in tropical carbonate localities around the world. Field investigation demonstrated that the conical hills are roughly symmetrical in shape and consist of mid to late Pleistocene eolian calcarenites (carbonate sand dunes) partly mantled by talus. The original hummocky depositional topography of the eolian ridges has been dissected by a variety of processes including dissolution pit formation that enhances slope failure, vegetative disruption of the rock surface, and fire-induced exfoliation of the bedrock. The original asymmetrical shape of continuous dune ridges has thus been modified into a series of hills with a symmetrical cone shape, in which the steeper leeward depositional slopes of the dunes have been masked by talus to create a lesser slope that approximates the dip of the exposed bedrock slope of the more gentle windward depositional faces of the dunes. The conical hills are primarily constructional in nature, modified by mass-wasting slope processes only partly influenced by dissolution; therefore these conical hills are not true cone karst, but pseudokarst, despite their cone shape and their development in soluble carbonate rock. Abaco is the only island in the Bahamian Archipelago with both high eolian relief and a significant positive water budget; that water budget supports the degree of dissolution and forest growth necessary to create the root wedging and fire- induced exfoliation that most modify the steep leeward slopes of the dunes. As the eolian calcarenites were deposited only during the brief glacioeustatic sea-level highstands of the last few hundred thousand years, the development of cone-shaped hills in these eogenetic rocks has been geologically very rapid.

Mylroie, J.E., 2018. Superstorms: Comments on Bahamian fenestrae and boulder evidence from the Last Interglacial. Sea level during the last interglacial (Marine Isotope Substage 5e [MIS 5e]) was ∼6 m above present, interpreted to represent a warmer climate, with increased storm intensity and storm frequency. Two hypotheses have been advanced to demonstrate an increase in storm intensity during MIS 5e. The first considers fenestrae in eolian calcarenites at elevations up to 43 m in the Bahama Archipelago to be evidence of superstorm washover. Additional observations include rip-up clasts and loss of bedform and root structures as a result of wave scour. Such an event should produce a tempestite with a wide-ranging footprint, but none exists above 10 m. This paper argues that the fenestrae are rainfall slurries, rip-up clasts are weathering products of calcarenite protosol development, and bed-form and root structure absence or presence reflects transgressive-phase vs. regressive-phase eolian forma...

Coastal areas on carbonate islands commonly contain two types of caves: sea caves developed by wave erosion processes, and flank margin caves developed by dissolution at the edge of the fresh-water lens. Differentiating sea caves and flank margin caves in coastal settings is important, but can it be done reliably and quantitatively? Current methods use the degree of intricate wall-rock dissolution and the presence or absence of dense calcite speleothems to separate the two cave types. This study reports how analysis of cave maps creates three separate tools to differentiate coastal caves: area to perimeter ratio, entrance width to maximum width ratio, and rectangle short axis to long axis ratio. The study also presents some of the first sea cave data from eogenetic carbonate islands, specifically eolian calcarenites. The morphological and geometrical comparisons between Bahamian flank margin cave and sea cave maps using the three tools allows the two cave types to be statistically differentiated. The Bahamian sea cave data were also compared to sea cave data from California and Maine to demonstrate that Bahamian sea caves have a unique quantitative signature based on the youth and homogeneity of the host eolian calcarenite rock. The Bahamian sea cave data also indicate that sea cave formation may not be solely determined by differential rock weaknesses, as reported in the literature, but may also be a result of wave dynamics such as constructive interference.

The Bahama Islands offer a unique opportunity to examine Late Quaternary sea-level position, as the island group places significant constraints on the time and space boundary conditions for climatic events recorded there. The Bahamian Archipelago extends as a series of large and small islands on shallow carbonate banks of various sizes for 1400 km, across a climatic gradient wet in the northwest to dry in the southeast. The entire island group is tectonically stable, and consists solely of Quaternary carbonate sediments with interspersed paleosols. The islands reflect glacioeustatic sea-level highstand positions in their eolian and subtidal suite of limestones, a depositional record of platform flooding and carbonate sediment production. A coeval record of phreatic cave development in the island's fresh-water lenses also documents sea-level highstand positions. Absolute dating of late Pleistocene fossil corals and cave stalagmites by U/Th methods has produced an excellent record of the last interglacial (marine isotope substage (MIS) 5e). Holocene eolianites have been dated by 14 C to reveal platform flooding at ∼5000 ybp, and sea-level stabilization at ∼3000 ybp. Pleistocene eolianites have been dated by amino acid racemization analysis, but subdivisons of the eolianites into separate MIS 5a, 5c and 5e deposits are controversial. Paleosols, representing integrated aerosol dust deposition of ∼100 ka-long platform exposure events during glaciations, have been differentiated by paleomagnetic secular variation measurements. Previous interpretations of a beach unit to indicate a +20 m MIS stage 11 sea-level highstand, and of large boulders to represent a mega-tsunami, appear to be incorrect. Phreatic caves in today's subaerial environment have been ascribed to MIS 5e, but some may have formed earlier. Carbonate deposition and dissolution cycles create a mass flux of CO 2 sufficient to explain the atmospheric CO 2 excursions of the Quaternary.

A major challenge in groundwater and petroleum modeling is how to represent the diagenesis effect "sensu lato" and its associated features (e.g., karst cavities, porosity and permeability characteristics). Both geometrical descriptions and genesis are necessary for modeling diagenetic features, because they allow the restitution of phenomenon in subsurface settings where they cannot be fully observed. This study focuses on flank-margin caves developed on carbonate islands (as in the case of the Bahamian islands). Over the last twenty years numerous measurements and observations have been carried out on Quaternary carbonate islands. These, together with reasonable hypotheses of genesis (fresh-water lens dissolution), make island karst an appropriate subject for developing concepts and modeling methods which can be then applied to other diagenetic features, such as reflux dolomitization and hydrothermal fluid effects. The speleogenesis of flank-margin caves was modeled following deterministic and stochastic methods to achieve a description of dissolution genesis. A fresh-water lens surface was built based on the topography of Long Island, Bahamas, and was then used to simulate virtual development of flank-margin caves at several formation phases, including uncertainty coefficients applied to both fresh-water-lens location and stability time by using 3D probability cubes. The cave simulations were compared with over sixty Bahamian cave surveys, in order to substantiate our modeling processes and results. Finally, the model was exposed to a cave collapse situation. The likelihood of preservation and the extent of the area affected were measured to provide an evaluation of the spatial distribution of associated petrophysical characteristics (e.g., porosity and permeability). The results reveal close resemblance and coherence between modeled and field data (including collapse features). Therefore the optimum method for restituting diagenetic features is by stochastic modeling actively driven by process concepts and most up-to-date methods.

San Salvdor Island, Bahamas, provides unique opportunities to study modern geologic processes on carbonate platforms as a result of constraints in time and space. The time span of exposed geology is limited to the middle Pleistocene through Holocene (

In a pragmatic test conducted on vertical stratigraphic sections in Quaternary platform limestones of San Salvador Island, The Bahamas, gamma-ray spectrometric (GRS) and magnetosusceptibility (κ) data confirmed that characteristic geophysical patterns are coupled with depositional cycle boundaries. These geophysical patterns appear to develop in the early stages of diagenesis and are long lasting, because similar patterns are found both in the very young Bahamian limestones and in very old Devonian (Givetian-Frasnian) platform limestones of Moravia, Czech Republic. Because the Devonian limestones retain gamma ray and magnetic signatures similar to those seen in the Bahamian rocks, these signals are apparently resistant to changes that occur in later diagenetic alteration, including deep-burial diagenesis and 380 million years of rock-fluid interactions. Each sedimentary cycle on the Bahamian carbonate platform is marked by a terra rossa paleosol horizon that represents a lowstand emergent surface. The paleosol is typically characterized by a GRS-spike related to increased Th concentration. There is only a subtle downward infiltration of that GRS signal, but the Th signal may diffuse upward via sediment recycling. Two U-related GRS maxima are regularly developed within short distances below and above the cycle boundary. The lower anomaly reflects U enrichment in the sub-soil cementation zone, whereas the upper anomaly is related to increased U-content in the flooding beds of the next cycle. Such a combination of one Th-spike between two U-anomalies forms a distinctive tripartite GRS pattern.