Flank margin caves are karst features that develop in the freshwater/saline mixing zone within the carbonate islands of the Bahamas. The flank margin caves that are currently exposed developed during the last interglacial sea level highstand (+6 m; ~125 ka). Initially small ovid chambers, the caves increase in size to about 100 m2, then interconnect with adjacent chambers to form medium-sized caves. At about 1000 m2, these medium-size caves interlink forming large caves that are laterally extensive, vertically restricted, do not penetrate the fresh-water lens a significant amount, and run parallel to the axis of the ridge in which they formed. Small caves have a much smaller area to perimeter ratio than do large caves. As cave chambers grow and interconnect, perimeters become much more complex, and the number of bedrock columns in the cave increases. These results have implications for water resource management, and porosity modeling.

Caves on carbonate islands are useful indicators of past sea level because cave formation is dependent on sea-level controlled freshwater lens position (flank margin caves), or form in direct contact with coastal processes (sea caves). Sea-level curves present a useful proxy for glacioeustatic and paleoclimate studies, so caves offer useful data. Once a flank margin cave is breached, it may be modified and eroded by waves. This overprinting leads to morphology similar to that of sea caves. While both indicate past sea level, they reveal differing information about the amount of denudation that has occurred to expose them (a paleoclimate indicator), so differentiation of these cave types is important. This study presents some of the first sea cave data from carbonate islands, and makes morphological comparisons between flank margin caves and sea caves from the Bahamas, California, and Maine. Using morphometric techniques, these caves can be distinctly identified.

Tafoni have been confusingly defined in many ways: variations in size, rock type, and forming mechanisms. This study addresses tafoni in Quaternary eolian carbonates to help better define the term. Large tafoni were differentiated from other coastal caves in the Bahamas, specifically flank margin and sea caves, using morphometric analyses. The differentiation is important as all three cave types form in the same area, but flank margin and sea caves can be used as paleo-sea level indicators, while tafoni cannot. Small tafoni show a growth rate of 0.022 m3/yr; and may amalgmate to form larger tafoni, which grew at 0.65 m3/yr. Petrographic analysis helped identify tafoniorming mechanisms; results revealed no evaporites present, removing crystal wedging as a mechanism, while indicating wind erosion as the primary mechanism. This analysis found significantly greater cements within the Holocene rocks compared to previous studies, and SEM analysis revealed organic cements preserved by oil-based cutting.

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Sinkhole collapse is a common karst land-use risk around the world. In the Bahamas cover-collapse sinkholes do not exist because soil cover is thin; almost all collapse is due to cave ceiling failure. The most common cave types in the Bahamas are flank margin caves and banana holes. Flank margin caves have three entrance types: dissolution pit, side breach, or ceiling collapse. Both side breach and ceiling collapse are the result of mass erosional forces; pits by focused dissolution. It was previously proposed that slope was a controlling factor in Bahamian cave collapse. This study demonstrated that 7.5 minute topographic maps cannot resolve slopes accurately enough to predict potential collapse locations. Field surveys with 1 m contours allowed for a more concise slope range in which each entrance type preferentially occurred; collapse breaches and pits were common on gentle slopes and side breaches on steep slopes.

Banana holes are a common karst feature of The Bahamas and several theories have been presented to explain their origin. The current model for banana hole formation places their dissolution at the mixing zone at the top of the fresh water lens. This theory is based on the observation that banana holes are often found in the interior of islands, far from the dissolutionally aggressive fresh water lens margin. This study proposes that banana holes form at the lens margin as it follows a prograding strandplain. Spatial observations show that banana holes appear to be associated with low inland ridges and their orientation appears to correlate with features found on modern shorelines. Bedding features such as herringbone cross beds and back-beach rubble found in banana hole wall rock point to a progradational environment of deposition for banana hole host rock.

A geodatabase and a data management program have been created to store and manipulate cave and karst feature data from the Bahamas. A geographic information system was used to recognize any spatial patterns in the cave and karst data from San Salvador Island. Elevation data for banana holes, vadose pits and flank margin caves were obtained from a digital elevation model and are consistent with values predicted by the Carbonate Island Karst Model. The slope and aspect of the hill on which a flank margin cave is found showed no relationship to cave sizes and shapes, emphasizing the hypogenic nature of flank margin caves. The digital elevation model further demonstrated the position of lakes on San Salvador Island during the last interglacial (OIS 5e) highstand, and the lack of flank margin caves along the shores of these lakes provides evidence for a paleoclimate on San Salvador Island similar to today?s.

Rota Island, the southernmost island in the Commonwealth of the Northern Mariana Islands in the western Pacific, has the types of caves previously documented on the other limestone mantled islands in the Mariana Arc that have been investigated for caves: Aguijan, Guam, Tinian and Saipan. Caves developed at the edge of the fresh-water lens by zones of enhanced carbonate dissolution produced by fresh-water/salt-water mixing are most common. Among these mixing zone caves, flank margin caves dominate. Flank margin caves were found singly and in extensive horizons representing significant sea-level still stands. However, another type of mixing zone cave was found on Rota in numbers not documented on neighboring islands. Mixing zone fracture caves, apparently formed as zones of enhanced dissolution, produced fresh-water discharging from the lens along fractures, migrated vertically as sea-level changed. Some mixing zone fracture caves on Rota are developed in clusters from two to four caves. The mixing zone caves of Rota reflect the interaction of eogenetic limestone, glacioeustasy, local tectonics and enhanced carbonate dissolution via mixing of disparate waters. The development of mixing zone caves on Rota is in agreement with the Carbonate Island Karst Model (CIKM). Rota has a few caves developed along the contact between limestone and the insoluble volcanic rock that makes up the core of the island. The most important of these is Water Cave, a large spring that is the source for most of the municipal water on Rota. Rota also two extensive zones of vertical fissures developed along bedrock fractures; Fissure City and As Mundo Fissure Zone. In addition, Rota has one cave apparently developed along a fault; Gagani Cave. Some of the caves documented on Rota are difficult to classify and warrant further investigation.

Abaco Island is located on Little Bahama Bank at the northwestern extent of the Bahamian Archipelago. Karst features on Abaco include: flank margin caves, karren, blue holes, pit caves, banana holes, and cone karst. As part of this study all known flank margin caves on Abaco were GPS located and surveyed. The presence and locations of the other karst features were recorded as part of the karst inventory of Abaco. The cone karst is of particular interest because cone karst has not been documented on other Bahamian islands. These cones form from the dissection of an eolianite ridge due to karst, fire, and vegetative processes. Tafoni-like recesses, originally believed to be high flank margin caves, were formed during cliffing of an eolianite ridge during the OIS 5e highstand. The geologic evolution of representative depositional sequences on Abaco fits within the accepted Bahamian stratigraphy.

Flank margin caves of the Bahamas are formed by mixing dissolution in a fresh-water lens. As they evolve, the probability of intersecting neighboring voids increases, and they enlarge in a nonlinear fashion. Large flank margin caves become constrained by surface topography and their morphology is influenced by the shape of the enclosing land mass as a result. High phreatic ceilings can be dissolved if the fresh-water lens is distorted by lithological heterogeneities or hydrologic loading due to storm events. Early diagenesis of the host rock causes the reorganization of porosity and permeability through dissolution and cementation processes. Meteoric overprinting occurs but cannot be used as a tool in determining the age of eolianites or the climatic conditions at the time of deposition. Current evidence indicates an OIS 5e speleogenesis of large flank margin caves. An OIS 11 origin can be advanced only with compelling evidence of a pre-OIS 5e highstand.