Paper No. 7
Presentation Time: 3:15 PM
THE ROLE OF KARST IN BAHAMIAN GEOLOGY
Karst processes play an important role in understanding Bahamian geology. The most obvious aspect is the presence of the epikarst, which develops in concert with the terra rossa paleosols that are the main stratigraphic markers in the Bahamas. The degree of epikarst development is a measure of the time of exposure, as well as the climatic conditions operating during that time. Karst denudation must be taken into account when epikarst is present over subtidal facies, as the amount of denudation must be added to the current elevation (along with isostatic subsidence) to accurately place paleo sea-level position. Phreatic dissolution at the edge of the fresh-water lens to form flank margin caves creates a reliable paleo sea-level position indicator, as the edge of the fresh-water lens is at sea level. These caves are opened and exposed by surface denudation, the degree of which removes other standard sea-level indicators, such as bioerosion notches; as a result breached flank margin caves have commonly been mis-identified as fossil bioerosion notches throughout the Bahamas (but the paleo sea-level signal is the same). Banana holes are flank margin caves formed in prograding strandplains, their small size and immature form an indicator of their sequential formation and abandonment as the strandplain progrades seaward and the active fresh-water lens margin follows, an example of syndepositional caves. Banana holes are therefore facies specific, allowing the strandplain facies to be mapped by remote sensing. Banana holes also demonstrate the power of the lens margin as an extremely rapid dissolutional environment, and how quickly carbonate sediments cement sufficiently to support a cave roof. Pit caves transport terra rossa paleosol material to depth in the carbonates, and these infills, especially if associated with flank margin caves, can create the illusion of an exposure surface; this situation is especially problematic when examining core. Blue holes in platform interiors are mostly progradational collapse features originating in deep paleo-conduit flow systems; on the open bank, Holocene sedimentation has infilled these features. Tidal flow through the Holocene sediment column has been hypothesized as the cause for whitings on the Bahama Banks as abiotic precipitates similar to ooid formation conditions.