DIFFERENTIATION OF FLANK MARGIN CAVES, SEA CAVES, AND TAFONI CAVES IN BAHAMIAN QUATERNARY EOLIAN CALCARENITES

Flank margin caves, sea caves and tafoni caves are found in Bahamian Quaternary eolian calcarenites. All three cave types can be found in coastal exposures being cliffed by Holocene wave activity, but also inland where last interglacial (OIS 5e, ~ 125 ka) coastal cliffing occurred. Flank margin caves are dissolutional features that form within the eolianites by water mixing, as sealed chambers. Sea caves and tafoni caves form by non-dissolutional weathering processes acting from the outside inward. Based on their size, shape and configuration, flank margin caves carry information on paleo fresh-water lens conditions. Flank margin and sea caves are tied to sea-level position during development, and are good paleo sea-level indicators, whereas tafoni caves form at random elevations on exposed cliffs. Differentiating between the cave types is important. Sea caves have been classified in the literature based on the nature of structural differences (e.g. faults and intrusions) in the host rock, but sea cave distributions in the relatively uniform eolian calcarenites of the Bahamas implicate off-shore focussing of wave energy as an additional factor. Subaerial erosion progressively removes sea caves, then breaches flank margin caves, allowing denudation rates to be determined. Tafoni caves form wherever the calcarenites are cliffed to present an unweathered surface lacking a calcrete crust, and where cementation by marine spray is inhibited by cliff height or protected coastal configuration. Collapse of dissolution voids to form cliffed hillsides also allows tafoni development in interior settings. Tafoni development was caused by wetting/drying cycles and wind, as no halite or gypsum were found within tafoni. Tafoni meters in size are found in Holocene eolian calcarenites, and small ones (tens of centimeters) have developed in quarry walls, road cuts, and building stone within 30 years, indicating rapid development. These three cave types, while having very different forming mechanisms and paleoclimate indications, can have a similar appearance in outcrop. This study looked at morphometric differences between the cave types to determine a method of differentiation. Results show this can be done with application of two measures: area to perimeter ratio, and entrance width to maximum cave width ratio.