MID-QUATERNARY SEA-LEVEL HIGHSTANDS IN THE BAHAMIAN ARCHIPELAGO: EVIDENCE FROM KARST DENUDATION AND FLANK MARGIN CAVE POSITION

The Bahamian Archipelago has abundant rock-record evidence of the last interglacial (MIS 5e) sea-level highstand, mostly as fossil coral reefs and related subtidal deposits, but such evidence of earlier highstands from the Mid-Quaternary is scanty and controversial (excepting Mayaguna Island). Data from flank margin cave elevations, used as a sea-level measure, were initially interpreted to demonstrate only a MIS 5e origin from ~60 mapped caves from across the archipelago. A major cave location and survey effort has now produced 346 maps of flank margin caves, and demonstrates that 15 caves with elevations between +6 to +20 m above modern sea level (higher than MIS 5e sea-level position) are found from the northwest (Moores Island) to the southeast (Crooked Island) in the archipelago. The reason for flank margin caves being the sole remaining land-form evidence of past sea-level position is that the Mid-Quaternary subtidal deposits, and related sea-level indicators such as sea caves and bioerosion notches, have been stripped away by karst denudation (at a rate of 1–5 m /100ka). The Mid-Quaternary flank margin caves, forming inside the rock as opposed to on it as for surficial features and deposits, escaped total denudational loss and a few remain as sea-level indicators. The elevation of some caves at up to 20 m indicates that prior assumptions as to the rate of subsidence of the Bahama Banks at 1-2 m /100ka may not be correct. 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.