T252 Advances in Cave and Karst (Posters): A Tribute to the Distinguished Career of E. Calvin Alexander Jr.

Tuesday, 27 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

QUATERNARY GLACIOEUSTATIC SEA-LEVEL HIGHSTANDS FROM THE BAHAMAS: THE KARST SIGNATURE

Paper number: T252-12
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The Bahamian Archipelago, because of the young age of its surficial rocks, 100% carbonate geology, and tectonic passivity, has long been used as a test of Quaternary glacioeustatic sea-level highstand position and chronology. With the exception of Mayaguana Island, which displays slight vertical rotation to the south exposing much older units, fossil coral reef U/Th dates from the archipelago all fall within the MIS 5e time window, ~120 ka. It has been argued that older corals formed either below modern sea-level elevation (MIS 7), or have been taken below modern elevation by isostatic subsidence of 1 to 2 m per 100 ka (MIS 9, 11, etc.). Flank margin cave position, on average at 0 to 6 m elevation, and a scattering of stalagmite dates less than 120 ka, supports a MIS 5e origin interpretation for the caves. In contrast, some caves, primarily in the southern Bahamas, display phreatic dissolution at elevations up to 17 m above sea level, and a stalagmite from Conch Bar Cave on the Caicos Platform was recently dated by U/Th to 266 ka. These observations suggest a lack of subsidence, or perhaps mild uplift, in the southern Bahamas. If so, where are the pre-MIS 5e fossil corals and related subtidal deposits? An often overlooked aspect is the karst denudation rate. Work on Guam in the western Pacific discovered 5 m of landscape denudation of a MIS 5e reef, extrapolating that rate of 5 m per 100 ka to the Bahamas (and accounting for climatic differences) suggests that those older reefs are entirely denuded, and that the remaining sea-level signature is preserved only in remnant flank margin caves, formed within the eolian high ground topography, which allowed survival to the present.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-280561

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