Abstract
The growth of large, bank-barrier coral reefs on the Bahamian islands of Great Inagua and San Salvador during the last interglacial was interrupted by at least one major cycle of sea regression and transgression. The fall of sea level resulted in the development of a wave-cut platform that abraded early Sangamon corals in parts of the Devil's Point reef on Great Inagua, and produced erosional breaks in the reefal sequences elsewhere in the Devil's Point reef and in the Cockburn Town reef on San Salvador. Minor red caliche and plant trace fossils formed on earlier interglacial reefal rocks during the low stand. The erosional surfaces subsequently were bored by sponges and bivalves, encrusted by serpulids, and recolonized by corals of younger interglacial age during the ensuing sea-level rise. These later reefal deposits form the base of a shallowing-upward sequence that developed during the rapid fall of sea level that marked the onset of Wisconsinan glacial conditions. Petrographic studies reveal a diagenetic sequence that supports this sea-level history. Preservation of pristine coralline aragonite, coupled with advances in U/Th age dating, allow these events in the history of the reefs to be placed in a precise chronology. We use these data to show that there was a time window of 1,500 years or less during which the regression/transgression cycle occurred and that rates of sea-level change must have been very rapid. We compare our results with the GRIP ice-core data, and show that the history of the Bahamian coral reefs indicates an episode of climate variability during the last interglacial greater than any reported in what is widely believed to be the more stable climate of the Holocene interglacial.
Highlights
Bank-barrier and patch coral reefs flourished on the Bahamian islands of San Salvador and Great Inagua (Fig. 1) duringthelastinterglacial-variously knownas substage 5eof the marine isotope scale, the Sangamon of North America, and theEemianof Europe
We haveconducted detailed field studiesof fossilreefs near Devil's Point on the west coastof Greatlnagua,and of the Cockburn Townand SuePointfossil reefs on the west side of San Salvador (Fig. 2) in order to determine their geologic history, with respectto sea-level events. These three fossil reefs are the largest currently documented from the Bahamas
A compelling body of field and petrographic evidenceshows that the development of coral reefs on Great lnagua and San Salvador islands during the Sangamon interglacial was interrupted by a fall of sea level that exposed the reefs and associated sedimentary facies to non-marine conditions
Summary
Bank-barrier and patch coral reefs flourished on the Bahamian islands of San Salvador and Great Inagua (Fig. 1) duringthelastinterglacial-variously knownas substage 5eof the marine isotope scale, the Sangamon of North America, and theEemianof Europe. A well-developed wave-eut platform withintheSangamonian sequence at Devil's Point (Fig. 3A) provides the most prominent field evidence for a fall and subsequent riseof sea level during the last interglacial. Of red calichethat lines fissurewallsand the adjacentfissurefilling subtidal calcarenites thatweredeposited in the interval betweenthe two soil-forming episodes This first generation of paleosol/caliche provides additional evidence for a brief sea-level lowstand duringthe overalldevelopment of thereef. No wave-cut platform or erosional surface interrupts the reefal sequence, suggesting thatthis reef may have developed only duringthe later interglacial sea-level highstand following the sea-level lowstand recordedat the Devil's Point an
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