The beautifully preserved fossil reefs of the Bahama Islands are ideal for the study of eustatic sea-level change, due in part to their tectonic stability and low, regular subsidence rate. This project is an attempt to further describe a brief and dramatic intra-Eemian sea level event which left its mark on the fossil coral reefs of San Salvador and Great Inagua Islands. Recent work by Mark Wilson (College of Wooster), Brian White and Al Curran (both of Smith College) has described an erosion surface sandwiched within the Eemian reefs of these islands. This surface was the result of a distinct eustatic regression and transgression; most unusual, as the Eemian was a warm interglacial period, previously thought to be quite stable. There is a host of paleontological evidence supporting the event, including rhizomorphs and truncated burrows and corals. I was able to travel to San Salvador Island this summer to study the reefs themselves. In order to gather a better understanding of these fossil reefs, I also spent time examining their living counterparts just offshore. Previous petrological analysis from the body of the reef above and below the erosion surface has shown that marine and meteoric cements overlap each other; further examination of thin sections may reveal more about the regressive and transgressive phases of the event. Using the stable isotopic composition of fossil corals sampled from both San Salvador and Great Inagua Islands, I am generating a climatic picture for this part of the Eemian. In doing so, I will be able to search for clues to the climatic shifts which would have precipitated such a dramatic change in global sea level. By studying these and other bodies of evidence, I hope to better illustrate the climatic changes surrounding such an unusual global event. Link here for the text of Allison's April 2000 Geological Society of America abstract on her I.S. work.

Allison Cornett is a senior geology major at The College of Wooster. Her hometown is Kendallville, Indiana. Allison's summer work on San Salvador Island, the Bahamas, and in Wooster was made possible by a Summer Fellowship award from the Council on Undergraduate Research and a grant from the Henry J. Copeland Funds at The College of Wooster.

The coral Diploria sitting directly on the Eemian erosion surface, seen here in cross-section; Cockburntown Reef, San Salvador, The Bahamas.

The coral Montastrea sitting directly on the Eemian erosion surface; Cockburntown Reef, San Salvador, The Bahamas.

Polished section through the bivalve boring Gastrochaenolites; the first generation of sediment (white) partially filled the boring before the erosion event; the succeeding brown sediment is a paleosol produced during subaerial exposure; the shell and white sediment were emplaced on top of the paleosol after sea levels rose again and inundated the boring; Cockburntown Reef, San Salvador, The Bahamas.

A rhizolith (produced by terrestrial plant roots) encrusting the Eemian erosion surface in the middle of the fossil coral reef on Great Inagua Island, The Bahamas.

Superb preservation of bivalve shells in the Eemian sediments immediately above the erosion surface; Great Inagua Island, The Bahamas.

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