THE BAHAMIAN EOLIANITE PROJECT: AN UNKNOWN VENTURE OF R.N. GINSBURG IN THE EARLY 1990'S

In the early 1990's, Bob Ginsburg was mostly preoccupied with the Bahamian Drilling Project, the study of the slopes of the Tongue of the Ocean, and the formation of oncoids. He also took the time to supervise a small project on Bahamian eolianites. The aims of this project, as determined by Ginsburg, were (1) to figure out why, in the Bahamas, Holocene eolianites essentially contain skeletal particles, whereas Pleistocene counterparts are made of ooids, and (2) to present a sedimentological model explaining the occurrence of Pleistocene oolites on the windward islands of the Great Bahama Bank, to the E of which no obvious source of ooids now exists.

Responding to the first question showed that the petrographic composition of Bahamian eolianites is not related to age (i.e. Holocene oolites and Pleistocene bioclastic calcarenites both exist), but is controlled by the elevation of sea level relative to the platform top. This facet of the project further helped refining the stratigraphic record of the Bahamas islands that now includes seven units going back to the middle Pleistocene. Eventually, it led to the identification of Cretaceous eolianites in the French Jura Mountains, demonstrating these deposits are not characteristic of icehouse periods. The second aspect was not addressed until now. Three models can be proposed to account for the presence of Pleistocene oolites on the windward islands: (1) ooids formed on platform expanses located to the E that have now been eroded; (2) ooids formed on the W side of the islands, were brought to the E side through tidal channels, and transported back onshore by easterly flows; (3) ooids formed on the lee side and were transported directly onto the islands by westerly flows opposite to common sediment transport media on GBB. Supported by the orientation of sedimentary structures, this model implies the existence of time intervals when paleoceanogaphic and paleoclimatic conditions in the Bahamas were significantly different than present.