Sands of Lime Tell of Chaotic Climes: The Record of Last Interglacial Climate and Storms from Bahamian Eolianites

Due to fast cementation rates, the carbonate eolianites of the Bahamas Platform can be very sensitive to sea-level changes and short-term climatic events. The sedimentary structures preserved within last interglacial (MIS 5e) eolianites on several islands provide a detailed record of extreme climatic events as the interglacial period drew to a close.

Detailed examination of exposures on Eleuthera, San Salvador and Providenciales, reveal that MIS 5e eolianites were deposited rapidly, as evidenced by an overall lack of rhizomorphs and the burial of trees and palm fronds in growth position at several localities. Also, in contrast to eolianites from other highstands, MIS 5e eolianites are dominated by fine-scale, top- and back-set bedding, suggesting limited lateral migration. Finally, fenestrae (keystone vugs) can be found within MIS 5e eolianites, in some cases up to 43m above sea-level. Though typically associated with beach facies, outcrop evidence shows these eolian fenestrae formed as storm waves ran over, ran up, and ran out on coastal dunes.

Facies stacking patterns, fossil reefs, and emergent bioeroded notches in the Bahamas all indicate that sea-level fluctuated dramatically during the latter half of the last interglacial. As climate destabilized, ooidal platform sediments were rapidly remobilized into voluminous eolian ridges. At the end of the last interglacial period, tropical storms intensified throughout the platform due to the onset of glacial conditions and the compression of global wind belts. The more frequent storms reworked lowland dunes into storm-beach ridges with tabular, fenestrae-rich bedding and few original eolian structures. At moderate elevations, storm waves scoured the dunes leaving meter-thick fenestral zones, while in the highest eolian ridges waves and wave spray formed wispy, discontinuous fenestrae beds. These dramatic climate events recorded by the MIS 5e eolianites serve as a sobering bellwether for the future stability of the current interglacial.