WINDS OF CHANGE: CLIMATIC INSTABILITY OF THE LAST INTERGLACIAL AS RECORDED IN PLEISTOCENE EOLIANITES OF THE BAHAMAS

The carbonate eolianites on the windward islands of the Bahamas have tremendous potential to preserve short-term climatic events thanks in part to rapid cementation rates and exposure to the full energy of the Atlantic Ocean. In particular, eolianites deposited during the last interglacial (MIS 5e) on several islands preserve evidence of climatic instability and intensified storms as the interglacial drew to a close.

Exposures of MIS 5e eolianites on the islands of Eleuthera, San Salvador and Providenciales are marked by fine-scale laminations, scarce vegetation and rhizomorphs, fossil trees in growth position, and a prevalence of top- and back-set bedding geometries, which all together suggest rapid deposition with limited lateral migration. Perhaps most striking is the occurrence of fenestrae (keystone vugs) within several MIS 5e eolian exposures, often in beds dozens of meters above sea-level. Such fenestral porosity is commonly associated with wave-swashed beach environments, however outcrop evidence demonstrates that these eolian fenestrae formed as storm waves ran over, ran up, and ran out on coastal dunes.

Thus, as sea-level fluctuated at the end of the last interglacial, ooidal sediments were rapidly remobilized from the shallow platform into immense eolian ridges. As climate deteriorated, wind belts likely compressed, and tropical storms intensified. In low-lying areas, dunes were run-over and reworked by frequent storms, forming storm-beach ridges with tabular, fenestrae-rich bedding and few remnant eolian structures. At moderate elevations, storm waves ran up the dunes scouring out and depositing meter-thick, fenestrae-rich zones. In the highest and most inland eolian ridges, the effects of the storm waves finally ran out, leaving behind only wispy, discontinuous fenestrae beds.