SUPERSTORMS OF THE LAST INTERGLACIAL: THE RECORD FROM CARBONATE EOLIANITES OF THE BAHAMAS

Throughout the Bahamas, several lines of geologic evidence point to intensification of storms as climate destabilized at the end of the last interglacial (MIS 5e). Impacting the platform with variable effects, storm waves deposited massive boulders along the cliffs of Eleuthera, reworked lowland sediments into storm-beach ridges, and formed distinct storm beds high on the eolian ridges.

It is the MIS 5e oolitic eolianites in particular, especially those on the exposed Atlantic margin, that yield a detailed record of storm events thanks to rapid cementation and superb preservation of bedding and fenestral porosity. Classically associated with wave-swashed beaches, fenestral porosity is observed in MIS 5e eolianites platform-wide, in some locations 30-40 meters above the concomitant sea level defined by MIS 5e reefs and sedimentary facies.

We present detailed outcrop descriptions and petrography from eight MIS 5e localities, separated by over 600 km, on the islands of Eleuthera, San Salvador, and Providenciales. Evidence shows that lowland sediments on Eleuthera (Licrish Hill and Airport Junction) were repeatedly inundated by storm waves, and reworked into storm-beach ridges dominated by tabular, fenestrae-rich beds. At higher elevations and inland localities (Two Pines and Tarpum Bay, Eleuthera; Watling’s Castle, San Salvador; Turtle Cove, Providenciales), wave run up formed discrete packages of fenestral beds within the dunes, often associated with scour and rip-ups. Within the highest and most landward dune ridges (Annie Bight and Savannah Sound, Eleuthera; Turtle Cove, Providenciales), wave energy ran out, leaving only thin, discontinuous, fenestral beds.

With increasing elevation and distance from shore, the character of fenestral bedding changes in MIS 5e eolianites, as does the abundance and geometry of individual pores, yielding a spatial transition consistent with the attenuation of long wavelength ocean waves. Fenestrae beds also occur in distinct onlapping horizons, often interspersed with rhizomorphs, suggesting periodic inundation by multiple storm events. This, coupled with prior observations from Bermuda and other Bahamian islands, makes a strong case for superstorm activity at the close of the last interglacial, and the implications for our current interglacial ever more serious.