The geology of Eleuthera Island, Bahamas: A Rosetta Stone of Quaternary stratigraphy and sea-level history

A 5-km stretch of coastline in north Eleuthera reveals a long and detailed stratigraphy that includes ail known surficial limestone units in the Bahamas, and supplements the record with several previously unrecognized ones. Eight paleosol-bounded limestone parasequences comprise at least six interglacial periods. The lithostratigraphy demonstrates cyclicity at several frequencies (10(5), 10(4) (20-40 ka), and 10(3) years) and displays a variety of distal to proximal shoreline facies indicative of shifting depocenters associated with changing sea-levels. Stratigraphy, petrology, pedology and whole-rock aminostratigraphy are used to correlate units and subunits among the 12 described sections. Amino acid ratios are also converted to absolute age estimates which support the lithostratigraphy. The parasequences are correlated with marine Oxygen Isotope Stages 1 to 13 or older. Evidence of middle Pleistocene highstands are abundant in the Eleutheran stratigraphy, including paleo-sea-levels of decreasing age at + 2 m, + 7 m, + 20 m associated with Stages 11 and/or 9, and two near-present highstands during Stage 7. A complex sea-level history is associated with Substage 5e, while Substage 5a is represented by near shore aggradation of coastal dune complexes in Eleuthera and throughout the Bahamas. Concordance of sea-level deposits between Bermuda and the Bahamas reinforce their tectonic stability, while the abundance of highstand evidence during the middle Pleistocene contradicts suggestions that platform subsidence has obscured all evidence of these events below present sea-level. The high-resolution late Quaternary stratigraphy of Eleuthera is unrivaled among geologic records from stable carbonate coastlines, and thereby offers a 'Rosetta Stone' for interpretation of the Quaternary evolution of the Bahamas and sea-level history over the past 500 ka. (C) 1998 Elsevier Science Ltd. All rights reserved.