Quaternary geology of Long Island (Bahamas): an alternative perception of Bahamian island formation and relative sea-level changes in this area during the Last Interglacial

Abstract

Relying on a multi-method approach including morphostratigraphy, sedimentology, petrology, and Sr-isotope, U-Th, amino-acid racemization and ¹⁴C dating, we have identified, described, and mapped eight allostratigraphic units on Long Island (NE Bahamas). These units mostly consist of eolianites, but locally include reefal and sandy coastal deposits. They range in age from the middle Pleistocene to the late Holocene, are usually separated by terra-rossa paleosols, and can generally be correlated with the members and formations previously defined on other Bahamian islands. However, the Buckley Settlement and the Dean's Bay units, respectively equivalents of the mid-Holocene North Point Member and of the late Pleistocene Whale Point Formation, are more widespread on Long Island than on other islands, possibly due to a difference in the width of the windward shelf. Furthermore, we could not identify on Long Island a counterpart of the French Bay Member, an extensive rock body supposedly accumulated during the transgression at the onset of the last interglacial period (LIG). The lack of such deposits brings about questions about the volume and the nature of transgressive sediments that can possibly be preserved during a sea-level cycle in the Bahamas, and leads us to reconsider previously proposed models of Bahamian island development. Finally, the examination and, in some cases, the dating of paleo sea-level markers of LIG age suggest that RSL on Long Island was about +3 m above modern datum in the first half of the LIG, and rose to about +5 m in the middle of this period. This rise was likely not preceded by an exposure event.