Changing Carbonate Sedimentation During the Holocene Transgression: New Providence Platform, Bahamas

Abstract

The sedimentary record of New Providence Platform (NPP) and the Exumas windward margin portions of Great Bahama Bank reveals complex, shifting sediment patterns during the Holocene sea-level transgression. Understanding these patterns provides a more robust analog for interpreting and correlating depositional cycles in subsurface examples. Sea-level changes drive sediment dynamics in shallow-water carbonate settings, producing facies indicative of relative sea-level positions and making them excellent sea-level archives. Rising sea level and concomitant sedimentation constantly change the energy distribution and locations of sedimentation and erosion. A shift in the energy balance across NPP during the Holocene transgression is recorded in the coarsening-upwards sedimentary succession documented in the platform interior (Yellow Banks). This succession indicates an increase in energy with increasing water depth, changing the once restricted platform to high-energy, open-marine conditions (i.e. change from muddy to high-energy, grapestone/skeletal sediments). The preservation potential varies from the platform interior (highest preservation potential) eastwards towards the outermost Exuma Cays platform margin (poorest preservation potential). The Exumas windward platform margin features islands dissected by high-energy channels and ooid shoals. Pleistocene antecedent topography acts as a barrier to the erosion caused by the Holocene transgression and also provides a template for complex Holocene carbonate sediment deposition and accretion. Eastward of the islands, very little Holocene sediment is preserved; sediments on this sloping margin are either transported towards the platform or into Exuma Sound. In many places, the sloping outer margin is eroded down to the Pleistocene surface. Locally, the windward margins of the islands contain steep, eroding sea cliffs and small relicts of older Holocene eolianites. On leeward sides of the islands towards the platform interior, the erosion is minimal and a more complete record of Holocene sedimentation is commonly present. The Pleistocene islands mark the boundary between low and high sediment preservation. In addition, in the present-day energy situation, they are also focusing the tidal currents, producing high-energy environments with increased sedimentation. These sediments are deposited in ooid shoals or as accreting beaches on both the open-ocean and the bankside of the Pleistocene islands.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015