Neogene stratigraphic architecture and dynamic evolution of the great Bahamas bank slope : role of resedimented carbonate deposits and bottom currents

Abstract : Sediment instabilities commonly occur on carbonate slopes and constitute the major processes involved in their geometry and presentday morphology. The Bahamian archipelago represents an outstanding example of re-sedimented carbonate margin which enables to precisely buil-up a detailed stratigraphic and geometric architecture. Core and logging data from ODP Leg 166 and newly acquired 2D High- Resolution multichannel seismic reflection from the first Leg of the CARAMBAR Cruise allowed a re-evaluation of the Neogene seismic stratigraphy and architecture of the windward slope of the western Great Bahama Bank (GBB). The slope-to-basin Neogene deposits are controlled by two types of sedimentation : (1) the downslope gravity-driven carbonate deposits prograding westward and (2) bottom currents deposits progressively migrating northward along the margin. These two sedimentary systems are simultaneously active during Pliocene and interfinger at the toe-of-slope whilst the slope sedimentation, typified by turbidite aprons and slumps, prevails during the Miocene and the Pleistocene. This work is centered on high-resolution seismic data and the refinement of carbonate depositional sequences. The seismic observations allow to highlight a broad variety of facies for each sequence which range from gravity-flow slope carbonates, pelagic ooze to contourite deposits. Seismic facies display rapid lateral along strike and downdip transitions ranging between 1 and 10 km. The depositional cycles are interpreted as resulting from the global sea-level variations whilst the drift currents come from a geodynamic re-organisation affecting the Central American Seaway. Indeed, the Panama Isthmus occuring during the Neogene which significantly modified the north Atlantic thermohaline circulation and amplified the Florida Current intensity and pathway.