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

Mélanie Principaud; Jean-Pierre Ponte; Thierry Mulder; Cecile Robin; Hervé Gillet; Jean Borgomano

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.

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

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