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