AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Re-Evaluation of Sedimentation Patterns at Bahamian Carbonate Slopes


A renewed reconnaissance of the Bahamian carbonate slopes with an integrated approach encompassing hydroacoustic measurements (Parametric Sediment Echosounder, Multibeam, Acoustic Doppler Current Profiler), multichannel seismics, sedimentological sampling and CTD measurements has been performed during the Meteor Cruise M95-CICARB along the western slope of Great Bahama Bank (GBB) and the eastern slope of Cay Sal Bank (CSB). The new data allow us to re-evaluate and sharpen the established models for carbonate platform slope facies distribution and slope geometry. Slope facies of the carbonate banks are not arranged into sediment-texture controlled and depth-dependant strike-parallel facies belts, but in a pattern controlled by the interplay of shallow-water input, succeeding sediment sorting as well as redistribution and erosion processes. This significantly deviates from facies patterns established in the literature. The following facies could be distinguished along the GBB to CSB transects: (1) At the foot of the steep submarine cliff seawards of GBB edge, there is a 300 m broad and up to 30 m deep moat with a complex shape; (2) Basinward, this moat passes over into a sediment wedge which consists of carbonate sands with peloids and Halimeda flakes in its proximal part and of muddy carbonate sands further down the slope. The surface of the sediment wedge is covered by a complex system of up to 3 m high mud waves, dissected by broad and flat channels; (3) Towards the toe of slope, the sediment wedge thins out and a facies with coarse-grained sands with abundant lithoclasts occurs; (4) In the central part of the Santaren Channel, there is a major confined drift body; drift sediments are dominated by calcareous ooze rich in components derived from the neritic carbonate factory; (5) The flank of CSB is either covered by plastered drifts with dominantly muddy sediments or by a basinward-thickening wedge of carbonate sands, depending on the exposure of the slope to currents; (7) Deep-water coral reefs occur at locations of the Santaren Channel, were bottom currents winnow the sea floor. Multichannel seismic data allow us to trace this facies pattern back in time.