Variability of Slope Morphology and Processes along Southwestern Great Bahama Bank

Jo, Andrew; Eberli, Gregor P.; Grasmueck, Mark

Understanding the processes of carbonate slope deposition has been greatly enhanced with the acquisition of multibeam bathymetry, backscatter, and sub-bottom profiles surrounding modern carbonate platforms. The data set of this study provides a magnificent visualization of the slope and basin morphology along the southwestern Great Bahama Bank. The data reveal a great variability of slope deposits, mounds, and large mass transport complexes along 100 km of bank margin.

The 6,512 km² study area contains three depositional environments: 1) a slope and margin with an onlapping mud wedge, channels, sediment lobes, mounds, and mass transport complexes, 2) a basin floor covered by homogeneous soft sediments, and 3) a northeast sloping sea-floor with pockmarks.

The uppermost slope is steep, with declivities varying from 30° to 76°, with the steepest declivity found in the southernmost portion. The steep slope is onlapped by a soft sediment wedge, which is up to 125 m thick and thins basinward. On top, the mud wedge creates a moat that is up to 30 m deep and is ornamented by regularly spaced gullies. In the middle and lower slope, channels and sediment lobes funnel coarse-grained sediment 20 km out into the basin floor. The toe-of-slope and adjacent basin floor are in some places littered by large boulders and large blocks that are up to 30 m high and 500 m long. These debris fields are partially buried remnants of mass wasting complexes. In the southernmost area, multiphase mass wasting complexes with a slump scar over 11 km long sheds large blocks 13 km into the basin. In the western part of study area, 22 pockmarks are scattered along a gently dipping basin floor. These pockmarks are up to 130 m deep and 2,200 km wide, and to a variable degree filled with sediment.

Backscatter data and sub-bottom profiles, calibrated with cores and observations from the northern part of the Great Bahama Bank, give insight into the sediment characteristics and distribution. The margin and upper slope portion are covered by 6-7 km wide tracts of muddy sediments. The sediment type changes abruptly in the ~20 km wide middle to lower slope, where coarse-grained sediment dominates between the large blocks and channels. The sediments finally transition into fine-grained basin floor sediments.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013