Slope Facies Controlling Processes Along Western Great Bahama Bank

Abstract

Models for carbonate platform slope deposition are generally thought to be line-sourced sediments with the grain size distribution that is controlled by down-dip orientation of sediment transport. Increased sedimentation is expected on the leeward side of the platform, such as the western slope of GBB, that receives the fines from the producing platform. High-resolution multibeam, subbottom profiles, and a new map based on morphological classification of the area from attributes of bathymetry data, reveal the duality of the slope processes in an unprecedented way. The slope facies distribution is a result of: 1) platform-derived gravity-driven sediment transport and 2) the sediment distribution parallel and down-slope by benthic and cascading density currents, respectively. The classic interpretation of the platform margin acting as line-source for slope sediment facies distribution should be refined. Karst features produced during platform emergence influences cascading density currents by confining and channelizing the flow. The regular nature of these karst features (grooves) is responsible for the regular spacing of the plunge pools and gullies. As such, the gullies dissecting the upper slope along southwestern GBB have a hydrodynamic origin. Grain size distribution is not solely controlled by down-dip, but rather reflects the complex interplay of bathymetry and sediment transporting currents. Changes in inclination provide hydraulic jumps to transform current regime of downslope currents, which ultimately results in the deposition of characteristic bedforms. Slope parallel currents erode and redistribute the sediment along platform strike (winnowing), leaving the coarse-grained sediment fraction behind.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015