Controls of the Antecedent Topography from Holocene Carbonate Shoals: Ocean Cay, Western Great Bahama Bank

Francisco E. Cruz¹ and Gregor P. Eberli^2
1E&P-EXP, PETROBRAS S.A, Rio de Janeiro, Brazil
²Comparative Sedimentology Laboratory, University of Miami, Miami, FL

High-resolution seismic profiles across the Holocene carbonate shoals on the western, leeward margin of Great Bahama Bank reveal variable Pleistocene topography below the shoal complex that influenced sediment distribution and morphology of carbonate shoals. Antecedent topography and shoal geometry were interpreted from 120 km of shallow, high-resolution sub-bottom profiles. Around Ocean Cay attributes including grain type and U/Th age of Holocene deposits within the shoals were obtained from bottom sediment samples. North of Ocean Cay, a laterally continuous and thick sand belt (the Cat Cay Ooid Shoal) is situated behind and not on a Pleistocene high, indicating that Holocene sediments initially accumulated in the more protected area. In contrast, the Ocean Cay tidal deltas exhibit laterally discontinuous bar belts, alternating with inlets floored by rocky bottom and areas covered with sea grass. Thin sand bodies, mostly skeletal in composition, developed during early stages of bank-flooding on a shallower and undulated Pleistocene surface. Distribution and morphology support the interpretation that Holocene sediments north of Ocean Cay initially accumulated east of a rock ridge, over a more protected area than to the south of this island. This ridge acted as a barrier to offbank transport of sediments across the bank-margin. The Pleistocene surface underlying the Ocean Cay tidal deltas affected sediment distribution as flow across the bank-margin was constrained by inlets, causing a net bankward transport during initial stages of bank-flooding. This study documents the influence of antecedent topography on sediment distribution, morphology and thickness of a shoal complex at the western margin of Great Bahama Bank and illustrates the heterogeneity of carbonate systems at bank-margins of shallow carbonate platforms.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas