Abstract: Sediment Facies, Depositional Geometries and Sequence Boundary Architecture on Northern Great Bahama Bank: A Modern Exploration Model for Carbonate Platforms

Stephen K. Boss, A. C. Newmann

Holocene carbonate deposits and the Holocene-Pleistocene Sequence Boundary of northern Great Bahama Bank were mapped using high-resolution seismic profiles, cores and submarine excavations. Examination of sediment facies, depositional geometries and sequence boundary architecture provides insight into dynamics of carbonate sedimentation during the most recent phase (<6 ky) of carbonate platform flooding and yields a refined model of transgressive sequence development which assists prediction of potential reservoir-quality deposits on ancient carbonate platforms.

Within 50 km of the Great Bahama Bank margin, the dominant sediment facies is a medium-to-fine-grained (500-125 microns), well-winnowed (<5% mud), peloidal sand of normal marine affinity typical of reservoir facies observed for ancient carbonate platforms. However, the potential reservoir quality of this sand is strongly influenced by its depositional geometry. Across the bank-top, these sands are relatively thin (<4 m) and submarine cementation can be extensive, occluding much of the primary porosity. In contrast, thick (5-15 m), uncemented accumulations of this sand are most common near the platform margin and occur as wedge-shaped deposits leeward of topographic highs (submerged rock ridges) on the Holocene-Pleistocene Sequence Boundary. Asymmetry of early transgressive seque ces with thin, cemented sands across the platform top and thick, uncemented sands along the platform margin may explain the occurrence of off-structure (i.e. platform margin) petroleum production and reservoir contiguity observed in some ancient platform settings.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994