Late Pleistocene Bryant Canyon Turbidite Facies: Implications for Gulf of Mexico Mini-Basin Petroleum Systems

Abstract

The Western Ancestral Mississippi shelf-margin delta fed the Bryant Canyon/Fan Turbidite System in the intraslope basin province of the northwestern Gulf of Mexico (GOM) during the Penultimate Glacial (MIS 6) lowstand of sea level. The Bryant Submarine Canyon links a chain of 15 fill-and-spill mini-basins on the continental slope. On the upper and lower continental slope, these mini-basins are narrow (1-3 km), elongate (3-6 km), and follow salt ridges. On the middle slope, the mini-basins are larger (8-15 km), semi-circular basins. Interpretation of seismic facies displayed by the mini-basin deposits reveal three main depositional facies: (1) ponded turbidites (T), (2) mass transport-deposits (MTD), and (3) bypass channelized turbidites (C). These deposits are capped at many locations by thick deposits of intrabasinal, muddy MTD wedges sourced from the high-relief walls of the mini-basins. These intrabasinal MTD wedges are interbedded with the externally derived basin deposits. Extrabasinal MTD deposits were derived from shelf-margin delta or canyon-wall failures and then transported through bypass channels to the mini-basin depocenters. The T and MTD facies deposits each make up about 40% of the basin fill and the C facies deposits comprise about 20%. The T facies deposits form perched lobes at canyon inlets into basins and ponded units on the distal sides of the basins. Channels in the C facies are similar in width (500-2000 m) and relief (20-100 ms) to channels in productive GOM subsurface mini-basins. Syntectonic activity of salt diapirs typically began midway through filling of the Bryant Canyon mini-basins and then preferentially uplifted the northern portions of basin deposits. Salt-tectonic activity in the Bryant Canyon area has caused greater basin relief and thicker capping MTDs than in subsurface mini-basins to the east (e.g., Brazos Trinity Basin IV) or west (e.g., Mississippi Canyon). The modern Bryant Canyon mini-basins exhibit the same scales (e.g., basin size, facies thickness, and channels) and depositional facies as older GOM subsurface mini-basins. Thus, the Bryant Canyon mini-basins provide excellent “modern” analogues for the subsurface Miocene to Pleistocene GOM chains of mini-basins such as in the Mississippi Canyon area. The youngest Bryant T facies deposits and their overlying incised, thick, channel deposits contain the most sand-prone facies and suggest the best potential for petroleum reservoirs in subsurface mini-basins.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018