Late Pleistocene Bryant Canyon turbidite system: Implications for Gulf of Mexico minibasin petroleum systems

Abstract

The western ancestral Mississippi shelf-margin delta fed the Bryant Canyon turbidite system in the intraslope basin province of the northwestern Gulf of Mexico (GOM) during the penultimate glacial lowstand of sea level (130–160 year BP). The Bryant Canyon links a chain of 15 fill-and-spill minibasins on the continental slope. On the upper and lower continental slopes, minibasins are narrow (1–3 km), elongate (3–6 km), and follow salt ridges. On the middle slope, minibasins are larger (8–15 km) semicircular basins. Three main depositional facies are recognized based on seismic-facies interpretation: (1) ponded turbidites (T), (2) mass-transport deposits (MTDs), and (3) bypass channelized turbidites (C). Thick, intrabasinal, muddy MTD wedges sourced from high-relief internal walls of the minibasins alternate with and frequently cap externally derived deposits. Tabular extrabasinal MTD deposits originated from shelf-margin delta or canyon-wall failures upslope. The T and MTD facies deposits each make up approximately 40% of basin fill, and the C facies deposits comprise approximately 20%. The T facies deposits form perched lobes at canyon inlets into basins and ponded units on distal sides of basins. Channels in the C facies are similar in width (500–2000 m) and relief (20–100 ms) to channels in productive GOM subsurface minibasins. Syntectonic activity of salt diapirs typically began midway through filling of Bryant Canyon minibasins and then preferentially uplifted northern portions of basin deposits. Local salt-tectonic activity caused greater basin relief and thicker capping MTDs than in subsurface minibasins to the west (e.g., Brazos-Trinity Basin IV) or east (e.g., Mississippi Canyon). Bryant Canyon minibasins provide excellent modern analogs for subsurface Miocene to Pleistocene GOM chains of minibasins because of similar scales and depositional facies. 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 minibasins.