Architecture and Processes in the Late Pleistocene Brazos-Trinity Turbidite System, Gulf of Mexico

Badalini, Gianluca, Ben Kneller, School of Earth Sciences, University of Leeds, LS2 9JT Leeds, United Kingdom, and C. D. Winker, Shell E&P Technology Company, Bellaire Technology Center, Houston TX

Abstract

A close grid of high-resolution sleeve-gun seismic data, conventional seismic data, 2 wells with continuous petrophysical logs and discontinuous core, and NOAA multibeam seafloor images have been used to study the late Pleistocene Brazos-Trinity turbidite system. The system consists of four linked mini-basins in the northern Gulf of Mexico continental slope, three of which (up-dip) are filled up to the spill point, and one (the most down-dip) is still underfilled. The basins are connected by a surface channel system and lie downdip of a lowstand shelf-edge delta. They are relatively undisrupted by halokinesis. The sedimentary fill consists of onlap-fill packages in each basin, deposited during the last glacial (Wisconsin) event. The packages have been divided into seismic stratigraphic units calibrated by well data. Five main seismic elements have been identified: turbidite complexes (represented by a great variety of seismic facies, showing variable external geometries, and exhibiting a spectrum of margin al pinch-out styles), debris flows, condensed section, channels and levees. Detailed mapping, analyses of seismic facies, well calibration and preliminary dating results allowed us to:

• determine the architecture of the system;
• reconstruct a complex basin fill history made of high-frequency forward and backstepping of the system;
• improve our understanding on lithofacies distribution;
• demonstrate that channel levee systems do not represent the first establishment of bypass to downdip basins and are representative of the last sequence within a glacial cycle; and
• suggest an external (climatic) control on the deposition of 5th order sequences.