Depositional Framework of Louisiana Shelf and Upper Slope

James M. Colman

Approximately 500 deep offshore foundation borings and thousands of kilometers of high-resolution seismic data form a data base for the first comprehensive appraisal of the near-surface sedimentary framework of the Louisiana shelf and upper continental slope. These data are used to document sedimentological characteristics, spatial depositional patterns, and seismic/lithofacies responses during three complete sea level cycles over the entire continental shelf/upper slope of offshore Louisiana.

Sedimentation during periods of high sea level is characterized by (a) thin, slowly accumulated depositional sequences, referred to as condensed sections, (b) calcareous-rich deposits, including hemipelagics and shell hashes, (c) wide lateral continuity, and (d) high-amplitude acoustic response. Sedimentation during periods of low sea level is characterized by (a) rapidly accumulated sequences of variable thickness, referred to as expanded sections, (b) coarse-grained clastic deposits, including abundant sands and gravels, (c) well-defined depositional trends, and (d) a wide variety of seismic responses.

Even though the data set covers only a short period of geologic time (240,000 years), these high-frequency events are responsible for the deposition of excellent reservoir-quality facies in well-defined and predictable trends and can be used as a model for exploration in the Gulf Coast Neogene sedimentary sequence.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.