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Abstract: Shelf-Slope Break Sedimentation and Erosion During Deposition of the Claiborne Group in Colorado and Wharton Counties, Texas

Robert A. Hull

Geological and geophysical data over a 6,500 square kilometer area across Wharton and Colorado Counties, Texas, are utilized to understand sedimentary processes that occurred along the shelf-slope break of the Eocene Claiborne Group. Sedimentation models based on seismic profile data and well log data are critical to the oil and gas industry.

It can be demonstrated that while deposition on the shelf generally took place in middle neritic water depths, sediment did bypass the shelf expanding into deeper waters during deposition of most of the formations of the Claiborne Group. Even sands of the Yegua Formation were transported basinward from the deltaic and fluvial depositional environments updip in Colorado County, bypassing shelf deposition. In general there was little sedimentation taking place along the shelf except during short periods of transgression. Downdip at the shelf-edge subsidence rates were higher and sedimentation became more aggradational. Possible drops in sea-level and/or changes in depocenters brought about downdip deposition of sediment beyond the shelf edge during most periods of Yegua-age deposition. t appears that even during low accumulation times on the shelf, sediment was being deposited downdip beyond the shelf-edge.

Slumping along the over-steepened shelf margin was common during Yegua deposition. The style of Yegua age slumping was controlled by many factors including the placement of the earlier Wilcox shelf. During high sedimentation times, erosion of the shelf margin from slump mass scrape appears to have taken place.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana