The Impact of the Brazos Deltaic System on Upper Slope Stratigraphic Sequence Evolution
Published:December 01, 2013
Carmen M. Fraticelli, John B. Anderson, 2013. "The Impact of the Brazos Deltaic System on Upper Slope Stratigraphic Sequence Evolution", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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In the offshore of East Texas, fluvial deltaic systems did not significantly impact upper slope stratigraphic sequences until very late during a sea level fall. During the last glacial-eustatic cycle, the ancestral Brazos River system prograded across the shelf depositing six separate delta lobes that compose the highstand systems tract. Over the same period, sedimentation on the upper slope was characterized by a condensed section. During deposition of the late Highstand Systems Tract, the Brazos fluvial-deltaic system deposited a shelf-margin delta 5 km updip of the shelf-edge, causing an increase in sedimentation on the upper slope. As sea level continued to fall, the Brazos system shifted to the east to merge with the Trinity-Sabine shelf-edge delta system. However, upper slope sedimentation during formation of the lowstand systems tract did not dramatically decrease with the removal of the updip source, rather a thick healing phase wedge developed. Such sedimentary wedges constituted a significant component of slope stratigraphic sequences during both the last, and previous, glacial-eustatic cycles. Development of these healing phase deposits intrinsically was connected to a shelf-edge deltaic source, but this source did not need to be located directly updip. In the east Texas slope, the sediments were sourced by a shelf-margin delta to the east of the study area, and transported westward along the upper slope.
Despite its name, healing phase deposition is not tied to a specific interval of the eustatic cycle. It can occur at anytime between late highstand through the transgression, as long as a shelf-edge system exists.