Late Quaternary Stratigraphic Evolution of the West Louisiana/East Texas Continental Shelf
Julia S. Wellner, Sabrina Sarzalejo, Martin Lagoe, John B. Anderson, 2004. "Late Quaternary Stratigraphic Evolution of the West Louisiana/East Texas Continental Shelf", Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin, John B. Anderson, Richard H. Fillon
Download citation file:
High-resolution seismic data, boring descriptions, and core samples were used to conduct a sequence stratigraphic analysis of the west Louisiana and east Texas outer-shelf and upper-slope depositional systems formed during the last glacioeustatic cycle. The main objective of this research was to see how these systems responded to falling and rising sea level and how the delivery of sediment to the shelf responded to climatic fluctuations.
During the Stage 5 to Stage 2 highstand, the relatively high-sediment-supply western Louisiana fluvial-dominated delta reached the outer shelf and formed an extensive sand body. A nearly continuous ridge of salt diapirs on the shelf edge blocked offshore sediment transport, forcing the delta to prograde to the west. During the last glacial maximum, the western Louisiana fluvial system shifted to the east so that only prodelta clays were deposited in the study area. The Trinity, Sabine, and Brazos rivers merged on the shelf and formed an incised valley that extended to the outer shelf. Sediment bypass to upper-slope minibasins occurred at this time. The rise in sea level during the transgression resulted in the development of thick and complex shelf-edge deltas associated with the Trinity–Sabine–Brazos fluvial system. Prograding deltaic sediments and sediment gravity flows were deposited in minibasins situated between diapiric uplifts. Remobilization of salt caused considerable displacement of these deposits. The Brazos River then shifted to a new valley situated west of the study area, greatly reducing sediment supply to the shelf-margin delta.
Our results show that there is no simple relationship between sea level and outer shelf–upper slope deposition in the study area. The two deltas that existed were active at different times, and the sand bodies associated with these deltas have different sequence-stratigraphic settings. The western Louisiana delta is a highstand delta that is situated between the Stage 5e maximum flooding surface and the Stage 2 sequence boundary. The latter surface is poorly defined, because this was an interfluve during the Stage 2 lowstand. There is no slope fan associated with this system. The Trinity–Sabine–Brazos shelf-margin delta formed mainly during the early transgression, and its sandy distributary-mouth-bar complex is situated above the Stage 2 sequence boundary. Sediment bypass during the lowstand nourished slope fans within minibasins.