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
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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.
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Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin
The northern Gulf of Mexico margin encompasses a variety of depositional settings characterized by different drainage basin size, physiography, fluvial morphology, climatic setting, and structural and diapiric activity. This, plus the abundance of long sediment cores and platform borings from oil industry activities, make it an unparalleled natural laboratory for sedimentological and stratigraphic studies and for testing sequence stratigraphic concepts. This volume contains twelve papers describing results from high-resolution stratigraphic studies of late Quaternary strata of the northern Gulf of Mexico, from the mouth of the Apalachicola River to the Rio Grande. These papers focus on fluvial response to climate and base-level change, variations in delta growth and evolution across the shelf, lowstand delta-fan evolution, the evolution of transgressive deposits on the shelf, the preservation of these deposits. The robust chronostratigraphic frameworks developed for the different study areas allows comparison of stratal geometries produced by contemporaneous depositional systems operating under identical eustatic conditions. This volume will appeal to sedimentologists and stratigraphers interested in source to sink issues, such as how various forcing mechanisms influence strata formation on continental margins.