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Late Holocene Sedimentary Provinces, South Texas Outer Continental Shelf

1977; American Association of Petroleum Geologists; Volume: 61; Linguagem: Inglês

10.1306/c1ea3dca-16c9-11d7-8645000102c1865d

1558-9153

Gerald D. Shideler,

Methane Hydrates and Related Phenomena

The late Holocene sedimentologic framework of the South Texas outer continental shelf (OCS) from Matagorda Bay to the United States-Mexico border was studied as part of the national OCS environmental studies program associated with offshore petroleum lease sales. Late Quaternary sea-level fluctuations have resulted in the development of three genetically distinct sedimentary provinces based on textural-morphologic equilibrium criteria. Seafloor topography and surficial sediment patterns delineate a southern province dominated by relict topography of the Pleistocene and Holocene ancestral Rio Grande delta; the province is composed of a heterogeneous mixture of modern mud and relict muddy sands in textural disequilibrium with the present hydraulic regime. A northern provinc is dominated by relict topography along the southwestern flank of the ancestral Brazos-Colorado delta; it is composed of palimpsest sandy-mud deposits that have achieved partial equilibrium with present hydraulic conditions, and that appear to be undergoing some net-southward transport. A central interdelta province is characterized by a modern depositional surface; it contains an extensive modern mud blanket that appears to be encroaching southward over relict deposits of the ancestral Rio Grande delta. Surficial-sediment texture suggests a modern sediment-dispersal system characterized by net-offshore and net-southward transport components. Shallow subsurface sediments penetrated by gravity cores indicate that the modern dispersal pattern was established during earlier Holocene time b t has been modified during the later stages of the Holocene transgression. Relative to the sand facies, the mud facies has expanded and migrated shoreward with time, thus reflecting a transgressive overlap relation.