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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 44 (1994), Pages 85-92

Glacio-Eustatic and Climatic Controls on Quaternary Alluvial Plain Deposition, Texas Coastal Plain

Michael D. Blum (1), David M. Price (2)


The Texas Gulf Coastal Plain consists of a series of low-gradient, fan-shaped alluvial plains emanating from each major river valley. Most alluvial plain surfaces have been mapped as Pleistocene Beaumont Formation or younger unnamed strata and interpreted to represent glacio-eustatically controlled deposition during the penultimate and modern interglacial highstands. This paper summarizes recent studies that reexamine construction of Beaumont and younger alluvial plains of the Colorado River in response to interacting glacio-eustatic and climatic controls.

Mapping from satellite imagery, field documentation of geomorphic and stratigraphic relationships, and consideration of the stratigraphic significance of surface and buried soils suggest that Beaumont and younger alluvial plains consist of multiple cross-cutting and/or superimposed valley fill complexes of widely varying age and may represent the last 600 ky or more. Valley fill complexes become partitioned by initial lowering of sea level below interglacial highstand positions, when channels rapidly incise and valley axes become fixed in place as they extend across the newly subaerial shelf. While shorelines remain basinward of highstand positions, the remainder of the alluvial plain is characterized by nondeposition and soil development. During this time, multiple episodes of lateral migration, aggradation, degradation, and/or floodplain abandonment occur within incised and extended valleys in response to climatic controls on discharge and sediment supply. This creates a composite basal valley fill unconformity, as well as minor allostratigraphic units within the valley fill complex. With late stages of transgression and highstand, valleys fill at paces set by upstream controls on sediment delivery. As valley filling nears completion, veneers of floodbasin sediments spread laterally to bury soils developed on downdip margins of the alluvial plain. Complete valley filling during highstand is one of several processes that promotes avulsion, with possible relocation of valley axes and refocusing of sediment input before the next sea-level fall.

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