MORTON, ROBERT A., JACK L. KINDINGER, JAMES G. FLOCKS, U.S. Geological Survey, St. Petersburg FL; and LAURA B. STEWART, Texaco Exploration and Production, Midland TX

Abstract: Climatic-Eustatic Control of Holocene Nearshore Parasequence Development, SE Texas Coast

Sediment cores, seismic profiles, radiocarbon dates, and faunal assemblages were used to interpret the depositional setting and geological evolution of the southeastern Texas coast during the last glacio-eustatic cycle. Discrete lithofacies and biofacies zones in the ebb-dominated Sabine Lake estuary and adjacent chenier plain record alternating periods of rapid marine flooding and gradual shoaling related to linked climatic/eustatic fluctuations. Monospecific zones of Rangia cuneata and Crassostrea virginica, respectively, indicate high freshwater outflow followed by invasion of marine water, whereas intervening organic-rich zones record bayhead delta deposition.

High-frequency parasequence stacking patterns within the valley fill and across the adjacent interfluve reflect an initial rapid rise in sea level about 9000 yr BP that flooded abandoned alluvial terraces and caused onlap of Holocene marsh in the incised valley. Next was a phase of slowly rising and oscillating sea level when the incised valley was filling with fluvially-dominated estuarine deposits, and then a maximum highstand (+1 m msl) about 5000 yr BP that flooded the former subaerial coastal plain between the incised valleys and constructed the highest beach ridges. Between 3500 and 1500 yr BP, sea level oscillated and gradually fell causing, a forced regression and rapid progradation of both the chenier plain and regressive barrier islands. The only significant sand deposits in the valley fill are (1) falling-stage and lowstand-fluvial sediments between the basal sequence boundary and transgressive surface unconformity, and (2) highstand beachridge sediments of the chenier plain. 

AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana