Abstract: Suspended-Sediment Distribution on South Texas Outer Continental Shelf, Northwest Gulf of Mexico

Gerald L. Shideler

The regional distribution of suspended sediments on the South Texas Outer Continental Shelf (OCS) from Matagorda Bay southward to the United States-Mexico border was evaluated as part of a regional environmental studies program. Quasisynoptic measurements of water-column turbidity and temperature were obtained over the 25,000 sq-km area during the late fall season, 1975. Relative turbidity was determined in terms of both water-transmissivity measurements obtained with a continuously recording light-beam transmissometer, and total-particle counts (0.63 to 81µ range) obtained by electronic-particle counting of collected water-column samples.

South Texas OCS waters exhibit both lateral and vertical turbidity gradients, with wide ranges of optical transmissivity (0 to 99% T/m) and particle counts (5 to 237 × 10⁴/cc). Increasing suspended-sediment concentrations shoreward reflect increasing wave-surge intensity and coastal source areas, with estuarine inlets functioning as the dominant contributors of sediment flux. Regional water thermostructure and transmissivity patterns during the fall season also suggest the landward intrusion of a relatively warm, clear gulf water mass from the adjacent continental slope into the shelf environment. The mixing of relatively transparent slope waters with the shallower and more turbid indigenous shelf waters appears to have substantial influence in establishing regional sh lf turbidity patterns. The lateral extent of shelf intrusion by adjacent continental-slope waters appears to increase southward toward Mexico, and it is associated with a progressive southward development of a shelf near-bottom nepheloid layer.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC