Monday, 6 October 2008: 4:05 PM
George R. Brown Convention Center, 320DE
During the last lowstand, coastal plain and piedmont rivers along the northwestern Gulf of Mexico incised valleys into the exposed shelf to an average depth of approximately 20 m. Throughout the subsequent transgression, these valleys back filled with fluvial, deltaic, bay, tidal, coastal, and offshore deposits. This study quantifies the volume of sediment sequestered on the shelf and near-shore coastal plain in these incised valleys during the most recent sea-level rise. This volume is on the order of 102 km3 over an area of 104 km2. During similar sea-level cycles a comparable volume of sediment is ultimately transferred to the slope and basin during sea-level fall. In addition to incised valley fill, a significant volume of Holocene sediment currently resides on the central Texas shelf as a mud drape. The mud drape is derived, in part, from sediment that is ravined from high-stand shelf deltas during transgression. The sand derived via this process is a major component of coastal barriers as opposed to direct river sourcing. The total volume of sediment sequestered on the shelf in valleys and in the mud drape during transgression represents a minimum measurement of the sediment flux. With the exception of the deeper central Texas shelf, reworking of this sediment during transgression and lowstand plays a key role in nourishing of lowstand deltas and fans and transgressive barriers.