THE EVOLUTION OF THE MATAGORDA/LAVACA BAY COMPLEX, CENTRAL TX COAST

An expected sea level rise of 10 to 90 cm over the next century makes a thorough understanding of coastal response to external forcing mechanisms imperative for preservation of coastal cities and wetlands. Predicted rates of sea level rise are analogous to those during the Early Holocene transgression, therefore an examination of antecedent topography and eustatic and climatic impact on the evolution of Matagorda and Lavaca Bays provides a model for future coastal response. With the acquisition of 110 km of high resolution boomer seismic data and 100 m of sediment cores, the lithofacies and seismic facies of both bays were mapped in detail revealing abrupt changes in depositional environment. These changes occur across major flooding surfaces at approximately 15 m and 10 m below sea level. Given that sea level rise in the Gulf of Mexico was relatively constant throughout the Holocene, these changes demonstrate the importance of both antecedent topography and sediment supply in controlling bay evolution. We are currently awaiting radiocarbon dates that will provide information on the timing and speed at which these changes occurred.