2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 121-6
Presentation Time: 9:00 AM-6:30 PM


ODEZULU, Christopher I., Earth Science Department, Rice University, 6100 Main Street, Houston, TX 77005, LORENZO-TRUEBA, Jorge, Earth and Environmental Sciences, Montclair State University, Montclair, NJ 07043, ANDERSON, John B., Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005 and WALLACE, Davin J., Department of Marine Science, University of Southern Mississippi, 1020 Balch Blvd, Stennis Space Center, MS 39529, cio1@rice.edu

Parts of the Texas coast appear to have experienced unprecedented landward migration in historical time, which are in the range of 1-4 m/yr. A likely cause of this change is accelerated sea-level rise, currently about 3 mm/yr in the northern Gulf of Mexico. This is five times the rate for the previous 4,000 years.

Follets Island is a transgressive island located on the upper Texas coast, an ideal location to study coastal response to accelerated sea-level rise. It is currently in a rollover phase, meaning the rate of bayline migration appears to be keeping pace with Gulf shoreline migration. In addition, the island has a limited sand supply, which makes it vulnerable to erosion during storms and relative sea-level rise. Five core transects that extend from the upper shoreface to the back barrier bay are used to constrain the thickness of washover, barrier and shoreface deposits and to estimate the sediment fluxes and the overall sediment budget for the island over centennial timescales.

Stratigraphic architecture reveals two prominent transgressive surfaces. The first is a flooding surface separating red fluvial clay from overlying bay mud and the second is a surface of erosion, ~ 2m deep, which separates back-barrier deposits from overlying shoreface/foreshore deposits. Radiocarbon ages are used to constrain the evolution of the barrier and its long-term rate of landward migration. Results from grain size analyses reveal that significant washover sands were deposited in the bay and about double this volume was deposited as sub-aerial washover deposits. Summing up the total overwash volume shows that overwash processes can account for the total volume of sand produced during shoreline erosion in historical time.

Results indicate that the current rate of the shoreline migration is unprecedented. With the current shoreline erosion and sea-level rise rate, Follets Island’s barrier is predicted to disappear in next century.