BENTLEY, SAMUEL J., Sr., Coastal Studies Institute, Louisiana State University, Baton Rouge, Louisiana; YOKO FURUKAWA and CHAD W. VAUGHAN, Naval Research Laboratory, Stennis Space Center, Mississippi

A geochemical and fabric record of combined hurricane activity and sediment bioturbation is recorded in the seabed of western Mississippi Sound. Cores were collected from Mississippi Sound near Bay St. Louis (3-4 m water depth), and were studied for X-radiography and radioisotope geochronology. ²¹⁰Pb_xs profiles reveal regions of uniformly exponential gradients alternating with zones of more irregular ²¹⁰Pb activity. X-radiographs of the cores show that two zones of irregular ²¹⁰Pb activity correspond to regions of stratified sediments that have undergone partial bioturbation. Estimated dates for the tops of these two units (apparent ²¹⁰Pb accumulation rate ~0.45 cm y^-1) are 1967 and 1985. In contrast, depth intervals characterized by uniform ²¹⁰Pb gradients display no evidence of primary stratification and are instead totally bioturbated. Based on these observations, it is likely that the basal partially stratified unit was created by the passage of Hurricane Camille (1969) and that the upper stratification was produced by any of several tropical systems that impacted Mississippi Sound between 1979 and 1986.

The most rapid bioturbation (D_b ~15 cm² y^-1, from ⁷Be profiles) occurs within the upper 3-5 cm of the seabed, below which bioturbation is slower. As a result, sediment layers that are buried rapidly below 3-5 cm depth (i.e., the ~10 cm-thick Camille layer) have the best preservation potential with respect to bioturbation. Thinner sediment layers are more readily bioturbated, producing zones where uniform ²¹⁰Pb gradients are controlled by both mixing and accumulation.

BENTLEY, SAMUEL J., Sr., YOKO FURUKAWA and CHAD W. VAUGHAN

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas