Abstract

A geochemical and fabric record of combined hurricane activity and sediment bioturbation is recorded in the muddy seabed of western Mississippi Sound. Cores collected from Mississippi Sound near St. Louis Bay have been analyzed using X-radiography, radioisotope geochronology, and a multi-sensor core logger (MSCL). MSCL data reveal two prominent maxima of compressional wave speed and bulk density that correspond to zones of sandy lenticular bedding in a matrix of bioturbated mud evident in X-radiographs. ²¹⁰Pb and ¹³⁷Cs geochronology (apparent accumulation rate 0.3 cm y^-1) suggest these sandy beds to be partially preserved event layers produced by an unnamed hurricane in 1947 and Hurricane Camille (1969).

Sedimentary fabric and geochronology data indicate that sedimentation associated with hurricanes comprises ~50% of the local sediment budget over the last ~55 years. Also, preservation potential of event layers is strongly dependent on the timing and magnitude of erosion and deposition events as well as depth and rate of bioturbation. Both hurricane-induced erosion and bioturbation appear to rework the study area seabed to depths of at least 5-10 cm. As a result, event layers that are buried rapidly below ~10 cm depth have the best preservation potential, whereas thinner sediment layers are more readily reworked by subsequent storms and bioturbation.