THE FORAMINIFERAL SIGNATURES OF HURRICANE EVENTS FROM THE MISSISSIPPI RIVER DELTA, USA

Tropical cyclones passing over the Mississippi River delta trigger off-shelf flow of sediment causing deposition of event layers on the shelf. The event layers off the Mississippi delta caused by the recent hurricanes Rita, Katrina and Ivan exhibit foraminiferal assemblages distinct from the non-event sediment that overlies and underlies them. The event layers are characterized by sparse foraminifera and a high relative abundance of Textularia earlandi and Ammonia tepida. This research evaluates whether the foraminiferal signature of hurricanes can be preserved over a multi-decadal time-scale (based on Pb-210 age determinations). Three kasten cores (approximately 2m in length) were collected in 2007 at depths of 59 m, 75 m, and 87 m on a transect between Southwest Pass and the Mississippi Canyon. X-radiographs showed less-defined hurricane units compared to post-Katrina cores, and these were used to determine sampling locations. Samples were also taken in 10-cm increments to determine if foraminiferal signatures revealed hurricane units were detectable by grain size. Preliminary research has yielded assemblages rich in foraminifera and dominated by Epistominella vitrea and Uvigerina peregrina. T. earlandi and A. tepida are in very low amounts. These observations suggest that the sedimentological and foraminiferal signature of hurricanes on the Mississippi River delta over a multi-decadal timescale may be present but significantly muted as a result of bioturbation.