THE FORAMINIFERAL SIGNATURE OF HURRICANES: SOUTHWEST PASS TO THE MISSISSIPPI CANYON, GULF OF MEXICO, USA

This study investigates the utility of foraminifera as indicators of hurricane events in the northern Gulf of Mexico. Deposits from Hurricanes Ivan, Katrina, and Rita have been identified in cores from the Mississippi delta shelf using radionuclide analysis (7Be, 234Th, and 210Pb) coupled with X-radiography. By comparing foraminiferal assemblages contained within these known hurricane deposits with those of non-storm deposits in these cores and in post-hurricane surface samples from the offshore Mississippi delta, it is hoped to gain a better understanding of how hurricanes transport sediments in a neritic deltaic environment.

Box- and multi-cores as well as ponar surface grab samples were collected in a series of cruises off the Mississippi Delta in 2004, 2005, and 2007, reoccupying some stations twice or all three years. Eight cores from three revisited stations and five surface grab samples were selected in a transect trending southwest from Southwest Pass from ca. 20 m water depth to the head of the Mississippi Canyon at 170 m water depth. Two 20 mL foraminiferal subsamples were taken from each hurricane deposit in each core, as well as two samples from the pre-storm deposits and two from post-storm sediments, where available.

Identification of foraminifera was confirmed via comparison with type specimen lodged in collections of the Smithsonian Institution. ANOVAs performed on percentages of common species in several cores indicate that there is a statistically significant difference in foraminiferal assemblages between storm and non-storm deposits. Storm beds analyzed generally contained fewer foraminifera in 20 mL than non-storm units and were dominated by Textularia earlandi and often Bolivina lowmani, whereas non-storm units were dominated by Epistominella vitrea and Buliminella morgani. Further analyses will investigate foraminiferal distribution data and the provenance of individual storm beds.