PRESERVATION POTENTIAL OF EVENT-BEDDING IN A GULF OF MEXICO SALT MARSH

Numerous studies have attempted to recreate tropical cyclone landfall frequency by examining coastal sediments for evidence of storm-induced deposition. Few of these studies have sought to establish or evaluate the preservation potential of storm beds in these highly bioturbated sediments; intense mixing may destroy all but the thickest storm beds. St. Vincent National Wildlife Refuge, located in Apalachicola Bay, FL, provides a research area with minimal human impact and frequent occurrence of tropical cyclone landfall. Using a conceptual model based on Wheatcroft (1999) preservation potential is related to biologic mixing depth and intensity, storm layer thickness, and sediment accumulation rate. Radioisotopes were used to quantify mixing depth and intensity as well as accumulation rates; mixed depths were 2 - 3 cm, mixing intensity is estimated at ~30 cm^2 yr^-1, and sedimentation rates are between 0.2 and 0.4 cm yr^-1. Storm deposition was detected by changes in bulk density, magnetic susceptibility, lithology, or x-radiography. The most important control on preservation is the storm bed’s initial thickness which is expected to be highly variable for each storm. Additionally, using a numerical model (Bentley & Sheremet, 2003) it may be possible to use the bioturbation depth and intensity to establish a reasonable estimate of initial thickness. It may also be possible to determine if preservation within the salt marsh is adequate to establish salt marshes as reliable depocenters of storm related event-bedding.