600-YEAR SEDIMENTARY ARCHIVE OF HURRICANE STRIKES IN A PROGRADING BEACH RIDGE PLAIN, SOUTHWESTERN LOUISIANA

This study tests a novel approach to paleotempestology, substituting the lateral time-depth of a prograding beach ridge plain for the vertical time-depth of an aggrading coastal lake, pond, lagoon, swamp or marsh. Trenching and coring of a beach ridge plain in southwestern Louisiana revealed six sand beds and one shell bed, interpreted as hurricane washover deposits. The sand beds are readily distinguished from enclosing marsh sediments by their higher sand content, lower organic content and contrasting microfossil assemblages. Based on the modern analogs of hurricanes Audrey (1957), Rita (2005) and Ike (2008), and consideration of nearby landfalling hurricanes in the historical record, it was determined that the storm intensity threshold of the study site is equivalent to a Category 3 hurricane. There is a wide variation in hurricane strike frequency between this site and other sites bordering the Gulf of Mexico. This variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records. The approach demonstrated by this study could have applicability at many sites around the world where beach ridge plains are subject to tropical cyclone strikes.