Abstract: Erosion and Deposition in Northern Gulf of Mexico Estuaries

Wayne C. Isphording

Nearly two dozen estuaries fringe the southern margin of the United States in the Gulf of Mexico region. These estuaries annually receive approximately 50% of the nation's total runoff and, as such, serve as depositional basins for some 65 million tons of sediment each year. While it is an established geological principle that the ultimate fate of an estuary is to become infilled with sediment, when depositional rate data from some Gulf estuaries are examined it becomes apparent that either (1) present-day rates of infilling differ markedly from those in the past or (2) natural events periodically occur that cause extensive erosion and scouring of the estuaries (or both). While major fluctuations in sea level and eustatic uplift could explain large-scale scouring during the ice ages, cause for the same during the postglacial period is not as apparent.

Examination of sediment data from several Gulf estuaries, however, does provide an explanation as to why these features may well persist for time intervals that are considerably longer than would be predicted by their annual infilling rates. Evidence present in several of the bays shows that major storms have removed significant quantities of sediment, thereby substantially extending the life of these water bodies. Because of the proclivity for such storms in the Gulf of Mexico region, it is likely that many estuaries have been impacted by similar events or will be impacted in the future. Hence, prediction of the longevity of a Gulf Coast estuary from depositional rates, and even those rates supported by radiocarbon dating, is hazardous at best. In the space of a few hours, a single s orm can remove a volume of sediment that was deposited over hundreds, or even thousands, of years.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994