HOLOCENE DEVELOPMENT OF SHELF-PHASE MISSISSIPPI RIVER DELTA PLAINS

Abstract

ABSTRACT Early delta plain scientists emphasized the concept of the Mississippi River building a single delta plain at the end of the Holocene transgression beginning about 3000-4000 yBP Their work suggests that during the Holocene transgression the rate of relative sea level rise was sufficient enough to prevent delta plain development and as a consequence, the Gulf of Mexico flooded the alluvial valley until the end of the Holocene transgression. Using new geophysical, geotechnical, and radiometric techniques, recent geologic studies of the Mississippi River delta plain and continental shelf reveal the occurrence of several relative sea level stillstands during the last stages of the Holocene transgression. Three shelf-phase delta plains have been identified to date, each separated by a regional transgressive surface of erosion produced by a rise in relative sea level. Sequence stratigraphic relationships suggest that whenever relative sea level rise rates exceed 2 cm/yr for several centuries, the delta cycle process of the Mississippi River stops, and the shelf-phase delta plain undergoes regional submergence and transgression. In contrast, it appears that whenever relative sea level rise rates drop below 2 cm/yr, the delta cycle process operates building a new shelf-phase delta plain.