CONTRASTING PLEISTOCENE AND HOLOCENE FLUVIAL SYSTEMS OF THE LOWER PEARL RIVER, LOUISIANA AND MISSISSIPPI, USA

The geologic mapping of eastern St. Tammany Parish, Louisiana, and adjacent parts of Mississippi for the preparation of 1:24,000 and 1:100,000 scale maps has revealed the presence of three, possibly four, distinct fluvial systems related to the Pearl River. The oldest fluvial system lies on the surface of the Hammond alloformation of the Prairie Allogroup. It consists of well-defined relict meander belts of the Late Pleistocene Pearl River with relict sinuous courses and oxbows with large meander loops. One relict course ends in a delta-like feature. Another one is associated with a large, well-defined crevasse splay complex. Within the southeastern corner of St. Tammany Parish, an isolated relict channel segment appears to be a second, younger fluvial system characterized by an unusually deeply incised channel. A third, youngest, Pleistocene fluvial system consists of relict courses and oxbows exhibited by the surfaces of the Gum Hollow and Mitchell Hammock alloformations of the Deweyville Allogroup. These relict courses and oxbows, as clearly seen in the eastern half of the Industrial 1:24,000 quadrangle, Pearl River County, Mississippi, are characterized by channel widths and radii that greatly exceed those of the modern Pearl River. The modern Pearl River is characterized by an anastomosing channel system. Individual channels that compose it are sinuous and have actively meandered. These contrasting channel systems preserve a discontinuous record of how the Pearl River has adjusted to changes in climate, discharge, and base-level during the Pleistocene and Holocene epochs.