Possible Relict Meanders of the Pliocene Mississippi River and Their Implications

Abstract

AbstractAlthough the late Quaternary history of the Mississippi River, the largest North American river, has been intensely studied, its Pliocene history is largely unknown. We assert that large relict meander bends (oxbows) of the Pliocene Mississippi River are preserved as arcuate valleys of local streams in the northwest area of the state of Mississippi. These arcuate valleys are within the Pliocene Upland Complex stratigraphic unit that occurs as a high-level alluvial terrace along the lower Mississippi River Valley. Outside these arcuate valleys, the Upland Complex is a braided-river gravel deposit that shows southward (downvalley) paleoflow directions. Interiors of the arcuate valleys are occupied by Upland Complex point bar deposits with large-scale cross-bedding showing a range of paleoflow directions, commonly upvalley flow indicative of a meandering regime. We used measurements of the radii of the putative relict meander bends and of their paleochannel widths to estimate paleodischarge of the Pl...