Stratigraphic Implications of Coarse-Grained Gravel Deposited as Overbank Sediment, Southern Illinois

Coarse-grained gravel lifted from the channel of Sexton Creek during flash flooding was deposited on the floodplain surface in three distinct lobes. The overbank gravel was laid down passively on the floodplain and no scouring of that surface preceded the depositional event. The deposits have a flat lower surface and are convex-up in shape. Similar deposits are exposed as gravel lenses in the stratigraphic sequence underlying the floodplain. Failure to recognize the overbank origin of the gravel lenses could lead to incorrect interpretations of the paleoenvironment.