Paleochannel across Louden Anticline, Fayette County, Illinois: its relation to stratigraphic entrapment of petroleum in the Cypress Sandstone.

Structure mapping on the base of the Beech Creek Limestone of Chesterian age has revealed a NW-trending saddle more than 1.6 km wide and 6 km long that crosses the Louden Anticline. This apparent depression results from the abrupt appearance of a thick, fine-grained, argillaceous limestone subjacent to the thin bed of coarse-grained, bioclastic upper Beech Creek Limestone. Sandstone beds in the underlying Cypress Sandstone were found to be thin or absent beneath this area of limestone. This saddle is believed to be a major tidal channel that breached deposits of shallow marine or eolian sands that had accumulated along the crest of the anticline.- from Authors