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Franklin County Geology

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Neogene System

High-level stream deposits

Deposits of late Pliocene? and early Pleistocene age are mapped as chert gravels on Plate 1. The higher accumulations, which are remnants of stream-laid beds, are chert, sand, and gravel in a gray-green to red-brown clayey matrix. The lower deposits comprise chert, sand, gravel, silt, and clay. Loess deposits as much as 3 feet thick are found locally on the uplands. Colluvium and "soil" are locally as much as 25 feet thick. Loess, colluvium, and "soil" conceal much of the Pennsylvanian rocks but are not mapped on Plate 1 or discussed in the text.

The higher chert-gravel deposits containing no glacial erratics and lying at altitudes of 970 to 990 feet, about 85 to 100 feet above the Marais des Cygnes River floodplain, along bluffs north of the river (Pl. 1) between Ottawa and Richter, are judged to be of late Pliocene or early Pleistocene age. These chert gravels are well exposed in gravel pits northwest of Richter (sec. 27, T. 16 S., R. 18 E.). There the chert gravel, predominantly pebble size, and chert sand are included in a red-brown clayey matrix. No calcareous material was observed in these deposits, which probably correspond to the terrace remnants of intermediate elevation noted by O'Connor (O'Connor and others, 1955, p. 7) in Osage County.

Lower chert gravel and sand in a red-brown to gray-green clayey matrix overlie Pennsylvanian bedrock along the bluffs both north and south of the Marais des Cygnes River east of Ottawa. These terrace remnants lie at altitudes of 900 to 920 feet and are about 55 to 70 feet above the floodplain. They contain few glacial erratics, appear to be thoroughly leached, and are well exposed in several gravel pits (e.g., NE SW sec. 33, T. 16 S., R. 20 E.).

Younger Alluvium

Valley-fill material younger than the chert gravels described above was mapped as younger alluvium" (Pl. 1). A skull and jaw of Bison bison was collected from alluvial deposits along Middle Creek (NW sec. 19, T. 18 S., R. 19 E.) by the J.F. Halleys, who stated that these vertebrate fossils were found at a depth of about 15 feet. Staff members of the Museum of Natural History, The University of Kansas, identified the skull and estimated its age as late Wisconsinan to early Recent.

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Kansas Geological Survey, Geology of Franklin County
Web version July 2002. Original publication date Jun. 1963.
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