Stratigraphy of the Pre-Greenhorn Cretaceous Beds of Kansas

Abstract

Field work undertaken primarily to determine the occurrence and ceramic properties of clay deposits in the pre-Greenhorn Cretaceous beds of central and north-central Kansas has resulted in much detailed stratigraphic information. The newly acquired data indicate needs for reclassification of these beds.

Numerous classifications have been proposed for the Cretaceous rocks of Kansas by various workers during the past 75 years. For the most part, the proposed formations have been either inadequately defined or have been of such non-persistent nature that they were not useful outside of the type area.

The classification proposed in this paper is as follows: The oldest Cretaceous rocks known in Kansas, which are of continental origin, are classed as the Cheyenne sandstone. Dark marine shale and sandstone above the Cheyenne sandstone are assigned to the Kiowa shale. These two stratigraphic units, named from Kiowa county, Kansas, have been recognized by workers for many years and can be correlated with beds in the north-central Kansas region.

Nonmarine clay and sandstone deposits that overlie the Kiowa shale are here designated as the Dakota formation. The Dakota is limited upward by the base of the Graneros shale. The formation is here subdivided into two members: the Terra Cotta clay member at the bottom and the Janssen clay member at the top. The marine shale above the Dakota formation and below the Greenhorn limestone is classified as the Graneros shale.

The continental or near-shore Cheyenne sandstone is thought to represent deposits made near the strand line of the northward-advancing Cretaceous sea. The Kiowa shale was deposited in a relatively shallow sea. The Dakota formation comprises clay and sand deposited on flats not far above sea level. Deposition of the Dakota beds was terminated by a re-advance of the sea, and in this sea the marine shale and sandstone of the Graneros formation accumulated.