INVESTIGATIONS OF THE LITHO- AND SOIL-STRATIGRAPHY OF PLIO-PLEISTOCENE STRATA IN THE CIMARRON RIVER VALLEY, SOUTHWESTERN KANSAS

The High Plains Ogallala Drilling Program at the Kansas Geological Survey is designed to advance the scientific understanding of the sedimentary facies, stratigraphy, and paleoenvironmental conditions of the High Plains succession. Preliminary results from part of this program, focused on the Plio-Pleistocene strata, are presented herein. These units have received limited attention, in part, because of a lack of good exposures as well as the fact that Plio-Pleistocene stratigraphic sequences have, until recently, been extremely difficult to date.

A transect of three cores was drilled across the Cimarron River valley in southwestern Kansas, capturing the stratigraphy of two distinct alluvial fills as well as the Ogallala Formation into which the fills are inset. The valley fills contain a total of 7 paleosols, representing episodic landscape stability. Paleosols are typically silty or silty-clay loams with Bk and Btk horizons and stage I-II carbonate morphologies. The paleoenvironmental record preserved in these paleosols is being investigated through δ¹³C and δ¹⁸O analyses. Age control is being provided through ¹⁴C and OSL dating techniques. One core was drilled on the High Plains surface and captures the Ogallala Formation as well as the overlying eolian succession. The eolian succession is 20 m thick and comprises silty and sandy facies. Eight paleosols are preserved in this sequence. Paleosols are typically 1-3 m thick, with Bk-Btk-BC-C horizonation, and have stage II to III carbonate morphologies. The eolian sediments bury a thick (7.5 m) well-developed pedocomplex formed in alluvium. This pedocomplex represents slow sedimentation accompanied by pedogenesis during the final phase of Ogallala deposition. The dating of this paleosol, through Al/Be dating of quartz and U/Pb dating of volcanogenic zircons, will help address long standing questions regarding the incisional and depositional history of the High Plains during the late Cenozoic.