The purpose of this paper is to present the stratigraphic framework of rocks previously referred to the Pliocene Rexroad Formation in canyons immediately north of the Cimarron River in southern Meade County, Kansas (figure 1). This project is part of a larger effort to develop a refined biostratigraphic model for the entire Meade Basin, leading eventually to a detailed examination of small mammal community evolution over at least the past five million years. In a series of studies from 1936 until his death in 1973, the late C.W. Hibbard and his students provided a faunal and stratigraphic succession for the basin (see bibliography of C.W. Hibbard in Smith and Friedland, 1975). The lowest part of this succession includes mammalian assemblages from the Rexroad Formation and rocks referred to the Rexroad Formation. Most of these older assemblages were recovered from localities in upland areas away from the Cimarron River where stratigraphic correlation is very difficult because the sites are located in small outcrops isolated by ranchand farmlands. Early in this project we recognized that the longest sections and more extensive exposure in relatively deep canyons along the Cimarron River might provide a superposed series of mammalian localities from which a more refined biostratigraphy could be determined.
Prior to our work, sites reported from the north bank of the Cimarron River included only KU Loc. 22 in Keefe Canyon and UMMP K1-47 in Fox Canyon. The mammalian assemblages from these sites are referred to as the Keefe Canyon and Fox Canyon local faunas (Hibbard and Riggs, 1949; Hibbard, 1950). Although the stratigraphy near the quarries was described in these reports, correlations between the localities were only briefly discussed, usually by reference to stratigraphic position relative to a formal rock unit (?Meade Gravels?), or a presumed widespread caliche. Stratigraphic and paleontologic work carried out in this area has led to the discovery of many new fossil localities and indicates a more complex stratigraphy than that presented in these older reports.
Below, we first provide a stratigraphic overview of the rocks exposed along the north bank of the Cimarron River and introduce the fossil localities and lists of rodents recovered from them. We also briefly discuss some interpretive problems with specific localities. This is followed by a detailed discussion of the basis for correlations of the fossil localities, utilizing both stratigraphic and faunal information. Detailed stratigraphic descriptions are provided in Appendix I, and preliminary mammalian faunal lists for fossil localities are given in Table 1. We conclude with a synthesis of the geological and faunal correlations leading to a biostratigraphic framework for early Blancan local faunas of the region.
In this paper we do not use the formal name ?Rexroad Formation? for the rocks along the Cimarron River. Our stratigraphic work in progress is revealing what we think are problems involving the inferred stratigraphic position, and consequent correlation of, some rocks outside the type area to rocks within the type area of the Rexroad Formation. These problems directly involve rocks along the north bank of the Cimarron River, which were referred by Hibbard (Hibbard and Riggs, 1949; Hibbard, 1950) to the Rexroad and ?Meade? (=Ballard) Formations. Until we have resolved the lithostratigraphic position of the type Rexroad Formation to the rocks along the Cimarron River, we refrain from applying a formal nomenclature to the rock units between Keefe and Fox Canyons.
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