DEPOSITIONAL ENVIRONMENTS OF THE QUARTERMASTER GROUP: EVIDENCE OF ACID SALINE LAKES AND SOILS IN WEST-CENTRAL KANSAS DURING THE LATE PERMIAN?

There has been controversy concerning the depositional history of Permo-Triassic red beds and evaporites. Recent studies of the Nippewalla Group of Kansas suggest these red beds and evaporites formed in acid saline lakes and adjacent environments. However, the overlying late Permian Quartermaster Group has not been as well studied. The goal of this study is to determine the depositional environments of the Whitehorse Sandstone, Day Creek Dolomite, and Big Basin Formation of the Quartermaster Group of Kansas.

We documented sedimentary characteristics of the Quartermaster Group as found in the Amoco Rebecca K. Bounds core of Greeley County, west-central Kansas. In this exceptionally preserved core, the Quartermaster Group is ~212 feet thick. We used measured sections, petrography, and XRD analysis for depositional interpretation. Field work in Barber and Clark Counties in southcentral Kansas provided supplemental data.

The Whitehorse Sandstone consists of red halite/gypsum cemented sandstones, siltstones, and claystones exhibiting small-scale ripple marks and ripple cross-bedding, mud drapes, mudcracks, soil slickensides, root features, and ped structures. These features suggest episodic flooding and desiccation typical of dry mudflats, as well as fluctuating water tables in adjacent soils.

The Day Creek Dolomite is composed mainly of bedded gypsum/anhydrite with some finely laminated red siltstones. Planar laminae, ripple marks, and mudcracks in gypsum/anhydrite may be indicative of an ephemeral saline lake environment.

The Big Basin Formation is composed of red sandstones and siltstones exhibiting small-scale ripple marks and cross-bedding, mudcracks, small ball and pillow structures, and soil slickensides. These features suggest formation in mudflats and soils.

Our results suggest that the Quartermaster Group in western Kansas formed in extremely dry to moderately dry continental environments that became slightly more humid and less saline from the middle to late Permian. Environments were relatively similar to the underlying Nippewalla Group, which contains fluid inclusion evidence of extremely low pH lake and groundwaters. The presence of red beds with gypsum/anhydrite and paucity of carbonates and fossils suggest these units may have been associated with acid saline waters.