ENOS, PAUL, and F. E. ABEGG,* University of Kansas, Lawrence, KS
The lower member of the St. Louis Limestone (Meramecian) contains two anhydrite intervals in the Hugoton embayment of southwestern Kansas. Anhydrite intervals are 20.4-43.6 and 9.8-12.8 m thick and are separated by 8.5-17.7 m of skeletal, oolitic, and peloidal carbonates that were deposited as an influx of marine waters interrupted evaporite deposition.
Anhydrite structures are dominantly mosaic. Carbonate matrix is typically less than 20%. Individual anhydrite beds are up to 8.2 m thick and are interstratified with peloid to ooid grainstone to packstone, lime mudstone, dolomite, algal boundstone, and skeletal packstone to wackestone. Thickness, interbedded subtidal strata, rarity of subaerial exposure features, and sparseness of carbonate matrix suggest subtidal deposition of the anhydrite. Restricted conditions probably resulted from oolite-skeletal shoals in the underlying Salem Limestone.
North and east of the preserved anhydrite, the lower St. Louis is marked by breccias with sharp bases and upward gradation into in situ brecciated and fractured carbonates. Calcite pseudomorphs after gypsum, length-slow chalcedony spherulites, and megaquartz with anhydrite inclusions indicate the former presence of evaporites. Brecciation probably resulted from groundwater dissolution during subaerial exposure associated with the sub-Pennsylvanian unconformity. Anhydrite is preserved only in the deeper portions of the Hugoton embayment. Distribution of anhydrite and solution-collapse breccias indicate that St. Louis evaporites were deposited throughout most of the Hugoton embayment of western Kansas, a much wider aerial extent than previously known.
AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)