Depositional environments and conodont biofacies of the Council Grove Group (Early Permian) in the Hugoton Embayment, southwestern Kansas and Oklahoma Panhandle.

摘要

Detailed examination of cores from nine wells in the southern Hugoton Embayment indicates that strata of the Council Grove Group of Early Permian age consist of laterally continuous, mixed carbonate siliciclastic depositional sequences. The strata can be grouped into vertically repetitive units of marine carbonates and local thin marine siliciclastic units interbedded with nonmarine siliciclastics. The purposes of the study are to describe the lithofacies that make up the depositional sequences and to apply conodont biofacies analysis to interpreting the paleoenvironments.; Twelve marine and nonmarine facies and subfacies can be recognized. Marine lithofacies range from carbonate mudstones to grainstones and boundstones, shales, and sandstones deposited on a low-relief shelf. Nonmarine depositional systems are primarily represented by variegated mudrocks (red beds) that accumulated as coastal mud-rich sabkhas that form a large portion of the depositional sequences. Carbonate depositional systems developed during progradation across a deeper water open shelf that resulted in a shallowing-upward succession of facies. Each carbonate shallowing-upward succession is disconformably bounded by nonmarine mudrocks at the base and top. The lithofacies represent depositional environments that include deeper water open-shelf, shallow-water inner shelf, shallow-water to emergent shoals, and a marginal marine to nonmarine sabkha complex that comprises intertidal to supratidal algal mud flats and terrigenous mud flats.; The marine strata contain a modest, but varied conodont fauna. The fauna is dominated by representatives of Streptognathodus. Hindeodus is abundant, while specimens of Sweetognathus are common, and specimens of Ellisonia, Diplognathodus, Cavusgnathus , and Ubinates are minor constituents. Relative frequency analysis indicates that five nominative and one mixed biofacies dominate the samples and reflect environmental controls.; Conodont biofacies substantiate lithofacies interpretations that indicate that the carbonate successions represent a regressive sequence passing from open- to shallow-shelf shoal deposits. Normal marine, low- to moderate-energy environments associated primarily with mud-supported lithofacies can be assigned primarily to the Idiognathodus-Streptognathodus plexus biofacies. The Hindeodus biofacies replaces the Idiognathodus-Streptognathodus plexus-biofacies in mud-supported lithofacies possibly due to higher energy conditions, or variable salinity. The Cavusgnathus biofacies is associated with nearshore, shoal water conditions where conditions of variable salinity existed. The Diplognathodus-biofacies and the newly established Sweetognathus-biofacies occupied variable-energy, schizohaline environments common during the initial stages of transgression, or late stages of regression.