Conodont biostratigraphy and stratigraphic framework of the Englewood Formation, Black Hills, South Dakota, USA

The Englewood Formation comprises four distinct lithostratigraphic members formally named, in ascending stratigraphic order: the Crook City, Little Crow, Griffis Canyon and Mickelson members. The Crook City Member is a yellow to gray, silty and dolomitic shale. The Little Crow Member is a pinkish-red, silty to argillaceous to fossiliferous dolomitic limestone. The Griffis Canyon Member is a dull yellow, stromatolitic, argillaceous, dolomitic microbialite. The Mickelson Member is a yellow, slabby, thin bedded, argillaceous to silty fossiliferous limestone. The Crook City, Little Crow and Griffis Canyon members have gradational contacts with each other, possess conodonts of the Bispathodus aculeatus aculeatus Zone and comprise the upper Famennian Devonian sequence of the Englewood. A regional disconformity lies at the base of the Mickelson Member, which yielded conodonts of the Siphonodella sandbetgi Zone and comprises the lower Tournaisian Mississippian sequence of the Englewood. The basal beds of the Pahasapa Formation rest on a regional disconformity on the top of the Mickelson Member. The Pahasapa beds comprise gray, massive to thickly bedded, crinoidal, vuggy, dolomitic limestone that possess conodonts of the Siphonodella crenulata Zone, of early Tournaisian, Early Mississippian in age. The Englewood Formation in the Black Hills region represents a shallow marine carbonate with interbedded, bioturbated siltstones, argillaceous and microbial limestones, fossiliferous pack-wackestones and coral boundstones. These carbonate deposits are age equivalent to organic-rich black shales in the Williston, Sappington and South Alberta petroleum basins to the northwest.