The Early Permian age of the Dunkard Group, Appalachian basin, U.S.A., based on spiloblattinid insect biostratigraphy

Abstract

The Dunkard Group of the Appalachian basin, Ohio–Pennsylvania–West Virginia, is a >340m thick sequence of primarily fluvial and lacustrine deposits that contain a diverse fossil record including a blattoid insect forewing identified as Sysciophlebia balteata (Scudder). This wing originates from the Cassville Shale in the Waynesburg Formation, at the very base of the Dunkard Group. S. balteata is a zone species of a Late Paleozoic spiloblattinid insect zonation that is calibrated by the co-occurrence of spiloblattinid zone species with conodont- and fusulinid-zone species in Kasimovian to Early Asselian mixed marine-continental profiles of New Mexico, USA, and the Donets basin in the Ukraine, as well as by the isotopic ages of volcanic intrusions into the Late Stephanian (Gzhelian) strata of the Saale basin in Germany. The base of the zone underlying the S. balteata Zone is defined by the FAD of Sysciophlebia ilfeldensis in the Late Gzhelian, and has an upper limit (LAD) of Early to Middle Asselian. An Early or Middle Asselian to earliest Sakmarian range of both the subzones of the S. balteata Zone can be inferred. Given that the mean duration of a spiloblattinid insect zone is about 1.5 to 2Ma, the upper limit of the S. balteata Zone is Early Sakmarian. Hence, the base of the Dunkard Group should be maximally of Early Asselian or minimally of earliest Sakmarian age.