UC Santa Barbara

The Permian redbeds of the Midcontinent U.S.A. are thought to contain important clues to the climate history of western Pangaea. However, before these units can be used as paleoclimatic archives, better constraints are needed on their age, depositional environment, and provenance. In this study, 43 stratigraphic sections were measured within the Lopingian Cloud Chief Formation of western Oklahoma. The sections were complemented by strontium isotope analysis and detrital zircon geochronology. Nine facies were recognized within the measured sections. These facies include massive gypsum, gypsiferous sandstones, channelized very fine sandstones, thickly-bedded sandstones, siltstones, variegated mudstones, ripple cross-laminated very fine sandstones, interbedded sandstones and mudstones, and silty claystones. These facies are interpreted to represent subenvironments of widespread arid-land fluvial systems flowing into a sabkha. These interpretations fit well with other recent work calling for arid conditions within the midcontinent during the middle Permian. Detrital zircon geochronology points to a dominant sediment source to the east (Ouachita Mountains) with a subordinate source to the west (Ancestral Rocky Mountains in Colorado and New Mexico). Strontium isotope values of the massive gypsum facies provide evidence for marine encroachment during periods of high relative sea level. These isotope values point to an age for the Cloud Chief of 262 ± 3 Ma to 255 ± 3 Ma, providing some of the first numerical ages from the redbeds of western Oklahoma.