STRATIGRAPHY, DEPOSITIONAL ENVIRONMENTS, PALEONTOLOGY AND AGE OF THE CLARON FORMATION, SWEETWATER CREEK AREA, GARFIELD COUNTY, UTAH

The Claron Formation forms the dramatic pink cliffs of Bryce Canyon National Park and Cedar Breaks National Monument, but relatively little is known about the formation’s geologic history. A well exposed and accessible 405-m-thick section is present north of Sweetwater Creek, just west of the Table Cliffs Plateau. The section rests unconformably on a deeply weathered concretionary horizon at the top of the locally thinned (25 m) Pine Hollow Formation and is composed dominantly of fluvial sandstones and pedogenically altered floodplain mudstones and siltstones. There are two major lacustrine episodes recorded by thick white limestones and minor episodes represented by thinner limestones. The floodplain mudstones and siltstones are generally more poorly cemented than in other sections of the Claron Formation and are amenable to screen washing techniques to recover fossils. Gastropods, ostracods, and charophytes have been recovered throughout the formation and vertebrates, including mammals, were found in one of the upper units. Mollusks are the most common taxa present and include at least seven gastropod taxa and a unionid. The mammalian specimens are size-sorted and small (~1–1.5 mm) and include isolated teeth of rodents, insectivores, and marsupials. The presence of two species of the rodent Knightomys indicates that the upper part of the section (but not necessarily the capping white limestone) is early Eocene in age (Wasatchian North American Land-Mammal Age). Three charophyte species, Peckichara varians, Peckichara torulosa, and Microchara cristata, were recovered from the Claron Formation. Taking into account the worldwide biostratigraphic distribution of these charophyte species, we can suggest that the Claron Formation may be late Paleocene or early Eocene in age. Preliminary examination of the ostracod fauna indicates it is moderately to richly diverse and includes at least nine genera: Scottia?, Candona, Psuedoeucypris, Candoniella, Timiriasevia, Procyprois, Gen. aff. Bisulcocypridae, Gen. 1, and Gen. 2. The assemblage of these genera is characteristic of early Eocene strata throughout neighboring Wyoming and Colorado. Based on the fossil mammal, charophyte and ostracod record, we conclude that the age of the Claron (exclusive of the uppermost white limestone) is most likely early Eocene.