LATE CRETACEOUS TO EARLY TERTIARY TECTONOSTRATIGRAPHY OF SOUTHWESTERN UTAH Patrick M. Goldstrand Env. Sciences Division Oak Ridge National Lab. Oak Ridge, TN 37831 James H. Trexler, Jr. Depart. of Geo. Sciences University of Nevada Reno, NV 89557 Bart J. Kowallis Department of Geology Brigham Young University Provo, UT 84602 Abstract Jeffrey G. Eaton Utah Mus. of Natl. Hist. University of Utah Salt Lake City, UT 84112 Tbe Upper Cretaceous to Paleogene sedimentary rocks of southwest- ern Utah record three temporally overlapping tectonic phases: 1) active Sevier-style thrust activity and foreland sedimentation; 2) cessation of thrust activity; and 3) active Laramide-style folding and intermontane sedimentation. Tbe formations recording this tectonic evolution are, from oldest to youngest: the Iron Springs (and eastern equivalents), Kaiparowits, Canaan Peak, Grand Castle (new informal name), Pine Hollow, and Claron formations. Tbe Santonian to lower Campanian(?) upper part of the Iron Springs and mid-to-upper Campanian Kaiparowits formations repre- sent synorogenic, fluvial sedimentation derived from the Sevier fold and thrust belt. Tbe Iron Springs Formation received sediment from Precambrian to Upper Paleozoic strata exposed in the Wah Wah and Blue Mountain thrust sheets of southwestern Utah. Tbe upper Campan- ian(?) to lower Paleocene Canaan Peak Formation was deposited in an east-to-northeast-directed, braided fluvial system. Petrographic and geochemical analysis of volcanic and siliceous clasts indicate that the Canaan Peak and Kaiparowits formations were derived from the juras- sic Deifonte Volcanics of southeastern California and the Mississippian Eleana Formation of southern Nevada. Tbe early Paleocene Grand Cas- tle formation represents an east- to southeast-flowing braided river tem. Clast and sandstone lithologies indicate that the Grand Castle formation had the same provenance as the Iron Springs Formation. Conglomerate of the Grand Castle formation overlaps the easternmost Sevier thrust faults, suggesting a post-Sevier origin. The lower Pine Hollow Formation records active Laramide parti- tion of the foreland basin associated with the development of the johns Valley anticline and possibly the Circle Cliffs uplift. Fluvial, deltaic, and lacustrine deposits of the Claron Formation overlap paleotopographic highs of the Pine Hollow basin and indicate cessation of Laramide deformation by the middle Eocene. Goldstrand, P. et at. 1993. Late Cretaceous to Early Tertiary Tectonostratigraphy of Southwestern Utah. In: Aspects of Mesozoic Geology and Paleontology of the Colorado Plateau. Morales, M., ed. MusEuM OF NoRTHERN ARizoNA BUL- LE71N59, pp 181-188.