INITIAL PROVENANCE ANALYSIS OF THE LATE JURASSIC LACUSTRINE WANAKAH FORMATION, EASTERN UTAH AND WESTERN COLORADO
Samples (n=6) from the Entrada Formation, Wanakah Formation and the Tidwell Member were collected from Escalante Canyon in western Colorado for detrital zircon provenance analysis. U/Pb dating of the Entrada Formation grains (n=190) showed significant peaks in the typical North American Jurassic distributions for the Colorado Plateau with an atypically large peak at ~520Ma. In contrast the Wanakah Formation grains (n=207) present a nearly unimodal distribution at ~520Ma with very little in the traditional Colorado Plateau grains. The Tidwell Member grains (n=197) return to the wider age distribution seen in many Jurassic rocks of the Colorado Plateau. Detrital zircon analysis from the Entrada Sandstone, Wanakah Formation and the Tidwell Member suggest a shift in provenance between the Entrada Formation and the Wanakah Formation and a major shift in provenance from the Wanakah Formation to the overlying Tidwell Member of the Morrison Formation. Results suggest the J-5 unconformity is between the Wanakah Formation and the Tidwell Formation; however, an unconformity is also documented between the Entrada Sandstone and the Wanakah Formation. Understanding this shift in provenance will help to define this late Jurassic depositional basin.