Lithologic Evidence of Jurassic/Cretaceous Boundary Within the Nonmarine Cedar Mountain Formation, San Rafael Swell, Utah
The Jurassic/Cretaceous boundary in central Utah occurs at a major unconformity within a foreland basin. Paleontological data are absent and the boundary is typically placed at the lower contact of the Buckhorn Conglomerate Member of the Cedar Mountain Formation based on the assumption that this contact represents an erosional unconformity. Lithologic and petrographic evidence from this study indicate the presence of a Stage 6 calcrete and a groundwater silcrete, which both indicate long-term geomorphic stability. These data suggest that the Jurassic/Cretaceous boundary should be placed at the top of the calcrete within the basal Cedar Mountain Shale Member. The fluvial architecture of the strata below and above the boundary suggests that the lower Cedar Mountain Formation records the subtle transition from deposition within the distal foredeep depozone during the Early Cretaceous.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:cedar mountain formation stratigraphy jurassic cretaceous boundary calcrete silcrete
Date of Publication:01/01/2004