Abstract

Strata of the Upper Cretaceous Indianola Group (3950 m) in the Cedar Hills reveal development of a thrust-faulted (Sevier) highland to the west beginning in middle(?) Cretaceous time. Facies successions record the complex interaction of proximal fluvial/alluvial fan and marginal marine deposition in the westernmost part of the Late Cretaceous foreland basin in central Utah. Intercalation of marine and nonmarine strata within the Indianola Group probably reflects the combined influence of tectonic subsidence, sediment delivery and eustatic change. Stratigraphic and structural evidence suggest that at least the uppermost part of the Indianola Group was deposited and deformed simultaneously with initial development of the Nebo fold nappe to the west. Final emplacement of the Nebo allochthon in latest Cretaceous time resulted in folding and thrusting of the Indianola strata on a buried sub-horizontal splay of the Nebo thrust. The Indianola section of the Cedar Hills is parautochthonous whereas the Nebo allochthon may be far-travelled. Subsequent to the final emplacement of the Nebo thrust, an “overlap assemblage” of inferred Paleocene(?) age was deposited across the erosionally beveled folded strata. The North Horn strata were folded into a northeast-trending monoclinal flexure (Laramide) prior to deposition of the Flagstaff Limestone of Lower Eocene(?) age.

Recognition of Jurassic Twist Gulch Member of the Arapien Shale (>200 m) and Lower Cretaceous(?) Morrison(?) Formation (400 m) resulted in redefinition of the base of the Indianola Group in the Cedar Hills. The previously undivided Indianola Group is now correlated with equivalents of the Sanpete, Allen Valley, Funk Valley and Sixmile Canyon Formations of the western Wasatch Plateau based on facies-correlative lithostratigraphic units supplemented by limited fossil control.