Abstract

Regression of the western shoreline of the Upper Cretaceous Mancos sea during middle and late Turonian time culminated in deposition of the Ferron Sandstone Member of the Mancos Shale in east-central Utah. The Ferron is an eastward-thinning clastic wedge of predominantly sandy sediment enclosed in marine shale of the Mancos. Offshore-marine, delta-front and delta-plain/alluvial-plain facies of the Ferron can be recognized on geophysical logs from oil and gas wells drilled in the study area. Facies relationships in the subsurface, and concepts developed as the result of studies of the Ferron outcrop are synthesized to produce an interpretation of Ferron paleogeography in east-central Utah. Sediments deposited during transgressions and regressions of the shoreline of the Mancos sea record the interplay between sediment input from the Sevier orogenic belt to the west, basin subsidence, and eustatic fall and rise of sea level. Speculations are presented on the contributions of these factors in the shaping of Ferron stratigraphy and middle and late Turonian paleogeography.