Abstract

Cretaceous marine and continental rocks preserved in the Henry Mountains region total about 4,300 feet (1,310 m) in thickness. Previous correlations of some of these rocks with those in nearby areas are revised, based on new fossil collections, studies of depositional environments, and relations to transgressive-regressive cycles. The Lower Cretaceous Cedar Mountain Formation consists of continental strata that lie unconformably on Jurassic rocks and are unconformably overlain by the Lower(?) and Upper Cretaceous Dakota Sandstone. The Dakota and overlying Upper Cretaceous Tununk Shale and Ferron Sandstone Members of the Mancos Shale are a conformable sequence of marine and continental beds deposited during a single transgressive-regressive cycle. No changes in previous correlations of any of the foregoing units are suggested.

A regional unconformity representing about six faunal zones separates the Ferron from the underlying offshore marine Blue Gate Shale Member of the Mancos. The Blue Gate in the Henry Mountains region correlates with units in the Wasatch Plateau known as the Blue Gate Shale, Emery Sandstone, and Masuk Shale Members of the Mancos. The Emery in the Henry Mountains region was deposited in nearshore marine and continental environments. It correlates with the Star Point Sandstone and lower part of the Blackhawk Formation in the Wasatch Plateau, not with the Emery Sandstone Member in that region. The Masuk Member in the Henry Mountains region is correlated with the middle and upper parts of the Blackhawk Formation in the Wasatch Plateau. The Masuk probably is entirely continental in origin; marine fossils reported from the lower part may have come from beds now included in the Emery.

The Mesaverde Formation was deposited in fluvial and possibly near-shore marine environments, and it probably correlates with the Castlegate Sandstone in the Book Cliffs. A thin continental unit informally named the beds on Tarantula Mesa lies on the Mesaverde. These beds probably correlate with the lowest beds in the Price River Formation of the Book Cliffs. Younger rocks have been eroded but regional relations suggest that several thousand feet (several hundred metres) of uppermost Cretaceous continental rocks once covered the region.