Abstract

A field guide is presented to highlight the stratigraphy and sedimentology of the Cretaceous succession exposed along the northern and western sides of the Henry Mountains in south-central Utah. The basal (Cenomanian) Dakota Sandstone disconformably overlies Upper Jurassic Morrison Formation (or locally, Lower Cretaceous Cedar Mountain Formation), and crops out in low ridges and cliffs. In the Henry Mountains, the Dakota Sandstone can be divided into three informal units: a lower fluvial sandstone and conglomerate, a middle estuarine heterolithic interval, and an upper bioturbated and fossil-bearing transgressive marine interval. Following a thick marine mudrock interval, the Tununk Shale Member (of the Mancos Shale Formation), the deltaic Ferron Sandstone Member (Turonian) is well-exposed in high and semi-continuous cliffs. Overlying this is the offshore marine Blue Gate Shale, succeeded by the high cliff-forming Muley Canyon Sandstone (Campanian). This unit comprises alternating units of tidally-influenced fluvial and shoreface origin. The Masuk Formation (Campanian) then comprises a stack of tidally-influenced fluvial and estuarine deposits with a major coal zone at its base. Overlying the Masuk Formation, and capping the high mesas of the region, is the Campanian Tarantula Mesa Sandstone, a fluvial sheet sandstone interval. A distinctive feature of the Ferron Sandstone, Muley Canyon Sandstone and Masuk Formation is the preservation of genetic sequences bounded by sequence boundaries that have essentially planar geometry. These are in marked contrast with the more topographically irregular sequence boundaries with incised valleys that are typically documented or invoked in sequence stratigraphic models.