Interim Geologic Map of the West Part of - Utah Geological Survey

John Henry Member of the Straight Cliffs Formation. Ongoing stratigraphic studies atthe west edge of the Markagunt Plateau may further elucidate relationships among theseforedeep basin strata.Figure 5. Strata of the Greenhorn Cycle, showing maximum flooding surfacerepresented by the open-marine strata of the Tropic Shale and intermediate floodingsurfaces represented by coal zones (4 to 9) that accumulated in brackish, estuarineenvironments near the margin of the Western Interior Sea. Note numerous smaller cyclessuperimposed on the larger Greenhorn Cycle, which are due to changes in subsidence,compaction, and climate. Note also the diachronous nature of the strata, meaning thatthe same facies differ in age from place to place. The upper Dakota Formation isequivalent in age to the lower part of the Tropic Shale exposed farther east ― that is,they are the time-correlative coastal-plain and estuarine facies of the deeper water,offshore mud deposits of the Tropic Shale. Similarly, the Tibbet Canyon Member of theStraight Cliffs Formation is older in western exposures; it respresents eastwardprograding shoreline deposits that also are time-correlative with offshore Tropic muds.The Iron Springs Formation was deposited principally in braided-stream and floodplainenvironments of a coastal plain and is considered correlative with the Straight CliffsFormation, Tropic Shale, and Dakota Formation. Simplified from Tibert and others(2003).Kw? Wahweap Formation(?) (Upper Cretaceous, Campanian? or Santonian?) –Varicolored and mottled mudstone of brown, gray, reddish-brown, and pinkishhues, and lesser interbedded yellowish-brown fine-grained sandstone and siltysandstone; upper part of formation contains more sandstone than mudstone, also55