| Description |
In southeastern Utah, the Triassic Moenkopi Formation is composed mainly of red and yellowish-gray siltstone, sandstone, mudstone, and limestone. Continuity of individual units is one of the characteristics of this formation and provides a basic for regional correlation. For the purpose of this study, the Moenkopi Formation was divided into five members: (1) Hoskinnini, (2) lower slope-forming, (3) Sinbad Limestone, CO ledgeforming, and (5) upper slope-forming. The Moenkopi Formation was deposited on a moderately uniform and gentle west slope which was bordered and sometimes covered by an epicontinental sea. Throughout Moenkopi deposition, a number of environments moved across this slope; however, five fairly distinct sequences of deposition can be recognized. The Hoskinni.ii Member consists of subaqueous but probably nonmarine deposition in an enclosed basin or restricted bay. The lower shallow marine and paralic sequence of rocks includes the lower slope-forming, Sinbad, and basal ledge-forming members. They were deposited in a variety of shallow marine and shoreline environments and contain locally abundant fossils, including the Meekocevas fauna. Most of the ledge-forming member consists of deltaic sediments. An extensive deltaic system spread westward into the Sinbad sea. Recognition of this delta is based upon the horizontal distribution of ledge-forming sandstone and the vertical sequence of facies. A marine transgression reworked deltaic sediments and deposited the extremely continuous beds of the upper slope-forming member in a variety of paralic and shallow marine environments. Evidence of a regressive depositional sequence, followed by fluvial deposition, is present at the top of the Moenkopi at several localities. The petroleum potential of the Moenkopi Formation of southeastern Utah is related to delta front sandstones in and adjacent to the San Rafael Swell, Circle Cliffs, and Teasdale uplifts. |
