PETROLOGY OF SANDSTONES FROM JOHN HENRY MEMBER, STRAIGHT CLIFFS FORMATION, LATE CRETACEOUS, SOUTHERN UTAH

Stratigraphic and petrographic analysis of the John Henry Member of the Straight Cliffs Formation (Coniacian-Santonian) on the eastern margin of the Paunsaugunt Plateau records changes in sedimentary sources and dispersal patterns in the foreland basin. Petrographic samples were compared to samples previously taken from the overlying Drip Tank Member of the Straight Cliffs Formation and the Wahweap Formation, as well as from the underlying Smoky Hollow Member of the Straight Cliffs Formation. Petrographic analysis shows that the lower John Henry Member is dominated by monocrystalline quartz (>80%), chert, and microcline, which is consistent with the petrology of the sandstones in the underlying Smoky Hollow Member. Higher in the John Henry Member, carbonate clasts become more pervasive (>30%), as does calcite cement, and the microcline disappears. Previous work indicated that lithics in the Drip Tank Member are dominated by chert, metamorphic quartzite and microcline and that the Wahweap Formation lithics are dominated by carbonates (>85%) and lack the quartzite and microcline. The change in petrology from the Drip Tank Member to the Wahweap Formation represents a relatively abrupt shift in provenance from a southern source (Mongollon Highlands of Arizona) to the Sevier orogenic belt to the west, which contains abundant carbonates. The petrographic change from lower to upper John Henry Member indicates a similar but more gradual change from a southern source (Mongollon Highlands) to a western source (Sevier thrust belt). Changes in sediment supplied to the foreland basin reflect both allocyclic and autocyclic controls, and these changes can be abrupt (Drip Tank/Wahweap transition) or gradual (John Henry Member).