--> ABSTRACT: Clastic Facies Architecture Associated with a Major Marine Transgression--the Mid-Cretaceous of the Kaiparowits Plateau, Utah, by Robert D. Hettinger, Peter J. McCabe, Keith W. Shanley; #91002 (1990).

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ABSTRACT: Clastic Facies Architecture Associated with a Major Marine Transgression--the Mid-Cretaceous of the Kaiparowits Plateau, Utah

Robert D. Hettinger, Peter J. McCabe, Keith W. Shanley

Recognition and interpretation of subtle sedimentary structures is critical to the successful interpretation of depositional sequences. High resolution facies analysis of a 130 m thick section of upper Turonian and Coniacian strata in the northern Kaiparowits Plateau study has resulted in the description of a well-exposed fourth-order sequence.

The lower part of the section consists of 30 m of pebbly sandstones deposited by braided rivers. These strata overlie a major third-order sequence boundary unconformity and grade upward into tidally influenced strata. This unit is capped by an abrupt deepening surface that gently dips to the northeast and is mantled by a thin extraformational conglomerate interpreted as a ravinement surface lag. Two meters of swaley bedded sandstone separate the conglomerate from a condensed interval that marks the top of the transgressive system tract.

The condensed interval is overlain by a series of coarsening-upward, seaward-stepping parasequences constituting a highstand systems tract that is 75 m thick. Typical parasequences consist of interbedded mudstones and hummocky cross-stratified sandstones that grade upward into swaley bedded sandstones. This highstand systems tract is unconformably overlain by tidal channel deposits. The channels represent part of a valley fill sequence that infilled with pebbly sandstones containing abundant oyster and inoceramid debris. These strata comprise a lowstand to transgressive systems tract related to a fourth-order sequence boundary. To the west, tidal channel sandstones interfinger with terrestrial mudstones and coals. These coals formed in mires several kilometers landward of coeval shore ines of the highstand systems tract to the east.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990