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AAPG Bulletin

Abstract


Volume: 79 (1995)

Issue: 3. (March)

First Page: 444

Last Page: 462

Title: Sequence Stratigraphic Significance of Sharp-Based Lowstand Shoreface Deposits, Kenilworth Member, Book Cliffs, Utah

Author(s): Simon A. J. Pattison (2)

Abstract:

The Kenilworth Member of the Blackhawk Formation (Upper Cretaceous, Campanian) is nearly continuously exposed from Price to Hatch Mesa in the Book Cliffs, Utah. Five main depositional environments are recognized: coastal plain, foreshore and upper shoreface, lower shoreface, inner shelf, and incised valley-fill deposits. The shelf-to- shoreface deposits combine to form nine coarsening-upward, wave- to storm-dominated parasequences that are 7-32 m thick, and that split basinward into smaller coarsening-upward successions or bedsets that are 2-18 m thick. A maximum of four bedsets occurs within an individual parasequence. Bedset bounding surfaces are occasionally marked by thoroughly bioturbated, iron-rich carbonate-cemented sandstones within the parasequences. In the subsu face, similar bedset bounding surfaces may act as permeability barriers or baffles, leading to reservoir compartmentalization.

Parasequences 1-6 form an aggradational-to-progradational parasequence set of the highstand systems tract, parasequences 7 and 8 occur as sharp-based lowstand shoreface deposits at Price River and Battleship Butte forming the attached lowstand systems tract, and parasequence 9 forms the transgressive systems tract. The base of each lowstand shoreface is marked by an organic-rich lag deposit that consists of granules, coarse-grained sandstone, wood fragments, coal intraclasts, and shell debris. The sharp base, basal lag deposit, and basinward shift in facies delineate a sequence boundary at the base of each lowstand shoreface deposit. The presence of two sharp-based lowstand shorefaces suggests that the Kenilworth lowstand was punctuated by a stillstand. The sharp-based lowstand shoref ce sandstones form the bulk of the attached lowstand systems tract and represent one end member in a continuum of lowstand deposits. The other end member is the detached lowstand systems tract. Revising existing sequence stratigraphic models to include both types of lowstand systems tracts is a first step toward improving the accuracy of these models, which are often used as prospecting tools in lowstand deltaic environments.

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