--> Abstract: Sequence Boundary Development and Influence on "Stranded" Deltaic Parasequences, Upper Cretaceous Blackhawk Formation, Utah, by D. L. Kamola and J. E. Huntoon; #90987 (1993).

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KAMOLA, DIANE L., Old Dominion University, Department of Geological Science, Norfolk, VA; and J. E. HUNTOON, Department of Geological Engineering, Geology and Geophysics, Michigan Tech. Univ., Houghton, MI

Sequence Boundary Development and Influence on "Stranded" Deltaic Parasequences, Upper Cretaceous Blackhawk Formation, Utah

Sequence boundaries in the Upper Cretaceous Blackhawk Formation,

Utah, generally reflect rapid sea-level fall through a marked seaward shift in depositional facies. One particular sequence boundary within the Aberdeen Member, however, suggests that sea-level fall occurred in two phases; an initial sea-level fall which was slow and/or moderate, followed by a second stage of more rapid and/or extreme sea-level fall. Evidence for this two-phase sea-level fall is seen in correlated stratigraphic sections of a river-dominated delta. This delta has limited strike-oriented dimensions, overlies a surface of minor sea-level fall, and is immediately overlain by a well-developed sequence boundary. When traced landward, the river-dominated delta thins depositionally and merges with a wave-dominated shoreface parasequence (Standardville parasequence). This stra igraphic relation suggests the following sequence of events. Deposition of a progradational wave-dominated shoreface was succeeded by an initial sea-level fall too limited to cause an extensive seaward displacement of facies. The change in base level associated with the initial sea-level fall activated a new point source of sediment that built a river-dominated delta directly on the wave-dominated shoreface of the Standardville parasequence. A second phase of sea-level fall then occurred, interpreted to be of greater magnitude and/or more rapid, and resulted in a rapid seaward displacement of the shoreline. The sequence boundary associated with the second phase of sea-level fall is well developed, and is characterized by localized downcutting where meandering stream deposits directly ove lie the river-dominated delta. This river-dominated delta is analogous to a "stranded" lowstand parasequence of Van Wagoner and others.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.