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ABSTRACT: Recognition of Depositional Sequences in the Upper Cretaceous Seabee Formation, Central North Slope, Alaska

S. Phillips, J. Decker, J. D. Shane, D. M. Hite, S. C. Bergman

Integration of genetic stratigraphic information from detailed measured sections, subsurface data, and regional observations allows a recognition of four unconformity bounded depositional sequences within the Upper Cretaceous Seabee Formation, traditionally considered to represent a conformable succession. These Seabee sequences comprise the stratigraphic interval bounded at the base by an lower(?) Cenomanian unconformity within the uppermost Nanushuk Group and at the top by an lower Campanian(?) unconformity that preliminary interpretations suggest coincides with the Seabee-Prince Creek/Schrader Bluff formation boundary.

Sequences are defined in outcrop based on identification of erosional unconformities, flooding surfaces, and condensed intervals. In bluff exposures along the Colville River, Seabee strata record the sedimentary architecture of systems tracts deposited landward of the shelf slope break. Thick-bedded, fluvial to shoreface sandstones and coastal-plain deposits or small-scale olistostromes characterize deposits of the lowstand systems. Strata of the transgressive systems exhibit a rapid upward deepening of marine facies accompanied by a decrease in terrigenous influx. Field gamma-ray measurements provided accurate identification of condensed intervals within thick sections of interbedded shale and bentonite. These condensed sections mark the transition to highstand systems tracts, and pr vide key biostratigraphic and radiometric age control. Upward-thickening, regressive strata occur within the highstand systems and are sand prone in some of the Seabee sequences.

Recognition of unconformities and depositional sequences within the Seabee and other previously undifferentiated intervals provides a robust tool for stratigraphic correlations on the North Slope. Integration of outcrop and subsurface data allows sequence stratigraphy concepts to be tested and predictive exploration models to be developed.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990