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Genesis, Architecture, and Numerical Modeling of Intra-Parasequence Discontinuity Surfaces in Wave-Dominated Deltaic Deposits: Upper Cretaceous Sunnyside Member, Blackhawk Formation, Book Cliffs, Utah, U.S.A.

By
Tor O. Sømme
Tor O. Sømme
Department Of Earth Science, University of Bergen, Allegaten 41, N5007 Bergen, Norway, e-mail: tor.somme@geo.uib.no
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John A. Howell
John A. Howell
Department Of Earth Science, University of Bergen, Allegaten 41, N5007 Bergen, Norway, e-mail: tor.somme@geo.uib.no
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Gary J. Hampson
Gary J. Hampson
Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK
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Joep E.A. Storms
Joep E.A. Storms
Section Of Geo-Engineering, Delft University of Technology, P.O. Box 5048, Delft, The Netherlands
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Published:
January 01, 2008

Abstract

Detailed mapping of two wave-dominated deltaic parasequences in the Sunnyside Member (Upper Cretaceous BlackhawkFormation) in the Book Cliffs outcrop belt, Utah, U.S.A., reveals an intra-parasequencearchitecture that includes a clearly defined set of coarsening-upward sandstone packages, termed bedsets, which are bounded by nondepositional discontinuity surfaces. In vertical section the bedsets show an upward-shoaling succession of facies from offshore mudstones to lower-shoreface sandstones. When traced depositionally up dip, the bounding surfaces are truncated by lower-shoreface sandstones, and are commonly represented by heavily bioturbated intervals; the surfaces are absent in upper-shoreface deposits. Mapping and regional correlation indicate that these packages were deposited during normal regression, when the shoreline had a subhorizontal but positively inclined trajectory.Mapping also indicates that the bounding surfaces are more restricted than the parasequence boundaries, and in at least one case (S3.2) the bedset boundary is associated with a change in the depositional environment going froma wave-dominated to a mixed river- and wave- dominated system. These observations indicate that although the bedsets superficially resemble parasequences bounded by flooding surfaces in restricted shoreface-shelf strata outcrops, they have a different genesis.

The driving mechanisms for the formation of the bedset boundaries have been investigated via numerical forward-modeling experiments. Results indicate that nondepositional discontinuity surfaces, similar to the ones observed in the Sunnyside Member, can be generated by a local decrease in wave climate coupled with a local reduction in sediment supply and high-frequency, low-amplitude changes in relative sea level. The field observations suggest a slight reorientation of the shoreline across the bedset boundaries. This, combined with the results of the forward modeling, indicates that the bedsets resulted from river-mouth migration and a relatively abrupt decrease in sediment supply coupled with minor changes in coastal morphology. The increases in water depth suggested bythe modeling occurred as a result of ongoing loading and auto-compaction.

This study suggests good sandbody connectivity both up depositional dip and along depositional strike betweenadjacent bedsets. Good understanding of the formation and pinch-out style of these units is important in understanding sandbody connectivity within hydrocarbon reservoirs and distinguishing localized bedset boundaries from more laterally extensive parasequence boundaries.

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SEPM Special Publication

Recent Advances in Models of Siliciclastic Shallow-Marine Stratigraphy

Gray J. Hampson
Gray J. Hampson
Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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Ronald J. Steel
Ronald J. Steel
Department of Geosciences, Jackson School, University of Texas at Austin, Austin, Texas 78712, U.S.A.
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Peter M. Burgess
Peter M. Burgess
Shell International Exploration and Production, Kessler Park 1, P.O. Box 60, 2280 AB Rijswijk, The NetherlandsPresent address: Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
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Robert W. Dalrymple
Robert W. Dalrymple
Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
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SEPM Society for Sedimentary Geology
Volume
90
ISBN electronic:
9781565763180
Publication date:
January 01, 2008

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