Seismic Stratigraphy of a Forearc
Depositional System: Shelf-Margin Deltas to Basin Floor Fans, Northern
Armentrout, John M.1,
David H. Suek2, Denise H. Harrison3, Paul J. Harrison3,
David B. Codding4, Steve D. Jones5, Scott Lewis6,
Steve Graham7 (1) Cascade Stratigraphics,
Inc, Damascus, OR (2) Black Coral LLC, Denver, CO (3) Fall-Line Exploration,
Dillon, CO (4) Yates Petroleum, Artesia, NM (5) Black Coral, Centennial, CO (6)
QuantStrat, Denver, CO (7) Stanford University, Palo
Alto,
The ‘traditional' sequence stratigraphic depositional model was formulated from
passive margin data and subsequent computer simulations. Convergent forearc basin tectonics provide a
markedly different setting and yet 2D and 3D seismic observations of the Upper
Cretaceous of the
Regional 2D reflection profiles down a
fault controlled paleo-valley system image a
succession of sand-prone, depositionally thick bodies
in inner-shelf, outer-shelf, shelf-margin, canyon-mouth, toe-of-slope and basin
floor settings. Analysis of a 3D seismic volume demonstrates that each of these
depositional elements can be placed into a sequence stratigraphic
framework for this tectonically driven system. Each of the depositional
elements occurs where dramatic geomorphic transitions provided accommodation
space and changes in flow velocity resulting in the sand-prone facies being deposited in a spatially foreshortened
configuration when compared to passive margin deposition.
Periods of tectonic emergence of the
basin margin repeatedly forced relative lowstands of
sea level across the narrow shelf. Sand-prone sediment flux was very high and
accumulation was largely restricted to the depositional axis of the forearc basin. The lowstand
depositional facies include basin-floor fans,
toe-of-slope prograding complexes, canyon-mouth ‘thicks', and shelf-margin prograding
complexes. As the basin margin subsided and sediment flux decreased, depocenters transgressed first across the upper slope and
onto the outer shelf as retrograde packages and subsequently toward the basin
margin where paleo-river systems supplied relative highstand prograding systems.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California