Repeated Cycles
of Progradation and Incision of Upper Cretaceous
Shelf-Margin Deltas, Northern
Harrison, Denise H.1, Steven
D. Jones2, Paul J. Harrison1, John M. Armentrout3,
David H. Suek4, David B. Codding5 (1) Fall-Line Exploration,
Dillon, CO (2) Lariat Exploration, Centennial, CO (3) Cascade Stratigraphics, Inc, Damascus, OR (4) Black Coral LLC,
Centennial, CO (5) Yates Petroleum, Artesia, NM
Detailed analysis of 2D and 3D seismic
data and log facies demonstrates that the shelf
margin on the east side of the
Some of the canyons are aligned with
basement faults on a relatively steep slope influenced by ongoing tectonic
activity. The first cycle of progradation
downlaps within the basement canyons and the adjacent
upper slope. This initial cycle of progradation
is deeply incised by subsequent phases of erosion associated with relative
falls in sea level. It appears that the initial laterally extensive prograding system was dissected into a series of locally
preserved shelf-margin deltas separated by younger canyons. The presence of
sand in the preserved deltas is supported both by differential compaction
across the preserved prograding facies
and coarsening-upward sands in a well penetrating the edge of one delta. A
shoreward well with fining upward sequences suggests that as sea level
continued to rise, shore-face sediments were deposited over the preserved
deltas.
The progradational
and canyon erosion cycles are followed by a regional transgression that
deposited the predominantly mudstone facies of the
Sacramento Shale which provides an updip seal for
potential hydrocarbon traps. The sealing potential is supported by overpressure
in the sandstones in an updip canyon-head well, and
by the overlying regional high-amplitude drape seismic facies
associated with the shale.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California