Structural
Evolution and Petroleum Potential of
Fold- Thrust Structures Beneath the Coastal Plain in ANWR, Alaska
By
C.J. Potter, J.A. Grow, W.J. Perry, T.E. Moore (U.S. Geological Survey), and P.B. O’Sullivan (Syracuse University)
The coastal plain in the Arctic National Wildlife Refuge conceals an array of contractional structures in the frontal zone of the northeastern Brooks Range orogen. These structures were imaged on seismic profiles (1984–85) that were reinterpreted as part of the 1998 USGS oil and gas assessment of the “1002 area.” Deformational timing was deduced through seismic-stratigraphic correlations, augmented by apatite fission-tack analyses.
In the western 1002 area, a thin-skinned passive-roof
duplex (PRD) is bounded below by a floor thrust near the base of the Brookian
section, and above by a north-dipping roof thrust near the base of Eocene
strata. Buried basement-involved thrusts appear to feed displacement into the
thin-skinned system
, and locally, late basement-involved thrusts post-date the
thin-skinned thrusting. Both the basement-involved thrusts and the thin-skinned
PRD were principally active in Miocene time.
In the eastern 1002 area, a thin-skinned PRD system
advanced northward during Paleocene through early(?) Oligocene time across the
present location of the Niguanak high. The Niguanak high and Aurora dome, the
two largest structures in the subsurface beneath the coastal plain, formed in
Oligocene to Miocene time above thrust ramps in the pre-Mississippian basement.
The overlying, older thin-skinned structures were broadly domed above the
Niguanak high. Due to erosional truncation of the Ellesmerian Group south of the
Niguanak high, Ellesmerian reservoir facies are not draped across the basement
domes.
Rationale for relatively small quantities of oil and
gas assigned to the deformed area in the 1998 assessment of the 1002 area
include late trap
formation, poor reservoir quality and suspect seal integrity.
AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.