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.