The Tertiary Northeastern Brooks Range Fold-Thrust Belt: An Onshore-Offshore Synthesis
By
T.E. Moore, C.J. Potter, A. Grantz (U.S. Geological Survey), and P.B. O’Sullivan (Syracuse University)
The eastern coastal plain of ANWR is part of an
extensive north-vergent fold-thrust belt that extends from the northeastern
Brooks Range across the Arctic margin into the Canada basin. An integrated view
of the fold-thrust belt is depicted in a balanced cross
section
constructed from
field and map data and onshore and offshore seismic data. Beneath the present
Beaufort Sea coast, the basal detachment lies above the Lower Cretaceous
(breakup) unconformity and descends northward with stratigraphy from a depth of
about 7 km onshore to about 10 km under the modern continental rise. Large-scale
structures offshore are interpreted as faulted detachment folds cored by syn-
and post-rift strata, including the pebble shale. Near the coast, structures are
thin-skinned and comprise a frontal triangle zone composed of a duplex of
Cretaceous and Paleocene units beneath a roof thrust at the base of Eocene
strata. Southward (rearward) from the coastal area, the basal detachment drops
stepwise to a depth of >15 km in pre-Mississippian basement under the Brooks
Range. Large subsurface antiforms under the coastal plain (Niguanak, Aurora) are
modeled as fault-bend folds of basement as are major antiforms exposed in the
Brooks Range. Fission-track data and stratigraphic relations indicate that
folding and thrusting in the southern part of the profile began in the latest
Cretaceous and propagated northward to the frontal triangle zone in the
Oligocene. Thrusting in basement antiforms under the coastal plain fed
detachment folds offshore in the Miocene to Holocene. About 72 km (43%) total
shortening is required to restore pre-Mississippian basement.
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.