Regional Structural Framework and Petroleum
Assessment of the Brooks Range Foothills and Southern Coastal Plain, National
Petroleum
Reserve, Alaska
By
C.J Potter, T.E. Moore (U.S. Geological Survey), P.B. O’Sullivan (Syracuse University), and J.J. Miller (U.S. Geological Survey)
New interpretations of the frontal part of the Brooks
Range orogen beneath the foothills and coastal plain in the National Petroleum
Reserve-Alaska (NPRA) are based on reprocessed regional seismic reflection data,
recent geologic field observations, and new apatite fission-track analyses.
Three long north-south transects illustrate the configuration of thrust faulting
above a basal detachment that, within the southern part of NPRA, steps up from
the Triassic Shublik Formation, to the Jurassic Kingak Shale, and finally into
Cretaceous Torok mudstones. This thrust
system
represents the youngest
recognized pulse of major shortening, about 60 Ma.
The transects, along with other seismic-reflection
examples, illustrate four play concepts being used in the deformed area for the
2002 U.S. Geological Survey oil and gas assessment of the National Petroleum
Reserve-Alaska (NPRA). The Brookian topset structural play includes broad
west-northwest-trending anticlines in the Cretaceous Nanushuk Group, developed
above structurally thickened Torok mudstones in the incipiently-deformed, most
northerly part of the thrust
system
. The Torok structural play includes
prominent anticlines affecting deep-basin sandstones, many of which are detached
from folds exposed at the surface. The Ellesmerian structural play includes
closures developed in the clastic part of the Ellesmerian sequence, mainly above
a detachment in the Shublik Formation. The thrust belt play includes antiformal
stacks of allochthonous Endicott Group clastic rocks and Lisburne Group
carbonates; these stacks were assembled at about 120 Ma, and were transported to
their present positions in the foothills at about 60 Ma.
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.