Tectonic Geomorphic Characterization of a Transcurrent Fault Zone, Western Brooks Range, Alaska

By

R.R. Casavant (University of Arizona), and S.R. Miller (Pennsylvania State University)

We present a hypothesis that the western Brooks Range is partitioned by several large, possibly tectonically active, NW- and NNE-trending transverse fault zones that trend obliquely to the range. The study has implications for petroleum exploration in the adjacent NPRA and mineral exploration to the south. Our hypothesis of neotectonic activity is not novel, but represents the first foray of such thinking into the westernmost foothills. In the northwestern DeLong Mountains north of the Red Dog mine, we surveyed a large, high-angle transpressional fault zone with inferred sinistral offset that intersects and is parallel to an anomalous long, linear, NNE-trending stretch of the Kukpowruk River, along with adjacent strath terraces and pediments. The river parallels several NE-trending thrust faults in the adjacent area and generally exhibits a graded longitudinal profile with the exception of a west-facing, 1 m-high channel knickzone that correlates with a prominent NE-trending linear scarp on an uplifted planation surface on the north side of the river, and with a lesser scarp on river terraces on the south side. The alignment suggests that the knickzones and scarps may be the result of active faulting. Down-to-west throw on these non-structural surfaces matches the sense of offset on nearby thrust faults. Block tilting within the fault zone is inferred from consistent shifts in channel avulsion toward one margin of the river floodplain. Multiple levels of strath terrace formation suggest a neotectonic base-level drop. Further mapping and dating of key surfaces are necessary to clarify this region’s complex structural history.

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.