The U.S. Geological Survey (USGS) has conducted the Trans-Alaska Crustal Transect (TACT), a combined geophysical and geological study along the Trans-Alaska Pipeline route from Valdez to the North Slope. The final phase of this project addressed the northern part of the Brooks Range from Atigun Pass to the mountain front. Wes Wallace worked with Tom Moore and other USGS researchers in the geological studies along this northernmost part of the transect.
This work documented a well-exposed cross-section across the external part of a mountain belt, which can serve as a basis for comparison with other mountain belts throughout the world. Among the most striking and significant features of the region are the many well-exposed examples of fold-and-thrust structures. The exposures allow three-dimensional reconstruction of the geometry of thrust-truncated detachment folds, thrust faults, and duplexes, thereby providing new insights into the geometry and evolution of these important types of structures. The transect crosses the boundary between greatly deformed rocks that have been displaced great distances and other rocks that have been displaced much less, including some that were derived by erosion from the ancestral Brooks Range. Such boundaries are an important element of all mountain belts, and this study offers clues to the complex relationships among age, displacement, and the geologic structures associated with such a boundary. This study is of regional significance because it documented structures typical of those found throughout the north-central Brooks Range, as well as documenting the boundary between these structures and the very different structures typical of the northeastern Brooks Range.
The geologic maps and other field observations from the project will be used to construct a series of restorable cross sections across the north-central Brooks Range. These will be combined with the results of the TACT geophysical studies and fission-track dating to develop an interpretation of the subsurface structure of the north-central Brooks Range and foothills, and how that structure evolved over time. In addition to the insights gained into the evolution of mountain belts, this will have direct implications for the subsurface structure of the Alaskan North Slope petroleum province, and for the timing of sediment deposition and hydrocarbon generation, migration, and trap formation.
ARCO Alaska, BP Exploration (Alaska), Chevron USA, Exxon Company USA,
Japan National Oil Corp., Mobil Exploration and Producing US, Phillips
Petroleum, Unocal, and U.S. Geological Survey funds.
UAF scientific personnel:
W.K. Wallace.