Preliminary Map Showing Thermal Maturity of Sedimentary Rocks in Alaska

JOHNSSON, MARK J., KENNETH J. BIRD, DAVID G. HOWELL, LESLIE B. MAGOON, RICHARD G. STANLEY, and ZENON C. VALIN, U.S. Geological Survey, Menlo Park, CA, ANITA G. HARRIS, U.S. Geological Survey, Reston, VA, and MARK J. PAWLEWICZ, U.S. Geological Survey, Denver, CO

Since 1976, we have been compiling thermal maturity data for sedimentary rocks in Alaska from the U.S. Geological Survey and other public sources. These data consist primarily of vitrinite reflectance and conodont color alteration index (CAI) determinations, but also include thermal-alteration-index, ROCK-EVAL, coal-rank, and fission-track information. A preliminary map depicting these data portrays the thermal maturity of sedimentary rocks at the Earth's surface in terms of five map units ranging from undermature (R(0) < 0.6) to supermature (R(0) = 3.6-5.0). The map also indicates the configuration of thermal maturity isograds at depth in the Colville and Cook Inlet basins. The preliminary map includes information from roughly 1200 outcrop localities (700 vitrinite reflectance and 500 CAI localities), many of which represent multiple samples, and some 2500 vitrinite reflectance determinations from 211 wells.

The thermal maturity map of Alaska will be a useful tool in the evaluation of the petroleum potential and paleotectonic history of Alaska. For example, the preliminary map has been used to analyze the dynamics of thrusting and the hydrocarbon potential of the northern margin of the Brooks Range thrust belt. The map indicates that the 0.6% R(0) isograd intersects the land surface just north of the Brooks Range front, and that the 2.0% R(0) isograd lies within the northen part of the range, thus indicating post-maturation uplift of approximately 3-5 km. The configuration of the isograds reflects a similar thermal history for both the north margin of the orogen and the adjoining foreland deposits, suggesting that petroleum resources may be found at shallow depths beneath the northern mar in of the thrust belt and beneath all of the Colville basin.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)