Thermal maturation history of Arctic Alaska and the southern Canada Basin

Abstract

The emerging global focus on the oil and gas potential of the Arctic underscores the importance of understanding petroleum systems with limited data. Geohistory modeling of Arctic Alaska (including the Chukchi shelf) and the southern Canada basin indicates that regional patterns of thermal maturity and timing of petroleum generation reflect geologic processes associated with rift-opening of the Canada basin and collision orogenesis along the Brooks Range–Herald arch from Jurassic through Tertiary time. The base of the Cretaceous–Tertiary Brookian sequence provides a regional reference horizon because most oil generation occurred as the result of Brookian burial. In Arctic Alaska, basal Brookian strata on the Beaufort rift shoulder grade from immature in the west to overmature in the east. From the crest of the rift shoulder, thermal maturity of basal Brookian strata increases southward into the oil window on the north flank of the Colville foreland basin and into the gas window in the foredeep. A .200-mile-wide area of immature to mature strata in the Chukchi Sea narrows eastward as the Brooks Range converges with the rift shoulder in the eastern North Slope. These patterns reflect generally low Jurassic to Tertiary sediment accommodation on the rift shoulder, large Cretaceous sediment accommodation in the Colville foredeep, and northward impingement of the Brooks Range onto the eastern part of the rift shoulder during the Tertiary. Fewer geologic data in the Canada basin increases the uncertainty of modeling. Projection of stratigraphy from the rift shoulder, reconstruction of regional sediment dispersal patterns, and consideration of source rocks in Arctic Alaska and Canada indicate the potential for four source rocks in the Cretaceous and Paleogene. Model results indicate that all four source rocks are mature or overmature across much of the southern Canada basin. The highest thermal maturity occurs in depocenters immediately north of the rift shoulder and on the eastern margin of the study area, which is the distal Mackenzie delta. The lowest thermal maturity occurs at the northern limit of modeling, more than 200 miles north of the rift shoulder and on the western margin of the study area, adjacent to the Chukchi borderland. A potential source rock in the Lower Cretaceous likely matured during the Early Cretaceous in a western depocenter related to sediment by-pass of the Chukchi shelf, but maturation of all source rocks elsewhere occurred during the Paleogene when large volumes of sediment were shed from the Brooks Range and through the Mackenzie delta.