Thermal and Deformational History of the Sadlerochit Mountains: Implications for Hydrocarbon Accumulations in the Arctic National Wildlife Refuge

By

P.B. O’Sullivan (Syracuse University) and W. K. Wallace (University of Alaska, Fairbanks)

Fission-track thermochronology and structural analysis constrain the timing and structural development of the Sadlerochit Mountains, located along the southern edge of the coastal plain in the Arctic National Wildlife Refuge (ANWR) of northeastern Alaska. Thermochronology results indicate that rocks within the region of the Sadlerochit Mountains experienced progressive heating during the Tertiary up to Middle Eocene time, after which two major episodes of rapid cooling occurred in the Middle Eocene at ~45 +/- 3 Ma and in the Late Oligocene, at ~27 +/- 2 Ma. These episodes of rapid cooling are interpreted to have occurred in response to km-scale erosional denudation, which resulted from uplift due to structural thickening during the emplacement of horses in a basement-involved duplex. Initially, at least one horse was probably emplaced to the north of the Sadlerochit Mountains at ~45 Ma. Subsequently, at ~27 Ma: 1) the Sadlerochit Mountains horse was probably emplaced behind the earlier emplaced horse(s), and 2) basement-involved deformation formed structures beneath the coastal plain to the north. These results indicate that potential hydrocarbon source rocks within the region were exposed to peak burial temperatures prior to the Middle Eocene, after which they experienced rapid cooling during the initial episode of structural deformation. Therefore, it is likely that hydrocarbon generation from these source rocks occurred before the formation of the basement-involved structures within the Sadlerochit Mountains region and to the north beneath the adjoining coastal plain. These timing relationships significantly limit the potential for structures beneath the ANWR coastal plain to contain recoverable hydrocarbons.

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.