CONSTRAINTS ON THE JURASSIC - TERTIARY EXHUMATION HISTORY OF THE CHUKCHI SHELF FROM APATITE FISSION TRACK DATA

The U.S. Chukchi Shelf, estimated to hold huge petroleum potential, has been tested by just five, >20 year-old exploration wells. The shelf also occupies a critical juncture among Paleozoic – Tertiary tectonic elements, including the Hanna trough, Alaska rift shoulder, Wrangel-Herald “arch” thrust belt, and North Chukchi basin. To elucidate the thermal and exhumation history of these tectonic elements, we integrate new apatite fission track (AFT) data from 27 sample intervals in the five exploration wells plus four shallow cores, legacy thermal maturity data, and seismic reflection data.

Most AFT samples are cuttings from exploration wells, and most exhibit a spectrum of annealing kinetic proxy measurements. Thus, AFT data interpretation involved defining AFT age and length subdistributions for samples that include cavings, partially annealed grains, and mixed kinetic populations. Nevertheless, stratigraphic and regional trends in AFT ages indicate a robust dataset. Interpretation of AFT data was aided by inverse models, which were statistically constrained by AFT age and length data and vitrinite reflectance measurements.

Data from the northeastern-most well (Diamond) indicate complete annealing in Triassic strata and subsequent cooling initiating between 200 and 170 Ma; we attribute the cooling to exhumation of the Alaska rift shoulder during opening of the Canada Basin. Data from the southernmost well (Klondike) indicate complete annealing in Neocomian – Aptian strata and prolonged cooling from ~80 to <30 Ma; we attribute the cooling to exhumation of the Wrangel-Herald foreland during waning phases of Chukotkan orogenesis. Samples from the other wells and shallow cores were either not annealed or partially annealed; those samples generally yielded cooling ages ranging from mid-Jurassic to mid-Cretaceous and are interpreted to record exhumation of the Wrangel-Herald and Chukotka provenance areas. Collectively, the new AFT data illuminate the Jurassic-Tertiary deformational history on the Chukchi Shelf, with exhumation related to both Alaska rift shoulder uplift in the northeast and contractional tectonism in south.