Late Jurassic through Cretaceous Tectonics and Basin Evolution, Chukchi Shelf and Northwestern Alaska

The Late Jurassic through Cretaceous geological history of the Chukchi Shelf and adjacent onshore Alaska is the focus of an integrated study using seismic, well, outcrop and geochronological data across a 150,000 km 2 area. This work suggests several fundamental linkages between tectonics and basin evolution, and clarifies offshore-onshore relations. Inherited tectonic elements influenced Late Jurassic and subsequent structural response to stresses related to the Chukotka (Late Jurassic through Cretaceous) and Brooks Range (Early Cretaceous and Tertiary) orogenies, as well as Beaufortian and Brookian sediment routing and accumulation patterns. Particularly important elements include the Chukchi Platform, a long-lived and high-standing block of pre-Mississippian rocks beneath the western Chukchi shelf; Hanna Trough, a Late Paleozoic failed rift system that bisects the shelf from north to south; and Alaska rift shoulder, a Jurassic and younger uplift related to opening of the Amerasia Basin. Contractional deformation, apparently related to the Chukotka orogeny, spanned at least the Late Jurassic through Late Cretaceous on the Chukchi Shelf. The initial pulse of contraction is evidenced by a series of en-echelon, northsouth trending reverse or transpressional faults, which display up to 1 km of structural relief and root into older normal faults associated with the Hanna Trough. These inversion structures likely reflect maximum stress oriented obliquely to relict normal faults. Petroleum-prospective Upper Jurassic – Neocomian strata display eastward growth across the faults, and include east-dipping clinoforms. East-facing shelf-margins in this clinothem merge beneath the east-central Chukchi Shelf with southwest-facing shelf margins in younger parts of the Kingak clinothem, which trends northwestward across the North Slope, thus forming a southeast-facing embayed shelf margin. The Chukchi clinothem, projected onshore to the south, crops out in the western Brooks Range as the Tingmerkpuk sandstone, whose origin has been considered enigmatic. (continued)