CRETACEOUS TO PALEOGENE EVOLUTION OF NORTH CHUKCHI FOLD-AND-THRUST BELT AND WEDGE-TOP BASINS

The North Chukchi fold-and-thrust belt (NC-FTB) comprises a Late Cretaceous, doubly vergent FTB and wedge-top basin system overprinted by grabens formed during Cenozoic extensional and strike-slip deformation. The belt occupies more than 30,000 km² of the US, Russia, and international outer shelf of the Chukchi Sea and forms the eastern end of the North Chukchi Basin (NCB). We interpret the history of the NC-FTB using seismic-reflection and sparse well data.

The NC-FTB developed above attenuated crust deformed during Jurassic to Early Cretaceous rifting of the NCB and Canada Basin. The belt is up to 130 km wide, from a southern boundary beneath the northwestern US Chukchi shelf to a northern boundary on the southeastern margin of the Chukchi Borderland; it extends more than 300 km westward into the Russian part of the NCB. The North Chukchi High, an area formed by contraction and crustal thickening where Upper Cretaceous or younger strata lie directly on high-standing pre-Mississippian basement rocks, delineates the east-central part of the NC-FTB.

Deformation along the southern margin of the NC-FTB is constrained by Popcorn anticline, a south-verging fault-related fold uplifted and exhumed (>1.5 km) during the Late Cretaceous and penetrated by the northernmost exploration well on the Chukchi shelf. The anticline collapsed with the onset of regional extension, forming the Cretaceous-Paleocene (KP or Mid-Brookian) unconformity, which is onlapped by lower Paleocene strata. North-verging fault-related folds are predominant in the northern part of the belt and seismic correlation suggests timing of deformation was similar throughout the NC-FTB.

Although wedge-top basins are present throughout the FTB, larger and thicker ones are located above the most highly attenuated crust. Wedge-top basin successions thin by onlap across, or pinch out by onlap onto, structurally higher parts of the underlying FTB. These successions display complex stratal geometries that may form a gradation from Late Cretaceous contraction to Paleogene extension. The wedge-top basins accommodated sediment derived locally from the FTB and regionally from orogens to the south, and partitioned sediment dispersal from all sources westward into the deep NCB.