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Regional Tectonic and Petroleum Implications of Cretaceous Strata of Alaska Chukchi Shelf

Abstract

Integration of seismic, well, shallow core, 40Ar/39Ar (Ar), apatite fission track (AFT), detrital zircon U/Pb (DZ), and biostratigraphic data from the Alaska Chukchi shelf provides a record of Cretaceous tectonics and sedimentation from the front of the Wrangel-Herald arch, across its foreland, and into the North Chukchi, Canada, and Colville basins. Geochronology of tephra (Ar) and analysis of minimum DZ crystallization and AFT cooling ages, effective tools as the result of coeval volcanism on the Russian Chukotka peninsula, and biostratigraphy confirm a complete Aptian through Campanian (and perhaps younger) stratigraphy preserved in parts of the Chukchi shelf. AFT analysis suggests prolonged Cretaceous exhumation of the Chukotka thrust belt, rapid cooling at the front of the thrust belt (Wrangel-Herald arch) between 120 and 80 Ma, and slow cooling in the proximal foreland beginning between 90 and 80 Ma. Lower Cretaceous stratal geometry displays proximal, topset seismic facies that grade northward and eastward into clinothems comprising bottomset, foreset, and topset seismic facies. Upper Cretaceous stratal geometry in the west includes a series of north-dipping, shingled unconformities and in the east includes a series of low relief sequence-bounding disconformities. The up-section change in strata geometry likely reflects a temporal gradation in tectonic influences. Early Cretaceous influences included relict accommodation domains (positive and negative) inherited from Late Paleozoic extension (Hanna trough and flanking platforms), approaching north-vergent contraction in the Chukotka thrust belt, and presence of high accommodation domains to the north (North Chukchi and Canada extensional basins) and east (Colville foreland basin). Late Cretaceous influences included waning of north-vergent contraction in the Chukotka thrust belt, rejuvenation of extensional accommodation in the North Chukchi basin, and filling of the Colville basin. In essence, the Chukchi shelf during the Cretaceous was an area of moderate to low accommodation, decreasing sediment supply, and increasing sediment by-pass between provenance areas to the south (Chukotka thrust belt) and high accommodation (>8–12 km) to the north (North Chukchi and Canada basins) and east (Colville basin, Early Cretaceous only). A significant consequence of this setting is a huge area (>80,000 km2) across which key source rocks and prospective reservoirs are in the oil window.