The Cook Inlet Basin

The Cook Inlet Basin is a northeast-trending collisional forearc basin that stretches from the Gulf of Alaska into South central Alaska, just east of the Matanuska Valley. It is located in the arc-trench gap between the Alaska-Aleutian Range batholith and contains roughly 80,000 cubic miles of sedimentary rocks. These sediments are mainly derived from Triassic, Jurassic and Cretaceous sediments.

The region is heavily influenced by two major tectonic elements which are still active in the area today. The western side of the basin lies directly above the Aleutian subduction zone where the Pacific Plate is subducting beneath the North American Plate. However the eastern side of the basin overlays the subduction of the Yakutat microplate beneath the North American plate. Active subduction along various sides of the basin produce regional compression that lead to major folding, faulting and the formation of anticline structures within the sediments. Anticline structures provide ideal hydrocarbon traps, and so the Cook Inlet Basin is widely known for its hydrocarbon accumulations and its overall production of oil and gas.

The geology of Alaska is characterized by the collision and accretion of terranes over the last 100 Ma and its features formed as a response to plate convergence and subduction.

Alaskan tectonism is mainly dominated by the subduction of the Pacific Plate beneath the North American Plate. The subduction boundary is marked by a 4,000 km long trench known as the Aleutian Trench, where seismic activity is common and the volcanic arc produced is part of the Pacific Ring of Fire. The initial subduction of the Pacific Plate triggered the formation of the Burin Bay Fault system, which is responsible for northeast trending faults throughout the western portion of the Cook Inlet Basin. Thrust type shearing is present along this active margin and it causes the sediments to form anticline structures as a response to regional compression.

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