Cook Inlet Basin
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.
[1] 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.
Thrust type shearing is present along this active margin and it causes the sediments to form anticline structures as a response to regional compression.
The collision of the Yakutat microplate and the Alaskan superterrane is believed to have happened sometime during the Miocene epoch, after the subduction of the Pacific Plate had already begun.
This collision is also causing the buildup of an accretionary prism known as the Kenai Mountains, which borders the southeast region of the Cook Inlet basin.
[4] The Fault system originated during the pre-miocene period as a result of megathrust subduction and it was subsequently filled with turbidity deposits.
[6] These formations are present along the East-West margin of the Bruin Bay Fault zone and are intruded by igneous plutons originating from dehydration melt produced by Pacific Plate subduction.
The Kamishak Formation is reflective of a shallow reef environment that graded into deeper marine sediments that were deposited during a transgressive ocean sequence.
The formation records periods of shallow, intermediate and deep crustal levels originating in an oceanic island arc environment.
[8] During the middle to late Jurassic, an amalgamated superterrane of Tertiary, Quaternary and Mesozoic sediments collided into the continental margin of Alaska.
The stratigraphy of this time period records the synorogenic sedimentation of marine Jurassic and Cretaceous sandstone, shale and limestone.
[1] The Lower Tuxendi Group is composed of deep water marine sediments that indicate two instances of a transgressive and regressive oceanic sequences.
The lithologies display dramatic facies changes from large sediments (cobbles, boulders) to bioturbated sandstones which contain an abundant amount of fossils.
[10] The Hemlock Formation is roughly 600 feet thick and dominated by conglomerate deposits which are consistent with a fluvial-deltaic type of environment.
[10] In the Sterling Formation, there is roughly 10,000 ft of thick sandstone that was deposited in the central and eastern regions of the Cook Inlet Basin during the late Tertiary-early Quaternary period.
