Print this pageSubsidence History of Cook Inlet Basin, Southern Alaska: Basement Control on Forearc Basin Development
The Cook Inlet, lying between the Aleutian Trench and the Alaska-Aleutian batholith, has often been cited as a typical forearc basin. Upper (northeast) Cook Inlet Tertiary sediments have produced oil for over 25 years. Lower (southwest) Cook Inlet exploration, however, has been unsuccessful; previous studies have noted extensive zeolitization of potential Jurassic reservoirs. Geohistory analysis (backstripping) of published stratigraphic sections from outcrop and bore holes reveals two different tectonic mechanisms of basin development in the lower and upper Cook Inlet. Thermal subsidence coincident with radiometrically determined cooling ages of the Alaska-Aleutian batholith predominated in the lower Cook Inlet during the Jurassic, suggesting that this part of the basin ay be underlain by an extension of the batholith. Previous workers have noted a typical arc-unroofing sequence in Jurassic sandstones. The Tertiary section here is relatively thin.
In contrast, the upper Cook Inlet has had a more complex history. Accumulation of nearly 5,000 m of Tertiary sediments over a thin Mesozoic section appears to have resulted from crustal loading, possibly through accretionary thickening of trenchward metasediments. These accreted terranes may extend beneath the upper Cook Inlet basin, resulting in a relatively ductile basement susceptible to load deformation. Published sandstone QFL compositions in the Tertiary indicate mixed or recycled orogene provenances, with source terrains both arcward and trenchward.
Local basement type appears to have exerted a strong influence on sediment accumulation and petroleum potential in the Cook Inlet basin. Further study of the basin may thus lead to a better understanding of the overall construction and tectonic history of this complex convergent margin.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.