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Abstract

Abstract The Cook Inlet basin in south-central Alaska is an intermontane half-graben about 200 mi (325 km) long and 60 mi (95 km) wide. The basin contains roughly 20,000 cu mi (84,000 cu km) of Tertiary sedimentary rocks estimated to have at least 1.5 billion bbl of proved reserves recoverable by present production techniques and 5 trillion cu ft of proved gas reserves in place, possibly 70 percent of which are recoverable.

This paper concerns the more extensively explored northern part of the basin. The stratigraphie and tectonic development of the basin includes three Mesozoic cycles of marine sedimentation and two Tertiary cycles of estuarine to nonmarine sedimentation. Each cycle was closed by an orogenic episode accompanied by a major geographic shift in the depocenter for the succeeding cycle and generally by some increase in the relative land area; thus, progressively more extensive land areas and a more restricted basin of deposition were produced. The stratigraphie succession in the basin includes a cumulative total of more than 40,000 ft (12,195 m) of Mesozoic sedimentary rocks and up to 30,000 ft (9,150 m) of Tertiary sedimentary beds.

The structural trend of the basin between its confining mountain borders is approximately N30°E. The enclosed Tertiary sedimentary beds are deformed into en échelon anticlines with more northerly trends diverging from the basin margin about 15°. The folds are concentric in habit and contain Mesozoic sedimentary and volcanic rocks in their cores. They have an essentially westward asymmetry, except along the northwest margin of the basin, where the structural development is influenced by the basin-bounding Castle Mountain fault system. In that system there is evidence for a right-lateral component of movement. Northwesterly-directed continental underthrusting along the Aleutian Trench could be an adequate mechanism to account for the structural shortening evident in the basin.

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