About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 50 (1966)

Issue: 10. (October)

First Page: 2221

Last Page: 2244

Title: Stratigraphy and Petroleum Potential of Lower Cretaceous Inyan Kara Group in Northeastern Wyoming, Southeastern Montana, and Western South Dakota

Author(s): Dudley W. Bolyard (2), Alexander A. McGregor (3)

Abstract:

The Inyan Kara is a varied group, consisting of sandstone, shale, conglomerate, variegated siltstone, and claystone, at the base of the Cretaceous in the Black Hills and in the subsurface of surrounding areas. It includes the Lakota Formation, below, and the Fall River Formation, above; the two are separated by a disconformity. Whereas the Lakota has a dominantly continental aspect, the Fall River consists of deltaic and other marginal marine deposits, littoral to neritic sandstone, and offshore shale deposited during the first major Cretaceous marine transgression. The Fall River intertongues northwestward with the overlying marine Lower Thermopolis Shale.

Correlation of thin marine shale beds and an intervening sandstone unit west of the Black Hills with a medial variegated facies east of the Black Hills permits subdivision of the Fall River into Liscom Creek, Morton, and Coyote Creek Members, in ascending order. Gross arrangement of these members is shingle-like; where one is thick, the others tend to be thin or absent.

During the time of Lakota deposition, a northwest-flowing river developed along a regional synclinal depression which extended through the modern Black Hills. Southward encroachment of the sea and shifting of deltas along its margin explain the thickness and facies relations within the Lakota and the members of the Fall River Formation.

Oil fields on the eastern flank of the Powder River basin in Wyoming produce from sandstone beds up to 80 feet or thicker. Most of the oil is trapped behind convex updip permeability barriers. The producing sandstone reservoirs are believed to have been deposited in meandering channels which are approximately parallel with the present-day structural contours. Although petroleum has been found only in the Wyoming part of the tri-state area of Wyoming, Montana, and South Dakota, geologic conditions favorable for oil entrapment also occur in parts of western South Dakota and southeastern Montana.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24

AAPG Member?

Please login with your Member username and password.

Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].