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Source rock potential of middle cretaceous rocks in Southwestern Montana

American Association of Petroleum Geologists Bulletin

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Abstract

The middle Cretaceous in southwestern Montana is composed of a marine and nonmarine succession of predominantly clastic rocks that were deposited along the western margin of the Western Interior Seaway. In places, middle Cretaceous rocks contain appreciable total organic carbon (TOC), such as 5.59% for the Mowry Shale and 8.11% for the Frontier Formation in the Madison Range. Most samples, however, exhibit less than 1.0% TOC. The genetic or hydrocarbon potential (S1+S2) of all the samples analyzed, except one, yield less than 1 mg HC/g rock, strongly indicating poor potential for generating commercial amounts of hydrocarbons. Out of 51 samples analyzed, only one (a Thermopolis Shale sample from the Snowcrest Range) showed a moderate petroleum potential of 3.1 mg HC/g rock. Most of the middle Cretaceous samples are thermally immature to marginally mature, with vitrinite reflectance ranging from about 0.4 to 0.6% Ro. Maturity is high in the Pioneer Mountains, where vitrinite reflectance averages 3.4% Ro, and at Big Sky Montana, where vitrinite reflectance averages 2.5% Ro. At both localities, high Ro values are due to local heat sources, such as the Pioneer batholith in the Pioneer Mountains.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Source rock potential of middle cretaceous rocks in Southwestern Montana
Series title:
American Association of Petroleum Geologists Bulletin
Volume
80
Issue:
8
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
American Association of Petroleum Geologists Bulletin
First page:
1177
Last page:
1184
Number of Pages:
8