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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 5. (May)

First Page: 869

Last Page: 870

Title: Oil and Gas Potential of Idaho Thrust Belt North of Snake River Plain: ABSTRACT

Author(s): John R. Warne

Article Type: Meeting abstract

Abstract:

The thrust belt north of the Snake River plain in south-central Idaho has the elements necessary for major oil and gas accumulations: large traps, thick reservoir rocks, top seals, rich oil-source rocks, and in at least parts of the area, a favorable temperature history. Only drilling is lacking.

The Utah-Wyoming Sevier thrusting extended north of the Snake River plain into southwestern Montana and south-central Idaho. Styles of thrusting and resulting traps are similar to the Utah-Wyoming portion of the thrust belt. After thrusting, large listric normal faults formed northwesterly trending valleys that were filled with Tertiary sediments. Some companies are looking for traps in thrusted Paleozoic rocks; others are exploring the valleys looking for stratigraphically trapped oil generated from deeply buried Tertiary sediments.

Paleozoic strata thicken westward from a normal cratonic sequence consisting of about 5,000 ft (1,524 m) of chiefly carbonate rocks in the east to more than 30,000 ft (9,144 m) of sandstones, conglomerates, shales, and carbonates in the west. Of particular importance as a hydrocarbon source rock was the accumulation of about 3,000 ft (914 m) of organic-rich Mississippian McGowan Creek Shale in a starved basin between the Antler uplift on the west and the craton on the east. Outcrop samples of this shale contain from 0.8-6.3% total organic carbon.

Paleotemperatures in much of the area were too hot for preservation of oil according to alteration of conodonts. At least two important exceptions to the generally high paleotemperatures exist. The Tendoy thrust plate in the eastern part of the area has a conodont alteration index of 1,

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which is immature. Surface samples from the White Knob thrust plate in the Pioneer Mountains west of Arco in the southwestern part of the area have a conodont alteration index of 2 and vitrinite reflectance ranging from 0.45 to 0.64. Where the McGowan Creek Shale on the White Knob plate extends into the subsurface to appropriate depths, it should be generating oil and gas at the present time. Additional sampling and drilling may indicate the existence of other cooler areas.

The McGowan Creek Shale acts as a seal on 5,000 ft (1,524 m) of lower Paleozoic dolomite. At least 1,500 ft (457 m) of this dolomite section may have enough porosity to be effective oil or gas pay.

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