Omaha Pool and Mica-Peridotite Intrusives, Gallatin County, Illinois1
R. M. English, R. M. Grogan, 1948. "Omaha Pool and Mica-Peridotite Intrusives, Gallatin County, Illinois", Structure of Typical American Oil Fields: A Symposium of the Relation of Oil Accumulation to Structure, J. V. Howell
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The Omaha pool was discovered in November, 1940, by the Carter Oil Company’s York No. 1, SE. ¼, SE. ¼, SW. ¼ of Sec. 33, T. 7 S., R. 8 E., Gallatin County, Illinois. The producing area is now defined and extends over 450 acres located generally southwest of the discovery well. Production is from the Palestine and Tar Springs formations of the Chester (Upper Mississippian) series.
The pool is on the crest of a large dome and is exceptional in that igneous rock is found in intrusive contact with the producing sands. Sills and dikes ranging from less than one foot to 50 feet in thickness, composed of mica-peridotite, occur at many levels in the Pennsylvanian and Chester series.
Contact effects indicate that some oil was in the sands before intrusion of the igneous material, suggesting a certain amount of prior uplift. The pronounced doming of the structure and the intrusion of dikes and sills may have accompanied intrusion of a hypothetical subjacent laccolithic or stock-like igneous body, probably in post-Pennsylvanian-pre-Cretaceous time. Minor folding occurred earlier at the close of the Mississippian period.
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Structure of Typical American Oil Fields: A Symposium of the Relation of Oil Accumulation to Structure
Modern petroleum geology in the United States had its beginning in the first decade of the 20th Century when the U.S. Geological Survey began mapping the structure of the rocks in and near old fields in order to discover the various types of structural conditions under which oil and gas are trapped. Structural geology has evolved as a branch of the broader science far more rapidly than have methods of mapping the attitude of rocks at the surface. This volume, published in the late 1920s, was designed to afford authoritative and modern descriptions of the structure of typical oil fields in the United States. Each of the 39 fields contained here is described by an author who is intimately familiar with the available data. The relationship of structure at the surface and at depth for different terranes is clearly set forth wherever the strata are not parallel. The volume concludes with a summary paper on the role of geologic structure in the accumulation of petroleum. Fields include: Florence, Colorado; Stephens, Arkansas; Kevin-Sunburst, Montana; Bradford Pennsylvania; and Salt Creek, Wyoming.