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The Omaha pool was discovered in November, 1940, by The Carter Oil Company's York No. 1, SE.-SE.-SW. Sec. 33, T. 7 S., R. 8 E., Gallatin County, Illinois. The producing area is now defined and extends over 360 acres located generally southwest of the discovery well. Production is from the Palestine and Tar Springs formations of the Chester series.
The pool lies 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 low-angle dikes from less than one foot to fifty feet in thickness composed of porphyritic lamprophyric rock rich in biotite and olivine occur at many levels in the Pennsylvanian and Chester series.
Contact effects indicate that at least some of the oil was in the sands prior to intrusion of the igneous material, suggesting a structure predating the intrusion. Pronounced doming of the structure probably accompanied intrusion. Earlier minor folding occurred at the close of the Mississippian.
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