HOW MONTANA'S DEEPEST HOLE CUT MISSISSIPPIAN CARBONATES UNDERNEATH PRECAMBRIAN BELT

Chris H. Peterson, Robert C. Nims Unocal Corp. Los Angeles The Unocal 1-B30 Federal Canyon Creek well was drilled in the Montana thrust belt about 27 miles northwest of Helena to test Mississippian carbonates in a seismic structure in the footwall of the Eldorado thrust (Fig. 1). The well penetrated more than 12,000 ft of thrusted Precambrian belt metasedimentary rocks before encountering a faulted and fractured footwall section of Cretaceous through Mississippian shales, sandstones, and

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