Pittsburg Anticline

Part of the Cottage Grove Fault System

Location

T8S, R3E, Williamson County (J-6)

References

Nelson and Krausse 1981

Description

The Pittsburg Anticline was mapped from numerous coal test boreholes and from elevation surveys and geologic mapping in underground mines. It strikes west-northwest and is approximately 6 miles (10 km) long and 2 miles (3 km) wide (fig. 26). The fold is relatively flat-topped and has dips as steep as 15° to 20° on the northwest and southeast flanks. Many faults, most of which strike northwest, cross the fold axis.

Nelson and Krausse (1981) interpreted the Pittsburg Anticline as a subsidiary fold resulting from the compressional component of right-lateral wrenching in the Cottage Grove Fault System. An alternate explanation is that the Pittsburg Anticline is part of a positive flower structure (Harding 1985, Harding and Lowell 1983). This interpretation is supported by the presence of reverse faults dipping inward on the northeast and southwest flanks of the fold (fig. 59). The anticline thus occupies an up-faulted block, partially surrounded by branches of the Cottage Grove Fault System. The steeply dipping flanks of the anticline are adjacent to the bordering faults. The anticline may have developed as the central block was squeezed upward by oblique slippage along the bordering faults.

The Pittsburg North, Johnston City East, and Stiritz Oil Fields were developed in Mississippian pay zones on the Pittsburg Anticline. The three fields together have yielded approximately 1.5 million barrels of oil and more than 1 billion cubic feet of gas.

Figure(s)

Figure 59   Pittsburg Anticline, according to mine survey data on the Herrin Coal Member. The anticline is flanked on both sides by faults that dip inward. Seismic data suggest that the faults join at depth and that the anticline lies at the crest of a flower structure in the Cottage Grove Fault System.