New Names
Many large and significant structural features in Illinois have never been named on published maps or in reports. Treworgy (1981) listed 19 "significant unnamed structures" in Illinois. Most of these, along with several features that were not mentioned previously, are named in this report (table 3). A search of the literature revealed additional unnamed structures not listed or shown by Treworgy; these newly named structural features are included in this catalog (table 4). Among the newly named structures are several of the largest domes and anticlines that support major oil fields in Illinois. For example, the Bridgeport Anticline in Lawrence County is 10 miles (16 km) long, 2 miles (3 km) wide, and has closure of more than 200 feet (60 m) on Mississippian strata. The Lawrenceville Dome, just south of the Bridgeport Anticline, is about 6 miles by 3 miles (10 km by 5 km) and has closure of more than 100 feet (30 m). These two structures provide traps for oil fields that account for most of the nearly 400 million barrels of oil that have been produced in Lawrence County. The Johnsonville Dome in Wayne County is about 3 miles (5 km) in diameter and has closure of more than 100 feet (30 m). It supports the Johnsonville Oil Field, which has yielded approximately 55 million barrels. Two large monoclines, previously unnamed, are major elements in the La Salle Anticlinorium. On the north, the Peru Monocline is 65 miles (105 km) long and shows relief of up to 1,600 feet (400 m). The Charleston Monocline on the south, is more than 100 miles (160 km) long and shows relief of up to 2,500 feet (750 m) on pre-Pennsylvanian horizons. Its relief makes it the largest fold in the Illinois Basin.
