Assumption Anticline (New)

Location

T13 and 14N, R1E, Christian County (F-5)

References

Bell and Leighton 1949, Whiting 1956, Howard 1979, Nelson 1987b

Description

Although this is one of the largest anticlines in central Illinois, it has not been named. Treworgy (1981) listed it as a "significant unnamed structure." The name Assumption Anticline is introduced for this structure, which provides the structural trap for the Assumption Consolidated Oil Field and lies about 3 miles (5 km) northwest of the town of Assumption.

Whiting (1956) stated that about 50 feet (15 m) of structural closure exists on the top of the productive Middle Devonian carbonates in the Assumption Consolidated Oil Field. The map of the base of the New Albany Group (Cluff et al. 1981) has a contour interval of 100 feet (30 m) and shows a northeast-trending anticline with one contour line of closure. The anticline is mapped as trending north-northeast on the Beech Creek ("Barlow") Limestone (ISGS open files) and is about 5 miles (8 km) long by 1.5 miles (2.5 km) wide. Two separate highs are mapped on the Beech Creek. The larger high has about 70 feet (21 m) of closure and is centered in Section 9, T13N, R1E. A smaller high is centered in Sections 20 and 29 of the same township and has only about 20 feet of closure. Howard (1979) mapped a basal Pennsylvanian paleovalley crossing the Assumption Anticline and inferred that the structure was extant or rising during earliest Pennsylvanian time. The Assumption Anticline has almost the same areal extent and vertical relief on the Herrin Coal Member (Middle Pennsylvanian) as on the Beech Creek Limestone (Nelson 1987b). In this respect, the Assumption Anticline differs from many of the large anticlines of central Illinois, which have considerably less relief on Pennsylvanian than on pre-Pennsylvanian horizons. Most of the uplift of the Assumption Anticline evidently took place after deposition of the Herrin Coal.