Waterloo-Dupo Anticline
Location
Western Monroe and St. Clair Counties, Illinois
(H,I-3); St. Louis County, Missouri
References
S. Weller 1906, Fenneman 1911, Mylius 1921, Lamar 1922, Bell 1929b, S. Weller and J. Weller 1939, Cole 1961, Tikrity 1968, Buschbach and Bond 1974, Nelson and Lumm 1985
Description
The Waterloo-Dupo Anticline is a sharply asymmetrical structure, the axis of which strikes slightly west of north. Some early reports refer to it as the Waterloo Anticline, and others, as the Dupo Anticline. The names were derived from two oil fields developed in separate areas of closure on the same structure. The compound form Waterloo-Dupo Anticline has become widely; but not universally accepted in later reports.
The east limb of the anticline dips at 2° to 4°, whereas the west limb dips steeper than 45° in places. Lamar (1922) and S. Weller and J. Weller (1939) both asserted that the western limb is faulted, although details are lacking. Bristol and Buschbach (1973) mapped more than 300 feet (90 m) of closure on the top of the Galena (Trenton) Group in the Waterloo Oil Field near the south end of the anticline. The Dupo Oil Field, farther north, is in a separate smaller area of closure.
The Waterloo-Dupo Anticline apparently underwent at least two separate periods of movement. Late Devonian uplift is indicated by subsurface thinning of Silurian and Devonian strata across the crest of the fold (Tikrity 1968). The main episode of folding took place near the end of the Mississippian or early in the Pennsylvanian Period. Nearly horizontal strata of the Carbondale Formation (middle Pennsylvanian) overlie Chesterian formations dipping 40° to 50° on the west limb of the fold (fig. 69, Nelson and Lumm 1985). Slight post-Pennsylvanian folding may have taken place, but is difficult to demonstrate because Pennsylvanian rocks are absent along the anticlinal crest.
The structural style and timing of deformation of the Waterloo- Dupo Anticline are similar to those of the La Salle Anticlinorium, Salem and Louden Anticlines, and most other major anticlines north of latitude 38°N in Illinois. Drape-folding of sedimentary layers across a basement fault is strongly suggested.
More than 405,000 barrels of oil have been produced from the Galena (Trenton) Group in the Waterloo Oil Field, which was discovered in 1920 and converted in part to gas storage in 1951. The Dupo Oil Field, discovered in 1928, has yielded more than 3 million barrels from the Galena.
