Wittenberg Trough (Discarded)

Location

From central Union County, Illinois, to Perry and Ste. Genevieve Counties, Missouri

References

Meents and Swann 1965, North 1969, Nelson and Lumm 1985, Devera 1986, Tarr and Keller 1933

Description

As defined by Meents and Swann (1965), the Wittenberg Trough was a narrow fault-bounded trench that contained outliers of Devonian rocks. As mapped, it was 70 miles (113 km) long, 1 to 10 miles (1.6-16 km) wide, and 100 to more than 1,000 feet (30-300 m) deep. Meents and Swann (1965) stated that the Wittenberg Trough developed before or during deposition of the Grand Tower Limestone (Middle Devonian) and persisted into the Mississippian Period.

More recent studies indicate that the Wittenberg Trough was not a depositional basin, but merely the product of structural movements along the Ste. Genevieve Fault Zone. The history of the fault zone was first worked out by S. Weller and St. Clair (1928) and refined by Nelson and Lumm (1985). Late in the Middle Devonian Epoch, just after deposition of the Grand Tower Limestone, the north side of the Ste. Genevieve Fault Zone was uplifted. Devonian strata then were eroded from the upthrown northern block; Mississippian rocks now unconformably overlie pre-Devonian strata north of the fault. Then late in the Mississippian to early in the Pennsylvanian Period, the southern (Ozark Dome) side of the fault zone was raised; Devonian rocks subsequently have been eroded from most of the area south of the Ste. Genevieve Fault Zone. Because the later movements took place on faults mostly located a few miles south of the faults that moved in Devonian time, a narrow strip of Devonian rocks has been preserved within the Ste. Genevieve Fault Zone. Devonian rocks originally may have covered a much larger area of the present Ozark Dome and Sparta Shelf. Partial onlap of Devonian rocks onto the Ozark Dome is indicated by the finding of residual chert containing fossils from the lower-Middle Devonian Series (Grand Tower) in a diatreme near Avon, Missouri, about 10 miles (16 km) outside the Wittenberg Trough (Tarr and Keller 1933).

Additional evidence against the existence of a trough during deposition of the Grand Tower is provided by the paleoecology and sedimentary features of the Grand Tower Limestone. A shallow, well-agitated marine environment ranging from shallow subtidal to above storm wave base is indicated (Devera 1986).

In summary, the term Wittenberg Trough is misleading and does not accurately represent the depositional and structural setting of Devonian rocks in the east flank of the Ozark Dome; therefore, use of the term should be discontinued.