Delta Fault

Part of the Ste. Genevieve Fault Zone

Location

T14S, R2W, Alexander County (K-5)

References

J. Weller 1940, J. Weller and Ekblaw 1940, Nelson and Lumm 1985

Description

The Delta Fault was named by J. Weller (1940) for a now-abandoned village near the fault trace. Recent mapping (Devera et al.1994) confirms the Delta Fault to be essentially as shown by J. Weller. The fault trace is nearly linear and strikes N15°W for a distance of about 4 miles (6.4 km). It is a normal fault, dipping 60° to 80° east and having 100 to 200 feet (30-60 m) of throw down to the east. Slickensides and mullion on the fault surface indicate nearly pure dip-slip displacement. Zones of chert breccia, heavily cemented by silica and iron oxide have been observed along the fault. In places the fault splits into several closely spaced parallel fractures, which displace strata in a stepwise fashion. Minor faults and joints adjacent to the Delta Fault strike parallel with the latter.

The youngest rocks offset by the Delta Fault are Middle Devonian, and were clearly well lithified when faulting took place. The time of faulting cannot be bracketed more closely than post-Devonian, pre-Quaternary. The Atwood Fault and several smaller, unnamed faults are similar in trend and style to the Delta Fault.