Mud Creek Fault Zone (New Name)
Part of the Sandwich Fault Zone
Old Name: Mud Creek Fault
Location
T24N, R9 and 10E, Ogle County (A-5)
References
Templeton and Willman 1952, Kolata et al. 1978, Kolata et al. 1983
Description
Templeton and Willman (1952) described and illustrated the Mud Creek Fault in a quarry in Section 30, T24N, R10E. Their illustrations of the structure indicated several faults, therefore, the feature should be called a fault zone. Kolata et al. (1978) mentioned the faults in the quarry and also mapped several more faults in T24N, R9 and 10E. These newly discovered faults were mapped on the basis of outcrop data.
Templeton and Willman (1952) illustrated a sharp flexure cut by steep faults and downthrown on the north side (ffig. 54). Displacement observable within the quarry is 100 feet (30 m); overall displacement undoubtedly is greater, because rocks at both ends of the exposure dip steeply. Most of the faults are normal. Reverse movement is indicated on the south fault (fig. 54). Along this fault a narrow slice of sheared shale of the Decorah Subgroup is upthrown relative to dolomite of the Galena Group on either side. Templeton and Willman (1952) mentioned open horizontal tension cracks and evidence for bedding-plane slippage within the quarry.
The Mud Creek Fault Zone lies on the northeast flank of the Oregon Anticline near its northwestern end. The Oregon Anticline is immediately northeast of the Sandwich Fault Zone. If projected northwestward, the Mud Creek Fault Zone would intersect the Plum River Fault Zone. Structural relationships in this area are poorly known because of the scarcity of outcrops and well data.
