A BURIED RIVER VALLEY WITHIN THE SPRING VALLEY QUADRANGLE IN NORTH-CENTRAL ILLINOIS

The Spring Valley 7.5’ Quadrangle occupies the area between 89º07’30” and 88º15’ west longitude, and 41º15’00” and 41º22’30” north latitude. The quadrangle includes the towns of Peru, Spring Valley, Granville, Standard, Cedar Point, and Dalzell. The principal drainages in the area are the Illinois River, Cedar Creek, All Forks Creek, and Spring Creek. A buried valley (Ticona Valley) located in the southeast portion of this Quadrangle was explored by using the s-wave seismics, borehole logs, and a surficial geologic mapping. This Quadrangle contains the confluence of the Illinois River and the ancient Ticona Valley.

The Ticona Channel is a major pre-Wisconsin buried bedrock paleovalley, which was formed during Illinoian (approximately 200,000 years) time. The channel is filled with Illinoian deposits, capped with later Wisconsinan deposits, and dissected the Pennsylvanian aged units in this area. The Illinoian deposits, formally known as the Pearl Formation, averages 20 m (60 ft) in thickness and consists of grayish tan to brown, sand, silt, and gravel. The Pearl Formation crops out just east of Illinois Highway 29 near south of Spring Valley, Illinois. According to earlier literature, the buried channel enters the Quadrangle at the southeast corner trending toward the center of the valley, and then dipping toward the southwest corner where it would join the ancient Mississippi Valley. This valley has steep walls, ranges about 10- 37 m (30-110 ft) deep, and is about 2.4-4.8 km (1.5-3 miles) wide.

The results of this investigation provide a better understanding of the geometry and material of the ancient river valley. The new data afford a revised interpretation of the Ticona Channel’s orientation and geometry. The channel's confluence with the modern Illinois River is about 15 km upstream than what was previously thought. Also the channel's walls are much steeper and its course is straighter than its representation in previous models.