North-Central Section - 46th Annual Meeting (23–24 April 2012)

Paper No. 28
Presentation Time: 8:00 AM-11:40 AM


OOSTENRYK, John B., Geology Department, Augustana College, 639 38th St, Rock Island, IL 61201,

Moline Chert was named after the city of Moline, Rock Island County, Illinois. It is known from two small outcrops and erosional float in the Rock River Valley 7 miles from its confluence with the Mississippi River. The type locality exposes bedded chert layers within carbonaceous shale of the Caseyville Formation. The Illinois Basin extends to the west under the Mississippi River into Scott and Muscatine Counties in Iowa. This is currently the only Pennsylvanian age chert reported in the Illinois Basin area. The occurrence is further defined by its location between two major unconformities. The Middle Devonian limestone is unconformably overlain by the Caseyville Formation shales which are then truncated by Quaternary tills.

First mention of this layer is by Worthen and Shaw, (1882). It is next mentioned by Birmingham and Van Dyke, (1981), who modify the stratigraphic column by Anderson, R.C.,(1967), to document its relative location while doing archaeological survey work.

The archaeological field is interested in a formal description of this material as it was utilized by prehistoric people from paleo culture until historic contact. Regional workers in archaeology may easily identify this material but it is acknowledged as being problematic further afield due to other Midwest cherts with similar coloration or texture. One notably similar material is Upper Mercer Chert from East Central Ohio which is also a Pennsylvanian age strata.

An initial, regional ground survey has documented the outcropping and float occurrences. Field survey is followed by an investigative review of regional drilling records in an expanding pattern from Moline, Illinois to develop a subsurface structural map of the currently undefined strata. Samples obtained from the mapping initiative will be processed by XRF analysis at Augustana College in Rock Island, Illinois to investigate a geochemical signature. An addititional selection of specimens will be prepared to document distinct diagenetic variations observed within the chert’s separate bedding planes within the formation. These procedures will maximze interpretation of this unusual material.