NEW DIMENSIONS OF THE WEAUBLEAU STRUCTURE: A POSSIBLE METEORITE IMPACT SITE IN SOUTHWESTERN MISSOURI

Controversies surrounding enigmatic geologic structures along the 38th parallel from Hicks Dome in southern Illinois to Rose Dome in eastern Kansas have arisen from interpretations of their possible exogenic versus endogenic origin and the hypothesis that these were produced by serial meteorite impacts. Both sides of these debates acknowledge the need for fundamental geologic studies because little is known of the magnitudes of events that formed these features or their precise age or ages. For example, dimensions of the Weaubleau Structure in southern St. Clair County, Missouri previously were unknown, but new data suggest that it is circular, circa 19 km in diameter, and the product of a significant sub-Pennsylvanian event. The goal of our working group is to more fully characterize the Weaubleau Structure in order to determine its origin and its relationship to other reputed impact structures along the 38th parallel.

Structural complexity of the Weaubleau Creek area in the southeastern part of the structure was documented by Beveridge in 1951; in several locations, thrust slices of Lower Ordovician Cotter Dolomite are interposed with folded Mississippian Burlington Limestone. Undeformed Pennsylvanian strata overlie part of the structure, indicating a narrowly constrained age of middle Mississippian (Osagean) to early Pennsylvanian (Atokan). Ironically, the most complex geology lies at the junction of four 7.5' quadrangles and on the border between two 1°x 2° sheets, so the circular aspect of this structure was not detected previously.

A new digital elevation model (DEM) of the Weaubleau Creek area, superimposed over a topographic base map, reveals the structure: three-quarters of its perimeter is delineated by arcuate segments of the Sac River arm of Truman Reservoir, Bear Creek, and Coon Creek. The structure extends from approximately 1.5 km north of Collins to Osceola. A 50-km north-south topographic low bisects the structure and parallels Missouri Highway 13 in the southern part. Gravity and magnetic anomaly lows coincide with the circular structure, suggesting it is not related to a basement high or intrusive body. Nevertheless, the central part of the structure shows intense compressional deformation with isolated pods of polymict breccia and pervasive pressure-solution features.