PROVENANCE ANALYSIS OF THE GROVER GRAVEL

The Grover Gravel caps ridgetops in St. Louis County, Missouri. The deposit is mostly chert, but includes large erratic clasts of purple quartzite. These erratics appear to require glacial transport, but they are present south of the Missouri River, which is the accepted glacial boundary in northeast Missouri. Nevertheless, several facts show a genetic link between the Grover and the oldest glacial deposit in Missouri, the 2.4 Ma Atlanta Formation. First, the gravel composition closely matches clasts within the Atlanta till west of St. Louis County; and secondly, the gravel has been found directly atop pediment surfaces in its type area truncating weathered remnants of a till closely resembling the Atlanta. The Atlanta till has a relatively high proportion of metamorphic:igneous clasts and a heavy mineral composition that also implies a metamorphic source area east of the Grenville Front. Therefore detrital zircon analysis is an ideal means of evaluating the provisional assignment of the till in St. Louis County to the Atlanta Formation and any genetic links between this till and the Grover Gravel.