Date of Graduation

Fall 2017

Degree

Master of Science in Geospatial Sciences

Department

Geography, Geology, and Planning

Committee Chair

Charles Rovey II

Keywords

detrital zircon, geochemistry, uranium-lead dating, provenance analysis, glacial, Missouri, Grover Gravel

Subject Categories

Geochemistry | Geology

Abstract

The Grover Gravel in the St. Louis, Missouri area contains a mix of chert, quartzite, jasper, and ironstone in clast sizes ranging up to 60 cm. The gravel varies in thickness from a veneer to over 30 feet and rests on upland surfaces at elevations sometimes exceeding 300 feet above the floors of major valleys. A pre-Pleistocene age generally has been proposed or assumed for the gravel, which classically has been interpreted to be a meandering-stream deposit atop an extensive flat upland surface, which was subsequently eroded and dissected by rejuvenated streams. However, large quartzite boulders in the gravel also indicate a history of glacial transport. In this study, the Grover Gravel is compared to the Mill Creek till and Atlanta till as possible sources, along with another gravel known as the Mounds Gravel located in southeastern Missouri and southern Illinois. Detrital zircon uranium-lead geochronology analysis reveals that the gravels and the Mill Creek till are all dominated by the Western Cordillera and Grenville Provinces. A pebble count and heavy mineral analysis of the Mill Creek and Atlanta tills shows that the two deposits are not from the same glaciation. The Mill Creek till contains more unstable weathered mafic grains, less tourmaline and garnet, and a much higher percentage of polished chert, oolitic chert, vein quartz, agate, and quartzite pebbles than the Atlanta till. However, the Mill Creek and Grover Gravel share similar amounts of those types of pebbles and both units have a very similar distribution of zircon ages. This implies that the Mill Creek till represents a major glaciation that reached south of the Missouri River in St. Louis County. In addition, the small percentage of grains from the Superior Province within the Grover and Mounds Gravels indicate that these two units do not require fluvial transport from the north via a giant ancestral Mississippi River as has been hypothesized by recent studies.

Copyright

© Grant Spoering

Open Access

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