AbstractsEarth & Environmental Science

"A geological investigation of the northeast portion of Des Arc Quadrangle in southeast Missouri was completed during the summer of 1958. Exposed Precambrian rocks include, from oldest to youngest, undifferentiated purple rhyolites with an interlayered tile-red rhyolite, andesine basalts with interlayered tuff, and an andesite. A diabase dike intrudes the lower purple rhyolites. The purple rhyolites account for about ninety-seven percent of the Precambrian exposures. Exposed Paleozoic rocks belong to the Bonneterre formation and include three members: (1) Lower Brown dolomite; (2) Light Gray dolomite with Tom Sauk limestone and arkosic sandstone and conglomerate facies; and (3) Upper Brown dolomite. These members correlate with zones 2, 3, and 4, respectively, of McQueen and Stewart for the Bonneterre formation of the Fredericktown area. Residuum derived from the Davis, Derby-Doerun, Potosi, Eminence, Gasconade, and Roubidoux formations covers much of the area. The Precambrian rocks show gentle dips, possibly of primary origin. Locally the tile-red rhyolite is inclined forty degrees. Primary structures include flow layering and poorly developed bedding in the rhyolites, plus contraction joints in all the Precambrian rock units. At least one fault occurs in the purple rhyolites. Initial dips off Precambrian knobs are the main structures in the Paleozoic rocks. Joints related to differential compaction occur around these knobs. Aeromagnetic data appear to correlate well with the calculated susceptibilities for the various exposed igneous rock types of the area, using Slichter's method of calculation. Possible economic use might be made of the Tom Sauk limestone exposed in Marble Creek valley for agricultural lime, in manufacture of portland cement, or for terrazzo. Small quartz veins in the Precambrian rhyolites show no apparent metallic values. Aeromagnetic positive anomalies in the area are not considered indicative of buried iron-ore bodies. A tuff exposed near the Blue School, however, shows a relatively high hematite content and might constitute low-grade iron ore of not more than 5,000,000 tons reserves. Lead ores in the Bonneterre formation are unlikely in the area since the favorable stratigraphic horizon of the nearby Fredericktown area (zone 1 of McQueen and Stewart) is missing" – Abstract, pages v-vi.