Geologic Interpretation of Magnetic Map, Keokuk County, Iowa

In 1964, surface measurements of the vertical component of the earth\u27s magnetic field were made in Keokuk County, Iowa. The geologic conditions responsible for the magnetic anomalies can be attributed almost entirely to changes in the lithology of the Precambrian crystalline basement complex about which no direct information is available. The basement complex probably includes granitic, basic igneous and/or metavolcanic rocks, and the estimated depth to the top of the complex is about 3,000 feet. There is little correlation between the magnetic anomalies and known Paleozoic structures, but knowledge of the structures is very limited