Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa
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Abstract
The basal beds of the Maquoketa Shale in northeastern Iowa include a basal silty phosphorite layer that is thickest near Dubuque. In Clayton County, Iowa, the bed averages about 1 foot thick (30 centimeters) and contains 22.5 percent P205 . Phosphatic dolomite that is 8 10 feet (2.4 3 meters) thick and occurs higher in the Maquoketa was observed only in Dubuque County. The thickest and most phosphatic rock in the Maquoketa appears to be coextensive with dark-brown shale, which also occurs mainly in Dubuque County. Rare-earth content of the phosphatic rock decreases southeastward across the area, ranging from 2,000 to about 120 parts per million. The thin low-grade phosphorite is typical of the platform-type phosphorite facies and may be' genetically related to the emergence of the Ozark uplift as an island late in the Ordovician period.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa |
| Series title | Journal of Research of the U.S. Geological Survey |
| Volume | 2 |
| Issue | 2 |
| Year Published | 1974 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Description | 14 p. |
| First page | 219 |
| Last page | 232 |
| Country | United States |
| State | Iowa |
| County | Clayton County, Dubuque County |
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