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.
Suggested Citation
Brown, C., 1974, Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa: Journal of Research of the U.S. Geological Survey, v. 2, no. 2, p. 219-232.
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 |