Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa

C. Ervin Brown

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USGS · 70232378

Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa

C. Ervin Brown

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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 P 2 0 5 . 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.

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Journal of Research of the U.S. Geological Survey Article

Source-reported bounding extent: 42.216313604344776° to 43.08894918346591° latitude; -91.549072265625° to -90.4339599609375° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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C. Ervin Brown. 1974. Phosphatic zone in the lower part of the Maquoketa Shale in northeastern Iowa. https://pubs.usgs.gov/publication/70232378

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