Retort Phosphatic Shale Member

The Permian Phosphoria Formation in the northwestern Interior United States contains two phosphatic and organic-ncarbon-rich shale members, the Meade Peak Phosphatic Shale Member and the Retort Phosphatic Shale Member. Ihese rocks were formed at the periphery of a foreland basin between the Paleozoic continental margin and the North American cratonic shelf. The concentration, distribution, and coincidence of phosphorite, organic carbon, and many trace elements within these shale members probably were coincident with areas of optimum trophism and biologic productivity related to areas of upwelling. In the Phosphoria sea upwelling is indicated to have occurred by sapropel that was deposited adjacent to shoals near the east flank of the depositional basin. 

General geology. The Phosphoria Formation lies above the Permian Park City Formation, formed largely of limestone, and is overlain by the Triassic Dinwoody Formation (Fig. 8). The Phosphoria Formation contains two primarily phosphatic shale members, the Retort and the Meade Peak. The Meade Peak Member is the larger of the two main phosphorite bodies, and is the source of samples considered in our current work discussed here. The Meade Peak Phosphatic Shale Member is comprised of phosphorites, phosphatic shales, dolostones, siltstones, and mudstones (Fig. 9). 

---