Ordovician to Lower Mississippian cherts of the Roberts Mountains allochthon in central Nevada contain nodules, lenses, and streaks of phosphate as apatite. Major marine phosphate deposition is limited to latitudes less than 50° on margins facing large oceans to the east or west, or of Tethyan (equatorial sea) type; the Nevada margin was suitably located in the lower to middle Paleozoic. The Roberts Mountains allochthon overthrust the shelf of western North America very soon after deposition of the youngest phosphatic cherts, implying that they are most likely not far-traveled or exotic to North America. Phosphates of similar age and nature in the northern Sierra Nevada suggest proximity of Nevada and the northern Sierra Nevada in the early to middle Paleozoic.

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