Investigation shows that trace-element assemblages and clay-mineral ratios are in some respects characteristic of the environment of deposition of shales. Boron and rubidium are more abundant in a group of marine shales than in a group of fresh-water shales of Pennsylvanian age, whereas gallium is more abundant in the fresh-water group. Nickel and vanadium are concentrated in the organic fraction of the marine shales whereas lead, zinc, copper, and tin are more highly concentrated in the organic fraction of the fresh-water shales. In the region studied it appears possible to differentiate marine shales from fresh-water shales by quantitative spectrographic determination of boron, gallium, and rubidium.
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Egon T. Degens (1957) studied this question.
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