Abstract

Discussion of a paper by J.W. Gruner (Geoscience Abstracts 1-3102). Nonmarine Cretaceous sediments in the Maryland Coastal Plain contain authigenic rutile, pyrite, and siderite. The presence of siderite and pyrite indicate a redox potential of between -0.1 and -0.3. The pH was about 3 - 4 because many of the clays are now acid. The alteration of ilmenite to rutile and pyrite accounted for only a small part of the total pyrite. Certain bauxites formed in reducing conditions also contain authigenic minerals.

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