Black shales formed under anaerobic conditions and devoid of bioturbation structures display fine lamination and a primary fabric characterized by parallel clay flakes.
Gray to dark-gray shales correspond to more oxic conditions and comprise either extensively or only partly bioturbated facies. The first facies shows a homogeneous aspect on X-radiographs with few recognizable burrows, as well as individually, randomly oriented particles similar to unbioturbated, flocculated clay; however, there are no the cardhouse structures typical of flocculated clays. The second facies includes both areas of randomly oriented particles and areas of parallel to subparallel particle orientation, which suggests a less important sediment mixing by benthic species.
KeywordsSulfide Zeolite Calcite Pyrite Montmorillonite
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