Lithology and geochemistry of Silurian black graptolitic shales of the Carnic Alps (Austria)

Geoscience Research Reports 33, 2000 (GRR for 1999), pages 157–162

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Abstract

The distribution of major and trace elements in Silurian graptolitic shales of the Carnic Alps suggests important changes of depositional environment. With the beginning of the Silurian transgression and progressing subsidence, mostly chemically mature "siliceous" shales with generally higher Zr values were deposited in normal marine environment. The character of sedimentation has rapidly changed during Wenlock when chemically less mature calcareous shales together with carbonate dominated. The termination of basinal subsidence in Upper Silurian (Ludlow-Přídolí), has resulted in the deposition of chemically well mature graptolithic shales. Sulphidic graptolitic shales were mostly deposited inrestricted marine environment (low O2 concentrations) with local periods of inhospitable bottom conditions (little or no O2 was present and H2S may have been continually or intermittently present). These facies can be classfied as metalliferous black shales and represent a potential environmental harm especially in areas where carbonate lithology is missing.