Graptolitic argillite

Sedimentary rock found in Estonia

Graptolitic argillite is a marinite-type black shale of sapropelic origin. It is a blackish to greyish lithified claystone. The known occurrence of this rock is a graptolitic argillite of the Türisalu Formation in northern Estonia and northwest Russia. It is correlated with Swedish alum shale being its younger facial eastward continuation, and both being a part of the Baltoscandic Cambrian-Ordovician black shale, together with black shales in the Oslo region in Norway, Bornholm, Denmark, and Poland. Other known occurrences are in North America, the Malay Peninsula, and New Zealand.

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