Lithistid spicules in Turonian sediments of the Variegated Shale in the Silesian Nappe, Polish Outer Carpathians

Abstract

Turbiditic silty and sandy intercalations in the Turonian Variegated Shale from the Silesian Nappe (Polish Outer Carpathians) contain numerous sponge spicules among siliciclastic fine-grained particles. The highest amount of spicule admixture is nearly 50%. In such layers, they create spiculitic sublitharenite microfacies. Sponge spicules contain forms belonging mostly to the Lithistida group (97% of morphotypes), with small admixture of spicules from the Hexactinellidae group. Tetraclones with a high content of different types of triaenes dominate among desmas, what indicates the dominance of sponges from subfamily Tetracladina . Preservation state of spicules is generally poor. The Variegated Shale that consists the sponge spicules were accumulated in deep sea basin, below the calcium compensation depth. Most probably, the spicules derive from loose material accumulated earlier in various parts of the basin slopes, from which they were exhumed and again redeposited by turbidity currents during the Turonian.