Biostratinomy and sedimentary environment of the echinoderm-sponge biostromes in the Karchowice Beds, Middle Triassic of Upper Silesia

Adam Bodzioch


Biostratynomia i środowisko sedymentacji biostrom szkarłupniowo-gąbkowych z warstw karchowickich (środkowy trias Górnego Śląska)

Echinoderm-sponge biostromes occur in the Karchowice Beds in the western part of Upper Silesia. The biostromes occur in pelitic limestones strongly burrowed by enteropneustans. Skeletal epifauna, represented mainly by hexactinellid sponges, crinoids and echinoids, accompanied by less numerous brachiopods, bivalves, gastropods and polychaetes, was living on marine shallows and formed small bioherms in the central parts of the biostromes. Sedimentation was strongly influenced by storms which destroyed the bioherms by covering them with sediments, and redistributed bioclastic material disintegrated earlier by microbial activity and dissolution. The material was sorted during the transport in this way that only carbonate mud was deposited in the low areas of the bottom between the biostromes. The mud was later colonized by enteropneustans. Episodic stroms decreased the sedimentation rate by remowing carbonate mud and fine bioclastic fraction from the shallows. The narrow zone of bioherms, oriented NWW - SEE, was probably forming a barrier between a coastal lagoon to SSW and the open epicontinental sea to NNE. Coral bioherms are present inthis zone above the sponge bioherms, indicating the shallowing of the sedimentary basin.

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