Middle Jurassic stromatactis mud-mounds in the Pieniny Klippen Belt (Carpathians) — A possible clue to the origin of stromatactis

Four occurrences of Jurassic stromatactis mud-mounds were found in the Czorsztyn Unit of the Pieniny Klippen Belt (Western Carpathians) — in western Slovakia (Slavnicke Podhorie, Babina), and in the Transcarpathian Ukraine (Priborzhavskoe and Veliky Kamenets). Their stratigraphic range is from Bajocian to Callovian. The mounds consist of micropeloidal mudstones, wackestones to packstones with a fauna including pelecypods, brachiopods, ammonites and crinoids. Spicules and skeletons of siliceous sponges are abundant in every section. All of the mounds contain networks of stromatactis cavities that are partially filled with radiaxial fibrous calcite (RFC) and locally by internal sediments. At Slavnicke Podhorie, the sparry masses that fill stromatactis cavities are weathered out and show casts of sponges. Parallel study of the weathered casts and their cross-sections in slabs showed that they bear all the signs of stromatactis (relatively flat bottoms and digitate upper parts, RFC initial fillings and eventual blocky calcite later filling). Almost no original sponge structures were preserved. This strongly supports the possible sponge-related origin for stromatactis cavities.