Abstract

An isolated limestone deposit preserving thousands of specimens of the dimerelloid brachiopod Peregrinella multicarinata is exposed in fossil-poor Hauterivian strata northwest of the town of Planerskoje on the Crimean Peninsula in southern Ukraine. The limestone consists of micrite that encloses abundant detrital components, mostly brachiopod shell fragments, and also contains authigenic, framboidal pyrite. Cavities are rare; a few have been filled by a sequence of anhedral yellow calcite, seam micrite, banded and botryoidal cement, and equant calcite spar. The limestone preserves a diverse mollusk fauna of low abundance, including modiomorphid, lucinid, and buchiid bivalves and abyssochrysoid, ampullinid, and neritid gastropods. The negative δ13C values of the micrite (as low as −13.6‰) and the character of the associated mollusk fauna indicate that this limestone formed at an ancient hydrocarbon seep. This evidence supports the earlier interpretation of Peregrinella as a seep-restricted brachiopod. The new Ukrainian records of some of the mollusk taxa—notably Caspiconcha and Paskentana—significantly extend the geographic range of these apparently seep-restricted mollusks, suggesting that mollusks at Early Cretaceous seeps had a wider geographical distribution than previously appreciated.

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