The fauna of a Danian fossil Conservation Lagerstätten from the cold-water coral mound complex at Faxe, Denmark

Abstract

Fossil cold-water coral mound ecosystems are rare in geological history. One of the best known examples are the Danian coral mounds of Faxe comprising a complex interplay between corals, bryozoans, and a diverse associated fauna. The Baunekule facies is a special type of weakly consolidated coral rudstone to floatstone found in the Faxe Formation. The facies has a rich fauna of 220 species that are extremely well-preserved due to an early diagenetic recrystallization of aragonite to calcite prior to dissolution and is regarded as a fossil conservation Lagerstätten. The fauna lived between dead and living coral fragments on the flank of a growing Dendrophyllia coral mound. The fauna is authocthonous and dominated by small gastropods, polychaete tubeworms, bivalves and brachiopods. The fauna from Baunekule facies are compared to other parts of the Faxe Formation which have experienced a significantly different diagenesis. More than 57% of the fauna are not described from others parts of the Faxe Fm. More than 80% of the studied species from the coral limestone are unknown from other parts of Danian localities worldwide. The study of the Baunekule facies compares well with data from modern living coral mounds of Lophelia with a low species richness of framebuilding corals and a high species richness of the associated highly specialised fauna that show a dominance of attached suspension feeders, mobile carnivores, and grazers. The small gastropods are apparently lacking on the modern mounds, probably related to the sampling methods in the deep ocean. In general, there is agreements between the ecology of the fossil and the modern cold-water coral ecosystems with evidence for similar environments from Danian to modern time. The fossil cold-water coral mounds probably acted as diversity hotspots in the outer shelf – slope settings in the Danian epicontinental sea. • Palaeoecological studies of 21,000 specimens from rare fossil cold-water coral mounds • Identifying a rich fauna of 220 well-preserved small species (mainly gastropods) • Preservation is due to an early diagenetic recrystallization of aragonite to calcite. • The ecology of the fossil and the modern cold-water coral ecosystems are comparable. • The fossil cold-water coral mounds acted as diversity hotspots on the Danian shelves.