Middle Givetian echinoderms from the Schlade Valley (Rhenish Massif, Germany): habitats, taxonomy and ecostratigraphy

Abstract

Crinoids and ophiocistioids from classical fossil localities of the National Geosite “Schlade Valley”, NE of Bergisch Gladbach (Germany) are reported for the first time. The fossils were derived from the reefal Buchel Formation (lowermost Middle Givetian, Middle Devonian) at the northern flank of the Bergisch Gladbach-Paffrath Syncline (eastern Rhenish Massif). From the abandoned quarry “Im Grubenfeld”, skeletal elements of holothuroids, ophiocistioids and crinoids are documented from a bituminous marly shale horizon in the middle Buchel Formation. The finely bedded shales suffocated an already stressed, muddy “reefal” fauna, which followed on top of a massive Actinostroma stromatoporoid biostrome. The shales characterise an apparently regionally occurring event, herein denominated as “Schlade Event”. It is considered to represent the climax of the transgressive Lower pumilio Event. The autochthonous and vagile epibenthic echinoderm fauna on top of the “Schlade Event Layer” is low diverse. It is regarded, herein, as post disaster fauna, recolonising the dysaerobic softground/soupground together with the well-adapted trilobite Goldius. The cupressocrinitids Halocrinites and Procupressocrinus were recognised from a younger stratum of the upper Buchel Formation within the abandoned “Zimmermann Quarry” near-by. The crinoids settled in high-energy environments of a reef flat in association with characteristic brachiopods (Uncites, Stringocephalus) and bivalves (Eomegalodon) and were swept by storms into reef flat pools. In those exceptional fossil lagerstatten, which are marl-filled obrution deposits, they were parautochthonously preserved together with an autochthonous fauna composed mostly of gastropods and extremely rare allochthonous biota from the open marine realm. Published biozonations of the Buchel Formation, especially on ammonoids, are evaluated, partly corrected and supplemented by ecostratigraphic associations of rugose corals and crinoids. Schlade Event below and Taghanic Event above are major factors controlling biozonation. Taxonomic notes concern revision of the holothuroids from the Schlade Valley and discussion of taxonomic attribution of ophiocistoids and crinoids. All species formerly included in “Abbreviatocrinites” are transferred to genus Halocrinites, which has priority.