Drowning, extinction, and subsequent facies development of the Devonian Hönne Valley Reef (northern Rhenish Massif, Germany)

Abstract The Hagen-Balve Reef is one of the largest Devonian carbonate complexes in Rhenish Massif exposed many former or active, economically significant quarries, especially Hönne Valley region at its eastern end. timing and patterns reef drowning, final extinction, middle Frasnian to Famennian post-reefal facies history, including details global Kellwasser Crisis, were studied based on two boreholes (HON_1101 B102) outcrop Beul near Eisborn. More than 100 conodont samples provided a fine biostratigraphic framework included new forms left open nomenclature. ca. upper 80 m Asbeck Member Formation consists relatively monotonous lagoonal successions assigned four microfacies types. local diversity builders, mostly stromatoporoids, low. Fenestral microbialites indicate very shallow rather hostile back-reef settings. Near Middle/Upper boundary, eustatic pulses Frasnes Events led backstepping margin, with core/outer slope overlying facies. This flooding drastically reduced accumulation rate enabled invasion drowned areas by open-water organisms, such as polygnathid conodonts. Within this Eisborn Member, five types numerous subtypes are distinguished low-diversity “coral gardens” final, top lower parabiostrome dominated tabulate colonial rugose corals. There was no cap stage (“Iberg Facies”). Two phases Basal Event marked dark, organic rich limestones subordinate builders. Based fauna from nodular new, (hemi-)pelagic Formation, extinction caused Middlesex lower/middle boundary. eight subphotic submarine rise distinguished. After phase extreme condensation, faunas enable recognition most zones. semichatovae regionally unique intercalation organic-rich, laminated black shales intervening thin core HON_1101. Lower represented HON_1101 atypical, moderately C org -rich, recrystallized, peloidal ostracod-mollusk pack-grainstones. Upper level begins an ostracod bloom, followed either recrystallized mollusk wacke-packstones (HON_1101) laminated, argillaceous mudstones (B102). first indicates rarely documented subphotic, better oxygenated setting typical As elsewhere, top-Frasnian severe. for oxic, pelagic rise. youngest recorded fall Palmatolepis marginifera utahensis Zone. Regionally uniform lydites Hardt show that palaeotopography levelled before base Viséan. case study comparisons western parts other reefs underline significance Givetian anoxic events causes extinctions.