The initial phase of the Hönne Valley Reef at Binolen (northern Rhenish Massif, Middle Devonian)

Abstract The Hagen-Balve Reef Complex of the northern Rhenish Massif, Germany, is one best examples for globally widespread Givetian to Frasnian reefs. At its eastern end, in Hönne Valley, it reaches up 1000 metres thickness. In general, there limited knowledge concerning faunas and palaeoecology initial reef phases. A unique section at Binolen exposes sharp boundary between underlying, siliciclastic Upper Honsel Formation lower part reefal Formation. ca. 14 m thick succession assigned new Member investigated terms carbonate microfacies, micro-, macrofaunas. Seven microfacies types ( MF ) characterise a crinoidal coral-stromatoporoid garden setting MF-2 MF-6 or allobiostrome an open platform turning upsection into coral parabiostrome MF-7/8 ). base Asbeck locally defined by appearance back-reef facies types, such as fenestral limestones MF-9 ), which indicate transformation bioherm. Low-diversity conodont prove influx shelf organisms suggest age (probably Polygnathus timorensis Zone). There are two biofacies characteristic biostrome settings, Bipennatus Biofacies Simple Cone Biofacies. Thin sections reveal over 40 different builders (rugose tabulate corals, stromatoporoids, chaetetid sponges). Around 4200 microfossils from residues consist agglutinating foraminifers, calcareous sponge spicules (e.g. Heteractinida), scolecodonts, echinoderms (mostly crinoid ossicles holothurian sclerites), pyritised benthic ostracods, assumed calcified moulds chitinozoans, subordinate microvertebrates, other groups. They were analysed quantitatively order document changing distribution patterns environments through time. We distinguish six microfossil-based BF namely Ostracoda BF-O Foraminifera BF-F Scolecodont BF-S Chitinozoa BF-C Porifera-Scolecodont BF-PS Porifera-Echinodermata BF-PE Microfacies microfossil assemblages led reconstruction local development, consisting seven successive depophases with further subdivisions. base, sudden termination enabled proliferation microfaunas (Depophase I), followed longer deepening phase characterised exclusive bioclastic wackestones II). Depophase III short regressive floatstones. IV fluctuations relative sea-level, results three subphases. V resembles III, but argillaceous interbeds more abundant scolecodonts. It interval rudstones, grade coral-dominated bafflestones (auto)parabiostrome (both VI). VII represent facies, including pack-bindstones basal Member. systematic analysis represents pioneer work that should be tested expanded reefs Massif beyond.