Microhabitat complexity—an example from Middle Devonian bryozoan-rich sediments in the Blankenheim Syncline (northern Eifel, Rheinisches Schiefergebirge)

A Middle Devonian section in the Blankenheim Syncline (northern Eifel, Rheinisches Schiefergebirge) contains a rather diverse fauna dominated by bryozoans, brachiopods, corals and other taxa, such as calcimicrobes. The section covers sediments of the Junkerberg Formation and the transition to the Freilingen Formation. The transition between the Junkerberg and Freilingen formations coincides with the base of the otomari Event Interval. The section displays an overall transgressive trend in shallow subtidal and deeper subtidal environments below fair-weather wave base. In contrast to the general transgressive trend, one horizon is interpreted to represent a regressive trend of local origin. Sedimentation rates were quite low, as indicated by the abundant occurrence of suspension-feeding organisms. According to Standard Microfacies Types (SMF), the carbonates represent mainly wackestones and floatstones and can be assigned to SMF 5 and SMF 8, respectively. Complex fossil communities in some horizons suggest excellent living conditions during deposition. Large abundances of calcifying taxa, such as Girvanella, occur in some layers, particularly at the base of the Junkerberg Formation. Other encrusting/calcifying organisms are present in various layers, suggesting deposition during supersaturation of CaCO3 minerals in a calcite sea in a low-energy environment. The studied bryozoan fauna is very diverse throughout the entire section, erect branching colonies being dominant. Five new taxa are described: the trepostomes Trachytoechus globosus sp. n., Multihemiphragma minor sp. n. and Eridotrypella multaeformis sp. n., and the rhabdomesine cryptostomes Isostylus vulgaris n. sp. and Bigeyella prima n. sp. Lenaporidae fam. n. is erected for the genera Lenapora and Bigeyella.