Radiolarian cherts and associated siliceous rocks of the Rhenish Massif and Harz Mountains, lower Carboniferous (Mississippian), Germany

Abstract Siliceous sedimentary rocks are major constituents of the rock succession in Central European part Kulm Basin (Mississippian) and crop out eastern Rhenish Massif western Harz Mountains. These occur five lithostratigraphical units: Oberrödinghausen Formation, subdivided into Kahlenberg Subformation (“Untere Alaunschiefer”) Hardt (“Schwarze Kulm-Kieselschiefer/-Lydite”), Laisa Formation (“Helle Kulm-Kieselschiefer”) coeval Hillershausen (“Kulm-Kieselkalke”), as well Bromberg (“Kieselige Übergangssschichten”); upper Hastarian to Asbian. Biostratigraphically, formations can be dated by means radiolarians and, succession, also ammonoids. Various siliciclastic, calcareous locally, mafic volcanic pyroclastic associated with these strata. Four palaeogeographical facies zones have been identified. Radiolarian chert, spiculitic homogenous silicified tuff main siliceous types. mostly form current-laminated grey, black, greenish or reddish beds rhythmically alternating layers mudstone are, places, variably intercalated grey black mudstones siltstones, phosphorites, metabentonites, turbiditic limestones, greywackes quartz arenites. The depositional area was situated at northwestern margin elongate, relatively narrow tropical Palaeotethys Ocean, a shallow-bathyal sea strait between Gondwana Laurussia that successively closed during Variscan Orogeny. Westbound nutrient-rich currents favoured high fertility plankton (radiolarians). latter gave rise formation pure biosiliceous oozes muds under temporarily anoxic conditions seafloor, when, contemporaneously, terrigenous detrital input sedimentation rates became low (approx. 2 mm/1000 a) due level dry climate. Biosiliceous terminated, Gondwana–Laurussia collision, multiplied, basin narrowed oceanic circulation restricted resulting lowering radiolarian productivity.