MICROBIAL CARBONATE PRODUCTION IN A STARVED BASIN - THE CRENISTRIA LIMESTONE OF THE UPPER VISEAN GERMAN KULM FACIES

The crenistria Limestone is a set of three autochthonous massive limes tone beds occurring with great lithological persistence in the Kulm Fa cies (ed III alpha. upper Visean) of the eastern Rheinisches Schieferg ebirge., Microfacies analysis reveals mainly minipeloidal fabrics and homogeneous micrite. Uncrushed, sediment-filled conchs of gonaitites r epresent loci of Sheltered preservation of primary carbonate textures. Calcified radiolarians are abundant, forming between 20 and 80% of to tal rock volume. The alleged algal genus Rectangulina is common in the crenistria Limestone. It is reinterpreted to represent the faeces of goniatites. For the first time the presence of in situ preserved spong es is reported. They can be recognized as delicate networks of microsp aritic needles embedded in peloidal fabrics. Hexactinellids with prima ry spicule arrangements can be found embedded in homogeneous micrite. The carbonate forming the limestone beds was produced microbially duri ng decomposition of soft tissue of the radiolarians and sponges. Durin g the ed III alpha. anoxia in the bottom waters of the Kulm Basin pers isted for long periods due to stable density stratification of the wat er column under humid climatic conditions. Oxic conditions in the bott om waters during formation of the limestone are indicated by bioturbat ion. the presence of sponges and the high Mn-contents of the carbonate . The latter derived from reduction of Mn-oxides during microbial carb onate formation. (C);, Elsevier Science B.V.