An example for black shale development on a carbonate platform (Late Triassic, Seefeld, Austria)

Abstract

East of Seefeld/Tyrol the Hauptdolomit facies (Triassic, Norian) is accompanied by an organic-rich intercalation, the Seefeld facies. Three facies were distinguished, which developed within a separate basin within the Hauptdolomit carbonate platform. These facies have been investigated in an environmental and palaeoecological context applying microfacies analysis, palynology, organic petrology, organic geochemistry and stable isotope geochemistry. As the controlling factors of sedimentation, sea level changes are suggested for large scale fluctuations, and climatic changes for variations on a smaller scale. Within the basin facies a mum-scaled rhythm can be observed, which was obviously seasonally controlled. A major amount of organic material of the deposit has been produced by microbial activity under anoxic conditions. Causes for the absence of pollen and spores in many black shale deposits are discussed.