Original paper

The Kupferschiefer: Lithology, stratigraphy, facies and metallogeny of a black-shale.

Paul, Josef

Abstract

The Kupferschiefer Fm. is a well-known stratigraphic marker horizon throughout central Europe. It is a typical black shale, representing the lowermost unit of the marine Upper Permian Zechstein Group of the Central European Basin. It is missing only in peripheral subbasins and bights, like the South German Bight. Thickness and facies depend on the palaeogeography and hydrography of the Zechstein Sea. Generally, the Kupferschiefer is less than one metre thick and consists of laminated black mudstones, marls and carbonates. A thin basinal, a thicker marginal and a swell facies rich in carbonates can be distinguished. There is a fossiliferous carbonate bed, called Mutterflöz, on swells and marginal areas below the typical black shale facies. Other names of this bed are Border Dolomite, Border Limestone, or Productus Limestone. It is time equivalent with the lower part of the Kupferschiefer in basinal sites and therefore a subformation of the Kupferschiefer. The typical Kupferschiefer was deposited under anoxic conditions in a stratified sea. Three cycles consisting of varying carbonate and TOC contents can be traced all over the basin. Most likely, these cycles were caused by a fluctuating redox discontinuity layer (RDL) which corresponds to Milancovitch cycles.Benthic fauna is missing in the Kupferschiefer Sea because of the H2S containing water. The lacking oxygen protected the dead and at the bottom lying nekton against decay. The benthos occurring in the schwellen facies was transported to the black shale facies from shallow water areas above the RDL. Brachiopods, bryozoa, pelecypods, gastropods, cephalopods, crinoids, and corals, nearly all organisms found in the overlying Zechstein Limestone also occurred in the Kupferschiefer Sea. But only pollen and spores facilitate the biostratigraphic classification of the Kupferschiefer to subzone Ia of the Lueckisporites virkkiae assemblage Zone which corresponds to the Abadeh Stage (early Dzulfian).On swells and in marginal facies, the carbonate fraction of the Kupferschiefer consists to a large amount of dolomite, which, most likely, has been formed early diagenetically under reducing conditions. The basinal facies consists of calcite, but this is a late diagenetic dedolomite. A further contribution to the formation of dolomite provided descendent Mg-rich solutions from the gypsum deposits of the Zechstein. Epigenetic ascendent solutions, abounding with Fe, Mn, and Mg favoured the formation of dolomite, ankerite, and pyrite.The main components of the organic matter in the Kupferschiefer are kerogenes. Under the light microscope, only structureless particles are to be seen, whereas under the fluorescence microscope algal or bacterial cysts can be recognized. The analysis of the biomarkers, e.g. hopane, sterane, and porphyrines, proved that photosynthetic micro-organisms are producers of the organic matter.In terms of sequence stratigraphy, the Kupferschiefer is deposited in the Transgressive Systems Tract (TST) of the first Zechstein Sequence. The position of the maximum flooding surface (mfs) of this first sequence is in the lower part of the Zechstein Limestone.The Kupferschiefer hosts a large quantity and variety of heavy metals like copper, lead, zinc, silver and other precious metals. High concentrations of these metals are restricted to small regions of the depositional area. Ascending epigenetic solutions leached these metals from Rotliegend sediments and volcanics. The metal-containing areas are situated at the margins of the Zechstein basin or above deep-reaching faults. In the other areas, the synsedimentary contents of heavy metals do not exceed values which are normal for black shales. The epigenetic flux of metals containing solutions took place in several phases starting from the Triassic up to the Tertiary. High concentration areas are in Lower Silesia in Poland, east of the Harz Mountains, and in the Richelsdorf area. In Germany, mining of the Kupferschiefer stopped 1990, whereas in Lubin, Silesia, a large quantity of copper, silver, and other precious metals is produced. It is one of the largest copper mines in the world.

Keywords

zechsteinkupferschieferstratigraphylithologypalaeogeographymetallogeny