(Table 1, page 215) Chemical composition Mn deposits from the Middle Jurassic part of the Austrian Kalkalpen

The X-ray diffraction analyzes of two ferromanganese crust samples found at the base of the Klaus red Jurassic limestone beds of the Unterberg formation indicate pyrolusite as the main mineral. The crusts contain also a range of trace elements in concentrations comparable of present day oceanic deposits. The low Fe/Mn ratio found in sample 06-32a is in agreement with the geochemical data from Pacific Ocean manganese nodules and crusts of hydrothermal genesis. However, the simultaneously high contents in cerium and yttrium (rare earth metals) are more likely to suggest a precipitation of the manganese from the free water column (hydrogenetic origin). In addition, there are no identified hydrothermal sources in the vicinity of the hosting limestone beds. Iron-rich manganese nodules have also been found in the Jurrasic limestones beds of the Ruhpolding formation. In these deposits, hematite is the dominant mineral phase. The high Fe/Mn ratio as well the detritic material they contain (quartz, mica) lead to a possible continental margin origin for these nodules.