The Kojetice coticules: An important geological and age marker within the Moldanubian Zone?

The name coticule was first used for spessartine-bearing quartzites (Renard 1878) that represent metamorphosed finegrained Mn-rich sedimentary rocks. Based on metamorphic conditions and the composition of the siliciclastic sedimentary protolith, coticules contain different Mnminerals such as carpholite, hausmannite, or Mn-versuvianite. Although the Mn-rich sediments of the type locality were deposited on the continental shelf, the term coticule also was incorrectly applied to metamorphosed Mn-rich deep marine deposits and even exhalites. Within Variscan Europe and Acadian North America, coticules sensu Renard (1878) occur in sedimentary units deposited on the continental shelf and typically are of Ordovician age (Romer et al. 2011). Most importantly, they seem to be restricted to the Avalonian shelf. The provenance of the metasedimentary rocks of the Monotonous (Ostrong) and Variegated (Drosendorf) units of the Moldanubian Zone is not well constrained. There are however rare occurences of Mn-rich sedimentary rocks. We investigate whether these rocks show the geochemical and isotopic features of coticules from the Avalonian shelf, e.g., those from Nova Scotia (Canada) and the Ardennes (Belgium), which would provide a provenance proxi, and whether they also have an early Palaeozoic age. CONSTRAINTS FOR COTICULE FORMATION Mn-rich sediments form when redoxcontrolled dissolution and precipitation of Mn (and Fe) keeps pace with siliciclastic input, i.e., in sediment-starved settings. Early Palaeozoic coticules on Avalonia formed when sediment input from Avalonia was drastically reduced and the subordinate sediment component derived from Gondwana became chemically and isotopically distinct in the coticule-bearing layers, most prominently by negative Ndtvalues, elevated 87Sr/86Sr, and the REEpattern.