Determining sedimentation ages of high-grade metamorphic gneisses by theirpalynological record: a case study in the northern Schwarzwald (Variscan Belt, Germany)

In the northern Schwarzwald (Moldanubian Zone of the Variscan belt), paragn eisses drilled from approximately 2500 m depth at the Buhl-1 drilling site have experienced amphibolite-facies metamorphism and were later partly tran sformed to mylonites under greenschist-facies conditions. Completely graphi tised acritarchs and chitinozoans were recovered from these paragneisses an d mylonitic gneisses. Whereas both groups of palynomorphs give evidence of a marine depositional environment, only the chitinozoans are stratigraphica lly useful in this case and indicate a Paleozoic age. Previous findings of acritarchs in a different high-grade metamorphic gneiss unit within the Sch warzwald indicate an Upper Proterozoic marine sedimentation age. The spectr um of palynomorphs found thus far in the Schwarzwald in combination with pe trological data suggests that within the Moldanubian domain of the Armorica n microplate, rocks with different sedimentary records later experienced di verging prograde metamorphic histories. In general, the results reveal that palynological studies in combination with petrological data are a promisin g tool for reconstructing pre-orogenic settings in collisional belts.