Acritarch evidence on Silurian age of the low-grade metamorphic Palaeozoic rocks in the Kraishte area (Morava Unit)

The age and relationships between the sedimentary Palaeozoic formations of the Morava Unit in Kraishte area are well known. However, the low-grade metamorphic Palaeozoic formations - Cheshlyantsi, Bazovitsa and Kosovo, cropping out in the area of the town of Zemen and the village of Treklyano, Kyustendil Region, are in complicated tectonic relationships and contain scarce or no fossils. The Bazovitsa and Kosovo Formations, along with the whole sedimentary Palaeozoic of the Morava Unit, belong to the Penkyovtsi Thrust, whereas the Cheshlyantsi Formation is included in the Milevets Thrust. In this paper, new evidence on Silurian age of the Cheshlyantsi and Kosovo Formations are presented which are based on acritarchs and other organic-walled microfossils. The Bazovitsa Formation contains no microfossils in Bulgaria but similar meta-sedimentary rocks in Eastern Serbia were dated as Silurian and Devonian. There is no confirmation of Ordovician age for any of the studied formation as it was supposed by previous authors. The palaeontological constraints on Silurain age, here reported, rather support the concept that the Cheshlyantsi and Kosovo Formation were in primary lateral relations between each other, as well with the Silurian non-metamorphic Shale Series and Shale-Carbonate Series of the Penkyovtsi Thrust.