Silurian graptolites from Bohemia, Czech Republic

Sammanfattning: The only relatively undisturbed Ordovician to Middle Devonian sequence in the Bohemian Massif is preserved in the central parts of the Prague Basin. This part stretches c. 35 km from Prague in the north towards Zelkovice in the southwest. During Ordovician and Silurian times this area is thought to have been a part of the northern Gondwana margin. The lower Silurian shales were deposited in a tectonically controlled depression on a sediment-starved shelf with about 100-200 m water depth. Marine sedimentation in the Prague Basin started in the Tremadoc and continued to its culmination in mid-Devonian times during the Variscan Orogeny. The lower Silurian in the Prague Basin is composed of a continuous sequence of black shales, rich in fairly well preserved and highly diverse graptolite faunas. These faunas were the most cosmopolitan during graptolite evolution. Graptolites mainly collected by J. C. Moberg in Bohemia in the summer of 1893 have been examined. The collections consist of more than 400 samples of shale and mudstone. 39 species (predominantly monograptids), ranging in age from lower Llandovery to lower Pridoli, have been identified. 16 of these are index graptolites in Bohemia, but since the material was not collected for stratigraphical purposes a proper correlation with other areas is difficult. No obvious trend of size variations between species from different faunas was discovered, though slight differences from coeval assemblages of Britain, Bornholm and Bohemia can be observed.