Trace fossils in Ordovician radiolarian chert successions in the Southern Uplands, Scotland

ABSTRACTRadiolarian chert and associated siliceous claystone in the Southern Uplands of Scotland are examined, in order to study the Great Ordovician Biodiversification Event of benthic animals on the pelagic ocean bottom. Trace fossils which are uncommon, but convincing, are found in the grey chert and siliceous claystone of Gripps Cleuch. These observations constitute firm evidence that large benthic animals which could leave visible trace fossils had colonised the Iapetan Ocean by the late Middle Ordovician, confirming previous studies from Australia for Panthalassa, the other huge ocean. Red chert is, however, a poor recorder of trace fossils, probably because the highly oxidising environment breaks down organic matter, both inhibiting high-density activity of large benthic animals and removing clear traces of benthic animal life.

Late Norian (Late Triassic) Radiolarian assemblages from chert pebbles of the Pentalofos Formation (Mesohellenic basin, Greece). Palaeogeographic implications

Well-preserved Late Norian Radiolaria were extracted from two pebbles of radiolarian chert included in Lower Miocene conglomerates of the Pentalofos Formation, in the area of Meteora (Mesohellenic basin, Greece). Both samples yielded a similar assemblage characterized by the presence of species Betraccium deweveri PESSAGNO & BLOME, Bipedis acrostylus BRAGIN, Pylostephanidium ankaraense BRAGIN & TEKIN and several other taxa typical of the Betraccium deweveri zone (uppermost Norian). This is the first evidence of Upper Norian radiolarian cherts from Greece. It is likely that the studied chert pebbles were derived from ophiolitic complexes or distal continental margin series situated to the east of the Mesohellenic basin; they were part of the Upper Norian oceanic realm that was obducted, during the Late Jurassic, over the Pelagonian continental crust. During the Late Miocene they were still present east of Meteora and they have been eroded since.