Palynostratigraphy and palaeobiogeography of Lower Palaeozoic Strata in the Ghelli Area, Northeastern Alborz Range of Iran (Kopet - Dagh Region)

Acritarchs from the Lashkarak, Ghelli and Niur formations of the western part of Kuh-e-Saluk were examined to more precisely determine the stratigraphical age. This study was also undertaken to assess the palaeogeographic relationships of the northeastern Alborz Range to the Southern and Northern Hemispheres during the Palaeozoic interval represented by these formations. A total of 78 acritarch taxa were encountered. Four new species together with two species in open nomenclature are described: Multiplicisphaeri-dium iranicum, Multiplicisphaeridium sp., Veryhachium membranispinum, Stelliferidium persicum, Leiofusa sp., and Estiastra iranicum. The encountered acritarch species have been arranged in six ascending local stratigraphic Zones. Zones I-II occur in the Lashkarak Formation, suggesting an Early Ordovician age (Tremadoc-Arenig). Zones III-V are present in the Ghelli Formation, indicating a Mid and Late Ordovician age. Zone VI appears in the lower part of Niur Formation and suggests the Early Silurian age (Llandovery). The Early Ordovician acritarchs of the Lashkarak Formation were com-pared with those from other parts of world. This comparison indicates a broad similarity with those of the same age in northern Africa, southern Europe and southwestern China. This similarity suggests that the northeastern Alborz Ranges were part of the Peri-Gondwanan supercontinent during the Early Ordovician. The Mid to Late Ordovician and Early Silurian acritarch taxa were also compared with those of the same age from elsewhere. This comparison indicates a broad similarity with those of northern Africa, southern Europe, the Middle East and the United States. This similarity suggests that the Peri-Gondwanan palaeocontinent began to move toward the Northern Hemisphere palaeocontinent during the Mid and Late Ordovician and by the Silurian formed the supercontinent of Pangea. Diverse acritarch taxa in the Early Ordovician (Lashkarak Fm.), Mid and Late Ordovician (Ghelli Fm.) and Early Silurian strata (Niur Fm.) reveal a marine environment for each formation.