As so ci ate Ed i tor-Wojciech Granoszewski A di verse Late Oligocene to Early Mio cene cal car e ous nannofossil as sem blage was ex am ined from the Qom For ma tion in the Cen tral Iran Ba sin, and the Oligocene-Mio cene bound ary was iden ti fied based on the quan ti ta tive anal y sis of the as semblages in 303 smear slides. Eleven well-es tab lished cal car e ous nannofossil bio-events are de lin eated in the Up per Oligocene through Lower Mio cene. The re sults clearly show that the High est Oc cur rence (HO) of Sphenolithus delphix is the clos est bio-event to the bound ary as tra di tion ally de lin eated on the lithostratigraphic cri te ria, and pro vides a dis tinct biohorizon be low it. The Low est Oc cur rence (LO) of the spe cies Discoaster druggii is the old est Mio cene bio-event that is observed shortly af ter the HO of S. delphix, show ing that cal car e ous nannofossils are well suited for ap prox i mat ing the Oligocene-Mio cene bound ary in the Qom For ma tion. The Oligocene-Mio cene bound ary is placed in the up per part of Sub-mem ber "c1" in all three sec tions stud ied here and it is trace able through out the Cen tral Iran Ba sin, which makes a poten tially re li able marker ho ri zon for se quence strati graphic and hy dro car bon stud ies in the area.
Oceanic Red Beds studied are well known in the upper Cretaceous (CORBs, i.e. Cretaceous Oceanic Red Beds), but their presence and genesis have hitherto not been intensively discussed for equivalent Paleogene deposits. We describe a red to purple shale interval from the Pabdeh Formation, Zagros basin, Iran, which can be assigned to Late Paleocene to Early Eocene age, nannofossil zones NP9-NP12. Parts of the purple marl interval within NP9/NP10 coincide with the PETM (Paleocene-Eocene Thermal Maximum) interval. Coccolithus pelagicus, Sphenolithus moriformis, Sphenolithus orphanknollensis, and Toweius ssp. are dominant in nannofossil assemblages in this interval, and PETM event taxa such as Discoaster araneus appear. Based on whole rock geochemistry and microfossil assemblages, the red to purple marls were deposited in an oligotrophic environment with low nutrient (Ba) values, and were accompanied by a shift to more oxic conditions and low amount of TOC in an oceanic basin. Low amount of major elements like Si, Al and Fe indicates low terrestrial input and relatively high amount of CaO (biogenic element) emphasizes the open sea and pelagic deposition of the shale. Warm deep water can be inferred by the presence of the dinoflagellate taxa Impagidinium and nannoplankton taxa, Discoaster. As a result, the purple shale can be considered as typical Paleogene ORBs in the Zagros basin deposited under very similar conditions as well studied Tethyan Cretaceous oceanic red beds.
For the first time, the calcareous nannofossils of the chalky limestone of upper Abderaz Formation and lower part of Abtalkh Formation have been studied. In this study, 83 nannoplanktonic species of 45 genera were identified and presented. A biostratigraphic study of calcareous nannofossils from this section has allowed the recognition of five calcareous nannofossil biozones of Sissingh (Geol Mijnbouw 56:37-65, 1977) CC17-CC21. On the obtained calcareous nannofossils, the age of this section is Late Santonian/Early Campanian-Early Late Campanian.
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