Document Type : Research Paper
Department of Geology, Faculty of Sciences, University of Tehran, Tehran, Iran.
Exploration Directorate of the National Iranian Oil Company, Tehran, Iran.
The study area is located in the Zard-Darreh village nearby Damavand city in the eastern part of Tehran province. Late Cretaceous strata are well-exposed in the Zard-Darreh village, comprising siliciclastic sediments with limestone stringers, which are overlain by red conglomerate deposits of the Fajan Formation. This study was carried out on a 96 m interval of the K3 and Fajan Formation to determine the precise age of the sampling interval. Eighty-nine surface samples were collected and treated for calcareous nannofossils. 53 species (27 genera) and 15 families were identified and nine biozones were established. Biozone CC20/UC15bTP occurs in the lowermost part of the K3 and represents the Late Cretaceous (Campanian) age. The NP1 to NP8 biozones are present the rest of the study interval, suggesting Early Paleocene (Danian-Thanetian) age. Based on calcareous nannofossils the Early Paleocene is recorded for the first time in the Zard-Darreh village in the Alborz Mountains. Likewise, a hiatus exists between the Late Cretaceous (CC20/UC15bTP ) and Early Paleocene (NP1), which encompasses the Maastrichtian stage and part of Early Paleocene. Finally, some small size calcareous nannofossils such as Biantholithus sparsus, Cruciplacolithus primus, Cruciplacolithus intermedius, and Cruciplacolithus asymmetricus are present in the NP1 biozone of Early Paleocene, which may indicate the effect of various environmental factors. Furthermore, some calcareous nannofossils such as Sphenolithus spp. and Discoaster mohleri are present in NP6 and NP7 biozones of the study area that may indicate a warning climatic condition toward the Eocene.