Original paper

Stratigraphic distribution of planktonic foraminifera from the Qom Formation: A case study from the Zanjan area (NW Central Iran)

Daneshian, Jahanbakhsh; Ghanbari, Maliheh


The Miocene epoch represents one of the most critical intervals in earth history affected by Plate tectonics, climate changes and faunal turnovers. The Lower – Middle Miocene outcrops of sedimentary rocks are present in Iran in several sections and are found in the Zagros, Central Iran, Alborz and Makran areas. Two stratigraphic sections in the northwest of Central Iran (Qom Basin), which are relatively rich in foraminifera, were considered for this study. Several studies have been conducted in this basin, but age determinations and stratigraphic correlations of these sediments still remain con- troversial. This study focuses on the critical role of planktonic foraminifera for biostratigraphy and chronostratigraphy of Cenozoic sediments. The micropalaeontological study conducted resulted in the detection of 15 genera and 28 species of planktonic foraminifera. Particularly the presence of planktonic foraminifera such as Praeorbulina transitoria, Globigerinoides sicana, Praeorbulina curva and Orbulina bilobata along with other planktonic index foraminifera suggest that the deposits belong to the Upper Burdigalian to Langhian. We have analyzed the planktonic foraminiferal taxa present to provide a better understanding of chronostratigraphic and biostratigraphic concepts for sediments of the Qom Basin. From a biostratigraphic point of view, the bioevents of both sections confirm the evolution of two lineages of Globigerinoides-Praeorbulina and Orbulina species and shed new light on the age of the Qom section sediments in northwestern Iran.


qom formationburdigalianplanktonic foraminiferairanlanghian