Calcareous nannofossil biostratigraphy and paleoenvironment of the Eocene–Oligocene interval in the Pabdeh Formation in southwestern Iran

Abstract:

Studies of the Paleogene sequence in the Zagros Basin of Iran are crucial due to the existence of large oil fields such as the Pazanan oil field. This study examines calcareous nannofossils from the Eocene–Oligocene interval in the upper part of the Pabdeh Formation in the Zagros Basin. Samples were taken from a well drilled in the Pazanan oil field, located in the Dezful Embayment (Zagros Basin, southwestern Iran). The studied section is ~ 54 m thick and comprises mainly a succession of marls and limestones. Calcareous nannofossil biostratigraphy allows the studied interval to be assigned to Martini (Standard tertiary and quaternary calcareous nannoplankton zonation. In: Proceedings of the 2nd planktonic conference. Roma, Italy, p 739–785, 1971) Zones NP19 (Isthmolithus recurvus Zone) through NP22 (Helicosphaera reticulata Zone), which spans the Priabonian and Rupelian stages and includes the Eocene/Oligocene boundary. The nannoflora paleoecology allows us to characterize major changes in paleoproductivity during this interval. Late Eocene (Priabonian) assemblages are dominated by oligotrophic nannofossils. Above the Eocene/Oligocene boundary, there is a diverse assemblage of eutrophic calcareous nannofossils, with a significant decrease in the abundance of oligotrophic species. As well as nutrient supply, water temperature also appears to be another main controlling factor of the paleoenvironment in this region, where there is an increase in cold-water species recorded at the base of the Oligocene (Zone NP21), accompanied by a decrease in warm-water species. These variation in the calcareous nannofossil assemblages may indicate increased nutrient supply, climatic imbalances—associated with weather changes—and eventually sea-surface temperature (SST) cooling in this part of the Zagros Basin (Neo-Tethys domain) throughout the Eocene/Oligocene transition (EOT).

Año de publicación:

2022

Keywords:

• biostratigraphy
• Eocene
• Zagros Basin
• Oligocene
• Calcareous nannofossil

Fuente:

scopus