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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). [ABSTRACT FROM AUTHOR]

During the Messinian, the sensitivity of the Mediterranean Basin to ecosystem perturbation was enhanced in response to the progressive restriction of water exchange with the Atlantic Ocean. The widespread deposition of organic-rich layers (i.e. sapropel) during the Messinian testifies the perturbation of the carbon and oxygen cycles; indeed, these sediments were deposited under conditions of oxygen starvation, presumably in response to a periodic deterioration of the thermohaline circulation strength. Disentangling the causes, the effect and magnitude of the thermohaline circulation weakening during the geological past is crucial for better constraining present and near-future deoxygenation dynamics in the Mediterranean region under the current climate warming. For this purpose, we investigate a Messinian sapropel-bearing succession cropping out at Monte dei Corvi (Ancona, central Italy) with mineralogical, petrographic, micropaleontological and stable Carbon and Oxygen isotopic analyses. We show that sapropel layers were deposited in response to an increase of the sea surface buoyancy, which hampered the thermohaline circulation and thus the oxygenation of bottom water, in turn affecting the bioturbating organisms. Within the lithological cycle, the recovery of an efficient thermohaline circulation is recorded by thin packstone layers underlying the marly limestone/marlstone, which record intense bottom currents. The marly limestone/marlstone accumulated during periods of intense primary productivity and organic carbon export to the sea bottom, which promoted bottom hypoxia but not organic matter preservation. We infer that these lithological changes resulted from variations in the Adriatic Deep Water formation system, controlled by precession-driven climatic and oceanographic changes. By integrating previously published Sea Surface Temperature (SST) with new isotopic and mineralogical data, we show that variations in Sea Surface Salinity (SSS) were the leading factor controlling sapropel deposition, minimizing the role of primary productivity. The SSTs characterizing the sapropel deposits are close to the range of those projected in the Eastern Mediterranean at the end of this century under climate warming. In this scenario, future warming will be coupled with SSS increase, which will counteract the density loss provided by temperature, making the bottom deoxygenation in the Eastern Mediterranean abysses unlikely. However, additional forcing, such as winter heat waves and eutrophication, could contribute to negatively affecting the Mediterranean oxygen balance and should be considered in model-based projections. • The Monte dei Corvi recorded the changes in the ADW formation during the Messinian. • The bottom deoxygenation resulted from variations in the freshwater input. • Future deoxygenation in Mediterranean can be provided by productivity or heatwaves. [ABSTRACT FROM AUTHOR]