Paleoecology of Abtalkh Formation based on planktonic and benthic foraminifera in Padeha section, Kopet-Dagh Basin

Abtalkh Formation is a part of Late Cretaceous sedimentary unit in the Kopet- Dagh basin, NE Iran. This study deals with the study of this formation in the eastern parts of the basin in Padeha village. It thickness is about 991m, and lithologically consists of grey, greyish to blue shale and marl. The lower contact with Abderaz Formation is conformable and transitional, but the upper boundary with Neyzar Formation is disconformable. At this study, Paleoecology (paleobathymetry, oxygen and productivity) determined, based on planktonic and benthic foraminifera. Also, benthic foraminifera species, planktonic to benthic ratio and Van der Zwaan et al., (1990) equation were used as an indicator for investigation of bathymetry and sea level change. Therefore, in the view of bathymetry, the lower and middle parts of the formation are deposited in the bathyal (approximately 170-470 m in depth); while the upper part attributes to neritic zone (approximately 40-170 m in depth). In addition, analysis of epifaunal to infaunal benthic morphotypes and biserial planktonic foraminifera, this formation at this locality divided into two parts: the lower part of the section in which epifaunal to infaunal ratio is abundance, and biserial foraminifera decrease, indicating environmental conditions with high oxygen and low nutrients flux and the upper part of section that epifaunal to infaunal morphotype ratio decreases and biserial foraminifera increase, showing a decrease in oxygen and increase in nutrient flux.