New insights into the middle Eocene environmental conditions and biogeographic setting of the Fergana Basin (Central Asia): Micropaleontological approaches

The middle Eocene transformation of the Fergana Basin, one of the largest basins in Central Asia situated between the Peri-Tethys and the Asian continent, plays a key role in understanding the transition to regional aridification of Central Asia. The basin’s transformation not only contributed to regional aridification but also affected global ocean circulation and climate. This study examines the micropaleontological communities, especially foraminifera and ostracoda assemblages as proxies, within the Turkestan and Rishtan formations, which corresponding to the Lutetian and Bartonian stages of the middle Eocene, respectively. Statistical analyses were performed to estimate species diversity, structure, and composition of the microfauna, shedding new light on their distribution across facies and stratigraphic profiles, and contributing to a paleoecological reconstruction. The environment is interpreted as a nearshore coastal intertidal or high subtidal zone with a substrate consisting of low-oxygen subsurface sediments and well-oxygenated benthic zone surface habitats. The results of this research provide a deeper understanding of the area, proposing that the middle Eocene of Fergana Basin was a complex configurated realm rather than a gulf, as previously recognized.