Problems of Paleogene stratigraphy and paleogeography in the middle latitudes of Eurasia

Abstract

The present-day notions of the Paleogene history, paleogeography, and paleobiogeography of Central Asia middle latitudes are based on studies carried by A.L. Yanshin in the second quarter of the 20th century. Here, main phases in the geologic history of the West Siberian and Turan Plates and Turgai depression are considered. In the Paleocene and Eocene, these regions were key links of a continuous meridional marine communication system connecting the Tethys and Arctic Oceans. Before the emergence of the latitudinal Alpine–Himalayan orogenic belt, the Tethys and its marginal seas formed a united shelf area. The closest linkage of the water bodies and biota exchange between them existed in the Thanetian and in the first half of the Ypresian. There was intense heat transfer from tropical to higher latitudes through the entire system of epeiric seas and straits. From the end of the Paleocene, this system was supplemented and complicated by latitudinal straits that ensured the connection of the seas of the Northern Peri-Tethys with the Northern Sea basin and the Atlantic. The combination of two sea systems determined the climatic history of this region from the Paleocene till the Late Eocene. The Arctic Basin influenced mainly the structure of cold-water benthos, and the Tethys, the composition of planktonic biota in the photic zone. During the Bartonian and Priabonian, in the last phase of marine sedimentation, the West Siberian epeiric sea was completely isolated from the Arctic Basin and connected only with the Turan sea through the Turgai strait. The Azolla beds accumulated during the low stand of the World Ocean in desalted surface waters and in disoxic bottom waters inhabited by depauperated benthos. At the Eocene/Oligocene boundary, the drainage of the Tavda–Chegan sea was followed by the formation of an N-S-directed river network in the vast areas of West Siberia, Turgai, and the northern cis-Aral region. The climate was unstable, moderately warm to subtropical, with variable humidity. The formation of the Turgai ecotype of mesophytic conifer-broadleaved flora was completed by the end of the Early Oligocene.

Piecing the barcoding puzzle of Palearctic water frogs (Pelophylax) sheds light on amphibian biogeography and global invasions

“…Ranid frogs originate from Asia (Yuan et al., 2016) and putatively gained access to Europe in the Early Oligocene (~30 Mya), a timing confirmed by German and French fossils from the Paleogene zone MP22 (32.5–30.9 Mya, Lemierre et al., 2023). This timeframe suggests that the closing of the Turgai Sea—a large body of salt water that previously fragmented Eurasia since the Cretaceous (Akhmet'ev, 2011; Briggs, 1995; Duellman & Trueb, 1994)—opened the route for colonization (a in Figure 10). The lack of secondary dispersal events emphasizes that European and Asian faunal exchanges remained limited overall, potentially due to the aridification of Central Asia and the westward retreat of the Paratethys Sea (b in Figure 10), two side effects of the first uplift of the Qinghai‐Tibetan Plateau (QTP, ~55–35 Mya) (Bougeois et al., 2018; Meijer et al., 2019; Sun et al., 2020).…”

“…Ranid frogs originate from Asia (Yuan et al, 2016) and putatively gained access to Europe in the Early Oligocene (~30 Mya), a timing confirmed by German and French fossils from the Paleogene zone MP22 (32.5-30.9 Mya, Lemierre et al, 2023). This timeframe suggests that the closing of the Turgai Sea-a large body of salt water that previously fragmented Eurasia since the Cretaceous (Akhmet'ev, 2011;Briggs, 1995;Duellman & Trueb, 1994)-opened…”

Survival of halophiles of Altai lakes under extreme environmental conditions: implications for the search for Martian life

“…This region is highly continental, with low and unstable precipitation. Numerous lakes in the region are likely to represent the remains of an ancient sea, as they are localized within the paleosea or larger paleolakes (Kuz'mina et al ., 2003; Akhmet'ev, 2011; Iakovleva, 2011). These drainless lakes have high salt content (up to the saturation point), and pH as high as 10 (Ermolaev and Vizer, 2010), and the majority of them are shallow (average depth 2–3 m) and small (area up to 2.5 km 2 ) (Beirom et al ., 1986).…”

Benthic foraminiferal and isotopic patterns during the Early Eocene Climatic Optimum (Aktulagay section, Kazakhstan)

“…The early Eocene is characterized by long-term global warming culminating in the Early Eocene Climatic Optimum (EECO; Zachos et al, 2001;2008). During this time interval, of which previously only the Paleocene Eocene Thermal Maximum was intensively studied, the Peri-Tethys was connected to the Arctic and Atlantic Oceans by north-south and east-west trending seaways (Akhmetiev, 2011). The Aktulagay section in Kazakhstan provides an expanded record of the middle Ypresian (NP11-13, ~54-50 Ma; King et al, 2013), including the EECO.…”