Late Eocene palaeogeography of the proto-Paratethys Sea in Central Asia (NW China, southern Kyrgyzstan and SW Tajikistan)

Abstract

The Cretaceous and Palaeogene sediments of the basins in Central Asia include the remnants of the easternmost extent of a vast shallow epicontinental sea, which extended across the Eurasian continent before it retreated westwards and eventually isolated as the Paratethys Sea. To improve understanding of its long-term palaeogeographical evolution, we complement the well-constrained chronological framework of the Tarim Basin in China with stratigraphic records of the sea retreat from the Fergana Basin and the Alai Valley Basin in southern Kyrgyzstan and the Afghan–Tajik Basin in SW Tajikistan. By lithostratigraphic analyses and identification of bivalve assemblages, this study establishes for the first time a clear and detailed regional correlation of Palaeogene marine strata across Central Asia, showing that the basins share a similar palaeogeographical evolution characterized by a long-term stepwise retreat punctuated by short-term shallow-marine incursions. Our correlation shows that the last two marine incursions recognized in the Tarim Basin can be traced westwards. The permanent disappearance of the sea from Central Asia probably occurred with limited diachroneity in the late Eocene, before the isolation of the Paratethys Sea, shifting the easternmost margin of the sea hundreds of kilometres westwards and probably significantly reducing moisture supply to the Asian interior.

Paleogene evolution and demise of the proto‐Paratethys Sea in Central Asia (Tarim and Tajik basins): Role of intensified tectonic activity at ca. 41 Ma

“…A Bartonian–Priabonain age is assigned for the Kushan and Sanglak formations, correlated to the 2nd, 3rd and 4th member of the Bashibulake Formation in the Tarim Basin (Bosboom et al, ). Few diagnostic species were present, but the short ranging taxon Dracodinium rhomboideum was recorded in sample CD10 indicating an age close to or corresponding with C18n.2n (Bijl et al, ; Eldrett et al, ).…”

“…The Beshkent–Lower Tochar formations, correlated to the Wulagen Formation in Tarim Basin (Bosboom et al, ), are assigned to nannofossil zone CP14 (~NP16/NP17, upper Lutetian–lower Bartonian; ca. 42.8–37.8 Ma) based on the presence of Neococcolithes and Dictyococcites bisectus (samples CD03 and CD04) and the absence of Lanthernithus arcanus .…”

“…From the late Cretaceous and to the late Eocene, the Tarim Basin witnessed several transgressions and regressions, resulting in the deepening/shallowing of the epicontinental proto‐Paratethys Sea and concomitant transitions from marine to continental depositional environments or vice versa (Bosboom et al, ; Burtman, ; Guo et al, ; Xi et al, ; Zhang et al, ). The easternmost portion of the proto‐Paratethys Sea in the western Tarim Basin was connected with the Tajik Basin, as evidenced by the similar stratigraphic and sedimentary successions in both basins (Bosboom et al, ; Burtman, ). Similarities of the fossil assemblages with other basins in Central Asia and Europe indicate that this portion of the Proto‐Paratethys in the western Tarim Basin was also a part of the Tethyan Realm (Bosboom et al, ; Mao & Norris, ).…”

Geological evolution of Central Asian Basins and the western Tien Shan Range

“…Subsequently, in Neogene times the basin fill was progressively deformed by folding and thrusting. Bosboom et al (2015) investigate the Cretaceous and Palaeogene sedimentary successions in three areas (Tarim Basin, China; Fergana Valley and the Alai Valley, Kyrgyzstan; Afghan -Tajik Basin, Tajikistan) in order to reconstruct the epicontinental sea that was present across the region at that time. The results indicate that the various locations, while geographically distant, shared a similar palaeogeographical evolution, one characterized by a long-term stepwise retreat punctuated by shortterm shallow-marine incursions.…”

“…Hendrix et al 1992;Shao et al 2003;Cecca et al 2005;Fü rsich et al 2015;Jolivet 2015;Jolivet et al 2015;McCann 2016a, b;Schnyder et al 2016;Brunet et al 2017). Subsequently, during the early Cenozoic regionally well-correlated marine transgressions occurred (Bosboom 2013;Bosboom et al 2015). These transgressive events have been linked to Paratethys Sea which was open to the west (Black Sea, Caucasus, Caspian Sea) and extended eastwards through the Amu Darya, Tajik, Fergana and Tarim basins of Central Asia (Popov et al 2004).…”