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

Abstract

The proto‐Paratethys Sea covered a vast area extending from the Mediterranean Tethys to the Tarim Basin in western China during Cretaceous and early Paleogene. Climate modelling and proxy studies suggest that Asian aridification has been governed by westerly moisture modulated by fluctuations of the proto‐Paratethys Sea. Transgressive and regressive episodes of the proto‐Paratethys Sea have been previously recognized but their timing, extent and depositional environments remain poorly constrained. This hampers understanding of their driving mechanisms (tectonic and/or eustatic) and their contribution to Asian aridification. Here, we present a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy as well as a detailed palaeoenvironmental analysis for the Paleogene proto‐Paratethys Sea incursions in the Tajik and Tarim basins. This enables us to identify the major drivers of marine fluctuations and their potential consequences on Asian aridification. A major regional restriction event, marked by the exceptionally thick (≤ 400 m) shelf evaporites is assigned a Danian‐Selandian age (ca. 63–59 Ma) in the Aertashi Formation. This is followed by the largest recorded proto‐Paratethys Sea incursion with a transgression estimated as early Thanetian (ca. 59–57 Ma) and a regression within the Ypresian (ca. 53–52 Ma), both within the Qimugen Formation. The transgression of the next incursion in the Kalatar and Wulagen formations is now constrained as early Lutetian (ca. 47–46 Ma), whereas its regression in the Bashibulake Formation is constrained as late Lutetian (ca. 41 Ma) and is associated with a drastic increase in both tectonic subsidence and basin infilling. The age of the final and least pronounced sea incursion restricted to the westernmost margin of the Tarim Basin is assigned as Bartonian–Priabonian (ca. 39.7–36.7 Ma). We interpret the long‐term westward retreat of the proto‐Paratethys Sea starting at ca. 41 Ma to be associated with far‐field tectonic effects of the Indo‐Asia collision and Pamir/Tibetan plateau uplift. Short‐term eustatic sea level transgressions are superimposed on this long‐term regression and seem coeval with the transgression events in the other northern Peri‐Tethyan sedimentary provinces for the 1st and 2nd sea incursions. However, the 3rd sea incursion is interpreted as related to tectonism. The transgressive and regressive intervals of the proto‐Paratethys Sea correlate well with the reported humid and arid phases, respectively in the Qaidam and Xining basins, thus demonstrating the role of the proto‐Paratethys Sea as an important moisture source for the Asian interior and its regression as a contributor to Asian aridification.

Parathethys Last Gasp in Central Asia and Late Oligocene Accelerated Uplift of the Pamirs

“…Magnetostratigraphy of the Shurysay member in the CD section is more reliable and can be correlated with C17-C15 of the GPTS 2016 ( Figure 2). This preferred correlation suggests that the age of the base of the Shurysay member is~37.4 Ma, consistent with the U-Pb age of the volcanic ash from the PE section (Carrapa et al, 2015) and with paleontological data from the Eocene strata in the Tajik and the southwestern Tarim basins (Bosboom et al, 2017;Kaya et al, 2019).…”

“…Our magnetostratigraphic dating suggests that the penultimate (fourth) and ultimate (fifth) retreat of the Paratethys from the Tajik Basin occurred at~41 and~37.4 Ma, respectively. The penultimate retreat in the Tajik Basin corresponds to the~41-Ma retreat event reported from the Mine (MI, Kaya et al, 2019), Aertashi (AT, Bosboom et al, 2014), and Keliyang (KLY, Sun et al, 2016) sections in the southern Tarim Basin (Figure 1). After the fourth regression, the eastern edge of the Paratethys withdrew to a location west of the Tajik Basin.…”

“…The Tian Shan is part of a Paleozoic orogenic system that was reactivated during the late Cenozoic (Sobel & Dumitru, 1997;Worthington et al, 2017). Paleogene strata in the Tajik Basin are characterized by alternating shallow-marine and continental redbed deposits, which can be correlated with those from the southwestern Tarim Basin, and record the last three (third to fifth) transgressive-regressive cycles of the Paratethys over central Asia (Bosboom et al, 2017;Carrapa et al, 2015;Kaya et al, 2019;Klocke et al, 2017;Sun et al, 2016;Wang et al, 2014Wang et al, , 2016. The Neogene sequences in the Tajik Basin are dominated by syntectonic clastic deposits with high temporal and spatial variability in facies, thickness, and composition (Klocke et al, 2017;Chapman et al, 2019; Figure S1 and Table S1 in the supporting information).…”

Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 3. Preorogenic to Synorogenic Retro‐foreland Basin Evolution in the Eastern Tajik Depression and Linkage to the Pamir Hinterland

“…The basal décollement of the Tajik fold‐thrust belt of the Afghan‐Tajik depression lies within the Kimmeridgian‐Tithonian evaporites (e.g., Gubin, ; Leith et al, ). Biostratigraphy and partly magnetostratigraphy provide a firm control on the age and lateral correlation of the Jurassic, Cretaceous, and Paleogene basin‐wide marine strata (Bosboom et al, , ; Chapman et al, ; Dzhalilov et al, ; Kaya et al, ). In contrast, the chronostratigraphic classification of the Neogene synorogenic deposits is controversial.…”

“…Cenozoic stratigraphic subdivisions. Global stratigraphic scale (GSS; Cohen et al, ; numerical ages in Ma according to Gradstein et al, ); regional stratigraphic scale (RSS; Vjalov, ; Simakov, ; Kreydenkov & Raspopin, ; Vlasov et al, ; Nikolaev, ); local stratigraphic scale (LSS; Davidzon et al, ; Dzhalilov et al, ); alternative local stratigraphic scales: LSS*—Forsten and Sharapov (); LSS**—Kaya et al () with timing of Paleogene incursions; LSS***—synthesis of Carrapa et al () with date of volcanic ash bed and Chapman et al () with detrital zircon fission‐track ages, considered maximum depositional ages for the formations. The right column shows the subdivision into preorogenic and synorogenic stages and timing of formations adopted in this paper.…”