• Mountain building and syn-tectonic deposition in the Issyk-Kul Basin began at ~22 Ma and accelerated at ~7 Ma • Deformation propagated northward at ~5 Ma, initiating the closure of the basin and facilitating the formation of a deep Lake Issyk-Kul • Comparable depositional ages of equivalent strata throughout the central Tian Shan suggest regionally synchronized geologic processes Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Uplift of the Tian Shan range modified regional climate during Cenozoic aridification in Central Asia. This study presents facies analyses and Neogene oxygen and carbon isotopic records from magnetostratigraphically dated terrestrial sedimentary sections on the southern side of the intermontane Issyk-Kul basin in the Kyrgyz Tian Shan and 26 Al/ 10 Be isochron burial ages from the southern and eastern sides of the basin. The δ 18 O and δ 13 C data show a positive ca. 2‰ shift in values between ca. 8 and 7 Ma and a change from a negative to a positive trend. This change is attributed to the upwind growth of the Kyrgyz, Kungey and Trans Ili (Zaili) ranges, which diverted the westerlies, thereby changing the Issyk-Kul basin from a windward to a leeward position, enhancing aridification and establishing the modern-day spring and summer precipitation regime within the basin. Two 4 to 5 Ma 26 Al/ 10 Be isochron burial ages constrain the onset of Sharpyl Dak deposition on the eastern side of the basin; southward paleocurrent directions there suggest the eastward growth of the Kungey range in the Pliocene. Increased subsidence on the southern side of the basin and local tectonically 1194 | EAGE KUDRIAVTSEVA et al.

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<p>We present two carbonate oxygen and carbon isotope records from late Miocene – early Pleistocene stratigraphic sections from the southern flank of the Issyk Kul basin, Kyrgyz Tien Shan. The two sections are 700 and 500 m thick and composed of fluvial and lacustrine sediments. They were dated using magnetostratigraphy (Roud et al., G-Cubed, in review) and <sup>26</sup>Al/<sup>10</sup>Be isochron burial dating (presented here).</p><p>Carbonate stable isotope data is useful for reconstruction of climate in Asia over the Cenozoic. Oxygen isotopes are commonly used to detect moisture sources and their interaction with topography. Pedogenic carbon isotopes are used to reconstruct past atmospheric CO<sup>2</sup> levels or the spread of C4 vegetation.</p><p>The environment of Central Asia is primarily affected by the northern mid-latitude westerlies − winds transporting moisture eastward across Eurasia. Issyk Kul basin is situated on the windward side of the northern Tien Shan. Published data suggest that the Tien Shan mountain ranges interacted with the westerlies since late Oligocene and reorganized Central Asian climate during Neogene (Caves et al., 2017; Charreau et al., 2012; Macaulay et al., 2016; Wang, et al., 2020). The amount of existing published paleoclimate data from northern Central Asia is scarce compared to interior China, and therefore the influence of the Tien Shan uplift on climate in Asia during the Cenozoic is poorly reconstructed.</p><p>Our data provide new insight into the role of the range and its interaction with the westerlies in forming climate on the windward side of the northern Tien Shan in the late Neogene. We combine our data with published stratigraphically-older sections nearby (Macaulay et al., 2016) to complete the Neogene stable isotope record of the Issyk Kul basin and study how the evolution of the basin influenced regional climate.</p><p>Our d18O and d13C values show slightly positive trends, unlike stratigraphically-older data from the Issyk Kul basin. The preliminary interpretation suggests that the circulation pattern within the range was changed in late Miocene possibly reflecting active tectonic uplift northward of the basin and an increase in aridification.</p>