ORCID Profile
0000-0002-8710-9919
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Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-12907
Abstract: & & We present two carbonate oxygen and carbon isotope records from late Miocene & #8211 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& & /sup& Al/& sup& & /sup& Be isochron burial dating (presented here).& & & & 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& & /sup& levels or the spread of C4 vegetation.& & & & The environment of Central Asia is primarily affected by the northern mid-latitude westerlies & #8722 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.& & & & 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.& & & & 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.& &
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2020GC009556
Abstract: The Issyk‐Kul Basin (Kyrgyzstan), situated in the central Tian Shan Mountains, hosts the largest and deepest mountain lake in Central Asia. Erosion of the surrounding Terskey and Kungey ranges led to the accumulation of up to 4 km of sediment in the adjacent depression. Creation of the basin from regional shortening and uplift likely initiated around the Oligocene‐Miocene, yet precise age control is sparse. To better understand the timing of these processes, we obtained magnetostratigraphic age constraints on fossil‐poor, fluvio‐lacustrine sediments exposed south of Lake Issyk‐Kul, that agree well with previous age constraints of the equivalent strata outside the Issyk‐Kul Basin. Two 500–650 m thick sections comprised mainly of Chu Group sediments were dated at 6.3–2.8 Ma and 7.0–2.4 Ma (late Miocene to early Pleistocene). Together with reinterpreted magnetostratigraphic constraints from underlying strata, we find that syn‐tectonic deposition commenced at ∼22 Ma with average sedimentation rates cm/ka. Sedimentation rates increased to 10–30 cm/ka at 7 Ma, concurrent with accelerated uplift in the Terskey Range to the south. A deformation event in one section (Kaji‐Say) between 5 and 3 Ma together with concurrent shifts of depositional centers throughout the basin signal the onset of substantial uplift of the Kungey Range to the north at ∼5 Ma. This uplift and deformation transformed the Issyk‐Kul area into a closed basin that facilitated the formation of a deep lake. Lacustrine facies deposited around 3 Ma mark the existence of Lake Issyk‐Kul by that time.
Publisher: Wiley
Date: 23-01-2023
DOI: 10.1111/BRE.12751
Abstract: 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 erted 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 induced river system reorganization led to the commencement of lake formation at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. The transition from sandstones of the Chu sedimentary group to conglomerates of the Sharpyl Dak group, marking a change from fluvial‐alluvial deposits to a proximal alluvial fan, is dated at 2.6–2.8 Ma by 26 Al/ 10 Be isochron burial dating on the southern side of the basin, driven either by tectonics or Northern Hemisphere glaciation. This study concludes that the late Miocene–Pliocene northward growth of Tian Shan significantly altered environmental conditions within the range, preventing the moisture‐bearing westerlies from reaching the intermontane Issyk‐Kul basin and promoting lake formation and expansion.
No related grants have been discovered for Anna Kudriavtseva.