Neogene aridification and lake development in the Issyk‐Kul basin, Kyrgyzstan

• Published in: Basin research Vol. 35; no. 3; pp. 1193 - 1227
• Main Authors: Kudriavtseva, Anna, Sobel, Edward R., Codilean, Alexandru T., Meijers, Maud J. M., Mulch, Andreas, Hoke, Gregory D., Fink, David, Mikolaichuk, Alexander V., Fülöp, Réka‐H., Wilcken, Klaus M., Enge, T. Gabriel
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01.06.2023
• Subjects: Alluvial deposits; Alluvial fans; Alluvium; Aridification; Beryllium 10; Cenozoic; Cenozoic aridification; Central Asia; Conglomerates; cosmogenic 26Al/10Be; Environmental conditions; Fluvial deposits; Glaciation; Glaciology; Growth; Lake basins; Lakes; Miocene; Moisture effects; Neogene; Northern Hemisphere; Palaeocurrents; Pliocene; Sandstone; Sedimentary facies; tectonic uplift; Tectonics; Uplift; Westerlies; δ18O and δ13C stable isotopes
• ISSN: 0950-091X; 1365-2117
• DOI: 10.1111/bre.12751

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 26Al/10Be isochron burial ages from the southern and eastern sides of the basin. The δ18O and δ13C 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 26Al/10Be 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 26Al/10Be 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. The late Miocene–Pliocene northward growth of Tian Shan created an orographic barrier that diverted the moisture‐bearing westerlies and enhanced aridification in the Issyk‐Kul basin. Reorganization of the river systems and enhanced subsidence led to the formation of an internally drained lake in Pliocene. The transition from sandstone to conglomerate (Sharpyl Dak group) deposition, linked to a change in climate and/or tectonic activity, occurred diachronously within the basin.