TY - JOUR A1 - Roud, Sophie A1 - Wack, Michael Richard A1 - Gilder, Stuart A. A1 - Kudriavtseva, Anna A1 - Sobel, Edward T1 - Miocene to early pleistocene depositional history and tectonic evolution of the Issyk-Kul Basin, Central Tian Shan JF - Geochemistry, geophysics, geosystems : G 3 ; an electronic journal of the earth sciences N2 - 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 similar to 22 Ma with average sedimentation rates <10 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 similar to 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. KW - Central Asia KW - Lake Issyk‐ Kul KW - magnetostratigraphy KW - Neogene KW - Tian KW - Shan Y1 - 2021 U6 - https://doi.org/10.1029/2020GC009556 SN - 1525-2027 VL - 22 IS - 4 PB - Wiley CY - Hoboken, NJ ER - TY - THES A1 - Kudriavtseva, Anna T1 - Interactions between tectonics, climate, and surface processes in the Kyrgyz Tian Shan N2 - During the Cenozoic, global cooling and uplift of the Tian Shan, Pamir, and Tibetan plateau modified atmospheric circulation and reduced moisture supply to Central Asia. These changes led to aridification in the region during the Neogene. Afterwards, Quaternary glaciations led to modification of the landscape and runoff. In the Issyk-Kul basin of the Kyrgyz Tian Shan, the sedimentary sequences reflect the development of the adjacent ranges and local climatic conditions. In this work, I reconstruct the late Miocene – early Pleistocene depositional environment, climate, and lake development in the Issyk-Kul basin using facies analyses and stable δ18O and δ13C isotopic records from sedimentary sections dated by magnetostratigraphy and 26Al/10Be isochron burial dating. Also, I present 10Be-derived millennial-scale modern and paleo-denudation rates from across the Kyrgyz Tian Shan and long-term exhumation rates calculated from published thermochronology data. This allows me to examine spatial and temporal changes in surface processes in the Kyrgyz Tian Shan. In the Issyk-Kul basin, the style of fluvial deposition changed at ca. 7 Ma, and aridification in the basin commenced concurrently, as shown by magnetostratigraphy and the δ18O and δ13C data. Lake formation commenced on the southern side of the basin at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. 26Al/10Be isochron burial dating and paleocurrent analysis show that the Kungey range to the north of the basin grew eastward, leading to a change from fluvial-alluvial deposits to proximal alluvial fan conglomerates at 5-4 Ma in the easternmost part of the basin. This transition occurred at 2.6-2.8 Ma on the southern side of the basin, synchronously with the intensification of the Northern Hemisphere glaciation. The paleo-denudation rates from 2.7-2.0 Ma are as low as long-term exhumation rates, and only the millennial-scale denudation rates record an acceleration of denudation. This work concludes that the growth of the ranges to the north of the basin led to creation of the topographic barrier at ca. 7 Ma and a subsequent aridification in the Issyk-Kul basin. Increased subsidence and local tectonically-induced river system reorganization on the southern side of the basin enabled lake formation at ca. 5 Ma, while growth of the Kungey range blocked westward-draining rivers and led to sediment starvation and lake expansion. Denudational response of the Kyrgyz Tian Shan landscape is delayed due to aridity and only substantial cooling during the late Quaternary glacial cycles led to notable acceleration of denudation. Currently, increased glacier reduction and runoff controls a more rapid denudation of the northern slope of the Terskey range compared to other ranges of the Kyrgyz Tian Shan. N2 - Während des Känozoikums veränderten die globale Abkühlung und die Hebung des Tian Shan, des Pamir und des tibetischen Plateaus die atmosphärische Zirkulation und verringerten die Feuchtigkeitszufuhr nach Zentralasien. Diese Veränderungen führten während des Neogens zur Aridifizierung der Region. Danach führten die Vergletscherungen des Quartärs zu einer Veränderung der Landschaft und des Abflusses. Im Issyk-Kul-Becken des kirgisischen Tian Shan spiegeln die Sedimentabfolgen die Entwicklung der angrenzenden Gebirgszüge und die lokalen klimatischen Bedingungen wider. In dieser Arbeit rekonstruiere ich die spätmiozäne bis frühpleistozäne Ablagerungsumgebung, das Klima und die Entwicklung der Seen im Issyk-Kul-Becken anhand von Faziesanalysen und stabilen δ18O- und δ13C-Isotopenaufzeichnungen aus Sedimentabschnitten, die durch Magnetostratigraphie und 26Al/10Be-Isochron-Bestattungsdaten datiert wurden. Außerdem präsentiere ich 10Be-abgeleitete moderne und paläo-Denudationsraten aus dem kirgisischen Tian Shan und langfristige Exhumierungsraten, die aus veröffentlichten thermochronologischen Daten berechnet wurden. So kann ich räumliche und zeitliche Veränderungen der Oberflächenprozesse im kirgisischen Tian Shan untersuchen. Im Issyk-Kul-Becken änderte sich der Stil der fluvialen Ablagerung bei ca. 7 Ma. Wie die Magnetostratigraphie und die δ18O- und δ13C-Daten zeigen, setzte gleichzeitig die Aridifizierung des Beckens ein. Die Bildung von Seen begann an der Südseite des Beckens bei ca. 5 Ma, gefolgt von einer lokalen Ablagerungspause von ca. 2 Ma. 26Al/10Be-Isochron-Vergrabungsdatierungen und Paläostromanalysen zeigen, dass das Kungey-Gebirge im Norden des Beckens nach Osten wuchs, was zu einem Übergang von fluvial-alluvialen Ablagerungen zu proximalen alluvialen Fächerkonglomeraten bei 5-4 Ma im östlichsten Teil des Beckens führte. Dieser Übergang vollzog sich um 2,6-2,8 Ma auf der Südseite des Beckens, zeitgleich mit der Intensivierung der Vergletscherung der nördlichen Hemisphäre. Die Paläo-Denudationsraten von 2,7-2,0 Ma sind so niedrig wie die langfristigen Exhumierungsraten, und nur die Denudationsraten auf der Jahrtausendskala zeigen eine Beschleunigung der Denudation. Diese Arbeit kommt zu dem Schluss, dass das Wachstum der Gebirgsketten im Norden des Beckens zur Entstehung der topografischen Barriere bei ca. 7 Ma und einer anschließenden Aridifizierung im Issyk-Kul-Becken führte. Eine verstärkte Absenkung und eine lokale tektonisch bedingte Umstrukturierung des Flusssystems auf der Südseite des Beckens ermöglichte die Bildung von Seen bei ca. 5 Ma, während das Wachstum des Kungey-Gebirges die nach Westen abfließenden Flüsse blockierte und zu einer Verknappung der Sedimente und einer Ausdehnung der Seen führte. Die Denudationsreaktion der kirgisischen Tian Shan-Landschaft verzögerte sich aufgrund der Trockenheit, und erst die erhebliche Abkühlung während der Gletscherzyklen des späten Quartärs führte zu einer merklichen Beschleunigung der Denudation. Gegenwärtig wird die Denudation des Nordhangs des Terskey-Gebirges im Vergleich zu anderen Gebirgszügen der kirgisischen Tian Shan durch den verstärkten Gletscherrückgang und den Abfluss beschleunigt. KW - Central Asia KW - δ18O and δ13C stable isotopes KW - 26Al/10Be cosmogenic radionuclides KW - magnetostratigraphy KW - Cenozoic aridification KW - denudation rates KW - Tian Shan KW - Zentralasien KW - δ18O and δ13C stabile Isotope KW - 26Al/10Be kosmogene Radionuklide KW - Magnetostratigraphie KW - Känozoische Aridifizierung KW - Denudationsraten KW - Tian Shan Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-603728 ER - TY - JOUR A1 - Meijer, Niels A1 - Dupont-Nivet, Guillaume A1 - Abels, Hemmo A. A1 - Kaya, Mustafa Y. A1 - Licht, Alexis A1 - Xiao, Meimei A1 - Zhang, Yang A1 - Roperch, Pierrick A1 - Poujol, Marc A1 - Lai, Zhongping A1 - Guo, Zhaojie T1 - Central Asian moisture modulated by proto-Paratethys Sea incursions since the early Eocene JF - Earth and planetary science letters N2 - The establishment and evolution of the Asian monsoons and arid interior have been linked to uplift of the Tibetan Plateau, retreat of the inland proto-Paratethys Sea and global cooling during the Cenozoic. However, the respective role of these driving mechanisms remains poorly constrained. This is partly due to a lack of continental records covering the key Eocene epoch marked by the onset of Tibetan Plateau uplift, proto-Paratethys Sea incursions and long-term global cooling. In this study, we reconstruct paleoenvironments in the Xining Basin, NE Tibet, to show a long-term drying of the Asian continental interior from the early Eocene to the Oligocene. Superimposed on this trend are three alternations between arid mudflat and wetter saline lake intervals, which are interpreted to reflect atmospheric moisture fluctuations in the basin. We date these fluctuations using magnetostratigraphy and the radiometric age of an intercalated tuff layer. The first saline lake interval is tentatively constrained to the late Paleocene-early Eocene. The other two are firmly dated between similar to 46 Ma (top magnetochron C21n) and similar to 41 Ma (base C18r) and between similar to 40 Ma (base C18n) and similar to 37 Ma (top C17n). Remarkably, these phases correlate in time with highstands of the proto-Paratethys Sea. This strongly suggests that these sea incursions enhanced westerly moisture supply as far inland as the Xining Basin. We conclude that the proto-Paratethys Sea constituted a key driver of Asian climate and should be considered in model and proxy interpretations. (C) 2019 Elsevier B.V. All rights reserved. KW - Paleogene KW - magnetostratigraphy KW - Central Asia KW - Xining Basin KW - westerlies KW - Asian monsoon Y1 - 2019 U6 - https://doi.org/10.1016/j.epsl.2018.12.031 SN - 0012-821X SN - 1385-013X VL - 510 SP - 73 EP - 84 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kaya, Mustafa Yücel A1 - Dupont-Nivet, Guillaume A1 - Proust, Jean‐Noël A1 - Roperch, Pierrick A1 - Bougeois, Laurie A1 - Meijer, Niels A1 - Frieling, Joost A1 - Fioroni, Chiara A1 - Altiner, Sevinç Özkan A1 - Vardar, Ezgi A1 - Barbolini, Natasha A1 - Stoica, Marius A1 - Aminov, Jovid A1 - Mamtimin, Mehmut A1 - Zhaojie, Guo T1 - Paleogene evolution and demise of the proto-Paratethys Sea in Central Asia (Tarim and Tajik basins) BT - Role of intensified tectonic activity at ca. 41 Ma JF - Basin research N2 - 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. KW - aridification KW - Asia KW - biostratigraphy KW - climate KW - magnetostratigraphy KW - microfossil KW - Paleogene KW - Pamir KW - proto-Paratethys KW - regression KW - Tajik Basin KW - Tarim Basin KW - tectonism KW - westerlies Y1 - 2018 U6 - https://doi.org/10.1111/bre.12330 SN - 0950-091X SN - 1365-2117 VL - 31 IS - 3 SP - 461 EP - 486 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Szurlies, Michael A1 - Geluk, Mark C. A1 - Krijgsman, Wout A1 - Kurschner, Wolfram M. T1 - The continental Permian-Triassic boundary in the Netherlands implications for the geomagnetic polarity time scale JF - Earth & planetary science letters N2 - In Central and NW Europe, the transition from the Permian to the Triassic (i.e., the Zechstein-Buntsandstein boundary interval) is developed mainly in red bed facies. This continental sedimentary succession is marked by relatively high sedimentation rates providing a high temporal resolution favorable for magnetic polarity stratigraphy. Here, we present a Zechstein to Lower Buntsandstein magnetostratigraphy obtained from the c. 100 m thick Everdingen-1 core from the Netherlands. Seven magnetozones (EV1n to EV4n) and five submagnetozones (EV1n.1r to EV3r.1n) have been delineated. The Everdingen-1 magnetostratigraphy has been integrated into the well-established high-resolution Zechstein-Buntsandstein stratigraphic framework, and verifies the geomagnetic polarity record from Central Germany. This confirms the hypothesis of nearly synchronous base-level cycles within the interior of the Central European Basin. These cycles are related to solar-induced similar to 100 ka eccentricity cycles. The most distinctive feature of the Everdingen-1 magnetostratigraphy is a transition from a thin reverse to a thick dominantly normal magnetic polarity interval. This reversal predates both the terrestrial mass extinction, which is indicated by a palynofloral turnover and a major sediment provenance change at the base of the Buntsandstein, and the marine Permian-Triassic Boundary (PTB). The PTB is located within the lowermost Buntsandstein and is approximated by the last occurrence of the conchostracan Falsisca postera and a negative excursion in the carbon isotope record. According to the Buntsandstein cyclostratigraphy, the R/N reversal predates the marine end-Permian extinction event by about 0.1 Ma and the marine biostratigraphic PTB by about 0.2 Ma. The thick normal magnetozone is estimated to have lasted c. 700 ka, and roughly coincides with the main phase of Siberian Trap volcanism. KW - magnetostratigraphy KW - cyclic stratigraphy KW - wireline logs KW - Permian-Triassic boundary KW - Zechstein-Buntsandstein interval KW - The Netherlands Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2011.11.043 SN - 0012-821X VL - 317 SP - 165 EP - 176 PB - Elsevier CY - Amsterdam ER -