Displays

The Cenozoic uplift history of Tibet and its impact on the Asian monsoon and vegetation is complex. The building of the Tibetan Plateau is not a simple story of the rise of a single geological entity driven by the relentless northward passage of India as depicted in numerous modelling exercises, but was a complex process involving a succession of collisions of several Gondwanan terranes with Asia. The talk will review our current understanding of the uplift history of Tibet and show new climate model simulations of how Tibet has influenced climate, vegetation and biodiversity in the region. We make use of isotope-enabled Earth System models, as well as high resolution models to show that the complex history of Tibet has important consequences for understanding the evolution of both the summer and winter Asian monsoon. We show that post-Oligocene growth of north and north-eastern Tibet is crucial for the evolution of vegetation and biodiversity in the region by altering the strength of the winter monsoon system over Asia.

How to cite: Valdes, P., Farnsworth, A., Su, T., Spicer, R., Ding, L., Li, S., Zhou, Z., and Li, S.: Modelling the Interaction between Tibet and Climate and Biosphere during the Cenozoic., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7711, https://doi.org/10.5194/egusphere-egu2020-7711, 2020.

The paleogeographic evolution of the India-Asia collision and the resulting formation of the Himalayan orogen remain an intensely debated topic. A variety of disputed models propose different collision ages for the numerous terranes incorporated into the collision with variable paleolatitudes and tectonic rotations that can be constrained using paleomagnetism. Recent plate tectonic reconstructions have shown that the Burma Terrane (BT), a microplate at the eastern edge of the Himalayan orogen, is a key element to solve the India-Asia collision puzzle. Here we provide new paleomagnetic and geochronological data of Paleocene, Eocene, Oligocene and Miocene age, in addition to our previously published Late Cretaceous and late Eocene results. We present a robust plate tectonic reconstruction for the BT with GPlates software, and show that the BT moved towards southern hemisphere latitudes between the Late Cretaceous and Paleocene without significant rotation. Starting in the Paleocene, the BT and India coevally moved northwards and the BT started to undergo a major clockwise rotation of ~60 ̊. By the late Eocene, most of this rotation was completed and the BT was translated ~2000 km northward from near-equatorial latitudes without significant rotation. This northward translation culminated with the early Miocene indentation of the BT into the eastern Himalayan collision zone, leading to the setup of the modern Eastern Himalayan Syntaxis. These first order constraints are used to infer a Trans-Tethyan arc collision model including timing of rollback, extrusion and initiation of strike-slip systems. Our model has important implications for Asian biotic and climatic evolution.

How to cite: Westerweel, J., Roperch, P., Licht, A., Dupont-Nivet, G., Win, Z., Poblete, F., Cogné, N., Ruffet, G., Huang, H., Swe, H. H., Thi, M. K., Hoorn, C., and Aung, D. W.: India-Asia collision paleogeography constrained by Burma Terrane (Myanmar) Late Cretaceous to Miocene paleomagnetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1523, https://doi.org/10.5194/egusphere-egu2020-1523, 2020.

New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90–70 Ma and at ∼50–40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2. Based on these results, we suggest that the low-latitude closure ofoceanbasins alongeast–west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean.

How to cite: Jagoutz, O., Royden, L., and Macdonald, F.: Low-latitude arc–continent collision as a driver for global cooling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5992, https://doi.org/10.5194/egusphere-egu2020-5992, 2020.

The CO₂ degassing by plate tectonic process has long been thought to be balanced by weathering of silicate rocks on continents, keeping the Earth a relative stable global carbon cycle and temperature suitable for life creation, survival and evolution. The uplift of the Tibetan Plateau (TP) is hypothesized to enhance erosion and silicate weathering and organic carbon burial, thus cool the global temperature. However, the imbalance resulting from accelerated CO₂ consumption by uplift of the TP and a relatively stable CO₂ input from volcanic degassing during the Cenozoic should have depleted atmospheric CO₂ within a few million years; therefore, a negative feedback mechanism must have stabilised the carbon cycle. Here, we present the first almost complete Paleogene silicate weathering intensity (SWI) records from continental rocks in the northern TP, based on detailed volcanic ash and paleomagnetic dating of two continuous Cenozoic sections in the Xining and Qaidam Basin in NW China. They show that the Paleogene silicate weathering in this tectonically inactive area was modulated by global temperature. These findings suggest that Paleogene global cooling was also strongly influenced by the temperature feedback mechanism that regulated silicate weathering rates and hydrological cycles and maintained a nearly stable carbon cycle. It acted as a negative feedback through decreasing CO₂ consumption resulting from the lower SWI and the kinetic limitations in tectonically inactive areas that followed the global cooling. This means that the enhanced erosion and silicate weathering by the uplift of the south and central Tibetan Plateau, thus accelerated CO₂ consumption, must be compensated by reducing CO₂ consumption of the rest vast continents through their reduced silicate weathering from cooling.

How to cite: Fang, X., Galy, A., Yang, Y., Zhang, W., Ye, C., and Song, C.: A new negative feedback mechanism for balancing Tibet uplift-driven CO2 drop: Evidence from Paleogene chemical weathering records in the northern Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4042, https://doi.org/10.5194/egusphere-egu2020-4042, 2020.

At ca. 34 Ma the Eocene-Oligocene transition (EOT) marks the shift from greenhouse conditions during the Eocene to the icehouse of the Oligocene and was the most pronounced cooling event during the Cenozoic. This event is well documented in marine records with a significant increase in benthic foraminifera δ18O values suggesting a 5°C cooling in air temperature through the EOT. Instead, the few but growing number of terrestrial records suggest a much larger cooling of 4-9°C. Yet, details regarding the exact timing of cooling and ensuing terrestrial changes in climate, hydrology, and ecology are sparse. Here, we investigate the impact of the EOT cooling event and associated climatic changes on the hydrology and vegetation in central China. We use stable isotopes of hydrogen (δD_wax) and carbon (δ¹³C_wax) from leaf-waxes, a paleo-hydrology proxy obtained from organic material in sedimentary rocks, in combination with pollen data from a continuous well-dated, high-resolution sedimentary section from the Xining Basin in NE Tibet (36°42' N, 101°43' E). We then compare our results to a fully-coupled, global climate model (GCM) simulating the pre- and post-EOT conditions in central Asia.

The obtained δD_wax record ranges between -160 to -190‰ and shows a complex two-step transition through the EOT with a rapid initial drop of -30‰ from 33.9 to 33.7 Ma, a recovery to pre-EOT values between 33.7 to 33.4 Ma and a second drop similar in magnitude as the first one. In contrast, δ¹³C_wax values remain unchanged at -29 to -28‰ through the EOT. The GCM indicates a difference in temperature throughout the year between pre- and post-EOT runs of 8-9°C at the Xining Basin with change in seasonality due to the collapse of the pre-EOT wet spring season, yielding mainly autumn precipitation after the transition. The overall precipitation amount remained in both simulations dry with < 500 mm/yr. The combined results show that the region experienced: (a) a significant temperature drop of 8-9°C through the EOT being the first-order control on the records decrease in δD_wax  (1-2 ‰ per 1°C in mid-latitudes and up-to 5 ‰ per 1°C in higher latitudes) through the EOT; (b) constant bioproductivity and/or similar water-use efficiency within plants displayed by unchanged δ¹³C_wax values; (c) a changeover from a “warm-wet” desert abundant in Nitraria and Ephedra shrubs to a “temperate” desert with an expansion of conifers and broad-leaf trees in the higher-elevation hinterlands. We interpret that this change in seasonality and cooler EOT temperatures reduced the plant’s overall transpirational pressure, contributing to the spread of conifers and broad-leaf trees after the EOT under regionally new hydrologic conditions.

How to cite: Rohrmann, A., Dupont-Nivet, G., Hren, M., Sachse, D., Meijer, N., Barbolini, N., and Tardif, D.: Temperature decrease through the Eocene-Oligocene transition controls eco-hydrologic shifts in Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10034, https://doi.org/10.5194/egusphere-egu2020-10034, 2020.

The Siwalik deposits of Himalayan foreland basin (HFB) preserved the Miocene records of the Himalayan tectonics, monsoonal variation and evolution of C₄ plants. Previous vegetation reconstructions emphasized   the Late Miocene expansion of C₄ plants (ca. 7 Ma) with an implicit assumption that the vegetation thrived in the floodplain of lowland rivers. The coarsening-upward sequence of the Siwalik Group suggests deposition  in an alluvial fan setting in which the Middle and Lower Siwaliks are deposits of distal area whereas the Upper Siwaliks represent proximal areas of the fan. The modern alluvial fans forming in the Himalayan foothills show a significant difference in elevation and vegetational composition between proximal and distal areas. In the HFB, the elevation difference between the proximal and distal areas is expected to be more pronounced due to surface exhumation of the Siwalik deposits. The increased elevation would have had affected the vegetation distribution in the Upper Siwaliks which implies that vegetation  inproximal part of the fan might not represent lowland floodplain. However, the vegetation composition is less understood from the Upper Siwaliks region as conventional proxies are scanty in these younger foreland deposits.

In the present study, the impact of elevation on vegetation distribution in the HFB is examined from comparatively higher exhumed Late Plio-Pleistocene Siwalik deposits at SuraiKhola (Nepal). The δ¹³C values of bulk soil organic matter (SOM), n-alkane and n-alkanoicacid from the SuraiKholapaleosols suggest most commonly observed expansion of the C₄ plants at ca. 7 Ma, and a unique second phase of expansion of C₃ plants after ca. 3 Ma. The higher δD values in n-alkane and n-alkanoicacid suggest that the climate was drier in last 4 Myr; most likely driven by the onset of the Northern Hemisphere Glaciation (NHG). The growth of C₃ plants was favored due to cool climatic condition induced by higher elevation in the proximal part of the fan. The water-bearing conglomerate units in the Upper Siwaliks helped the C₃ plants to thrive in a relatively drier climate. Therefore, the higher abundance of C₃ plants in the Upper Siwaliks suggests morpho-tectonic control on vegetation with the possible influence of NHG.

How to cite: Sanyal, P., Roy, B., and Ghosh, S.: Morpho-tectonic control on the distribution of C3-C4 plants during Late Plio-Pleistocene in the central Himalayan Siwaliks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-550, https://doi.org/10.5194/egusphere-egu2020-550, 2020.

Since late Eocene (40 Ma), atmospheric CO2 drastically decreased from 4 to 1 PAL.  During this period, two major geological events occurred over Asia: the India/Asia collision producing the uplift of large mountain ranges and the shrinkage of the Paratethys (G. Ramstein et al., Nature, 1997; F. Fluteau et la., JGR, 1999). Most modeling studies focused first on the sensitivity of AGCMs to the Tibetan plateau elevation through simple experiments; then new simulations accounting for more realistic description of paleogeographic reconstructions have been published. Indeed, progress has been done concerning both: paratethys evolution (Z. Zhang et al., PAL PAL PAL, 2007), chronology of uplifts of different mountain ranges (R. Zhang et al., JGR, 2017) and large TP northern shift (R. Zhang et al., EPSL, 2018), but again these experiments focused mostly on atmosphere circulation and hydrologic pattern (monsoon evolution) not specifically on their impacts on ocean dynamics.

Therefore, this study aims to investigate the role of TP uplift on Northern hemisphere ocean circulation through long runs of coupled ocean atmosphere model to analyze its impact not only on atmosphere but also on ocean dynamics. We provided a series of sensitivity simulations disentangling the two different factors, pCO2 decrease and TP uplift. These simulations allow analyzing the response to TP uplift in a warm high CO2 world as Eocene and in a cold low CO2 world as Quaternary (B. Su et al., CP, 2018).

We describe how the TP uplift through changes of atmosphere (surface winds and planetary waves) and hydrology (runoff and precipitation/evaporation patterns) modified the meridional circulation in the North Atlantic and Pacific basins with emphasize on the causes of the two different basins sensitivity to this major mountain range uplift in both contexts.

How to cite: Ramstein, G., Su, B., Jiang, D., Zhang, R., and Sepulchre, P.: Quantifying the contribution of Tibetan Plateau (TP) uplift and CO2 decrease for late Eocene and present day climate with emphasis on Meridional Ocean Circulation., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14895, https://doi.org/10.5194/egusphere-egu2020-14895, 2020.

Constraining spatial and temporal patterns of topography and exhumation along the Himalayan orogen is a starting point for studies aimed at understanding the development of Asian climate and tectonic evolution. Starting from the pioneering work of Cerveny et al. (1988), many scientists have applied a detrital thermochronologic approach to reveal the Cenozoic exhumation history of the Himalayas. Thermochronologic studies involve analyses of modern river sediments and sedimentary successions either accreted on the southern side of the orogen or accumulated in the Indus and Bengal fans. As datasets have grown and techniques evolved, the available interpretations are often contradictory.

In this contribution, we analyse previously published detrital-thermochronology datasets in the Himalayan region using the interpretive keys illustrated in Malusà and Fitzgerald (2020). These keys reinforce existing approaches and provide new perspectives for the application of detrital thermochronology to tectonic settings where the geologic evolution is often still debated. Different thermochronologic systems applied to proximal and distal sedimentary successions derived from Himalayan erosion yield a complex exhumation and tectonic history, but a relatively consistent picture for the Cenozoic evolution of India-Eurasia collision emerges. Detrital thermochronology data are supportive of a progressive southward thrust propagation towards the Himalayan foreland, progressively involving new eroding sources. The onset of fast exhumation in the Lesser Himalaya is constrained by different thermochronologic methods and datasets, indicative of onset at ~10 Ma, in line with independent geologic evidence. Coeval fast exhumation is also recorded in detritus derived from the Greater Himalaya. These findings are supportive of a major morphogenic phase of mountain building in the Himalayas at ~10 Ma, prior to the onset of fast exhumation in the Namche Barwa syntaxis.

Cerveny PF et al (1988). History of uplift and relief of the Himalaya during the past 18 million years: Evidence from fission-track ages of detrital zircons from sandstones of the Siwalik Group. In: New perspectives in basin analysis, Springer.

Malusà MG, Fitzgerald PG (2020). The geologic interpretation of the detrital thermochronology record within a stratigraphic framework, with examples from the European Alps, Taiwan and the Himalayas. Earth-Science Reviews, https://doi.org/10.1016/j.earscirev.2019.103074

How to cite: Malusa', M. G. and Fitzgerald, P. G.: Detrital thermochronology evidence of a major morphogenic phase of mountain building in the Himalayas at 10 Ma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3398, https://doi.org/10.5194/egusphere-egu2020-3398, 2020.

The alluvial sediments deposited in the Indo-Gangetic Plains originated as a result of tectonic and climatic factors controlling the exhumation and erosion of the Hinterland Himalaya. However, erosion distribution over the Himalaya and sediment delivery to the plains, on a shorter millennial time scale, are primarily controlled by the climatic factors such as glacial cover over the Himalaya and intensity of Indian summer monsoon (ISM) precipitation. Therefore, these alluvial sediment archives record important information about the past climatic changes. Here, we report the geochemical record of ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd (ε_Nd), and δ¹³C of sediment organic matter (δ¹³C_SOM) in a ~45 m long drill-sediment core collected from a buried channel of the paleo-Yamuna River in the northwest Indo-Gangetic Plains, Haryana to infer variations in provenance, paleoclimate, and paleovegetation during the late Quaternary. The Sr–Nd isotopic compositions (⁸⁷Sr/⁸⁶Sr: 0.75144–0.79241, ε_Nd: –15.9 to –19.7) of the core sediments suggest their derivation from isotopically distinct Higher Himalaya and Lesser Himalaya end-member sources in the catchment. Down-core variability in the isotopic compositions show increased contribution from the Higher Himalaya during marine isotope stage (MIS) 1 and late MIS 3 interglacial periods due to receding glacial cover and intense ISM. The δ¹³C_SOM values (−21.6‰ to −27.0‰, average: −25.6‰) in the core samples imply a C₃ dominant paleovegetation in the catchment. Down-core variability in the δ¹³C_SOM exhibits significant correlation with the ISM precipitation intensity, implying an increased abundance of C₄ plant in response to the ISM intensification during MIS 1, and early and late MIS 3.

How to cite: Amir, M., Tarique, M., Rahaman, W., and Paul, D.: Climate controlled catchment erosion in the Himalaya during the late Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4206, https://doi.org/10.5194/egusphere-egu2020-4206, 2020.

Paleogeographic reconstructions are essential across disciplines in Earth and Environmental Science from geodynamics to climate, as well as related fields of biology and ecology. They are at the foundation of many academic as well as industrial applications. As for geologic maps, paleogeographic reconstructions integrate a vast amount of multidisciplinary data and interpretations. Building such reconstructions thus requires a large set of sequential procedures to position around the globe various oceanic and continental features and to modify their topographies, bathymetries and shorelines according to the considered dataset included.

We present here a tool that enables to perform simply these operations. It is under development as a plugin for QGIS. With a graphical user interface, preset options can be readily applied to generate quickly multiple reconstructions with varying parameters. This makes project data management and treatment considerably easier, more intuitive and user-friendly. As most tools in GIS do, Terra Antiqua includes help texts incorporated to its interface to guide the user through each module.  The Plugin is divided into modules and this format allows a high degree of flexibility in the order of the reconstruction steps. These are: the compilation of topography and bathymetry, the definition of the paleoshorelines, the topography modification and the interpolation. Resulting paleogeography digital elevation model (DEM) can be visualized and exported in any GIS-supported format – NetCDF, GeoTIFF, Grid (.grd) or as PDF, JPEG, SVG etc. for publication. The tool is tested to make global reconstructions at 50 and 30 Ma.

How to cite: Ruiz, D., Dupont-Nivet, G., Aminov, J., Poblete, F., van der Linden, T., and van Hinsbergen, D.: "Terra Antiqua" : a paleogeographic reconstruction plugin for QGIS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20362, https://doi.org/10.5194/egusphere-egu2020-20362, 2020.

The Tibetan Plateau (TP) has undoubtedly played an essential role in the evolution and strengthening of the coupled climate system of the Asian monsoon and inland arid climate since the Cenozoic. However, a growing number of studies have found that regional and relatively smaller scale topography also has significant impact on Asian climate.
By using high resolution atmospheric circulation model, we analyzed the effect of the main body of the TP and its surrounding topography on the evolution of Asian climate. The surrounding topography includes the Yunnan-Guizhou Plateau (YG) at the southeastern margin of the Tibetan Plateau, the Pamir Plateau (Pr) and Tian Shan mountains (TS) at the northern margin and the Mongolian Plateau (MP) further north. The results show that different from the strengthening effect of the main TP, the YG significantly weakens the Indian monsoon. With the uplift of the YG, an anomalous anticyclonic circulation appeared in the lower troposphere over the southwest, resulting in the weakening of monsoon circulation from the Bay of Bengal to the Indian subcontinent and the Arabian sea. The decline in Indian monsoon precipitation caused by the YG accounts for one-third of the total increase in precipitation caused by the entire TP.
For the arid interior Asia, the main TP, YG, Pr and TS, as well as the MP all have reduced the annual precipitation in some extent. However, different from the consistent inhibiting effect of the main TP on the precipitation over the arid interior Asia throughout the year, the decreasing effect of the YG and the MP is mainly effective in boreal winter, which is closely related to the mechanical blocking effect. In addition, the Pr and TS play a key role in the temporal and spatial differentiation of precipitation in the arid interior Asia. Before the appearance of the Pr and TS, the precipitation seasonality over the eastern sub-region was characterized with maximum rainfall in spring and winter and minimum rainfall in summer. With the uplift of Pr and TS, the precipitation over the eastern part decreases in winter and significantly increases in summer, which leads to the change of precipitation seasonality to summer dominated.
The above results indicate that different part of the extensive-third pole have different influences on the Asian monsoon and inland aridity. It suggests that the Asian monsoon-inland arid climate may have undergone complex evolutionary processes on tectonic scale.

How to cite: Sha, Y. and Shi, Z.: Complex Role of the Tibetan Plateau and its Surrounding Topography in the Formation of Asian Climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13623, https://doi.org/10.5194/egusphere-egu2020-13623, 2020.

The growth of the Tibetan Plateau (TP) is one of the important forcings acting on the evolution of the Asian climate during the Cenozoic. However, whether vegetation and ocean feedbacks play a specific role in the Asian climate response to TP uplift remains unclear. Here we investigate this issue through a set of numerical experiments with the Community Earth System Model. The results indicate that vegetation and ocean feedbacks have important but different effects on the Asian climate change in association with TP uplift, which are intrinsically related to the adjustment of thermal structure. The vegetation feedback leads to excess annual precipitation in East China and South Asia and a weakening of the Asian winter monsoon winds. By comparison, the ocean feedback induces a deficit of annual precipitation particularly in most areas of the Bay of Bengal and the South China Sea and a weakening of the Asian summer and winter monsoon winds. These results highlight the importance of vegetation and ocean feedbacks and further facilitate a better understanding of the paleoclimatic response to the uplift of the TP.

How to cite: Zhang, R., Jiang, D., and Zhang, Z.: Vegetation and ocean feedbacks on the Asian climate response to the uplift of the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5171, https://doi.org/10.5194/egusphere-egu2020-5171, 2020.

The Pamir is an along-strike continuation of the Tibet-Himalaya orogen and penetrated ~300 km into the Tarim and Tajik basins in Cenozoic times. This northward indentation led to regional paleoenvironmental changes and facilitated northward transport of the far-field stress from the India-Asia plate boundary. Due to the compressional stress from the India-Asia boundary and Cenozoic lithosphere delamination, the Pamir underwent intense exhumations, which well recorded its Late Cenozoic mountain building processes. However, the very rapid Late Cenozoic exhumation also erased earlier cooling records and hinders a clear understanding of the Early Cenozoic tectonic evolution of Pamir. Thus, the onset and magnitude of the northward movement of Pamir are loosely constrained (Eocene-Late Oligocene) and long debated. In particular, the Early Cenozoic tectonic evolution of Pamir is unclear.

Provenance study of sediments in the adjacent sediment basins is a widely used method to reconstruct the tectonic-geomorphologic evolution of a mountain range. We carried out paleocurrent measurements and detrital zircon analysis of the Cretaceous-Pliocene sediments in the northern Pamir-Tian Shan convergence zone. Our study area, the Tierekesazi section, is located immediately south to the southern Tian Shan and is evolved in the present foreland basin of the southwestern Tian Shan. The provenance data show that the Tian Shan was the primary source area of the northwestern Tarim basin in the Cretaceous. The appearance of the Triassic-Jurassic detrital zircon grains and northward paleo-flow directions in the Eocene (~41 Ma) to Middle Miocene sediments suggest the Pamir became an important source area of the northwestern Tarim basin. Combining with the regional crustal shortening and paleoclimate data, we speculate that the northward indentation of the Pamir initiated before ~41 Ma. In contrast with the northward movement and Middle-Late Miocene accelerated exhumation of the Pamir, the source area of the studied section shifted back to the Tian Shan after the Middle Miocene. It consists with the Middle-Late Miocene uplift of the southwestern Tian Shan. Simultaneously, the crustal shortening of Pamir propagated to its northern foreland. Newly formed fold-and-thrust zones probably blocked the sediment transport from Pamir to the Tierekesazi section, and the present-day east flowing drainage system in the Pamir-Tian Shan convergence zone was established. We infer, in this period, the Pamir likely reached its present position, which is consistent with the appearance of an extreme arid climate in the Tarim basin.

How to cite: Jia, Y., Glotzbach, C., Ehlers, T., and Lü, L.: Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6692, https://doi.org/10.5194/egusphere-egu2020-6692, 2020.

The Pamir orogen in Central Asia has formed by the amalgamation of several Gondwana-derived terranes and their accretion to the southern Eurasian margin in the Mesozoic. Later on, the crust of the Pamir orogen was strongly deformed and uplifted as a result of the Cenozoic India-Asia collision. The deformation of the Pamir orogen, which resulted in shortening, crustal thickening and exhumation of deep crustal rocks within the gneiss domes of the Central and Southern Pamir makes the area an ideal site for studying the India-Asia collision and its paleogeographic and climatic effects. To account for today’s 70-km-thick crust of the Pamir orogen and more than 400 km of convergence accommodated in the Pamir, pre- and syn-collisional processes have been proposed including, continental subduction, delamination, extrusion and oroclinal bending of the Pamir arc. However, testing these models requires constraints on the pre-collisional state of the Pamir lithosphere and its tectono-magmatic evolution. During most of the Cretaceous, the southern Pamir terrane was a site of a widespread arc-related magmatism, which resulted in the formation of many plutons and a volcanic suite of intermediate to acidic composition, whereas the central Pamir terrane lacked any sign of magmatic activity. However, in the late Cretaceous to early Paleogene (78 – 61 Ma) a less widespread magmatic activity in the western part of the Central Pamir resulted in the formation of the Bartang mafic to intermediate volcanic and volcaniclastic rocks. We report here the geochemical and Sr-Nd isotopic features of the late Cretaceous – early Paleogene Bartang volcanics. This volcanic suite bears geochemical and radiogenic isotope features that differ from the arc-related southern Pamir igneous rocks. Mafic basalts that comprise the lowest portion of the section exhibit MORB-like pattern with slightly depleted light rare earth elements (LREE) and large ion lithophile elements (LILE). Further up in the section this pattern shifts towards an arc-related pattern with enriched LREE and LILE. The 87Sr/86Sr_i isotope ratios are lower (0.705335 – 0.706693) than those from the southern Pamir igneous rocks (0.706915 – 0.711105) and epsilon Nd values exhibit ratios close to mantle domain, ranging between -0.7 and -2.7, with the lower part of the section showing less negative values then the upper. In contrast to the Bartang volcanics, the southern Pamir igneous rocks exhibit more negative epsilon Nd values (from -4.7 to -13). The relatively low initial 87Sr/86Sr isotope ratios and slightly negative epsilon Nd values of the Bartang volcanic rocks together with the trace elements pattern that shifts from MORB-like to arc-related indicate mixing of two magmas derived from depleted and enriched mantle sources, with the latter inheriting the arc-related pattern from the subduction stage. Alternatively, the arc-related pattern could be derived through contamination of the primary magma by the crustal material. These features, compared to the southern Pamir arc-related igneous rocks, also indicate that the tectonic setting in the Pamir changed during the late Cretaceous from a continental arc to a within-plate extensional setting.

How to cite: Aminov, J., Dupont-Nivet, G., Ding, L., Guillot, S., Glodny, J., Cordier, C., Roperch, P., Mamadjanov, Y., and Mirvaisov, M.: Late Cretaceous – early Paleogene tectonic evolution of the Central Pamir inferred from the geochemical features of the Bartang volcanics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12681, https://doi.org/10.5194/egusphere-egu2020-12681, 2020.

The Pamir Plateau, as the west extension of the Tibetan Plateau, forms a prominent salient into central Asia. Previous studies have suggested that the Pamir indented northward, causing retreat of the proto-Paratethys Sea and aridification of Central Asia. However, its indentation and surface uplift history are poorly constrained, with existing studies focusing mainly on the eastern side of the Pamir salient. This study presents new multi-proxy data from the southeast Tajik Basin, located on the western side of the salient, to explore the tectonic evolution of the Pamir Plateau. In the southeast Tajik Basin, our magnetostratigraphic study indicates that the fluvial and alluvial strata were deposited between ~20-8 Ma, with thick conglomerates starting at ~15 Ma. Provenance data from sandstone detrital zircon U-Pb ages and mudstone eNd values indicate a pronounced shift in sediment source from the Central Pamir to the North Pamir around 12 Ma. This provenance change is corroborated by carbonate stable oxygen isotopes showing a gradual decreasing trend between 12-8 Ma, which most likely reflects surface uplift of the North Pamir. Collectively, our results indicate that the North Pamir was originally part of the broad Tarim-Tajik Basin, and has been gradually uplifted since ~12 Ma.

How to cite: Li, L., Dupont-Nivet, G., Roperch, P., Najman, Y., Kaya, M., Meijer, N., and Aminov, J.: Late Miocene deformation and surface uplift of the North Pamir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6105, https://doi.org/10.5194/egusphere-egu2020-6105, 2020.

The ongoing surge of international research on Asian Climate and Tectonics enables to better assess interactions between forcing mechanisms (global climate, India-Asia collision, Tibetan Plateau growth) and paleoenvironmental changes (monsoons, aridification), land-sea distribution, surface processes, paleobiogeographic evolution and the global carbon cycle. We review here the progress of the ERC MAGIC project (Monsoons in Asia caused Greenhouse to Icehouse Change?) integrating regional geodynamic constraints, well-dated environmental / biodiversity records and climate modeling. MAGIC focuses on the Paleogene period that includes the global Greenhouse to Icehouse cooling, the early collision and plateau growth and associated regional development of monsoons and westerlies over the Proto-Paratethys sea. Our work focuses on three areas constraining Asian paleoenvironments. (1) In Myanmar, paleomagnetic results, new dating of magmatic rocks and sediments along with additional detrital geochronology and basin analysis of the Burmese subduction margin and implications for the history of India-Asia convergence. (2) Along the Northeastern Tibetan Plateau margin, the combination of multiple proxies (leaf wax stable isotope, pollen, grain size, etc…)  applied to an extended lacustrine Paleogene record enables to identify precisely Asian climate changes and their consequences on ecosystems. (3) In westernmost China and Tajikistan, the proto-Paratethys sea fluctuations and the sedimentary records of Pamir tectonic evolution are now precisely dated enabling to constrain driving mechanisms and paleoenvironmental consequences. Together these results are used to constrain climate modeling experiments which permit validation of hypotheses on interactions between paleogeography, paleoenvironments and paleobiodiversity at Asian and global scales in response to long-term and short-term events.

How to cite: Dupont-Nivet, G., Meijer, N., Kaya, M., Westerweel, J., Tardif, D., Barbolini, N., Rohrmann, A., Aminov, J., Ruiz, D., Woutersen, A., Huang, H., Poblete, F., Licht, A., Roperch, P., Hoorn, C., Proust, J.-N., Fluteau, F., Donnadieu, Y., and Guillot, S.: Asian paleoenvironments, paleogeography and paleobiodiversity interactions during the Greenhouse-Icehouse transition , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18291, https://doi.org/10.5194/egusphere-egu2020-18291, 2020.

Removal of carbon on geological timescales is generally assumed to be governed by the relative strength of silicate weathering and organic carbon burial. For past transient warming phases organic carbon burial has been considered as a relevant negative feedback, but it remains uncertain how this compares to present-day anthropogenic emissions. The ocean is very effective at organic carbon remineralization and, only certain regions bury significant amounts of organic carbon. Organic carbon burial hotspots include shallow water regions along active continental margins and permanently oxygen-deficient zones.

Shallow inland seas covering continents bear depositional settings with broad low-energy facies and delivery of low-reactivity, fossil (ancient) and terrestrial (both contemporary and aged, i.e., soil) organic carbon and lithogenic particles when they are associated with an active margin. These epicontinental seas might be hydrographically and geographically restricted resulting in oxygen-depleted environments. As such, epicontinental seas might serve as significant carbon sinks for all types of organic carbon components (i.e. marine, fossil, contemporary and aged terrestrial) with a high organic carbon preservation efficiency. However, oxygen deficient environments associated with epicontinental seas are currently rare and, as a consequence, organic carbon burial may be overestimated in importance as a negative feedback to anthropogenic emissions compared to the past.

As part of the ERC “MAGIC” project, we study the mechanics, relative contribution and preservation efficiency of ancient epicontinental seas as carbon sinks, using organic rich deposits dated to the Paleocene – Eocene Thermal Maximum (PETM) from the proto-Paratethys and West Siberian seas. We then calculate and compare the amount of organic carbon sequestered in these basins, relative to modeled estimates of global organic carbon burial. Our data corroborates the view that the sequestration of organic carbon arises due to enhanced recycling of phosphorus from sediments under anoxic conditions and coupled increase in biological productivity. We estimate ca. 1380 Gt C burial, plausibly more than half of the estimated global total excess burial across the PETM is focused in the proto-Paratethys and West Siberian seas. This supports the hypothesis that alongside the organic carbon burial on other continental margins, the proto-Paratethys and West Siberian basins acted as significant carbon sinks, leading to the termination of the PETM. An important implication of this is that, for the present-day and other periods in the geological past with small epicontinental seas, the effectiveness of this negative carbon cycle feedback is likely greatly diminished.

How to cite: Kaya, M., Dupont-Nivet, G., Frieling, J., Fioroni, C., Rohrmann, A., Özkan Altıner, S., Vardar, E., Plessen, B., Mamtimin, M., and Zhaojie, G.: Epicontinental seas as efficient carbon sinks: proto-Paratethys & West Siberian seas during the PETM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8570, https://doi.org/10.5194/egusphere-egu2020-8570, 2020.

The evolution of Asian climate during the Cenozoic is traditionally linked to shifts in paleogeography such as the proto-Paratethys Sea incursions and uplift of the Tibetan Plateau driving monsoonal circulation and affecting the mid-latitude westerlies in Central Asia. In contrast, the role of global climate in the Asian hydrological cycle remains unclear. Here, we present a new stratigraphic record from the terrestrial Xining Basin in central China, which covers the Early Eocene Climatic Optimum (EECO), a period characterized by long-term global warmth and elevated atmospheric CO₂ levels. The record is dated using magnetostratigraphy and extends the previously studied Paleogene strata down to 50.9 Ma (chron C23n). We use a variety of paleoclimate proxies, to derive the hydroclimatic evolution of the basin at this time. The lithostratigraphy is characterized by organic-rich mudrocks and gypsum beds (reaching TOC contents of up to 1.7%) interpreted as an alluvial mudflat to saline lake. The higher organic content of the strata indicates either increased organic productivity or preservation, both of which suggest a wetter depositional environment during the EECO. This is corroborated by palynological records showing a large increase in the abundance and diversity of trilete spores, indicating a wetter biome at this time. In addition, the d¹³C values of the bulk organic matter and leaf waxes (both C₂₉ and C₃₁), suggest a reduction in water stress on plants and a wetter environment as well. These observations are in stark contrast to the arid red beds, evaporites and xerophytic pollen observed in the underlying Cretaceous-Paleocene strata and overlying middle-late Eocene deposits. The peak global warmth of the EECO is thus clearly linked to an intensified Asian hydrological cycle suggesting a major driving role for global climate.

How to cite: Meijer, N., Dupont-Nivet, G., Licht, A., Roperch, P., Rohrmann, A., Woutersen, A., Hoorn, C., Barbolini, N., Sun, A., Abels, H., Meyer, H., and Nowaczyk, N.: Intensified hydrological cycle during the Early Eocene Climatic Optimum (EECO) recorded in the Xining Basin, NE Tibet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8597, https://doi.org/10.5194/egusphere-egu2020-8597, 2020.

Cenozoic changes in climate, erosion, and atmospheric circulation in Asian interior continents can be reconstructed from records of eolian dust deposition from sediments of the North Pacific Ocean (NPO). Through a careful investigation of Nd isotope as eolian dust source tracer, the well-known core GPC3 in the central NPO has provided so far the most complete Asian dust records since ~40 Ma. Nd isotope in the GPC3 eolian dust thus documented an integrated history of Nd isotopic change of very fine eolian dust contributed from various geological terranes in Asian dust source areas. Unraveling this ~40 Myr-long Nd isotopic change in the NPO provides a first order constraint on the provenance change of the Asian dust source areas as a whole. However, this work cannot be done without an explicit Nd isotopic history for each geological terrane within the broad Asian dust source areas, since the Asian dust source area can be at least divided isotopically into two regions with distinct Nd isotopic values, e.g., the northern Tibetan Plateau (NTP) and the Central Asian Orogen (CAO). In this work, we present new data of river sediment Nd isotopic data around the entire Qaidam and Xining Basins to yield a more comprehensive Nd isotopic regimes at the NTP with compiling previously reported data. We have established an integrated Cenozoic Nd isotopic records of finer dust in the NTP based on previous records and our new Nd isotopic records in the Xining Basin from 52 to 17 Ma and Linxia basin from 23 to 5 Ma using both bulk sediments and clay fractions (<2 μm). After comparison of the reconstructed Nd isotopic variation in fine dust at the NTP with that in the NPO, we have further assessed the relative contributions of NTP and CAO to the Asian dust preserved in the NPO during the last 40 Myr, which indicates a dominant late Oligocene-Neogene uplift and growth of the mountains at the NTP and the CAO regions.

How to cite: Yang, Y., Fang, X., Galy, A., Yang, R., Song, B., and Liu, Y.: Cenozoic Nd isotopic variation of Asian dust in the northern Tibetan Plateau and the North Pacific Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12228, https://doi.org/10.5194/egusphere-egu2020-12228, 2020.

Early Cenozoic continental sediments deposited contemporaneously or soon after the onset of India-Asian collision provide an obvious target for gaining insight into the early stages of the growth of the Tibetan plateau. These continental sequences are generally found in an arcuate belt that extends from the central plateau into the western Yunnan province (e.g. Nangqian-yushu Basin, Gongjo Basin and Jianchuan Basin). With limited exposure and elusive datable horizons except for a few dikes cross-cutting stratigraphy and interbedded lava flows, there were few constraints on absolute time of these Cenozoic sediments, limiting further studies of the tectonic, topographic and environmental evolution in southeast Tibet. Here, we focus on the Jianchuan basin, the age of which was mapped from the Paleocene up to the Pliocene but recently reassigned to the Paleocene/Eocene as a whole. The Xinsong section with 1547 meters in thickness was measured at the meter scale to determine vertical changes through the depositional facies. The lower part of the section consists of 1027 m thick red-colored, massive siltstone with many fine sandstone interlayers, while the upper part of the section is composed by a series of basal-scoured, upward-fining and stacked sand bodies with the thickness of 520 m. A total of 981 standard paleomagnetic oriented samples were collected. Samples were subjected to stepwise thermal demagnetization that revealed either two or three component magnetizations with the high temperature component (HTC) unblocked at ∼660-680 °C. Our preliminary results show multiple polarity reversals that can be well correlated with the Geomagnetic Polarity Time Scale (GPTS) between ca. 50 and ca. 40 Ma. We interpret that these sediments were deposited in a restricted, narrow basin in the footwalls of thrust fault where the depositional environments were highly related to the compressional deformation. Our new result may be of great significance for understanding the kinematic and dynamic models of the deformation and evolution of the Tibetan plateau.

How to cite: Luo, C., Wang, P., Li, Y., Li, S., Wei, X., and Huang, Y.: Magnetostratigraphy of the Eocene Jianchuan Basin in southeast Tibet: A preliminary result, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13422, https://doi.org/10.5194/egusphere-egu2020-13422, 2020.

The evolution of the longest river in Asia, Yangtze, provides a spectacular example to understand the Cenozoic interaction between tectonic, climate and surface processes. The oldest Yangtze deposits in southeast China, characterized by thick sequence of unconsolidated gravel, sand and silty clay, referred as “Yangtze Gravel”, has been recently found in its lower reach and dated back to > 23 Ma, indicating a pre-Miocene establishment of a through-going river. However, the link between river reorganization and tectonic evolution has never been well understood. Far-field effects of the Indian–Eurasia collision are often invoked to explain the widespread East Asia lithospheric deformations and the opening of the marginal, as well as the through-going of the large rivers. However,  some geological and geophysical investigations challenge this model and suggest that the Pacific Plate subduction beneath Eurasia plays an much more active role in East Asia lithospheric deformation during the Cenozoic. Here, we study the sedimentology, chronology and provenance of the Yangtze Gravel based on 17 stratigraphic sections exposed along the Lower Yangtze River. Our results indicate a braided alluvial system (Paleo-Lower Yangtze) established since early Miocene across the Jianghan Basin, North Jiangsu Basin and East China Sea Shelf Basin. Compared with the Early Cenozoic red-colored, halite-bearing lacustrine deposits, our results indicate a larger tectonically controlled shift from rifting to post-rift down-warping across these basins. During Early Cenozoic, the initial subduction of Pacific Plate may contribute to the back-arc extension and affect the continental deep interior of East Asia many thousands of kilometers from the subduction margin. During Oligocene to Miocene, the ongoing subduction of the Pacific plate produced a stagnant slab that may have significantly triggered the post-rift subsidence and the connection of these basins. The deposition of the “Yangtze Gravel” reflect the dynamic response of surface processes to western Pacific subduction in East Asia.

How to cite: Wang, P., Zheng, H., Wang, Y., Wei, X., Tang, L., Jourdan, F., Chen, J., and Huang, X.: Lower Yangtze drainage reorganization response to western Pacific Subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13156, https://doi.org/10.5194/egusphere-egu2020-13156, 2020.

The two great lacustrine fossil Konservat-Lagerstätten of northeastern China producing feathered dinosaurs, the Jurassic Yanliao Biota and the Jehol Biota, were deposited during relatively humid times and are separated by a major redbed interval, typified by the Tuchengzi Formation deposited under a much more arid climate (1). We present new zircon CA-TIMS U-Pb ages for the peaks of the Yanliao [~160 Ma] and the Jehol biotas [Yixian Fm ~125 Ma] constraining a shift in that region from a higher-latitude temperate zone to a lower-latitude semiarid zone consistent with a ~30° arc distance shift true polar wander shift (1, 2, 3). The Yanliao Biota and the Jehol Biota are preserved in remarkably similar facies almost lacking signs of desiccation, while the Tuchengzi Formation has abundant evidence for desiccation and even eolian dune sands. This suggests, under a simple zonal climate model, a rapid shift to the south from Jurassic times and a shift back into Early Cretaceous times. A very similar and even more dramatic shift is seen in northwest China in the Junggar Basin where Triassic-Middle Jurassic coal bearing sequences with evidence of seasonal freezing (4) is replaced by a Late Jurassic [~150 Ma (5)] redbed sequence [including the famous dinosaur- and crocodiliomorph-bearing Shishugou Formation], and again replaced by coal-bearing strata in the Early Cretaceous, suggesting a similar magnitude shift south and back north of the region. The hypothesis that the monster polar shift is transient, swinging south and then north in ~35 million years necessitates rigorous testing by inclination-error-corrected paleomagnetic data to cleanly separate rapid latitudinal effect from rapid global climate change or regional orographic effects.

1. Olsen P E et al. (2015) Geological Society of America, Abstracts with Programs 47, 378.
2. Muttoni G, Kent D V (2019)Journal of Geophysical Research. Solid Earth 124, 3288-3306.
3. Yi Z, Liu J, Meert, G (2019) Geology 47, 1112-1116.
4. Olsen P E et al. (2018) Geological Society of America Abstracts with Programs 50, doi: 10.1130/abs/2018AM-325061 (2018).
5. Fang Y et al. (2019) Topographic evolution of the Tianshan Mountains and their relation to the Junggar and Turpan Basins, Central Asia, from the Permian to the Neogene. Gondwana Research 75, 47-67 (2019).

How to cite: Olsen, P., Sha, J., Maclennan, S., Kinney, S., Fang, Y., Chang, C., Kuhn, T., Fu, R., Kent, D., and Schone, B.: Monster polar shift, shifts back: paleoclimate and CA-ID-TIMS evidence from northern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20827, https://doi.org/10.5194/egusphere-egu2020-20827, 2020.

In this study, the major winter wheat planting area of China is selected as the study area, with the time scale of the growth period of winter wheat (a total of 56 growth periods during 1961/10-2016/5). The significance, stability, magnitude of the trend and the average trend of the study area with 8 temperature indices and 7 precipitation indices of 453 meteorological stations are tested by Mann–Kendall method and Sen's nonparametric method. The following observation can be made: (1) the cold extreme indices show strong and stable downward trend in most of the stations in the study area, while the hot extreme indices show strong and stable upward trend, especially in the northern winter wheat planting area and the north of the southern winter wheat planting area. (2) The trends of extreme precipitation indices in most of the sites in the study area are insignificant and unstable. Only in R20mm, a significant and stable decreasing trend is showed in some stations, which mainly located in the northern winter wheat planting area and part of the central and western regions in study area. The results in some ways could enrich the references for understanding the climate change in the growth period of winter wheat in the region and help to formulate a better agronomic management practice of winter wheat.

How to cite: Nie, H., Qin, T., Lv, Z., and Wang, J.: Trend analysis of extreme climate indices during winter wheat growth period in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3865, https://doi.org/10.5194/egusphere-egu2020-3865, 2020.