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Soil moisture is an important component of the soil–vegetation–atmosphere terrestrial hydrological cycle and is an important factor affecting terrestrial ecosystems. In the context of extensive vegetation greening on the Tibetan Plateau (TP), it is important to investigate the effect of vegetation greening on soil moisture to maintain ecosystem stability and protect the sustainability of ecological restoration projects. To evaluate the effect of vegetation greening on soil moisture on the TP, the spatial distribution and trends of soil moisture and vegetation on the TP were analyzed using GIMMS NDVI data and ERA5 soil moisture data from 1982 to 2015. The effects of grassland NDVI, precipitation, and temperature on SM were also explored using multiple regression apparent and SEM. The main results are as follows: from 1982 to 2015, both grassland NDVI and SM showed a stable increasing trend. Precipitation was the most important factor influencing SM changes on the TP. In the context that vegetation greening is mainly influenced by temperature increase, vegetation plays a dominant role in SM changes in soil drying and soil wetting zones. In this paper, the climate–vegetation–soil moisture coupling mechanism of grasslands on the TP is investigated, and the related results can provide some theoretical references and suggestions for global ecosystem conservation and the sustainable development of ecological restoration projects. [ABSTRACT FROM AUTHOR]

Sedimentary records indicate that subtropical and mid-latitude East Asia exhibited considerable drying and wetting, respectively, during the mid-Cretaceous, which is considered to be relevant to much higher atmospheric carbon dioxide (p CO 2) concentrations and/or proto-Tibetan Plateau (proto-TP) uplift. In order to explore and compare their roles on the East Asian climate evolution, we conducted simulations of the mid-Cretaceous climate system with different atmospheric p CO 2 levels and varying topographies. The results show that both factors had significant influences on the East Asian climate. As the increase in atmospheric p CO 2 levels from ∼560–1120 ppmv to ∼1120–2240 ppmv, the precipitation increases considerably over mid-latitude East Asia, but only small changes in the subtropical portion of East Asia occur. Simultaneously, the effects of the proto-TP uplift are opposite to those of global warming trend during that period. Generally, it leads to a precipitation decrease over subtropical East Asia, but rather minor changes over mid-latitude East Asia. These changes are qualitatively consistent with the deduction based on the geological records, but the magnitudes of the modeled precipitation changes are relatively smaller. Therefore, we can conclude that the subtropical East Asian drying during the mid-Cretaceous can be partly explained by the proto-TP uplift, while the mid-latitude East Asian wetting was partly due to global warming. However, additional factor(s) also played a significant role in the East Asian climate evolution during the mid-Cretaceous. • East Asian climate evolution was dependent on the latitude of the proto-Tibetan Plateau in the deep past; • Global warming induced wetting at mid-latitude East Asian in the mid-Cretaceous; • The proto-Tibetan Plateau uplift led to drying in the subtropical East Asian in the mid-Cretaceous. [ABSTRACT FROM AUTHOR]

• Large provenance dataset of the Lower Cretaceous are presented. • A transcontinental paleo-river exist in SE Tibet. • Transcontinental river was driven by warm and humid climate. The evolution of fluvial drainage systems reflects interactions of tectonic uplift and climate change. Many previous studies have emphasized how Cenozoic tectonic uplift of the Tibetan Plateau has driven the reorganization of large-scale rivers. However, Cretaceous fluvial drainage configurations of the region are poorly constrained. In this study, we present a comprehensive provenance dataset of Lower Cretaceous deposits in the Lanping and Simao basins in southeast Tibet based on petrology, detrital zircon U-Pb dating and Lu-Hf isotopes. Our results show that the quartz-rich Cretaceous fluvial deposits yield major detrital age modes in the 2400–2600 Ma, 1700–1900 Ma, 750–1000 Ma, 400–490 Ma, and 200–290 Ma periods, and are mainly recycled from older siliciclastic strata exposed in the Southern Qiangtang terrane, Songpan-Garze terrane, Sichuan Basin, and Kangdian Basement. Zircon age clusters of 150–200 Ma and 200–290 Ma yield mostly negative and slightly positive εHf(t) values indicating volcanic detritus supplied from the Yidun Arc and Southern Qiangtang magmatic rocks. Lower Cretaceous fluvial units in the Sichuan, Lanping, Simao, Vientiane, Khorat, and Phuquoc basins share similar detrital zircon age spectra, which we interpret as the existence of a unified fluvial drainage system. We thus propose a transcontinental paleo-river with its headwater from the Southern Qiangtang and Songpan-Garze terranes, and northern Sichuan Basin and flow from Lanping and Simao basins to the Khorat Plateau. We suggest that a warm and humid climate, rather than tectonic uplift, drove rapid erosion rates of the source terranes and establishment of the transcontinental river. [ABSTRACT FROM AUTHOR]

The Jurassic marine sequences of the Qiangtang Basin in the northern part of the Tibet Plateau have the best petroleum exploration prospect. The prototype basin has undergone multi-stage and complicated tectonic events since the Cretaceous, especially the mid-Cretaceous tectonic event and the Cenozoic uplift of Tibetan Plateau. However, little information about the impact of these tectonic events on petroleum preservation has been done. In this paper, the burial and thermal histories modeling using vitrinite reflectance (R) are used to characterize the impact. The results showed that there is a regional falling of palaeotemperature in the Qiangtang Basin during the mid-Cretaceous indicating a regional tectonic event caused by the collision between Lhasa and Qiangtang blocks. However, the Cenozoic tectonic event caused by the uplift of Tibetan Plateau since 30 Ma was only recorded in the Southern Qiangtang Depression and not obvious in the Northern Qiangtang Depression, which indicates that uplift-denudation caused by the mid-Cretaceous tectonic event was extensive in whole Qiangtang Basin and more significant to the hydrocarbon accumulation than those in the Cenozoic. The event could damage the previously formed hydrocarbon traps and caused the leaking of cap-rocks for the dramatically denudation especially in the Southern Qiangtang Depression. We speculated that the Northern Qiangtang Depression has the lower thickness of denudation and barely influenced by the Cenozoic tectonic events and thus is primary exploration target for gas or gas hydrate. [ABSTRACT FROM AUTHOR]

To understand the early topographic growth of the Tibetan Plateau and the causes and effects of climate change in this region, it is important to reconstruct the drainage evolution across Southeast Tibet. Based on age constraints provided by detrital zircons in the fluvial sandstones in the Khorat Plateau Basin, we identified a major Early Cretaceous drainage disruption and reorganization event. The ages and Hf isotope compositions of the detrital zircons in the Upper Jurassic-Lower Cretaceous Phu Kradung to Phu Phan formations (166–122 Ma) suggest the existence of an exorheic continental-scale paleo-Mekong River with headwaters in the Songpan-Garze and Qiangtang terranes. This paleo-river flowed southwards across the Khorat Plateau to what is presently the offshore Phuquoc Basin, which was then part of the Neo-Tethys Ocean. In contrast, the U-Pb-Hf compositions of the detrital zircons in the Lower Cretaceous Khok Kruat Formation (122–113 Ma) indicate that a prominent detrital supply from the Sibumasu magmatic rocks was transported by the paleo-Salween River. This major change reflects the occurrence of ancestral transcontinental river disruption at around 122 Ma, which was driven by the final collision between the Lhasa and Qiangtang and Woyla Arc and Sibumasu terranes. The tectonic uplift and ensuing arid climate corresponded to the reorganization of the ancestral Mekong drainage system during the Mid-Cretaceous (113–94 Ma). [ABSTRACT FROM AUTHOR]

The Cenozoic lacustrine Lunpola oil shale, located in the central Tibetan Plateau, has received little research interest in its depositional history although it is estimated to be a huge resource reserve. This study investigates the palaeoclimate, provenance, and regional drainage system of the ancient lakes using a combined analysis of element geochemistry and stratigraphy to elucidate the depositional history of the Lunpola oil shale. Most of the samples in the lower part of the section have chemical index of alteration (CIA) values between 65 and 75, reflecting a moderate weathered source, while samples in the upper part the section have CIA values between 60 and 65, which indicate relatively weak chemical weathering in the source area. This stratigraphic grouping suggests a paleoclimate transition from a relatively warm or humid period to a cold or dry period. The Zr/Sc and Th/Sc ratios of the samples reveal that sorting and recycling were minor during deposition of the oil shale. The geochemical results (Al 2 O 3 –(CaO ⁎ + Na 2 O)–K 2 O (A–CN–K) diagrams, high contents of Th, plots of Co/Th–La/Sc and Cr/Th–Sc/Th) demonstrate that the sedimentary sources were felsic rocks. Plots of La–Th–Sc, Th–Sc–Zr/10, Th–Co–Zr/10, and Ti/Zr versus La/Sc illustrate that the source rocks were from continental arc and active continental margin. The Baingoin batholiths to the south of the Lunpola Basin consisting mainly of Cretaceous granodiorite and adamellite are likely responsible for supplying materials to the Lunpola oil shale. Similar special REE patterns further suggest the affiliation of the oil shale with the batholiths. Provenance analyses indicate a main river from the south; moreover, stratigraphic study confirms an upstream ancient Baingoin Lake between the source area and the ancient Lunpola Lake. In this drainage system, paleoclimate clearly restricted the development of rivers around the lakes. Although terrestrial organic matter (higher plants) dominated the drainage area, the main river originating from the south could only bring a certain amount of them to the lakes. Moreover, considering the filtration of the upstream ancient Baingoin Lake, minor terrestrial organic matter could be carried and deposited in the ancient Lunpola Lake. Therefore, lacustrine algae could proliferate as the main organic source and preserve in the stratified hypersaline lake to form the largest oil shale resource in Tibet. [ABSTRACT FROM AUTHOR]

Abstract: The Late Cretaceous Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in the Simao Basin, southeastern Tibet, is thought to be genetically related to the Maha Sarakham Formation in the Khorat Basin. The provenance and paleogeography of these two basins have been under debate, although little diagnostic evidence has been previously published. A combined analysis of whole rock geochemistry, zircon U–Pb chronology, and Hf isotopic compositions was performed to characterize the provenance of the Mengyejing Formation. These formation's sandstones are characterized by moderate chemical index of alteration (CIA) values. These values, together with plots of the Th/U–Th ratios, suggest that certain samples have undergone moderate weathering and sedimentary recycling. The major and trace elements (La/Th–Hf, Th/Sc–Zr/Sc, Eu/Eu*–Th/Sc, TiO2–Fe2O3 T +MgO, Al2O3/SiO2–Fe2O3 T +MgO, K2O/Na2O–SiO2) indicate that the sedimentary sources were felsic rocks from an active continental margin or continental arc with a minor amount of recycled sediment from a passive continental margin. The Mengyejing Formation contains detrital zircons primarily with U–Pb ages of 2.45–2.57Ga, 1.8–1.9Ga, 740–880Ma, 410–470Ma, and 215–300Ma. The results reveal that the pre-Devonian zircons are derived from the recycled sediments of the Yangtze block originating in the Qinling Orogenic Belt, and they share this provenance with the coeval sediments in the Khorat Basin. The magmatic rocks of the Ailaoshan and Lincang areas are responsible for supplying the Devonian to Triassic detrital zircons. These provenance data combined with published paleocurrent results suggest that the Simao Basin was situated on the western margin of the Khorat Basin during the Late Cretaceous. The basins were connected when marine incursion occurred. We propose that pre-Devonian materials from the southwestern Sichuan Basin first supplied detritus to the Simao Basin and subsequently to the Khorat Basin. [Copyright &y& Elsevier]

Abstract: The Zhuonai Lake and Lunpori oil shale, located in the central Tibetan Plateau, were deposited in a Tertiary lacustrine environment in the Hoh Xil and Lunpola Basins, respectively. A combined investigation of sedimentary, organic geochemistry, and organic carbon isotope was performed to define source rock potential, the palaeoenvironment, and source of the organic matter. Three types of facies sequences are developed in the Zhuonai Lake section and oil shale mainly occurs in the oil shale-marl sequence. The oil shale-silty claystone and oil shale-marl facies sequences are developed in the Lunpori section. Both oil shales are finely stratified especially for the Lunpori oil shale with thickness of the laminae about 10μm which contains abundant pyrite crystals and fossilized fish bones. Both the Zhuonai Lake and Lunpori oil shale contain high values of total organic matter (TOC), S2, and hydrogen index (HI), indicating the oil shales have good oil source rock potential. Tmax values show an immature stage of organic matter for the Zhuonai Lake oil shale and thermally marginally mature for the Lunpori oil shale because of difference in their burial history. Lunpori oil shale shows the characteristics of amorphous organic matter (AOM) dominance, odd-over-even predominance, maximum n-alkanes peak at nC25 or nC23, higher proportion of C29 sterane, light δ13Corg values (−30.0‰ to −27.4‰), high concentrations of phytane (Pr/Ph ratio ranging from 0.02 to 0.18), high values of gammacerane index (up to 25.26), and presence of β-carotane, which are consistent with a reducing, stratified, and hypersaline palaeo-lake with main contribution of algae and bacteria to the organic matter (OM). Oil shale samples from the lower and upper part of the Zhuonai Lake section are characterized by low H/C ratios and high O/C ratios, amorphous humic OM and vitrinite dominance, odd-over-even predominance with long-chain n-alkanes dominance, heavy organic carbon isotope, and C29 >C27 sterane distribution, in agreement with a main contribution of land plant. The heavy organic carbon isotope suggests the expanding of C4 land plant during the early Miocene. While the most samples show characteristics of AOM dominance, maximum peak at nC29 or nC31, and high C27 sterane concentration, consistent with a main contribution from algae to the OM. The Pr/Ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects. Biomarker analysis indicates that the salinity during the deposition of the Zhuonai Lake oil shale was not enhanced. The Oligocene Lunpori oil shale and the Early Miocene Zhuonai Lake oil shale recorded the variation of palaeolimnological water chemistry. The development history of the palaeo-lakes from the Oligocene saline to the Early Miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central Tibetan Plateau. [Copyright &y& Elsevier]

The Tertiary lacustrine Niubao Formation is well exposed in the middle-western part of the Lunpola Basin, central Tibetan Plateau, where crude oil was once discovered during drilling campaigns. Sedimentological, organic petrographic and geochemical work was performed on the upper and middle members of this formation in order to investigate its hydrocarbon source rock potential. Sedimentological analyses indicate that both members were deposited in relatively deep lake conditions away from the influence of big stream system, with the upper Niubao Formation (UNF) having higher sand content. The two members contain abundant high-quality Type I kerogen derived mainly from plankton, algae, and bacteria. Compared with samples of the middle Niubao Formation (MNF), UNF samples also contain more Type II and Type III kerogens of terrestrial origin. Biomarkers of source rock extracts suggest that a long-standing anoxic, stratified, and saline ancient lake occupid the basin during deposition of the two members, which was conducive to the preservation of organic matter. However, higher gammacerane content and the presence of β-carotane in MNF samples imply a more saline lake condition. Rock-Eval T max and biomarker parameters reveal marginal maturity and immaturity for samples from MNF and UNF, respectively. Therefore, MNF has better source rocks of higher maturity might be the main hydrocarbon generating member of the basin; similar diagnostic biomarkers and biomarker parameters reported in the crude oil also imply its affiliation with the source rocks of MNF. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang Ocean played an important role in the formation of the Tibetan Plateau prior to the Cenozoic India–Eurasia collision. However, there are still uncertainties about the subduction polarity and timing of the Lhasa–Qiangtang collision. We conducted sandstone petrologic and detrital zircon U–Pb–Hf isotopic analyses on the Cretaceous Wada mélange, trench-fill strata and Duoni Formation in the Basu area in the eastern Bangong–Nujiang Suture Zone. The Wada mélange (∼114 Ma) exhibits block-within-matrix features and a detrital zircon U-Pb age spectrum characterized by multiple peaks at 114–180 Ma, 200–300 Ma, and 1800–2000 Ma. The trench-fill strata consist of coherent chert, sandstone, and mudstone, with a detrital zircon age spectrum dominated by a single peak at ∼120 Ma. The ε Hf (t) values of the 110–300 Ma detrital zircon grains in the Wada mélange and trench-fill strata range from −20 to +10 and are consistent with those of the South Qiangtang Terrane. The ε Hf (t) values of the ∼120 Ma detrital zircons are all negative, and these grains were likely derived from a remnant Cretaceous arc in the South Qiangtang Terrane to the north. These data suggest that the accretionary wedge was derived from the South Qiangtang Terrane during the northward subduction of the Bangong–Nujiang Ocean. The Duoni Formation (∼113 Ma) represents peripheral foreland basin deposits with the Lhasa Terrane as the basement. Provenance analysis indicates that these deposits received clastic material mainly from the South Qiangtang Terrane and to a lesser degree from the North Lhasa Terrane. Our results suggest that the Lhasa–Qiangtang collision occurred in the Early Cretaceous (∼113 Ma) in the eastern segment of the Bangong–Nujiang Suture Zone. • The Wada mélange and trench-fill strata (∼114 Ma) are associated with northward subduction. • The Duoni Formation (113 Ma) represents the peripheral foreland basin in the Basu area. • The eastern Bangong–Nujiang Ocean closed at ca. 113–114 Ma. [ABSTRACT FROM AUTHOR]