Northeast Tibetan Plateau Research Articles

Zn Isotopic Composition Variability in Glacier-Fed Alpine Rivers of the Northeast Tibetan Plateau: Response to Migration Processes and Anthropogenic Impacts.

Elucidating the migration processes of zinc (Zn) is crucial for comprehending its influence on global biogeochemical cycling. However, significant gaps remain in the knowledge of these processes in glacier-fed rivers of the northeast Tibetan Plateau (NETP). This study determined the isotopic compositions (δ66Zn) of dissolved and particulate Zn in three alpine rivers fed by the Laohugou Glacier (LHG), the Lenglongling Glacier (LG), and the Yuzhufeng Glacier (YG) in the NETP. Results show that the δ66Zn of particulate Zn varies from -0.01 ± 0.04 to +0.97 ± 0.12‰, generally higher than that of dissolved Zn (-0.82 ± 0.06 to +0.19 ± 0.03‰). This suggests a migration behavior in which isotopically lighter Zn is enriched in the dissolved phase and isotopically heavier Zn preferentially adsorbs onto the particulate matter. Moreover, the δ66Zn in the dissolved phase exhibits obvious spatial variation, with an upward trend from the LHG-fed river to the YG-fed river and subsequently to the LG-fed river. In contrast, this trend is less pronounced in the particulate phase due to an anomalously high δ66Zn value (0.97 ± 0.12‰). This isotopic anomaly is primarily attributed to anthropogenic impacts. A comparison with global terrestrial aquatic environments emphasizes the unique response of Zn isotope variability in NETP glacier-fed rivers to both migration processes and anthropogenic impacts.

Permafrost impacts on chemical weathering and CO2 budgets in the Tibetan Plateau: Micro-watershed perspective on a headwater catchment

Understanding the balance between alkalinity generation from carbonate and silicate weathering, and the effect of sulfide weathering, is crucial for comprehending the impact of these processes on atmospheric CO2 levels. However, the sequestration potential and the net balance of CO2 between the release from sulfide weathering and the consumption by silicate weathering in permafrost environments remain contentious. This study examines the Shaliu River, a typical permafrost-dominated headwater catchment in the Northeast Tibetan Plateau, from a micro-watershed perspective to elucidate the effects of permafrost on chemical weathering and CO2 budgets during ablation period. Silicate weathering in the Shaliu River contributes 25–32 % to solute load, while carbonate weathering contributes 39–45 %. Sulfuric acid (H2SO4) plays a key role in carbonate weathering, accounting for 74 % of it and 37 % of the river’s solute load, especially in the permafrost-covered upstream areas. In contrast, bicarbonate (HCO3–) impacts are more evident in the lower reaches without permafrost. By integrating silicate and carbonate weathering with H2SO4-driven reactions, CO2 budget analysis indicates that the Shaliu River basin acts as a carbon source. The MEANDIR inversion model consistently depicts the watershed as a carbon source, influenced by permafrost and lithology. This implies that sulfide oxidation to produce sulfuric acid (H2SO4) drives carbonate weathering may significantly counterbalance the carbon sequestration associated with silicate weathering over geological timescales. The study provides a comprehensive understanding of the carbon budget dynamics within the permafrost-dominated watersheds of the Tibetan Plateau, enhancing the comprehension of carbon cycle processes in high-altitude ecosystems.

Miocene evolution of vegetation, climate, and elevation in the Wulan Basin of northeast Tibetan Plateau based on a CRACLE analysis of palynological assemblages

The uplift of the Tibetan Plateau (TP) during the Cenozoic has played a pivotal role in shaping global climate and vegetation evolution, however, understanding the uplift history of its various tectonic blocks remains complex. In this paper, we analyze palynological samples from the Miocene Xiayoushashan and Shangyoushashan formations in the Wulan Basin to explore the relationship between climate change and TP uplift. The analysis identified four distinct pollen zones: Zone I (18–15.3 Ma) characterized by Artemisia-Lycopodium-Aster-Polygonaceae; Zone II (15.3–12.7 Ma) dominated by Pinus-Picea-Aster-Artemisia; Zone III (12.7–11.7 Ma) featuring Lycopodium-Picea-Pinus-Polygonaceae; Zone IV (11.7–8.7 Ma) characterized by Picea-Chenopodiaceae-Lycopodium-Artemisia. Results indicate that the whole study interval was dominated by shrubs and grasses, interspersed with conifers and broad-leaved trees, exhibiting an altitudinally zonal pattern. Using the Coexistence Likelihood Estimation (CRACLE) method, we estimate a mean annual temperature (MAT) ranging from 6.0 to 14.7 °C and a mean annual precipitation (MAP) between 919.1 and 1612.4 mm during Miocene times. While minor climatic fluctuations occurred, the region experienced a cool-temperate and sub-humid climate significantly warmer and more humid conditions compared to the present. Based on MAT differences, the paleoelevation of the Wulan Basin during the Miocene was estimated to be c. 1655–2025 m, suggesting an uplift of c. 1275–1645 m since that time. These findings corroborate previous suggestions that the northeastern TP had not reached its current elevation prior to the Late Miocene.

Characteristics of soil microplastics and ecological risks in the Qilian Mountains region, Northeast Tibetan Plateau

Microplastics (MPs) pollution has become a vital global environmental issue. However, comprehensive understanding of the ecological risks of MPs in soils of Northeast Tibetan Plateau still requires further study. In this study, we used the Agilent 8700 Laser Direct Infrared (LDIR) spectroscopy to analyze the characteristics of 10–1000 μm MPs in soils of different vegetation types throughout the Qilian Mountains basin, and to comprehensively explore the ecological risks of MPs in various ecological environments. The results indicate that MPs abundance is highest in soil of shrub areas (26,369 ± 32,147 items kg−1-dry weight (dw)), followed by woodland (22,215 ± 22,544 items kg−1-dw), desert (17,769 ± 9,040 items kg−1-dw), grassland (16,462 ± 12,872 items kg−1-dw), and forest (15,662 ± 13,857 items kg−1-dw). MPs in soils of different vegetation types show similar physical and chemical characteristics, with the shape dominated by fragments (93%–96%), followed by fibers and a few beads, with dominant sizes of 10–30 μm (63%–76%), and polymers dominated by polyamide (PA) and polyethylene terephthalate (PET). Additionally, the environmental risks posed by the fundamental characteristics of MPs have been quantified through the Pollution Load Index (PLI), Pollution Hazard Index (PHI), and Potential Ecological Risk Index (PERI) models. According to the PLI assessment, the current levels of MPs in the environment have not yet imposed significant burdens on the ecosystem. However, the results of PHI and PERI indicate a higher risk of MPs pollution in the Qilian Mountains. This study offers vital information for MPs pollution in the whole Qilian Mountains regions and their potential environmental risks in remote areas’ soil.

An aggregation framework to diagnose the compound hydroclimatic change of the Tibetan Plateau using multiple reanalysis data

Study regionThis study was carried on Tibetan Plateau (TP), which is recognized as the “Third Pole” and “Asia Water Tower”. Study focusTP is suffering extreme hydroclimatic change under global climate warming. Quantifying the hydroclimatic change pattern and strength is necessary to protect local to downstream hydrology and water resources. This study promoted an aggregation framework to diagnose the compound hydroclimatic change on TP using several high-resolution reanalysis data. New hydrological insights for the regionThe promoted aggregation framework is efficient to diagnose the compound hydroclimatic change on TP. Both individual applied data and compound result indicate a warming and wetting environment on most TP, combined with increased trend of evapotranspiration (ET) and soil moisture (SM), while decreased trend of runoff (ROF). The hotspots with strong hydroclimatic change mainly located at inner-southeast TP and northeast TP, including Changtang Plateau, sources of Yellow-Yangtze-Mekong-Salween-Brahmaputra river basin, and Qaidam Basin. The compound warming strength is above 0.06 Celsius/mon/a in winter while the wetting trend is above 0.5 mm/mon/a in summer at most hotspots. ET is increased with trend above 0.1 mm/mon/a in spring, summer, autumn at most hotspots. SM is drying at south periphery while wetting at the remaining area with annual and seasonal trend above 0.0005 mm3/mm3/mon/a at hotspots. ROF is decreased with trend above 2 mm/mon/a at south-southeast hotspots in summer and autumn.

Multiple Exhumation Stages During the Cenozoic Evolution of the Northeast Tibetan Plateau

AbstractThe Cenozoic growth history of the northeast (NE) Tibetan Plateau has been strongly debated in the past few years with three deformation models being proposed: progressive northeastward propagation, out‐of‐sequence deformation, and episodic deformation. Reconstruction of the long‐term deformation and exhumation history of the different blocks can help elucidate the growth pattern and tectonic processes involved in the formation of the Plateau. Both the Qaidam and Jiuquan basins—the two largest basins of the NE Tibetan Plateau—contain continuous and well‐exposed successions of synorogenic sediments that span the entire Cenozoic. We used apatite fission‐track thermochronology, sedimentary facies, and structural and provenance analyses of these successions to determine the exhumation history of the Tibetan Plateau. Five distinct fast exhumation events were recognized and dated: 65–54, 43–39, 34–29, 24–21, and 16–15 Ma. Comparison with existing morphotectonic information enabled us to reconstruct a multiple‐stage growth scenario for the NE Tibetan Plateau in the context of the surface uplift phases across the Himalayan‐Tibetan orogen during the Cenozoic. Overall, our findings support the episodic deformation model and emphasizes that the current relief of the NE Tibetan Plateau is largely derived from these five of stage of exhumation.

Provenance differentiation and earth surface process of the Mu Us sandy land constrained by detrital zircon U–Pb dating

Understanding the provenance and sediment surface processes of the Mu Us sandy land (MU) is critical for comprehending aeolian deposits and dust transportation in inland Asia and the Chinese Loess Plateau (CLP). In this study, we analyzed the detrital zircon U–Pb ages in the sediments of the MU, together with the previously collected data from sediments in the Hobq desert and CLP. Our findings demonstrate that there is spatial heterogeneity in the sediment characteristics of the MU and Hobq regions, with noticeable differences between northeastern and southwestern areas. In addition, the northeastern part of the CLP displays significant dissimilarities from other regions of the CLP. The NE MU, Eastern Hobq, and NE CLP inherit the main characteristics of basement rocks from the Western North China Craton, with prominent age ranges of 1600–2200 Ma and 2200–2800 Ma, indicating that this region is likely more controlled by in-situ weathering and recycling. In contrast, the SW MU, West-Middle Hobq and most parts of CLP show multiple sources, with a higher proportion of 200–350 Ma and 350–600 Ma, reflecting that the aeolian deposits in this area may be associated with more frequent earth surface processes such as sand-driving winds and fluvial transport. Although all three regions are situated within the square bend of the Yellow River and under the prevailing winds direction, sediments in the first two areas appear to have a more mixed contribution of both local and distal sources. In contrast, deposits in the CLP region were primarily sourced from the northeast Tibetan Plateau via the upper Yellow River. This indicates a variation in dust sources from north to south and suggests that the MU is part of the same sedimentary system as the CLP, rather than its direct source.

Provenance Indication of Rare Earth Elements in Lake Particulates from Environmentally Sensitive Regions

The provenance of lake particulate matter in environmentally sensitive areas is crucial to understanding regional environmental and climatic changes. This study investigated two regions in the Northeast Tibetan Plateau, China: Region I (Keluke, Tuosu, and Gahai Lakes) and Region II (Qinghai Lake and nearby rivers). The results showed that: (1) The two regions have greater differences in the enrichment of rare earth elements (REEs) and heterogeneity in spatial distribution, both of which are characterized by relative enrichment of LREE and depletion of HREE, but to different degrees; (2) the source and formation of particulate matter in two regions are consistent. Particulate matter in Region I (Keluke and Tuosu Lakes) predominantly originates from granite rocks, which undergo weathering and transportation through rivers. Region II (Qinghai Lake and nearby rivers) particulate matter is affected by chemical weathering and partial recycling of detrital material. Diagenesis had a minimal impact on the particulate REEs. (3) This study primarily provides a preliminary understanding of REEs in lake particles, assessing particle changes during the water-to-sediment process and their provenance indication. Future studies will incorporate the solid fugacity (solid speciation) of REEs in particles, contributing to a comprehensive understanding of rare earth element geochemical processes. This study provides valuable insights into REEs distribution, source, and geochemical behavior in the Tibetan Plateau, underscoring the importance of REEs in understanding provenance processes, and is indicative of provenance studies in other climate change-sensitive regions of the world.

Crustal structure and deformation mechanism of the western northeast Tibetan Plateau

The collision between the Indian and Eurasian plates continues to drive significant deformation and uplift within the interior of the Tibetan Plateau, together with its outward expansion along the margins. In particular, the North Qilian Shan fold-thrust belt (NQLS) and the Hexi Corridor basins (HXBS) represent the northernmost region of the northeastern Tibetan Plateau. This area serves as a natural laboratory for deciphering mechanisms of crustal deformation and thickening along the plateau’s margins. Specifically, the northeastern Tibetan Plateau has been attributed to 1) southward underthrusting of the Asian lithosphere, 2) distributed shortening and crustal thickening, 3) vertical inflation of the Tibetan crust due to mid-lower crustal channel flow, and 4) intracontinental subduction facilitated by large-scale strike–slip faults. The exact mechanism underlying the most concentrated convergent stress in the western segment of NQLS–HXBS remains a subject of debate. To address this uncertainty, we gathered seismic data along a 130-km-long linear array that extends northward from NQLS, traversing the Jiuquan Basin and reaching the Huahai Basin. Our analysis, conducted through the receiver function method, reveals intriguing findings. The Moho depth deepens from 45–50 km beneath the Huahai Basin to 55–60 km beneath NQLS. Notably, a double Moho structure emerged, marked by a distinctive near-flat positive amplitude at a depth of 45–50 km beneath NQLS within a distance of 0–50 km. Our study presents a comprehensive analysis of the crust-scale deformation mechanism, shedding light on the following key aspects: 1) the development of a decollement at 12–20 km depth decoupling the upper and lower crust; 2) deformation of the upper crust occurring through south-dipping brittle thrust faults, while the lower crust features imbricate structures and duplexes; 3) evidence pointing to the underthrusting of the Beishan Block beneath NQLS, indicated by the double Moho beneath NQLS; and 4) the formation of a Moho ramp beneath the Jiuquan Basin, facilitating the transfer of shortening stress from beneath NQLS and HXBS to the north. In the context of the western segment of NQLS and HXBS, our speculation is that coupled distributed shortening and Beishan Block subduction beneath NQLS work in tandem to accommodate crustal deformation.

Tectonic and climatic controls for fluvial terraces of the Yellow River over the past 2.6 Ma at Northeast Tibetan Plateau and Ordos Block

Tectonic and climatic controls for fluvial terraces of the Yellow River over the past 2.6 Ma at Northeast Tibetan Plateau and Ordos Block

Structure of the Gonghe Sedimentary Basin in the northeastern Tibetan Plateau: evidence from teleseismicPwaves recorded by a dense seismic array

SUMMARYThe Gonghe Basin in the northeast Tibetan Plateau presents significant potential for hot dry rock (HDR) geothermal resources. A 1990 Mw 6.4 earthquake in the basin furthers the need for an improved understanding of its sedimentary structure. In this study, we utilize data from a dense seismic array of 88 short-period seismometers deployed at an interstation spacing of approximately 3 km to scrutinize the sedimentary structure of the Gonghe Basin. By analysing teleseismic P waveforms, we identify P-to-S converted waves (Ps wave) originating from the sedimentary basement. We then determine the delay time between the Ps waves and the direct P waves (P wave) through waveform cross-correlation. By integrating this delay time with empirical velocity structure models, HDR borehole data and results from teleseismic receiver function analysis, we derive a sediment thickness model of the Gonghe Basin for the Qabqa geothermal area. Our findings reveal a gradual increase in sediment thickness from around 500 m in the east to approximately 3000 m in the west, which is consistent with other geophysical surveys and borehole data. The thick sediments in the basin could potentially serve as an excellent thermal storage cover for HDR. The strong ground motion simulation using our sediment thickness model shows that thick sediments can amplify seismic waves, increasing the risk of seismic hazards. Moreover, our study indicates that the clear Ps waves can be effectively extracted to construct a dependable sediment thickness model using teleseismic P waves recorded by a short-period dense seismic array.

Pollen analysis of middle to late Holocene records shows little evidence for grazing disturbance to alpine grassland on the Tibetan Plateau until modern times

Understanding human impact on the vegetation of the Tibetan Plateau through the Holocene is important for developing strategies for sustainable ecosystem management in the region. In this paper, 53 pairs of surface-soil samples from inside and outside livestock enclosures were obtained from across the Tibetan Plateau to investigate the differences in pollen assemblages between grazed and ungrazed sites. This modern dataset was then applied to palynological records from four lakes in the northeast Tibetan Plateau region to investigate middle to late Holocene grazing history. Results show that modern grazing activities have a limited impact on the vegetation, although grazing activity leads to an increase in the pollen proportion of Cyperaceae, Artemisia, Ranunculaceae, Brassicaceae, Taraxacum-type, Fabaceae, and Saxifrageceae while representatives of Poaceae, Chenopodiaceae, and Aster-type pollen decrease. Application of these grazing indicators to the pollen spectra obtained from the four lake sites, together with other proxies, reveals that grazing activity only commenced during the last few hundred years in the northeast marginal areas of the Tibetan Plateau at c. 3000 m a.s.l, while there is no grazing signal in pollen records from above 4000 m a.s.l. Our study emphasises the importance of using multi-proxy methods in estimating signals of past human activity.

Comparison on distribution and sources of typical major and toxic trace elements in various glacial watersheds of the northeast Tibetan Plateau

Toxic and major elements, such as As and Fe, in watersheds can significantly impact the surrounding water environment and ecosystem. Thus, in this study, we conducted an investigation into the origins and spatial distribution of typical toxic trace elements (As and Mn) and crustal major elements (Al, Fe, and Ti) in suspended particulate matter (SPM) across various glacial watersheds located at different elevations in the northeastern Tibetan Plateau (NETP) from June to July in 2017. The results revealed that the mean value of each element followed the order of abundance in the samples, with Al having the highest mean value at 21307 µg/L, followed by Fe at 13366 µg/L, Ti at 1520 µg/L, Mn at 245 µg/L, and As at 66.6 µg/L. Moreover, our study identified high content of these elements from the Dabanshan Snowpack, Laohugou Glacier No.12, and Yuzhufeng Glacier in the upper reaches of the basin, which were found to be 9.9, 10.2, and 19.4 times higher, respectively, than that of the upper reaches of the Heihe River. We found that As and Mn exhibited clear indications of anthropogenic influence on a local and regional scale. The calculated enrichment factor (EF) demonstrated a significant As enrichment (EF>100) in the Qiyi and Lenglongling Glaciers, possibly resulting in the release of upstream glacier melt and anthropogenic-derived As deposition. Our findings suggested that the upstream region was primarily linked to glacier meltwater discharge. In contrast, the middle and lower reaches of the basin exhibited a more pronounced influence from local human activities. Based on the findings, the water environment of the glacier watershed appears to be in good condition overall. However, the presence of elevated levels of As element in the water system can be traced back to both anthropogenic and natural factors. As a result, ensuring the safety of the water supply for nearby residents is a matter of utmost concern. This study provides a comprehensive examination of hydrochemical variations and the overall water environment of high-altitude glacier basins in the NETP, offering valuable insights into the topic.

Cosmogenic nuclide chronological constraints on the late Cenozoic strata of the Linxia Basin, northeast Tibetan Plateau

The thick Cenozoic sedimentary sequence of the Linxia Basin contains abundant well-preserved mammalian fossils, which provide significant information on the paleoenvironmental processes and mammalian evolution associated with the uplift and expansion of the Tibetan Plateau. Ambiguous age estimations have been made for some coarse-grained sedimentary units in the basin, which have led to the misinterpretation of biostratigraphic and magnetostratigraphic age models. To resolve these issues, we present radiometric dating of three late Cenozoic sedimentary units (“Liushu”, Hewangjia, and Jishi formations) in the eastern Linxia Basin using cosmogenic 26Al/10Be and 10Be/21Ne burial methods. isotope measurements for the upper “Liushu” Formation indicate a 10Be/21Ne burial age of 11.70 ± 0.17 Ma. This age is older than, but not contrary to, recently revised bio-magnetostratigraphic work. The 26Al/10Be burial age of the Hewangjia Formation is 3.06 (+0.36/−0.31) Ma and had been underestimated by post-burial muon production possibility, while the 26Al/10Be burial age of the Jishi Formation is 2.50 (+0.20/−0.18) Ma and had been overestimated due to inherited cosmogenic nuclides from recycled deposits. The new age from the Jishi Formation delays the initial deposition of conglomerates in the Linxia Basin to no earlier than 2.5 Ma and constrains an important episode of tectonic uplift of the northeastern Tibetan Plateau to 2.5–3.1 Ma. The age of the Equus fauna of Longdan is revised to the Early Quaternary (ca. 2.1–1.9 Ma). Our new age determinations significantly refine the terrestrial sequence chronology of the Linxia Basin and associated mammalian faunas of the late Miocene to the early Pleistocene.

Determination of plutonium in cryoconite on glacier surfaces in the northeast Tibetan Plateau: Implications for source identification and accumulation

Plutonium isotopes have drawn public attention because of their high radiotoxicity and risk for internal radiation. Cryoconite, dark sediments on the surface of glaciers, is rich in anthropogenic radionuclides. Therefore, glaciers are regarded as not only a temporary sink for radioactive pollutants in the past decades, but also a secondary source during their melting. However, study on activity concentration and source of Pu isotopes in cryoconite materials in Chinese glaciers have not been studies thus far. The present study determined the 239+240Pu activity concentration and 240Pu/239Pu atom ratio in cryoconite and other environmental samples collected in August-one ice cap, northeast Tibetan Plateau. The results showed that the 239+240Pu activity concentration in cryoconite is 2–3 orders of magnitude higher than the background value, suggesting the exceptional capacity of cryoconite to accumulate Pu isotopes. The high 239+240Pu level in cryoconite in the study area was significantly correlated with organic matter and slope, indicating their dominant influence. The average values of the 240Pu/239Pu atom ratio for proglacial sediments (0.175) and grassland soils (0.180) suggested that the global fallout is the dominant source of Pu isotopes pollution. In contrast, the measured 240Pu/239Pu atom ratios in the cryoconite were distinctly lower at 0.064–0.199, with an average of 0.157, indicating that the close-in fallout Pu isotopes from Chinese nuclear test sites is another source. In addition, although the relatively lower activity concentrations of 239+240Pu in proglacial sediments implies that most Pu isotopes are retained in this glacier instead of being redistributed along with cryoconite by meltwater, the potential health and ecotoxicological risks to the proglacial environment and downstream areas cannot be ignored. These results are important for understanding the fate of Pu isotopes in the cryosphere and can be applied as baseline data for radioactivity evaluation in the future.

Cenozoic tectonosedimentary evolution of the Linxia Basin, northeast Tibetan Plateau based on an analysis of detrital zircon provenance

The Linxia Basin is an important region for understanding the tectonism and uplift history in the northeast Tibetan Plateau, and also contains rich mammalian faunas of evolutionary significance. In this paper, we conduct a provenance study of Cenozoic sediments, relying primarily on U-Pb dating of detrital zircons, to investigate the exhumation history of surrounding terranes and to gain a better understanding of the relationship between tectonism, basin development and paleoenvironment.Samples were collected from the Maogou section in the central Linxia Basin, which has been recently dated by magnetostratigraphy. Detrital zircon populations show five UPb age groups of 65–350 Ma, 350–600 Ma, 600–1600 Ma, 1600–2200 Ma and 2200–2600 Ma; however, UPb age patterns varied up-section, indicating different sources at different times.Sediments from the lower part of the section (>27.8 Ma) were sourced from multiple regions, including the distal East Kunlun Shan, Qilian Shan, and Songpan–Ganzi terranes, and as well as the proximal West Qinling region. Contributions from the Songpan–Ganzi terrane increased considerably during the late Oligocene (27.8–23 Ma), as a result of strong tectonic movements of the northeastern Tibetan Plateau. During the early Miocene (23–17.2 Ma), the northern sources of the Laji Shan–Maxian Shan region supplied more sediments to the basin, indicating the uplift and exhumation of these mountain ranges. Until the middle Miocene (17.2–12.8 Ma), the Songpan-Ganzi terrane and the northern sources dominated the basin sediments, while the northern sources and the Jishi Shan region became increasingly important sources at around 11.6 Ma. This study explores the tectonosedimentary evolution of the Linxia Basin in the northeastern Tibetan Plateau, providing a reference for further research of the paleoclimate and mammalian evolution in this critical region.

Revised magnetostratigraphy of the Linxia Basin in the northeast Tibetan Plateau, constrained by micromammalian fossils

The Linxia Basin along the northeastern margin of the Tibetan Plateau has drawn enormous attention due to its rich mammalian fossils and great potential for exploring regional tectonics, paleoenvironmental history, and bio-evolution. However, the geochronology of the sedimentary sequences is in great dispute owing to uncertain lithostratigraphic correlation and poorly calibrated magnetostratigraphy. From 2017 to 2021, we carried out lithostratigraphic correlation of the strata from the southern part of the basin, which is rich in fossils, to the Maogou section in the central basin, and established a solid intra-basinal lithostratigraphic framework with accurate fossil locations. Then, high-resolution magnetostratigraphic investigations were performed on the Maogou section, which comprises, from oldest to youngest, the Jiaozigou, Shangzhuang, Dongxiang, Liushu/Hujialiang, and “Liushu” formations. Magnetostratigraphic results show that the Maogou sedimentary sequence (from Jiaozigou to Liushu/Hujialiang formations) spans from chron C10r to chron C5r.2n, yielding an age of 29–11.6 Ma, with constraints from four mammalian assemblage levels. The revised magnetostratigraphy indicates that the Jiaozigou Formation corresponds to chrons C6Cn.3n–C10r (∼23–29 Ma), with Paraceratherium fauna from the lower Jiaozigou Formation being determined as ∼29 Ma, and that the Hujialiang Formation, containing Platybelodon fauna, corresponds to chrons C5r.2n–C5Ar.2r (∼11.6–12.8 Ma). The revised magnetostratigraphy of the Maogou section has significantly refined the chronology of the Linxia Basin sedimentary sequences and its associated mammalian evolution, tectonism, and climate change in Central Asia.

Historical reconstruction and future projection of mass balance and ice volume of Qiyi Glacier, Northeast Tibetan Plateau

Study regionQiyi Glacier in the Qilian Mountains, northeast Tibetan Plateau. Study focusFuture glacier changes are critical to the sustainable use of regional water resources and the survival and development of the densely populated Tibetan Plateau and surrounding regions. A distributed energy-mass balance model is applied to simulate the historical and future mass balance and ice volume of Qiyi Glacier from 1980 to 2100. The aims of this study are to illuminate the spatial and temporal patterns of mass balance and energy balance, to forecast future changes of this glacier under different scenarios of CMIP6, and to identify the timing of peak ice loss. New hydrological insights for the regionCompared to the historical reconstruction, future projections show that ablation will increase, and accumulation will decrease due to less snowfall and increased net shortwave radiation that is induced by lower albedos. The average mass balance increases by a factor of 1.08, 1.67 and 2.68 under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios during 2021–2100, respectively. By the end of the 21st century, Qiyi Glacier ice volume will reduce by 107.61 × 106 m3 (95.3 %) for the SSP1-2.6 scenario, and 112.12 × 106 m3 (99.3 %) for the SSP2-4.5 scenario, and will disappear entirely by 2082 for the SSP5-8.5 scenario. In all scenarios, the glacier mass loss rate will peak around 2030–2045, then decrease in parallel with the decreasing ice volume.

New radiocarbon dates and the prehistoric human occupation at the Lake Qinghai Basin, northeast Tibetan Plateau

The Tibetan Plateau is known as the rooftop of the planet. Its hypoxic atmosphere in low oxygen partial pressure, extreme seasonal climate variation, and aridity poses severe challenges as harsh living environments for prehistoric human to occupy in such high-altitude niches. However, the Lake Qinghai is the largest lake on the Tibetan Plateau and the basin has rich water, mineral, and wild food resources, and prehistoric human occupied the Lake Qinghai Basin long before local farming was in practice. In this paper we present results of faunal assemblages associated with variable stone artifacts and pottery shards with bone collagen accelerator mass spectrometry radiocarbon (AMS 14C) dates from 3 new archaeological sites to investigate human occupation history in the southern Lake Qinghai Basin. The AMS 14C dating results reveal that the occupation occurs intermittently from the late Glacial to entire Holocene. Through compilation and synthesis of regional archaeological records, we found that prehistoric humans went through 3 phases of subsistence strategies: 1) hunting large and medium ungulates; 2) hunting medium ungulates; 3) foraging small size mammals with birds and fish diets. At the end, prehistoric humans increasingly adapted to forage and consume caprinaes species (goat), which represents a precursor of domestication or semi-domestication of wild animals in the Lake Qinghai Basin. We further attribute the utilization of caprinaes animal resources to the lower limbs of toe and phalange bones with low nutritious values to advanced social organization that implied prehistoric humans separated hunting activity from protein processing practices. Our investigation of zooarchaeology with reliable bone collagen AMS 14C dates could become a novel approach to study adaptation strategy and social structure changes of prehistorical Tibetan humans.

Dynamic changes in forest cover and human activities during the Holocene on the northeast Tibetan plateau

Human activities strongly influenced the present-day environment of the Tibetan Plateau, especially in the northeastern area. The questions over when and to what extent humans began to utilize the plateau environment have been long investigated, but there are still gaps in our understanding, such as the relationship between forest dynamics and anthropogenic activities. Here, we simulate the potential Holocene geographical distribution of the three dominant coniferous species in the Northeast Tibetan Plateau in response to climate/environment and analyze pollen records and multi-proxies for anthropogenic activities to explore human impact on natural forest dynamics. Simulation results show marked expansion of Picea and Pinus coniferous forests in the Early Holocene (11.5–8.3 ka BP), continuing into the Mid Holocene (8.3–4.0 ka BP). However, there was a slight contraction of forest in the Late Holocene (4.0–2.6 ka BP) in the western part of the region, and near disappearance in the eastern Qaidam Basin, although both Pinus and Picea slightly increased in Hehuang Valley. Pollen analysis confirms the patterns, with an increase in arboreal pollen mainly comprising Pinus and Picea from Early to Early Mid Holocene (11.5–5.3 ka BP), followed by a decrease. Proxies of anthropogenic activities, including carbon concentration, archeological sites, and, synanthropic plants, increased significantly after 5.3 ka BP, with archeological evidence for intensive exploitation of forest and turnover of natural vegetation. We argue that forest retreat at 5.3–4.0 ka BP was due to the expansion of cropland and increasing demand for wood. Significant coniferous forest retreat and degradation from 4.0 to 2.6 ka BP, with forest succession in Hehuang Valley, was driven by the booming population, extensive grazing, and forest exploitation; the drying cooling climate may have aggravated the pace of deforestation at higher elevations. This study presents new insights into the deforestation on the Northeast Tibetan Plateau in the Holocene.