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Exceedingly strong aeolian dust activity has occurred in inland Asia. Comparisons of the late Cenozoic sedimentation rates between aeolian and fluvial‐lacustrine sequences around the northern Tibetan Plateau suggest that aeolian process has played an important role in the erosion, weathering and deposition of sediment. However, recognizing dust as an important source in fluvial‐lacustrine sequences is a vital but difficult task. Here, clay‐sized mineral and elemental records of regional silicate weathering histories are revisited during the period of Asian dust expansion at ~9–8 Ma. The aeolian dust input from the Tianshan‐Altay Orogens into the Jiuquan Basin is identified using the Th/Sc ratio while that from the Qilian Shan into the Xining Basin is identified based on inconsistent fine‐grained silicate weathering proxies. Our study suggests that the use of appropriate dust provenance tracers and recognition of wind transport‐induced changes in dust grain size and chemistry can provide useful aeolian dust discrimination approaches. [ABSTRACT FROM AUTHOR]

The arid interior of Asia is the largest source of dust deposited in the North Pacific Ocean, and some dust is even transported to Greenland. Investigating the provenance history of Asian dust can provide strong constraints on the evolution of topography and climate in the Asian interior. Eolian dust Nd isotopic records preserved in North Pacific Ocean sediments since ∼40 Ma provide a spatially integrated first-order constraint on the provenance changes of Asian dust. However, a lack of similarly long dust Nd isotopic records from Asian dust source areas, namely, the northern Tibetan Plateau and the Central Asian Orogenic Belt, has hindered a full understanding of Asian dust provenance changes linked to the Cenozoic evolution of tectonics, climate and topography in inland Asia. Here, we have constructed the first fine-grained and whole-rock Nd isotopic records from sediments deposited on the northern Tibetan Plateau since ∼52 Ma. The results indicate two major changes, a gradual increase in ε Nd (0) values between ∼42 Ma and ∼25 Ma and a general decrease since ∼25 Ma, which were probably caused by the incremental northward growth of the Tibetan Plateau. Further mass balance estimates based on comparisons between the Nd isotopic characteristics of dust from the northern Tibetan Plateau and the North Pacific Ocean indicate that a rapid increase in the contribution of the Central Asian Orogenic Belt to Asian dust at ∼25 Ma can be closely linked to rapid exhumation caused by tectonic uplift and aridification in inland Asia. Our provenance analyses, together with the onset of eolian sediment in central and eastern Asia, suggest that a modern-like regime promoting Asian dust emissions and transport might have been in place since the late Oligocene. [ABSTRACT FROM AUTHOR]

As one of the largest dust sources on the Earth's surface, dryland in Central Asia gives rise to thick eolian deposits over East Asia (e.g., the Chinese Loess Plateau, CLP) and significantly influences the regional hydrochemistry in the downwind drainage areas. However, the formation of thick eolian dust deposits requires not only climatic prerequisites for dust emission and transport but also climatic and topographic conditions favourable for deposition and accumulation. The scarcity of widespread eolian deposition around the CLP before 7-8 Ma hinders a full understanding of the processes and mechanisms of Central Asian aridification. The deposition of eolian dust also impacts the hydrogeochemistry of fluvial systems and the precipitation of authigenic phases in continental sedimentary systems could be an archive for studying eolian dust dynamics when pure eolian deposits are scarce. Here, we present the Ca-Mg-Sr concentrations and 87Sr/86Sr isotope compositions of bulk carbonates in a new fluvial sequence (12.7-4.8 Ma) of the Xining Basin. The Mg/Ca and Sr/Ca ratios of the carbonate describe a power law relationship with a power coefficient of ∼0.8, lower than the coefficient characteristic of prior calcite precipitation (PCP). An input of eolian dust with the dissolution of Mg-rich carbonate is likely responsible for the deviation from a pure PCP process. The bulk carbonates also show a general decrease of 87Sr/86Sr ratios from 12.7 to 4.8 Ma, with a transition around 8.6 Ma revealed by lower Sr/Mg ratios. The comparison of these proxies to a previously reported fluvial section (12.2-5.1 Ma) in the Linxia Basin, ∼200 km to the southeast, shows that the 87Sr/86Sr ratios of the bulk carbonates and water-soluble salts in the Linxia Basin are around 0.7098, which is 0.0018 lower than those in the Xining Basin before 8.6 Ma, but shows a significant rise between 8.6 and 7.0 Ma. The two basins share the same range of carbonate 87Sr/86Sr ratios when sediments are younger than 7 Ma. For the last 7 Myrs, the evolution of the 87Sr/86Sr ratios in bulk carbonates of fluvial sediments and Pliocene-Quaternary eolian deposits found in the Xining Basin are similar to those in typical eolian red clays/loess-palaeosol sequences on the CLP. These results suggest a transition of the hydrochemical regime at 8.6 Ma in the Linxia Basin from a catchment only influenced by the weathering of its bedrock to one significantly impacted by eolian dust input. In the Xining Basin, the carbonate elemental and 87Sr/86Sr ratios are consistent with a hydrochemistry more impacted by the presence of the eolian dust. There, the dust input occurred earlier, at ≥12.7 Ma, though it has strengthened since 8.6 Ma. The eolian dust impact on fluvial systems in the Xining Basin was much earlier than in the Linxia Basin and also preceded the initial accumulation of widespread eolian red clays on the CLP (7-8 Ma), suggesting a temporally propagating and spatially stepwise expansion of eolian dust delivery across the Asian inland during the late Cenozoic. • Fluvial carbonate elemental and Sr isotopic geochemistry reveals eolian dust input. • Eolian dust affected the river chemistry of the Xining Basin at least since 12.7 Ma. • The impact of eolian dust in the Xining Basin has strengthened at ∼8 Ma. • Eolian dust affected the river chemistry of the Linxia Basin but only since ∼8 Ma. • A south-eastward expansion of the dust impact on river water occurred in NE Tibet. [ABSTRACT FROM AUTHOR]

• Clay-sized geochemistry reveals the Qaidam Basin (QB) Paleogene weathering history. • QB Paleogene silicate weathering intensity presents a continuously decreasing trend. • Global cooling was the main regulator of Paleogene chemical weathering processes. • Clay-sized geochemical indices aptly reveal weathering histories in coarse sediment. An integrated multiproxy dataset involving both mineralogical and geochemical investigations of the northern Tibetan Plateau helps in assessing regional weathering processes linked to topographic evolution and environmental change. However, changes in landscape and drainage reorganizations caused by active tectonics and remarkable climate change during the Cenozoic characterize the basins in and around the Tibetan Plateau by frequent facies changes and coarse lithologies, which largely limit the reliability of bulk geochemical indicators for revealing the regional weathering history. Here, we present detailed geochemical investigations of clay-sized sediments collected from the Hongliugou section (54–26 Ma) in the northern Qaidam Basin to reconstruct high-resolution chemical weathering records of the northern Tibetan Plateau. To prevent chlorite bias when calculating the chemical index of alteration (CIA) in the clay-sized sediments, we propose a modified CIA formula (CIA Mg+), in which Mg is added as a soluble cation that can be removed during weathering, similar to Na, K and Ca; thus, CIA Mg+ = Al 2 O 3 /(Al 2 O 3 + Na 2 O + K 2 O + CaO* + MgO) × 100. The CIA Mg+ and illite chemistry indices are generally the highest values in the early Eocene Climate Optimum (∼52–49.5 Ma) and a long-term decreasing trend is present from ∼ 49.5–26 Ma; the Mg/Al ratios of the clay-sized sediments and hydrochloric acid leachates are the lowest during the EECO and present a long-term increasing trend in the following 49.5–26 Ma, thus collectively indicating a continuous decrease in the regional chemical weathering intensity. The weakening weathering process during the Paleogene is mainly attributed to the decreasing global temperature and decline in precipitation caused by global cooling. Our study suggests that the proposed geochemical index based on clay-sized sediments can serve as an efficient proxy for regional chemical weathering reconstruction, even in thick sedimentary sequences with frequently changing facies and lithology. [ABSTRACT FROM AUTHOR]

Climate change in the Asian interior during the early Cenozoic remains poorly constrained due to difficulties in distinguishing the impacts of global cooling, the early uplift of the Tibetan Plateau and the retreat of the Paratethys. A quantitative estimation of paleolake salinity enables a better understanding of the regional hydrological cycle and contemporaneous climate change. Here, we present a quantitative record of paleolake salinity in the Qaidam Basin between ~42 and 29 Ma using detailed mineralogical investigations and clay boron content data. This paleolake salinity record generally covers a tectonically less active period in the Asian interior characterized by continuous global cooling, the abrupt Eocene–Oligocene climate transition and the Paratethys transgression/regression cycles, thus offering an opportunity to explore the roles of global cooling and the Paratethys retreat in regulating the regional hydrological cycle. The results of two boron-derived paleosalimeters, equivalent boron and Couch's salinity, collectively indicate a two-stage paleolake salinity evolution, from an oligohaline–mesohaline environment in the middle–late Eocene (~42–~34 Ma) to a mesosaline environment in the early Oligocene (~34–~29 Ma). This transition is also supported by qualitative chloride-based and ostracod-based paleosalinity estimates in the Qaidam Basin. Our quantitative paleolake reconstruction between ~42 and 29 Ma in the Qaidam Basin yields a generally good match with the hydroclimate change in the neighboring Xining Basin, thus indicating a comparable regional drying trend. The synchronous changes in quantitative paleolake salinity and silicate weathering processes derived from the illite weathering index and chlorite content in the studied section suggest climate control of silicate weathering. Global cooling is speculated to have been the first-order driving factor in regulating long-term climatic evolution and weathering responses in the Asian interior between ~42 and 29 Ma. Superimposed on this trend, the Paratethys transgression/regression cycles served as an important factor regulating wet/dry fluctuations in the Asian interior between ~42 and ~34 Ma. • A clay boron-derived quantitative salinity record (~42–29 Ma) in the Qaidam Basin • Long-term lake salinization with weakened catchment weathering in ~42–29 Ma • Global cooling was the main driver regulating long-term paleosalinity variation. • The Paratethys transgression/regression cycle regulated short-term wet/dry fluctuation. [ABSTRACT FROM AUTHOR]

Late Cenozoic changes in chemical weathering and the dust cycle in response to the regional aridification and global cooling in the tectonically active northern Tibetan Plateau is an intriguing issue, although it remains poorly understood. The change in the 87Sr/86Sr ratio of basin water is linked to variations in the overall input of various Sr sources with different 87Sr/86Sr ratios, and analyses of such changes can be a useful tool for revealing changes in regional lithology, weathering regimes and the dust cycle linked to tectonics and climate. In this study, we collected fossil shells of ostracods and gastropods from the Miocene Dahonggou section to reconstruct the paleolake water 87Sr/86Sr ratio from 14.8 Ma to 11.1 Ma in the northern Qaidam Basin on the northeastern Tibetan Plateau. The reconstructed paleolake water 87Sr/86Sr ratios based on fossil shells and bulk carbonates from sediments display a coincident and stable 87Sr/86Sr ratio of approximately 0.7115, which did not show any detectable change in response to the enhanced aridification since ~13 Ma as inferred by the ostracod assemblage and its stable carbon and oxygen isotopes. The results indicate that the Sr influx regime from various sources did not change significantly during the aridification processes ~13 Ma, which may have been caused by a less detectable change in proportion of silicate versus carbonate weathering, and/or an overwhelming Sr source (e.g., extrabasinal eolian dust) that occurred from 14.8 Ma to 11.1 Ma. Further, the 87Sr/86Sr ratios of modern lake water and river sand carbonates in the study region are significantly higher, approximately ≥0.001, than those of the Miocene lake water. This observation can be explained by two possible mechanisms that need to be tested in the future: 1) given a Miocene Sr input regime that is similar to today, a large contribution from some extrabasinal Sr source (e.g., eolian dust) with a much lower 87Sr/86Sr ratio is expected to have prevailed from 14.8 Ma to 11.1 Ma but is absent in the modern setting or 2) given a Miocene Sr input regime that could yield an overall lower lake water 87Sr/86Sr ratio of approximately 0.7115, a significant increase in the 87Sr/86Sr ratio of catchment-scale Sr source may have occurred after 11 Ma in response to the uplift of the Qilian Mountains, which would have enhanced hydrothermal activity, metamorphism, glaciation and landslide processes, thereby resulting in more-radiogenic Sr source. Our study suggests that reconstructions of river/lake water 87Sr/86Sr ratios can place powerful constraints on the complex interactions among tectonics, climate and landscape evolution in the northeastern Tibetan Plateau based on a new perspective. • 87Sr/86Sr ratios of paleolake water at 14.8–11.1 Ma in the northern Qaidam Basin. • Ostracod shell and bulk carbonates show stable 87Sr/86Sr ratios at ~0.7115. • Paleolake water 87Sr/86Sr ratio is lower than modern lake water value of ~0.7128. • The paleo and modern lake 87Sr/86Sr contrast links to eolian input or Qilian uplift. [ABSTRACT FROM AUTHOR]

Magnetic parameters are widely used in the loess-palaeosol sequence tracing Quaternary climate change on the Chinese Loess Plateau (CLP). However, the climatic implication and magnetic enhancement mechanism in aeolian Red Clay on the CLP is still debated. Chlorite is a common Fe-bearing silicate in Red Clay and it is easily to be weathered. The transformation of weakly magnetic ferrihydrite, a product in chlorite weathering process, into strongly magnetic iron oxides has been linked to magnetic enhancement in many soils. Here, we present a complete chlorite weathering record within the Red Clay sequence through a detailed mineralogical investigation, from a 125-m thick eolian Red Clay deposit in the Chaona section (~8.1 to 2.6 Ma) of the central CLP to explore the link between changes in chlorite geochemical composition and magnetic susceptibility enhancement and regional climate. The results suggest a concomitant evolution of chlorite Fe content and magnetic susceptibility, indicating that Fe released from chlorite brucite-like interlayers, which induced ferrihydrite formation, is responsible for the enhanced magnetic susceptibility in the CLP Red Clay deposits. Moreover, the results also show that the chlorite Fe content exhibited a stepwise decrease, with two accelerated stages at ~6.2 Ma and ~3.6 Ma. The post-6.2 Ma evolution of chlorite Fe content is related to increased precipitation caused by phased enhancement of the East Asian summer monsoon (EASM). Our study also suggests that changes in chlorite chemical composition and crystallinity linked to soil weathering are useful proxies in tracing past weathering intensity and climate change within arid-less humid regime. • Significant chlorite weathering was identified in the Chaona Red Clay section. • Chlorite Fe/Mg ratios exhibit a three-stage decrease in the late Miocene-Pliocene. • Fe released in chlorite weathering may be responsible for increased χ in Red Clay. [ABSTRACT FROM AUTHOR]

The paleoenvironment and paleoclimate of Asia dramatically changed during the late Cenozoic, such as enhanced Central Asian aridification and East Asian monsoon development. The uplift of the Tibetan Plateau in the late Cenozoic is considered one of the major drivers forcing the Asian paleoenvironmental changes. However, the complex interaction between tectonic and climate change is still unclear. This is largely due to 1) the combined effect of aridification of the continent by global cooling, oceanic closure and uplift of the plateau, and 2) the lack of temporally and spatially matching tectonic and climatic records in a critical zone. The Xining Basin lies in the transitional zone between the arid Asian interior and the East Asian monsoon region. Here, we present detailed paleomagnetic analysis of a fluvial-lacustrine sequence in the Xining Basin and the first record of clay mineralogy and elemental geochemistry. High-resolution paleomagnetism revealed 16 normal and 16 reversed zones that correlate well with chrons 3n to 5Ar.1r of the Geomagnetic Polarity Time Scale, constraining the section to ~12.7–4.8 Ma. The changes in lithofacies from floodplain to braided river at ~8.6 Ma with predominantly southerly paleocurrent directions occur simultaneously with an increase in the sedimentation rates, representing a rapid uplift in the eastern Qilian Shan to the north. Geochemical provenance proxies (Th/Sc, Zr/Sc and Cr/Zr) in the <2 μm fraction show a significant provenance change at ~8.8 Ma. Silicate-based weathering indexes (CIA, CIW and PIA) displayed coeval changes with provenance but discrepant changes with regional climate. Since the clay mineralogy exhibit significant change at ~7.8 Ma uncorrelated with modifications in provenance, it can be employed to reveal regional climate change. The rise in illite, and associated decrease in the sum of smectite and illite/smectite mixed-layers reflect gradual and slow aridification since ~12.7 Ma with intensified drying since ~7.8 Ma until approaching the modern climate status. Our results, together with other regional climatic and tectonic records, clearly illustrate that accelerated uplift of the northeastern TP since ~8-9 Ma has mainly modulated the regional erosion, weathering, transportation and sedimentation, and amplified the global cooling and drying trend towards the regional climate of modern conditions. Our study suggests that in the tectonically active northeastern TP, a comprehensive mineralogical and geochemical investigation of the fine-grained fraction of the basin sediments could retrieve the interactions between tectonics and climate behind the complex change in exhumed lithology and sedimentary routing systems. [ABSTRACT FROM AUTHOR]

A closed Quaternary saline paleolake, currently still a lake and named Dalangtan after one of its largest sub-basins, has widely distributed sediments in the western Qaidam Basin, NE Tibetan Plateau. Lacustrine salt minerals and fine sediments from this paleolake provide an environmental record for investigating paleoclimatic evolution in the Asian interior. However, detailed continuous Pliocene–Quaternary paleoclimatic records are broadly lacking from the NE Tibetan Plateau owing to poor exposure of the outcrops in section. For this study, we performed a detailed magnetostratigraphic dating and rock magnetic analysis on a 590-m-long core from the SG-5 borehole in the western Qaidam Basin. The results demonstrate that the lacustrine sediments in the SG-5 borehole were deposited more than ~3.0 Ma. Saline minerals began to increase at 1.2 Ma, and the magnetic susceptibility (χ) also changed at that time; the percentage frequency-dependent magnetic susceptibility was relatively low and uniform throughout the whole core. These observations, combined with the χ, pollen, salt ion, and grain-size records from other boreholes, indicate that the western Qaidam Basin and the greater Asian interior had a significant climate transition at 1.2 Ma during an extreme drought. [ABSTRACT FROM AUTHOR]

The Khorat Plateau holds one of the world's largest potash deposits. Although many attempts have been made, the age of the potash-bearing strata remains poorly determined. Here, we report a high resolution magnetostratigraphic study of a 595.4 m-deep potash bearing borehole (ZK2893) in the southeast Sakhon Nakhon Basin in central Laos. This borehole penetrated the whole potash-bearing Nong Boua Formation and reached the underlying sandstone beds of the Nam Noy Formation. A total of 500 (383 level) cubic paleomagnetic samples were collected. k -T curves and hysteresis loops revealed that hematite and magnetite were the main magnetic carriers and were likely of detrital origin, as indicated by microscopic and Electron Microprobe Analysis (EMPA) examinations. Progressive thermal and alternating field (AF) demagnetization isolated 229 valid characteristic remnant magnetizations (ChRMs), which showed a normal and antipodal distribution of the inclination data. Both the microscopic and EMPA examinations and inclination-only analysis suggest primary magnetizations of the ChRMs, yielding nine normal and seven reversed polarity zones. Combined with regional palynological, isotopic and sedimentologic evidence, the obtained polarity zones were best correlated to the geomagnetic polarity time scale of Gradstein et al. (2012) (GPTS2012), yielding magnetostratigraphic ages of > 63.5 Ma to ~ 92 Ma for the potash-bearing Nong Boua Formation and ~ 85 Ma for the potash bed in its lower salt unit. [ABSTRACT FROM AUTHOR]

[Display omitted] • Paleoecological and paleohydrological changes in the Qaidam Basin occurred during the EOT. • Changes in CPI, ACL, Paq and L/H, indicating bacterial, algal and aquatic plants shrink , and terrestrial plants flourish. • δ2H 31 values were increased by 18.1‰, indicating a decrease in water vapor content and an increasingly arid climate. The Eocene/Oligocene transition (EOT) at ∼34 Ma has been considered the most prominent climatic cooling event in the Cenozoic Era. However, few organic biomarker studies have attempted to reconstruct relevant terrestrial ecological and hydrological responses to an age characterized by drastic temperature changes. This research aims to reconstruct the paleoecological and paleohydrological evolution of the Qaidam Basin (QB) on the northeastern Tibetan Plateau (NE TP) between 40.2 and 29.9 Ma, based on analyses of n -alkane chain length distributions as well as compound-specific hydrogen isotopic compositions (δ2H alk). Research showed the presence of a sequence of pronounced ecological and hydrological variations at 35.0–33.1 Ma, including: 1) a significantly decreased input of bacteria, algae and aquatic plants, allied with a markedly increased input of terrestrial plants, reflected in a significant increase in carbon preference index (CPI) and the average chain length (ACL) ratio, as well as an abrupt decline in the relative ratio of mid- to long-chain length homologue (Paq) values and the ratio of low- to high- molecular-weight n -alkanes (L/H); and 2) drier climatic conditions, reflected in an 18.1‰ increase in δ2H 31 values, as well as more positive hydrogen isotopic precipitation values (δ2H p). These features demonstrate significant paleoecological and paleohydrological changes in the QB in response to the drier and cooler climate during the EOT. [ABSTRACT FROM AUTHOR]

Late Cenozoic sediments in the Linxia Basin of China, on the northeastern Tibetan Plateau, bear abundant fossils of the Hipparion fauna. From late Miocene times, these sections record a history of aridification in the Asian Interior, the evolution of the east Asian monsoon, and multiple uplifts of the Tibetan Plateau. In this paper, a new detailed magnetostratigraphic study of a sedimentary sequence from the Duikang (DK) section containing the Hipparion fauna is presented, to better understand interconnected ecologic and environmental changes. The 90-m-thick section reveals nine normal and nine reversed zones that span from chron. C5n.2n to chron. C3Ar or from chron. C4n.2n to chron. C2Ar, yielding magnetostratigraphic ages of ~8.1 Ma - 3.7 Ma for the studied section and 5.3 Ma for the Hipparion fauna-bearing bed. Combined with all the previous magnetostratigraphic ages of the fauna-bearing sediments in the Linxia Basin, Hipparion can be distinguished as mainly having lived during five periods: Phase I (11.5 Ma), Phase II (8.2 Ma), Phase III (6.3 Ma), Phase IV (~5.3 Ma) and Phase V (2.5 Ma). Based on comparison of climate records in the Linxia Basin with aridification records from surrounding regions and global cooling during the late Cenozoic, we suggest that the evolution of Hipparion from the Linxia Basin was mainly driven by continuous global cooling and tectonic uplift of the northeastern Tibetan Plateau since the late Miocene. • Depositional age of the DK section in the Linxia Basin is between 8.1 Ma and 3.7 Ma. • Hipparion lived during five different periods (11.5, 8.2, 6.3, 5.3 and 2.5 Ma). • Linxia Basin experienced the stepwise aridification since the late Miocene. [ABSTRACT FROM AUTHOR]

The modern Qaidam Basin (QB) is one of the highest and driest deserts on Earth and an important dust source in Asia. However, a large paleolake existed in the 150,000 km2 large basin during most of the Cenozoic. How and why this paleolake system collapsed is crucial for understanding of the dramatic drying processes in central Asia. We present a comprehensive assessment of a large data set of new oxygen isotope and grain size data and published proxy records from a drill core in the western QB spanning the period from ~2.7 to near present, based on statistical, wavelet and recurrence quantification analyses. Moreover, we compare the QB paleolake evolution with East Asian summer monsoon (EASM) records in the nearby Chinese Loess Plateau. The results indicate a similar evolution pattern of the lake system in the western QB and the EASM system until ~1.2 Ma, indicating a larger scale forcing of solar insolation change on both systems. A decoupling between the two systems was noticed after ~1.2 Ma, under which drier intervals in the QB were synchronous with stronger EASM. We suggest that the congruence of decreasing amplitude of obliquity and eccentricity minima at ~1.2 Ma facilitated ice sheet expansion which disturbed the response of both systems to solar insolation, and eventually led to their decoupling. At ~0.9 to 0.8 Ma, synchronous minimum states in obliquity amplitude and eccentricity, and the meantime prominent reduction in CO2 concentration, presumably forced continuously growing ice sheets. The resulting cooling may have reached a critical temperature that caused a negative water balance in the regional water cycle of the QB, leading to the collapse of Qaidam paleolake since ~0.6 Ma. [ABSTRACT FROM AUTHOR]