Rising utilization of stable isotopes in tree rings for climate change and forest ecology

Analyses of stable isotopes(C,O,H)in tree rings are increasingly important cross-disciplinary programs.The rapid development in this field documented in an increasing number of publications requires a comprehensive review.This study includes a bibliometric analysis-based review to better understand research trends in tree ring stable isotope research.Overall,1475 publications were selected from the Web of Science Core Collection for 1974-2023.The findings are that:(1)numbers of annual publications and citations increased since 1974.From 1974 to 1980,there were around two relevant publications per year.However,from 2020 to 2022,this rose sharply to 109 publications per year.Likewise,average article citations were less than four per year before 1990,but were around four per article per year after 2000;(2)the major subjects using tree ring stable isotopes include forestry,geosciences,and environmental sciences,contributing to 42.5%of the total during 1974-2023;(3)the top three most productive institutions are the Chinese Academy of Sciences(423),the Swiss Federal Institute for Forest,Snow and Landscape Research(227),and the University of Arizona(204).These achievements result from strong collaborations;(4)review papers,for example,(Dawson et al.,Annu Rev Ecol Syst 33:507-559,2002)and(McCarroll and Loader,Quat Sci Rev 23:771-801,2004),are among the most cited,with more than 1000 citations;(5)tree ring stable isotope studies mainly focus on climatology and ecology,with atmospheric CO_(2) one of the most popular topics.Since 2010,precipitation and drought have received increasing attention.Based on this analysis,the research stages,key findings,debated issues,limitations and direc-tions for future research are summarized.This study serves as an important attempt to understand the progress on the use of stable isotopes in tree rings,providing scientific guid-ance for young researchers in this field.

Effect of petroleum chemical fraction and residual oil content in saline lacustrine organic-rich shale: A case study from the Paleogene Dongpu Depression of North China

Halite and gypsum minerals in saline shale make the retention mechanism and chemical fractionation of residual oil unique. The Dongpu Depression in North China is a typically saline lacustrine basin with developing halite and gypsum. The effect of gypsum minerals on residual oil content and chemical fractionation remains unclear. In this study, shale samples with different gypsum contents were used in organic geochemical experiments, showing that the high total organic matter (TOC) content and type II kerogen leads to a high residual oil content, as shown by high values of volatile hydrocarbon (S1) and extractable organic matter (EOM). XRD and FE-SEM result indicate that the existence of gypsum in saline shale contributes to an enhanced pore space and a higher residual oil content in comparison to non-gypsum shale. Additionally, the increase in the gypsum mineral content leads to an increase in the saturated hydrocarbon percentage and a decrease in polar components percentage (resins and asphaltene). Furthermore, thermal simulation experiments on low-mature saline shale show that the percentage of saturated hydrocarbons in the residual oil is high and remains stable and that the storage space is mainly mesoporous (> 20 nm) in the oil expulsion stage. However, the saturated hydrocarbons percentage decreases rapidly, and oil exists in mesopores (> 20 nm and < 5 nm) in the gas expulsion stage. In general, gypsum is conducive to the development of pore space, the adsorption of hydrocarbons and the occurrence of saturated hydrocarbon, leading to large quantities of residual oil. The data in this paper should prove to be reliable for shale oil exploration in saline lacustrine basins.

Diagenetic evolution and effects on reservoir development of the Dengying and Longwangmiao formations,Central Sichuan Basin,Southwestern China

The deeply buried Lower Cambrian Longwangmiao Formation and Upper Ediacaran Dengying Formation from the Sichuan Basin,China,have a total natural gas reserve up to 3×10^(12)m^(3).The complex diagenetic evolution and their impacts on the present-day reservoir quality have not been systematically elucidated,hampering the current exploration.Crucially,the integration and comparation diagenetic study on these two formations,which may be able to shed new lights on reservoir formation mechanism,are yet to be systemically evaluated.By compiling geochemistry data,including carbonate U-Pb ages and petrophysics data,coupled with new petrology,trace elements,and strontium isotope data,of various types of diagenetic carbonates,this study aims to decipher the potential links between diagenesis and reservoir development of both formations.Intriguingly,similar diagenetic sequence,which contains five distinctive dolomite phases,is established in both formations.The matrix dolomite(D1)and early dolomite cement(D2)were likely formed by reflux dolomitization,as inferred by their nearly syn-depositional U-Pb ages and elevatedδ^(18)O caused by seawater evaporation.The subsequent moderate burial dolomite cement(D3)was most plausibly the product of burial compaction as indicated by its lighterδ^(18)O and slightly younger U-Pb ages compared with D1 and D2.Whereas deep burial dolomite cements(D4 and D5)yield markedly depletedδ^(18)O,elevated ^(87)Sr/^(86)Sr,along with much younger U-Pb ages and higher precipitation temperatures,suggesting that they were likely linked to hydrothermal fluids.Despite the wide occurrence of meteoric and organic acids leaching and thermochemical sulfate reduction,they may have only played a subsidiary role on these reservoirs development.Instead,superior reservoir quality is tightly linked to tectonics as inferred by higher reservoir quality closely related to the well-developed fractures and faults filled with abundant hydrothermal minerals.Notably,good reservoirs in both formations are mainly attributed to high permeability caused by tectonics.Hence,this new contribution emphasizes the crucial role of tectonics on spatially explicit reservoir prediction of deep to ultra-deep(up to>8000 m)carbonates in the Sichuan Basin,as well as other sedimentary basin analogues in China.

Crude oil cracking in deep reservoirs:A review of the controlling factors and estimation methods

The natural cracking of crude oils in deep reservoirs has gained great interest due to continuously increasing depth of petroleum exploration and exploitation.Complex oil compositions and surroundings as well as complicated geological evolutions make oil cracking in nature much more complex than industrial pyrolysis.So far,numerous studies,focused on this topic,have made considerable progress although there still exist some drawbacks.However,a comprehensive review on crude oil cracking is yet to be conducted.This article systematically reviews the controlling factors of oil cracking from six aspects,namely,oil compositions,temperature and time,pressure,water,minerals and solid organic matter.We compare previous experimental and modelling results and present new field cases.In the following,we evaluate the prevailing estimation methods for the extent of oil cracking,and elucidate other factors that may interfere with the application of these estimation methods.This review will be helpful for further investigations of crude oil cracking and provides a guide for estimation of the cracking extent of crude oils.

Geochemical-geomorphological Evidence for the Provenance of Aeolian Sands and Sedimentary Environments in the Hunshandake Sandy Land, Eastern Inner Mongolia, China

Identifying the provenance of aeolian sediments in the Hunshandake Sandy Land is of great importance for understanding the formation of the dune fields in the mid-latitudes and for deciphering information about desert＇s responses to global change. By determining the major and trace elements concentrations of aeolian sands in three grain size fractions from the central and western parts of the Hunshandake Sandy Land, we systematically study the provenance and the depositional history of aeolian sands in this desert environment. Our results show that aeolian sands from the Hunshandake Sandy Land are enriched in SiO2 and are depleted in many other elements compared to those of the Upper Continent Crust （UCC）. Variations of the immobile elements ratios like Zr/Hf, La/Yb, Th/Nb, La/Nb, LaN/YbN, GdN/YbN are relatively large in the coarse and medium fractions but minor in the fine fractions. Eu anomalies are quite different in the coarse fractions, but mostly positive in the medium fractions and all negative in the fine fractions. Decreasing tendency of Zr concentrations from the west to the east in the Hunshandake Sandy Land is evident in the coarse sands but rather weak in the fine grain size fractions. Our geochemical data indicate that the sources for the coarse and medium fractions of aeolian sands are diverse, influenced by local geology and geomorphology, while the fine sand fractions are more homogenous due to intensive mixture mainly by aeolian processes. Various ratios of immobile elements suggest that these sands should be sourced primarily from the surrounding mountains by fluvial/alluvial processes rather than from any remote territories. Aeolian sands with Ce negative anomalies are widely distributed in the Hunshandake Sandy Land, indicating that aquatic environments have occurred extensively prior to the occurrence of the dune field.

Method to measure tree-ring width,density,elemental composition,and stable carbon and oxygen isotopes using one sample

Tree-ring width(RW),density,elemental com-position,and stable carbon and oxygen isotope(δ^(13)C,δ^(18)O)are widely used as proxies to assess climate change,ecology,and environmental pollution;however,a specific pretreat-ment has been needed for each proxy.Here,we developed a method by which each proxy can be measured in the same sample.First,the sample is polished for ring width meas-urement.After obtaining the ring width data,the sample is cut to form a 1-mm-thick wood plate.The sample is then mounted in a vertical sample holder,and gradually scanned by an X-ray beam.Simultaneously,the count rates of the fluorescent photons of elements(for chemical characteriza-tion)and a radiographic grayscale image(for wood density)are obtained,i.e.the density and the element content are obtained.Then,cellulose is isolated from the 1-mm wood plate by removal of lignin,and hemicellulose.After producing this cellulose plate,cellulose subsamples are separated by knife under the microscope for inter-annual and intra-annual stable carbon and oxygen isotope(δ^(13)C,δ^(18)O)analysis.Based on this method,RW,density,elemental composition,δ^(13)C,and δ^(18)O can be measured from the same sample,which reduces sample amount and treatment time,and is helpful for multi-proxy comparison and combination research.

Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge:evidence from sulfide chronology

The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.

A Preliminary Study of Holocene Climate Change and Human Adaptation in the Horqin Region

Human activity during the Holocene in the Horqin region, northeastern China, has been widely documented. As an important proxy record of human activity, black carbon（BC） in sediments has been linked to climate change and human adaptation. A loess-paleosol section located in south Horqin was chosen for this study. Holocene climate change and human adaptation to the environment were discussed by analyzing BC, organic carbon（OC） and other proxies. The conclusions included：（1） before 3900 cal BP, human activity was closely related to the natural environment and cultural development was dominated by climate change. For example, the rapid decline of the agrarian Hongshan culture was caused by a slight decrease in temperature at ~5000 cal BP;（2） during 3900-3200 cal BP, the heavy dependence of human societies on nature gradually lessened and the ability of those human societies to adapt to the environment was enhanced. However, the farming-dominated Lower Xiajiadian culture was nonetheless replaced by the pastoralist Upper Xiajiadian culture due to an extremely cooling event at ~3200 cal BP;（3） during the late Holocene period, the marked influence of climate change on human activity might have lessened as a result of a clear improvement in human labor skills. After this, human living styles were influenced by cultural developments rather than climate change because humans had mastered more powerful means of productivity.

Understanding the Interactions between Climate Change,Landscape Evolution,Surface Processes and Tectonics in the Earth System:What Can the Studies of Chinese Deserts Contribute?

Due to large deserts on Earth surface a thorough understanding of climate change, landscape evolution and geomorphological processes having occurred in deserts is crucial for Earth System Science. The landscapes in deserts are, however, diverse and different over the globe with regard to their geomorphological nature, human activities and geological histories. In the last decades a great number of efforts have been put to the investigation of the initial timing of the occurrence of arid climate, e. g. in northwestern China. Silty sediments in the downwind directions have been used to deduce the histories of deserts. In general, there is a lack of knowledge about processes and landscapes in Chinese drylands between the initial Miocene silt sedimentation at desert margins and the late Quaternary multiple occurrences of wetter climate with assumed large lakes in many of the deserts in northern China. The geomorphological concept of three primary triggering factors, i.e., the sediment supply, sediment availability and transport capacity of wind, and additionally the underground geology need to be fully considered for a better understanding of the environmental histories of sand seas which should not be viewed as equivalent for deserts because sand seas cover between 〈 1% and ca. 45% of the desert areas in various continents dependent on a complex interaction between various processes of both exogenous and endogenous origins.

Paleoclimatic and provenance implications of magnetic parameters from the Miocene sediments in the Subei Basin

Thick sediments from foreland basins usually provide valuable information for understanding the relationships between mountain building,rock denudation,and sediment deposition.In this paper,we report environmental magnetic measurements performed on the Miocene sediments in the Subei Basin,northeastern Tibetan Plateau.Our results show two different patterns.First,the bulk susceptibility and SIRM,ARM,and HIRM mainly reflect the absolute-concentration of magnetic minerals;all have increased remarkably since 13.7 Ma,related to provenance change rather than climate change.Second,the ratios of IRM100mT/SIRM,IRM100mT/IRM30mT,and IRM100mT/IRM60mT,together with the redness and S ratio,reflect the relative-concentration of hematite,being climate-dependent.Their vertical changes correlate in general with the long-term Miocene climatic records of marine oxygen isotope variations,marked by the existence of higher ratios between 17 and 14 Ma.This may imply that global climate change,rather than uplift of the Tibetan Plateau,played a dominant role in the long-term climatic evolution of the Subei area from the early to middle Miocene.

Linking moisture and near-surface wind with winter temperature to reveal the Holocene climate evolution in arid Xinjiang region of China

An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle-to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds;and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally,we develop a conceptual model to explain the pattern of Holocene climate changes in this region.From the early to the late Holocene, the increasing atmospheric COcontent and winter insolation,and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system,which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.

Types,Petrophysical Properties and Pore Evolution of Late Ediacaran Microbial Carbonates,Tarim Basin,NW China

The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.

Geochemical and Mineral Characteristics of Jurassic Volcanic Rocks from ODP Sites 304, 1149, and 801:Implications for Magmatic Evolution in the Northwest Pacific

The regular variations in magmatic activities along the Northwest Pacific plate have been little studied in spite of their importance. In this contribution, systematic analyses were conducted on tholeiitic basalts from three Ocean Drilling Program sites(Sites 304, 1149, and 801), including the petrographic features, major and trace elements, Nd isotopic compositions, and mineral structure and compositions of whole rocks. Volcanic rocks from Sites 304, 1149, and 801 belong to tholeiites and exhibit depleted light rare earth elements(LREE), large ion lithophile elemental contents(LILE), and relatively depleted Nd isotopic ratios(143Nd/144Nd=0.513139-0.513211), similar to those of normal mid-ocean ridge basalts(NMORB). Comprehensive data on mineral compositions, whole-rock geochemistry, and geochronology demonstrate that a regular variation trend exists in the north-south direction along the Northwest Pacific plate. The 143 Nd/144 Nd values(0.513139-0.513211) and trace-element ratios for whole rocks(Sm/Th=15.35-30.00; Zr/Hf=28.53-35.76; Zr/Y=2.58-3.67; Th/La=0.04-0.06; Th/Y=0.33-0.70), as well as the trace-element ratios(Zr/Hf, La/Yb, Ti/Zr) of clinopyroxenes from Sites 1149 and 801 tholeiites show larger variations compared to those from Site 304 tholeiites(143Nd/144Nd=0.513185-0.513195; Sm/Th=18.19-20.58; Zr/Hf=31.07-33.26; Zr/Y=2.62-3.03; Th/La=0.05-0.06; Th/Y=0.48-0.57). Mineral zoning textures were obvious in tholeiites from Sites 1149 and 801 but were rarely observed in Site 304.These regular features were likely attributed to the differences in the heterogeneity of the magma source,the process of magmatic evolution, the plate-spreading rate, and the effective and ineffective mixing.

Formation of the Huajiang Grand Canyon (southwestern China) driven by the evolution of a Late Pleistocene tiankeng

Collapse is a common geomorphic process in karst areas,especially on the Yunnan-Guizhou Plateau,which has a tectonic background of integral uplift.The frequent occurrence of collapse processes in karst underground caves and canyons indicates that collapses play an important role in the formation of canyons.Through an analysis of the morphology of a semicircular cliff in the Huajiang Grand Canyon and an investigation of sediments at the bottom of the cliff,a large-scale collapse event was found to have occurred.U-series dating of secondary calcium carbonate cement in the collapse breccias indicates that collapse processes occurred approximately 200 ka.According to the geomorphological evolution of the Huajiang Grand Canyon,the following geomorphic evolutionary process is proposed:underground river-cave hall-collapse of a tiankeng-tiankeng degradation-canyon formation.These findings also show that the dating of collapsed breccia cement can be effectively used to determine the development times of karst canyons and the formation ages of tiankengs.

Geochemical and Geological Characterization of Marine-Continental Transitional Shale: A Case Study in the Ordos Basin, NW China

The organic-rich shale of the Shanxi and Taiyuan Formation of the Lower Permian deposited in a marinecontinental transitional environment are well developed in the Ordos Basin,NW China,which is considered to contain a large amount of shale hydrocarbon resources.This study takes the Lower Permian Shanxi and Taiyuan shale collected from well SL~# in the Ordos Basin,NW China as an example to characterize the transitional shale reservoir.Based on organic geochemistry data,X-ray diffraction(XRD)analysis,field-emission scanning electron microscopy(FE-SEM)observations,the desorbed gas contents of this transitional shale were systematically studied and the shale gas potential was investigated.The results indicate that the Lower Permian Shanxi and Taiyuan shale has a relatively high total organic carbon(TOC)(average TOC of 4.9%)and contains type III kerogen with a high mature to over mature status.XRD analyses show that an important characteristic of the shale is that clay and brittle minerals of detrital origin comprise the major mineral composition of the marine-continental transitional shale samples,while the percentages of carbonate minerals,pyrite and siderite are relatively small.FE-SEM observations reveal that the mineral matrix pores are the most abundant in the Lower Permian shale samples,while organic matter(OM)pores are rarely developed.Experimental analysis suggests that the mineral compositions mainly govern the macropore development in the marine-continental transitional shale,and mineral matrix pores and microfractures are considered to provide space for gas storage and migration.In addition,the desorption experiments demonstrated that the marine-continental transitional shale in the Ordos Basin has a significantly potential for shale gas exploration,ranging from 0.53 to 2.86 m^3/t with an average value of 1.25m^3/t,which is in close proximity to those of terrestrial shale(1.29 m^3/t)and marine shale(1.28 m^3/t).In summary,these results demonstrated that the Lower Permian marine-continental transitional shale in the Ordos Basin has a significantly potential for shale gas exploration.

Riverine sulfate sources and behaviors in arid environment,Northwest China:Constraints from sulfur and oxygen isotopes

The fate of riverine sulfate ion (SO_(4)^(2-)) and its environmental effects in arid environment are difficult to evaluate due to its complicated sources and strongly coupled behaviors with water cycle which is significantly modified by humans.To understand the sulfur cycle in aquatic systems in arid environment,the chemical and sulfur and oxygen isotopic compositions (δ^(34)S_(SO4)and δ^(18)O_(SO4)) of major rivers around the Badain Jaran Desert,northwestern China,were investigated.These rivers had averaged SO_(4)^(2-)content at 1336μmol/L,over 10times higher than the global average.The δ^(34)S_(SO4)and δ^(18)O_(SO4)values ranged from-5.3‰to+11.8‰and+1.6‰to+12.8‰,respectively.The end-member analysis and the inverse model showed that riverine sulfate was mainly derived from evaporites dissolution (0-87%),sulfide oxidation (13%-100%) and precipitation (0-33%),indicating heterogeneity in sulfur sources and behaviors along the river drainage with the lithology variations and climate gradients.Multiple isotopic tools combining with hydro-chemistry compositions could be applied to reveal sulfur cycle in arid environment.Based on the calculation,sulfide oxidation plays the primary role in the headwater and upstream in the Qilian-Mountains area,where sulfide is widely exposed.While the proportion of evaporites dissolution contributing to riverine sulfate is much higher in downstream in a drier environment.Besides,less precipitation and higher temperature can lead to more intensive evaporation,affecting the process of sulfide oxidation and enhancing the rates of evaporites dissolution and sulfate precipitation in the basin.

Organic Matter Accumulation in the Upper Permian Dalong Formation from the Lower Yangtze Region,South China

The Late Permian was marked by a series of important geological events and widespread organic-rich black shale depositions,acting as important unconventional hydrocarbon source rocks.However,the mechanism of organic matter(OM)enrichment throughout this period is still controversial.Based on geochemical data,the marine redox conditions,paleogeographic and hydrographic environment,primary productivity,volcanism,and terrigenous input during the Late Permian in the Lower Yangtze region have been studied from the Putaoling section,Chaohu,to provide new insights into OM accumulation.Five Phases are distinguished based on the TOC and environmental variations.In Phase I,anoxic conditions driven by water restriction enhanced OM preservation.In Phase II,euxinic and cycling hydrological environments were the two most substantial controlling factors for the massive OM deposition.During Phase III,intensified terrestrial input potentially diluted the OM in sediment and the presence of oxygen in bottom water weakened the preservation condition.Phase IV was characterized by a relatively higher abundance of mercury(Hg)and TOC(peak at 16.98 wt%),indicating that enhanced volcanism potentially stimulated higher productivity and a euxinic environment.In Phase V,extremely lean OM was preserved as a result of terrestrial dilutions and decreasing primary productivity.Phases I,II and IV are characterized as the most prominent OM-rich zones due to the effective interactions of the controlling factors,namely paleogeographic,hydrographic environment,volcanism,and redox conditions.

Late Cenozoic uplift of the Liupan Mountains:Evidence from the Neogene loess deposits

The Liupan Mountains,one of the important mountain ranges in western China,are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block.The uplift history of the Liupan Mountains remains controversial.Loess deposits are good tracers of regional tectonic and geomorphic changes,because loess is sensitive to erosion and the formation and preservation of loess requires relatively flat highlands and relatively stable tectonic environments.We investigated the distribution of Neogene loess deposits on the western piedmont of the Liupan Mountains and examined a near-continuous loess section(Nanping section)on the piedmont alluvial highlands.Correlation of magnetic susceptibility stratigraphy with the QA-ⅠMiocene loess sequence dates this 56-m section covering the interval from~8.1 to 6.2 Ma.The lower boundary age of this section,together with previously reported Zhuanglang red clay(sand-gravel layers with intercalated loess during~9–8 Ma and near-continuous loess during~8–4.8 Ma)and Chaona red clay(~8.1–2.58 Ma),indicates that the Liupan Mountains were uplifted in the late Miocene(~9–8 Ma)and basically formed by~8 Ma,attesting to no intense mountain building since that time.In addition,based on the information from the Zhuanglang core and the QA-Ⅰsection,we infer that sizable parts of the Liupan Mountains were uplifted during the late Oligocene–early Miocene and did not experience intense uplift during~22–9 Ma.

Spatiotemporal variation of rainy season span and precipitation recorded by lacustrine laminated pollen in the Tibetan Plateau during the past two millennia

The quantitative reconstruction of the length of the rainy season and precipitation on the Tibetan Plateau(TP) is crucial for revealing the spatiotemporal evolution of the Westerlies and Asian summer monsoon, as well as its ecological and environmental effects. Accurately determining the start and end times of the rainy season on the Plateau remains challenging.This study determined the start and end times of the rainy season in different locations on the Plateau by identifying precipitation inflection points. We calculated the duration and precipitation amount of the rainy season and established a transfer function between the modern pollen assemblages and them. Then, we reconstructed the rainy season variations in Kusai Lake(northern TP) and Jiang Co(central TP) during the past two millennia. The results showed that, the rainy season precipitation in Kusai Lake recorded five periods of high precipitation: AD 580–680, 1000–1100, 1200–1450, 1550–1780, and 1920–present, corresponding to the stages with long rainy season. The rainy season precipitation sequence in Jiang Co recorded four periods of high precipitation: AD 80–500, 800–950, 1250–1450, and 1780–present, which is consistent with the long rainy season before AD 1000 but unclear afterward. Spatially, rainy season precipitation on the Plateau exhibited four patterns: “wet in both north and south” may be related to abnormally strong summer monsoons;“dry in both north and south” likely associated with weak Westerly wind and weak summer monsoon;“wet in the south and dry in the north” linked to strong summer monsoon and weak Westerly wind;and “dry in the south and wet in the north” connected to weak summer monsoon and strong Westerly wind. This study revealed the spatiotemporal evolution pattern of the rainy season onset and end, duration, and precipitation amount on the Plateau over the past two millennia. It provides natural background support for further understanding the coupling between Westerly wind and Asian summer monsoon.

Rare-earth element geochemistry reveals the provenance of sediments on the southwestern margin of the Challenger Deep

The hadal zone represents one of the last great frontiers in modern marine science,and deciphering the provenance of sediment that is supplied to these trench settings remains a largely unanswered question.Here,we examine the mineralogical and geochemical composition of a sediment core(core CD-1)that was recovered from the southwestern margin of the Challenger Deep within the Mariana Trench.Major element abundances and rare-earth element patterns from these sediments require inputs from both terrigenous dust and locally sourced volcanic debris.We exploit a two-endmember mixing model to demonstrate that locally sourced volcanic material dominates the sediment supply to the Challenger Deep(averaging^72%).The remainder,however,is supplied by aeolian dust(averaging^28%),which is consistent with adjacent studies that utilized Sr-Nd isotopic data.Building on a growing database,we strengthen our understanding of Asian aeolian dust input into the northwestern Pacific,which ultimately improves our appreciation of sedimentation in,and around,the hadal zone.