Paired δ13Ccarb and δ13Corg records of the Ordovician on the Yangtze platform,South China

During the Ordovician, huge biological revolutions and environmental changes happened in Earth’s history, including the Great Ordovician Biodiversification Event, global cooling and so on, but the cause of these events remains controversial. Herein, we conducted a paired carbon isotopic analysis of carbonate (δ¹³C_carb) and organic matter (δ¹³C_org) through the Ordovician in the Qiliao section on the Yangtze platform of South China. Our results showed that the δ¹³C_carb trend of the Qiliao section can be correlated with local and global curves. The δ¹³C_org trend seems is less clear than the δ¹³C_carb trend for stratigraphic correlations, but some δ¹³C_org positive excursions in the Middle and Upper Ordovician may be used for correlation studies. These carbon isotopic records may have global significance rather than local significance, revealing several fluctuations to the global carbon cycle during the Ordovician. Several known δ¹³C_carb and δ¹³C_org negative and positive excursions have been recognised in this study, including the early Floian Negative Inorganic Carbon (δ¹³C_carb) Excursion (EFNICE), as well as the early Floian Positive Organic Carbon (δ¹³C_carb) Excursion, the mid-Darriwilian Inorganic Carbon (δ¹³C_carb and δ¹³C_org) Excursion (MDICE), and the early Katian Guttenberg Inorganic Carbon (δ¹³C_carb and δ¹³C_org) Excursion (GICE). These positive excursions and a smooth decline trend of δ¹³C_org values during the early to mid-Floian may imply multiple episodes of enhanced organic carbon burial that began at the early Floian stage, probably resulting in further decline in atmospheric pCO₂ and then global cooling.     

Antarctic Glacial Retreats and the Records of Sea Level Change in Deposits at the North Bank of the Shenzhen Bay,South China

In view of the huge ice cover of 24.5 X 10⁶ km³ in Antarctica, which accounts for over 90% by volume of the ice body on earth, the movement of Antarctic glaciers is a major control on global sea-level change and climatic fluctuation. As recorded in the Quaternary deposits in King George Island, West Antarctica, three rapid ablations can be recognized at 11000, 9000 and 6100 years ago and the global climate within the past 6000 years is characterized by small-amplitude warm-cold fluctuation. Intertidal deposits at the north bank of the Shenzhen Bay suggest a periodic variation in sea level in about every 670 years over the last 6000 years with low sea levels recorded in the periods of 5500-4900, 3900-3600, 2400-2200 and 1300-1200 years ago. Between these periods the sea level rised for about 80 cm on average. The modern warming climate in the last century corresponds with a rise of sea level at the rate of 2~3 mm/a. A state key project under the Antarctic Science & Technology Program (No. 905-02-04-03) and is partially financially supported by the Natural Science Foundation of Guangdong Province.     

350 ka Organic δ13C record of the monsoon variability on the Oman continental margin, Arabian Sea

The stable isotope compositions of sedimentary organic carbon and content of organic carbon for sediment cores recovered at two sites (sites 724C and 725C) during Ocean Drilling Program (ODP) Leg. 117 on the Oman continental margin are used to document variability of the monsoon winds for the past 350 ka. Although both sites have a mean δ¹³C value of -20.1‰, three zones depleted in¹³C are observable at site 724C during isotope stages 3, 8 and 10, while only one zone is recognizable at site 725C. Increased coastal upwelling during isotope stage 3 owing to intense SW monsoon winds resulted in higher concentration of CO₂ in the water column causing the formation of organic matter that was depleted in¹³C. The other two zones deposited during oxygen isotope stages 8 and 10, which are also characterized by low values of organic carbon, nitrogen and C/N ratios, could be attributed to the dilution by terrestrial material derived from paleosol by transported by northwester lies. Because of utilization of¹³C enriched dissolved CO₂ during the last glacial maximum Holocene sedimentary organic materials are depleted in¹³C relative to the the fomer. The content of residues organic carbon (ROC) is higher at site 724C (with an average of 2.3 ± 1.2%) relative to site 725C, which averages to 0.9 ± 0.4% probably because of differences in the degree of preservation. Organic material deposited at site 725C has undergone more degradation relative to site 724C as reflected by a systematic downcore decrease in¹³C resulting from a loss of¹³C enriched organic compounds. Owing to lack of good chronology at site 725C, a zone that is characterized by low δ¹³C values it could not be correlated with the other three zones observed at Site 724C.     

A Comparative Analysis of Evaporate Sediments on Earth and Mars：Implications for the Climate Change on Mars

The knowledge of Martian salts has gone through substantial changes during the past decades. In the 70th of last century, Viking landers have noticed the existence of salts on Mars. Several salt species have been suggested from then on, such as sulfates and chlorides. However, their origin was a mystery due to the lack of observations. The recent explorations and related studies at the beginning of this century revealed that the crustal composition of Mars is similar to that of Earth, and it was hypothesized that almost one third of Martian surface was covered by oceans and lakes in the early stage of Mars. The huge water bodies may have dissolved a large quantity of ions from Martian primary rocks during the whole Noachian and Hesperian epoch. After the enormous drought event happened during the late Hesperian and the early Amazonian, these dissolved ions have formed huge salts deposits and most of them were preserved on Mars until today. To date, carbonates, sulfates, chlorides have all been detected by orbital remote sensing and by landers and rovers. However, the salt mineral assemblages on Mars seems to have some differences from those on Earth, e.g., rich in sulfates and lack of massive carbonates. To explain this difference, we propose that most of the surface carbonates precipitated from the ancient oceans may have been dissolved by the later ubiquitous acidic fluids originated from the global volcanism in the Hesperian era, and formed the enormous sulfate deposits as detected, and this hypothesis seems to be supported by the evidence that most of the sulfate deposits distribute around the Tharsis volcanic province while the survived carbonates located far from it. This process can release most of the carbon on Mars to the atmosphere in the form of CO2 and then be erased by the late heavy bombardments, which might have profound influence on the climate change happened in the Hesperian age. The positive correlation between the GRS results of the potassium distributions and the distribution of chlorides on Mars, together with the high Br concentration measured from the evaporate sediments at two Mars exploration rover landing sites, indicate that the brines in the regions where the chlorides deposited may have reached the stage for potassium salts deposition, thus we propose for the first time that potassium salts deposits might be prevalent in these regions.     

Response of biomass accumulation and nodulation by Vicia villosa to soil conditions: Evidence from δ13C and δ15N isotopes

Vicia villosa is an annual legume plant,and is mainly used for green manure by farmers in southwest China.Field growth experiments were performed on six plots.The concentrations of mineral nutrients and soluble sugar,and the changes of carbon and nitrogen isotopic composition within and among organs of Vicia were deter- mined.Significant differences in legume growth were found in response to soil type and its moisture conditions.The Vicia villosa was relatively well adapted to growth in limestone soils than sandstone soils.The distribution of sugar concentrations andδ1 3C-differences between roots and leaves indicate that the translocation of sugars from leaves to roots may be restricted by soil drought.Therefore,there was an inhibition of Pi distribution from roots to leaves, resulting in over optimum threshold of N/P ratio.Those may originate from the feedback regulation in the legume, where soluble sugar could not be distributed from leaves to roots.The results ofδ1 5N values in tissues suggest that there should be different preferential use of nitrogen resource by legume during the formation of nodules:before nodule formation the legume preferentially utilizes inorganic nitrogen from soils,but afterwards the nitrogen should be mainly from N2-fixation.Our results indicate that the lack of nodulation development,except for S2,should be ascribed to the factor controlling bi-direction nutrient transfer,which should be efficiency of establishment symbiosis with arbuscular mycorrhiza before nodulation formation.It is predicted that the species of Vicia villosa should be a legume associated with dual symbiosis with rhizobia and mycorrhiza.     

Isotopic Composition (δ13C and δ18O) and Genesis of Mn-bearing Sediments in the Ushkatyn-III Deposit,Central Kazakhstan

Lithology and Mineral Resources - The Ushkatyn-III deposit is located 300 km west of Karaganda (Central Kazakhstan). It is classified as a weakly metamorphosed Atasu-type hydrothermal-sedimentary...     

A pronounced negative δ13C excursion in an Ediacaran succession of western Yangtze Platform: A possible equivalent to the Shuram event and its implication for chemostratigraphic correlation in South China

A pronounced negative δ¹³C shift that can be potentially correlated with the Shuram excursion has been reported from middle Ediacaran strata in the Yangtze Gorges area of South China. Whether it represents a perturbation to the ocean carbon cycle or a record of post-depositional alteration is still open to debate. Resolving this controversy will help clarify if δ¹³C variations can be used for chemostratigraphic correlation of Ediacaran successions. To further understand the regional pattern of Ediacaran carbon isotopic excursions in the Yangtze platform, we carried out a detailed δ¹³C analysis of the Lianghong section in the western part of the Yangtze platform. The Ediacaran System at Lianghong is overlain by the Maidiping Formation yielding early Cambrian small shelly fossils and underlain by the Cryogenian Lieguliu Formation diamictite and tuffaceous siltstones. It comprises the Guanyinya and Hongchunping formations, which have been traditionally correlated with the Doushantuo and Dengying formations, respectively, in the Yangtze Gorges area. Two negative δ¹³C excursions occur in the Lianghong section. The lower one at the uppermost Guanyinya Formation, with a nadir at − 8.6‰, may be correlated with the pronounced negative δ¹³C shift (EN3) in the uppermost Doushantuo Formation in the Yangtze Gorges area and possibly with the well known Shuram event in Oman. The upper negative δ¹³C excursion occurs in the upper Hongchunping Formation and may be correlated with negative excursions (EN4) near the Ediacaran/Cambrian boundary. Other negative δ¹³C excursions (e.g., EN1 and EN2) are not expressed in the Lianghong section because the lower Guanyinya Formation is dominated by siliciclastic rocks. Combined with previously published Ediacaran δ¹³C profiles, our results indicate that the EN3 excursion (likely a Shuram equivalent) may occur widely in South China and can be a useful chemostratigraphic feature for regional and global stratigraphic correlation.     

The δ13C excursions spanning the Cambrian explosion to the Canglangpuian mass extinction in the Three Gorges area,South China

A remarkable increase of the animal genera and a subsequent mass extinction in the late Early Cambrian are well known as the “Cambrian explosion” and the “Botomian–Toyonian crisis.” A composite global curve of the carbon isotope ratios for inorganic carbon (δ¹³C_carb) shows multiple fluctuations during the evolution events, and it indicates significant changes of the oceanic carbon cycle at that time. This study reveals a new continuous isotopic chemostratigraphy for inorganic carbon (δ¹³C_carb) from the bottom of the Shipai to the base of the Shilongdong formations in Three Gorges area, South China. This section covers the Canglangpuian to the Longwangmiaoian stages in the Lower Cambrian. The δ¹³C_carb variation exhibits three negative excursions: a remarkably negative excursion down to ca. − 12‰ in the middle Canglangpuian stage, a negative excursion to ca. − 1.0‰ in the upper Canglangpuian stage, and a negative excursion to ca. − 1.0‰ in the Longwangmiaoian stage, respectively. The largest negative δ¹³C_carb excursion and a positive excursion before the excursion are definitely consistent with the δ¹³C_carb negative shift (AECE) during the mass extinction and the δ¹³C_carb positive values (MICE) during the increase of animal genera, respectively. However, the minimum values of the negative shifts among South China, Siberia, and Canada sections are different from each other. The positive δ¹³C_carb excursion at the bottom of the Canglangpuian stage indicates that primary productivities and organic carbon burial were enhanced. A sea level rise in the Qiongzhusian to bottom of the Canglangpuian stages in South China corresponds to the Sinsk transgression event in Siberia and Canada. A eutrophication due to higher continental weathering during the transgression after the long-term retrogression enhanced the high primary production and consequently promoted the significant increase of animal diversity.On the other hand, deposition of laminated black shales without bioturbation signatures and a decline of trilobite diversity are observed during the negative δ¹³C_carb excursion in the Canglangpuian stage, indicating that the shallow water environment became anoxic at that time. The negative δ¹³C_carb shift indicates an influx of abundant ¹²CO₂ due to oxidation of organic carbons in seawater. The difference of the minimum values among sections implies the local difference in size of the organic carbon reservoirs and extent of the degradation of the carbons. The largest δ¹³C anomaly in South China suggests the presence of the largest OCPs due to higher activity of primary production and high degree of oxidation of the OCPs because of higher activity of animals. The coincidence of the timing of the negative δ¹³C excursions in the Canglangpuian stage among the sections indicates a global event, and suggests that the onset was caused by increase of oxygen contents of seawater and atmosphere. Abundant oxygen yielded by the increased primary productivity in the Atdabanian and the Qiongzhusian stages caused onset of the oxidation of OCP, and possibly led to the shallow water anoxia and the mass extinction of benthic animals in the Botomian and the Canglangpuian stage.     

Isotopic Compositions of Sulfur in the Jinshachang Lead–Zinc Deposit, Yunnan, China, and its Implication on the Formation of Sulfur-Bearing Minerals

The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou(SYG) Pb–Zn–Ag multimetal mineralization area in China.Sulfides minerals including sphalerite,galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite,quartz,and barite,making this deposit distinct from most lead–zinc deposits in the SYG.This deposit is controlled by tectonic structures,and most mineralization is located along or near faults zones.Emeishan basalts near the ore district might have contributed to the formation of orebodies.The δ34S values of sphalerite,galena,pyrite and barite were estimated to be 3.6‰–13.4‰,3.7‰–9.0‰,6.4‰ to 29.2‰ and 32.1‰–34.7‰,respectively.In view of the similar δ34S values of barite and sulfates being from the Cambrian strata,the sulfur of barite was likely derived from the Cambrian strata.The homogenization temperatures(T ≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria,therefore,the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district.Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur,it was not the main mechanism.Considering other aspects,it can be suggested that sulfur of sulfides should have been derived from magmatic activities.The δ34S values of sphalerite were found to be higher than those of coexisting galena.The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions,suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium.     

Geochronology and geochemistry of the Shilu Cu–Mo deposit in the Yunkai area,Guangdong Province,South China and its implication

Shilu is a large porphyry–skarn deposit in the Yunkai district in Guangdong Province, South China. The Shilu granitic intrusion in the mine area is a granodiorite which is genetically related to Cu mineralization. Plagioclase in the granodiorite has a zoned texture and is mainly andesine with minor amounts of labradorite, whereas the K-feldspars exhibit Carlsbad twins and some are also characterized by a zonal texture. K-feldspars from the granodiorite show high contents of Or (87–92 wt.%) with minor Ab (8–13 wt.%) and negligible An value of 0–0.3 wt.%. Biotite can be classified as magnesio-biotite, and is characterized by Mg-rich [Mg/(Mg + Fe) = 0.54–0.60] and Al^VI-low (average values = 0.11). Hornblende is chiefly magnesiohornblende and tschermakite. LA-ICP-MS zircon U–Pb age of the Shilu granodiorite is 107 ± 0.7 Ma, which is consistent with molybdenites Re–Os age of 104.1 ± 1.3 Ma. Geochemical data indicate that the Shilu granodiorite is silica-rich (SiO₂ = 63.43–65.03 wt.%) and alkali-rich (K₂O + Na₂O = 5.45–6.05 wt.%), as well as calcium-rich (CaO = 4.76–5.1 wt.%). Trace element geochemistry results show enrichments in large ion lithophile elements (e.g., Rb, K, and Ba) and depletions in some high field strength elements (e.g., Nb, P, Ta, and Ti). The total rare earth element (REE) content of the granodioritic rocks is low (∑ REE < 200 ppm), and is characterized by light REE enrichment [(La/Yb)_N > 9] and moderately negative Eu anomalies (Eu/Eu* = 0.83–0.90). These mineralogical, geochronological, and geochemical results suggest that the Shilu granodiorite has a mixed crust–mantle source with a geochemical affinity to I-type granitoids. Hornblende thermobarometry yielded magmatic crystallization temperatures of 686–785 °C and crystallization pressures between 1.0 and 2.34 kbar, which is converted to depths in a range of 3.31 to 7.71 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 680–780 °C and 0.8–2 kbar (depth 2.64–6.6 km), respectively. The parent magma had a high oxygen fugacity. The Shilu granodiorite has a relatively low ε_Nd/t–t value and high (⁸⁷Sr/⁸⁶Sr)_i value, and Nd isotopes yield two-stage depleted mantle Nd model ages of 969–1590 Ma. Our new data, combined with previous studies, imply that the granodiorite and the associated Shilu Cu–Mo deposit was formed in an extensional environment, closely related to remelting of residual subducted slab fragments in the Jurassic.     

Research Status and Advance in Carbon Isotope (δ13C) Variation from Stalagmite

The application of carbon isotope (δ¹³C) collected from stalagmite to reconstruct the past climate and/or ecologic evolution, relative to other preserved indicators, is much limited due to its complex influencing factors including climate outside cave and complicated and site-specific karstic process. In terms of various climate and non-climate limiting factors on stalagmite δ¹³C, and combined with a large number of geological records and modern cave monitoring data of the latest researches, the pathway and behavior of the signal transmission of δ¹³C in the cave system were analyzed. The possible relationship between δ¹³C excursions and climate oscillations under different time scales was thus discussed. Although the degree of noise becomes increasing mixed with δ¹³C on centennial scales or shorter, the climatic elements, such as temperature and humidity (or precipitation), as predominant modulators exert directly or indirectly influence on vegetation overlying the soil and associated soil CO₂ productivity on millennial-orbital scales. Future work should be focused on further deeply extracting the common δ¹³C signals from specific caves by exploring the controlling factors, both including climatic and non-climatic ones, attaching importance to the seasonal characteristics of stalagmite δ¹³C, and taking full advantage of its potential in the indication of local environmental events. The use of multi-proxy and multi-method will contribute to better understanding the interesting linkages among the δ¹³C characteristics, karstic process, global carbon cycle and associated climate change.     

Estimating past leaf-to-air vapour pressure deficit from terrestrial plant δ13C

δ¹³C was determined in lignin extracted from present-day cladodes of Phyllocladus alpinus (a small coniferous tree) from seven well-lit sites across New Zealand. The δ¹³C values ranged from −30.9‰ to −23.6‰ and were compared with monthly means of temperature, precipitation, relative humidity and vapour pressure deficit from the nearest recording stations. Of these parameters, the leaf-to-air vapour pressure deficit of the first month of cladode growth and expansion proved to be the most significantly correlated with lignin δ¹³C, over a range of 0.3 to 0.8 kPa, confirming the importance of atmospheric moisture content on stomatal conductance. The carbon isotopic signature of lignin from fossilised cladodes preserved under the Kawakawa Tephra (22.6 k ¹⁴C yr BP) on the North Island is identical to that of the whole tissue, suggesting that for this species at least, fossil material can be used to approximate the lignin δ¹³C. The δ¹³C of species- and organ-specific fossil terrestrial plant material therefore provides an excellent method to quantify past changes in leaf-to-air vapour pressure deficit. Copyright © 1999 John Wiley & Sons, Ltd.     

Bulk organic δ13C and C/N ratios as palaeosalinity indicators within a Scottish isolation basin

Microfossils in isolation basin sediments are frequently used to reconstruct sea‐level change, but preservation problems and non‐analogue situations can limit their usefulness. Here we investigate the potential of stable carbon isotopes (δ¹³C) and C/N ratios from bulk organic matter, as an alternative proxy of salinity within isolation basin sediments from a basin in northwest Scotland. Within the Holocene sediment δ¹³C and C/N are determined largely by the mean weighted values of the predominant source of the organic material. Analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high δ¹³C and variable C/N. In the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low δ¹³C and high C/N. The application of δ¹³C and C/N ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins. Copyright © 2005 John Wiley & Sons, Ltd.     

Assessment of δ13C and C/N ratios in bulk organic matter as palaeosalinity indicators in Holocene and Lateglacial isolation basin sediments,northwest Scotland

Carbon isotopes (δ¹³C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ¹³C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ¹³C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ¹³C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO₂ concentration, poor vegetation development and temperature influence δ¹³C values during this period. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of landscape evolution on the distribution of floristic patterns in northern Amazonia revealed by δ13C data

The Amazonian lowlands include large patches of open vegetation which contrast sharply with the rainforest, and the origin of these patches has been debated. This study focuses on a large area of open vegetation in northern Brazil, where δ¹³C and, in some instances, C/N analyses of the organic matter preserved in late Quaternary sediments were used to achieve floristic reconstructions over time. The main goal was to determine when the modern open vegetation started to develop in this area. The variability in δ¹³C data derived from nine cores ranges from ?32.2 to ?19.6‰, but with nearly 60% of data above ?26.5‰. The most enriched values were detected only in ecotone and open vegetated areas. The development of open vegetation communities was asynchronous, varying between estimated ages of 6400 and 3000 cal a BP. This suggests that the origin of the studied patches of open vegetation might be linked to sedimentary dynamics of a late Quaternary megafan system. As sedimentation ended, this vegetation type became established over the megafan surface. In addition, the data presented here show that the presence of C₄ plants must be used carefully as a proxy to interpret dry paleoclimatic episodes in Amazonian areas. Copyright © 2012 John Wiley & Sons, Ltd.     

The δ18O stratigraphy of the Hoxnian lacustrine sequence at Marks Tey,Essex, UK: implications for the climatic structure of MIS 11 in Britain

Marine Isotope Stage 11 (MIS 11) is considered one of the best analogues for the Holocene. In the UK the long lacustrine sequence at Marks Tey, Essex, spans the entirety of the Hoxnian interglacial, the British correlative of MIS 11c. We present multiproxy evidence from a new 18.5‐m core from this sequence. Lithostratigraphy, pollen stratigraphy and biomarker evidence indicate that these sediments span the pre‐, early and late temperate intervals of this interglacial as well as cold climate sediments that post‐date the Hoxnian. The δ¹⁸O signal of endogenic carbonate from this sequence produces several clear patterns that are interpreted as reflecting the climatic structure of the interglacial. As well as providing evidence for long‐term climate stability during the interglacial and a major post‐Hoxnian stadial/interstadial oscillation the δ¹⁸O signal provides strong evidence for abrupt cooling events during the interglacial itself. One of these isotopic events occurs in association with a short‐lived increase in non‐arboreal pollen (the NAP phase). The results presented here are discussed in the context of other MIS 11 records from Europe and the North Atlantic, particularly with respect to our understanding of the occurrence of abrupt climatic events in pre‐Holocene interglacials. Copyright © 2016 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

Geochemical Constraints on the Origin and Evolution of Spring Waters in the Changdu‐Lanping‐Simao Basin,Southwestern China

Chemical and isotopic data were measured for 51 leached brine springs in the Changdu-Lanping-Simao Basin (CD-LP-SM), China. The predominance of Cl and Na, saturation indices of carbonate minerals, and Na/Cl and Ca/SO4 ratios of ~1 suggest that halite, sulphate, and carbonate are the solute sources. Integration of geochemical, δ18O, and δD values suggests that springs are mainly derived from meteoric water, ice-snow melt, and water-rock interactions. B concentrations range from 0.18 to 11.9 mg/L, with δ11B values of ?4.37‰ to +32.39‰, indicating a terrestrial source. The δ11B-B relationships suggest B sources of crustal origin (marine carbonates with minor crust-derived volcanics); we did not identify a marine or deep mantle origin. The δ11B values of saline springs (+4.61‰ to +32.39‰) exceed those of hot (?4.37‰ to +4.53‰) and cold (?3.47‰ to +14.84‰) springs; this has contributed to strong water-rock interactions and strong saturation of dissolved carbonates. Conversely, the global geothermal δ11B-Cl/B relationship suggests mixing of marine and non-marine sources. The δ11B-Cl/B relationships of the CD-LP-SM are similar to those of the Tibet geothermal belt and the Nangqen Basin, indicating the same B origin. These differ from thermal waters controlled by magmatic fluids and seawater, suggesting that B in CD-LP-SM springs has a crustal origin.     

Origin of Paleofluids in Dabashan Foreland Thrust Belt:Geochemical Evidence of 13C,18O and 87Sr/86Sr in Veins and Host Rocks

In the last ten years, with important discoveries from oil and gas exploration in the Dabashan foreland depression belt in the borderland between Shanxi and Sichuan provinces, the relationship between the formation and evolution of, and hydrocarbon accumulation in, this foreland thrust belt from the viewpoint of basin and oil and gas exploration has been studied. At the same time, there has been little research on the origin of fluids within the belt. Based on geochemical system analysis including Z values denoting salinity and research on δ13C, δ18O and 87Sr/86Sr isotopes in the host rocks and veins, the origin of paleofluids in the foreland thrust belt is considered. There are four principal kinds of paleofluid, including deep mantle-derived, sedimentary, mixed and meteoric. For the deep mantle-derived fluid, the δ13C is generally less than ?5.0‰PDB, δ18O less than -10.0‰PDB, Z value less than 110 and 87Sr/86Sr less than 0.70600; the sedimentary fluid is mainly marine carbonate-derived, with the δ13C generally more than ?2.0‰PDB, δ18O less than ?10.0‰PDB, Z value more than 120 and 87Sr/86Sr ranging from 0.70800 to 0.71000; the mixed fluid consists mainly of marine carbonate fluid (including possibly a little mantle-derived fluid or meteoric water), with the δ13C generally ranging from ?2.0‰ to ?8.0‰PDB, δ18O from ?10.0‰ to ?18.0‰ PDB, Z value from 105 to 120 and 87Sr/86Sr from 0.70800 to 0.71000; the atmospheric fluid consists mainly of meteoric water, with the δ13C generally ranging from 0.0‰ to ?10.0‰PDB, δ18O less than ?8.0‰PDB, Z value less than 110 and 87Sr/86Sr more than 0.71000. The Chengkou fault belt encompasses the most complex origins, including all four types of paleofluid; the Zhenba and Pingba fault belts and stable areas contain a simple paleofluid mainly of sedimentary type; the Jimingsi fault belt contains mainly sedimentary and mixed fluids, both consisting of sedimentary fluid and meteoric water. Jurassic rocks of the foreland depression belt contain mainly meteoric fluid.     

Elemental δ13C at Allen's Cave,Nullarbor Plain,Australia: assessing post‐depositional disturbance and reconstructing past environments

The degree to which post‐depositional disturbance can be assessed in archaeological sequences is critical for the development of robust chronologies for such deposits. A common approach is the identification of conjoined artefacts distributed through the sequence as a measure of disturbance following deposition, although this method is relatively labour intensive and does not provide a continuous record of disturbance through the entire sequence. Here we present δ¹³C values for different size fractions (<125 and >125 µm) of chemically resistant charcoal distributed through a sedimentary profile at Allen's Cave, South Australia. The curves generated from both size fractions parallel one another, indicating minimal disturbance through the entire profile and providing greater confidence in the luminescence and radiocarbon chronologies reported previously for the site. In addition, the elemental δ¹³C values provide an indication of greater aridity (compared with present) persisting in this area from ca. 45 to 12 ka, consistent with other proxy records. The onset of the Holocene is marked by a shift to wetter conditions, probably as a result of post‐glacial marine transgression and closer proximity to the coastline. Copyright © 2001 John Wiley & Sons, Ltd.     

Late Holocene stable isotopic (δ13C and δ15N) records of lacustrine organic matter in Guangdong Province,south China,and their palaeoenvironmental implications

This study presents the results of TOC/TN (C/N) ratio, δ¹³C and δ¹⁵N analyses of lake sedimentary organic matter (OM) from the Hedong section, western Guangdong Province in south China, with the objective to reveal the history of hydrological and ecological variations in the region influenced by both the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM). Variations in δ¹³C and δ¹⁵N of sedimentary OM may be closely related to past climatic conditions, which results in variations in surface runoff, lake level, allochthonous and autochthonous sources of OM, and lake productivity. Based on the interpretation of these proxies, four periods, i.e. 4370–4100, 3700–2900, 2400–2100 and 1900–900 cal. a BP, are characterized by low lake level, weakened surface runoff and deteriorated status of terrestrial and aquatic ecosystems, whereas the periods 4100–3700, 2900–2400, 2100–1900 and 900–600 cal. a BP are dominated by high lake level, strengthened surface runoff, and flourishing terrestrial and aquatic plants. A remarkable positive correlation between the δ¹³C values of the section and the ENSO number record obtained from the tropical Pacific implies that the impact of the ISM is greater than that of the EASM in the study area. The abnormal correspondence between the δ¹³C and solar activity reconstructed from ¹⁰Be and ¹⁴C records in GRIP ice‐core occurred from 1500–800 and particularly from 4200–4000 cal. a BP, suggesting that these two cool and dry intervals may be caused by stronger volcanic activities that are recorded in the GISP2 and Dome C ice‐cores. This study reveals that changes in solar insolation and solar activity, as well as changes in oceanic–atmospheric circulation (e.g. the ENSO intensity) and intensive volcano eruptions may have exerted influence on late Holocene climate variability in the study area.