Analysis of carbon and oxygen stable isotopes in carbonate rocks by the laser micro-sampling technique

The analysis of stable isotopes of carbon and oxygen in different carbonate rocks by the phosphoric acid method is not easier than that by the laser sampling method developed in recent years, which optically focuses laser beams with sufficient energy on a micro area of a thin section in a vacuum sample box via microscope. CO 2 produced by heating decomposition of carbonate was purified by the vacuum system, and the stable isotopic values of carbon and oxygen were calculated and analyzed on a mass spectrometer. This paper adopted the laser micro-sampling technique to analyze the stable isotopes of carbon and oxygen in dolomite, carbonate cement, stromatolite and different forms of dawsonite (donbassite). Results indicated that the laser micro-sampling method is effective in analyzing carbonate composition and could be a convincing proof for justification on carbonate composition analysis.

Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang,China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition （δ^13C） values of the carbonate sediment （-1‰ to -2‰） have no relation to the oxygen isotope composition of the carbonate （δ^18O） values （-7‰ to -8‰）, with both isotopes showing a low variability. The carbonate content is low （〈20%）. Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ^13C values between approximately ＋0.5‰ and ＋3‰, and δ^18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.

基于碳氢氧同位素的桉树人工林水循环过程研究进展

桉树是我国南方地区重要的速生用材树种,在我国人工林资源中具有十分重要的地位。然而,桉树种植带来的生态环境问题日益受到关注,尤其在对桉树是否为“抽水机”、桉树大面积种植是否导致土壤干旱和地下水位下降等问题上一直存在诸多争议。碳氢氧稳定同位素为陆地生态系统水循环过程定量研究提供了有效和便捷的方法,能系统和定量地阐明桉树人工林生态系统水文过程、不同水体转化关系和桉树水分利用效率等。系统归纳了碳氢氧同位素在桉树人工林生态系统水循环过程(包括大气降水、林冠穿透水、地表水、土壤水、植物水、地下水及蒸发水等)和植物水分利用效率中的应用研究进展,指出了当前研究中存在的不足,展望了其未来研究和应用前景。研究结果可为我国桉树人工林可持续经营理念下的水资源优化管理提供科学依据。

Sedimentation Geochemistry and Environmental Changes during the Late Pleistocene of Paleolake Qarhan in the Qaidam Basin

On the basis of the analyses of TOC, CaCO3, δ13Corg, δ18O, and δ13C of the shell bar section in the Qaidam basin, and compared with grain size data, the environmental change history of the high water level of paleolake Qarhan was reconstructed and it could be divided into five stages. From 39.7 to 35.8 kaBP was the development period of high paleolake level. From 35.8 to 33.6 kaBP and 33.6 to 27.2 kaBP, TOC and CaCO3 contents and δ18O values were high, whereas, δ13Corg values and median size content were low, reflecting a warm-humid climate and high lake level. During 27.2-22.3 kaBP and 22.3-17.5 kaBP, both temperature and the lake level were lower than those in the previous stages, but the climate was still warmer and more humid than that of today. The lake level decreased between 32.4 and 32.2 kaBP, 30.4 and 29.8 kaBP, and 28.4 and 27.2 kaBP. Generally, the climate was warm and humid in Qaidam basin and the high lake level sustained between 39.7 and 17.5 kaBP. The lake retreated abruptly at 17.5 kaBP, with a very strong increase in evaporation, which resulted in salt formation and the extinction of Corbicula.

Understanding Miocene Climate Evolution in Northeastern Tibet: Stable Carbon and Oxygen Isotope Records from the Western Tianshui Basin, China

To investigate climate evolution during the Miocene, especially during the Middle Mio- cene climate transition on the northeastern Tibetan Plateau, stable oxygen and carbon isotopes of car- bonates from a 288-m-thick lacustrine-fluvial sediment sequence covering the period from 17.1 to 6.1 Ma from Tianshui Basin, China, were analyzed. The relatively low stable oxygen isotope values indicate the prevalence of wet climate conditions during the period of 17.1-13.6 Ma, an interval corresponding to the well-known Middle Miocene Climate Optimum. The interval between 13.6 and 11.0 Ma （i.e., the late Middle Miocene） is marked by a progressive increase in the δ18O values, indicative of a decrease in precipitation, probably linked to the expansion of the East Antarctic Ice Sheet and global cooling since about 14 Ma. The climate in the study area continued to get drier as shown by the enrichment of the heavy oxygen isotope from 11 Ma. We attribute these stepwise climatic changes as revealed by our car- bonate δ18Orecord from the northeastern Tibetan Plateau to the sustained global cooling that may have reduced moist transport to Central Asia, which in turn led to a permanent aridification.

Application and verification of simultaneous determination of cellulose δ^(13)C and δ^(18)O in Picea shrenkiana tree rings from northwestern China using the high-temperature pyrolysis method

Stable isotopes in tree-ring cellulose provide important data in ecological,archaeological,and paleoenvironmental researches,thereby,the demand for stable isotope analyses is increasing rapidly.Simultaneous measurement of cellulose δC and δO values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement.In this study,we compared the δC and δO values of tree-ringα-cellulose from Tianshan spruce(Picea schrenkiana)in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements,using the combustion method(at1050°C)and the high-temperature pyrolysis method(at 1350°C and 1400°C).We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods(separate and simultaneous)produced similar δC values.The two-point calibrated method improved the results(range and variation)of δC and δO values.The mean values,standard deviations,and trends of the tree-ring δC obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration.The simultaneously measured δO from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature.However,they showed similar variations in the time series.The climate responses inferred from simultaneously and separately measured δC and δO did not differ between the two methods.The tree-ring δC and δO values were negatively correlated with standardized precipitation evapotranspiration index from May to August.In addition,the δO was significantly correlated with temperature(positive),precipitation(negative),and relative humidity(negative)from May to August.The tree-ring δC and δO values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series.The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement.These results are consistent with the previous studies at humid sites,suggesting that the simultaneous determination of δC and δO in tree-ringα-cellulose can be used in wide regions.

Tracing the Methane Events by Stable Carbon Isotopes of Benthic Foraminifera at Glacial Periods in the Andaman Sea

Stable isotopes of carbon and oxygen variations in foraminiferal shells have been widely used in paleo-environment studies.However,studies about the shells of benthic foraminifera in methanehydrate-bearing sediments as reliable geochemical proxies to reconstruct the potential methane release events in the geologic past are rare.In this study,we present the stable carbon and oxygen isotopes of fossil benthic foraminifera including one epifaunal species(Cibicidoides wuellerstorfi)and two infaunal species(Bulimina mexicana and Uvigerina peregrina)from the Site U1447 of IODP 353 Expedition to trace methane events in the Andaman Sea,where one of the thickest and deepest gas hydrate stability zones was discovered.Theδ^(13)C values of benthic foraminifera show that there are eight distinct intervals with negative values in the last~10 Myr,interpreted as a record of long-term fluctuations in methane emission.Six of these methane events occurred during the glacial sea-level lowstands in the last~1.1 Myr.We,therefore,infer that the trigger mechanism for these events might be the hydrate destabilization caused by sea level fall.The methane events that occurred at~2.11 and~5.93 Ma are more likely related to the sudden changes in sedimentation,either slide events or marked variations in sedimentation rate.

The Sedimentary Features and Significances of Dripwater and Modern Speleothems in Xueyu Cave,Chongqing,China

Based on the continuous monthly monitoring works of the dripwater and modem speleothems in Xueyu Cave,we measured a high deposit rate of the secondary sediments.Impressively,the mean deposit rate of calcite is 5.33 mg/day,but the variation amplitude is significant during the year.Besides,the monthly variation does not coincide with the geochemical characteristics of the relevant dripwater, and a preliminary test of some hydrophilic and

Carbon cycle variability in tropical Atlantic across two Early Eocene hyperthermals

Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth’s ecosystem due to massive additions of isotopically light carbon to the ocean-atmosphere system.They serve as ancient analogs for understanding how the oceanic carbonate system and surface-ocean ecosystem would respond to ongoing and future climate change.Here,we present a continuous carbonate record across the Eocene Thermal Maximum 2(ETM2 or H1,ca.54.1 Ma)and H2(ca.54 Ma)events from an expanded section at Ocean Drilling Program Site 1258 in tropical Atlantic.The abundant calcareous nannofossils and moderate carbonate content throughout the studied interval suggest this record was deposited above the calcite compensation depth(CCD),but below the lysocline and under the influence of terrestrial dilution.An Earth system model cGENIE is used to simulate the carbon cycle dynamics across the ETM2 and H2 to offer insights on the mechanism of the rapid warming and subsequent recovery in climate and ecosystem.The model suggests moderate changes in ocean pH(0.1–0.2 unit)for the two scenarios,biogenic methane from a rechargeable methane capacitor and organic matter oxidation from thawing of the permafrost.These pH changes are consistent with a recent independent pH estimate across the ETM2 using boron isotopes.The carbon emission flux during the ETM2 is at least an order of magnitude smaller than that during the Paleocene–Eocene Thermal Maximum(PETM)(0.015–0.05 Pg C yr^(-1)vs.0.3–1.7 Pg C yr^(-1)).The comparable pre-and post-event carbonate contents suggest the lysocline did not over deepen following the ETM2 at this tropical Atlantic site,indicating spatial heterogeneity in the carbonate system due to strong dilution influence from terrestrial weathering and riverine discharge at Site 1258.

湘西奥陶系红色碳酸盐岩碳、氧同位素组成特征及古环境意义

红色碳酸盐岩是华南奥陶系的一种具有紫红—砖红色调的代表性沉积岩,其中可能蕴含特殊的古环境信息。湖南湘西三百洞地区具有一条出露良好、厚层为主的红色碳酸盐岩剖面,主要发育于大湾组和牯牛潭组内,文章对该段地层采集了355件碳、氧同位素和Mn、Sr元素分析样品,以及10件牙形刺化石样品进行研究。根据牙形刺样品约束,大湾组底界可能大致相当于弗洛阶顶界,大湾组和牯牛潭组界线在达瑞威尔阶中下部,牯牛潭组顶界大致相当于达瑞威尔阶顶界。据显微薄片鉴定、δ^(13)C-δ^(18)O相关性分析和Mn-Sr元素评估,推断样品受到成岩作用影响不大。355件同位素测试样品显示三百洞剖面的δ^(13)C和δ^(18)O均为低幅高频振荡,δ^(13)C在-0.38‰~1.67‰之间,δ^(18)O在-9.34‰~-7.21‰之间,其中可与全球对比的同位素事件有大坪阶底部碳同位素负漂事件(BDNICE)和达瑞威尔阶中部碳同位素漂移事件(MDICE),可以间接对比的有达瑞威尔阶下部碳同位素负漂事件(LDNICE),此外还有2次前人未命名的具有潜在对比价值的漂移。总体来看,冈瓦纳大陆北缘沿赤道由东向西具有δ^(13)C波动幅度逐渐增强的趋势,华南的波动幅度普遍偏小,可能由海水循环过程中不同块体的底层海水分层差异造成。另外基于δ^(13)C、δ^(18)O的古盐度计算,红色碳酸盐岩应属于盐度中等到较高的海相碳酸盐岩,并且剖面自下到上盐度增高,大湾组底部可能存在一次氧化事件。结合剖面岩石组成、颜色、古生物丰度以及区域古地理研究,认为红色碳酸盐岩可能是暂时性相对海平面下降叠加氧化事件的产物。

末次冰盛期山东半岛高分辨率气候环境变化

末次冰盛期是末次冰期以来地球表面最寒冷的时期。通过对山东半岛地下画廊溶洞石笋DXHL3进行高精度230Th定年和高分辨率氧-碳稳定同位素分析,重建了该地区23.2~18.8 ka时期高分辨率夏季风气候环境变化历史。结果发现,山东半岛末次冰盛期夏季风气候存在显著的千年尺度波动;REDFIT分析表明,氧、碳同位素值均存在显著的2.2 ka周期。末次冰盛期山东半岛总体处于冷干状态,具体又可细分为4个阶段,即冷干(23.2~22 ka)-相对暖湿(22~21 ka)-冷干(21~19 ka)-相对暖湿(19~18.8 ka)。石笋DXHL3的δ18O变化趋势总体上与亚洲季风区内其他石笋记录相似,也与西太平洋暖池婆罗洲的石笋记录类似。这反映了末次冰盛期西太平洋暖池气候环境变化可能对山东半岛的夏季风气候变化产生了重要影响,推测西太平洋暖池表层海水温度变化引起的大气环流和黑潮的变化,是将气候环境变化信号从低纬地区传递到中高纬地区的纽带。

矿质元素与稳定同位素结合的葡萄酒产地鉴别研究

我国西北产地具有生产优质葡萄酒的能力,但仍存在风土特征不明和监管技术缺乏等问题,影响了产业发展。本研究利用电感耦合等离子质谱(ICP-MS)、液相色谱同位素质谱仪(LC-IRMS)及同位素质谱仪(EQ-IRMS)分别对新疆、河西走廊和贺兰山东麓葡萄酒样品中的24种矿质元素及3种单体稳定同位素进行测定;并利用皮尔逊(Pearson)相关性分析和单因素方差分析(one-way ANOVA)明确3个产地的指纹图谱,并结合多元分析技术评估地理起源。结果显示,在不同产地9种元素和葡萄酒中水的氧同位素具有显著性差异,各元素间相关性也显示出一定差异;葡萄酒中水的氧稳定同位素比的平均值为3.06‰,甘油碳、乙醇碳稳定同位素比的平均值分别为-31.78‰和-26.53‰。在有监督学习的逐步线性判别分析中单独使用同位素的分类正确率较低,结合元素数据,分类正确率可达95.2%,交叉验证分类结果正确率可达88.7%。综上所述,矿质元素与稳定同位素构成的多元指纹图谱是一种适合西北地区葡萄酒的有效评估方法。

Carbon and Oxygen Isotope Stratigraphy of the Oxfordian Carbonate Rocks in Amu Darya Basin

Based on the detailed research on petrologic and geochemical characteristics of deposi- tion and diagenesis of Oxfordian carbonate rocks in Amu Darya Basin, Turkmenistan, carbon and oxygen isotopes were analyzed. The results show that the paleoenvironmental evolution reflected by the samples with well-preserved original carbon isotopes coincides with the carbon-isotope stratigraphic curve and is almost consistent with the global sea-level curve, the Mid-Oxfordian wide transgression, and the positive carbon-isotope excursion event. The Mid-Oxfordian continuing transgression not only laid the foundation for the development of the Oxfordian reef and shoal reservoirs in Amu Darya Basin but also provided an example for the Oxfordian global transgression and the resulting development of reefs and banks and high-speed organic carbon burial events. The response of oxygen isotopes in diagenetic environment showed that micrite limestones and granular limestones underwent weak diagenetic alteration, and the samples largely retained the original seawater features. Dolomitization and the precipitation of hydrothermal calcites filling solution vugs and fractures before hydrocarbon accumulation occurred in a closed diagenetic environment where the main controlling factor is the temperature, and the diagenetic fluids were from the deep hot brine. The chalkification of the lime- stones after hydrocarbon accumulation occurred in the oilfield water systems.

Stable isotope and trace element record of a stalagmite in Heshang Cave,Hubei and its palaeoclimatic significance

Through a combined analysis of sedimentary characteristics, C and O isotopes, Mg and Sr trace elements of a stalagmite from Heshang Cave, Hubei, with uranium-series dating, alaeo-palaeoclimatic and palaeoenvironmental information from 19.0ka to 6.9ka in the Hubei area is obtained. The Average resolution is 17a, and the local resolution is 7a. The following results are obtained: (1) from 19.0-16.6 kaBP: C and O isotope is lighter, the climate is cold and wet;(2) 16.6-11.1 kaBP: C, O isotope is a little heavy, temperature rises, rainfall is inclined to be little;(3) 11.1-10.3 kaBP: an excursion during dry and hot period responds to Younger Dryas Event;(4) 10.3-6.9 kaBP: C, O Isotope is lighter, but Mg/Sr value is bigger, which shows temperature is continuing rising and rainfall is greater. These reflect the variation tends from wet-cold climate, to dry-hot climate, and to wet-warm climate in history, and some climatic variation trends of thousand years and hundred years cycle

Diets, eco-environments and seasonal variations recorded in the oxygen and carbon isotopic compositions of mammal tooth enamel from the Shunshanji site,Sihong County,Jiangsu Province,China

The carbon and oxygen isotopic compositions of the tooth enamel of mammals,including deer,wild pigs,buffaloes and domesticated pigs from the Shunshanji site,Sihong County,Jiangsu Province,China,were analyzed to reconstruct the mammals’ecoenvironments and diets,and to evaluate seasonal variations in the study area.Carbon isotopic compositions of buck samples revealed that the deer ate completely C3 plants and the environments they inhabited were relatively open and that wild pigs ate primarily C3 plants.Oxygen isotopic compositions indicated that the body sources of these two mammals were different,i.e.the deer and pigs lived in different niches within a relatively similar ecosystem.Modern domesticated pigs were isotopically more positive than the ancient wild pigs in carbon 13C values,suggesting the former ingested more C3 plants relative to the latter.Although the 18O data showed modern domesticated and ancient pigs had similar oxygen isotope compositions,their water sources were different.The carbon and oxygen isotopic patterns of premolar microsamples of ancient and modern buffaloes indicated that the plants ingested by the ancient buffalo varied with seasonal shifts,but plants ingested by the modern buffalo were relatively constant.The eco-environment of the modern buffalo was more open,warmer and drier than eco-environment of the ancient buffalo,which may be the result of the deforestation and other human activities.Ancient and modern seasonal changes were clearly recorded in the isotopic patterns and the seasonal variation amplitudes of the ancient and modern eco-environments were similar.

稳定同位素技术在植物水分利用研究中的应用

近20a稳定同位素技术在植物生态学研究中的应用得到了长足发展,使得对植物与水分关系也有了更深一步的了解。介绍稳定同位素性碳、氢、氧同位素在研究植物水分关系中的应用及进展,以期能为国内植物水分利用研究提供参考。由于植物根系从土壤中吸收水分时并不发生同位素分馏,对木质部水分同位素分析有助于对植物利用水分来源,生态系统中植物对水分的竞争和利用策略的研究,更好地了解生态系统结构与功能。稳定碳同位素作为植物水分利用效率的一个间接指标,在不同水分梯度环境中,及植物不同代谢产物与水分关系中有着广泛的应用。同位素在土壤-植被-大气连续体水分中的应用,有助于了解生态系统的水分平衡。随着稳定同位素方法的使用,植物与水分关系的研究将取得更大的进展。

晚更新世东亚季风气候不稳定性的洞穴石笋同位素证据

据南京汤山葫芦洞石笋的23个热电离质谱测年结果和分辨率达100～200 a的氧、碳稳定同位素测试数据,讨论了75～35 ka BP期间东亚季风气候的高频振荡特征。石笋氧同位素值的波动范围介于-9.165‰～-5.456‰之间,相邻峰谷的变幅可达2‰～3‰,由其构成的16个气候不稳定性事件与格陵兰冰心δ^(18)O记录中IS8～IS20和北大西洋冰漂碎屑事件H4～H6有良好的对比关系,揭示了东亚季风气候变化与高纬极地大气温度变化存在着动力机制上的联系。石笋碳同位素记录呈现类似于δ^(18)O记录的高频振荡形式,反映了洞穴上覆植被类型对气候变化的快速响应。石笋稳定同位素曲线上72 ka BP左右的快速降温事件与印度尼西亚 Toba火山喷发事件基本一致,有可能说明晚更新世全球气候事件的发生并非单一源于北大西洋深层水体的变化。

塔里木盆地寒武纪—奥陶纪优质烃源岩沉积与古环境变化的关系:碳氧同位素新证据

对塔里木盆地东部塔东2井上震旦统和寒武系—奥陶系样品进行TOC和碳、氧同位素及微量元素分析,发现该井稳定碳、氧同位素值在寒武系—中奥陶统发生明显变化,该层还赋存高有机质丰度烃源岩,其TOC值的高低可反映当时的生物产率和埋藏率。碳和氧同位素值在寒武系/上震旦统分界处正向漂移,说明正好在进入寒武纪前气候明显变冷,海平面下降。接着,下寒武统底部以碳和氧同位素值的快速负向漂移为标志,表明古气候迅速变暖和海平面大幅度上升,烃源岩TOC值也达到全井柱最高值。古气候显著波动、海平面最高及其频繁变化和沉积物高TOC是早寒武世的显著特征;而晚寒武世—早奥陶世,同位素正向漂移,暗示海平面下降,沉积物TOC也随之下降并降至最低;到了早奥陶世末,即早、中奥陶世的过渡时期,同位素又开始负向漂移,TOC又开始升高;中奥陶世,同位素强烈负向漂移,TOC又升至新高。稳定碳、氧同位素值的变化及其所指示的古气候与海平面变化,以及与TOC的响应关系,指示冰期、冰后期之交,古气候迅速变暖和海平面大幅度上升有利于烃源岩发育;同时暗示,δ13C、δ18O与生烃母质生物的有机生产率、有机埋藏率之间存在某种内在联系。即高TOC含量反映高的有机生产率和高的有机埋藏率;而与其同步反方向变化的δ13C、δ18O则暗示海平面较高,沉积环境属远陆海域,表层水中生烃母质生物的光合作用很强。而有机质的高产率和高埋藏率,导致海水中δ12C和δ16O被大量地固定在沉积物中。这样,就使海水中相对富集13C和18O重同位素而使海水变“重”;而这种“重”海水,又导致了同时期浅水区碳酸盐沉积物的δ13C和δ18O值明显增高。

重庆新崖洞XY6石笋4.5ka以来高分辨率δ^(18)O、δ^(13)C记录的气候变化

对采自重庆市东北部奉节县新崖洞XY 6石笋进行ICP-M S-U系测年表明,该石笋生长时期为4.5~0.25 ka。石笋在4.5~4.1ka、3.2~2.5ka、1.85~1.5ka期间相对偏负的1δ8O和1δ3C值记录了3个相对湿润的时期;其中以4.5~4.1ka时期δ18O最偏负,之后突然偏重,表示了中全新世气候适宜期的快速结束;之后东亚夏季风在波动中逐步减弱。该石笋没有明显记录到发生在1.1~0.9ka的“中世纪暖期”事件。在4.1~3.2ka、2.5~1.85ka、0.5~0.25ka期间相对偏正的1δ8O和1δ3C值代表3个相对冷干的时期,0.5~0.25ka是欧洲小冰期事件在本地区的表现。该地区气候在1.5~0.5ka相对平稳,从前半段的相对暖湿过渡到后半段的相对冷干。XY 6石笋1δ3C与1δ8O具有非常一致的变化趋势,可能暗示了该地区为“暖湿、冷干”的水热配套模式,也表明本地区植被对气候变化的响应是快速的,并没有明显的滞后期。δ13C与δ18O变化峰值的差异表明,在东亚季风区植被变化不仅取决于夏季降水的多寡,可能更主要的是受制于有效湿度的变化。

新疆阿尔泰蒙库铁矿床的成矿流体及成矿作用

蒙库大型铁矿床赋存于上志留统—下泥盆统康布铁堡组变质火山-沉积岩系中,容矿岩石为石榴子石矽卡岩、变粒岩、浅粒岩和大理岩。矿体总体顺层分布,空间上与矽卡岩密切相关。研究表明,矽卡岩期石榴子石以发育玻璃质熔融包裹体、流体熔融包裹体和流体包裹体为特征,晚期矽卡岩阶段矿物中发育液相包裹体,变质期矿物中主要发育液相包裹体和含子矿物包裹体。矽卡岩期熔融包裹体的均一温度为1100℃,早期矽卡岩阶段流体包裹体均一温度变化于193～499℃,在450℃、350℃和230℃出现峰值。中期矽卡岩阶段均一温度变化于236～550℃,峰值为350℃。区域变质期均一温度介于132～513℃,在350℃、230℃和190℃出现峰值。流体包裹体的盐度w(NaCleq)介于1.23%～60.31%,流体密度变化于0.60～1.16g/cm3。石榴子石、石英和方解石的δ18OSMOW变化于0.2‰～8.4‰,δ18OH2O介于-5.1‰～5.33‰,δD为-127‰～-81‰,表明矽卡岩期成矿流体主要是岩浆水,混合少量大气降水;变质期流体主要为大气降水,为混合变质水。方解石δ13CPDB变化于-6.1‰～-2.3‰,表明流体中碳来自深部或地幔。成矿时代为早泥盆世早期(略晚于404～400Ma),成矿作用与矽卡岩的退化变质作用有关。