珠江流域西江、北江河流溶解无机碳及其稳定同位素组成特征

 为了探讨珠江流域西江、北江河流溶解无机碳（DIC）及其稳定同位素组成（δ¹³C_DIC）特征,分别于2007年春季和夏季对流域低水期、高水期的西、北江及思贤滘河道DIC及其稳定同位素组成进行了实测调查。结合实测河道水体理化参数,采用碳的稳定同位素示踪技术和多参数相关分析法,对西、北江流域及其滘口的河流DIC组成、性质及其碳源汇机制进行了分析。结果表明,西、北江的河流DIC的组成、性质都有明显的差异且存在显著的季节变化。春季,西、北江的河道DIC浓度及其δ¹³C_DIC分别为1 942 μmol/L、1 637 μmol/L和-11.75‰、-12.44 ‰;而夏季,西、北江的河道DIC浓度及其δ¹³C_DIC分别为1 986 μmol/L、1 383 μmol/L和-13.03‰、-12.77‰。河道DIC浓度及其δ¹³C_DIC的这种差异反映出西、北江流域结构特性对DIC侵蚀、输移的显著影响。夏季汛期,流域的高温多雨环境致使大量有机质汇入河道、强烈分解、释放大量轻碳,使得西、北江河道δ¹³C_DIC都低于春季;由于汛期高温和径流的共同作用使得北江DIC远远小于春季,而西江DIC却略高于春季。思贤滘水道的DIC浓度及其δ¹³C_DIC受西、北江来水的控制发生季节变化。     

轮古西地区奥陶系碳酸盐岩古岩溶储层碳、氧同位素地球化学特征

中—下奥陶统鹰山组碳酸盐岩古岩溶储层是塔里木盆地轮古西地区的主要油气产层 .为了弄清储层的成因类型、储层古岩溶过程中的流体性质和古水文条件 ,为预测和评价此类储层提供有关的地球化学信息 ,讨论了储层形成过程中记录的碳、氧稳定同位素特征 .结果表明 :轮古西地区奥陶系鹰山组碳酸盐岩古岩溶储层中的δ13C和δ18O值的变化范围较大 ,δ13C值为 -0 .70‰～ -6.5 0‰ ,平均值 -1 .76‰ ;δ18O值为 -3 .75‰～ -1 7.1 0‰ ,平均值 -9.42‰ .碳酸盐岩基质、冲积岩和方解石胶结物的δ13C和δ18O分布具有一定的差异 .三类样品的δ18O值均具有明显偏负特征 ,表明在碳酸盐岩成岩过程中受到大气成因的淡水影响 ,反映了当时的风化壳岩溶成岩环境 .冲积岩样品的δ13C值的偏负程度较高 ,其物源可能来自石炭—二叠系地层     

鄂尔多斯盆地宜川—句邑地区长8储集层碳酸盐胶结物特征

鄂尔多斯盆地廷长组储层质量严重地受碳酸盐胶结物影响.通过对宜川—句邑地区长8储集层薄片、碳酸盐胶结物碳氧同位素及流体包裹体测试分析,表明碳酸盐胶结物主要是铁方解石(含铁方解石),在薄层砂岩中和厚层砂岩顶底与泥岩紧密毗邻的区域含量较高,以中细晶及粗—巨晶颗粒充填孔隙.碳酸盐胶结物δ13CPDB值为-5.56‰～0.22‰...     

Research progress in studies on the coalbed gas geochemistry

The current situation of geochemical studies on coalbed gas is reviewed in this paper. Generally, coalbed gas is compositionally dominated by methane with δ¹³C₁ values ranging approximately from -80‰ to -10‰. However, few isotopic studies have been carried out on other components of coalbed gas except for hydrogen and carbon dioxide, whose δD_CH4 values available for utilization vary from -333‰ to -117‰, and δ¹³C_CO2 values from -29.4‰ to +18.6‰. Two major types of coalbed gas, thermogenic gas and secondary biogenic gas, have been identified, and there are also some other classification criteria. Compared with conventional natural gases, coalbed gas has a wide distribution range of δ¹³C₁ and δ¹³C_CO2 values, especially possessing some extremely heavy values. Current problems that remain unsolved in the coalbed gas geochemistry include the variation mechanism, controlling factors and application of carbon and hydrogen isotopes of methane, the relation between the values of δ¹³C₁ and Ro, the systematic classification scheme and criterion of genetic types, and the application of the coalbed gas geochemistry in evaluating target districts of the coalbed gas exploration.     

Kinetic modeling the effects of primary migration, diffusion and waterwashing on Upper Paleozoic coal-derived gas at the center of Ordos Basin

Gold reactor pyrolysis system is used to model the gas formation from the Upper Paleozoic coal measures and the results show coal-derived gas characterized with δ13C1 of-33.46‰, δ13C2 of-23.1‰, dryness(C1/C1-4) 85.6%. And then, effects of the post-genetic processes on coal- derived gas are analyzed in turn: (i) About 27% coal-derived gases constituted with more methane are calculated to be lost during diffusion. The residual in reservoir are characterized with almost the same compositions as the original, which suggests faint influence by diffusion (the residual, δ13C1 of -32.78‰, δ13C2 of-23.1‰, C1/C1-4 83%); (ii) Water washing made about 8% coal-formed gases lost and their components and stable carbon isotopes are stable; (iii) In the final, it is speculated that primary migration makes much more wet gas (C2-4) leave in coal measures. The variance of gas dryness induced by this factor is estimated to be about 10%.     

廉州湾红树林大型底栖动物食物来源研究

【目的】了解可能性食物源对红树林大型底栖动物的贡献率。【方法】利用碳氮稳定同位素技术,对广西廉州湾红树林大型底栖动物及可能性食物源的碳、氮同位素比值(δ~(13) C值、δ~(15) N值)进行分析,并通过贝叶斯稳定同位素混合模型,估算不同食物源对大型底栖动物的贡献率。【结果】大型底栖动物的δ~(13) C值为-23.37‰~-18.09‰,δ~(15) N值为6.59‰~17.00‰,δ~(13) C值、δ~(15) N值的变化范围较大,表明大型底栖动物食物来源较为复杂多样。7种可能性食物源的δ~(13) C值为-29.09‰~-21.53‰,δ~(15) N值为6.85‰~15.67‰,其中红树植物的δ~(13) C值最为贫化。大型底栖动物的营养级别均小于3,表明它们基本属于初级消费者。SIAR混合模型计算结果显示,颗粒有机物(POM)对大型底栖动物有较高的贡献率,其次为表层沉积物(SOM),大型藻类、附生植物的贡献率较低,红树植物叶片、落叶、树皮对大型底栖动物的贡献率最低。【结论】POM、SOM是广西廉州湾红树林大型底栖动物重要的食物源,红树植物不是大型底栖动物碳的主要来源。     

The specific carbon isotopic compositions of branched and cyclic hydrocarbons from Fushun oil shale

Various branched and cyclic hydrocarbons are isolated from the Fushun oil shale and their carbon isotopes are determined. The analytical results show that the branched and cyclic hydrocarbons are fully separated from n-alkanes by 5 A molecular-sieve adduction using long time and cold solvent. The branched and cyclic hydrocarbon fraction obtained by this method is able to satisfy the analytic requests of GC-IRMS. The carbon isotopic compositions of these branched and cyclic hydrocarbons obtained from the sample indicate that they are derived from photoautotrophic algae, chemoautotrophic bacteria (-33.4‰— -39.0‰) and methanotrophic bacteria (-38.4‰— -46.3‰). However the long-chain 2-methyl-branched alkanes indicate that their carbon isotopic compositions reflect biological origin from higher plants. The carbon isotopic composition of C30 4-methyl sterane (-22.1‰) is the heaviest in all studied steranes, showing that the carbon source or growth condition for its precursor, dinoflageilate, may be different from that of regular steranes. The variation trend of δ^13C ValUes between isomers of hopanes shows that ^13C-enriched precursors take precedence in process of their epimerization. Methanotrophic hopanes presented reveal the processes of strong transformation of organic matter and cycling of organic carbon in the water column and early diagenesis of oil shale.     

Carbon and oxygen isotopes analyses for the Sinian carbonates in the Helan Mountain, North China

We conducted detailed studies of the Sinian carbonates from the Helan Mountain, Ningxia by both field investigation and laboratory analyses of carbon and oxygen isotopes. The carbon isotopic compositions of the Sinian Zhengmuguan Formation shows variations with regularity in the five studied sections, the δ ¹³C values all gradually decrease from bottom to top, with a total range from ?4.51‰ to 0.11‰, and the biggest negative excursion reaches up to ?6.88‰. In addition, abundant macro-body fossils were also found from the Tuerkeng Formation in this study, similar to those found from the Dengying Formation in the South China Block. This observation firmly constrained the age for the Zhengmuguan and Tuerkeng formations to the Sinian period. Here we interpreted that the Zhengmuguan Formation formed during a glacial period when the extremely cold climate substantially decreased the amount of burial of organic matter in the ocean and thus led to the general negative δ ¹³C excursion. The increasing δ ¹³C values in the Tuerkeng Formation dolomites imply the ending of the glacial period in the Zhengmuguan epoch, biological recovery and increase of organic matter burial in the ocean occurred during this period. Comparing our obtained carbon and oxygen isotopes of the Zhengmuguan and Tuerkeng formations with those of coeval carbonate successions from other places all over the world, the Zhengmuguang-aged glacial deposits might be deposited after the Gaskiers glaciation. This study provides important information for paleo-ocean, paleogeographic and biological evolution in the North China Block during the Ediacaran period and adds new carbon and oxygen isotopes data for the global Sinian carbon-oxygen isotopes dataset.     

柴北缘冷湖七号地区碳酸盐胶结物特征及其意义

碳酸盐胶结物是碎屑岩储层中最常见的胶结物类型,其形成环境、物质来源、反映的成岩温度对储层研究具有重要意义。通过对柴北缘冷湖七号下干柴沟组砂岩碳酸盐胶结物进行岩石学、矿物学和地球化学分析,研究区下干柴沟组砂岩碳酸盐胶结物包含方解石、含铁方解石、铁方解石和白云石等4种类型。碳同位素（δ¹³C_PDB）和氧同位素（δ¹⁸O_PDB）值分别为8.81‰~3.51‰和8.77‰~17.36‰,平均值分别为5.33‰及13.50‰;利用碳同位素和氧同位素计算出古盐度值和古温度值分别为113.61~102.85和63.03~123.06℃,平均值分别为109.66及94.47℃。反映出研究区下干柴沟组所处成岩阶段为早成岩阶段B期-中成岩阶段A期,形成过程受到有机质脱羧基作用影响,成岩环境偏酸性,成岩流体来自碎屑的析出水和大气淋滤淡水。储层物性除了受成岩环境和温度的影响外,与碳酸盐胶结物含量具有明显的负相关关系,随着碳酸盐胶结物含量的增加,储层的孔隙度和渗透率降低。     

碳酸盐岩碳、氧同位素分析激光微取样技术

碳酸盐岩碳、氧同位素分析激光微取样技术是利用高能聚焦激光束与碳酸盐岩样品作用,热分解产生CO₂气体,经真空提纯净化后送质谱仪分析测定其C、O同位素值。其空间分辨率优于20μm,能有效地对碳酸盐岩各细微组分结构分别取样,以满足同位素地质学研究的需要。经标样测定,δ¹³C和δ¹⁸O的最好分析精度可达±0.22‰(σ),与常规磷酸分解法分析精度相;δ¹³C无明显分馏现象,δ¹⁸O分馏明显,但对同种矿物是一个常量(方解石偏负1.72‰;白云石偏负1.59‰)易于校正。激光微取样主要应用于碳酸盐储集岩样品碳、氧同位素分析,能较好地解释油气储层孔隙演化和成岩过程。     

Petroleum-contaminated soil extent recorded by δ15N and δ13C of plants and soils

Petroleum contamination in terrestrial environments caused by industrial activities is a significant problem that has received considerable attention. Carbon and nitrogen isotopic compositions (δ13C and δ15N) effectively describe the behavior of plants and soils under petroleum contamination stress. To better understand plant and soil responses to petroleum-contaminated soil, δ13C and δ15N values of the plants (Trifolium repens, Leguminosae with C₃ photosynthesis pathway, and Agropyron cristatum with C₄ photosynthesis pathway) and the soil samples under one-month exposure to different extents of petroleum contamination were measured. The results showed that petroleum contamination in the soil induced the soil δ15N values to increase and δ13C values to decrease; from 1.9‰ to 3.2‰ and from ?23.6‰ to ?26.8‰, respectively. However, the δ13C values of Agropyron cristatum decreased from ?29.8‰ to ?31.6‰, and the δ13C values of Trifolium repens remained relatively stable from ?12.6‰ to ?13.1‰, indicating that they have different coping strategies under petroleum-contaminated soil conditions. Moreover, the δ15N values of Trifolium repens decreased from 5.6‰ to 0.8‰ near the air δ15N values under petroleum-contaminated soil, which implies that their nitrogen fixation system works to reduce soil petroleum stress. The δ13C and δ15N values of Agropyron cristatum and Trifolium repens reflect changes in the metabolic system when they confront stressful environments. Therefore, stable isotopic compositions are useful proxies for monitoring petroleum-contaminated soil and evaluating the response of plants to petroleum contamination stress.     

Oxygen isotope geochemistry of phosphorite and dolomite and palaeo-ocean temperature estimation: A case study from the Neoproterozoic Doushantuo Formation, Guizhou Province,South China

The Neoproterozoic Doushantuo Formation at Weng'an in Guizhou Province of South China consists of phosphorites and dolomites.Three types of samples are recongnized for the phosphate-bearing rocks.In Type I samples, interstitial phosphates occur within the dolomite rocks, whereas in Type III samples, interstitial dolomites occur within the phosphorites; both of them may have diagenetic origin.The Type II samples are interbedded phosphorites and dolomites.Oxygen isotopic compositions of phosphate and coeval carbonate were analyzed.Phosphates of Type I and II samples show similar low δ18Ophos (SMOW) values of 10.9‰～12.1‰ and 10.7‰～12.8‰, respectively, whereas Type III phosphates show higher δ18Ophos (SMOW) values of 13.2‰～15.0‰.Dolomites from Type I and II samples have δ18Ocarb (PDB) and δ13Ccarb (PDB) values of -6.2‰～-3.4‰ and -2.2‰～-0.7‰, respectively, whereas interstitial dolomites from Type III samples show lower δ18Ocarb (PDB) and δ13Ccarb (PDB) values of -12.9‰～-8.6‰ and -4.4‰～-2.6‰.Petrology and oxygen isotope data suggest that diagenetic alteration may have partially affected the studied rocks, but the dolomites from Type I and phosphates from Type III samples represent the most pristine isotopic compositions of primary carbonates and phosphates precipitated from seawater.Calculations of palaeocean temperatures from the most 18O enriched dolomite and phosphate indicate a temperature range of 32.2 ℃ to 34.0 ℃ for the seawater of the Doushantuo Formation period.Ce anomaly also suggests more oxic conditions and possibly shallower water depth in the upper strata of the Doushantuo Formation at Weng'an, Guizhou Province.     

巢湖地区早三叠世晚斯密斯亚期含鱼化石碳酸盐岩结核的地球化学特征及其地质意义

以安徽省巢湖地区下三叠统和龙山组顶部的黑色泥页岩段及其产出的含鱼化石碳酸盐岩结核为研究对象, 综合岩相学、地球化学(主微量元素和碳、氧同位素)和环境矿物学等分析手段, 探讨富有机质页岩中含鱼化石碳酸盐岩结核的形成机制及可能的地质环境指示意义。结核中心三维保存的鱼化石和较高的碳酸盐含量(80%)表明结核形成于早期成岩阶段, 结核内部呈同心环状结构, 从中心至边缘, 碳酸盐矿物含量降低, 硅质碎屑矿物增多并逐渐出现纹层, Fe和S含量升高、δ¹³C值增高、δ¹⁸O值降低和TOC含量逐渐增多等特征均表明结核为同心生长模式。对围岩中草莓状黄铁矿的粒径分析结果表明, 结核形成于硫化还原环境。结核出现在斯密斯亚阶与斯帕斯亚阶界线(SSB)之下1 m处, 与界线层有机碳埋藏增加、碳同位素组成快速正漂移(δ¹³C = -1.3‰~1.9‰)和水体硫化还原事件吻合, 有潜力作为华南地区SSB的辅助识别标志。     

新疆巴里坤湖全新世湖泊沉积物稳定氮同位素的气候与环境意义研究

选择位于西风环流显著影响的新疆巴里坤湖作为研究对象,结合对位于湖心部位的人工开挖剖面的多指标包括有机碳同位素（δ13C）、有机质含量（OM）和碳氮比（C/N）的对比分析和验证,发现该湖泊沉积物的δ15N记录较好地响应了过去9400年以来气候环境的变化,依据其波动变化特征,可以划分出以下阶段:9 400~7 300 cal. a BP期间,δ15N值偏低且剧烈波动,暗示了气候状况较为干旱且不稳定;7 300~5 900 cal. a BP期间,δ15N值偏高,指示气候相对湿润;5 900~3 100 cal. a BP期间,δ15N由相对高值降为低值,指示气候环境由湿转干;3 100~1 100 cal. a BP期间,δ15N总体呈现相对高值,但后期呈下降趋势,指示了此阶段中气候特征由相对湿润转向干旱;但在1100~0 cal. a BP期间偏高的δ15N值,则可能受到了增强的人类活动的影响．本研究表明,巴里坤湖沉积物δ15N记录对于恢复研究区全新世气候与环境变化的特征与历史等方面具有较好的应用潜力和前景．     

扰动KdV方程解的先验估计

对于带微扰的KdV方程u_t+6uu_x+u_xx=εR(u),(ε＞0),在初值u₀(x)∈C∞(-∞,+∞),当|x|→∞时指数衰减的条件下,分别构造出带两种不同扰动项的KdV方程的扰动孤立波解满足的能量关系式,并运用能量分析方法对扰动的孤立波解进行先验估计,得到如下结论：(1)R(u)=δ(εt)u, δ(s)∈C［0,+∞),δ(0)=0,时,解在-∞＜x＜+∞,0≤εt≤T内一致有界;(2)R(u)=-Δ(εt)u_xxx,Δ(0)=0,Δ(s)∈C¹［0,+∞), 解在-∞＜x＜+∞,0≤εt≤T,0≤ε≤ε₁内一致有界。     

Climatic changes documented by stable isotopes of sedimentary carbonate in Lake Sugan, northeastern Tibetan Plateau of China, since 2 kaBP

Lake Sugan at the northern edge of the Qaidam Basin was selected as the research object. The temporal sequence of sedimentary cores retrieved from Lake Sugan since 2 kaBP was reconstructed using the ^210Pb, AMS 14C and conventional 14C dating methods. Carbon and oxygen isotopes of carbonate in the fine-grained lake sediments were analysed. Combined with the changes of 8180 values of surface water and air temperature observation data in the study area, it might be thought that the δ^18O value of the carbonate indicates effective moisture, and the changes in δ^13C values are related to annual freeze-up duration of the lake and indirectly indicate air temperature changes in winter half year. From the above, the sequence of climatic changes in the region since 2 kaBP was established. The climatic changes experienced five stages： Warm-dry climate during 0-190 AD： cold-dry climate during 190-580 AD; warm-dry climate during 580-1200 AD （MWP）; cold-wet climate during 1200-1880 AD （LIA）; cold-dry climate during 1880-1950 AD： and climate warming since 1950s. The air temperature changes in winter half year reflected by carbon isotope since 2 kaBP are in good agreement with the historical literature records and other geologic records, which shows that the climate changes recorded by the stable isotopes from Lake Sugan since 2 kaBP are of universal significance.     

Calcium isotope fractionation and its controlling factors over authigenic carbonates in the cold seeps of the northern South China Sea

In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxygen as well as the mineral composition of authigenic carbonates were used to investigate control calcium isotope fractionation. The δ44/40Ca ratios of the southwestern Dongsha area samples ranged from 1.21‰ to 1.52‰ and the ratio of the Baiyun Sag sample was 1.55‰ of the SRM915a isotope standard. X-ray diffraction analysis showed that the carbonate samples consisted of dolomite, calcite and aragonite, with small amounts of high-Mg calcite and siderite. The δ13C values of the carbonates of the southwestern Dongsha area varied between δ49.21‰ and δ16.86‰ of the Vienna PeeDee Belemnite (VPDB) standard and the δ18O values ranged from 2.25‰ to 3.72‰ VPDB. The δ13C value of the Baiyun Sag sample was 2.36‰ VPDB and the δ18O value was 0.44‰ VPDB. The δ13C values of the carbonates of the southwestern Dongsha area revealed there is methane seeping into this area, with a variable contribution of methane-derived carbon. The sampled carbonates covered a range of δ13C values suggesting a dominant methane carbon source for the light samples and mixtures of δ13C values for the heavier samples, with possibly an organic or seawater carbon source. The δ18O values indicated that there is enrichment in 18O, which is related to the larger oxygen isotope fractionation in dolomite compared to calcite. The results of the Baiyun Sag sample exhibited normal seawater carbon and oxygen isotopic values, indicating that this sample is not related to methane seepage but instead to precipitation from seawater. The relatively high δ44/40Ca values indicated either precipitation at comparatively high rates in pore-water regimes with high alkalinity, or precipitation from an evolved heavy fluid with high degrees of Ca consumption (Raleigh type fractionation). The dolomite samples from the Dongsha area revealed a clear correlation between the carbon and calcium isotope composition, indicating a link between the amount and/or rate of carbonate precipitation and methane contribution to the bicarbonate source. The results of the three stable isotope systems, mineralogy and petrography, show that mineral composition, the geochemical environment of authigenic carbonates and carbon source can control the calcium isotope fractionation.     

重庆北碚嘉陵江组第三—第四段碳酸盐岩碳同位素组成对古海水代表性

早三叠世海水的碳同位素组成是近年来地学研究的热点之一,但全球早三叠世碳同位素组成并没有获得统一的认识。上扬子地区早三叠世晚期普遍发育蒸发岩,地表剖面则因表生成岩作用而形成一套夹盐溶角砾岩及次生灰岩的碳酸盐地层,其地球化学信息不同程度地偏离海水,因而样品成岩蚀变性对古海水碳同位素组成的代表性的评估显得十分重要。本文以中、下三叠统界线清楚的重庆北碚剖面为对象,研究了下三叠统嘉陵江组第三、第四段和中三叠统雷口坡组底部样品的元素组成,碳、氧同位素组成及彼此之间的相互关系,选择Mn含量和氧同位素作为条件评价碳酸盐岩的成岩蚀变性及其对海水碳同位素组成的代表性,在此基础上建立了早三叠世晚期海水的碳同位素演化曲线。研究表明:(1)北碚剖面嘉陵江组第三、第四段(嘉三、嘉四段)及雷口坡组底部碳酸盐岩的Mn、Fe含量与碳同位素组成之间具有良好的负相关性,氧同位素组成和碳同位素组成之间则具有良好的正相关性,大量样品具有低δ18 O值、低δ13 C值以及较高Mn、Fe含量的特征,说明其碳同位素组成偏离海水。(2)以δ18 O-7.5‰、方解石的Mn质量分数100×10-6、白云石的Mn质量分数120×10-6为评价条件,北碚剖面嘉三、嘉四段(含雷口坡组底部)的73个样品中有38个需要在建立海水碳同位素曲线时剔除,占全部样品的52%。其中嘉四段需要剔除的样品占嘉四段样品的78%,而嘉三段的该数值为11%,说明作为原始沉积的灰岩段对海水地球化学信息保存较好,而分布盐溶角砾岩及次生灰岩的层位对海水地球化学信息保存很差。(3)氧同位素作为成岩蚀变评价标准比Mn含量更为苛刻,并可基本覆盖Mn含量评价条件,说明对于嘉三—嘉四段这样的石灰岩—白云岩—蒸发岩地层的地表剖面的样品来说,选择氧同位素作为评价条件可较好地对碳同位素的原生性进行控制。(4)白云岩对海水地球化学信息总体上保存较好,与相邻石灰岩相比,白云岩具有更高的δ18 O和δ13 C值,但其原因仍然需要进一步研究,可能与同位素分馏系数的差别以及白云岩形成于盐度更高的流体有关,因而白云岩所代表的海水地球化学信息可能不完全与伴生石灰岩相同。(5)除绿豆岩附近出现了短时间的变化超过4‰的大幅度波动以外,早三叠世晚期海水的碳同位素演化相对平稳,大致在-0.3‰~-1.8‰的范围内波动,呈现一个低幅的"V"字形,显示早三叠世晚期地球生态的恢复与碳循环系统的重建。     

Carbon and sulfur isotopic compositions of basal Datangpo Formation, northeastern Guizhou, South China: implications for depositional environment

Isotopic compositions of Mn-carbonate and organic carbon from the same individual samples and sulfur isotopic compositions of pyrites in the basal Datangpo Formation were analyzed. Highly 34S-enriched pyrites （834Spyrite =31.7-59.4‰） were precipitated in rel- atively occlusive pore water under anoxic condition in sediments, which is consistent with the observation of large and scattered pyrite framboids. The sulfidic deep ocean was not ＂oxidized＂ in the early Datangpo interglacial interval, thus the level of seawater sulfate remained low and marine δ34Ssulphate remained high. Low δ13Ccar （average -7.4‰） and abnormal relationship between δ13Ccar and fractionation （ΔCar-ors） imply that the negative δ13CCar excursion may have resulted from oxidation of part of a large organic carbon reservoir. High Δcar-org （average 25.1‰） implicates high CO2 level in the atmosphere. Small standard deviation （1.0‰） of δ13CCar values indicates the Mn-carbonate was precipitated near the water-sediment interface under dysoxic conditions rather than in occlusive pore water in sediments.     

兰州远郊区春季碳气溶胶的质量浓度特征

 为探讨春季沙尘(暴)期间兰州大学半干旱气候与环境观测站(SACOL)碳气溶胶的变化特征, 2012 年5 月17-26 日于SACOL 站采用石英膜收集PM₁₀样品, 利用DRI-2001A 热/光碳分析仪测量元素碳(EC)和有机碳(OC)的质量浓度。结果显示, 沙尘(暴)是导致OC、EC 质量浓度增大的主要因素。采样期间EC、OC 和总碳(TC)的平均质量浓度分别为2.71、11.26 和13.97 μg/m³。进一步分析显示, 沙尘(暴)期间兰州城区碳气溶胶污染逐渐加重主要受本地源的影响。PM₁₀中OC 和EC 的相关系数达到0.94, 揭示SACOL 站OC、EC 的来源相对一致。OC/EC 的均值为5.05, 表明春季SACOL 站PM₁₀中碳气溶胶存在二次污染。二次有机碳(SOC)的质量浓度为3.37 μg/m³, 为OC 的29.9%。结合考察周边环境, 分析表明SACOL 站春季碳气溶胶的主要来源是直接污染源, 来自周边环境中的燃煤以及机动车尾气排放。对碳气溶胶8 种组分的因子分析结果也表明, 周边环境的燃煤和机动车尾气排放是春季SACOL 站碳气溶胶的主要贡献源。