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1.
The basinal facies of the Lopingian Zechstein Limestone in SW Poland consists of thin (often less than 1 m thick) limestones and/or dolomites, often containing the Kupferschiefer (few tens of centimetres thick) at their base, and local thick (up to 90 m) reefal carbonates. The δ13C curve of these basal Zechstein deposits strongly suggests that even when the Kupferschiefer is lacking, the thin (condensed) sequences record the entire interval of the Zechstein prior to the onset of evaporite deposition, in contrast to the thick reef sequences which lack the characteristic δ13C curve for the lowermost part of the Zechstein. The calcite samples show considerable ranges of δ18O values. If the maximum δ18O values are considered to be the closest to the pristine original ones and if δ18Owater value = 0 is assumed, then the calculated range of palaeotemperatures for the Kupferschiefer and Zechstein Limestone calcite ranges from 19 to 34 °C. The faunal restriction, common dwarf foraminifers and the predominance of lagenids in the foraminiferal assemblage indicate continual dysaerobic conditions and possibly elevated salinity of seawater during deposition of thin basinal Zechstein Limestone deposits. The mixing of shallow and deeper waters in the stratified Zechstein Basin caused by upwelling could result in prolific carbonate precipitation in reefs located at the slope of the marginal carbonate platform of the Zechstein Limestone and in isolated reefs related to palaeohighs within the basin; however, there is no isotopic record of eventual upwelling. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
陆生蜗牛响应气候环境变化敏感,其壳体化石碳氧同位素组成(δ13C和δ18O)具有重建古生态和古大气水文条件的巨大潜力。然而目前针对中国黄土古土壤沉积序列中蜗牛化石碳氧同位素组成开展的古环境古气候重建研究却仍然不足,根源在于对蜗牛壳体δ13C和δ18O指标气候意义的认识仍不明确。文章从现代过程研究着手,综述了目前有关蜗牛壳体δ13C和δ18O气候环境意义的研究进展,并指出各自指标存在受控因子的复杂性和多解性等问题。通过总结这些研究认为:陆生蜗牛壳体δ13C值主要通过反映植物(尤其C3)δ13C值变化来进一步响应当地降水量变化,进而指示环境的干湿程度,但同时需要考虑环境碳酸盐、大气CO2等额外因子对壳体δ13C的影响;壳体δ18O值可以在较大程度上反映大气降水δ18O值变化,但同时需要考虑蒸发作用和温度等因素对壳体δ18O的影响;壳体δ13C和δ18O在作为气候指标时常受区域和蜗牛种属等因素影响。此外,还介绍了目前中国北方黄土地层中蜗牛壳体化石稳定同位素组成重建季风变化的研究进展和近十年来有关蜗牛壳体团簇同位素新方法的研究进展。最后,论文针对壳体δ13C和δ18O指标存在的问题提出可能的解决办法,并对以后蜗牛碳氧同位素古环境研究方向进行展望。
相似文献3.
V. I. Vinogradov 《Lithology and Mineral Resources》2008,43(1):44-57
The carbon isotopic composition of carbonate rocks is widely used for the reconstruction of sedimentation paleoenvironment. Of special interest is the study of the Upper Proterozoic-Cambrian interval—the turning point in the Earth’s geological evolution. Rocks of this age show the widest variations in the carbon isotopic composition of carbonates typically correlated with epochs of global glaciations and change in the CO2 regime. In this paper, we attempted to show that carbon isotopic variations often indicate postsedimentary alterations of carbonates and reflect the specific geochemical transformations of the rocks. Study of variations of carbon and oxygen isotopic compositions in the Vendian-Cambrian rocks provide insight into lithogenetic processes. 相似文献
4.
在钻井岩心观察和岩石学分析的基础上,对川中东北部龙岗地区中-下侏罗统自流井组和凉高山组典型钻井取心段碳酸盐岩样品进行了碳氧同位素分析。40余件样品的测试结果表明,δ13CPDB值在-1.24‰~4.59‰之间,除了1个负值外,都为正值。δ18OPDB值在-15.7‰~-9.83‰之间,都为负值。与海相和陆相碳酸盐岩同位素值对比显示,自流井期和凉高山期古湖泊均表现出内陆开放性淡水湖泊的特点,没有经过明显的海水入侵。在中-下侏罗统广泛存在的碳同位素正偏移是由湖泊初级生产力提高所导致的。岩相和同位素变化显示了古湖平面经历了2次主旋回和6次次级旋回变化,湖平面变化总体表现为东岳庙段沉积期>大一三亚段沉积期>大一亚段沉积期>凉高山期>马鞍山段沉积期。古湖泊初级生产力的变化表现为大一三亚段沉积期>东岳庙段沉积期>大一亚段沉积期>凉高山期>马鞍山段沉积期。 相似文献
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6.
Carbon and oxygen isotopic analyses have been carried out on carbonates from lavas, ejectites and sedimentary formations in the region of the Alban Hills.The calcite occurring in the lavas, both in veins and cavities and dispersed in the groundmass shows within each flow a fairly uniform isotopic composition not different from that normally observed in sedimentary carbonates, except in the case of one particular flow, where unusually low 13C values were recorded. The latter are discussed in terms of a possible contribution of organic carbon or of isotopically light carbonates, the presence of which in the Alban Hills area had been previously recorded.The ejectites examined comprise both limestone and dolostone blocks of various degree of metamorphism and materials of uncertain origin, some of which containing carbon and oxygen of isotopic composition wholly different from that of all carbonates analysed in this work, approaching the range observed in some carbonatites. The isotopic data and the geochemical features of the latter materials are discussed in terms of thermal metamorphism of limestones and of a possible syntexis of evaporite materials.The 18O and 13C values of certain marine limestones from major Mesozoic sedimentary formations in the region are also reported. 相似文献
7.
Carbon and oxygen isotopic covariations in hydrothermal calcites 总被引:5,自引:0,他引:5
Isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes: (1) mixing between two different fluids which leads to the precipitation of calcite; (2) mixing between fluid and rock: (a) calcite precipitation due to fluid/rock interaction, (b) secondary alteration of primary calcite by interaction with a subsequent fluid. The models are derived from mass balance equations. A distinction among the three mixing processes can be made on a
13C vs
18O diagram, which places important constraints on the genesis of hydrothermal mineralization. The variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock, temperature, and dissolved carbon species. Owing to significant temperature-dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid, the mixing processes may be distinguished by telltale patterns of isotopic data in
13C vs
18O space. In particular, caution must be exercised in postulating the fluid mixing as the cause for mineral deposition. This is demonstrated for hydrothermal Pb-Zn deposits in the western Harz Mountains, Germany. A positive correlation between
13C and
18O values is observed for calcites from the Bad Grund deposit in the Upper Harz. Two sample profiles through calcite veins show similar correlations with the lowest -values at the center of the veins and the highest -values at the vein margins. Because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike, it is assumed that a fluid/rock interaction is responsible for the observed correlation and thus for the precipitation of calcite. A deep-seated fluid is inferred with a
13C value of — 7% and a
18O value of +10%., as well as H2CO3 as the dominant dissolved carbon species; precipitation temperatures of the calcites are estimated to be about 280 170°C. Quite different isotopic distributions are observed for calcites from the St. Andreasberg deposit in the Middle Harz. An alteration model is suggested based mainly on the isotopic distribution through a calcite vein. In addition to a primary fluid which has the same isotopic composition as that in the Bad Grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides, an evolved, HCO
3
-
-dominant subsurface fluid with
13C about -20 — 15% and
18O 0% is deduced to alter the primary calcite at low temperatures of 70 40°C. 相似文献
8.
We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction and isotopic studies reveal that the carbonate minerals are mainly authigenic and they do not preserve any evidence for detrital carbonate and diagenesis. The isotope data show large fluctuations in the δ18O and δ13C values in the middle–late Eocene, indicating relatively warm and seasonal dry climate. The positive correlation of the δ18O and δ13C values in the Oligocene and the positive shift of the δ13C values from the Eocene to Oligocene suggest that the climate changed to arid in the Oligocene. However, the δ18O values show negative shift, which is closely related to the global cooling event. During the Miocene, the δ13C values vary between –2‰ and –4‰, whereas the δ18O values show continuous negative shift. The mean δ18O values decrease from –8.5‰ in the early Miocene to –10.0‰ in the late Miocene. The stable isotope-based paleoaltimetry results suggest that the elevation of the southwestern Qaidam basin was approximately 1500 m in the middle–late Eocene and Oligocene. Subsequently, during Miocene the crustal uplift process started and the elevation reached approximately 2000 m in the early Miocene and 2500 m in the late Miocene, which suggests large-scale growth of the northern Tibet Plateau during the Miocene. 相似文献
9.
大别山北麓侏罗系大理岩砾石的碳—氧同位素组成及地质意义 总被引:16,自引:2,他引:14
在大别山北麓、合肥盆地南缘侏罗系三尖铺组和凤凰台组地层中含有大理岩砾石, 属山麓冲积扇环境沉积。它们的δ13 C数值范围为- 1.7‰~1.3‰, 大多数近于零值, 它们的δ18O数值从6.5‰~23.0‰。大别地块佛子岭群大理岩的δ13C数值为- 2.0‰~- 2.5‰, δ18O数值范围从6.3‰~13.1‰。大别地块高压和超高压变质岩带的大理岩的δ13 C数值为1‰~6‰,δ18O数值为5‰~23‰。碳同位素组成的明显差别表明现今大别地块佛子岭群和高压、超高压变质岩不是合肥盆地南缘侏罗系大理岩砾石的来源区。由于δ13C的数值不随δ18O值的降低而变化, 且分布在一个狭窄的范围, 合肥盆地南缘侏罗系大理岩砾石的碳同位素组成代表了它的原岩在沉积时海水的同位素记录。 相似文献
10.
Santanu Banerjee S.K. Bhattacharya Subir Sarkar 《Journal of Asian Earth Sciences》2007,29(5-6):823-831
Variations of carbon and oxygen isotopic ratios in response to cyclical sea level fluctuations have been documented from a Paleoproterozoic peritidal stromatolite succession. The upper division of the Kajrahat Limestone, Vindhyan Supergroup of central India consists of several shallowing upward stromatolite cycles identified by regular and systematic changes in stromatolite size. Normally, larger stromatolites are followed upward in the succession by smaller stromatolites and microbial laminites that occupy the top of the cycle. Desiccation cracks are found in all the facies indicating subaerial exposure. We investigated the stable isotope compositional variations across nine complete stromatolite cycles showing frequent subaerial emergence. Carbon and oxygen isotopic values of the limestones, in general, are comparable to contemporary marine values available from earlier studies but show regular depletion in response to shallowing of the water level. The δ13C and δ18O values of the limestones vary within an individual stromatolite cycle; depleted values characterize the topmost part of the cycles. The isotope pattern is explained by micritic carbonate deposition in different sub environments of the shallow marine domain having different salinity and variable duration of exposure. These variations also probably caused the observed scatter in δ13C and δ18O values of supratidal microbial laminites. 相似文献
11.
The isotopic composition of atmospheric O2 depends on the rates of oxygen cycling in photosynthesis, respiration, photochemical reactions in the stratosphere and on δ17O and δ18O of ocean and leaf water. While most of the factors affecting δ17O and δ18O of air O2 have been studied extensively in recent years, δ17O of leaf water—the substrate for all terrestrial photosynthesis—remained unknown. In order to understand the isotopic composition of atmospheric O2 at present and in fossil air in ice cores, we studied leaf water in field experiments in Israel and in a European survey. We measured the difference in δ17O and δ18O between stem and leaf water, which is the result of isotope enrichment during transpiration. We calculated the slopes of the lines linking the isotopic compositions of stem and leaf water. The obtained slopes in ln(δ17O + 1) vs. ln(δ18O + 1) plots are characterized by very high precision (∼0.001) despite of relatively large differences between duplicates in both δ17O and δ18O (0.02-0.05‰). This is so because the errors in δ18O and δ17O are mass-dependent. The slope of the leaf transpiration process varied between 0.5111 ± 0.0013 and 0.5204 ± 0.0005, which is considerably smaller than the slope linking liquid water and vapor at equilibrium (0.529). We further found that the slope of the transpiration process decreases with atmospheric relative humidity (h) as 0.522-0.008 × h, for h in the range 0.3-1. This slope is neither influenced by the plant species, nor by the environmental conditions where plants grow nor does it show strong variations along long leaves. 相似文献
12.
不同粒级黄土-古土壤中碳酸盐碳氧稳定同位素组成及其古环境意义 总被引:8,自引:3,他引:8
从黄土高原中部洛川和环县两个剖面选取若干黄土和古土壤样品,分为三种粒级(>45μm、2-45μm、<2μm),挑出>45μm粒级中的根状结核与蜗牛壳化石碎片,分别测定δ^13C和δ^18O值。结果显示,两个剖面不同粒级组分的δ^13C和δ^18O值表现出相似的分布规律。洛川剖面的根状结核和蜗牛壳与分粒级样品中的<2μm粒级中碳酸盐的δ^13C和δ^18O值最为接近,处于相同的区域内;而>45μm粒级中的δ^13C和δ^18O值与其他样品有明显的差别。因此,可以认为黄土-古土壤中<2μm粒级中所含的碳酸盐可代表成镶碳酸盐,其蕴涵的地球化学信息可用以重建成壤时的古气候和古环境条件。 相似文献
13.
贵州龙动物群是二叠-三叠纪大绝灭后海洋生态系统辐射发展阶段最晚期的典型代表,为了解其古环境信息,对贵州省兴义地区顶效及周边产地开展了精细剖面测量,采集碳酸盐岩进行了全岩碳氧同位素测试。测试结果显示:泥麦谷剖面δ13C值分布范围-6.3‰~2.6‰,δ18O分布范围在-5.7‰~-1.2‰;谢米剖面δ13C值分布范围在-4.5‰~2.5‰,δ18O在-5.7‰~-1.2‰;坝尾剖面δ13C值分布范围在0.5‰~2‰,δ18O在-6.4‰~0.1‰;顶效剖面δ13C值分布范围在-4.3‰~2.1‰,δ18O在-7.3‰~-2.5‰。根据碳氧同位素数据相关性分析显示泥麦谷、谢米、坝尾剖面的同位素值受后期成岩作用影响较小。在泥麦谷、谢米及顶效贵州龙动物群产出层位下段均出现明显的δ13C负异常,与低水位时期海洋生物快速死亡密切相关,也与火山作用存在一定的联系。由于顶效剖面受后期成岩作用影响,笔者利用泥麦谷、谢米及坝尾剖面δ18O数据对兴义地区古海水温度进行了恢复,结果显示温度分布在19~27℃,平均为23℃左右,说明当时属于温暖气候环境。 相似文献
14.
哈尼梯田麻栗寨河流域雨季大气降水氢氧同位素特征及影响因素 总被引:1,自引:0,他引:1
以红河哈尼梯田文化景观遗产核心区麻栗寨河流域的雨季大气降水为研究对象,对2014年雨季典型月7月的氢氧同位素组成进行了分析,拟合出大气瞬时降水线方程,并与邻近地区及全国、全球降水线方程进行对比,分析温度、湿度、降水量等气象参数和海拔对氢氧稳定同位素的影响,并初步判断该区的水汽来源。结果表明:(1)研究区雨季大气降水δ18O值变化范围大,与邻近的昆明、贵阳、成都地区相比,贫化明显;(2)大气降水线方程为δD=7.59δ18O+3.31,其斜率和截距较小,说明研究区雨季降水量大且蒸发强烈、降水的水汽来源非单一化,除受印度洋、孟加拉湾的变热性热带海洋气团的影响,还受研究区地表水体的二次蒸发影响;(3)研究区降水稳定同位素特征显示不但存在明显的降水量效应,也存在温度效应和海拔效应,但各因素是综合作用的,主导因素不明显。 相似文献
15.
E. M. Galimov O. V. Palazhchenko E. M. Verichev V. K. Garanin N. N. Golovin 《Geochemistry International》2008,46(10):961-970
The first data are reported on the carbon isotopic composition of diamond crystals from the Grib pipe kimberlite deposit of the Archangelsk diamond province (ADP). The δ13C value of the crystals ranges from ?2.79 to ?9.61‰. The isotopic composition of carbon was determined in three zoned crystals (δ13C of ?5.8 ?6.96 ‰, ?5.64/ ?5.85 ‰, and ?5.94/ ?5.69 ‰), two “diamond in diamond” samples (diamond inclusion with δ13C of ?4.05 and ?6.34 ‰ in host diamond crystals with δ13C of ?8.05 and ?7.54 ‰, respectively), and two samples of coated diamonds (cores with δ13C of ?6.98 and ?6.78‰ and coats with δ13C of ?7.51 and ?8.01 ‰, respectively). δ13C values were obtained for individual diamond crystals from bort-type aggregates (δ13C of ?4.24/ ?4.05 ‰, ?6.58/ ?7.48 ‰, and ?5.48/ ?6.08 ‰). Correlations were examined between the carbon isotopic composition of diamonds and their crystal morphology; the color; the concentration of nitrogen, hydrogen, and platelet defects; and mineral inclusions content. It was supposed that the observed δ13C variations in the crystals are most likely related to the fractionation of carbon isotopes rather than to the heterogeneity of carbon sources involved in diamond formation. The isotopic characteristics of diamonds from the Grib pipe were compared with those of previously investigated diamonds from the Lomonosov deposit. It was found that diamonds from these relatively closely spaced kimberlite fields are different; this also indicates the existence of spatially localized peculiarities of isotope fractionation in processes accompanying diamond formation. 相似文献
16.
17.
四川盆地H2S的硫同位素组成及其成因探讨 总被引:20,自引:3,他引:20
四川盆地天然气绝大部分含有硫化氢,部分含量高达15%以上。其中高含硫化氢天然气主要分布在三叠系飞仙关组、雷口坡组和嘉陵江组;震旦系、石炭系、二叠系属于低含硫化氢,上三叠统须家河组和侏罗系属于微含硫化氢或不含硫化氢天然气藏。研究表明,三叠系飞仙关组、雷口坡组和嘉陵江组、震旦系、石炭系储层中发育的膏质岩类为TSR形成硫化氢提供了物质基础;富含有机硫源岩的高温裂解是二叠系低含硫化氢天然气的主要成因。硫同位素组成表明,高含硫化氢天然气的硫同位素比储层硫酸盐硫同位素δ34S亏损7‰~11‰;而低含硫化氢天然气硫同位素分布区间较宽,在0‰~20‰之间,大部分比同期硫酸盐的硫同位素轻15‰左右。四川盆地三叠系膏岩的硫同位素值分布较宽,并呈现阶梯状变化,而硫化氢的硫同位素则呈现出相似的分布规律,表明各气层硫化氢中的硫来自于本层系的硫酸盐,即TSR发生在各自的储集层中;另外四川盆地三叠系TSR发生时各气藏的温度条件相近,即各气藏的硫化氢在大致相同的温度条件下发生;同时也说明TSR过程中硫同位素的分馏过程与硫酸盐本身硫同位素数值的高低无关,而与TSR反应的温度条件和反应程度有关。还建立了运用硫化氢的硫同位素和含量判识硫化氢成因类型的模式。 相似文献
18.
上黑龙江盆地中上侏罗统二十二站群的地层划分与时代 总被引:4,自引:2,他引:2
根据1∶5万区域地质调查,大兴安岭北端上黑龙江盆地内的原中侏罗统二十二站组的时代被重新厘定为中、晚侏罗世Bajocian─Tithonian期并改称为二十二站群。根据岩性特征和化石组合,将其进一步划分为两个组:下部称大西尔根气河组,其下部岩性以砂岩为主,上部以泥质粉砂岩─砂岩为主,含中侏罗世至晚侏罗世早期的双壳类动物群化石,可划分为Sibireconcha─Cuneopsis,Margaritifera─Unio,Fergannoconcha3个生物组合;上部称马林组,主要由粉砂岩组成,夹有少量砾岩和粉砂质灰岩,含晚侏罗世中晚期的介形类动物群化石,可称为Eoparacypris─Rhinocypris─Yanshanina组合。 相似文献
19.
The paper presents newly obtained data on the mineralogical and geochemical characteristics of Ukrainian endogenic and supergenic diamonds, including pioneering data on the carbon isotopic composition of individual diamond crystals. The endogenic diamonds occur as euhedral microcrystals (their morphology varies from octahedral to rhombododecahedral and cubic) with broadly varying concentrations of the structural nitrogen admixture and with mostly low aggregation of nitrogen centers. According to their carbon isotopic composition, Ukrainian diamonds range from kimberlitic–lamproitic to metamorphic and even carbonado-like, i.e., are polygenetic. Our data confirm the earlier conclusion that the supergenic diamonds are of impact genesis. 相似文献
20.
Kebede Seifu Abdalla Osman Sefelnasr Ahmed Tindimugaya Callist Mustafa Osman 《Hydrogeology Journal》2017,25(3):707-726
Hydrogeology Journal - Past discussions around water-resources management and development in the River Nile basin disregard groundwater resources from the equation. There is an increasing interest... 相似文献