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内蒙古岱海古水温定量恢复及其古气候意义 总被引:13,自引:4,他引:13
通过分析岱海岩芯沉积中介形类壳体(Limnocythere of.inopinata)的Sr/Ca比值,结合现代活体介形类生态特征研究,获取了湖水的定量古盐度.另外,在实验室内开展湖水蒸发模拟试验,建立了湖水盐度与氧同位素之间的定量函数关系,获取了古湖水的氧同位素.最后,根据岩芯沉积中自生碳酸盐矿物的氧同位素分析值,结合古湖水的氧同位素组成,定量恢复了岱海古湖水温度,并探讨了其古气候意义. 相似文献
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湖泊现代沉积物碳环境记录研究 总被引:37,自引:3,他引:37
通过对云南程海现代沉积物的精细采样和分析, 研究了湖泊沉积物中有机碳与无机碳含量阶段性的正相关和负相关变化. 结果表明, 温度及其引起的相关变化是控制沉积物无机碳含量、碳酸盐δ 13C和有机碳含量变化关系的主要因素. 当温度及其引起的光合作用强度变化对湖泊自生碳酸钙沉淀起主导作用时, 沉积物有机碳含量与无机碳含量及碳酸盐δ 13C呈正相关变化; 当温度及其引起的蒸发速率等其他物理化学因素变化对湖泊自生碳酸钙沉淀起主导作用时, 沉积物有机碳含量与无机碳含量及碳酸盐δ 13C呈负相关变化. 程海沉积物无机碳含量和碳酸盐δ 13C是湖区气候冷暖变化的良好代用指标. 相似文献
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地下水补给型湖泊表层沉积物矿物组成及其形成机制——以巴丹吉林沙漠湖泊群为例 总被引:1,自引:0,他引:1
盐湖中的矿物沉积记录着丰富的环境气候变化信息,是古环境研究的重要对象.在无地表径流补给的盐湖中,其矿物组成及沉积特征与有地表径流补给的湖泊相比是否有一定的特殊性,是值得探讨的问题.采集巴丹吉林沙漠33个不同矿化度地下水补给型湖泊的表层沉积物和10个地表风积砂样品,通过X衍射的方法,分析样品的矿物组成.结果显示:湖泊表层沉积物主要为石英、长石、辉石、云母等碎屑矿物,部分湖泊含有少量的碳酸盐和氯化物盐类矿物.湖泊沉积物的矿物组成与湖水矿化度的关系较为密切,淡水湖仅分布碎屑矿物,微咸水湖含有碎屑矿物和碳酸盐类矿物,盐湖含有碎屑矿物、碳酸盐类矿物和氯化物.风积砂样品中主要为碎屑矿物,占总矿物含量的90%,对湖泊沉积物的矿物组成影响较大,但对湖泊沉积物中的盐类矿物没有贡献,表明湖泊表层沉积物中盐类矿物主要是自生作用形成的.虽然本地区湖泊边缘的沉积物中盐类矿物种类相对较少并且含量较低,但其盐类矿物组成与分布能够响应湖水矿化度的变化,其环境指示意义与有径流补给的盐湖相同,可以指示其湖水的盐度.因此,可以从巴丹吉林沙漠地下水补给型湖泊沉积的盐类矿物中提取相应的古环境信息,用于恢复古气候和古环境的研究. 相似文献
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湖泊沉积的碳同位素组成因可记录地质历史时期C3/C4植被等环境变化信息,被广泛用于陆地生态系统和全球环境变化研究,在中国西北干旱区湖泊古环境研究中也广为应用.近年来,进一步深入研究的成果,为湖泊碳同位素地球化学所反映的环境意义注入了新的信息,使得我们需要从多方面考虑湖泊碳同位素在环境变化示踪研究中的解释.文章总结了过去几十年来西北干旱区湖泊碳同位素的研究结果,讨论可能存在的湖泊沉积物碳同位素变化机制问题,为更好地将碳同位素地球化学应用于湖泊环境变化研究提供参考. 相似文献
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青海湖沉积碳酸盐矿物之间氧同位素分馏的评估及其环境意义 总被引:1,自引:0,他引:1
青海湖沉积岩芯的矿物学和稳定同位素研究结果显示自生碳酸盐矿物以单种或多种矿物形式保存在沉积物中;不同碳酸盐样品的δ18O值的变化范围为5.47‰至-1.04‰,差值最高达6.5‰;δ18O值与总碳酸盐含量呈正相关关系,与碳酸盐矿物种类的改变则无明显关联.结果表明,造成δ18O显著变化的主导因素是湖水氧同位素组成,自然条件下生成的不同碳酸盐之间的氧同位素分馏不明显.说明δ18O是指示闭流湖泊降水蒸发水量平衡变化的敏感指标之一. 相似文献
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云南鹤庆盆地15万年以来的介形类及环境变迁 总被引:13,自引:3,他引:10
云南鹤庆盆地HQ钻孔剖面分析出介形类13属.32种.根据介形类丰度、分异度及百分含量的变化情况,结合孢粉、总有机碳含量(TOC)、碳氮比(C/N)、碳酸盐含量等的分布,将鹤庆盆地近15万年以来的古气候、古环境变化初步划分为5个阶段,同时又划分出若干亚阶段.总的气候特征为冷期偏湿、暖期偏干,在冷湿和暖干的宏观波动背景上存在次级波动,反映出其气候变化的区域特性.同时.各气候阶段基本可与深海氧同位素V28-38钻孔、黄土/古土壤序列邙山剖面反映的气候阶段相对比,又显示出其气候变化的协同性.在构造与气候的双重作用下.在11790aBP左右湖盆被彻底切开. 相似文献
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Giovanni Aloisi Ioanna BouloubassiSander K. Heijs Richard D. Pancost Catherine PierreJaap S. Sinninghe Damsté Jan C. GottschalLarry J. Forney Jean-Marie Rouchy 《Earth and Planetary Science Letters》2002,203(1):195-203
To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy. 相似文献
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Dhongil Lim Jinyong Choi Zhaokai Xu Moonkoo Kim Donglim Choi Hoisoo Jung Panmook Lee 《Continental Shelf Research》2009
Authigenic carbonates were sampled in methane-enriched piston core sediments collected from gas venting sites on the western continental slope of the Ulleung Basin, East Sea of Korea. Multidisciplinary investigations on these carbonates, including the scanning electronic microscope (SEM) observations and mineralogical-geochemical compositions, were carried out to identify the carbon and oxygen sources and the forming mechanism of these carbonates. The authigenic carbonates from the study area correspond to semi-consolidated, compact concretions or nodules ranging from 2 to 9 cm in size. X-ray diffraction and electron microprobe analyses showed that most of the sampled carbonate concretions were composed of almost purely authigenic high-Mg calcite (10.7–14.3 mol% MgCO3). Characteristically, microbial structures such as filaments and rods, which were probably associated with the authigenic minerals, were abundantly observed within the carbonate matrix. The carbonates were strongly depleted in δ13C (−33.85‰ to −39.53‰ Peedee Belemnite (PDB)) and were enriched in δ18O (5.16–5.60‰ PDB), indicating that the primary source of carbon is mainly derived from the anaerobic oxidation of methane. Such methane probably originated from the destabilization of the underlying gas hydrates as strongly supporting from the enriched 18O levels. Furthermore, the strongly depleted δ13C values (−60.7‰ to −61.6‰ PDB) of the sediment void gases demonstrate that the majority of the gas venting at the Ulleung Basin is microbial methane by CO2 reduction. This study provides another example for the formation mechanism of methane-derived authigenic carbonates associated with gas-hydrate decomposition in gas-seeping pockmark environments. 相似文献
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Located at the northeastern margin of the Qinghai-Tibet Plateau (QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian (ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity (KI) and chemical index (CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP. 相似文献
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This paper presents magnetic susceptibility results of 578 samples from three Devono-Carboniferous carbonate successions in
the Yangtze Block. They indicate that the magnetic susceptibility variations in carbonates are controlled by ancient sea-level
changes. It is particularly so if the supply of detrital materials was low, when the magnetic susceptibility was mainly controlled
by the content of authigenic minerals. If the supply of detrital materials was high, the average susceptibility value would
be higher, but there is still a correlation between susceptibility and sea-level curves. A sea level rise would lead to a
decrease in the content of the detrital materials, and therefore to a decrease in the susceptibility values. On the top of
HST, the uplift and exposure events may lead to elevated magnetic susceptibility values. Carbonate susceptibilities can therefore
be considered as one of the environmental proxy data for the research of sequence stratigraphy. 相似文献
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This paper presents magnetic susceptibility results of 578 samples from three Devono-Carboniferous carbonate successions in the Yangtze Block. They indicate that the magnetic susceptibility variations in carbonates are controlled by ancient sea-level changes. It is particularly so if the supply of detrital materials was low, when the magnetic susceptibility was mainly controlled by the content of authigenic minerals. If the supply of detrital materials was high, the average susceptibility value would be higher, but there is still a correlation between susceptibility and sea-level curves. A sea level rise would lead to a decrease in the content of the detrital materials, and therefore to a decrease in the susceptibility values. On the top of HST, the uplift and exposure events may lead to elevated magnetic susceptibility values. Carbonate susceptibilities can therefore be considered as one of the environmental proxy data for the research of sequence stratigraphy. 相似文献
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Evolution and global correlation for strontium isotopic composition of marine Triassic from Huaying Mountains,eastern Sichuan,China 总被引:2,自引:0,他引:2
ZuoWei Hu SiJing Huang HaiRuo Qing QingDong Wang ChunMei Wang XiaoYong Gao 《中国科学D辑(英文版)》2008,51(4):540-549
Strontium isotope stratigraphy (SIS) has progressively become an efficient chemostratigraphic tool in the research and correlation of global geological events, such as global sea level fluctuations, orogeny, and paleoclimatic and paleoenvironmental changes. In this paper, 87Sr/86Sr ratios of the Triassic marine carbonate rock samples from Huaying Mountains, eastern Sichuan are measured, and the corre-sponding Sr-isotopic curve is constructed, based on the fundamental principle of strontium isotope stratigraphy, analysis of rock fabric, luminescent intensity, chemical composition and representative evaluation for the coeval seawater information. The 87Sr/86Sr ratios show a rapid rise from 0.70721 near the Permian-Triassic transition to 0.70830 at the end of Early Triassic, and then they decline rapidly to 0.70787 in the early Middle Triassic. These data are generally coincident with 87Sr/86Sr ratios of coeval seawater from previous papers, and the curve is also similar to other previous curves. This indicates that the global geological events are the most important controlling factors to the strontium isotope evolution of the global seawater in the Early and Middle Triassic. 相似文献
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A new mechanism for the magnetic enhancement of hematite during heating: the role of clay minerals 总被引:1,自引:0,他引:1
The magnetic properties of loess, lake, and ocean sediments are often used as indicators for paleoclimatic/paleoenvironmental changes. Thermomagnetic analysis is a conventional approach for identifying magnetic phases and thermal alteration of samples. Magnetic concentration parameters are often enhanced after thermal treatment. In this study, the role of clay minerals in magnetic enhancement at elevated temperatures is systematically investigated. The results indicate that the clay minerals (saponite, Ca-montmorillonite, kaolinite, and chlorite) are dominated by paramagnetic behaviour and that the magnetic properties remain relatively stable after heating to 700°C in argon. In contrast, mixtures of hematite and chlorite have a high degree of magnetic enhancement after heating in argon, which indicates that clay minerals play important role in magnetic enhancement. These results improve our understanding of the processes involved in complicated mineral transformations, which is important for retrieving paleoclimatic/paleoenvironemntal signals from magnetic proxies. 相似文献
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Molar ratios of Mg/Ca and Sr/Ca were measured in two species of ostracod shells preserved in the upper core (15-55 m) of the Heqing Basin in Yunnan Province, southwest China. By correlating the molar ratios between Mg/Ca and Sr/Ca and comparing them with Sr concentrations of the sediments, we suggested that: (1) the molar Mg/Ca and Sr/Ca ratio variations in respective ostracod primo re- flected the changes in its ambient water composition and ecology; (2) the molar Sr/Ca ratios responded better to the salinity change linearly than Mg/Ca without aragonite precipitation in the system, and otherwise there was no linear relation between them; and (3) the molar Sr/Ca ratios were mainly con- trolled by salinity and authigenic carbonate precipitation, whereas the molar Mg/Ca ratios were related to both salinity and temperature. In fact, the rate of ostracod growth owing to temperature controls the fluctuation of Mg/Ca in shells. Here, more attentions should be paid to the constraint of authigenic mineral precipitation processes on the trace elements in ostracod shells and to the correlation between these trace elements in biogenic carbonates and compositions of the sediments in systems and in fu- ture in vitro experiments. 相似文献