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1.

As revealed from recent drilling and organic geochemical testing and research, a series of lacustrine high-grade hydrocarbon source rocks was discovered in the upper section of the Chang 9 oil reservoir member of upper Triassic in Ordos Basin. The hydrocarbon source rocks show average TOC content as high as 5.03%, average bitumen “A” content as high as 0.8603%, and good quality organic precursors, which are of the sapropelic type mainly derived from lower aquatic plants and have reached the thermal evolution stage featured by oil-producing climax. Generally the lacustrine high-grade hydrocarbon source rocks were developed in local depressions of a lake basin, and the Chang 91 member was particularly formed in a depositional environment characterized by fresh water to weakly saline water, weakly oxidizing to weakly reducing setting and semi-deep lake facies, as was demonstrated by a variety of organic to inorganic geochemical parameters. As a result, high productivity constitutes the principal controlling force for generation of this series of high-grade hydrocarbon source rocks. Deposition of thinly-bedded and laminated tuffs as well as positive Eu anomaly corroborate the possible occurrence of anoxic geological event closely related to contemporaneous volcanic eruption, which would play a key part in development of the Chang 91 member of high-grade hydrocarbon source rocks.

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2.
As revealed from recent drilling and organic geochemical testing and research, a series of lacustrine high-grade hydrocarbon source rocks was discovered in the upper section of the Chang 9 oil reservoir member of upper Triassic in Ordos Basin. The hydrocarbon source rocks show average TOC content as high as 5.03%, average bitumen "A" content as high as 0.8603%, and good quality organic precursors, which are of the sapropelic type mainly derived from lower aquatic plants and have reached the thermal evolution stage featured by oil-producing climax. Generally the lacustrine high-grade hydrocarbon source rocks were developed in local depressions of a lake basin, and the Chang 91 member was particularly formed in a depositional environment characterized by fresh water to weakly saline water, weakly oxidizing to weakly reducing setting and semi-deep lake facies, as was demonstrated by a variety of organic to inorganic geochemical parameters. As a result, high productivity constitutes the principal controlling force for generation of this series of high-grade hydrocarbon source rocks. Deposition of thinly-bedded and laminated tuffs as well as positive Eu anomaly corroborate the possible occurrence of anoxic geological event closely related to contemporaneous volcanic eruption, which would play a key part in development of the Chang 91 member of high-grade hydrocarbon source rocks.  相似文献   

3.
Based on GC-MS testing data of many saturated hydrocarbon samples, 17α(H)-C30 diahopanes (C30 *) are extensively distributed in the lacustrine hydrocarbon source rocks of the Yanchang Formation in Ordos Basin, but show remarkable differences in relative abundance among various source rocks. Generally, Chang 7 high-quality source rock (oil shale) developed in deep lake anoxic environment shows lower C30 * content, whereas Chang 6–9 dark mudstone developed in shallow to semi-deep lake, sub-oxidizing environment shows relatively high to high C30 * value. Particularly, Chang 7 and Chang 9 black mudstones in Zhidan region in the northeast of the lake basin show extremely high C30 * value. A comparative analysis was made based on lithology, organic types and various geochemical parameters indicative of redox environment, and the results indicate that environmental factors such as redox settings and lithology are key factors that control the C30 * relative abundance, while organic types and maturity may be minor factors. High to extremely high C30 * values are indicative of sub-oxidizing environment of fresh-brackish water and shallow to semi-deep lake. Therefore, research on C30 * relative content and distribution in lacustrine hydrocarbon source rocks in the Yanchang Formation, especially on the difference in C30 * between Chang 7 high-quality source rocks (oil shale) and Chang 6–91 source rocks (dark mudstone), will provide an important approach for classification of Mesozoic lacustrine crudes and detailed oil-source correlation in the basin. Supported by National Natural Science Foundation of China (Grant No. 40773028)  相似文献   

4.
东营凹陷波动古湖相烃源岩沉积特征   总被引：6，自引：2，他引：4  
陈中红  查明  金强 《湖泊科学》2006,18(1):29-35
以东营凹陷牛38井为例,研究显示,该井沙河街组沙三段烃源岩的沉积特征具有明显的波动性．宏观上体现为, 构造因素控制湖盆的整体升降和沉积构造旋回,但季节性气候及其它因素的影响使湖盆呈现次级旋回的复合性沉积．微观上表现为纹层的不连续性及生物扰动构造等事件性沉积.古湖面不同幅度的波动和变化导致相对稳定的泥岩沉积的不稳定性,有机质的分布也呈现较显著的非均质性．湖泊的沉积过程影响了微量元素、有机质以及烃源物质的分布,水体较深、盐度较高的沙三段下部多数微量元素含量较高以及B／Ca、Sr／Ba呈现高值;水体较浅、盐度较低的沙三段中部各元素的分布较为稳定,B／Ca、Sr／Ba比值及Sr的含量均显著降低.波动性沉积导致烃源岩呈现明显的优劣性分布,沙三段下部中的有机质富集,为优质烃源岩;沙三段中部的有机质分布较为分散,生排烃的资源潜力有限．  相似文献   

5.
Source rock extracts and crude oils from the Songliao Basin were analyzed by high-temperature gas chromatography (HTGC), gas chromatography-mass spectrometry (HTGC-MS) and gas chromatography-isotope ratio-mass spectrometry (GC-IRMS), for high molecular-weight alkanes. The distributions of n-alkanes in the Nenjiang Formation extracts are in the C14―C63 range; a bimodal distribution occurs in the C-21 and C21―40 regions. The C30―C37 n-alkanes are accompanied by C29―C35 hopanes, whereas the high molecular-weight C45―C47 n-alkanes co-occur with abundant isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The high δ 13C values of the n-alkanes and the microscopic maceral compositions indicate a highly diversified organic source input for the Nenjiang Formation source rocks, ranging from aquatic plants, blue alge-bacteria, to land plant material. In contrast, n-alkanes in the rock extracts of the Qingshankou Formation are characterized by a single modal distribution, with relatively low abundances of C29―C35 hopanes, but high molecular-weight isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The relatively low δ 13C values of C22―C44 n-alkanes and organic material compositions indicate that the source rocks in the Qingshankou Formation contain dominantly type I algal organic matter. The relative abundance of C 40 compounds in source rocks changes little at low maturity stage, but decreases drastically at higher maturity levels, with a concurrent reduction in the odd/even carbon predominance. In crude oils, in contrast, the relative abundance of C 40 compounds appears to relate closely with the oil source and oil viscosity.  相似文献   

6.
Aromatic hydrocarbons are generally main distillation of crude oil and organic extract of source rocks. Bicyclic and tricyclic aromatic hydrocarbons can be purified by two-step method of chromatography on alumina. Carbon isotopic composition of individual aromatic hydrocarbons is affected not only by thermal maturity, but also by organic matter input, depositional environment, and hydrocarbon generation process based on the GC-IRMS analysis of Upper Ordovician, Lower Ordovician, and Cambrian source rocks in different areas in the Tarim Basin, western China. The subgroups of aromatic hydrocarbons as well as individual aromatic compound, such as 1-MP, 9-MP, and 2,6-DMP from Cambrian-Lower Ordovician section show more depleted 13 C distribution. The 13 C value difference between Cambrian-Lower Ordovician section and Upper Ordovician source rocks is up to 16.1‰ for subgroups and 14‰ for individual compounds. It can provide strong evidence for oil source correlation by combing the 13 C value and biomarker distribution of different oil and source rocks from different strata in the Tarim Basin. Most oils from Tazhong area have geochemical characteristics such as more negative 13C9-MP value, poor gammacerane, and abundant homohopanes, which indicate that Upper Ordovician source rock is the main source rock. In contrast, oils from Tadong area and some oils from Tazhong area have geochemical characteristics such as high 13C9-MP value, abundant gammacerane, and poor homohopanes, which suggest that the major contributor is Cambrian-Lower Ordovician source rock.  相似文献   

7.
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8.
Lake Albano (Alban Hills volcanic complex, Central Italy) is located in a densely populated area near Rome. The deep lake waters have significant dissolved CO2 concentrations, probably related to sub-lacustrine fluid discharges fed by a pressurized CO2-rich reservoir. The analytical results of geochemical surveys carried out in 1989–2010 highlight the episodes of CO2 removal from the lake. The total mass of dissolved CO2 decreased from ∼5.8 × 107 kg in 1989 to ∼0.5 × 107 kg in 2010, following an exponential decreasing trend. Calculated values of both dissolved inorganic carbon and CO2 concentrations along the vertical profile of the lake indicate that this decrease is caused by CO2 release from the epilimnion, at depth <9 m, combined with (1) water circulation at depth <95 m and (2) CO2 diffusion from the deeper lake layers. According to this model, Lake Albano was affected by a large CO2 input that coincided with the last important seismic swarm at Alban Hills in 1989, suggesting an intimate relationship between the addition of deep-originated CO2 to the lake and seismic activity. In the case of a CO2 degassing event of an order of magnitude larger than the one that occurred in 1989, the deepest part of Lake Albano would become CO2-saturated, resulting in conditions compatible with the occurrence of a gas outburst. These results reinforce the idea that a sudden CO2 input into the lake may cause the release of a dense gas cloud, presently representing the major volcanic threat for this densely populated area.  相似文献   

9.
Study of Late Cretaceous lacustrine sedimentary strata in the eastern Songliao Basin, China revealed that the paleoclimate was relatively arid and hot during sedimentation of the upper Santonian of the Yaojia Formation, but became relatively humid and warm during deposition of the lower Campanian Nenjiang Formation. The upper Yaojia Formation was deposited in a freshwater lake environment, while the lower Nenjiang Formation was deposited in a slightly brackish to brackish environment. The average total organic carbon content in the upper Yaojia Formation is 0.15%, while the hydrogen index is 36 mgHC/gTOC, implying poor source rock for oil generation and the organic matter comprised of a mixture of woody and herbaceous organic matter. In contrast, the hydrogen index of oil shale and black shale of the lower Nenjiang Formation is 619 mgHC/gTOC, and total organic carbon content on average is 3.37%, indicating a mixed algae and herbaceous source of kerogen and an increase in aquatic bioproductivity. The black shale and oil shale have low Pristane/Phytane and C29 5α,14α,17α(H) ? stigmastane 20R/(20R + 20S) ratios, with maximum concentration of n‐alkanes at n‐C23, implying an anoxic depositional environment with algae, bacteria and higher plants providing most of the organic matter. Relatively abundant gammacerane and a higher Sr/Ba ratio in the oil shales suggest the presence of brackish water and development of salinity stratification in the lake. During sedimentation of the upper Yaojia through the lower Nenjiang Formations, the level of Songliao lake increased and a deep‐lake environment was formed with bottom waters being oxygen depleted. Concomitantly, as the lake deepened bottom conditions were changing from oxic to anoxic, and the input of organic matter changed from predominantly higher plants to a mixture of bacteria, algae and higher plants providing favorable conditions for oil source rock accumulation.  相似文献   

10.
古近系沙河街组是阳信洼陷最重要的生烃层段.其湖盆充填具阶段性和沉积演化的旋回性,形成了由沙四段、沙三段与沙一段组成的复合生烃系统和不同的地球化学特征.利用Rock-Eval生油岩评价仪、色谱-质谱仪等实验分析技术对不同层系样品进行了地球化学特征分析研究,其中生烃潜力指标包括有机碳含量(TOC)、残余生烃潜量(S1 S2)、氢指数IH、氯仿沥青"A";成熟度指标包括热解峰温Tmax、奇偶优势参数OEP、饱和烃轻重比(C21 C22)/(C28 C29)及∑C21-/∑C22 、镜质体反射率Ro、莫烷/藿烷及甾烷生物标志物参数C29ββ(ββ αα)、C29ααα20S(20S 20R);古环境指标包括异构烷烃参数Pr/Ph、Pr/n-C17、Ph/n-C18及伽马蜡烷等.结果表明,沙四段为弱还原-还原性的半深湖沉积,沉积了一套中等厚度、分布局限的烃源岩(TOC平均为1.5%),其较深位置的烃源岩基本进入成熟阶段,多形成成熟油;沙三段属弱还原-还原性的半深湖-深湖环境,其烃源岩中有机质丰度较高(TOC平均为3.5%),大部分烃源岩处于未成熟-低成熟状态,主要形成未熟油;沙一段为湖水咸化、还原性的半深湖相环境,其烃源岩中有机质丰度高(TOC平均为5%左右),但处于未成熟阶段,主要生成生物气.  相似文献   

11.
The fundamental assumption of 210Pb sediment dating is the stable flux of 210Pbex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbex activity in sediments will be exponentially reduced with sedimentation age. 210Pbex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly increased, 210Pbex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pb dating; on the other hand, the sudden enhancement of 210Pbex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of 210Pbex activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mechanism of constraining the transfer of 210Pbex into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(Corg)) of organic carbon (Corg) since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbex (F(210Pbex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(Corg)), especially in the years of 1972–1974 and 1986–1989. The variation of F(Corg) led to the variation of F(210Pbex); the variation of F(210Pbex) reflects, to some extent, the historical variation of lake productivity.  相似文献   

12.

Natural gases discovered up to now in Lishui Sag, the East China Sea Basin, differ greatly in gaseous compositions, of which hydrocarbon gases amount to 2%–94% while non-hydrocarbon gases are dominated by CO2. Their hydrocarbon gases, without exception, contain less than 90% of methane and over 10% of C2 + heavier hydrocarbons, indicating a wet gas. Carbon isotopic analyses on these hydrocarbon gases showed that δ 13C1, δ 13C2 and δ 13C3 are basically lighter than −44‰, −29‰ and −26‰, respectively. The difference in carbon isotopic values between methane and ethane is great, suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation. δ 13 \( C_{CO_2 } \) values of nonhydrocarbon gases are all heavier than −10‰, indicating a typical abiogenic gas. The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit, consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter. Moreover, δ 13C1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰ heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit while δ 13C2 and δ 13C3 values of the former are over 9‰ heavier than those of the latter. Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag, where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter, therefore, natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.

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13.
Natural gases discovered up to now in Lishui Sag, the East China Sea Basin, differ greatly in gaseous compositions, of which hydrocarbon gases amount to 2%–94% while non-hydrocarbon gases are dominated by CO2. Their hydrocarbon gases, without exception, contain less than 90% of methane and over 10% of C2 + heavier hydrocarbons, indicating a wet gas. Carbon isotopic analyses on these hydrocarbon gases showed that δ 13C1, δ 13C2 and δ 13C3 are basically lighter than ?44‰, ?29‰ and ?26‰, respectively. The difference in carbon isotopic values between methane and ethane is great, suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation. δ 13 \(C_{CO_2 } \) values of nonhydrocarbon gases are all heavier than ?10‰, indicating a typical abiogenic gas. The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit, consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter. Moreover, δ 13C1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰ heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit while δ 13C2 and δ 13C3 values of the former are over 9‰ heavier than those of the latter. Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag, where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter, therefore, natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.  相似文献   

14.
针对塔里木盆地库车坳陷北部侏罗系烃源岩受泥浆污染、分析数据少、样品分布不连续及类型多样等问题突出,利用测井资料来对有机地球化学参数进行评价难度大,无法满足勘探需求.本文阐述了不同类型烃源岩的有机质级别、测井响应特征、有机地球化学参数定量计算及品质评价等多种方法,来研究富集区烃源岩对致密气储层的持续供气能力.文中介绍了煤层、碳质泥岩、暗色泥岩等3种类型烃源岩的有机质级别和测井响应特征.首先,提出分不同岩性烃源岩的ΔlogR法,其计算结果与铀曲线相关法、多元回归法对比,效果最好;再次建立了生烃潜率、氯仿沥青“A”及镜质体发射率等多个有机质地球化学参数的测井评价模型;最终,考虑能够反映烃源岩性质的参数来综合定义烃源岩品质指数,形成了完善的烃源岩测井综合评价方法研究技术.研究表明,利用这套地球物理技术提供了烃源岩定量评价和品质分类研究方法及实际应用案例.  相似文献   

15.
Since the Meso-Cenozoic, controlled by paleoclimate, a series of fresh to brackish water basins and salt to semi-salt water basins were developed in wet climatic zones and in dry climate zones in China, respectively[1]. The geological and geochemical char…  相似文献   

16.
In this paper mafic sills and dykes found in Palaeogenic sedimentary rocks of the South Rhodope Massif (Greece) are studied. Their mineralogy is represented mainly by plagioclases (An45-An88), amphiboles (Mg-hornblende, Mg-hastingsite) and clinopyroxenes of salitic compositions with subordinate biotite. Chemistry and corresponding discriminant diagrams (Ti-Zr-Y, Ti-Zr-Sr) and discriminant functions (F1-F2 from pyroxene) classify them as basalts and basaltic andesites of the high-K calc-alkaline rocks series. According to their geochemical and petrological features an orogenic nature results for the rocks in study. REE abundances show an enrichement of LREE and a moderate fractionation in HREE patterns. The above together with the non significant europium anomalies (Eu/Eu*=0,92–0,85) and the relatively high contents of K, Ba and Sr in these rocks indicate a magma genesis by partial melting of an upper mantle source already enriched in LILE. A K-Ar determination on hornblende phenocrysts gave a Lower Oligocene age (33,5±1.2 m.y.) which is in accordance with the age of the andesitic lavas extended to the northwest of the studied area.  相似文献   

17.
The northeastern area of Sichuan Basin, southwestern China, is the area with the maximal reserve of natural gas containing higher hydrogen sulphide (H2S) that has been found among the petroliferous basins of China, with the proven and controlled gas reserve of more than 200 billion cubic meters. These gas pools, with higher H2S contents averaging 9%, some 17%, are mainly distributed on structural belts of Dukouhe, Tieshanpo, Luojiazhai, Puguang, etc., while the oolitic-shoal dolomite of the Triassic Feixianguan Fm. (T1f) is the reservoir. Although many scholars regard the plentiful accumulation of H2S within the deep carbonate reservoir as the result of Thermochemical Sulfate Reduction (TSR), however, the process of TSR as well as its residual geological and geochemical evidence is still not quite clear. Based on the carbon isotopic analysis of carbonate strata and secondary calcite, etc., together with the analysis of sulfur isotopes within H2S, sulphur, gypsum, iron pyrites, etc., as well as other aspects including the natural gas composition, carbon isotopes of hydrocarbons reservoir petrology, etc., it has been proved that the above natural gas is a product of TSR. The H2S, sulphur and calcite result from the participation of TSR reactions by hydrocarbon gas. During the process for hydrocarbons being consumed due to TSR, the carbons within the hydrocarbon gas participate in the reactions and finally are transferred into the secondary calcite, and become the carbon source of secondary calcite, consequently causing the carbon isotopes of the secondary calcite to be lower (−18.2‰). As for both the intermediate product of TSR, i.e. sulfur, and its final products, i.e. H2S and iron pyrites, their sulfur elements are all sourced from the sulfate within the Feixianguan Fm. During the fractional processes of sulfur isotopes, the bond energy leads to the 32S being released firstly, and the earlier it is released, the lower δ 34S values for the generated sulphide (H2S) or sulfur will be. However, for the anhydrite that participates in reactions, the higher the reaction degree, the more 32S is released, while the less 32S remains and the more δ 34S is increased. The testing results have proved the process of the dynamic fractionation of sulfur isotopes.  相似文献   

18.
The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg (?36 ‰ to ?27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.  相似文献   

19.
藏西北结则茶卡湖面到高位湖岸线间湖泊记录发育,沿岸湖积物中3个U系年龄分别为14.2±1.2kaBP、38.0±3.5 kaBP和41.6±3.2 kaBP,6个浅井沉积物中CaO、MgO、NaCl、LiCl、B2O3的含量与沉积物形成时代和环境有一定的关联性.在中更新末期,该湖可能处于高湖位期,随着晚更新世初期以来气候变干,湖面开始下降,湖泊逐渐萎缩,湖水盐度逐渐增加,Ca和Mg含量变高,但在30kaBP左右,气候有过短暂湿润期,湖水出现返淡趋势,之后湖水进一步浓缩,湖水中Na、B、Li含量显著增高,盐湖大约在15kaBP左右形成.  相似文献   

20.
On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the model that had been developed previously (2002–2003 eruption) and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic equilibrium between the volatiles (CO2 and SO2) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity. One of the major accomplishments of this study is a 4-year database of summit soil CO2 flux on the basis of which we define the thresholds (low–medium–high) for this parameter that are empirically based on the natural volcanological evolution of Stromboli. The SO2 fluxes of the degassing plume and the CO2 fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. It is noteworthy that geochemical signals of volcanic unrest have been clearly identified before, during and after the effusive activity. These signals were found almost simultaneously in the degassing plume (SO2 flux) and in soil degassing (CO2 flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results will be useful for future volcanic surveillance at Stromboli.  相似文献   

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