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黑碳和燃烧源多环芳烃作为大火燃烧的产物有很强的化学惰性及生物惰性,能够在地层中长期稳定地保存,所以成为恢复古代大火历史的最常用指标。近年来世界各地二叠系—三叠系(P-Tr)界线地层中相继发现了黑碳(木炭等)和燃烧源多环芳烃等记录,特别是在煤山P-Tr界线地层,黑碳和燃烧源多环芳烃含量在生物灭绝线附近(25～26层)出现极高的峰值,据此首次明确地提出了P-Tr界线大火事件。P-Tr界线大火的规模、性质如何,与P-Tr界线生物灭绝有什么关系等,值得深入讨论和研究。大火事件发生在陆地上,通过其燃烧及排放的烟尘等,把陆地、大气和海洋密切联系起来,有利于通过系统的整体观来研究当时的气候环境变迁。因此,在回顾和总结P-Tr界线地层中的大火燃烧记录基础上,评述了大火事件与生物灭绝及相关地质事件和环境变化之间的联系,以期引起国内外专家学者的关注,为P-Tr界线生物灭绝及相关研究提供新的思路。 相似文献
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沉积物微量金属元素在重建水体环境变化中的意义 总被引：7，自引：0，他引：7
沉积物所记录的微量金属含量与形态的变化是指示人类活动影响下水体环境变化的有效指标,主要用于指示沉积物重金属污染、水体初级生产力变化和氧化还原条件等方面的水体环境状况。总体而言,沉积物中微量金属含量在近一个世纪以来显著上升,反映了采矿、冶金、污水排放、化肥使用、煤炭和石油燃烧等各种人类活动造成水体和沉积物重金属污染的记录作为浮游植物微量营养元素,Cu、Zn、Ni、Ba、Cd等在沉积物中的记录可以指示水体初级生产力水平。U、Mo、V、Cu、Cd、Mn等氧化还原敏感元素在沉积物中的富集或贫化,及其比值(如Re/Mo、Cd/U、Th/U和V/Sc)的变化,是指示水体和沉积物氧化还原环境的有效指标。但需要指出的是,在受人类活动影响的水体中,这些生产力和氧化还原指标很少能指示水体生产力或氧化还原状况,可能主要与人类活动同时造成这些金属元素大量污染输入而掩盖了其自生来源和内在变化的沉积记录有关。所以,对沉积物中微量金属元素来源的判别(陆源碎屑输入、人为输入和水体自生来源)是重建水体环境变化的重要前提。本文总结了多种化学和统计学方法(包括同位素示踪法、化学提取法、富集因子法和主成分分析法等)在沉积物金属来源判别中的应用另外,成岩作用等多种因素会干扰沉积物金属记录对环境变化的指示作用,所以构建多元素指标来综合判断沉积物记录所反映的环境信息是今后的研究所必须关注的 相似文献
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埃迪卡拉纪是地球第二次大规模成磷时期,全球各大陆均有这次成磷事件的记录。目前对于该时期成磷事件的形成
尚未有广泛接受的地球化学模型解释。而磷酸盐的沉积受海水氧化还原条件的控制,因此通过该时期磷块岩沉积与海水氧
化还原条件演变之间关系的研究可为全球大规模成磷事件的沉积地球化学模型建立提供验证。文章通过对扬子板块埃迪卡
拉纪不同相区磷块岩中碳酸盐组分稀土元素分析,结果表明磷块岩形成时底层海水处于次氧化-接近氧化的不稳定状态,
氧化还原界面沿浅海-大陆架呈现动态变化的特征,为磷块岩的大规模形成提供最佳沉积地球化学条件。合适的海水化学
条件及丰富的磷质来源,大大增加了磷块岩沉积的空间和机会,导致了地质历史时期第二次全球规模成磷发生。 相似文献
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新元古代海洋氧化还原条件是影响这一时期生物演化的重要原因,海相沉积物记录的各种地球化学信息是研究古海洋氧化还原条件的主要方式.南沱冰期由于缺乏含铁建造等化学沉积岩及黑色页岩,极大地制约了对这一时期氧化还原环境的研究.本文通过对贵州剑河五河剖面南沱组红色富铁杂砾岩开展沉积学、矿物学和地球化学研究,认为杂砾岩中Si、Al、Fe含量与大陆上地壳组成类似,但Ca、Na、Mg显示显著的亏损特征,反映冰期大陆的氧化风化作用.杂砾岩中的氧化还原敏感元素Mo和U反映出不同程度的富集,其协变趋势指示了铁、锰氧化物在氧化还原分层的海水中的穿梭作用.杂砾岩的红色色调是其中赤铁矿的富集所致,红色富铁杂砾岩在南沱组中的不规则分布表明赤铁矿是同冰期海水中亚铁离子氧化后,经后期脱水形成.该剖面南沱组中流水波痕构造、氧化还原敏感元素Mo和U的富集特征和红色杂砾岩中赤铁矿的形成,反映华南地区南沱冰期极端缺氧的还原环境. 相似文献
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中国三大陆块中—新元古代地层格架中广泛分布低变质程度的泥质岩与碳酸盐岩,其元素地球化学特征为研究地表圈层的历史演化提供了重要的基础资料。本文收集了近十几年国内外已发表的近2000组泥质岩/碳酸盐岩中地球化学数据,包括40种常量、微量元素含量组成,涉及华北陆块长城系、蓟县系、待建系及青白口系,扬子和塔里木陆块南华系、震旦系。结合文献中样品的岩性、实验方法以及地质背景特征,主要得出了以下认识：① 泥质岩中常量元素的平均含量与中国东部未变质泥质岩中的相似,但其整体上受到了新元古代冰期的影响,化学风化作用较弱,易流失的Na、K及Ca元素含量相对较高;碳酸盐岩中的常量元素含量组成与中国东部未变质富泥碳酸盐岩对比,具有少量的陆源物质输入且以白云岩为主,Mg含量较高。② 碳酸盐岩中较高的Mn/Sr比值应与成岩蚀变作用有关,虽然硅酸盐矿物少于泥质岩,但Sc、REE+Y以及氧化还原敏感元素更加富集,Sc和REE+Y元素与陆源碎屑的混染作用有关,而后者与氧化的海洋环境有关。③ 中元古代早期,华北沉积物中记录了Ce元素负异常以及氧化还原敏感元素含量的增高,响应了一次浅海的氧化事件,并促使了生物的演化。④ 进入新元古代,“雪球地球”事件被塔里木陆块泥质岩大范围变化的化学蚀变指数所记录,伴随着间冰期及冰期后海洋的增氧,扬子陆块新元古代沉积物部分微量元素含量又一次增加,对应着伊迪卡拉生物群的出现。 相似文献
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沉积物中元素碳的提取、鉴定及其古气候环境意义 总被引：1，自引：0，他引：1
通过化学氧化方法提取沉积物中元素碳物质,采用拉曼光谱对其进行分析鉴定,实验结果表明:元素碳是介于单晶石墨碳和无定形碳之间的一系列物质,是一种操作上的定义;化学氧化法提取沉积物中元素碳是可靠的,控制好氧化条件和时间,则能有效去除有机碳,保留元素碳成份。鉴于目前不同工作者由于不同的实验条件和方法下得到了不同结果,我们认为确定标准样及其浓度,统一实验方法是亟待解决的问题,进而统一这种碳微粒的名称,明确其定义,以利于相关研究的横向对比和深入。而在纵向研究方面,我们利用该实验流程提取灵台黄土剖面长时间序列黄土—古土壤样的元素碳,并进行元素碳含量的测定,结果表明元素碳记录能有效揭示古气候环境变化。在不同时间尺度上,元素碳记录有不同的气候指示意义,并且与其他气候环境指标能进行较好的对比,元素碳记录为古气候环境变化提供一新的指标。 相似文献
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《地球科学进展》2016,(6)
长时间尺度的沉积记录可以提升对近岸低氧形成机制的理解,从而为预报、预测和发展减缓低氧措施等提供必要的依据。综述了近岸低氧发育与演化历史的主要研究进展,尤其侧重于沉积记录的研究。首先按水体受限程度将近岸低氧发育环境划分为半封闭型海盆/海湾和开阔陆架海2类,分别探讨了二者低氧发育的主要特征。其次分析总结了低氧沉积记录的替代性指标,包括对水体氧化还原环境具有较好指示意义的生物学、矿物学和地球化学指标,着重分析了各类替代性指标的适用性。最后对长江口外海域底层水体低氧发生机制与沉积记录的研究现状作了回顾与分析。目前长时间尺度的低氧沉积记录研究仍然较少,鉴于长江口外海域低氧的动态发育特征,提出了多钻孔、多参数结合的研究方案。 相似文献
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自生菱铁矿很好地记录了其形成时的地质信息及海洋中的生物地球化学过程，是示踪成岩作用带和氧化还原环境变化的绝佳载体。台湾国姓地区中新世猴洞坑组海相泥页岩中发育有大量自生菱铁矿结核，是次氧化带的产物。为进一步确认该菱铁矿形成时所处沉积环境的氧化还原状态和生物地球化学过程。本文对该区菱铁矿中保存完好的草莓状黄铁矿开展了粒径和硫同位素研究。结果显示，草莓状黄铁矿的粒径变化较大，平均粒径为9.23～11.55μm,最大粒径大于20μm,显示氧化-弱氧化的沉积环境特征；黄铁矿的δ34S为-28.5‰～+3.1‰,平均值为-11.7‰,相较于海水(+21‰)富集轻的硫同位素，表明黄铁矿形成于相对开放的浅表层沉积物。黄铁矿的粒径分布规律和硫同位素特征均指示台湾国姓地区中新世海相菱铁矿形成于浅层弱氧化的次氧化带内。 相似文献
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森林大火对冻土环境影响的研究进展 总被引：2，自引：2，他引：0
森林大火是森林生态系统最主要的干扰因素之一,不仅影响着森林生态系统内部的营养物质循环、水分和能量流动、土壤理化性质的变化,而且对冻土环境和冷生土壤和土壤碳库、碳氮循环等生物地球化学过程有着重要影响。随着气候变暖和人为活动不断增强,北方林区火灾日益频繁,对冻土的水热影响显著：活动层加深、薄层冻土退化、浅层有机碳大量快速释放、森林和湿地的逆向演替,导致热融沉陷、滑塌、泥石流等现象发生。通过综述国内外森林大火对冻土环境影响的研究进展,分析指出目前森林大火对冻土环境影响的研究主要集中在火烧之后短时间、小范围的定性描述与推断,缺乏长时间、大范围的定量分析。尤其是在大兴安岭地区,除了20世纪90年代初期的少量研究外,此后这方面研究虽有零星报道,但缺乏长期和系统的观测与模型研究,所以森林大火对冻土环境的研究,可以利用空间代替时间的方法,通过长、短期的野外观测和数值模拟相结合,定量研究森林大火之后,多年冻土的水热状态、过程和变化机制,可以为寒区林区、湿地保护、生态环境修复提供科学依据。 相似文献
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Modeling forest fire risk in the northeast of Iran using remote sensing and GIS techniques 总被引：3，自引：1，他引：2
Fire in forested areas can be regarded as an environmental disaster which is triggered by either natural forces or anthropogenic activities. Fires are one of the major hazards in forested and grassland areas in the north of Iran. Control of fire is difficult, but it is feasible to map fire risk by geospatial technologies and thereby minimize the frequency of fire occurrences and damages caused by fire. The fire risk models provide a suitable concept to understand characterization of fire risk. Some models are map based, and they combine effectively different forest fire–causing variables with remote sensing data in a GIS environment for identifying and mapping forest fire risk. In this study, Structural Fire Index, Fire Risk Index, and a new index called Hybrid Fire Index were used to delineate fire risk in northeastern Iran that is subjected to frequent forest fire. Vegetation moisture, slope, aspect, elevation, distance from roads, and vicinity to settlements were used as the factors influencing accidental fire starts. These indices were set up by assigning subjective weight values to the classes of the layers based on their sensitivity ratio to fire. Hot spots data derived from MODIS satellite sensor were used to validate the indices. Assessment of the indices with receiver operating characteristic (ROC) curves shows that 76.7 % accuracy of the HFI outperformed the other two indices. According to the Hybrid Fire Index, 57.5 % of the study area is located under high-risk zone, 33 % in medium-risk zone, and the remaining 9.5 % area is located in low-risk zone. 相似文献
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火的使用在人类进化过程中发挥了非常重要的作用。学术界对于人类使用火的历史与过程做了大量的研究,检验古人类遗址区域是否发生过燃烧事件的技术手段也在不断地进步。通过对南非开普敦Wonderwerk洞穴、以色列Qesem洞穴、北京周口店猿人洞以及湖北黄龙洞等地古人类用火相关文献的系统调研和归纳总结,认为探讨一个遗址是否存在古人类主动用火时,首先要获取该遗址的文化考古和地层资料,确定是否曾发生过燃烧事件,然后分析是何物质发生燃烧,以及与人类活动的联系。分析表明,目前还没有任何单一的方法可以确定更新世早期的古人类用火信息,多种方法的结合才可能得到比较准确的结论。选择宏观形态分析初步判断有火活动的区域,利用傅立叶红外光谱(FTIR)、元素碳含量分析等地球化学手段确定火事件发生的确切证据,再利微观形态及微地层分析对完整沉积物进行系统研究以揭示其就地用火的可能性,从而形成古人类用火的完整证据链。由于碳稳定同位素在植被、气候与人类活动相互联系方面的广泛应用,在古人类用火研究引入这一技术手段,可为该领域提供新的研究方法和思路。 相似文献
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Rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest Mexico and Washington State, with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen-deficient zone and on a typical western continental margin. Total carbon oxidation rates (including rates for individual electron acceptors: O2, NO3−, and SO4=) were determined at depths ranging from 100 to 3000 m on both margins. Carbon oxidation rates were generally higher on the Washington margin than on the Mexican margin. The relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of O2 and NO3− from the overlying water. The relative contribution of O2 consumption increased in deeper sediments (>2000 m) as aerobic processes began to dominate the total carbon oxidation rate. Denitrification rates were highest in Washington sediments; however, denitrification represented a larger fraction of the total carbon oxidation rate in the Mexican sediments (∼40% for Mexico vs. ∼30% for Washington). Sulfate reduction accounted for as much as 79% of the total carbon oxidation rate in shallow sediments and less than 20% in deep sediments on both margins. The offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate. Pore-water O2 and NO3− penetration depths were shallowest in nearshore stations and increased offshore. Regeneration ratios of C:N:P reveal “non-Redfield” behavior on both margins. Carbon budgets for the two margins demonstrate that off Mexico, a much greater percentage of the organic matter produced in the surface ocean reached the sediments (>15% vs. <8% for Mexico and Washington, respectively). On the Mexican margin, ∼8% of the primary production escaped oxidation in the surface sediments to be permanently buried, as compared with only ∼1.2% of the primary production on the Washington margin. This suggests that oxygen-deficient conditions on Mexican margin are linked to enhanced carbon preservation. 相似文献
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Wildfires are considered one of the most common disasters in southern Africa resulting in a high number of human fatalities and financial loss on an annual basis. It is believed that increased population growth, as well as more concentrated settlement planning, is likely to result in increased fire disasters and increased human fatalities as a direct result of wildfires. To better understand the spatial and temporal variations and characteristics of wildfires in the Southern African Development Community (SADC), an 11-year dataset of satellite-derived Active Fire Hotspots was analysed using an open source geographic information system. Results indicate that annual fire frequency for most SADC countries is highly variable. Increasing trends in annual fire frequency were observed in five out of 13 SADC countries with a decrease in annual fire frequency observed in four countries. An additional four countries displayed a somewhat stable trend in fire frequency. Temporally, fires have been observed in all months for the SADC region although distinct fire seasons were observed, largely driven by uni-modal rainfall seasons. The timing, location and strength of rainfall seasons have a marked influence on fire activity depending on the seasonal wet and dry (growing and desiccation) periods. Fire activity in vegetation eco-regions can be attributed to both natural and anthropogenic sources of ignition. However, increased anthropogenic agroforestry activities have resulted in increased fire activity in numerous SADC eco-regions with woodlands, savannahs and montane grassland eco-regions being most prone to wildfires. 相似文献
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边缘海沉积物是海洋重要的碳储库,其内部的碳循环主要是由有机质矿化分解过程来驱动的。有机碳进入边缘海沉积物后,矿化分解为溶解无机碳(DIC)进入沉积物孔隙水并扩散到上层水柱,参与海洋系统碳循环;同时还有部分DIC与钙镁等离子结合形成自生碳酸盐,保存于沉积物碳库。从生物地球化学角度探讨有机质埋藏机制和效率,在此基础上重点综述沉积物硫酸盐还原、产甲烷和甲烷厌氧氧化过程的耦合机制,以及有机质矿化对自生碳酸盐形成的影响等方面的研究进展,以期加深对陆架边缘海沉积物在全球碳循环收支平衡中的作用及其气候环境效应的认识。 相似文献
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We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P. contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis appeared most recently at 2000 cal yr BP. Fire frequency varies throughout the record, with significantly shorter mean fire return intervals in the early Holocene than the mid and late Holocene. Charcoal peaks are significantly correlated with an initial increase in macrofossil accumulation rates followed by a decrease, likely corresponding to tree mortality following fire. Climate appears to be a key driver in vegetation and fire regimes over millennial time scales. Fire and other disturbances altered forest vegetation at shorter time scales, and vegetation may have mediated local fire regimes. For example, dominance of P. contorta in the early Holocene forests may have been reinforced by its susceptibility to frequent, stand-replacing fire events. 相似文献
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Continental margin sediments are important ocean carbon repository, and the internal carbon cycle is mainly driven by the mineralization processes of sedimentary organic matter. Most organic carbon is transformed to Dissolved Inorganic Carbon (DIC) by mineralization processes after being delivered to continental margin sediments, and DIC from pore water diffuses into the upper water column and participates in the ocean carbon cycle. At the same time, some DIC combines ions such as Ca2+ and Mg2+ and precipitates as authigenic carbonate minerals so that carbon is stored in the deposits. Based on the biogeochemical study of the mechanism and efficiency of organic matter burial, we discussed the interaction among sulfate reduction, methanogenesis and anaerobic oxidation of methane, and the effect of organic mineralization on the formation of authigenic carbonate. By reviewing the above-mentioned aspects, we can obtain a better understanding of the role of continental margin sediments in the global carbon cycling budgets as well as its climate and environmental effects. 相似文献
19.
Elemental carbon was extracted from sediments by chemical oxidation and identified by Raman spectroscopy. The experimental
results indicate that elemental carbon, defined by processing, is a continuum ranging from single crystal graphite to amorphous
carbon. Chemical oxidation is a feasible method to extract elemental carbon from sediments, and when experimental condition
and time are properly controlled, it can remove organic carbon without any loss of elemental carbon. However, due to the differences
in experimental conditions and methods, different results have been obtained. Therefore, we believe that the determination
of standard sample and its concentration as well as the unification of the experimental method are of great importance. Also,
the unification and definition of all these carbon particulates can facilitate transect comparison and further research in
related fields. In profile research, elemental carbon was extracted and determined by using the same method. The elemental
carbon curve tends to change with other climatic proxies, indicating elemental carbon can provide another new proxy for climatic
and environmental changes. Based on the analysis, we deduce that the elemental carbon record has different implications for
climate and environmental changes on different time-scales.
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Translated from Acta Sedimentologica Sinica, 2007, 25(5): 745–752 [译自: 沉积学报] 相似文献
20.
Marc-André Parisien Gregg R. Walker John M. Little Brian N. Simpson Xianli Wang Daniel D. B. Perrakis 《Natural Hazards》2013,66(2):439-462
Fire and land management in fire-prone areas can be greatly enhanced by estimating the likelihood of fire at every point on the landscape. In recent years, powerful fire simulation models, combined with an in-depth understanding of an area’s fire regime and fire environment, have allowed forest managers to estimate spatial burn probabilities. This study describes a methodology for selecting input data and model parameters when creating burn probability maps in difficult-to-model areas and reports the results of a case study for a large area of the Columbia Mountains, British Columbia, Canada. In addition to having particularly mountainous topography, the study area is covered by vegetation types that are poorly represented in fire behavior systems, even though these vegetation types have experienced considerable (if highly irregular) fire activity in premodern times (before 1920). Parameterization of the fire environment for simulation modeling was accomplished by combining various types of fire information (e.g., fire history studies, reconstructed fire climatologies), new technologies (high-resolution remotely sensed data, wind flow modeling), and—a must in data-limited areas—ample expert advice. In this study, we made extensive use of personal accounts from experienced fire behavior officers for the creation of model inputs. Despite difficulties in validating outputs of burn probability models, the multisource model-building approach described here provides a conservative, yet informative, means of estimating the likelihood of fire. Due to the data-intensive nature of the modeling and paucity of input data, an argument is made that modelers must focus on the inputs that are the most influential for their study area. 相似文献