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1.
镁（Mg）作为主要的造岩元素及生物营养元素,是连接大陆、海洋和地球内部循环的重要纽带。碳酸盐岩作为Mg的主要储库,是全球Mg循环的重要组成环节,利用Mg同位素示踪碳酸盐岩沉积—成岩过程是有效反演深时海水Mg同位素组成（δ26Mg海水）、恢复全球Mg循环的基本前提。近二十年来,Mg同位素在示踪碳酸盐岩沉积—成岩过程研究中取得了较大进展:1）不同类型碳酸盐矿物形成过程中的Mg同位素分馏及其影响因素的研究得到完善;2）建立了Mg同位素地球化学模型,对不同白云石化过程进行半定量—定量模拟;3）初步探索了利用Mg同位素反演早期成岩流体体系的方法。以上研究进展为利用碳酸盐岩恢复δ26Mg海水奠定了理论基础,在选择有效的碳酸盐岩载体恢复δ26Mg海水时,需充分考虑碳酸盐岩的沉积—成岩过程及其对Mg同位素组成的影响,并适当结合地球化学模型,消除沉积—成岩因素的影响,进而恢复δ26Mg海水。 相似文献
2.
塔里木盆地荒漠植物与表土碳同位素组成研究 总被引：2，自引：1，他引：1
表土有机质碳同位素组成(δ13Corg)反映了来自于地表各种植物δ13Corg的一个混合信息.要从沉积物δ13Corg中提取可靠的植被信息,需要系统研究现代表土有机质δ13Corg与地表植被δ13Corg的差异.初步研究了塔里木盆地主要现代植被及土壤碳同位素组成,对比不同地区土壤和地表植被δ13Corg的差异.结果表明:塔里木盆地柽柳属种群中植物与表土碳同位素组成之间存在显著相关关系,说明在干旱地区土壤中微生物和水生生物等的干扰因素可以忽略,其现代土壤的同位素组成只与地表相应的主要植被类型有关.塔里木盆地柽柳属种群中表土有机质δ13Corg值比地表植被δ13Corg值平均偏正1.71‰左右,不同于其它地区表土和地表植被δ13Corg差异(2.2‰,1‰,0.5‰)的结果,反映不同地区表土和地表植被有机质δ13Corg值差异不同.在利用沉积物δ13Corg值提取古生态植被信息时,应考虑到不同地区土壤有机质与地表植被δ13Corg值的不同差异会影响植被中C3、C4植物组成情况. 相似文献
3.
选取采自南海天然气水合物赋存区海马冷泉,管状蠕虫区（ROV06站位）和贻贝区（HM101站位）的2个表层沉积物柱状样品,提取其中的生物标志化合物,对其种类和稳定碳同位素进行了测定,用以探讨海底表层沉积物中的有机质来源、微生物种群分布及其对冷泉渗漏活动的响应特征. 两个站位的沉积物中均发现了大量与甲烷厌氧氧化古菌（ANME）有关的生物标志物,如2,6,11,15?四甲基十六烷（crocetane）、2,6,10,15,19?五甲基二十烷（PMI）等类异戊二烯烃,古醇（archaeol）、sn2?羟基古醇（sn2?OH?Ar）等,以及来源于硫酸盐还原菌（SRB）的异构/反异构脂肪酸iso?C15和ai?C15等. 这些生物标志物均具有极低的碳同位素特征（古菌生标δ13C值低至-126‰,硫酸盐还原菌生标δ13C值低至?89‰）,表明沉积物中发生了甲烷厌氧氧化作用（AOM）. ROV06和HM101站位沉积物中均检测到了crocetane,大多数sn2?羟基古醇/古醇大于1,同时ai?C15/iso?C15脂肪酸比值小于2,这说明两个站位沉积物中的甲烷厌氧氧化古菌主要以ANME?2/DSS为主,指示甲烷渗漏强度较强. ROV06站位的表层沉积物含有crocetane,但sn2?羟基古醇/古醇小于1,且ai?C15/iso?C15脂肪酸比值大于2.1,指示了ANME?1/DSS和ANME?2/DSS混合存在的种群特征,说明ROV06站位顶部甲烷渗漏强度有减小的趋势. 根据古菌种群ANME?2化合物对甲烷的碳同位素分馏（Δ:-50‰）及古菌生物标志物（PMI、古醇、sn2?羟基古醇）的平均δ13C值,计算得到甲烷δ13C值（-58‰~-53‰）,显示甲烷为热成因和生物成因混合气. 虽然ROV06和HM101站位的甲烷具有相近的δ13C值,但ROV06站位的SRB生物标志物比HM101站位要更加亏损13C（Δδ13C:18‰）,这可能与管状蠕虫的共生菌（硫氧化菌）吸收硫化物并释放出硫酸盐有关,因为其不断释放出的硫酸盐很可能极大地增强了甲烷厌氧氧化作用,使沉积物中含有更多13C亏损的无机碳. 相似文献
4.
菱铁矿很好地记录了过去地质流体的信息,能够用于示踪生物地球化学反应相关的成岩作用带。台湾国姓地区中新世海相泥页岩中发育自生的菱铁矿结核,其成因尚未厘清。野外观察发现菱铁矿以不连续透镜体平行散布于泥页岩中,主要由自生碳酸盐菱铁矿（78.63%）等矿物组成。菱铁矿的稀土元素配分模式为轻稀土亏损、中稀土富集,无Ce异常,指示菱铁矿形成于弱氧化的沉积环境,弱氧化的环境促进了菱铁矿在次氧化带的沉淀。菱铁矿的δ13CVPDB和δ18OVPDB值分别为-3.69‰~+0.08‰和-1.09‰~+0.25‰,指示菱铁矿形成于次氧化带,碳源很可能是海水和有机质降解混合产生。研究表明自生菱铁矿能够被用于识别沉积物中的生物地球化学过程和指示成岩作用带。 相似文献
5.
海底天然气渗漏系统微生物作用及冷泉碳酸盐岩的特征 总被引：18，自引：3，他引：18
海底天然气渗漏系统是全球海洋环境中广泛分布的自然现象。部分渗漏天然气通过细菌作用转变为二氧化碳,同时海水硫酸盐被还原为硫化氢, 与孔隙水中的钙和铁结合而沉淀冷泉碳酸盐岩。冷泉碳酸盐岩的常见矿物有微晶方解石、文石、白云石和黄铁矿。冷泉碳酸盐岩常发育一些特殊的组构, 如黄铁矿环带结核、溶蚀面、平底晶洞、凝块和向下生长的叠层石组构等。碳酸盐岩特别负的δ13C值指示碳来源于生物成因的甲烷, 而18O富集可能与天然气水合物的分解有关。冷泉碳酸盐岩中黄铁矿的δ34S值低于海水的, 这指示硫来源于微生物还原的海水硫。冷泉碳酸盐岩中的生物标志化合物及其极负的δ13C值指示微生物的生命代谢活动。 相似文献
6.
海洋沉积物中的N和P随沉积物的粒度由粗到细,含量逐渐升高,而Si则降低;积物中N、P、Si的含量还随海区、输入源、季节、动力学过程及生物生产过程不同而变化.控制海洋沉积物-海水界面N、P、Si沉积、释放及循环的因素,包括有机质和溶解氧的浓度、有机质中C、N、P、Si的相对比例、沉积物-海水界面附近的氧化还原环境、生物扰动、温度、水深、pH值、不同形态S的浓度、金属离子以及水动力条件等.一般其综合作用的表现是,沉积物-海水界面之间NH+4、PO3-4和Si(OH)4从沉积物向上覆水扩散转移,而硝酸盐和亚硝酸盐的通量方向相反,通量的大小随着海区的不同差别较大. 相似文献
7.
碳酸盐岩的Fe/Mn元素比值,作为一项新的地球化学指标,可以用于恢复海洋的氧化还原状态.在氧化条件下,Fe3+和Mn4+均不可溶,因此氧化海水中的溶解Fe和Mn的含量均很低.Fe3+和Mn4+在还原条件下可以被细菌还原为可溶的Fe2+和Mn2+,而氧化还原电位的计算表明,Mn4+的还原要早于Fe3+的还原,因此细菌的Mn还原过程发生在沉积物的更浅层.可溶的Fe2+和Mn2+向上扩散到海水中,替代碳酸盐岩晶格里的Ca2+,因此碳酸盐岩晶格中的Fe2+和Mn2+的含量受控于来自沉积物孔隙水的扩散,而后者又与水岩界面的氧化还原状态相关.因此可以预测,随着海水变得逐渐缺氧,碳酸盐岩中的Fe/Mn比值会逐渐增高.为了验证这一假说,我们分析了中元古代高于庄组白云岩的Fe/Mn比值.研究发现,几乎所有的样品的Fe/Mn比值介于20～30之间,显著高于泥盆纪末期深水碳酸盐岩和浅水台地碳酸盐岩的Fe/Mn比值.高于庄组碳酸盐岩高的Fe/Mn比值一方面可能指示了中元古代低的大气氧气浓度和海洋的广泛缺氧,也可能反映了白云岩形成于缺氧的沉积物空隙水里. 相似文献
8.
海相沉积氧化还原环境的地球化学识别指标 总被引：6，自引：0，他引：6
全球海洋在10-5.4亿年间演变成氧化环境,此后历经多次全球性的缺氧事件后演变到现在的氧化环境.海水和沉积物中多种无素的循环、分异和富集明显受氧化还原条件的影响.Mn、Mo、Cr、V和U等变价元素的溶解度随氧化还原条件的改变产生极大变化,导致沉积物中的元素含量分异:Ni、Co、Cu和Zn等在还原条件下形成硫化物沉淀,导致沉积物中对应元素的富集.这些元素的地球化学行为是古海洋氧化还原条件的灵敏指示剂,作为恢复古海洋氧化还原条件环境变化的地球化学指标.黄铁矿化程度(DOP)、生物樗化合物和Ce异常等也是沉积物氧化还原条件的常用判别指标.泥岩石研究中通常采用DOP、U/Th、自生U、V/Cr、Ni/Co和生物标志化合物等指标,碳酸盐岩则主要采用Ce异常指标.当前各种指标的定性分析都取得比较一致的结果,但是用一种或几种定量的地球化学指标来恢复整个古海洋的氧化还原环境目前还有很大的问题. 相似文献
9.
海洋沉积物中氧化还原敏感元素对水体环境缺氧状况的指示作用 总被引：2，自引：0，他引：2
近年来由于人为污染水体富营养化加剧,缺氧区面积不断增大,利用沉积物中氧化还原敏感元素反演水体缺氧情况已经发展成为海洋化学领域的热点研究方向。本文详细阐述了氧化还原敏感元素的富集机制,并总结了利用沉积物中氧化还原敏感元素在不同氧化还原条件下的富集程度反映海水缺氧程度和底质氧化还原状况的一系列指标,如Re/Mo、Cd/U、Th/U、V/Sc、V/(V+Ni)值,U—Mo共变模型,δ~(98/95)Mo,多指标微/痕量元素模型以及氧化还原敏感元素-有机质共变模型等。沉积物中Re、Mo含量、Re/Mo值、自生Mo/U值、Th/U值对上层水体缺氧和氧化条件区分良好,可定量指征上层水体的缺氧情况。沉积物中Re含量近似于1 ng/g(地壳值),Mo含量1μg/g(地壳值),Re/Mo值接近0.3×10~(-3),Mo—U富集系数比为(0.1～0.3)×现代海水,Th/U值2,可指示氧化环境;Re含量在10～30 ng/g,Mo含量近似于1μg/g,Re/Mo值10×10~(-3)～30×10~(-3),Mo—U富集系数比1×现代海水,Th/U值在0～2范围内,可指示缺氧环境;Re含量30 ng/g,Mo富集达到20～40μg/g,Re/Mo值接近0.7×10~(-3)(海水中Re/Mo值),Mo—U富集系数比为(3～10)×现代海水,可指示极度缺氧的硫化环境。Mo_(EF)—U_(EF)交会对数坐标图、氧化还原敏感元素-有机质共变模型指标可定性分析上层水体的缺氧情况;V/(V+Ni)值对于次氧化沉积物指示效果不佳;Cd/U值在次缺氧条件下的变化机制复杂,还需进一步研究。生物扰动、成岩作用、人为污染、水体局限、高有机碳通量、Fe、Mn氧化物循环等因素通过影响氧化还原敏感元素在沉积物中的富集与迁移,从而影响氧化还原敏感元素指标的应用,应剔除有机质吸附与陆源输入等非自生部分的影响,结合各种指标互相印证,综合判别水体氧化还原状态。 相似文献
10.
本次研究对华南扬子地区下志留统布拖组沉积物进行了地球化学与同位素分析。结果显示，布拖组的δ15N和δ13Corg值由布拖组下部至上部逐渐升高，其中布拖组下部沉积物的低δ13Corg值与全球范围内强烈的火山活动有关，低δ15N值与缺氧海洋条件下的生物固氮作用有关，而布拖组上部沉积物的高δ15N值则与扬子海逐渐富氧化有关。研究结果表明，早志留世布拖期强烈的火山活动引发的生产力升高和海洋底层水体缺氧，导致了深水地区龙马溪组页岩和浅水地区灰岩、泥灰岩中有机质的富集，而布拖早期持续的海洋缺氧则可能抑制晚奥陶世生物大灭绝后生物的复苏。 相似文献
11.
华北寒武纪—奥陶纪豹皮状碳酸盐岩系生物扰动成因 总被引：1，自引：1，他引：0
华北地区寒武系和奥陶系发育了大量的生物扰动白云岩/生物扰动灰岩,选择两个代表性剖面——河南登封寒武系剖面和山西兴县奥陶系剖面进行碳酸盐岩系生物扰动成因研究。河南登封寒武系第二统朱砂洞组中的遗迹化石较单一,主要为Thalassinoides、含有少量Planolites;山西兴县中奥陶统马家沟组五5亚段中遗迹化石较丰富,识别出的遗迹化石共7个遗迹属,分别为Arenicolites、Cylindricum、Helminthopsis、Lorenzinia、Planolites、Teichichnus、Thalassinoides,其中Thalassinoides占主导地位。朱砂洞组主要为滨岸碳酸盐潮坪相,中奥陶统马家沟组五5亚段主要为局限台地相。通过野外地质考察及室内相关实验手段及方法,利用偏光显微镜、扫描电镜对生物潜穴及围岩进行了宏观和微观结构分析,发现生物潜穴内部主要为白云石,基质围岩主要为方解石,生物潜穴在野外露头上表现为颜色不一的斑块状。两个剖面大量发育遗迹化石Thalassinoides(海生迹),Thalassinoides的三维潜穴系统为白云石化流体提供了良好的运移通道,为回流渗透作用提供了有利条件,促进潜穴充填物白云石化,从而形成了大量豹皮状的生物扰动白云岩。 相似文献
12.
The geochemical cycles of iron and sulphur in marine sediments are strongly intertwined and give rise to a complex network of redox and precipitation reactions. Bioturbation refers to all modes of transport of particles and solutes induced by larger organisms, and in the present-day seafloor, bioturbation is one of the most important factors controlling the biogeochemical cycling of iron and sulphur. To better understand how bioturbation controls Fe and S cycling, we developed reactive transport model of a coastal sediment impacted by faunal activity. Subsequently, we performed a model sensitivity analysis, separately investigating the two different transport modes of bioturbation, i.e. bio-mixing (solid particle transport) and bio-irrigation (enhanced solute transport). This analysis reveals that bio-mixing and bio-irrigation have distinct—and largely opposing effects on both the iron and sulphur cycles. Bio-mixing enhances transport between the oxic and suboxic zones, thus promoting the reduction of oxidised species (e.g. iron oxyhydroxides) and the oxidation of reduced species (e.g. iron sulphides). Through the re-oxidation of iron sulphides, bio-mixing strongly enhances the recycling of Fe and S between their reduced and oxidised states. Bio-irrigation on the other hand removes reduced solutes, i.e. ferrous iron and free sulphide, from the sediment pore water. These reduced species are then reoxidised in the overlying water and not recycled within the sediment column, which leads to a decrease in Fe and S recycling. Overall, our results demonstrate that the ecology of the macrofauna (inducing bio-mixing or bio-irrigation, or both) matters when assessing their impact on sediment geochemistry. This finding seems particularly relevant for sedimentary cycling across Cambrian transition, when benthic fauna started colonizing and reworking the seafloor. 相似文献
13.
底栖生物在沉积物表面及其内部留下的各种活动痕迹——生物扰动构造(Bioturbation)具有指示环境的重要意义,这是由于底栖生物的生存和发展与沉积物的性质和沉积作用过程休戚相关,对沉积环境有极大的依赖性。同时,生物又通过其自身的觅食和摄食活动,反过来影响沉积作用过程,并可破坏和改造沉积物的原生构造。因此,这种原地生成的生物扰动构造如能保存在地层中,它们就可以为沉积环境的判别提供可靠的信息。 相似文献
14.
通过野外露头实地观测和室内薄片分析,对豫西北奥陶系马家沟组三段豹斑灰岩的发育特征及成因进行了研究。结果表明：研究区马家沟组三段豹斑灰岩中“豹斑”形态多样,形似生物潜穴,结合遗迹学特征分析,可将“豹斑”按其形态划分为Psilonichnus、Chnodrites、Thalassinoides、Helminthopsis及Planolites等5种生物潜穴类型,不同类型生物潜穴的出现主要受到沉积环境的制约;生物潜穴充填物按照其不同白云石化程度可被划分为泥晶白云石充填物及粉-细晶白云石充填物两种类型,其中泥晶白云石主要存在于Psilonichnus及Chnodrites两种潜穴中,而粉-细晶白云石则主要存在于Thalassinoides、Helminthopsis及Planolites之中;潜穴充填物的白云石化过程可被分为白云石化前的准备阶段、白云石的形成阶段及白云石的后期调整等三个阶段,不同潜穴的白云石化状态差异就是在此过程中形成的。 相似文献
15.
E. R. Hunting H. G. van der Geest 《International Journal of Environmental Science and Technology》2011,8(3):553-560
Redox potential has been adopted as a qualitative parameter for interpreting solubility changes of nutrients and contaminants and the biological activity within wetland systems for several decades. The majority of studies considering the redox geochemistry in sediments used measurements of bulked material and single point measurement of biogeochemical parameters for interpretation, yet it remains questionable whether this information is reliable for environments that are very dynamic, such as wetlands. In this study it is evaluated whether variations in redox potential reflect dynamics of denitrification and overall bacterial respiration using continuous measurements of redox potential in time-series experiments in laboratory microcosms, in which the biogeochemical variation was enhanced by bioturbation. The results presented here suggest that measurements of redox potential have predictive potential in approximating rates of denitrification and overall bacterial respiration in aquatic sediments. The data clearly suggest that, while sediment bulk measurements and measurements of single profiles of redox potential, denitrification and bacterial activity often fail to provide ecological relevant information in dynamic systems, measurements of spatial and temporal redox potential profiles provide a useful parameter that reflects biogeochemical processes and functioning of sediments. 相似文献
16.
Kristensen E 《Geochemical transactions》2001,2(1):92
Known effects of bioturbation by common polychaetes (Nereis spp. and Arenicola marina) in Northern European coastal waters on sediment carbon diagenesis is summarized and assessed. The physical impact of irrigation and reworking activity of the involved polychaete species is evaluated and related to their basic biology. Based on past and present experimental work, it is concluded that effects of bioturbation on carbon diagenesis from manipulated laboratory experiments cannot be directly extrapolated to in situ conditions. The 45–260% flux (e.g., CO2 release) enhancement found in the laboratory is much higher than usually observed in the field (10–25%). Thus, the faunal induced enhancement of microbial carbon oxidation in natural sediments instead causes a reduction of the organic matter inventory rather than an increased release of CO2 across the sediment/water interface. The relative decrease in organic inventory (G b /G u) is inversely related to the relative increase in microbial capacity for organic matter decay (k b /k u). The equilibrium is controlled by the balance between organic input (deposition of organic matter at the sediment surface) and the intensity of bioturbation. Introduction of oxygen to subsurface sediment and removal of metabolites are considered the two most important underlying mechanisms for the stimulation of carbon oxidation by burrowing fauna. Introduction of oxygen to deep sediment layers of low microbial activity, either by downward irrigation transport of overlying oxic water or by upward reworking transport of sediment to the oxic water column will increase carbon oxidation of anaerobically refractory organic matter. It appears that the irrigation effect is larger than and to a higher degree dependent on animal density than the reworking effect. Enhancement of anaerobic carbon oxidation by removal of metabolites (reduced diffusion scale) may cause a significant increase in total sediment metabolism. This is caused by three possible mechanisms: (i) combined mineralization and biological uptake; (ii) combined mineralization and abiogenic precipitation; and (iii) alleviation of metabolite inhibition. Finally, some suggestions for future work on bioturbation effects are presented, including: (i) experimental verification of metabolite inhibition in bioturbated sediments; (ii) mapping and quantification of the role of metals as electron acceptors in bioturbated sediments; and (iii) identification of microbial community composition by the use of new molecular biological techniques. These three topics are not intended to cover all unresolved aspects of bioturbation, but should rather be considered a list of obvious gaps in our knowledge and present new and appealing approaches. 相似文献
17.
塔河油田奥陶系鹰山组和一间房组生物扰动型储集层发育。在岩心观测的基础上,通过典型岩样切片、偏光显微镜、阴极发光显微镜和X射线显微镜观测以及XRD测试分析,对研究区奥陶系生物扰动型储集层的发育特征进行了研究。研究区奥陶系可识别的生物扰动分为2类,分别是 Thalassinoides和Helminthopsis,但以Thalassinoides最为发育,扰动体积可达90%;生物潜穴充填物以白云石颗粒为主,可达90%以上;宿主围岩为泥晶灰岩。随着塔河油田早—中奥陶世海侵、海退沉积环境的变化,生物潜穴的发育呈现出明显的周期性演化规律。在综合提取生物扰动型储集层特征信息的基础上,以沉积学和遗迹学理论为指导,应用3ds Max软件对研究区奥陶系生物扰动型储集层进行了三维重构。该研究虚拟再现了塔河油田生物扰动型储集层的内部结构与微观特征,不仅为后续研究这类储集层的宏观非均质性与微观各向异性、定量表征该类储集层微观尺度上的渗流特征奠定了基础,而且还为完善塔河油田奥陶系油藏模型提供了一种新思路。 相似文献
18.
Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most
significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low.
In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam
trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm
of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly
affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator,
and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing
box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and
chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos
biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of
bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar
to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium
due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance
scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important
carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems,
where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance
could cause large fluctuations in benthic chemical fluxes and storage. 相似文献
19.
Organic matter mineralization in sediment of a coastal freshwater lake and response to salinization 总被引：1，自引：0，他引：1
Richard W. Canavan Caroline P. Slomp Philippe Van Cappellen Gerard A. van den Berg 《Geochimica et cosmochimica acta》2006,70(11):2836-2855
Solid phase and pore water chemical data collected in a sediment of the Haringvliet Lake are interpreted using a multi-component reactive transport model. This freshwater lake, which was formed as the result of a river impoundment along the southwestern coast of the Netherlands, is currently targeted for restoration of estuarine conditions. The model is used to assess the present-day biogeochemical dynamics in the sediment, and to forecast possible changes in organic carbon mineralization pathways and associated redox reactions upon salinization of the bottom waters. Model results indicate that oxic degradation (55%), denitrification (21%), and sulfate reduction (17%) are currently the main organic carbon degradation pathways in the upper 30 cm of sediment. Unlike in many other freshwater sediments, methanogenesis is a relatively minor carbon mineralization pathway (5%), because of significant supply of soluble electron acceptors from the well-mixed bottom waters. Although ascorbate-reducible Fe(III) mineral phases are present throughout the upper 30 cm of sediment, the contribution of dissimilatory iron reduction to overall sediment metabolism is negligible. Sensitivity analyses show that bioirrigation and bioturbation are important processes controlling the distribution of organic carbon degradation over the different pathways. Model simulations indicate that sulfate reduction would rapidly suppress methanogenesis upon seawater intrusion in the Haringvliet, and could lead to significant changes in the sediment’s solid-state iron speciation. The changes in Fe speciation would take place on time-scales of 20-100 years. 相似文献
20.
An analysis of Thalassinoides ichnofabrics in the Cambrian Stage 4 Longwangmiao Formation from six sections near Chonqing in the Middle and Upper Yangtze Block of South China was conducted to promote the understanding of the paleoenvironment of this period. Thalassinoides ichnofabrics are divided into three types according to their morphology,bioturbation index, abundance and related parameters: banded, mottled and grid. The completeness of the ichnofabrics gradually increases from banded to gri... 相似文献