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1.
滨海红树林泥炭沉积物中硫的赋存特点及其控制因素 总被引：4，自引：0，他引：4
海南和厦门两地滨海红树林沉积物和埋藏泥炭中硫的成分分析表明,滨海红树林沉积物和泥炭中的硫以硫化铁硫为主,有机硫次之,硫酸盐硫含量最低。泥炭沉积物中硫的赋存形式和特点与沉积环境密切相关。海南福田地区红树林泥炭沉积物主要形成于红树林潮上坪和泥炭坪,硫含量较高,平均为2.60%,且有机硫含量与有机碳含量呈正相关,而硫化铁硫含量与有机碳含量没有明显的相关性;厦门海沧镇红树林泥炭沉积物形成于红树林潮间坪以及潮道环境,硫含量较低,平均值仅为0.43%,形态硫和有机质的相关性与海南红树林泥炭地沉积物相反。红树林泥炭沉积物中铁的硫化物主要以黄铁矿形式产出,且以莓球状形态为主。研究表明,黄铁矿与次生有机硫的生成与微生物活动密切相关,造成红树林泥炭中硫含量差异最主要的原因不是硫源,而是有机质的供给与沉积微环境的影响。现代滨海红树林泥炭沼泽中硫的赋存特征将对煤中硫成因的研究提供重要的科学依据。 相似文献
2.
Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide(H_2S) in oil and gas reservoirs. However,a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H_2S generation,in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H_2S have not been evaluated. In this study,laboratory experiments were conducted from 200 to 450° C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results,preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H_2S and thiophenes at as low as 330°C in the presence of water and n-pentane. High concentrations of H_2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However,much more organic sulfur compounds(OSCs) were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally,most of sulfur liberated from pyrite at elevated temperatures was converted to H_2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H_2S,given the main hydrogen source derived from hydrocarbons. In addition,cracking of pyrite in the presence of 1-octene under hydrous conditions was found to proceed at 200°C,producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H_2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction(TSR) due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long-chained hydrocarbons in natural gas. Nevertheless,in some cases,OSCs and/or low contents of H_2S found in deep buried reservoirs may be associated with the deposited pyrite-bearing rock and organic matters(hydrocarbons),which still needs further investigation. 相似文献
3.
铜官山矿田是铜陵矿集区内五大矿田之一,矿田内顺层产出的层状硫化物矿体是铜金矿床的主矿体,矿体内含有较多的胶状黄铁矿,其成因的争议制约了对铜金矿床成矿作用的解析。本文主要利用场发射扫描电镜(FE-SEM)等纳米矿物学手段,并结合光学显微镜、粉晶X射线衍射(XRD)、微区激光拉曼光谱分析等方法,对矿田内铜官山矿床及天马山矿床内层状硫化物矿体中胶状黄铁矿矿石的矿物组成、微形貌、微结构等特征进行系统研究,结果表明胶状黄铁矿矿石多呈胶状、鲕状结构,具有同心环状构造,同心环被赤铁矿、菱铁矿与黄铜矿脉穿切。同心环主要由白铁矿+有机质与胶状黄铁矿交替组成。胶状黄铁矿的黄铁矿颗粒粒径从纳米至亚微米均有分布,以自形-半自形立方体为主,少数呈他形,脉体边部胶状黄铁矿颗粒较大,自形程度较高,重结晶显著。矿石中含有少量白云石、伊利石微晶体,与胶状黄铁矿紧密共存,显示典型沉积特征。共存石英磨圆度较高,存在次生加大现象,表面存在胶状黄铁矿印模,显示为碎屑成因。这些综合信息表明胶状黄铁矿非岩浆热液成因,而是与石炭系地层同沉积成岩成因,并可能有微生物作用参与。高孔隙率、高化学活性及较高有机质含量的胶状黄铁矿可能为燕山期岩浆热液演化的含铜成矿流体提供了沉淀剂,对矿田内铜金硫化物矿体的层控性发挥了重要的控制作用。 相似文献
4.
Data on abundance and isotopic composition of porewater and sedimentary sulfur species are reported for relatively uncontaminated and highly contaminated fine-grained anoxic sediments of St. Andrew Bay, Florida. A strong contrast in amount and composition of sedimentary organic matter at the two sites allows a comparative study of the historical effects of increased organic loading on sulfur cycling and sulfur isotopic fractionation. In the contaminated sediments, an increase in organic loading caused increased sedimentary carbon/sulfur ratios and resulted in higher rates of bacterial sulfate reduction, but a lower efficiency of sulfide oxidation. These differences are well reflected in the isotopic composition of dissolved sulfate, sulfide, and sedimentary pyrite. Concentration and isotopic profiles of dissolved sulfate, organic carbon, and total sulfur suggest that the anaerobic decomposition of organic matter is most active in the upper 8cm but proceeds at very slow rates below this depth. The rapid formation of more than 90% of pyrite in the uppermost 2 cm which corresponds to about 3 years of sediment deposition allows the use of pyrite isotopic composition for tracing changing diagenetic conditions. Sediment profiles of the sulfur isotopic composition of pyrite reflect present-day higher rates of bacterial sulfate reduction and lower rates of sulfide oxidation, and record a profound change in the diagenetic cycling of sulfur in the contaminated sediments coincident with urban and industrial development of the St. Andrew Bay area. 相似文献
5.
《Applied Geochemistry》1998,13(2):257-268
We report the hydrogeochemical modeling of a complicated suite of reactions that take place during the oxidation of pyrite in a marine sediment. The sediment was equilibrated in a column with MgCl2 solution and subsequently oxidized with H2O2. The oxidation of pyrite triggers dissolution of calcite, cation and proton exchange, and CO2 sorption. The composition of the column effluent was modeled with PHREEQC, a hydrogeochemical transport model. The model was extended with a formal ID transport module which includes dispersion and diffusion. The algorithm solves the advection-reaction-dispersion equation with explicit finite differences in a split-operator scheme. Also, kinetic reactions for pyrite oxidation, calcite dissolution and precipitation, and organic C oxidation were included. Kinetic relations for pyrite oxidation and calcite dissolution were taken from the literature, and a coefficient equivalent to the ratio A/V (surface over volume), was adjusted to fit the experimental data. The comparison of model and experiment shows that ion exchange and sorption are dominant chemical processes in regulating and buffering water quality changes upon the oxidation of pyrite. Cation exchange was assigned to the colloidal fraction ( < 2 μm) and deprotonated organic matter, proton buffering to organic matter, and CO2 sorption to amorphous Fe-oxyhydroxide. These processes have been neglected in earlier modeling studies of pyrite oxidation in natural sediments. 相似文献
6.
位于湖南中部的城步铺头黄铁矿床,是产于泥盆系基维特阶的层状矿床,1984年作者在本刊报导过这个矿床的沉积环境。根据新的资料,再次对它的成因进行研究。该矿床位于华南古大陆边缘裂谷系的北东向深水盆地中,含矿岩系由暗色的硅质岩-泥灰岩组成,矿体呈层状整合产出,以黄铁矿为主,硫同位素以富含32S为特点（δ34S＝-17．4‰～-30.10‰）。含矿岩系及矿石中,有机质含量较高（3％～5％）,有机质类型为腐殖-腐泥混合类型,成熟度较高。矿石具致密块状及条带状构造,由大量草莓状黄铁矿组成,它们主要出现在致密块状矿石中。矿石及含矿围岩的稀土元素、微量元素组成,与现代大洋裂谷或隆起区中的热液沉积物的特征相似,表明它们具有相同的来源和成因,应属海底热液喷流沉积矿床,大量存在的有机质,对于矿床的形成也起了重要的作用。 相似文献
7.
Robert L Folk 《Journal of Earth System Science》2005,114(3):369-374
Study of sedimentary pyrite in the form of framboids, euhedral crystals or metasomatic masses has revealed that their surfaces
are commonly covered with spheroids of about 50 nm. This applies to all the examples studied, from modern to Proterozoic.
These spheroids are interpreted as the pyritized corpses of nannobacterial cells; if correct, this indicates that precipitation
of iron sulfide was performed by these dwarf forms of bacteria, often associated with decaying organic matter. 相似文献
8.
Gordana DEVIC Petar PFENDT Branimir JOVANCICEVIC Zoran POPOVIC 《《地质学报》英文版》2006,80(4):574-588
The early diagenetic characteristics of pyrite formation processes in a Miocene freshwater sequence of mixed sediments （coal fragments in clays, sandstones or shales） alternating with continuous brown coal layers was investigated. Based on abundant minerals, the following main sedimentary environments were distinguished： the illite-montmorillonitic （I-M）, calcitic （Ct） and coal-forming environment （CL）. For these hydrogeochemically differing environments the effects of limiting factors on the pyrite formation process （availability of sulphate and Fe, amount of organic matter and participation of organic sulphur） were assessed by correlation analysis. Significant differences in the effects of these limiting factors in the particular environments were observed. These differences were explained taking in account the different oxidative activity, Fe-complex and surface complex forming properties of humic substances in dependence of pH of environment and the abundance of sorptionally active clay minerals. In environments having a relatively low pH and containing clay minerals （I-M- and CL-environments） the oxidative activity of humic substances （Hs） on pyrite precursors was greatly prevented however pyrite formation depended on reactive Fe availability as the consequence of complex formation. On the contrary, in environments with a relatively high pH, as it was the calcitic, the oxidative activity of Hs was greatly enhanced, thus oxidizing the sulfur precursors of pyrite. The oxidation degree of organic matter was probably also a consequence of the differing activity of the humic electron-acceptors. 相似文献
9.
Various Fe–S minerals of the mackinawite–greigite–pyrite association, ubiquitous in biogenic remains from Jurassic mudstones, have been described in detail in an SEM–EDS study. Two diagenetic stages of Fe sulphide formation and preservation in the Jurassic organic skeletons are identified. In the first stage, pyrite formed as euhedra and framboids shortly after deposition, mainly in the interiors of the skeletons which still contained labile organic matter. The second stage of iron sulphide formation was related to the later stages of diagenesis, when the influence of the surrounding sediment was more dominant, although some organic matter was still present in the biogenic skeletons. A Fe-rich carbonate–aluminosilicate cement was then introduced between the earliest iron sulphides and later subsequently sulphidized, to form a metastable iron monosulphide of mackinawite composition and then greigite. 相似文献
10.
三水盆地古近系(土布)心组黑色页岩中黄铁矿的形成及其控制因素 总被引：3，自引：0，他引：3
黄铁矿是富有机质沉积的特征矿物。根据TOC/S、TOC/DOP、S/Fe关系以及S TOC Fe多重线性回归分析结果对三水盆地古近系〖HT5”,6”〗土〖KG-*3〗布〖HT5”SS〗心组红岗段黑色页岩中沉积黄铁矿的形成及其控制因素进行了分析。土布心组红岗段黑色页岩的黄铁矿有成岩黄铁矿和同生黄铁矿两种成因组分。红岗段下部（亚段A）有机碳含量普遍较低,底部水体以弱氧化条件为主,硫酸盐还原作用发生于沉积物/水界面以下,黄铁矿为成岩成因,其形成主要受有机质的限制。红岗段中上部（亚段B和C）的沉积条件变化频繁,其有机碳含量变化幅度大。富有机质（TOC>4%）岩层形成于缺氧的底部水体条件下。水体中可含H2S,碎屑铁矿物在埋藏之前即与之在水体中反应形成同生黄铁矿。这一过程不受有机质的限制,而是受活性铁与H2S接触时间的限制。同时,由于大量淡水输入导致硫酸盐浓度的降低,从而对硫化物形成有一定的限制作用。对于低有机质（TOC<4%）样品,黄铁矿由同生和成岩组分组成。其中以成岩黄铁矿为主,其形成过程主要受有机质限制,而同生黄铁矿受铁矿物与H2S接触时间的限制。 相似文献
11.
12.
鄂尔多斯盆地上三叠统延长组长7段富有机质页岩是该盆地中生界含油系统的主力烃源岩,其有机质丰度高,类型好,具有巨大的生烃潜力。该套烃源岩中有机质的富集很大程度上取决于长7期的高古生产力及其提供的充足的有机质。长7期藻类勃发的存在已被多数学者所接受,但是目前还缺乏直观、有力的证据。笔者等通过薄片和扫描电镜观察、能谱分析,在长7段的脉状黄铁矿附近和碳酸盐结核中发现了属种单一、分布丰度高的藻类化石,它们呈现出近似球状的轮廓,在中部分布着一条裂缝。这些藻类化石的发现具有重要的地质意义,它为长7期的藻类勃发提供了很好的证据,也为该时期热液活动的重要作用提供了有力的支撑。 相似文献
13.
鄂尔多斯盆地上三叠统延长组长7段富有机质页岩是该盆地中生界含油系统的主力烃源岩,其有机质丰度高,类型好,具有巨大的生烃潜力。该套烃源岩中有机质的富集很大程度上取决于长7期的高古生产力及其提供的充足的有机质。长7期藻类勃发的存在已被多数学者所接受,但是目前还缺乏直观、有力的证据。笔者等通过薄片和扫描电镜观察、能谱分析,在长7段的脉状黄铁矿附近和碳酸盐结核中发现了属种单一、分布丰度高的藻类化石,它们呈现出近似球状的轮廓,在中部分布着一条裂缝。这些藻类化石的发现具有重要的地质意义,它为长7期的藻类勃发提供了很好的证据,也为该时期热液活动的重要作用提供了有力的支撑。 相似文献
14.
Hydrothermal sedimentation characteristics of the Dajiangping superlarge pyrite deposit, Yunfu, Guangdong 总被引：1，自引：1，他引：0
The Dajiangping pyrite deposit is hosted in a carbonate-clastic rock series which is characterized by a bioreef-chert suite in its middle part.Conformable lenses of various sizes constitute the orebodies which often branch transitionally into the surroundings.Syngenetic deformation fabrics can be observed in orebody NO.3.Orebody No.4 is composed almost entirely of massive pyrite,with conspicuous hydrothermal sedimentation and bacterium-alga features.The hydrothermal sedimentation origin is also reflected by simple chemistry of the ore (predominated by quartz and pyrite),the presence of U and Th,and the REE compositions of pyrite and ankerite.The ores are rich in organic matter and the difference in organic content between the banded ores and the massive ores is mainly owing to the difference in the clastic components they contain rather than to the subsequent processes of reworking .Co/Ni rations in the ore may reflect the temperature pattern during hydrothermal sedimentation. 相似文献
15.
Sulphur Enrichment in Organic Matter of Eastern Mediterranean Sapropels: A Study of Sulphur Isotope Partitioning 总被引：1，自引：0，他引：1
Sulphur isotope compositions and S/C ratios of organic matter were analysed in detail by combustion-isotope ratio monitoring mass spectrometry (C-irmMS) in eastern Mediterranean sediments containing three sapropels of different ages and with different organic carbon contents (sapropel S1 in core UM26, formed from 5–9 ka ago with a maximum organic carbon content of 2.3 wt%; sapropel 967 from ODP Site 160-967C, with an age of 1.8 Ma and a maximum organic carbon content of 7.4 wt%; and sapropel 969 from ODP Site 160-969E, with an age of 2.9 Ma and a maximum organic carbon content of 23.5 wt%). Sulphur isotopic compositions (34S) of the organic matter ranged from -29.5 to +15.8 and the atomic S/C ratio was 0.005 to 0.038. The organic sulphur in the sediments is a mixture of sulphur derived from (1) incorporation of 34S-depleted inorganic reduced sulphur produced by dissimilatory microbial sulphate reduction; and (2) biosynthetic sulphur with an isotopic signature close to seawater sulphate. The calculated biosynthetic fraction of organic sulphur in non-sapropelic sediments ranges from 68–87%. The biosynthetic fraction of the organic sulphur of the sapropels (60–22%) decreases with increasing organic carbon content of the sapropels. We propose that uptake of reduced sulphur into organic matter predominantly took place within sapropels where pyrite formation was iron-limited and thus an excess of dissolved sulphide was present for certain periods of time. Simultaneously, sulphide escaped into the bottom water and into sediments below the sapropels where pyrite formation occurred. 相似文献
16.
G. A. Leonova A. E. Mal’tsev V. N. Melenevskii L. V. Miroshnichenko L. M. Kondrat’eva V. A. Bobrov 《Geochemistry International》2018,56(4):344-361
Organogenic sediments (sapropels) in lakes are characterized by a reduced type of diagenesis, during which organic compounds are decomposed, the chemical composition of the pore waters is modified, and authigenic minerals (first of all, pyrite) are formed. Pyrolysis data indicate that organic matter undergoes radical transformatons already in the uppermost sapropel layers, and the composition of this organic matter is principally different from the composition of the organic matter of the its producers. The sapropels contain kerogen, whose macromolecular structure starts to develop during the very early stages of diagenesis, in the horizon of unconsolidated sediment (0–5 cm). The main role in the diagenetic transformations of organic matter in sediments is played by various physiological groups of microorganisms, first of all, heterotrophic, which amonifying, and sulfate-reducing bacteria. SO42? and Fe2+ concentrations in the pore waters of the sediments are determined to decrease (because of bacterial sulfate reduction), while concentrations of reduced Fe and S species (pyrite) in the solid phase of the sediment, conversely, increase. Comparative analysis shows that, unlike sapropels in lakes in the Baikal area, sapropels in southern West Siberia are affected by more active sulfate reduction, which can depend on both the composition of the organic matter and the SO42? concentration in the pore waters. 相似文献
17.
Sedimentary pyrite formation: An update 总被引：1，自引：0，他引：1
Robert A Berner 《Geochimica et cosmochimica acta》1984,48(4):605-615
Sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time. The amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter, dissolved sulfate, and reactive detrital iron minerals. Organic matter appears to be the major control on pyrite formation in normal (non-euxinic) terrigenous marine sediments where dissolved sulfate and iron minerals are abundant. By contrast, pyrite formation in non-marine, freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic-rich fresh water shales from marine shales. Under marine euxinic conditions sufficient H2S is produced that the dominant control on pyrite formation is the availability of reactive iron minerals.Calculations, based on a sulfur isotope model, indicate that over Phanerozoic time the worldwide average organic carbon-to-pyrite sulfur ratio of sedimentary rocks has varied considerably. High ratios during Permo-Carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time. Low ratios, compared to today, during the early Paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean. The latter could have been due to lower oceanic oxygen levels and/or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time. 相似文献
18.
One of the key-principles of the iron-sulphur world theory is to bring organic molecules close enough to interact with each
other, using the surface of pyrite as a substrate in a hydrothermal setting. The present paper explores the relationship of
pyrite and organic matter in a hydrothermal setting from the geological record; in hydrothermal calcite veins from Carboniferous
limestones in central Ireland. Here, the organic matter is accumulated as coatings around, and through, pyrite grains. Most
of the pyrite grains are euhedral-subhedral crystals, ranging in size from ca 0.1-0.5 mm in diameter, and they are scattered
throughout the matrix of the vein calcite. The organic matter was deposited from a hydrothermal fluid at a temperature of
at least 200°C, and gives a Raman signature of disordered carbon. This study points to an example from a hydrothermal setting
in the geological record, demonstrating that pyrite can have a high potential for the concentration and accumulation of organic
materials. 相似文献
19.
利用厌氧微生物分离技术,对深度为1.2 m 的海南红树林湿地沉积物钻孔样品进行了分离培养,共获得11 株
厌氧sulfate-reducing bacteria（SRB） 菌株。经显微观察和16S rDNA序列分析,可归纳为6个属,其中已经报道有芽孢杆菌
属（Bacillus）、弧菌属（Vibrio） 和梭状芽胞杆菌属（Clostridium）,另外3个属分别为伯克霍尔德菌属（Burkholderia）、希瓦氏菌属（Shewanella） 和海杆菌属（Marinobacterium）。不同属的细菌对硫酸盐还原的速率最低为14.71%,最高可达
56.78%,并且以上6属11株菌都能将+6价的硫还原生成-2价硫,并与培养基中的Fe2+结合生成黑色FeS沉淀,而这些无定
形FeS沉淀是生成黄铁矿的前体。红树林湿地SRB种群数量随沉积物深度的增加而降低,结合沉积物的地球化学分析测试
结果表明,表层（0 cm） 水界面的沉积物由于处于氧化-还原界面,氧气的周期性输入在一定程度上抑制了SRB的生长;随着
深度增加（10~40 cm）,充足的有机质、偏中性的pH值以及厌氧环境的增强,使得SRB种类和数量明显增加;而60 cm以下
沉积物中因TOC含量降低,减少了微生物可利用的碳源,pH值明显降低,Na+和Ca2+离子浓度明显增加,这些因素都抑制了
SRB的生长,使得深部沉积物中SRB的种类和数量显著减少。 相似文献
20.
Intense pyrite formation under low-sulfate conditions in the Achterwasser lagoon, SW Baltic Sea 总被引：1，自引：0，他引：1
Thomas Neumann Nicole Rausch Thomas Leipe Zsolt Berner 《Geochimica et cosmochimica acta》2005,69(14):3619-3630
In comparison to similar low-sulfate coastal environments with anoxic-sulfidic sediments, the Achterwasser lagoon, which is part of the Oder estuary in the SW Baltic Sea, reveals unexpectedly high pyrite concentrations of up to 7.5 wt%. Pyrite occurs mainly as framboidal grains variable in size with diameters between 1 and 20 μm. Pyritization is not uniform down to the investigated sediment depth of 50 cm. The consumption of reactive-Fe is most efficient in the upper 20 cm of the sediment column, leading to degrees of pyritization (DOP) as high as 80 to 95%.Sediment accumulation in the Achterwasser takes place in high productivity waters. The content of organic carbon reaches values of up to 10 wt%, indicating that pyrite formation is not limited by the availability of organic matter. Although dissolved sulfate concentration is relatively low (<2 mmol/L) in the Achterwasser, the presence of H2S in the pore water suggests that sulfate is unlikely to limit pyrite authigenesis. The lack of free Fe(II) in the pore waters combined with the possibility of a very efficient transformation of Fe-monosulfides to pyrite near the sediment/water interface suggests that pyrite formation is rather controlled by (i) the availability of reactive-Fe, which limits the FeS formation, and by (ii) the availability of an oxidant, which limits the transformation of FeS into pyrite. The ultimate source for reactive-Fe is the river Oder, which provides a high portion of reactive-Fe (∼65% of the total-Fe) in the form of suspended particulate matter. The surficial sediments of the Achterwasser are reduced, but are subject to oxidation from the overlying water by resuspension. Oxidation of the sediments produces sulfur species with oxidation states intermediate between sulfide and sulfate (e.g., thiosulfate and polysulfides), which transform FeS to FeS2 at a significant rate. This process of FeS-recycling is suggested to be responsible for the formation of pyrite in high concentrations near the sediment surface, with DOP values between 80 and 95% even under low sulfate conditions.A postdepositional sulfidization takes place in the deeper part of the sediment column, at ∼22 cm depth, where the downward diffusion of H2S is balanced by the upward migration of Fe(II). The vertical fluctuation of the diffusion front intensifies the pyritization of sediments. We suggest that the processes described may occur preferentially in shallow water lagoons with average net-sedimentation rates close to zero. Such environments are prone to surficial sediment resuspension, initiating oxidation of Fe-sulfides near the sediment/water interface. Subsequent FeS2 formation as well as postdepositional sulfidization leads to a major pyrite spike at depth within the sediment profile. 相似文献