太平洋中部柱状沉积物中的自生矿物

根据《海洋四号》861—881航次获得的岩心资料,通过对沉积物类型的观察,对其中的几种自生矿物钙十字沸石、蒙脱石、重晶石、微结核、非晶质SiO_2等矿物的成因和与沉积物类型的相关性进行了探讨。     

黄海南部表层沉积物中的自生黄铁矿

本文对黄海沉积物中的黄铁矿的分布、形态、成分和结构方面的特征，以及成因作了讨论。作者在73个样的1／3样品中发现了自生黄铁矿，并对此矿物进行了X-射线、电子探针、光片及扫描电镜研究。黄铁矿主要呈生物内模状、球粒状(framboid)及胶结物状等形态，经X-射线衍射分析表明自生矿物为黄铁矿，不存在其他铁硫化物。     

南海中东部表层沉积物矿物组合分区及其地质意义

利用油浸系统鉴定法对南海中东部 2 86个表层沉积物样品 63— 1 2 5 μm粒级的矿物鉴定和分析结果表明 ,沉积物中矿物种类丰富 ,有 5 7种 ;矿物组成以轻矿物为主 ,重矿物含量较低 ;与中国其他海区相比 ,以铁锰微结核、磁铁矿、普通辉石和火山玻璃的高含量为特征。根据矿物来源和成因的研究 ,可分为陆源碎屑矿物、自生沉积矿物、火山碎屑矿物、生物骨屑矿物和宇宙来源矿物 5类。为了定量地探讨沉积物中矿物组合及其空间分布 ,根据特征矿物的相似性对 2 86个样品 2 2种矿物变量进行Q 型聚类分析 ,将南海中东部表层矿物分布划分为陆源、混合、自生、火山 4个矿物组合区。各组合区中矿物组成和含量上的变化反映了物质来源和沉积环境的差异。     

东太平洋表层沉积物中锐钛矿、重晶石矿物的发现及其指示意义

东太平洋以其发育大洋多金属结核而长期以来倍受地质学家关注,国内外在该区对多金属结核及相关的沉积物、沉积环境、古海洋学等进行了大量的调查研究[1～6],取得了许多重要的研究成果.在此基础上,笔者利用先进的电镜分析测试技术(包括电子衍射技术),对东太平洋克拉里昂和克利伯顿两条断裂带之间的CC区沉积物进行了系统的矿物学研究,在研究中发现了重晶石和锐钛矿矿物.本文将简要报道对这两种矿物的形貌和结构标型特征进行研究的结果,并初步探讨其成因[1].     

琼东南盆地与甲烷渗漏有关的早期成岩作用和孔隙水化学组分异常

X-射线衍射和扫描电镜观察表明,采自南海北部琼东南盆地的沉积物样品中有天然气水合物和甲烷渗漏指示意义的自生碳酸盐、硫酸盐和草莓状framboids黄铁矿,自生矿物组合和显微结构特征与冷泉沉积物类似,属微生物成因。沉积物孔隙水化学组分分析结果显示,随着埋藏深度加深,SO₄2-,Ca2+,Mg2+和Sr2+浓度明显降低,Mg2+浓度与Ca2+浓度和Sr2+浓度与Ca2+浓度的比值急剧增加,这些地球化学特征与世界上天然气水合物产区的浅表层沉积物孔隙水中离子浓度异常吻合较好,暗示采样站位深部可能有油气或天然气水合物藏。     

南黄海中部H-106柱状沉积物中自生黄铁矿的研究

自生黄铁矿是现代海洋沉积物中分布较广、含量较高的自生矿物之一。我国广阔的大陆架海域以及边缘海区(冲绳海槽)的现代和近代沉积物中都发现有黄铁矿,其中以南黄海盆地较为典型。H-106孔位于南黄海中部略偏西北(123°0''E,35°3''N),水深70m,岩芯长607cm,孔中黄铁矿含量较高。 研究现代和近代柱状沉积物中自生黄铁矿的结构、构造、矿物化学特征以及硫同位素组成及其与沉积环境和地球化学等因素的关系,对于了解沉积物早期成岩作用,认识沉积环境变迁和探讨黄铁矿成因都具有理论和实际意义,因此,早已引起国内、外学者的重视。国外具有代表性的学者Love(1957;1964)和 Berner(1969;1970)等分别从50年代和60年代末就开始了黄铁矿的研究工作。他们从不同角度、用不同方法对古地层和现代海洋沉积物中的黄铁矿进行了研究。随着我国海洋调査研究的深入,近年来国内学者也相继开展了这方面的工作(陈庆,1981;王琦等,1981)。然而以往国内、外的学者大都从形态、矿物和沉积化学的角度去研究黄铁矿,对现代自生黄铁矿单矿物的硫同位素组成涉及甚少。现代海洋硫同位素研究也仅限于沉积物与海水的范围,然而沉积物和海水的成分均很复杂,影响因素众多,不能反映黄铁矿的硫同位素组成。本文拟通过黄铁矿的硫同位素特征和黄铁矿集合体的结构、构造和矿物化学成分等矿物学特征,并结合沉积物成分与地球化学参数来探讨黄铁矿的形成环境与成因。     

中太平洋西部沉积碎屑矿物的研究

中太平洋西部沉积物细砂-极细砂中的碎屑矿物不下90种,根据矿物学标志和稀土配分模式论证了火山矿物主要源于早更新世及其后大洋拉斑玄武岩浆的喷发,矿物组合特征表明,矿物碎屑主要是远洋成因,但美拉尼西亚海盆中的陆源成分较多,其中石英含量在间冰期中普遍增加,瓦利斯群岛近区尤其是北斐济海盆则赋存较典型的远洋物质,陆源成分较少,自生锰结核的形成同褐色粘土关系密切,在碳酸钙沉积物中也能见到,但主要形成显微颗粒,而在北斐济海盆较松散的含钙质火山灰层中尚未发现.     

黄海南部表层沉积中的自生黄铁矿

陆架、陆坡以及深海沉积物中,都已发现有自生黄铁矿的存在。我们于1972年研究黄海南部的表层沉积时,观察到其中较普遍地出现这种自生矿物。东海表层沉积中也有。自生矿物是在沉积物堆积的同时或稍后形成的,研究它对于了解同生阶段以及成岩     

海洋磷块岩中铀和稀土的自生矿物

采用分析电子显微镜法对采自太平洋陆架沉积层和海底山脉不同时代和不同成分的磷块岩的研究表明，在其中存在着超显微颗粒的自生铀矿物，在稀少的情况下还有自生的稀土元素矿物。在一系列来自纳米比亚陆架的上新一更新世磷块岩标本中发现了这两种类型的矿物。铀矿物是沥青铀矿、科芬矿和磷钙铀矿；稀土元素矿物为独居石、磷钇矿和氟铈矿，这证明它们不仅可能以类质同像混入物的形态存在于钙的磷酸盐中，还能以独立矿物相的形态存在。     

山东半岛南部近岸海域碎屑矿物对中小河流的物源响应

对山东半岛南部近岸海域的106个表层沉积物样品及大沽河、五龙河和乳山河的94个表层沉积物样品进行碎屑矿物分析,系统地研究了碎屑矿物的分布特征及物源指示。研究区共鉴定出40种重矿物和13种轻矿物,重矿物以普通角闪石、绿帘石、黑云母和自生黄铁矿为主,轻矿物以石英、斜长石、钾长石和风化云母为主。根据碎屑矿物组合特征,将研究区分为4个矿物区:Ⅰ区为胶州湾口至崂山头的附近海域;Ⅱ_1亚区为丁字湾和鳌山湾附近水深约15m以浅的海域,Ⅱ_2亚区为研究区东南部水深20m的远岸区;Ⅲ区处于Ⅱ区和Ⅳ区的过渡带;Ⅳ区为乳山口西南部近岸海域。Ⅰ区和Ⅱ区的矿物组合均为普通角闪石-绿帘石-石英-长石,Ⅰ区和Ⅱ_1亚区受大沽河、五龙河和乳山河输入的物质及沿岸基岩、岛屿风化碎屑的影响较大,Ⅱ_2亚区主要为晚更新世低海平面时形成的陆架残留沉积。Ⅲ区矿物组合为普通角闪石-石英-长石-片状矿物,Ⅳ区矿物组合为云母类-自生黄铁矿-普通角闪石-石英,Ⅲ区、Ⅳ区物源多样,黄河物质对两区贡献显著。     

南黄海沉积物中自生黄铁矿的形态标型研究

得１９８９年采于南黄海的样品，通过实体显微镜、反应显微镜和电子显微镜对自生黄铁矿的集合体形和晶体形态进行研究，结合前人成果，对现代海底沉积物中自生黄铁矿集合体进行形态分类和成因－形态分类，在此基础上讨论其特征形态的成因及标型意义。研究表明，自生黄铁矿集合体形态可以分为聚莓、单莓和细粒３种，其中前二者可作为沉积物中自生黄铁矿和层控或沉积成因矿床黄铁矿集合体形态标型；成因－形态分类将黄铁矿集合体分为两     

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Paola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO₂-rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted ¹³C isotopic composition and slightly positive δ¹⁸O values. By contrast, siderite concretions, generally found within the first 6 m of sediments on the alleged mud volcanoes, yielded positive δ¹³C and δ¹⁸O values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the ¹³C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with ¹³C-rich dissolved inorganic carbon (DIC) and ¹⁸O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO₂.     

南黄海自生黄铁矿成因及其环境指示意义

样品为１９８９年采自南黄海，利用显微镜，电子显微镜，电子探针和化学分析方法，对自生黄铁矿的形态，成份和同位素特征进行研究，在此基础上就其成因与形成环境的关系进行初步探讨。研究结果表明，自生黄铁矿集合体形态可以分为聚莓，单莓和细粒３种，霉体特征的形态是早期成岩作用阶段沉积物随机堆积的结果，可以作了沉积成因黄铁矿的形态标型黄铁矿微量成份特征显示其沉积成因，同时亦表现对泥质沉积物地球化学背景值的继承性，     

Laboratory experiment and numerical simulation on authigenic mineral formation induced by seabed methane seeps

In natural gas hydrate marine settings, cold seepage of methane fluid is a widely observed phenomenon, where authigenic minerals serve as an indication of potential gas hydrate-bearing reservoirs at depth. In this study, based on the data from the site HD196 near Dongsha Island, northern continental slope of South China Sea, laboratory experiments and numerical simulation studies were conducted to investigate the biogeochemical processes of authigenic mineral formation induced by methane seepage. The bioreactor experimental results show that in response to methane flux, pH increased to 8.5 after 20 days of reaction, and Eh declined rapidly first and then remained unchanged at about 100 mV. The decrease in SO₄²⁻, HS⁻ and HCO₃⁻ concentrations indicated the occurrence of anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR). The depletion of Fe²⁺ implied the formation of iron-bearing minerals, e.g., iron sulfides. Carbonate minerals were also identified in the experimental phase of this study. Most iron sulfides existed as massive pieces, and in some cases as spherical or rod-shape pieces. The calcium carbonates were observed as blocky pieces. Numerical simulations were also performed to reproduce the biogeochemical reactions that occurred in the reactor experiments. Based on experimental data, kinetic parameters associated with the observed reactions were calibrated. The model simulated results are general consistent with those obtained by the experiments conducted in this study. The combination of simulation and experimental studies provided a powerful tool to investigate the biogeochemical processes in the methane leakage environment at different temporal and spatial scales. This study gave a new perspective to understand the formation of cold seep authigenic minerals in marine sediments, and was significant for future investigations on the effects of hydrate decomposition.     

Substrate control on formation and maturation of glauconites in the Middle Eocene Harudi Formation, western Kutch, India

Formation and maturation of glauconites within the early Middle Eocene Harudi Formation, built up in a lagoon to shelf transition in western Kutch, India is addressed taking recourse to a combined sedimentological, micropalaeontological and mineralogical investigation. The glauconite is authigenic and its occurrence coincides with maximum flooding. The glauconite is more matured within the fecal pellets and is less matured within the intra-particle pores of bioclasts namely, foraminifera, ostracoda, gastropoda and bryozoa. SEM-EDS, XRD and geochemical studies clearly document that the infilling within the intra-particle pores of bioclasts belong to nascent to slightly evolved glauconite (<5 wt% K₂O), while the pellet belongs to slightly evolved to evolved glauconite (5-7 wt% K₂O). Based on chemical characteristics and SEM investigations the glauconitization process can be best explained by the ‘verdissement theory’. The glauconite possibly formed as initial authigenic glauconitic smectite precipitates; while the pellet matured subsequently by addition of K, the process was hindered in case of infillings. The maturation process also involved addition of Si and release of Al, with or without release of Mg. The glauconite maturation was facilitated in case of fecal pellets because of higher porosity, inter-granular nature of pores and availability of necessary elements in semi-confined micro-environments. In contrast, the maturation was aborted at an early stage in case of infillings because of the minute, closed nature of the pores and prevalent alkaline conditions not allowing dissolution of calcitic tests. A low negative cerium anomaly suggests glauconite formation in sub-oxic micro-environments, created by decay of organic matters within the fecal pellets and bioclasts. A clear case of substratum control on glauconitization becomes apparent.     

Using iron speciation in authigenic carbonates from hydrocarbon seeps to trace variable redox conditions

Seepage of hydrocarbon-rich fluids out of the marine sedimentary column is characterized by temporal changes of flow intensity and resultant spatially variable redox conditions. Authigenic carbonates at marine hydrocarbon seeps provide excellent geological and geochemical archives that serve to explore seepage dynamics over time. In this study, we investigated the potential of Mössbuaer spectroscopy and Fe contents of seep-related authigenic carbonates from the Congo Fan, the Gulf of Mexico, and the Black Sea for reconstructing past redox conditions and fluid seepage activity at cold seeps. The Fe speciation observed by Mössbauer spectroscopy and Fe contents suggest that (1) the Congo Fan carbonates precipitated in a sulfidic environment, (2) the formation conditions of seep carbonates were variable at the Gulf of Mexico seep site, ranging from oxic to suboxic and anoxic and even spanning into the methanogenic zone, and (3) the stratified water column of the Black Sea or suboxic condition resulted in low Fe contents of Black Sea carbonates. The study reveals that Fe speciation can provide constraints on the wide range of redox conditions that imprinted seep carbonates during the life span of seepage. Similarly, Mössbauer spectroscopy – particularly when used in combination with the analysis of redox-sensitive elements – is a promising tool to trace variable redox conditions in marine paleoenvironments other than seeps.     

Oyster patch reefs as indicators of fossil hydrocarbon seeps induced by synsedimentary faults

The Late Jurassic deposits of the Boulonnais area (N-France) represent the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting as a result of the Atlantic Ocean rifting. In the Gris-Nez Cape area, i.e., close to the northern border fault zone of the Jurassic basin, the Late Jurassic sequence contains small-dimensioned oyster patch reefs (<1 m) that are specifically observed at the base of an abrupt deepening trend in the depositional sequence induced by well-defined pulses of normal fault activity. Petrographic analysis of these patch reefs shows that they are exclusively composed of Nanogyra nana embedded in a microsparitic calcite matrix. ™¹³C measurements, carried out within both the matrix and the shells, display significantly lower values in the matrix compared to the oyster shells which suggests that the carbonate matrix precipitation was involving a carbon source different from marine dissolved inorganic carbon, most probably related to sulfate reduction, which is evidenced by light ™³⁴S in pyrites. Similarities but also differences with lucinid-rich bioconstructions, namely, the Late Jurassic pseudo-bioherms of Beauvoisin (SE-France) suggest that the patch reefs developed at hydrocarbon seeps are related to synsedimentary faults. The extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times is thus believed to have induced a sort of small-dimension hydrocarbon seepage field, recorded by the patch reef distribution.     

Early diagenetic formation of carbonates in a clastic-dominated ramp environment impacted by synsedimentary faulting-induced fluid seepage – Evidence from the Late Jurassic Boulonnais Basin (N France)

The Late Jurassic deposits of the Boulonnais area (N-France) represents the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting in relation with the northward propagation of the Atlantic rifting. Within the terrigenous accumulations, some carbonate objects are visible at various conspicuous levels: oyster patch reefs and fine-grained carbonate beds, either continuous, or more or less nodular. Preliminary studies demonstrated that the carbonate beds of the Bancs Jumeaux Formation as well as the carbonate matrix of the oyster patch reefs are of diagenetic origin. In this paper, we extend the study to many other limestone beds of the Boulonnais with mud- or wackestone texture, examining facies and microfacies through various techniques as well as geochemical data (O, C and S stable isotopes, major and trace elements). We conclude that all examined carbonate bodies are of early diagenetic origin and that they precipitated at, or close to, the sea bed, from seawater mixing with ascending fluids containing isotopically light carbon of organic origin. Fluid circulation was probably induced by the extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times. Fluid seepages were either channelized along fault planes or more diffuse, as illustrated by the model we propose.     

Mineral-forming and diagenetic processes related to Tertiary hydrocarbon seepage at the Bohemian Massif/Outer Western Carpathians interface: Evidence from the Hrabůvka quarry,Moravia, Czech Republic

Ancient hydrocarbon seepage occurred in the Hrabůvka quarry at the boundary between the basement of the Bohemian Massif (represented by folded Lower Carboniferous siliciclastics of the Culm facies) and Tertiary sedimentary cover of the Carpathian Foredeep (formed by Lower Badenian siliciclastics and calcareous clays). The unconsolidated Lower Badenian sediments contain lithified domains composed of limestone and breccias with limestone cement, whereas the basement rocks are cut by subvertical neptunic dykes filled up by limestone and calcite-marcasite-pyrite veinlets representing sealed fluid conduits. The deeply negative δ¹³C values of both vein calcite and limestone (down to −38.1‰ V-PDB) indicate that oxidation of hydrocarbons was the major source of carbon for authigenic mineralization. A fluid inclusion study suggests low fluid temperatures (<50 °C) and low and variable salinities of aqueous fluids associated with hydrocarbons (0.7–6.7 wt. % NaCl eq.). The variability of δ¹⁸O values of authigenic carbonates (−1.7 to −8.2‰ V-PDB) could reflect either slight changes in temperature of escaping fluids (mostly within 15 °C), and/or some mixing with meteoric waters. The low δ³⁴S values of vein marcasite (∼–20‰ V-CDT) are consistent with bacterial reduction of sulfate in the hydrothermal system. Low C₁/(C₂+C₃) ratios in hydrocarbon gas extracted from authigenic carbonates (9.9 and 5.8) as well as the high δ¹³C values of methane (−31.8 and −32.4‰ V-PDB) are compatible with a thermogenic source of hydrocarbons. REE data indicate sequestration of REE from finely dispersed detrital material in the apical part of the hydrothermal system. The available data are compatible with two possible scenarios of fluid origin. The hydrocarbons could have been leached from underlying Paleozoic sedimentary sequence by aqueous fluids that infiltrated into the basement after Tertiary tectonic reactivation. Alternatively, an external source of hydrocarbon-bearing fluids can be found in the adjacent Outer Western Carpathians flysch nappes containing petroleum-producing lithologies. Nevertheless, a regional flow of hydrocarbon-bearing fluids is evidenced by the occurrence of very similar hydrocarbon-bearing vein mineralizations in a wider area.     

Fluid sources and stable isotope signatures in authigenic carbonates from the Northern Apennines,Italy

Authigenic carbonates are frequently associated with methane cold-seep systems, which extensively occur in various geologic settings worldwide. Of interest is the relation between the fluids involved in their formation and the isotopic signals recorded in the carbonate cements. Along the Northern Apennines foothills (Italy), hydrocarbons and connate waters still seeping nowadays are believed to be the primary sources for the formation of fossil authigenic carbonate found in Plio-Pleistocene marine sediments. Four selected outcrops of dolomitic authigenic carbonates were analysed to compare signature of seeping fluids with fractionation of stable carbon and oxygen isotopes recorded in the carbonate.Along the foothills, deep methane-rich fluids spontaneously rise to the surface through mud volcanoes or are exploited in wells drilled nearby to the fossil Plio-Pleistocene authigenic carbonates. The plumbing system providing fluids to present-day cold seeps was structurally achieved in Late Miocene and Plio-Pleistocene. δ¹³C values of methane, which vary from −51.9 to −43.0‰ VPDB, indicate that gas composition from the deep hydrocarbon reservoirs is relatively uniform along the foothills. On the contrary, δ¹³C in fossil authigenic carbonates strongly varies among different areas and also within the same outcrop.The different carbon sources that fed the investigated carbonates were identified and include: thermogenic methane from the deep Miocene reservoirs, ¹³C-enriched CO₂ derived from secondary methanogenesis and microbial methane from Pliocene successions buried in the Po Plain. The δ¹³C variability documented among samples from a single outcrop testifies that the authigenic carbonates might represent a record of varying biogeochemical processes in the hydrocarbon reservoirs. The sources of stable oxygen isotopes in authigenic carbonates are often ascribed to marine water. Oxygen isotopic fractionation in the dolomite cements indicates that marine pore water couldn't be the sole source of oxygen. δ¹⁸O values provide a preliminary evidence that connate waters had a role in the carbonates precipitation. The concomitant occurrence of active cold seepages and fossil record of former plumbing systems suggests that generation and migration of hydrocarbons are long-lasting and very effective processes along the Northern Apennines foothills.