动物非矿化组织化石化过程的地球化学作用研究进展

动物非矿物化组织在特异埋葬条件下可保存为化石.最稳定的保存形式是与成岩作用有关的保存类型和以碳化有机质薄膜形式存在的保存类型.与动物非矿化组织保存有关的常见成岩自生矿物有磷酸盐矿物、碳酸盐矿物和黄铁矿等.其中,磷酸盐矿物在成岩作用过程中结晶最早,可以保存动物的微细构造.这些矿物可以矿化交代动物的肉质和角质使其成为矿化实体.特异埋葬的化学机理还需要古生物学家和地球化学家更紧密的合作,做进一步的研究.     

粘土矿物研究在塔里木盆地石油勘探中的应用

以塔里木盆地粘土矿物的分布特征及其组合形式、演化与形成机理为依据,探讨了粘土矿物在地层划分对比中的应用及其与有机质热演化、成岩阶段的关系和对储层物性的影响。研究表明,在侏罗系和白垩系两个不同古环境中形成的粘土矿物及其组合特征,为地层对比提供了一定的证据。泥岩中伊利石／蒙皂石间层中蒙皂石含量的纵向变化与有机质热演化及成岩阶段的关系不大。对储层物性影响不大但有利于储集性能的是以高岭石为主的粘土矿物组合类型及粘土矿物的早期自生（伊利石／蒙皂石间层矿物）衬垫式以及非自生（伊利石）衬垫式产状。     

珠江口盆地珠江组混积岩中有孔虫的矿化特征与机制

珠江口盆地白云凹陷是我国现今深水油气勘探的重要地区,在其南侧的荔湾X构造的珠江组在3 000~3 281 m以混积岩沉积为主.以荔湾X构造内含有孔虫混积岩为研究对象,通过开展岩石学和同位素地球化学研究,确定了有孔虫宿主岩石类型以及有孔虫矿化的岩相学特征,重点探讨了有孔虫的矿化机制,并最终建立了有孔虫的矿化模式.荔湾X构造珠江组混积岩的生物碎屑以有孔虫碎屑为主,有孔虫壳由刃状、等径状方解石或铁方解石组成.有孔虫的房室可分为未充填、半充填和全充填3种类型.根据有孔虫房室充填的主要自生矿物类型、产状及相互关系,可将有孔虫矿化按其形成的先后分为黄铁矿化、铁方解石化、片钠铝石化和铁白云石化4种类型,其中黄铁矿的形成可能与有孔虫软体组织的生物降解有关,铁方解石可能与有机质热脱羧作用有关,片钠铝石和铁白云石中的“碳”有深部来源的岩浆成因CO₂的贡献.      

滇东北峨眉山玄武岩区的沉积型铜矿床

在滇东北峨眉山玄武岩分布区上二叠统宣威组中发现沉积型铜矿床。文章对此类沉积型铜矿床的地质特征和成矿作用特征进行了较系统的研究,结合矿物成分和硫同位素测试结果,探讨了矿床的形成过程和找矿前景。研究表明,区内沉积型铜矿床主要有两种矿化类型:结核状铜矿化和浸染状铜矿化,矿石矿物以辉铜矿、斑铜矿、铜蓝等为主;成矿受上二叠统宣威组沉积地层控制,与峨眉山玄武岩喷溢形成的古火山构造和古地形以及火山期后的热泉活动关系密切,有机质在成矿过程中可能发挥了作用;成矿过程可能从沉积成岩阶段一直延续到成岩期后。区域上假整合覆盖于上二叠统峨眉山玄武岩之上的宣威组沉积岩系具有良好的找矿前景。     

高家山生物群中的非矿化微生物假形化石：埃迪卡拉纪末期生物软躯体保存方式的新认识

陕西南部宁强地区的李家沟剖面灯影组高家山生物群产有大量磷酸盐化实体化石,包括各类管状化石、瓶状化石、疑难化石以及钙化蓝细菌等,类型丰富。近年来,随着研究的深入,微生物假形化石在该生物群中也被不断发现。由于微生物假形化石是生物死亡后腐解埋藏过程中生物体被微生物（球状和丝状蓝细菌）直接取代,因而原始生物体的结构形态得以完好保存。微生物可以通过改变环境中的物理化学条件使磷酸盐富集和快速堆积,对生物的非矿物组织包括软躯体的保存起到了很重要的作用。根据替代程度不同可以划分为完全替代类型和未完全替代类型。这一发现提供了高家山生物群中生物非矿化组织的另一种保存方式。微生物通过铸型完整复制了生物软躯体以及可能的胚胎形态特征,提供了对此时期软躯体保存的新认识。     

吐鲁番坳陷中——上侏罗统碎屑岩中的自生粘土矿物特征及其成岩意义

利用岩石薄片和扫描电镜观察以及Ｘ－衍射资料研究了吐鲁番坳陷中上侏罗统碎屑岩中的自生粘土矿物特征,发现碎屑岩中的自生粘土矿物主要有五种类型,即蒙脱石、伊利石－蒙脱石混层、伊利石、绿泥石和高岭石。自生粘土矿物的形成和转化取决于碎屑岩原始矿物组分及其成岩环境。蒙脱石的迅速转化和高岭石的大量析出与碎屑岩的大规模溶解有着密切的关系。根据自生粘土矿物的组合特征,可以有效地确定碎屑岩的成岩阶段及其孔隙发育特征。     

铜钵庙-南屯组砂岩成岩作用与相对高孔隙带的关系——以海拉尔盆地乌尔逊凹陷南部为例

海拉尔盆地乌尔逊凹陷南部铜钵庙-南屯组砂岩类型主要以岩屑长石砂岩为主,有少量长石砂岩和长石岩屑砂岩。成岩作用包括压实作用、胶结作用、交代作用、溶解作用等。孔隙度和渗透率随埋深的增加而逐渐减小,在1 500 m左右、1 850~2 050 m、2 300 m左右和2 600~2 800 m出现4个相对高孔隙带。造成相对高孔隙带出现的原因是原生孔隙保存和次生孔隙发育,压实作用、胶结作用较弱和自生粘土矿物包壳、自生石英微晶存在,有利于原生孔隙的保存;有机质热演化、粘土矿物转化过程中,次生孔隙形成。     

鄂尔多斯盆地苏里格气田北部盒_8、山_1段成岩作用及有利储层分布

通过对苏里格气田北部盒_8、山_1段24口钻井572块样品的成岩作用研究表明,苏里格气田北部盒_8和山_1段主要经历了压实作用、胶结作用、次生加大作用、自生矿物的生成、交代和蚀变作用、溶蚀作用、破裂作用等.根据它们对孔隙发育的贡献分为建设性成岩作用、破坏性成岩作用、保持性成岩作用3种类型.其中,约80%的砂岩粒间孔具有溶蚀现象,溶蚀作用使储集层孔隙结构得到有效的改善,以次生粒间孔最为常见,粒内溶孔较少见,粘土质微孔发育,并与岩石中保存下来的剩余原生粒间孔组合构成溶孔一原生粒间孔组合、溶孔-粘土质微孔组合及溶孔-微孔-(裂缝、粒缘缝)组合.保持性成岩作用所生成的环边绿泥石包膜使部分孔隙得以保存,对储层的发育具有积极意义.根据铸体薄片、扫描电镜下所观察到的自生矿物类型以及X衍射等测试手段所揭示的I/S混层粘土矿物的演变、粘土矿物组合及矿物中的混层比,这些成岩作用被划分为早成岩A期、早成岩B期、中成岩A期、中成岩B期和晚成岩期3个阶段5个期次;成岩作用研究认为S4井,S5井,S6井和T5井区为有利储层分布区.     

南海北部神狐水合物赋存区浅表层沉积物自生矿物特征及其成因探讨

通过对南海北部神狐海域Site5B和Site4B站位岩心柱沉积物中自生矿物的类型、形貌特点、丰度和稳定同位素特征的研究,探讨了自生矿物的成因机制。研究表明,沉积物中主要发育黄铁矿和碳酸盐类自生矿物。两个站位中发育的自生矿物的丰度、分布位置、晶体形貌和个体大小等存在明显差异,可能与不同站位中甲烷通量和深部构造有关。自生黄铁矿可能是硫酸盐与甲烷等烃类气体或有机质的厌氧氧化作用的产物,极低负值的硫同位素值可能与硫酸盐还原菌和单质硫歧化菌共同参与有关。自生碳酸盐矿物的成因则相对复杂,其形成过程受多种因素的综合影响。碳同位素值未表现出极低负值,可能是甲烷、有机质和正常海水等碳源混合的结果。     

中国南方东部震旦纪碎屑岩和泥质岩成岩作用

中国南方震旦纪碎屑岩的成岩作用主要有压实和压溶、胶结和固结、重结晶、交代作用及自生矿物形成等,泥质岩的成岩作用主要为压实作用和成岩过程中粘土矿物的转化。其成岩过程可分为同生、成岩、后生、表生四个成岩作用阶段。在沉积盆地演化的不同阶段和处在盆地的不同部位,出现了不同的岩石类型,往往呈现各自的成岩作用变化特点。     

Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks

Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.     

Phosphorites of the Chiatura manganese deposit and specific features of their formation

The paper presents results of the detailed study of phosphorites from manganiferous beds of the Chiatura deposit. The relatively high-grade (P₂O₅ 20–28%) phosphorites are represented by various rocks ranging from the variety dominated by massive phosphates with a rare aleuritic admixture of quartz and feldspar grains to rocks mainly composed of terrigenous material with phosphates in the matrix. Phosphates make up the matrix of various organic remains: differently preserved diatom algae and microbial species. Some relatively large organic remains (in particular, sponge spicules) are typically composed of iron minerals (with manganese admixture) rather than phosphates. Manganese ores comprise phosphorite fragments composed of phosphatized cyanobacterial mat. Phosphorites of the Chiatura deposit were likely formed in a shallow-water zone away from the continental land.     

华北地台中元古代碳酸盐岩中的微生物成因构造及其生烃潜力

华北地台中元古界主要由环潮坪石英砂岩、浅海碳酸盐岩和浅海—泻湖相暗色页岩3种沉积相组合构成,以陆表海浅水碳酸盐岩占主导。碳酸盐岩中除含有丰富的微古植物、宏观藻类和微生物建隆外,还发育大量的微生物成因构造(MISS)和微生物诱发的碳酸盐沉淀(MMCP)。微生物席和MISS构造在高于庄组上部(约1.6 Ga)和雾迷山组下部(约1.45 Ga)碳酸盐岩中尤为发育,表明活跃的微生物活动和高有机质产量。在石化微生物席中,发现有丝状、球状细菌化石和草莓状黄铁矿;围岩中发现有针状文石、花瓣状重晶石、放射状菱铁矿、铁白云石和葡萄状碳酸盐胶结物等多种自生碳酸盐矿物,指示甲烷厌氧氧化(AOM)导致的自生碳酸盐沉淀。中元古代的温暖气候和海洋分层、缺氧、硫化条件有利于微生物的高生产量和高有机质埋藏率。气隆构造和核形石状碳酸盐结核反映浅埋藏条件下活跃的成烷作用和甲烷排放,围岩和MMCP中富沥青质。华北地台中元古界富微生物席碳酸盐岩有良好的生烃潜力,有可能形成重要的烃源岩。据微生物席、MISS构造及MMCP的研究,初步估算华北地台中元古代碳酸盐岩的概略生烃潜力约为10×108t石油当量。     

Origins of authigenic minerals and their impacts on reservoir quality of tight sandstones: Upper Triassic Chang-7 Member,Yanchang Formation,Ordos Basin,China

Reservoir quality is critical for sweet-spot evaluation in tight sandstone plays, but few studies have focused on the origin of authigenic minerals in tight sandstones and their impact on reservoir quality. This study integrates petrographic analysis, carbon and oxygen isotopic data and mercury injection capillary pressure data of the Upper Triassic Chang-7 tight sand reservoir samples in the Ordos Basin, China to understand the origin of authigenic minerals and the impact of authigenic minerals on reservoir quality. Carbonate minerals, including calcite, ferroan calcite and dolomite, and kaolinite, are the major authigenic minerals in the Chang-7 sandstone. They were derived from the chemical diagenetic alteration of detrital feldspar and biotite, with the involvement of ions that are believed to be primarily from the connate water in interstitial pore space of the interbedded mudstones. Meteoric water and organic fluids from hydrocarbon generation may also have been involved in the alteration processes of the minerals in the Chang-7 tight sandstone. The origin of kaolinite indicates that the porosity was increased by dissolution of detrital grains, offsetting the porosity loss from burial compaction. Authigenic minerals appear to have a weak correlation with pore structure, suggesting that the pore structure of the Chang-7 tight sandstone is not only controlled by major authigenic minerals but also affected by other geological factors.     

Is the spring water responsible for the fossilization of faunal remains at Florisbad, South Africa?

It is has been suggested that faunal remains at Florisbad were fossilized in a spring context due to the mineralized spring water. However, the environment conducive to the precipitation of CaCO₃ and other authigenic minerals was formed largely through the salinization of the organic layers and clay, and the mineralization of the groundwater. Factors contributing to this favorable environment include: CaCO₃ saturation, pH, the decomposition of halophytes, Eh, rainfall, biomineralization, and aeolian deposition. With the exception of pH, none of the above factors feature in a spring context, with evidence suggesting that the spring water may historically never have carried sufficient minerals for fossilization, and that contact with the spring water may actually have resulted in the demineralization of previously fossilized material. In light of this evidence, it is concluded that the fossilization of faunal remains at Florisbad took place in a sedimentary organic matter and clay environment and could not have taken place in the spring vents where there is an undersaturation of Ca.     

Microbial Mats in the Mesoproterozoic Carbonates of the North China Platform and Their Potential for Hydrocarbon Generation

The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three llthological associations including peritidal quartz sandstone, shallow marine and lagoonai dark to black shales, and shallow epeiric carbonates, with a total thickness of up to 8 000 m. In addition to well-documented microplants, macroalgae, and microbial buildups, abundant microbially induced sedimentary structures (MISS) and mat-related sediments have been recognized in these rocks. Intensive microbial mat layers and MISS are especially well preserved in the carbonates of the upper Gaoyuzhuang (高于庄) (ca. 1.5 Ga) and lower Wumishan (雾迷山) (ca. 1.45 Ga) formations, Indicating diversified microbial activities and a high organic production. In these petrified blomats, putative microbial fossils (both coccoidal and filamentous) and framboidal pyrites have been identified. The abundance of authigenic carbonate minerals in the host rocks, such as, acicular aragnnites, rosette barites, radial siderites, ankerites, and botryoidai carbonate cements, suggests authigenlc carbonate precipitation from anaerobic oxidation of methane (AOM) under anoxic/euxinic conditions. Warm climate and anoxic/euxinic conditions in the Mesoproterozoic oceans may have facilitated high microbial productivity and organic burial in sediments. Although authigenic carbonate cements may record carbonate precipitation from anaerobic methane oxidation, gas blister (or dome) structures may indicate gas release from active methanogenesls during shallow burial Bituminous fragments in mat-related carbonates also provide evidence for hydrocarbon generation. Under proper conditions, the Mesoproterozoic mat-rich carbonates will have the potential for hydrocarbon generation and serve as source rocks. On the basis of petrified biomats, a rough estimation suggests that the Mesoproterozoic carbonates of the North China platform might have a hydrocarbon production potential in theorder of 10×108t.     

An excellent fossil wood cell texture with primary uranium minerals at a sandstone-hosted roll-type uranium deposit, NW China

A fossil wood cell texture with pitchblende and coffinite found at a sandstone-hosted roll-type uranium deposit, Xinjiang, NW China, is first reported here for the country. In the mineralized sandstone, detrital grains consisting of quartz, feldspar, rock fragments, carbonaceous trashes, mica and accessory minerals were deposited in early Turassic time and were cemented by clays and minor authigenic calcite and quartz. Pitchblende and minor coffinite are principal ore minerals at the deposit, and selectively replaced carbonized fossil wood remnants or filled fossil wood cells. An excellent fossil wood cell texture with primary uranium minerals formed. Replacement of organic debris by primary uranium minerals may be due to a local reducing environment resulting from the production of CH₄, H₂S or H₂SO₃ in its decomposition, and a biochemical reaction indicated by the common presence of framboidal pyrite.     

黑龙江东部盆地群白垩纪海侵存在的矿物学证据及其意义

前人研究所获得的海相化石证据表明,中国黑龙江东部早白垩世早期曾发生多次规模不等的海侵,多层厚度不等的海相夹层赋存于下白垩统中。对研究区白垩纪砂岩中的海绿石、独居石、莓状黄铁矿等自生矿物的显微特征、扫描电镜背散射特征和化学特征进行分析,结果证实,这些特征均与典型海侵相的特征接近,说明不仅含海相化石的层位系海侵成因,含这些自生矿物的砂岩、粉砂岩的层位也受到海侵的影响,从而为黑龙江省东部盆地在白垩纪发生过海侵提供矿物学的依据。     

Strate—bound Anorthites in the Dachang Sn—Polymetallic Ore Field,Guangxi,China

From the petrological study of ore-hosting focks which contain large anorthits crystals and the occurrence and chemical composition of anorthites and related minerals,the authors consider that the large anorthite crystals are of authigenic origin. The distribution characteristics of anorthites,i.e.,they are distributed along the bedding and structurally weak zones but not restricted to synsedimentary slump structures,and the relationship for some elements between anorthites and other minerals indicate that anorthites have resulted from reaction of circulating alkaline solutions rich in Al and Si with carbonated during the Indosinian orogeny.The results of this work suggest that the association of authigenic anorthites with bedded orebodies in the Dachang ore field may be the evidence that the mineralization is related to circulating underground hot waters.