徐州大北望寒武系徐庄组海绿石成因探讨

徐州大北望寒武系徐庄组发育不同类型海绿石，为探讨不同类型海绿石的成因，基于海绿石的矿物学、地球化学及沉积环境分析，利用偏光显微镜、X 射线衍射及电子探针等方法对各含海绿石岩层及不同类型海绿石进行系统对比研究查明海绿石的指相意义。结果表明，徐庄组发育颗粒状、碎屑假象状和胶团状三种类型海绿石，其中颗粒状海绿石具有中—高含量钾、高含量铁、砂岩中—高含量铝、石灰岩中低含量铝等特征；碎屑假象状海绿石具有变化大的钾、铁、铝，且保持着其母质形态特征；胶团状海绿石具有高钾、高铁、低铝特点。颗粒状海绿石成因符合颗粒绿化理论，砂岩中海绿石易受环境影响；碎屑假象状海绿石成因符合层状晶格理论及假象替代理论，受到交代和溶蚀作用，因受较强的水动力条件影响成分变化较大；胶团状海绿石是凝胶状海绿石通过胶结作用沉淀，形成于稳定环境中。     

Etude isotopique de l'altération naturelle d'une formation à glauconie (méthode à l'argon)

In Normandy (France), the glauconite bearing base of the Cenomanian has a wide distribution in outcrops and boreholes. Glauconite pellets are subjected to natural weathering and fluvial transport following separation from the glauconite-bearing bedrock by streams and creeks which dissolve the carbonate fraction. From the 100 samples collected, 19 samples from the studied horizon have been selected after X ray, diffaction studies. X ray diffractron techniques show that the non weathered glauconite pellets are composed of well-ordered gilauconites. In the reworked glauconite, the alteration is manifested by a slight opening of the structure. In addition, the diffractogramm yield a fast and sensitive estimation of the K contents of the glauconites. Lowering of the K content goes hand in hand with the opening of the glauconite structure. 12 samples were selected from the autochtonous horizon (fresh outcrop and borehole) a second group of 7 samples was taken from alluvions (streams and quaternary terraces) to study the effects of natural weathering. As actually, no other glauconite-bearing horizons are found in the region, the glauconite pellets in the alluvions can only be derived from the studied bedrock. Reworking and natural weathering of the glauconites leads to a decrease of the K content of 10–15%. Argon analysis shows that comparable percentage of radiogenic argon is lost at the same time so that the apparent ages do not change (in the errors limits). These results are only valid for well-ordered glauconites and continental alteration under moderate climate with basic fresh water. In conclusion, it can be stressed that the credibility of glauconite K-Ar ages does not change after such a reworking.     

The origin and maturation of lagoonal glauconites: a case study from the Oligocene Maniyara Fort Formation,western Kutch,India

An integrated study of the sedimentology, micropalaeontology, mineralogy and geochemistry of glauconites in the Oligocene Maniyara Fort Formation (western Kutch, India), has been undertaken. Authigenic glauconites, mostly of evolved type, formed within a back‐barrier lagoonal environment. Foraminifera help constrain the biostratigraphy and along with sedimentological evidence, provide information on the depositional conditions. Glauconite in the Maniyara Fort Formation occurs either as infillings within intra‐particle pores of larger foraminifers, or as an altered form of faecal pellets. X‐ray diffraction studies reveal the less mature nature of glauconite infillings compared to the glauconite pellets. Electron microprobe investigation confirms a relative enrichment of K₂O and total Fe₂O₃ in the latter. Both varieties of glauconite formed by initial authigenic precipitation of K‐poor glauconite and subsequently matured by addition of potassium in the interlayer sites and fixation of total iron in the octahedral sites; calcium, magnesium and aluminum were released from the glauconite structure concomitantly. Alkaline conditions during the entire process of glauconite formation did not allow dissolution of foraminiferal tests. Mineralogical and chemical characteristics of the Maniyara Fort Formation glauconites are more similar to deep marine glauconites than those reported from other shallow or marginal marine settings. A low negative cerium anomaly, as well as abundant pyrite, suggests formation of glauconite in sub‐oxic micro‐environments, created by decay of organic matter associated with foraminiferal chambers and faecal pellets. Sub‐oxic condition apparently prevailed relatively longer within the Maniyara Fort Formation lagoons. Copyright © 2011 John Wiley & Sons, Ltd.     

天津蓟县中元古界铁岭组叠层石灰岩中原地海绿石的沉积学意义

天津蓟县剖面中元古界铁岭组二段叠层石灰岩中普遍发育海绿石。野外观察表明,海绿石主要分布在叠层石柱体间的泥晶灰岩中,呈薄膜状富集在叠层石鞘外缘;微观特征分析表明,海绿石呈不规则状的胶体形式,显示了原地海绿石的基本特点。电子探针的组分分析表明,铁岭组中的海绿石为中成熟度的海绿石。由于产在潮下高能柱状叠层石灰岩中,铁岭组中的海绿石并不反映低沉积速率或沉积间断的沉积条件,与现代海绿石的形成环境具有明显的差异。因此,中元古界铁岭组叠层石灰岩中的中成熟度原地海绿石是特殊沉积背景下的独特产物,为研究海绿石在地质历史时期产出的多样性提供了一个重要实例。     

L'âge radiométrique du Miocène inférieur en Europe Occidentale et Centrale

Systematic research over years on datable horizons of lower Miocene age has led to an election of nine glauconite samples suitable for dating work. The chosen glauconites come from various regions of the tethys. Following careful sedimentological as well as stratigraphical studies the K-Ar ages of these glauconites were measured. The interpretation of the apparent ages found takes into consideration sedimentation, mineralogical quality and present knowledge of the genesis of the green glauconite pellets. The presented data allow to fix the basis of the Miocene at about 21–22 m. y. and the boundary of Aquitanian-Burdigalian at 18 m. y. The K-Ar data on glauconites presented here are in good agreement with newer measurements of other authors on high temperature minerals of the same age span.     

海绿石的成因、指相作用及其年龄意义

海绿石以独特的绿色自生色和球粒形状与围岩形成明显反差,关于其成因、演化、沉积和地层学意义目前存在3种普遍被认可并被采用的观点：海绿石是典型的海相沉积自生矿物,原地海绿石是“慢速、弱还原、较深水环境”的典型指相矿物之一;通常是海侵相的产物,含海绿石的地层在浅海沉积中常被作为海侵时期“凝缩段”及其相关沉积的识别标志之一;是沉积年代学中K-Ar、⁴⁰Ar/³⁹Ar年龄理想的测定对象。在采用海绿石作为典型指相矿物的过程中,应注意海绿石可以形成于多种沉积环境中,只有原地海绿石才能作为海侵时期“凝缩段”及其相关沉积的识别标志;海绿石年龄往往呈“年轻化”或“老化”,没有火成岩定年准确,只有成熟、富钾的海绿石才是最好的定年对象。     

东海沉积物中海绿石的研究

关于东海现代沉积物中的海绿石,前人曾有过报道,但都限于一般性的描述。近年来我们对东海表层沉积物中的海绿石进行了较为系统的研究,工作范围为东经121°-129°,北纬26°30′-32°00′,样品233个。分别进行了镜下鉴定、透射电镜和扫描电镜观察,并以多晶X-射线衍射法,化学全分析、差热分析、红外吸收光谱和电子探针等方法进行较系统的矿物学研究。本文就东海表层沉积物中海绿石的矿物学特征,产状及分布进行阐述,并对其成因作了初步的探讨。     

Mössbauer characteristics,mineralogy and isotopic age (Rb-Sr,K-Ar) of Upper Riphean glauconites from the UK Formation,the southern Urals

Comprehensive mineralogical analysis, Mössbauer spectroscopy and isotopic-geochronological study have been carried out for globular phyllosilicates (GPS) of glauconite group from the Uk Formation, the second one below the top of the Upper Riphean stratotype in the southern Urals. Glauconites have been sampled in the Kurtaza and Kulmas sections remote from each other in the Alatau anticlinorium that corresponds to western facies zone of the Bashkirian meganticlinorium. As is shown, size and density monomineral fractions of globules are represented by Al-glauconite according to established structural formula. The isotopic (Rb-Sr and K-Ar) dating of glauconites from the Uk Formation is performed for the first time along with computer simulation of cation arrangements in their crystal lattice and comparison of the results obtained with data of Mössbauer spectroscopy. It has been assumed by simulation that origin and transformation of the Rb-Sr and K-Ar systems in glauconite are concurrent to stages in structural evolution of this mineral, which have been controlled by geological and geochemical events in the history of sedimentary successions. The approach has been aimed at recognition of stratigraphically meaningful isotopic dates corresponding to the glauconite formation at the stage of the early diagenesis close to sedimentation time and the “rejuvenated” dates characterizing ages of subsequent geological events. The comparison of simulated cation arrangements with data of Mössbauer spectroscopy shows that the Rb-Sr (663 ± 9 Ma) and K-Ar (669 ± 16 Ma) dates established for glauconites correspond to the time of early diagenesis in their host sediments, being suitable for age assessment of the Uk Formation. The dates obtained are of interregional and wider significance, as they must be taken into consideration when constructing the general curve of Sr isotope variations in the Late Riphean oceans.     

吉林大阳岔地区小阳桥寒武-奥陶剖面中海绿石矿物学研究

本文总结了小阳桥剖面的寒武系-奥陶系界线附近海绿石矿物学特征,并对该地层剖面附近的沉积环境进行讨论。     

RbSr and KAr ages of paleozoic glauconites from Ohio—Indiana and Missouri,U.S.A.

Glauconite pellets from the Lower Silurian Brassfield Formation on both limbs of the Cincinnati Arch in Ohio and Indiana give a RbSr age of 370 ± 11 Ma, which is substantially younger than the stratigraphic age of the formation. The age is concordantcwith conventional KAr ages of 355 ± 6 and 368 ± 5 Ma for two of the same glauconites. Concordant ages were also obtained from the Viburnum Trend in Missouri, where glauconite pellets from the Davis Formation in an ore-zone collapse structure into the underlying Bonneterre Formation give a RbSr age of 387 ± 21 Ma and conventional KAr ages of 368 ± 5 and 369 ± 5 and 369 ± 5 Ma. A third suite of glauconite from the Bonneterre Formation in the Old Lead Belt ～ 10 km from the nearest ore body has given a RbSr age of 423 ± 7 Ma and slightly older conventional KAr ages of 434 ± 6, 445 ± 6 and 441 ± 11 Ma.Because these glauconite-bearing rocks have been buried to depths of less than 1 km, thermal resetting of the RbSr and KAr systematics appears unlikely. The initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the RbSr isochrons are similar to the ratios for vein- and vug-filling dolomite and calcite. This is consistent with resetting of the RbSr and KAr systems during diagenetic changes which included the isotopic equilibration (perhaps by cation exchange) of the Sr in the glauconite with that in the diagenetic and Mississippi Valley-type ore fluids. This interpretation implies that the age of the Mississippi Valley-type mineralization in the Viburnum Trend is Devonian rather than Carboniferous—Permian as has been inferred from paleomagnetic measurements.Cation-exchange experiments with a dilute Sr-bearing solution and an artificial oilfield brine indicate that glauconite adsorbs large amounts of Sr, some of which is sufficiently strongly attached to the glauconite lattice as to resist leaching with ammonium acetate. The introduction of this strongly attached Sr may be the first step in the resetting of the RbSr systematics of glauconite by cation exchange.     

K-Ar age of Ukra glauconites from the Kutch Basin, India

The present paper reports the K-Ar ages determined on glauconitic samples collected from the Ukra Member of the Mesozoic Bhuj Formation in two different sections, one located on the Ghuneri-Ghaduli road near Katesar Mahadeo temple and the other at the base of the Ukra hill in the northwestern part of the Kutch Mainland area. Three glauconite samples viz., Ukra_KT-1, Ukra_KT-4 and Ukra_UH-3 have yielded K-Ar ages of 107.9 ± 3.4 Ma, 105.5 ± 3.3 Ma and 103.5 ± 3.4 Ma, respectively. The sample Ukra_KT-l treated with 0.5N HC1 and analysed in duplicate has yielded a mean age of 104 ± 2.3 Ma while the sample Ukra_KT-4 treated with 0.1N HCl has given an age of 106.5 ± 3.3 Ma. The ages of the treated and untreated glauconites are indistinguishable within 2σ uncertainty with a mean of 105.2 ± 1.3 Ma, which has been interpreted as the depositional age of the Ukra Member of the Mesozoic Bhuj Formation. The study has further indicated that mild acid treatment (up to 0.5N HCl) does not lead to any loss of radiogenic argon in the glauconites and can be helpful in purification of the samples.     

陕北三叠系上统延长油层中海绿石的发现及其初步研究

本文对陕北三叠系延长群延长油层中的海绿石——延长海绿石进行了分析研究。结果表明,延长海绿石的矿物学特征与一般海绿石相同,其扩展层含量19%,属于无序低钾云母型结构。碳同位素及微量元素分析表明,延长海绿石系陆相淡水-半咸水湖泊环境下的自生矿物,延长海绿石存在于湖泊三角洲前缘远沙坝或三角洲间湖湾的粉-细砂岩中,也常与自生黄铁矿共生,其形成时水深为50-100m。海绿石的存在指示着该处为弱还原环境,对于成油较为有利。因此,在陆相湖泊三角洲环境中,也应当建立海绿石地球化学相。     

Glauconite

The term glauconite has been employed in two senses. It has been used most commonly as a morphological term for sand-sized greenish grains found in sedimentary rocks, but also as a name for a specific mineral species, a hydrated iron-rich micaceous clay mineral. The two uses are not synonymous, since not all morphological glauconite consists exclusively of mineral glauconite, nor is the latter restricted in its occurrence to such pellets. Mineral glauconite in sensu lato is a random interstratification of nonexpanding 10A?layers and expanding montmorillonitic layers. The amount of expandable layers may be over 50 % but it is customary to restrict the name mineral glauconite in sensu stricto to varieties with less than 10 % expandable layers. The variation in amount of expandable layers explains many of the observed variations in the properties of glauconite including chemical composition (especially potassium content), thermal characteristics, cation exchange capacity, colour, refractive index and specific gravity. Mineral glauconite is believed to form by the progressive absorption of potassium and iron by a degraded layer silicate lattice of low lattice charge and elimination of other silicate-lattice types under suitable environmental conditions, of which the most critical seems to be the redox potential. The catalytic activity of marine organisms is no longer thought to be essential, although decaying organic matter and empty foraminiferal tests supply the ideal environment for glauconite genesis. The process of glauconitization is arrested by rapid sedimentation, so that there is a relationship between the variety of mineral glauconite formed and the nature of the host rock. Glauconite is found associated particularly with marine transgressions. Morphological glauconite grains are believed to form as casts, faecal pellets or by accretionary growth, but may have their morphology modified by subsequent re-working. A number of characteristic internal and external morphologies have been recognised. The wide range of environmental conditions suitable for its formation and its common detrital occurrence debars the use of glauconite in palaeo-environmental studies. Its major use in geology is for the absolute age dating of sedimentary rocks by the K-Ar method. Glauconitic deposits have no present day commercial value, but soils formed on glauconitic parent materials are notable for their fertility. Glauconite weathers by loss of potassium to produce a montmorillonitic or vermiculitic product with the release of, or oxidation of, structural iron, so that the grain has the appearance of having weathered to limonite.     

Rb-Sr dating of Paleozoic glauconite from the Llano region,central Texas

Glauconite from eight stratigraphic horizons (Cambrian to Pennsylvanian) in the Llano Uplift, central Texas and two Cretaceous glauconites were analyzed by the Rb-Sr method. Only two untreated samples provide ages in agreement with those anticipated from current best estimates of the geologic time scale. With one exception all the other apparent ages fall short of the estimated age of deposition by as much as 22%. Low ages, the pattern customarily observed, are attributed to postdepositional loss of radiogenic ⁸⁷Sr from expandable layers by weathering or during diagenesis.Detailed leaching experiments using a variety of reagents were performed to characterize the behavior of glauconite. The most promising treatment, which we recommend as standard procedure in all future studies, is with ammonium acetate which is able to purge the mineral of loosely-bound Rb and Sr while leaving tightly-bound components intact. After appropriate leach, three other Rb-Sr ages were brought into coincidence with their estimated ages of deposition.In contrast an Upper Cambrian glauconite was found to be extremely resistant to further alteration by chemical attack′, providing an age of 429 ± 17 M yr. Although 17% short of the age of deposition, this age is interpreted as the time of a real event: diagenetic recrystallization induced by burial. Comparison of data from four samples indicates that for Paleozoic glauconite, conditions exist in which the Rb-Sr system is less susceptible to mild disturbance than is the K-Ar system.     

K–Ca ages of authigenic sediments: examples from Paleozoic glauconite and applications to low-temperature thermochronometry

K–Ca ages of Cambrian glauconites from the Llano uplift, central Texas, were determined in order to re-evaluate the ability of the K–Ca system to constrain the timing of deposition of sedimentary packages. All of the K–Ca ages presented here were found to be younger than their stratigraphic ages. In addition to being too young, the K–Ca ages are also highly variable, ranging in age from Silurian to Permian. The oldest subset of glauconite ages are in agreement with previously published Rb–Sr ages from the same outcrop and provide further evidence for there having been a post-depositional thermal or recrystallization event that reset both the Rb–Sr and K–Ca systems. The range of younger glauconite K–Ca ages is similar to the distribution of available apatite fission track ages for the Llano basement. K–Ca ages are interpreted as thermochronologic data reflecting partial retention of Ca in thermally fluctuating basin conditions. Estimates of the closure temperature of Ca in glauconite are found to be 60–90°C for cooling rates of ~0.5–1°C/My. The K–Ca system is potentially useful as a low-temperature thermochronometer with closure temperatures <100°C for glauconite.     

Compositional variation within some glauconites and illites and implications for their stability and origins

Textural, mineralogical and chemical data are presented for glauconites and illites from the Lower Cretaceous Glauconitic Sand Formation, Alberta, Canada. Single crystal analyses by scanning transmission electron microscopy (STEM) indicate that both glauconite (29 analyses) and illite (44 analyses) correspond very closely to ideal dioctahedral structures. Al dominates the octahedral sheet in illite. Very extensive A1 for Fe^III substitution was also found in some of the glauconites, much more than previously recorded. The dioctahedral mica structure is clearly very stable and flexible with respect to A1 for Fe^III substitution. Iron-poor glauconites were found associated with pyrite. We believe that glauconites tend to lose iron progressively during burial diagenesis, especially where pore water iron activities are low (high HS^? activity and low Eh). It seems probable that A1 for Si tetrahedral substitution also takes place during diagenesis with consequent loss of swelling properties. This is the same trend which is responsible for conversion of smectite to illite. Glauconite forms only where sediments reside for lengthy periods at the interface between oxidizing and reducing environments, where Fe³⁺ is transiently available in solution. Related marine and terrestrial nontronites also form only in similar ‘interface’ environments.     

Glauconites from the Late Palaeocene — Early Eocene Naredi Formation,western Kutch and their genetic implications

Glauconitic minerals are considered as one of the valuable input parameters in sequence stratigraphic analysis of a basin. In the present study glauconitic minerals are reported from subtidal green shale facies in the lower part of the Late Paleocene-Early Eocene Naredi Formation of western Kutch. On the basis of the foraminiferal assemblage the glauconite bearing beds are interpreted to have formed in a mid shelf depositional settings of an unstable marine conditions. XRD studies confirm the glauconite mineralogy of the green pellets and provide an estimation of glauconite maturity. Textural attributes of the glauconites confirm their derivation by different degrees of alteration of precursor feldspar grains. Because of the authigenic origin and autochthonous nature, these glauconites hold promise for understanding sequence stratigraphy of the Palaeogene succession of the western Kutch.     

Glauconitic greensand: A possible filter of heavy metal cations from polluted waters

Experiments using distilled water, spiked with heavy metal cations and passed through a filtration system composed of greensand containing 80% glauconite at a rate of 2–4 ml/min, showed: (1) starting fluids containing Cd, Co, Cu, Pb, Mn, Ni, Ag, or Zn had an average of 90% of the contaminating cation removed from acidic solutions and an average of 84% removed from the basic solutions; and, (2) filtration through greensand tended to neutralize both acidic and basic solutions. The removal of the contaminant cation from starting fluids containing K, Na, Ca, Mg, Fe, Si, or Al (the principal constituents of glauconite plus Ca from shell material) is not as consistently effective as for the first named metals.     

Thermal metamorphism of primitive meteorites—I. Variation of six trace elements in Allende carbonaceous chondrite heated at 400–1000°C

Determination by neutron activation of 6 trace elements retained in Allende (C3) samples heated at 400–1000°C for 1 week in a low-pressure (initially ~10^?5 atm H₂) atmosphere reveals loss of small proportions of Ga and Se and large proportions of Bi, In and Tl-Co being unaffected. The retentivity patterns for the 5 volatile elements differ and in no way duplicate a step-function. In contrast to these trace elements, sulfur is initially present in discrete mineral(s) and visually it appears to be released over a narrow temperature range. Elements are lost more easily from powder than from chips but the difference is ≤35 per cent. Above 600°C, the process of loss appears due to process(es) with apparent activation energies of 2 kcal/mole (Bi, Tl), 4 kcal/mole (Se) and 22 kcal/mole (In). Loss of Bi, Se and Tl below 600°C involves higher apparent activation energies. Two-element correlation diagrams involving Bi, In and Tl are consistent with the idea that trends among highly-volatile elements in enstatite chondrites arise from metamorphism.     

奥连特盆地白垩系海绿石成因类型及沉积地质意义

厄瓜多尔奥连特盆地白垩系Napo组UT段发育一套分布广泛的富含海绿石的硅质碎屑岩,针对海绿石的岩相、矿物学、地球化学及时空属性进行分析,可以揭示海绿石的组分、成熟度、形成及成因类型,结合地质约束有助于理解其形成的沉积地质意义.利用偏光显微镜、X射线衍射、电子探针及Qemscan对海绿石矿物的岩相、矿物组成和主量元素进行系统地分析.暗绿色、呈弯曲玫瑰花状的海绿石具有高的K₂O含量(平均值为8%,质量百分比),是形成于海相低沉积速率环境的高演化成熟型海绿石云母矿物或狭义范畴的海绿石.化学组分和时空属性揭示研究层段的海绿石经历了一定程度风暴流和/或潮汐流作用的搬运改造,属于层内准原地海绿石.UT段海绿石含量向上的增大趋势和成熟度的变化,以及横向上从盆地东部斜坡区埋深2~3 km到西部盆缘露头区相距约120 km的海绿石在形态和化学成分上具有相似性,指示其主要是层内准原地海绿石的特点.UT段垂向上海绿石含量增大的趋势同时反映外陆棚物源区原地海绿石向岸方向的短距离迁移,反映了相对海平面持续上升的海进过程;而且同时期海绿石平面上的广泛分布指示沉积时期的环境属于构造稳定的陆表海.