Resino-inertinites of Indian Permian coals — their origin, genesis and classification

Variously shaped discrete bodies with reflectance higher than the associated vitrinite occur in Permian coals in India, Australia and Africa and the Carboniferous coals of the United States, Canada and Europe. These bodies have been variously named by different authors. In the present paper they are described as ‘resino-inertinites’ as suggested by Lyons et al. (1982).Based on available information and our observations on Carboniferous and Permian coals, it is presumed that resino-inertinites were formed mainly from the resinous (resinite) and to some extent from the phlobaphinitic or corpocollinitic substances. Various morphological patterns developed on resino-inertinites have been interpreted to be governed by the chemical composition of their precursors and the degree of oxidation or fusinization during coalification. Influences of other vvariables viz., paleoenvironmental, paleodepositional, tectonic set up etc. on resino-inertinites are not clearly recognizable probably because all the previous effects were masked by subsequent fusinization.Different morphological features of resino-inertinites associated with early diagenetic and secondary mineralization have caused much confusion in their proper identification and classification. In order to resolve this problem, an attempt has been made to ascertain the source of resins in Indian Permian coals and their subsequent mode of transformation into resino-inertinites during coalification.Further, by critically evaluating morphological features of resino-inertinites and keeping the chemical nature of their precursors in view, a classification scheme has been proposed categorizing them into 3 types. The classification proposed may prove as a useful means for coal-seam correlation.     

不同煤化程度煤热解过程中汞释放规律

采用热重与测汞仪联用技术,对5种不同煤化程度的煤进行氧化热解实验,研究不同煤化程度煤的热解过程及煤中汞的释放规律。结果表明：X射线衍射（XRD）曲线中衍射峰的特征可反应煤化程度,衍射峰的高度越高,宽度越窄,煤化程度就越高。不同煤化程度的煤在氧气中热解,质量损失随煤化程度的加深而增大,且随着煤化程度的加深,氧化热解的起始温度、最大热分解温度、终止温度也逐渐升高。随着煤化程度的升高,煤中汞释放所需的时间逐渐增加,且汞释放最大值所对应的热重（TG）曲线热解率最大的温度随煤化程度的加深而升高。     

早期煤化作用机制与有机质早期成烃演化

近年来，未熟和低熟油气田的发现、生物气藏的勘探和开发，极大地促进了对有机质早期转变的研究；而有机质早期转变机制的正确认识对于煤和干酪根中显微组分的成因、后期热演化都有着重要的影响。对早期煤化作用机制和有机质早期成烃作用的研究现状、进展及存在的问题进行了综述。     

Coalification of organic matter in coal balls of the Pennsylvanian (upper Carboniferous) of the Illinois Basin, United States

An evaluation was made of the degree of coalification of two coal balls from the Illinois Basin of the Pennsylvanian (upper Carboniferous) of the United States. Previous interpretations are mainly misleading and contradictory, primarily because of the assumption that the brown color and exceptional cellular and subcellular preservation typical of American coal balls imply chemical preservation of cellulose and lignin, the primary components of peat. Xylem tissue from a medullosan seed fern contained in a coal ball and the coal attached to the coal ball from the Calhoun coal bed, Mattoon Formation, Illinois, was analyzed by elemental, petrographic, and nuclear magnetic resonance (NMR) techniques to determine the degree of coalification. The NMR and elemental data indicate the lack of cellulose and lignin and a probable rank of high-volatile C bituminous coal. These data corroborate data for a coal ball from the Herrin (No. 6) coal bed (Carbondale Formation, Middle Pennsylvanian) and support our hypothesis that the organic matter in coal balls of the Pennsylvanian strata of the United States is coalified to about the same degree as the surrounding coal. Data presented show a range of lower reflectances for xylem tissue and vitrinite in the analyzed coal balls compared with vitrinite in the attached coal.The data reported indicate that physical preservation of organic matter in coal balls does not imply chemical preservation. Also our study supports the hypothesis that compactional (static load) pressure is not a prerequisite for coalification up to a rank of high-volatile C bituminous coal.A whole-rock analysis of the Calhoun coal ball indicates a similarity to other carbonate coal balls from the United States. It consists primarily of calcium carbonate and 1–2% organic matter; silica and alumina together make up less than 0.5%, indicating the lack of minerals such as quartz and clays.     

Gelification of victorian tertiary soft brown coal wood. II. Changes in chemical structure associated with variation in the degree of gelification

The gross chemical structures of xylites and gelified soft brown coal woods, Latrobe Valley, Victoria, Australia, as determined by solid state nuclear magnetic resonance spectroscopy, are compared with those of present-day wood-derived materials prepared from an angiosperm, Eucalyptus regnans, and a gymnosperm (conifer), Pinus radiata. Also examined are the changes in the gross chemical structures of soft brown coal woods with increase in their degree of gelification and the relationship between these changes and variations in their chemical composition and microscopic appearance.The Victorian xylites exhibit greater affinities with the present-day gymnosperm than the present-day angiosperm. The progressive removal of cellulose with increasing degree of gelification can be equated with an increase in huminite reflectance, elimination of humotelinite autofluorescence and changes in the relative proportions of the humotelinite submacerals. The lignin structure of xylite is also modified during the gelification process, including the progressive loss of methoxyl groups and evidence of minor oxidation.     

腐泥煤的煤化作用研究

腐泥煤的煤化作用特征目前了解甚少.对我国产出的不同时代、不同煤化程度腐泥煤,结合热模拟试验,并通过与腐殖煤的对比,较系统地研究了在煤化作用过程中,腐泥煤的宏观和微观岩石学特征、元素组成和化学结构的演变规律。在此基础上,探讨了腐泥煤的煤化作用机理,研究了其煤化程度指标,提出了其煤级划分方案。      

Gelification of Victorian tertiary soft brown coal wood. I. Relationship between chemical composition and microscopic appearance and variation in the degree of gelification

The relationship between chemical composition and microscopic appearance of present-day wood-derived materials and Victorian xylites and gelified soft brown coal woods, Latrobe Valley, Australia, is discussed. The present-day wood-derived material consists of milled wood and lignin and holocellulose fractions prepared from an angiosperm, Eucalyptus regnans and a gymnosperm, Pinus radiata. The xylites and least gelified soft brown coal woods resemble the P. radiata lignin fraction; the latter contains residual cellulose.The atomic H/C ratio was found to be a useful guide to the degree of gelification. Increase in the degree of gelification was accompanied not only by an increase in the total huminite reflectance, but also by an increase in the reflectance of the individual huminite submacerals. The loss of hymotelinite autofluorescence under ultraviolet and blue light excitation with increase in the degree of gelification of Victorian soft brown coal woods was ascribed primarily to the elimination of cellulose and, possibly, modification of the lignin structure of xylite.     

The rank evaluation of South Brazilian Gondwana coals on the basis of different chemical and physical parameters

Rank evaluation of South Brazilian Gondwana coals according to the American (American Society for Testing and Materials, ASTM) and German (Deutsche Industrie Normen, DIN) standard specifications or on the basis of Alpern's Universal Classification has too often led to conflicting results.When any attempt is made to determine the rank of Brazilian coals by using methods established for the Northern Hemisphere coals, two sorts of difficulties arise: namely, (1) the reflectence measurements do not indicate the real degree of coalification of the organic matter because of the liptinitic impregnations of the vitrinites, and (2) random reflectance values (R_ran, moisture, volatile-matter and carbon contents as well as the calorific value do not correlate when plotted on the ASTM and DIN classification schemes.In addition, when rank determinations are carried out by using fluorescence measurements and geochemical analyses the results are at variance in relation to those determined by the conventional chemical and physical parameters.It is suggested that the rank evaluation of South Brazilian coals is far more meaningful if carried out by reflectance measurements on vitrinites along with fluorescence measurements on sporinites, alginites and coal extracts.     

煤岩单组分分离及其影响因素

采用密度分离技术成功地对3个系列不同煤化程度的19个煤层煤样进行了单组分分离。通过实验认为,煤岩单组分在煤中的赋存特征和煤的煤化程度是影响单组分分离效果的主要因素     

川北陆相砂岩型铀矿床成岩与成矿过程中有机质对铀的富集作用

川北陆相砂岩型铀矿主岩中有机质是铀的主要富集剂。铀在其中存在形式有:1.矿物铀;2.吸附铀;3.腐植酸合铀酰络合物。含铀有机质相当煤化程度较低的褐煤,铀矿化主要富集在结构镜质体之中。有机质对铀的富集作用表现在成煤作用的各个阶段。     

层间氧化带边界类型划分与铀成矿潜力评价

层间氧化带型铀矿床只与特定背景条件下形成的部分层间氧化带有关,铀元素沉淀富集于层间氧化带前锋线及其附近;在该区域地球化学性质完全不同的氧化与还原介质相互作用;对于铀成矿作用来说,氧化作用的效果是十分重要的,可以通过采集目的层相同岩性在正常氧化带和正常原生带的样品,分析其铀含量比值,间接反映氧化作用使铀从围岩中带出的能力;铀是否成矿主要取决于层间氧化带前锋线还原障的还原能力,参照岩石原生地球化学类型划分原则,岩石还原能力可划分为强还原能力(C有机质＞0.3%)、中等还原能力(C有机质0.05%～0.3%)、弱还原能力(C有机质＜0.05%)3个等级;以反映岩石还原能力的有机质含量为横座标,以0.05%和0.3%分别作为划分弱中、中强还原能力的分界线:以反映氧化作用效果的U氧化/U还原为纵座标,以 0.5和1分别作为氧化作用效果好与较好、较好与差的分界点:划分层间氧化带边界类型为9类:根据不同层间氧化带前锋线边界类型的成矿潜力差异,可作为对目标区进行层间氧化带型铀成矿潜力评价的依据.     

Coalification history of the Stephanian Ciñera-Matallana pull-apart basin,NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

The Stephanian Ciñera-Matallana Basin of NW Spain comprises 1,500 m of alluvial to lacustrine coal-bearing sediments, which were deposited in a late Variscan transtensional/transpressional pull-apart setting. The relationship between coalification pattern and rock deformation was evaluated by measurements of the anisotropy of vitrinite reflectance (AVR). The AVR ellipsoids reveal both pre-tectonic elements related to the bedding fabric and syn-tectonic elements related to folding, producing biaxial ellipsoid shapes with the maximum reflectance parallel to fold axes. The mean coalification gradient for the Stephanian succession is about 0.62 %Rr/km. Calculations of the mean palaeo-geothermal gradient are presented on the basis of three different empirical equations. A palaeo-geothermal gradient of 85 °C/km is considered the most realistic, with an overburden of about 1,000 m. 1-D numerical modelling of the burial history results in two possible scenarios, the most preferable involving a palaeo-heat flow of 150 mW/m² and an overburden of ca. 1,050 m. These results indicate that maximum coalification was related to a localised but high palaeo-heat flow/-geothermal gradient. The anisotropy of vitrinite reflectance highlights the interactive and transitional nature of sedimentary compaction and rock deformation on the maturation of organic material within strike-slip fault zones.     

Preliminary investigation on the metamorphism of Chinese coals

The fact that most Chinese coals are of a relatively high degree of coalification indicates that the metamorphism of Chinese coals has its own characteristics. As contact metamorphism and dynamic metamorphism have influenced the coals only to a restricted extent, they are not the causes of this distinguishing feature. Though geothermal metamorphism of coal occurs universally in China, the maximum subsidence as reflected by the thickness of coal measures and their overlying rock series is so small that the palaeo-temperature to which most Chinese coals were subjected was low and only low-ranking coals were formed. Hence, geothermal metamorphism is also not the principal cause of the higher ranking Chinese coals. Next to temperature, time is an important factor in geothermal metamorphism; the degree of coalification is dependent on the temperature and duration of heating that the coal has undergone.It is inferred that palaeogeothermal anomalies ought to be held responsible for most of the higher ranking Chinese coals. They are principally caused by magmatic intrusions, or by deep-seated faults, or by the uplift of the Moho with the corresponding uplift of the asthenosphere, and these three causes are interrelated. Telemagmatic metamorphism has so widely influenced Chinese coals that it accounts mainly for the majority of higher-rank Chinese coals. Consequently Chinese coals have first and universally been coalified by geothermal alteration to lower rank and then partially promoted by telemagmatic metamorphism to medium and high ranks. Based upon the patterns of magmatic intrusions and associated hydrothermal processes, the telemagmatic metamorphism of Chinese coals can be tentatively divided into the following types: (1) type a, produced mainly by hypabyssal or meso-epimagmatic intrusions; (2) type b, produced mainly by hydrothermalism from blind intrusive bodies; (3) type c, produced mainly by mesoepimagmatic and epimagmatic intrusions; and (4) type d, produced mainly by hydrothermalism and epimagmatic intrusions. Characteristics of coalification zones, wall rocks and coal itself may be used as criteria to differentiate the telemagmatic metamorphism from other kinds of metamorphism. Magmatic activities which caused the telemagmatic metamorphism and its extent are controlled by structural systems, especially by the latitudinal structural systems and other structural systems associated with the former.     

An overview of chemical properties of marine-influenced Oligocene coal from the northeastern part of the Assam-Arakan basin, India

The Oligocene coals from the northeastern part of the Assam-Arakan basin show a gradual decrease in the content of moisture, volatile matter and oxygen with corresponding increase in carbon content and calorific value from the Foreland Shelf to the deeper part of the geosyncline, reflecting the coalification trends in this basin. It has been suggested that the oxygen was replaced by organic sulphur, thereby lowering the oxygen content in the coals. The coals are perhydrous in nature with a high sulphur content. The high volatile content, perhydrous nature and high sulphur content in the Oligocene coals, as well as the presence of streaky facies and a very fine clastics unit, indicate that they were probably deposited in a marine-influenced deltaic and lagoonal environment.The plots of carbon versus hydrogen on Seyler's coal band follow a trend which differs from that of Seyler's band of Carboniferous bright coals. The coalification of the Oligocene coals represents the lignitic stage, in the case of the Foreland Shelf, and near subbituminous stage in the deeper geosynclinal part of the basin. A more intense, and probably sudden, dynamic process was involved in bringing about higher coalification in Oligocene coal of the geosynclinal facies than in Foreland Shelf area. This is possibly due to intense mountain-building forces acting from the southeastern direction of the basin.     

Coalification in Carboniferous sediments from the Lötschberg base tunnel

Vitrinite reflectance (Rr), proximate analysis and carbon isotope composition (δ¹³C) have been used to characterise coal samples from two zones of Late Carboniferous sediments (Gastern and Ferden) in the Aar massif where they are penetrated by the Lötschberg base tunnel (constructed between 1999 and 2005). Samples are characterised by variable ash yields (21.7–93.9%; dry basis); those with ash yields of less than ~50% and with volatile matter content (V;dry ash-free basis) within the limits 2 < V% ≤ 8 are anthracite. Values of Rr range from 3.89% to 5.17% and indicate coalification to the rank of anthracite and meta-anthracite in both Gastern and Ferden Carboniferous zones. Samples of anthracite and shale from the Gastern Carboniferous exhibit a relatively small range in δ¹³C values (–24.52‰ to –23.38‰; mean: –23.86‰) and are lighter than anthracite samples from the Ferden Carboniferous (mean: –22.20‰). The degree of coalification in the Gastern and Ferden Carboniferous zones primarily depends on the maximum rock temperature (T) attained as a result of burial heating. Vitrinite reflectance based estimates of T range from ~290° –360 °C. For a proposed palaeogeothemal gradient of 25 ° C/km at the time of maximum coalification the required overburden is attributable to relatively thin autochtonous Mesozoic/Cenozoic sedimentary cover of the Aar massif and Gastern granite and deep tectonic burial beneath advancing Helvetic, Ultrahelvetic and Prealpine (Penninic) nappes in Early Oligocene to Miocene.     

Chemical structural models for coalified wood (vitrinite) in low rank coal

Examination of a series of coalified gymnospermous woods ranging in rank from brown coal to subbituminous coal by solid-state ¹³C NMR and analytical pyrolysis has provided sufficient information to construct structural models depicting the changes that occur to lignin, the primary precursor of vitrinite, during coalification. Progressive changes in the chemistry of coalified wood suggest the following series of reactions: (1) demethylation to form catechol-like structures that are dominant components of brown coal and lignite A; (2) cleavage of aryl ether linkages to form phenols and reactive carbocations that alkylate the catechol rings; (3) dehydration of the catechol rings; (3) dehydration of the catechol-like structures to form the structures of subbituminous coal dominated by alkylphenols; and (4) reduction of the 3-carbon alkyl side chain derived from lignin to form propyl substituents. The models developed for each stage of coalification are derived from chemical modifications of the structure of lignin.     

Reconstruction of Late Paleozoic heat flows and burial histories at the Rhenohercynian-Subvariscan boundary, Germany

The thermal and burial history of the Herzkamp syncline, located in the transition zone between the Variscan Rhenish Massif and the Ruhr foreland basin (western Germany), was reconstructed using PDI/PC-1D-basin modelling software (IES). The models were calibrated with new vitrinite reflectance data measured on Palaeozoic outcrop samples. High sample density and quality of the calibration data allowed a 3D reconstruction of the heat flow as well as of burial and erosion history. Vitrinite reflectance values range from 0.8 to 4.9%R_r and generally increase with increasing stratigraphic age. The coalification pattern confirms pre-tectonic maturation, especially in the western part of the study area. A "low-coalification zone" showing stagnating/decreasing coalification with increasing stratigraphic age exists, however, northeast of the Ennepe thrust, indicating synorogenic coalification. This anomaly is explained by early thrusting in the northern Rhenish Massif resulting in restricted burial/early uplift and thus lower thermal maturity. One result of numerical modelling is that palaeo-heat flows during maximum burial (Westphalian or post-Westphalian) decreased southwards from approximately 65 to less than 50 mW/m². Maximum burial depths for the base and top of the Namurian also decrease southwards from 7000 to 3600 m and 4600 to 1800 m, respectively, resulting in southwards-decreasing coalification of the respective stratigraphic horizon. Eroded overburden increases southwards (3100-5700 m), with the exception of the low-coalification zone, which is characterised by lower amounts of eroded overburden (1300-2900 m) and an earlier onset of erosion, i.e. in the Westphalian B rather than Westphalian D or post-Westphalian.     

Optical properties of pseudovitrinite; implications for its origin

A set of Pennsylvanian coals from the North American coal basins, ranging in vitrinite reflectance from 0.65% to 1.75%, was examined, with special emphasis on the optical properties of pseudovitrinite. The results suggest that pseudovitrinite originates from the same material as telocollinite. Slits in the pseudovitrinite seem to have originated in situ due to low-temperature oxidation of woody material; their opening might have been facilitated by devolatilization during coalification. The dominant orientation of the slits is perpendicular to bedding. The intensity and orientation of the slits in pseudovitrinite could be important factors in predicting coalbed gas extraction from coal.     

湖南省煤的热谱特征及其研究意义

煤的热谱(DTA、DSC、TG)特征与煤的其他物化特征参数一样,是煤大分子结构特征的反映,可作为研究煤化作用的参考和无烟煤分类的辅助标志。本文介绍了湖南省不同变质程度煤的热谱特征和试验所发现的热谱曲线、峰温与煤及瓦斯突出强度、无烟煤三小类的关系,并试验证明利用热分析曲线进行煤层对比的可能性。     

有机地球化学方法在煤层对比中的应用

利用有机地化方法解决宁夏灵武煤田延安组煤层对比的研究表明:区内2、6、7、14、17煤的某些有机地化参数,如氯仿沥青“A”含量、氢指数、产烃潜量、正烷烃碳数分布和烷基菲构成均存在明显差异,这取决于煤层沉积环境、煤化作用程度和有机母质类型。有可能依据这些参数,使煤层本身成为对比的标志层。