Paleomires of Eocene lignites of Bhavnagar,Saurashtra basin (Gujarat), western India: Petrographic implications

The Tertiary basins of Gujarat have always been a potential target for their hydrocarbon resources. The lignite resources of the region have also been an important field of research. The present paper presents the results of the petrological study carried out on the lignites of the Saurashtra basin. For this purpose samples were collected from lower and upper lignite seams from the Surkha lignite mine of Bhavnagar, Saurashtra. These samples were subjected to detailed petrographic analysis (both maceral and microlithotype). The study reveals that these lignites are dominantly composed of huminite group macerals while liptinite and inertinite group macerals occur in subordinate amounts. These lignites have attained a thermal maturity up to 0.28-0.30 percent vitrinite reflectance (VRr) which classifies them as ‘low rank C’ coals. Moreover, Bhavnagar lower lignite seam shows relatively less gelification as compared to the upper seam which suffered relatively more biochemical degradation. These lignites are characterized by high gelification index (GI) and low tissue preservation index (TPI).With the help of petrography based facies models an attempt has been made to reconstruct the environment of the paleomire of these lignites.     

Petrographic and depositional characteristics of Tadkeshwar lignite deposits (Cambay Basin), Gujarat

Tadkeshwar lignite deposits are one of the important Lower Tertiary lignite deposits of Cambay Basin, Gujarat. These lignites are rich in huminite macerals followed by liptinite and inertinite with moderate to high proportions of associated mineral matter. Under fluorescence mode these are found to be rich in liptinite macerals, in particular the liptodetrinite and resinite. The type of huminite suggests that the lignite is formed from mixed vegetal source, i.e. woody forest vegetation and herbs, shrubs. The composition of macerals indicates the deposition of lignite in sub-aqueous condition in wet-reducing environment with intermittent exposure and subsidence of the peat surface. The rank of the Main and the Leader seams, determined through reflectance measurement, indicate that the lignite is less mature. The considerable amount of perhydrous huminite may have contributed to the lower reflectance values in some of the samples. Low rank and appreciable amount of mineral matter make the lignite suitable for its utilization in thermal power plants, however when upgraded or mixed with better quality coals it can be used for other industries.     

Petrography of low rank coals with reference to liquefaction potential

Ten sub-bituminous coals were analyzed petrographically and chemically as part of a program by the Alberta Research Council to investigate the compositional properties of Alberta coals and relationship to liquefaction potential. In addition, four lignites, two from Saskatchewan and one each from Texas and North Dakota, were studied for comparative purposes. Liquefaction experiments were carried out on three of the Alberta coals and on density fractions of the two U.S. lignites. Petrographically the ten sub-bituminous coals could be divided into two populations; one with high huminite and liptinite contents (>90%) and one with substantially lower contents (70–75%). The two U.S. lignites showed huminite plus liptinite contents of less than 70% while the Saskatchewan coals were somewhat higher. Reflectance measurements on the sub-bituminous coals showed a range of 0.33 to 0.51 with a rough correlation to the ASTM rank designations of these coals. Reflectivities determined on the lignites were generally lower. Float-sink fractionation of the two U.S. lignites and two sub-bituminous coals showed enrichment of huminite and liptinite in the lighter fractions and inertinite and mineral matter in the heavier splits. Examination of the relationship between liquefaction yields and petrographic composition showed a rough positive correlation with huminite-liptinite content. Examination of liquefaction residues suggested total conversion of the liptinite, extensive conversion of huminite and possible partial conversion and reactivity of the semifusinite maceral of the inertinite group.     

Petrographic and Geochemical Study of Gurha Lignites,Bikaner Basin,Rajasthan, India: Implications for Thermal Maturity,Hydrocarbon Generation Potential and Paleodepositional Environment

In the present study an attempt has been made to characterize the Gurha lignites employing petrographic and geochemical techniques on a large number of lignite samples. The data generated has been discussed to understand the hydrocarbon generation potential as well as the evolution of the paleomires of these lignites. The present investigation indicates that these lignites are mainly dominated by the huminite followed by inertinite and liptinites occurs in meager concentration. The huminite reflectance values rank the Gurha lignite as a low-rank B lignite.Petrographic result indicates these lignites are thermally immature in nature and comprised of Type-III kerogen and may generate only gas on maturation which is further supported by the rock-eval pyrolysis. The plots of rock eval data also indicates the same. The GI and TPI as well as GWI and VI values and the petrography-based facies critical models indicate that these lignites originated mostly under wet forest swamp condition. The microscopic constituents have also shown that these lignites are from herbaceous plants in wet forest swamp environment and ombrotrophic hydrological condition. The presences of framboidal pyrite in the study area infer the marine influence which also supported by the presence of high sulphur content.     

Distribution and geochemistry of selected trace elements in the lignites of Cambay basin,Gujarat, western India

In the present investigation all the working lignite seams of Cambay basin of Gujarat have been studied to see the distribution and geochemistry of selected major/minor elements like Fe, Ca, Na, K, Mg, and Mn and trace elements like Cu, Co, Cr, Cd, Ni, Pb and Zn. The vertical variation of these elements along the seam profiles has been studied to see the pattern of distribution of these elements and also to know the horizons of their enrichment and the probable cause. Further, these elements have been correlated among themselves and also with organic and inorganic matter of lignite. The correlation study indicates that in Tadkeshwar upper seam Fe has its affinity with huminite while Mg and Na have their affinity with liptinite and in Tadkeshwar lower seam Na has an affinity with liptinite. In Vastan upper seam Mn and Cu are associated with inertinite and Na with huminite while in Vastan lower seam Cu relates to huminite and Cd to liptinite and huminite. In Rajpardi seam Ca and Co are associated with huminite. The study provides information on the mode of occurrence of elements of less studied lignites of western India.     

准噶尔盆地侏罗纪煤成油研究

本文以有机岩石学和有机地球化学研究为基础，结合模拟实验，对中国西北地区准噶尔盆地侏罗纪煤成油问题进行了详细讨论，结果表明，准噶尔盆地侏罗纪煤含有丰富的类脂成分，壳质组特别是角质体含量高可能导致了本区高蜡石油的生成，壳质组和基质镜质体的含量决定了煤的氢指数和热解烃产值，它们共同构成了盆地内煤成油的母质。模拟排油实验证明了煤孔隙的吸附能力是有限的，在一定的压力条件下，煤中液态烃达到一定数量后就可以较好地排出。为了便于生产勘探，文中还讨论了煤系地层的沉积有机相，依据沉积相，有机地球化学和有机岩石学特征将煤系划分成四种沉积有机相:分别是高位沼泽有机相，森林沼泽有机相，流水沼泽有机相和开阔水体有机相，其中，流水沼泽有机相生成液态烃的潜力最大，以含有大量的角质体为特征；森林沼泽有机相的生烃潜力次之，以基质镜质体为主要成分；高位沼泽有机相生烃潜力最差，以惰性组和镜质组为主要的有机组分；而开阔水体有机相不是煤成烃研究的理想场所     

Limitation of petrographic indices in depositional environmental interpretation of coal deposits

Organic petrology based petrographic indices (Tissue Preservation Index and Gelification Index) is a widely utilized tool in the study of depositional palaeoenvironment of coal. Evaluation of these petrographic indices suggests that, at present, utilize only vitrinite/huminite and inertinite macerals to interpret depositional environment of coal. Liptinite group macerals have important depositional environment implications, but liptinite macerals have not been taken into account in earlier petrographic indices (TPI and GI) formulations. This article examines the limitation of TPI and GI, and proposes improved TPI and GI indices, including the liptinite and inertinite macerals having depositional environment significance.     

Facies analysis of coal seams from the Cracow Sandstone Series of the Upper Silesia Coal Basin, Poland

The main purpose of this study was to recognise the variability of petrographical structure of two coal seams occurring in the Cracow Sandstone Series (Upper Carboniferous/Pennsylvanian, Upper Westphalian), being exploited in the Siersza mine. This mine is located in the eastern part of the Upper Silesia Coal Basin (USCB). The chemical analyses and petrographical features allow the inclusion of these coals to the group of hard brown coals belonging to subbituminous class.Two coal seams (207 and 209/210) of a considerable thickness (7.44 and 6.54 m, respectively), representative of the Cracow Sandstone Series (CSS), were chosen for the petrographic studies. Dominant macroscopic constituents of both seams are banded bright coal and banded coal.The coal seams were sampled in 284 intervals using a channel profile sampling strategy. The microscopical examinations revealed the majority of macerals from the vitrinite group (55%), followed by inertinite (21%), liptinite (11%), and mineral matter (13%). Low values of the vitrinite reflectance (R_o=0.46%) confirm very low coalification of the coal in both seams. Facies analysis indicates that in the course of a mire development, in which the studied coal seams originated, wet forest swamp conditions dominated characterized by a high degree of flooding and gelification as well as by a prevalence of arborescent plants. In such conditions, lithotypes with a large content of bright coal were mainly formed. Petrographic and facies data point to the rheotrophic character of these peatbogs. Frequent changes of the conditions in the peatbog, as it is shown by the variability of petrographic structure of the studied profiles, as well as by lateral changes of the phytogenic sedimentary environment within the coal seams, indicate a strong influence of a river channel on the adjoining peatbogs. An accretion of clastic sediments within the wide river channel belts was balanced mainly by the peatbog growth on the areas outside channels. Frequency and rate of avulsion of the river channels influenced the size, continuity and variability of the peatbogs.     

新疆伊犁盆地侏罗纪煤岩特征及煤相

应用煤岩学方法，探讨了新疆伊犁盆地侏罗纪煤的煤岩特征及煤相划分，将煤相划分为９种类型即干燥森林沼泽相，潮湿森林沼泽相，草木混生型沼泽相或芦苇沼炭沼泽相。通过煤相分析，为伊犁盆地成煤环境的研究提供了佐证。     

Facies and genesis of Carboniferous coal seams of Northwest Germany

In order to get detailed information about the facies and genesis of Upper Carboniferous coal seams of Northwest Germany, maceral analyses of complete seam profiles (Westphalian B-D, mainly Westphalian C) were carried out. Four main facies and twelve subfacies could be distinguished. The main facies are:

1. (1) The sapropelic-coal facies, consisting of fine-grained inertinite and liptinite, which forms from organic sediments deposited at the bottom of moor lakes.

2. (2) The densosporinite facies which is high in inertinite and liptinite and low in vitrinite. Syngenetic pyrites, clastic layers, thick vitrains and fusains do not occur. This facies originates from peats of ‘open mires’ with higher groundwater table and herbaceous vegetation. The ‘open mire’ was situated in the centre of extensive swamps. Consequently, clastic sedimentation did not affect this swamp type and nutrient supply and pH values were low.

3. (3) The vitrinite-fusinite facies, which is high in vitrinite. This is the result of abundant vitrains. Under the microscope, fusains were mostly identified as fusinite. The vitrinite-fusinite facies originates from a forest mire. More or less abundant seam splits and clastic layers show that rivers flowed in the neighbourhood of this area.

4. (4) The shaly-coal facies, which represents the most marginal part of the former swamp frequently affected by clastic sedimentation.

Within the Carboniferous of the Ruhr Region it seems unlikely that the thin coal seams of the Namurian C and Westphalian A1 contain a densosporinite facies. The swamps were situated in the lower delta plain where they were often affected by marine influences. Consequently, coals are high in minerals and sulfur and they are thin and discontinous. The best conditions for the formation of extensive swamps, with open mires (densosporinite facies) in their central parts, prevailed during Westphalian A2 and B1 times. Low contents of sulfur and minerals and high content of inertinite are typical for these coals. Sedimentation mainly took place in the transitional zone from the lower to the upper delta plain. During the Westphalian B2 and C fluvial sedimentation dominated. Within the coal seams minerals, sulfur and pseudovitrinite increase while inertinite decreases. This is the consequence of coal of the densosporinite facies occurring with increased rarity. The coal seams of the Westphalian C2 contain no densosporinite facies because peat formation was restricted by increasing fluvial sedimentation and by a better drainage. As a consequence, extensive swamps with ‘open mires’ in the centre were no longer formed after the formation of the “Odin” seams. Above the “Odin” seams coal of the vitrinite-fusinite facies contains thick-walled torisporinites. Variations and lowering of the groundwater table caused mild oxidative influences during peat formation. This is documented by an increase in pseudovitrinite, the occurrence of torisporinites and the absence of spheroidal sideritic concretions. Sulfur content increases in the absence of the low-ash and low-sulfur coal of the densosporinite facies.In Upper Carboniferous coal seams of the Ibbenbüren Region the inertinite and telocollinite contents are higher than in those of the Ruhr Region. Therefore, variations of the groundwater table have been more pronounced and resulting oxidative influences must have been more severe. Seldom occurring marine and brackish horizons and a higher fusinite (fusain) content indicate a slight elevation of this area. From Early Westphalian D times onward, peat formation was no longer possible because of the better drainage. This resulted in severe oxidative conditions which excluded peat formation.     

The geology, petrology and geochemistry of coal seams from the St. Rose and Chimney Corner coalfields, Cape Breton, Nova Scotia, Canada

Seams from the St. Rose and Chimmey Corner coalfields, Nova Scotia, Canada, were sampled and examined for petrographic and geochemical composition. Rank determinations indicate a rank of high volatile C-B bituminous. Seams show regular alternations of dull and bright microbanded lithotypes, with dull lithotypes predominant in the central portion of the main seam (No. 5 seam). Brighter lithotypes are dominated by vitrinite (>80%), with minor inertinite (avg. 12%) and minor liptinite. Duller lithotypes contain greater amounts of inertinite (up to 40%) and liptinite (primarily sporinite). Mineral matter consists of epigenetic pyrite, with lesser amounts of clay and quartz. Cabonates are common in the Chimney Corner seams. Elemental composition of the seams is similar to other Canadian coals and fall within world coal ranges, with the exception of high concentrations of Cl, Zn, Ni, Mo, Pb, Cu and As.Depositional environment of the seams as indicated by maceral composition, lithotypes and geology suggest a predominance of wet forest to reed moor conditions, in a fluvial-lacustrine setting. Periodic episodes of flooding and drying are indicated by lithotype, maceral and mineral variations.     

Petrology, depositional environment and utilization potential of Late Paleocene coals from the Obed-Marsh deposit, West-Central Alberta, Canada

The Obed-Marsh coal deposit is of Late Paleocene age, and contains over 200 million tons of subbituminous-B to high-volatile bituminous-C coal.Petrographic analysis of three sections from seams 1 and 2 reveals high amounts of huminite and relatively low amounts of liptinite and inertinite, with the exception of some intervals in both seems. The persistent high ratio of huminite to liptinite and inertinite indicates a relatively reducing environment, a feature also expressed by the relatively low inertinite content. Examination of the in-seam profiles also indicates undisturbed peat accumulation over long periods of time.The Obed coals, similar in rank and composition to the Hat Creek coals of British Columbia, formed in a freshwater environment and can be used as feedstock for combustion/gasification. Furthermore, the intervals rich in liptinite and petroleum-like substances may be utilized for liquefaction (hydrogenation).     

Petrographic properties of major coal seams in Turkey and their formation

Most types of coal in Turkey are generally low in rank: lignite, and subbituminous. Most of the coal was formed during the Miocene, Eocene, and Pliocene ages. There are only a few thin Jurassic-age coal occurrences in Turkey. Pennsylvanian age bituminous coal is found on the Black Sea coast. General implications of the petrographic properties of Turkey's coal seams and coal deposits have not yet been taken into consideration comparatively or as a whole.For this study, about 190 channel samples were collected from different locales. The composite profile samples of the seams were taken into considerations. The content and depositional properties as well as some chemical and physical properties of the main coal seams are compared. All coal samples tend to have similar coal petrographic properties and were deposited in intermontane lacustrine basins. Later, they were affected by faulting and post-depositional volcanic activity. As a result, there are variations in the properties and rank of the coal samples. The most abundant coal maceral group is huminite and the most abundant maceral is gelinite. The liptinite and inertinite contents of the coal are low and the maceral contents of the coals show great similarity. The depositional environments of the all coals are lacustrine dominated.     

滇东田坝黔西土城晚二叠世煤系上段煤岩特征及煤相分析

本文通过滇东田坝黔西土城晚二叠世煤系上段沉积相、煤层特征和煤岩煤质的综合研究,系统分析了区内煤层形成时的沉积环境.按成煤的古地理位置分为上三角洲煤相和上、下三角洲过渡带-下三角洲煤相两大类型.根据成煤的原始质料、结构构造、煤岩特征和成煤前后环境,详细划分出八种泥炭沼泽相.着重探讨3号煤层形成时的泥炭沼泽相特征及其变化.     

Effect of maceral subtypes and mineral matrix on measured reflectance of subbituminous coals and dispersed organic matter

The variability in reflectance of huminite (texto-ulminite, eu-ulminite A and B, different types of corpohuminite) and liptinite groups of macerals in subbituminous coals was examined using reflected light microscopy. All macerals were selected from coal and interbedded carbonaceous shale and carbonate sediment samples from the 515-m-thick coal deposit No. 2 located in the Hat Creek valley of south-central British Columbia. The measurements obtained reveal that, in addition to burial depth, reflectance distribution depends on maceral subtypes and associated mineral matrix.Huminite in the coals and sediments (kerogen) consists mainly of humotelinite, with eu-ulminite B being the dominant maceral sub-type. Reflectance values determined on huminite in coals and Type IIIb kerogen increase from eu-ulminite A and phlobaphinite type 1 through eu-ulminite B and phlobaphinite type 2 to gelinite. The reflectance of all five huminite maceral subtypes studied increases with depth. However, the increase of phlobaphinite type 1 and gelinite reflectance with depth is irregular.A comparison of the reflectance values obtained for the same maceral subtype (eu-ulminite B) from the interbedded coal, shale and carbonate samples records consistent differences, implying some dependence of the reflectance (and perhaps rate of organic maturation) on the mineral matrix. Generally, the highest eu-ulminite B reflectance was recorded from carbonate rocks and the lowest from shale, whereas coal matrix produced intermediate values.At present, it is not known whether differences in reflectance of eu-ulminite found in the above lithologies are due to differential retention, efficiency of reaction products removal, thermal conductivity of the lithologies, or existence of a calcium carbonate catalyst.     

Petrographic characterization of Khadsaliya lignites,Bhavnagar district,Gujarat

The petrological studies on Khadsaliya lignites from Bhavnagar district have been carried out for their microconstituent’s characterization. Quantitative estimation of macerals reveal, due to high amount of macerals of huminite group, that this lignite deposits has formed from forest dominated vegetation in a fast subsiding basin, experiencing almost uniform environmental conditions, with slight intermittent fluctuations. The rank based on R_{o max} % values indicates that lignites are less mature and have not reached the sub-bituminous stage of coalification as those of the lignites from Panandhro (Gujarat) and Neyveli (Tamil Nadu) fields. High pyrite content in the Khadsaliya lignite makes it not much suitable for combustion purpose.     

Liptinite in coal and oil source rocks in northern Thailand

Palynological study of northern Thailand coal and oil deposits indicates a similar palynological association to that of the Borneo region. Coal petrographic studies of these deposits show variations in the liptinite macerals, especially alginite types. The oldest of these coal and oil deposits, which are of Late Oligocene to Early Miocene age, are dominated by Botryococcus sp. or Botryococcus-related algae. Thick-walled lamaginites and spores and pollen of temperate affinity, are found in some areas. By contrast, thin-walled lamaginite is dominant in late Middle Miocene time. Resinite, suberinite, and cutinite are dominant in forest swamp coal deposits whereas alginite, cutinite and lycopodium spores are dominant in lacustrine environments. Exsudatinite is common even at early levels of maturation. These liptinite macerals can be major sources of oil and gas.     

Observations on Indian Permian Gondwana Coals Under Fluorescence Microscopy: An Overview

Macerals like sporinite, cutinite, suberinite and resinite of the liptinite group have been insufficiently recorded in Indian Permian Gondwana coals, until the fluorescence microscopy came into existence. With the introduction of this technique, macerals like bituminite, fluorinite and exsudatinite were convincingly recognized and alginite and liptodetrinite, normally mistaken for mineral matter under normal reflected light in routine coal petrographic analysis, were identified with certainty. Thus, fluorescence microscopy has added certain new macerals to the tally of the liptinite group and has increased their overall proportion in Indian Gondwana coals.In addition to the liptinite group, collodetrinite (=desmocollinite) and a certain fraction of collotelinite (=telocollinite) macerals of the vitrinite group were found to be fluorescing with dull reddish-brown to dark brown colours. Certain semifusinite and inertodetrinite macerals of inertinite group were also found to fluoresce with almost identical intensity and colour as that of the associated perhydrous (fluorescing) vitrinite. Contributions of degraded resinite, algal matter and bitumen in the formation of perhydrous vitrinite have been established. The fluorescence behaviour of inertinite appears to be related with its genesis from partial oxidation of resin/bitumen-impregnated cell walls.     

Peat-forming environments of Westphalian A coal seams from the Lower Silesian Coal Basin of SW Poland based on petrographic and palynologic data

The petrographic and palynologic compositions of coal seams of the acler formation (Upper Carboniferous, Westphalian A) from northwestern and southeastern part of the Lower Silesian Coal Basin (LSCB) were examined. Coals studied are highly volatile bituminous coal, where R_o ranges from 0.91% to 1.09%. Seam 430 from the northwestern part of the basin contains high vitrinite percentage with rather low inertinite and liptinite contents, while percentage of mineral matter is variable. This petrographic composition is associated either with a predominance of Lycospora in miospore assemblage, or with a miospore assemblage of mixed character. The abundance of Lycospora reflects vegetation composed of the arborescent lycopsids while the mixed miospore assemblage is connected with diverse palaeoplant communities, namely, arborescent lycopsids, calamites and ferns. Seams 409 and 412/413 from the southeastern part of the LSCB are rich in inertinite and liptinite, while the vitrinite content is moderate. Their characteristic feature is the occurrence of a diagnostic crassisporinite (densosporinite). Amount of the mineral components in these coals is very low. Densosporites and related crassicingulate genera are main components of these miospore assemblages and were produced by herbaceous and/or sub-arborescent lycopsids. These petrographic and palynologic features were the basis for distinguishing three maceral–miospore associations: an arborescent lycopsid and mixed associations, occurring in the seam 430 and a herbaceous and/or sub-arborescent lycopsid association which was recorded in seams 409 and 412/413. The first two assemblages are interpreted as having been deposited in a planar rheotrophic mire, whereas the herbaceous and/or sub-arborescent lycopsid association is thought to have developed in an ombrotrophic, domed mire.     

Liptinite as an indicator of environmental changes during formation of coal seam No. 207 (Upper Silesia, Poland)

The coal seam No. 207 was a subject of palynological and petrographic studies. According to the results of the vitrinite random reflectance measurements supplemented by moisture and calorific value determinations, the rank of this coal is matching the boundary between sub-bituminous and bituminous coals. The aim was to reconstruct the environmental conditions during the biochemical stage of seam formation, as well as the facies development throughout the seam profile. The maceral (incident and fluorescence mode) and microlithotype compositions (incident light) supplemented by palynological analyses, show that there were two main facies developments. In the authors opinion, they correspond with a phase of ombrogenous, raised bog marked by the presence of crassidurite with Densosporites variabilis and a wet-forest swamp phase represented by vitrite and clarite with more diverse spore assemblage including densospores. Other minor but distinctive sediments, a cannel layer and a reeds facies, both occurring in the lower part of the seam. Above the tonstein horizon, a dry forest type of sedimentation is recognized.