B.K. Misra

Susceptibility to spontaneous combustion of Indian coals and lignites: an organic petrographic autopsy

Abstract A critical analysis of various genetic and physical factors associated with certain Early and Late Permian and Oligocene coal seams and early Eocene lignite seams of India revealed that the high secondary porosity and small particle size, irrespective of petrographic and rank properties in sub-humid climate, favour spontaneous combustion. Large particle size, high rates of gas emission and highly wet or dry seams, in combination with each other tend to inhibit spontaneous heating in sub-humid, per-humid and semi-arid conditions. The susceptibility to auto-ignition of a coal or lignite seam is not uniform throughout its lateral extent and a high inherent porosity at any given rank stage and a high content of susceptible or oxidizable constituents are not sufficient to cause auto-ignition. However, coal seams having high contents of exceedingly porous inertinite macerals become prone to spontaneous combustion in sub-humid climate even without secondary porosity. A scheme for indexing spontaneous combustion susceptibility, based on the present study, has been proposed which is particularly suited to the Indian context.

Optical properties of some Tertiary coals from northeastern India: their depositional environment and hydrocarbon potential

Abstract In northeastern India, the coalfields of Arunachal Pradesh, Assam and Nagaland are disposed along a linear belt of overthrusts, known as the “belt of Schuppen”, where Tertiary strata have been folded and dispersed into a number of thrust slices. The coal-bearing sediments in this belt are associated with the Baragolai and Tikak Parbat formations of the Barail Group (Oligocene). In Meghalaya, the Tertiary sediments were deposited on a stable shelf along the periphery of the Shillong Plateau. They are almost undisturbed and sub-horizontal in attitude. The coal seams are associated with the Sylhet/Tura formations (Palaeocene) of the Jaintia Group. The chemical properties of these coals show characteristics of both low (on volatile matter content) and high (on moisture and calorific value) ranks. The coals have a low softening temperature and a high swelling index, volatile matter, hydrogen and sulphur contents besides having the highest tar yield among Indian coals. The syncrude produced from these coals shows similarities with the identical fraction of crude oil from Nahorkatiya Oilfield, Assam. The coals from the “belt of Schuppen” and Meghalaya are non banded and bright in nature. Microscopically, their humic components are strongly decomposed with a common to frequent association of framboidal pyrite and calcite concretions. The coals are vitrinite-rich (52.0–80.0%) with moderate amounts of liptinite macerals (5.8–16.2%). The inertinite content is low (4.6–11.0%) to occasionally high (30.0%). Fluorescing vitrinite and liptinite macerals constitute 46.5 to 83.5% by volume (m.m.f.). Perhydrous vitrinite, liptodetrinite and resinite are the most common fluorescing macerals. The rank of the coal samples ( R 0 max: 0.57–0.74%) ranges between High Volatile Bituminous C and B stages. The Assam coals are higher in rank than those of Nagaland and Meghalaya. In northeastern India during the Palaeocene and Oligocene Epochs, peat-swamps formed in situ from tropical mangrove-rich angiospermous forest vegetation. The Palaeocene coals in Meghalaya were formed in estuaries or lagoons. However, the coal forming phase ceased shortly due to prolonged marine transgression. The Oligocene coals in the “belt of Schuppen” were formed during a regressive phase in back-water lagoons or brackish water swamps on a prograding delta complex. The hydrocarbon potential (mg CH/g C org. ) of the coal samples from northeastern India has been theoretically deduced on the basis of their kerogen types following Mukhopadhyay et al. (1985). The presumed hydrogen index varies from 250 to 430 and 300 to 470 mg CH/g C org. respectively for coals in the “belt of Schuppen” and Meghalaya. Evidence indicates that in Arunachal Pradesh, Assam and Nagaland oil has been generated from kerogen types II B and II A in the Oligocene mudstone-siltstone-shale association of the Coal-Measures of Barail Group. In Meghalaya, no oil is known so far. Nevertheless, the predominance of kerogen types II A and II B in coals indicates a good oil potential in the Palaeocene sediments of the Jaintia Group.

The Neyveli lignite deposits (Cauvery basin), India : organic composition, age and depositional pattern

Abstract The palynological, particulate organic material (palynodebris) and biopetrological aspects of the main lignite seam encountered in NLE-27, NLE-35 and NLE-36 borehole sections in mine III of the Neyveli lignite field of the Cauvery basin were investigated. The palynoflora is rich in angiospermic pollen (79.6%) distributed in 33 genera ( and 86 species). Pteridophytic (spores) representation is only 20.4% with 5 genera (and 9 species). Quantitatively, palynofossil assemblage of the seam from mine III resembles fairly well with those from the mines I and II. Based on geological, geophysical and palynological data the lignite seam has been assigned a Miocene age. The lignite seam has a very high proportion of structured terrestrial organic matter (OM) with a subordinate amount of biodegraded terrestrial, fungal and amorphous materials, in addition to resin. Petrologically, the seam is rich in the huminite group of macerals, usually dominated by attrinite, densinite (humodetrinite) macerals. Botryococcus is common, as are framboidal pyrite and concretions. The seam in mine III is lower in rank (Ro max 0.39%) than its counterpart in mine I (Ro max. 0.47%). From a critical assessment of the palynological, palynodebris and biopetrological data, together with published geological information, it is assumed that the main lignite seam was formed from in situ mangrove-mixed moist tropical forests vegetation, probably in a lagoon on a prograding delta with freshwater inlets from the western and restricted seawater channels from the east.

Trilatiporate pollen from Indian Palaeogene and Neogene sequences: evolution, migration and continental drift

Abstract The diagnosis of the genus Dorreenipites Biswas, 1962, incorporating heteropolar pollen with sub-equatorial pores, is emended to include morphological details observed on pollen recovered from the Miocene lignite, Neyveli, Tamil Nadu, India. A new genus Retitrilatiporites is proposed to assimilate trilatiporate pollen from Palaeocene-Eocene sediments of Kutch, which are distinct in having feeble pore-bearing projections, ± equatorial pores, and a smaller size. A speciation scheme for both trilatiporate genera is proposed based on significant morphological features, namely well-developed vs. feeble pore-bearing projections, and exine structure varying from psilate to reticulate on one or both poles. Evolutionary trends of these taxa in Africa and India and their stratigraphic significance are discussed, from the perspective of their migration and extinction, which was controlled by the northward drift of the Indian plate. Four new species and five new combinations are proposed, and the botanical relationship of this pollen type is discussed.

The Lower Permian coal seams from Singrauli coalfield (M.P.), India: petrochemical nature, rank, age and sedimentation

Abstract Biopetrographic and chemical investigations carried out on the Lower Permian (Barakar Formation) coal seams encountered in two bore-holes (NCSM-3 and CMSA-111) from the Singrauli coalfield, Son Valley, reveal that they are, in general, rich in inertinite and mineral matter towards the eastern part. Whereas, towards the western part they are rich in vitrinite with subordinate amounts of inertinite and mineral matter. The Turra and Purewa Top seams, in the eastern part, consist chiefly of mixed and fusic coal types and the Turra and Purewa Merged seams, in the western part of the basin, are characterized dominantly by vitric and mixed coal types. The basin of deposition was shallower in its major part but deepened towards west. Consequently frequent oxic fluctuations are most common in the coal seams of the eastern part. The rank of these coal seams ranges between subbituminous-A to high-volatile bituminous-C stages. They show normal increase in rank with depth. The coal seams in the western part of the area are higher in rank than their counterparts in the east. The Purewa Bottom seam (NCSM-3) is petro-palynologically correlatable with the Turra seam (CMSA-111) of the western part. It has been presumed that Glossopteridophyta (a complex group of gymnospermous plants), arthrophytes and ferns were the vegetal source for the formation of Barakar coal seams. These plants during the Early Permian grew as thick forests along river valleys and as upland and subaquatic vegetation, and experienced a warm, humid and windy temperate climate. The coal seams were presumably deposited in backwater and lacustrine swamps in fluvial environment from hypoauchthonous source material. An attempt has been made to explain reasons for the high incidence of mineral matter and its apparent relationship with inertinite content in the coal seams while also discussing the depositional history.

Spectral fluorescence analysis of some liptinite macerals from Panandhro lignite (Kutch), Gujarat, India

Abstract Spectrofluorimetric analyses of sporinite, alginite and resinite macerals of Eocene lignite from the Panandhro Lignite field indicate that they are distinguishable on the basis of their λ max and red/green quotients. Sporinite fluorescing with bright yellow colour has an average λ max at 570 nm with red/green quotient (Q) = 0.92. Alginite (Botrycoccus) with a bright yellow fluorescence colour has a peak (average) at 540 nm with Q = 0.71. Resinite in the Panandhro lignite has been categorized into five types. Resinite type-1 (yellowish green to greenish yellow) is characterized by average λ max at 510 nm with a Q value of 0.29. In resinite type-2 (bright yellow) the average λ max occurs at 520 nm with Q = 0.49. Resinite type-3 (yellowish orange to orange) shows a λ max (average) at 520 nm with a Q value of 0.69. Resinite type-4 has been subdivided into sub-types-a and b based on its mode of occurrence (primary and in situ remobilized). Sub-type-4a (pale orange) has a λ max (average) at 590 nm and Q = 0.99 whereas sub-type-4b fluoresces with faint brownish orange to pale brown colours and shows an average λ max at 610 nm and Q = 1.43. The average λ max at 610 nm and Q = 2.30 with pale yellowish grey, orangish brown and brown fluorescence colours characterize resinite type-5. The wavelength of maximum fluorescence intensities and red/green quotients of the sporinite and alginite macerals show a very good correspondence with the rank (R0 max) of the Panandhro lignites. The spectral parameters of the maceral resinite, on the other hand, do not show such a relationship with rank. Resinite types-1 to 3 are primary in origin whereas types-4 and 5 occur both as primary and in situ remobilized resinites. None of the resinite types have been observed as crack or fissure fillings. The origin of the resinite types is probably related to lignite-forming plant communities, chiefly angiospermous vegetation, as well as pre- and post-depositional conditions.

Revision of some Tertiary pollen genera and species

Abstract Three fossil pollen genera Dakshinipollenites Navale and Misra (1979), Grevilloideaepites Biswas (1962) and Jacobipollenites Ramanujam (1966) reported from Tertiary sediments of India, are revised. Vellaripollis gen. nov., four new species: Vellaripollis foveolatus, Jacobipollenties magniporus, J. distinctus, J. crassimurus and to new combinations: Grevilloideaepites inferius and G. pachyexinus are proposed.

A new spinose monosulcate genus Spinomonosulcites and an emendation of spinose porate Acanthotricolpites

Abstract Spinose monosulcate and spinose porate pollen of form genera Neocouperipollis and Acanthotricolpites recorded from Tertiary sediments of India, are critically evaluated. The type specimen Neocouperipollis kutchensis has pores rather than sulcus as previously considered. Moreover, both monosulcate and porate species have been described under the genus Neocouperipollis . The spine morphology and the nature of spine attachment with the exine in spinose porate pollen are different from those of the spinose monosulcate pollen. The type species Neocouperipollis kutchensis is transferred here to Acanthotricolpites . A new genus Spinomonosulcites is proposed here to accomodate monosulcate species of Neocouperipollis. Acanthotricolpites , found to be porate instead of colpate, is emended here.

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

Abstract 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.

New colporate pollen taxa from Neyveli lignite, South India

Four new pollen genera: Bacuspinulopollenites, Cuddaloripollis, Scrobiculatricolporites, Tamilipollenites and seven new species from the subsurface lignite samples of the Mine III area of the Neyveli Lignite Field are described. Tricolporopilites (Kar and Saxena) Kar 1985 is emended and three new species T. uniformis, T. differentialis and T. tectatus are assigned to it. These colporate angiospermous pollen taxa provide additional information on the palynofloral composition of the main lignite seam encountered in three boreholes.