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

International Journal of Coal Geology, 14 (1990) 277-293 Elsevier Science Publishers B.V., Amsterdam- Printed in The Netherlands

277

Resino-inertinites of Indian Permian c o a l s - their origin, genesis and classification

B.K. MISRA, B.D. SINGH al~d G.K.B. NAVALE

Department of Biodiagenesis, Birbal 3ahni Institute of Palaeobotany, 53, University Road, Lucknow-226 007, India

(Received April 13, 1988; revised and accepted May 23, 1989)

ABSTRACT

Misra, B.K., Singh, B.D. and Navale, G.K.B., 1990. Resino-inertinites of Indian Permian coals - their origin~ genesis and classification. Int. J. Coal. Geol., 14: 277-293.

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 variables viz., paleoenvironmental, paleodepositional, tectonic set up etc. on resino-inertin~ ites 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.

INTRODUCTION

Discrete inertinitic bodies showing widely variable shape without any apparent structure or with different patterns of cracks, fissures cr vesicles have been recorded in Paleozoic (Carboniferous to Permian) subbituminous to bituminous coals from America, Canada, some of the European countries, Aus-

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tralia, Africa and India. They have been termed as "sclerotinites" (ICCP, 1963) and latter as "secretion sclerotinites" (Stach et al., 1982 ). Various other workers named them differently of which the most commonly used term is "fusinized resins" (Kosanke and Harrison, 1957). Recently, Lyons et al. (1982, p.342) proposed a term "resino-inertinites" for such bodies of non-fungal origin. The same terminology has been followed in the present paper. For detailed references see Lyons et al. (1982).

In peninsular India, resino-inertinites have been commonly reported from coal seams associated with sediments of Karharbari, Barakar and Raniganj

RESINO-INERTINITES OF INDIAN PERMIAN COALS 279

formations of the Damuda Group of Lower Gondwana Sequence (Fig. 1). These coals occur in the Satpura, Son-Mahanadi, Damodar and Wardha-Godavari grabens and have been described by number of authors (Ganju, 1955b, 1961; Ganju and Pant, 1963; Pareek, 1964, 1966; Ramana Rao and Razvi, 1969; An- and Prakash, 1970; Rishi, 1970; Navale and Srivastava, 1970, 1972; Anand Prakash and Khare, 1976; Navale et al., 1983; Pant, 1987; Singh et al., 1987). In the extra-peninsular Gondwana coals of Arunachal Pradesh, resino-inertinites ere infrequent to absent (Misra et al., 1987).

The study of Lyons et al. (1982) on resin rodlets strengthens the concept of earlier coal petrologists that these discrete inertinitic bodies originated from resinous and to some extent phlobaphinitic materials during the course of coalification. Recently, Pant (1987) expressed a similar opinion based on transmitted and reflected light studies of Indian Permian coals. Pareek (1966, p.144) suggested possibilities to utilize them for correlation of coal seams and coal- bearing horizons. Yet, no serious attempt has been made for correlation of seams in spite of considerable data available on resino-inertinite. The apparent reason may be due to the lack of its proper diagnosis and classification. In the present paper, an attempt has been made to understand the genesis of resino-inertinites and to devise a classification applicable to those of the In- dian Permian coals in particular and of Paleozoic coals in general.

OCCURRENCE OF RESINO-INERTINITES IN PERMIAN SEQUENCES OF INDIA

The relative distribution of resino-inertinites in coals of the Permian (Lower Gondwana Sequence) of peninsular and extra-peninsular grabens/basins of India is given in Table 1.

Resino-inertinites occur as isolated bodies, in clusters and chains or rows. They are noticeably rare in vitrinite-rich coals as well as vitrinite-rich micro- lithotypvs. Ganju (1961) found them associated with durains. Pareek (1966) mentioned their association mainly with durite and also with trimacerite and fusite. However, from several investigations carried out at our laboratorj (Navale and Srivastava, 1970,1972; Navale et al., 1983; Singh et al., 1987 and unpublished data), it has been found that the durite content of a coal has no relation with its resino-inertinite content. Instead, some apparent relationship does exist between the proportion of resino-inertinite and total inertinite or trimacerite content of coal.

In the present work we have analysed the information available on resino- inertinites from Gondwana basins of India which revealed that in certain cases their highest concentrations are found in bottom sections of coal seams (e.g., Lalpeth, Sasti and Ballarpur, collieries of Wardha Valley, see Anand Prakash and Khare, 1976) or that they are common only in the lowermost seam of the area (e.g., Talchir coalfield, Mahanadi graben, see Nawlc and Srivastava, 1970). In some seam sections they are common but in other sections of the

280 B.K.MISHRAETAL.

TABLE I

Resino-inertinute occurrences in Permian coal basins of India

Graben/Basin Age Formation Coal rank (Ro,,,- ~ )

Occurrence

Damodar Late Permmn Raniganj 0.56-0.97

Middle Permian Kulti shale/ Barren Measure

Early Permian Barakar 0.60-1.90 Karharbari

Son- Late Permian Raniganj 0.50-0.60 Mahanadi

Satpura

Wardha- Godavari

Rajmahal

Kameng NE Himalaya

Middle Permian

Early Permian

Barren Measure/ Iron Stone Shale

Barakar Karharbari

Late Permian

Middle Permian

Early Permian

Late Pemian

Middle Permian

Early Permiar

Late Permian

Early Permian

Early Permian

Bijori ( - Raniganj)

Motur

Barakar Karharbari

Kamthi ( - Raniganj)

Chintalpudi (Motur like Fin. )

Barakar Karharbari

Plant beds ( - Raniganj)

Barakar

Garu ( - Barakar)

0.49-0.90

0.61-1.22

0.50-0.76

0.45-0.55

1.97-2.31

Usually in traces, rare to less common: 0.5-2.0% (rarely upto 5.0% )

No economic coal

Rare, less common to occasionally common: 0.5-3.0%

Absent, traces to rare: upto 0.5%

No economic coal

Less common to common: 1.0-6.0% (rarely upto 7.4% )

No coal

No coal

Less common to common: 1.0-6.4%

No coal

No economic coal

Less common to common: 1.0-6.5%

No coal

Only traces

Usually in traces, rare: upto 0.4%


same seam they are sporadic and impersistent (e.g., Turra seam, Singrauli coalfield, Son graben, see Singh et al., 1987). Occasionally, their content is quite high (upto 7.4% ) locally in a seam (e.g., Duman Hill Colliery. of Chirimiri coalfield, Mahanadi graben, see Sanyal and Subramanian, 1979; or upto 5.0% as in the Narainkuri seam of the Raniganj Formation, Raniganj coalfield, Da- modar graben, see Navale and Srivastava, 1972). In some other seams they are uniformly rare as well as impersistent throughout (e.g., Jhingurdah seams, Raniganj Formation, Singrauli coalfield, Son graben, see Singh et al., 1987).

Apparently, the impersistency in the distribution of resinc-inertinites both laterally and vertically in most of the Permian coal seams of India may reflect imperfect diagnoses in routine petrographic analyses of this maceral. Perhaps, an extensive seam-wise investigation on the nature and typology of resino- inertinite bodies may prove to be helpful in utilizing them for coal-seam correlation as envisaged earlier by Pareek ( 1966, p.144).

SOURCE OF RESIN IN P&RMIAN COALS OF INDIA

Plant fossils which commonly abound in Indian coal-bearing Lower Gond- wana sediments are usually compressions chiefly related to Glossopterido- phyta, an extinct complex of gymnospermous plants. During the Early Gond- wana time, these plants grew in widest possible habitats and varied from small swampy to arborescent upland plants (Lele, 1976). Because the resin contribution of herbaceous and shrubby plants is not known due to early decay and degradation of their soft tissues, only the fossil woods will provide some evidence of resin origin. In this case, preservation becomes a major factor in de- ciphering the presence of resins in fossil woods. From a large number of woods recorded, only 5-10% have revealed the necessary information. Even out of this, only secondary wood is usually found preserved, whereas resin ducts or secretory cells have been reported from pith only.

The record of fossil wood from Indian coal-bearing Lower Gondwana sediments is sporadic and strikingly does not match with the extent of their coal deposits. Nevertheless, their presence and large amounts of gymnospermous tracheids and other woody fragments in coal macerates of the Karharbari, Barakar and Raniganj formations (H.K. Maheshwari, pers. commun., 1987) establishes the common presence of arborescent vegetation since the Early Permian. Sofar, only one wood species has been recorded from the Karharbari Formation (basal coal measure - Lower Permian). The overlying Barakar For- mation (Upper Lower Permian), with which major Gondwana coals are associated, has only eight fossil-wood species reported from Jharia coalfield of the Damodar graben. In contrast~ from the l~niganj ~nd Kamth~ ( - Raniganj Fm.) formations in Damodar and Son-Mahanadi grabens respectively, a large number of fossil woods have been reported.

In India, resin-producing fossil woods are known from the Early Permian.

282 B.K. MISHRA ET AL.

Eight common fossil woods are known from the upper Barakar Formation. These are Barakaroxylonjhariense (Kulkarni et al., 1971), B. monocanalosum (Kulkarni, 1971), Damudoxylon indicum (Pant and Singh, 1987), Australox- ylon kharkhariense (Marguerier, 1973), A. barakarense (Marguerier, 1973), Araucarioxylon gondwanense (Maheshwari, 1972) and Chapmanoxylon par- enchymosum (Pant and Singh, 1987). Of these woods, the first four occur quite commonly and possess resin canals and/or secretory cells. The remaining four are devoid of resin. Australoxylon kharkhariense and Araucarioxylon gondwanense have only secondary wood whereas, Australoxylon barakarense and Chapmanoxylonpare,~hymosum have pith also. From the Upper Permian strata (Raniganj Formation) more than a dozen fossil-wood genera and about 50 species are known. Of them, many (e.g., 3-4 species of Damudoxylon, few species of Trigenomeylon etc. ) were resin-producing deciduous trees growing commonly in India (Maheshwari, 1967 and pets. commun., 1987).

Based on petrographic investigation, Ganju (1955a,b, 1961 ), Ganju and Pant (1963), Pareek (1966) and many others reported the common occurrence of resin bodies and resinc-inertinites from coals of Karharbari, Barakar and Raniganj formations. The finding is in contrast with the records of resin-producing fossil wood, particularly from Karharbari and Barakar formations. However, these evidences definitely indicate the presence of resin-producing trees even during Early Permian and their abundance probably increased towards the Late Permian. This increase in arborescent vegetation during the course of time outnumbered the contribution of herbaceous and shrubby plants in Permian coals of India.

MORPHOGRAPHIC DESCRIPTION OF R E S I N O - I N E R T I N I T E S

According to White (1914), Kosanke (1952), Kosanke and Harrison (1957), Taylor and Cook (1962) and Lyons et al. (1982) resino-inertinites are preserved in disoriented or parallel arrays, on the bedding planes of coal associated with fusain, mineral matter etc. Under reflected light on polished surfaces, resino-inertinites have high relief, high polishing hardness and high reflectance typical of inertinite macerals. They do not fluoresce and range in size from 20.0 to more than 2000.0/~m. In Indian coals, resin.o-inertinites range in size from 60.0 to more than 650.0/~m. In transmitted light they are opaque to

1 • semi-opaque (dark brown, see Ganju, _961, Ganju and Pant, 1963). They are solid and non-structured or with cracks (kerfs) which may be straight or curved; hollow with vesicles as well as fragmented, cracked and vesicled (Ganju, 1961; Pareek, 1964, 1966). Cracks, vesicles and pits are usually filled with mineral matter, generally black argillaceous matter, calcite and siderite. Pyrite infill- ings have not been recorded from Indian Permian coals.


MODE OF TRANSFORMATION OF RESIN BODIES TO RESINO-INERTINITES

Earlier workers assumed that morphological features developed on resino- inertinites were caused by shrinkage during drying and/or by devolatilizatio_.-_ of occluded gases in the primary resin (Ganju, 1961; Ganju and Pant, 1963; Pareek, 1964, 1966). Not much significance was attached to the chemical nature of resin bodies. However, before attempting any generalization about the transformation of resin bodies to fusinized state the following facts need crit- ical consideration:

(1) Resins produced in different plant tissues (leaf, bark, wood, etc.) have different physical and chemical properties. Resins (unsaturated compounds of highly polymerized acids and neutral substances mixed with terpene deriva- tives ) are most common in gymnospermous plants, whereas, fats (unsaturated and saturated compounds of monobasic aliphatic carboxylic acids) and waxes (esters of monohydric alcohols of higher homologues) are common in angiosperms (Stach et al., 1982). Evidently, the resins were the main contributors for maceral resinite in Paleozoic coals. On the other hand, since Mesozoic time, when angiosperms became dominant, fats and waxes apparently contributed most for resinite. This possibility is one of the main reasons for the presence of resino-inertinites in Paleozoic and their absence in Mesozoic-Cenozoic ~oals.

(2) Plant resins react with oxygen if exposed to air for some time after their release (in swamp). They get oxidized fairly strongly and altered chemically (Stach et al., 1982). After a marked degree of oxidation which leads to higher reflectance, resinites are changed to inertinites.

(3) So far, only three to five resinite types have been recognized by spectro- fluorimetric studies on coals of different ages and occurrences (Crelling and Bensley, 1983; Teerman et al., 1987). It has also been found that some of the resinite types have gradational characters overlapping with each other (Misra, 1989). Similarly, study by Ottenjann (1982) on Devonian (Paleozoic) to Cen- ozoic coals revealed that only two sporinite categories could be made - relating with (a) pteridophytic and gymnospermous plants and (b) angiospermous plants. Evidently, all the differences in chemical composition of resinites can- not be precisely determined as is possible with materials of recent plants.

(4) Almost the same general types of resino-inertinites have been recorded from Paleozoic coals of several countries in spite of their formation in a wide range of environmental, depositional and tectonic situations. This suggests that either these factors had indiscernible influences or all such influences were masked during oxidation/fusinization. However, abundances of resino- inertinites in a deposit may be related partly to the environmental conditioiis.

(5) Presence of resino-inertinites and resinites together in Indian Permian coals (Ganju and Pant, 1963) suggests either their selective fusinization or incorporation of the former from extreneous sources, e.g., incorporation of pyrofusinite and inertodetrinite.


(6) Since, resino-inertinites are mostly associated with inertinite-rich coals, their genesis requires a positively oxidative condition. Evidently, factors re- sponsible for transformation of resinites into resino-inertinites should be as- certained either from the chemical composition of their precursors and/or their mode of transformation.

It is quite reasonable to presume that chemistry of the resino-inertinite precursor and its subsequent oxidation or fusinization history have a major influ- ence on the distinctive morphology of its altered product. Certain chemical changes in resinites before oxidation, as revealed by their fluorescence properties (Stach et al., 1982) also influenced the resulting morphology. There is no possibility, as yet, to relate the chemical composition of the precursor material with the altered product. However, factual evidence and reasonable inJ ferences concerning precursor's physico-chemical behaviour will provide clues for interpreting morphology developed on resino-inertinites.

The preceding facts apparently explain the occurrence of a limited variety of resinites and ~sino-inertinites in coals formed under widely varying sets of conditions. Degree of cracking, fissuring, cren~ation of crack and vesicle mar° gins, fragmentation, etc. of resino-inertinites have been presumed to be depen- dent on the intensity of oxidation. Precursors of such resino-inertinites presumably became brittle during oxidation. The resinites with tendency to softening (viscous) and secondary mobilization (Jones and Murchison, 1963; Murchison and Jones, 1964) vesicularize due to escaping of occluded gases on devolatilization at low temperature during early diagenetic stages. They dis- play most irregular shapes caused by swelling and subsequent shrinkage.

Cracking, crenulation and fragmentation of resino-inertinites with vesicles, is a variation in type resulting either due to some difference in the nature of the precursor or caused by increase in the degree of oxidation. Since, both are the commonly occurring types in the coals of wide ranging ranks (Ro .A. in oil: 0.49-> 1.0%), the degree of alteration alone does not seem a favourable basis for relating them (vesicled and vesicled with cracks and crenulations) together. Vesicle formation in ohlobaphinite/corpocollinite, on the other hand, has been presumed to be the result of early nucleation of concretionary min- erals (calcite, siderite and pyrite) when the host material was still somewhat viscous prior to or during gelification stages.

CLASSIFICATION OF RESINO-INERTINITES

Literature review

Taylor and Cook (1962) attempted to classify resino-inertinites of Austra- lian Paleozoic coals and categorized them into two broad groups namely (1) 'round or oval bodies' and (2) 'interlaced fungal hyphae'. However, they pre- ferred to record massive discrete bodies as micrinite and vesicular discrete bod-


ies as well as irregular tissues as semifusinite or fusinite (1962, p.50). Pareek (1964) classified resino-inertinites of Indian Permian coals into six types. He based his categories on patterns and length and width of 'voids' or 'canals' and vesicles along with absence or presence of a peripheral rim. Anand Prakash (1970) classified them into seven types by using various patterns of cracks and vesicles and their visual refiectivity. Both of these, classifications are arbitrary, based on widely variable and overlapping characters.

The present classification

In view of the fact that re~ino-inertinites in I n ~ n Permian coals are selec- tively quite common in several coal-seam sections while in others, they are rare, the proposed classification intends to ascertain their utility in correlation of coal seams and coal-bearing horizons.

This classification is primarily morphographic based on the presumption that the coal-forming plant communities of Carboniferous and Permian in general and of Permian of India in particular produced at least three or four kinds of resinous material including phlobaphenes which served as resino- inertinite precursors. However, certain morphological features viz., length and width of cracks and fissures, variation in the size of vesicles, etc., ~ .. . . i^.. A..^ to variation in the degree of fusinization of resino-inertinite precursors. Such gradational features have been given only due credence. The present classification, thus, groups the Carboniferous and Permian resino-inertinites into three morphotypes. The diagnostic features are:

(1) Resino-inertinite bodies showing voids of variable size. (2) Resino-inertinite bodies: (A) without any apparent structure; (B)

showing cracks and fissures. (3) Resino-inertinite bodies: (A) showing tendency for both cracking and

vesicularization with a non-vesicled peripheral rim; (B) being vesicled or perforated with an imperforated peripheral rim.

Descriptions

Type I Elongated, oval, elliptical, subcircular to circular resino-inertinites in clus-

ters or as solitary bcdies with semifusinitic to fusinitic refle~ ~ivities. Presence of circular to subcircular voids of variable sizes render them an appearance like fungal sclerotinite (Plate I, 1-2; Plate If, 4 - bodies on left side). The resino- inertinites of this group have been presumed to have formed from resinous and phlobaphinitic/corpocollinitic materials. Ganju and Pant (1963, pl. Ill, 2 ) and Pant (1987, pl. V, 2) have also recorded similar resino-inertinites.

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Type 2 The resino-inertinites of the second category exhibit rather a wide range of

morphological patterns presumably controlled by the intensity of fusinization and hence subdivided into A and B subtypes:

(A) In shape, similar to resino-inertinite type 1. However, they are commonly without any apparent structure and have semifusinitic to fusinitic re- flectivities (Plate I, 3-4; Plate II, 5 - top left corner, 7 - top; Plate III, 4 - top right corner). These resino-inertinites may often have few cracks and small pits or holes but still their shape and body outline is disturbed only slightly.

(B) These resino-inertinites are characterized by variable shape, usually fusinitic reflectivity and cracks and fissures. The outer margin of the body is generally irregular and/or distinctly notched because of irregular fragmentation along the margin. The body is characterized by poorly to well developed, often coalescing, parallel, radiating or randomly oriented straight or curved cracks which are invariably filled with black argillaceous matter (Plate I, 5-8; Plate II, 8). Often brittle crack or fissure margins break away randomly in minute pieces producing crenulation or cavitation. The crenulation may be sparse or dense either along cracks or on the whole body of the resino-inertinites (Plate I, 9-10; Plate II, 1-6; Plate III, 3 - bottom right corner). Pareek (1964, fig. 2) and Lyons et al., (1982, fig. 13) h~ve al~o described similar bodies. Such resino-inertinites are common in the Singrauli coalfield.

Type 3 The resino-inertinites belonging to this category are similar to type 2B in

shape. In size their observed upper limit is higher than that of types 1 and 2. They generally have fusinitic reflectivity and show certain distinct as well as overlapping characters. Therefore, to avoid ambiguity, they have been subdivided into two sub-types:

(A) These resino-inertinites show a wide range of morpholo~cal character- istics including cracking, vesicularization, crenulation of vesicle and crack margins to fragmentation caused by widening of fissures (Plate II, 7 - bottom, v; Plates III, 1-4). Vesicles may be localized towards central part, distributed

PLATE I

Resino-inertinites: type 1, type 2A, type 2B (All photomicrographs were taken on polished surface, reflected light, oil immersion). 1-2. Type 1, showing voids of variable size. Magnification: 1 ×250; 2 ×200. 3-4. Type 2A, lacking any apparent structure. Magnification: 3 × 125; 4 × 250. 5-8. Type 2B, showing parallel and random cracks of uniform to non-uniform width. Magnifi-

cation: 5,7,8 × 200; 6 × 150. 9-10. Type 2B, showing parallel and disoriented fissures with crenulations on body as well as on

fissure margins, × 125.

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around a central imperforated core or all over the body but always a thin or thick non-vesicled peripheral rim is present. The presence of the peripheral rim distinguishes them from the resino-inertinites of type 2. Ganju and Pant (1963, pl. IV, 13), Pant (1987, pl. V, 3) and Pareek (1966, figs. 8,14,16) have also described similar bodies.

(B) These are characterized by a vesicled bedy surrounded by a thin or thick imperforated peripheral rim (Plate I ' 5 - bottom, left 10; Plate III, 4 . corner, - left top corner, 5-7). Vesicles of variable size occur interspersed together. They are either restricted in central part of dispersed all over the body. Occa- sionally, they are found in patches as well as around a imperforated central core. In some cases coalescing of vesicles may form a hollow structure which runs through the entire length of the rodlet-longitudinal section (Plate II, 10; Lyons et al., 1982, fig. 10). These resino-inertinites are normally devoid of cracks and fissures - a feature distinguishing them from type 3A. Similar bodies have been reported by Lyons et al. (1982, figs. 12,13), Pareek (1966, fig. 17) and Pant (1987, pl. IV: 6 - top, left corner).

CONCLUSIONS

The resino-inertinites of Carboniferous and Permian coals in general and of Indian Permian (Lower Gondwana) coals in particular have been presumed to have originated mainly from resins (resinites) and to some extent phlobaphenes (phlobaphinite/corpocollinite) of the then existing plant communities. Petrographic, mega- and microfloral evidences indicate that in India, arborescent plants were the common coal-forming source material right from the Early Permian period. The distinct and wide range of morphological charac- teristics shown by resino-inertinites are reflections of interaction between the chemical nature of the resino-inertinite precursors and variable as ,#ell selec-

PLATE II

Resino-inertinites: type 2B, type 3A (All photomicrographs were taken on polished surface, reflected light, oil immersion). 1-6,8. Type 2B, showing fine to widely gaping fissures with crenulation (sparse/dense) on fissure

margins and/or main body. Occasionally, some bodies of other types were figured. Magni- fication: 1,2 × 250; 3 × 125; 6 X 125; 8 × 125. 4. Body on left corner categorized ~s type 1, × 250. 5. Body on top left corner categorized as type 2A; body on bottom left corner as type 3A, × 175.

7,9. Type 3A, showing tendency to cracking and vesicularization with nonvesicled periteral rim. Occasionally, some bodies of other types were figured. 7. Body on top categorized as type 2A, × 175. 9. Longitudinal section, × 200.

10. Type 3B, showing vesicled and perforated body, longitudinal section, × 200.

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tive degree of oxidation or fusinization during coalification. Evidences are apparent that influences of other factors were either negligible or masked com- pletely during transformation of resino-inertinite precursors.

The present classification scheme is a synthesis of most, if not all, of the possible morphological variations of resino-inertinites in relation to the apparent physico-chemical behaviour of their precursors. The classification has been devised to utilize resino-inertinites in correlation of coal seams as envisaged by Pareek (1966, p.144).

ACKNOWLEDGEMENTS

The authors would like to express their sincere thanks to Drs. H.K. Maheshwari and P.K. Maithy of the Birbal Sahni Institute of Palaeobotany, Lucknow, for fruitful discussions on Indian Permian fossil woods.

REFERENCES

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PLATE III

Resino-inertinites: type 3A, 3B (All photomicrographs were taken on polished surface, reflected light, oil immersion). 1-4. Type 3A, showing ~ndency to both cracking and vesicularization witt- nonvesicled periferal

rim. Occasionally, bodies of other types were figured. Magnification: 1 × 175; 2 × 150. 3. Body on bottgm right corner categorized as type 2B, × 125. 4. Body on top right corner categorized as type 2A, × 125.

5-7. Type 3B showing vesicled/perforated bodies with imperforated peripheral rim. Magnifi- cation: 5 X 150; 6 X 250; 7 × 125.


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