JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.87, February 2016, pp.153-160

Sub-surface Coal Seams of Bhupalpalli and Golapalli Areas of Godavari Valley Coalfield and their Petrographic Characteristics OMPRAKASH S. SARATE Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow – 226 007, India Email: [email protected] Abstract: The research work details the maceral organization of eleven coal seams intersected at a maximum depth of 446.45 m from Bhupalpalli area of the Mulug coal belt, in Warangal district of Godavari valley. Samples for petrographic study have been collected from ten coal seams intersected between 106 m and 299 m depth range from Bore-hole No. 618 which includes, IA and its underlying I, II, Index below II, IIIB, IIIA, III, IVA, IV and Index below IV respectively. However, the coal samples from the bottom most V seam were collected from Bore-hole No. 616 encountered between 445.65 m and 446.45 m. The study has revealed that V seam is marked by vitric type and seam IVA contains coal of fusic nature. The seams I, II, Index below II, IIIB, IIIA and IV, however, are represented by mixed type of coal. Whereas, the seams IA and III have the prevalence of vitric as well as mixed coal types. IA seam has witnessed alternate oxic and anoxic moor condition and also wet moor with intermittent moderate to high flooding. All the other seams have been deposited during alternate oxic and anoxic moor conditions. The coal seams of the study area have shown a wide range of variation in vitrinite reflectance (Ro mean %). The top of III, basal part of IV and the entire Index below IV have recorded high vitrinite reflectance (Ro mean %), which ranges between 0.66-0.67% thus they have reached high volatile bituminous B stage, all the other seams show lower reflectance and therefore have attained high volatile bituminous C rank. Keywords: Coal-petrography, Bhupalpalli, Golapalli, Godavari valley, Andhra Pradesh. INTRODUCTION

The study area represents one of the most extensively explored coal reservoirs of the Godavari valley coalfield, Andhra Pradesh. However, very little is known about the petrogrhic composition of the coal seams of this area. Keeping in view this factor, systematic and detailed sampling has been done for coal petrographic analysis (maceral and reflectance) for evaluating the depositional scenario and its economic potential of the complete sub-surface coal sequence. Coal petrographic work in Godavari valley has mainly been taken up by Ghosh (1962), Moiz and Ramana Rao (1976), Pareek et al. (1964) on the coals of Tandur and Ramagundam areas of the Godavari valley. Rizwi and Ramana Rao (1969) however, has observed the resin distribution in the coals of Kothagudem coalfield. Navale et al., (1983) have also studied some coal samples of the from Kothagudem, Ramagundam and Ramkrishnapuram areas. Similarly, Sarate (1996, 1996a, 1998, 1999, 2001, 2001a, 2010, 2010a, 2010b, 2012) has carried out extensive petrographic work on several areas of the Godavari valley.

Bhupalpalli area delimits the north-western extremity of the Mulug coal belt which is located in the central part of the Godavari valley coalfield, marked between18o26'26" to 18o28'25" latitudes and 72o49'43" to 72o52'28" longitudes and 18o27'41" to 18o30'04" latitudes and 79o48'39" to 79o57´55´´ longitudes. The area is mostly sandy terrains showing slight undulations at places, sloping towards northwest. The lower Gondwana succession in the valley overlie the Archaean formations. Talchir Formation mostly occupies the western margin of the Chelpur-Lingala belt and includes basal tillite unit with overlying clay containing dispersed clasts, followed by alternate clay bands which in turn are succeeded by medium grained siltstones with intervening clasts. Repetition of tillites is not noticed in this region. The basal part of Barakar Formation, is arenaceous in nature having predominance of coarse grained sandstones containing conglomeratic lenses with no development of coal seam. A wide range of thickness variation from 70 m to 120 m is observed. The upper member is characterized by cyclic repetition of sandstone shale and coal seams; its thickness varies between 120 m and 150 m. Barren Measures Formation has steeper dip of 15o to 18o than the

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underlying Barakar Formation with low dip of 6o to 8o. Barren Measure Formation which has medium to coarse grained felspathic and ferruginous sandstone unit, exhibits greenish to grey white colouration. Presence of thin clay and carbonaceous bands are occasionally noticed. The conformably overlying strata is designated as Kamthi Formation, at the base it contains calcareous grayish white medium grained sandstones along with a few coal seams. The upper part, however, has brick red sandstone, siltstone conglomerates, white marble clasts and yellow shales. No coal seams are reported from this region. GENERAL GEOLOGY

In the Pranhita-Godavari valley coalfield Gondwana sediments have been deposited along the river course. The Gondwana deposits within the territory of Maharashtra state are referred as Wardha valley coalfield and those falling in the areas of Andhra Pradesh are described under Godavari valley coalfield. Godavari valley covers about 17000 km2 area delineated between 79o 12' and 81o 39'

longitudes and 16o 38' and 19o 32' latitudes. The valley displays a continuous sedimentary deposit of Permian to Triassic (Raja Rao,1982). The detailed lithological succession of the valley is given in Table 1. COLLECTION SITE

For coal petrographic study samples from ten seams (viz., IA, I, II, Index below II, IIIB, IIIA, III, IVA, IV and Index below IV), has been collected between 105 m and 305 m depth range from bore-hole No. 618, located at a distance of 3.5-4 km south-east of Golapalli village. The bottom most V seam was found missing in this bore-hole, therefore samples of this seam were taken at a depth range from 445.65 m to 446.45 m, in another bore-hole No. 616 situated nearly 2.5 km north of Bhupalpalli village (Table 2, Fig. 1 & 2). METHODOLOGY

The coal samples were crushed gently and cautiously and sieved to obtain ± 1-2 mm grain size. Specific plastic

Table 1. General geological succession of the Permian sediments exposed in the Godavari Valley Coalfield in Telangana, India (after Raja Rao, 1982) Age

Group

Formation

Lower Triassic Upper Permian Upper part of Lower Permian

Lower Permian

L O W E R G O N D W A N A

Lithology

500

Upper Member: Coarse-grained, ferruginous sandstones with clay clasts and pebbles and subordinate violet cherty siltstones and pebble beds.

600

Middle Member : Alternating sequence of medium grained white to greenish grey white sandstones and buff to greenish grey clays.

200

Lower Member : Medium to coarse grained, grayish white calcareous sandstones with a few coal seams.

Barren Measures

500

Medium to coarse grained, greenish grey to grayish white felspathic sandstones with subordinate variegated and micaceous sandstones.

Barakar

300

Upper Member: Coarse, white sandstones with subordinate shales and coal seams.

Kamthi

Upper Permian to

Maximum Thickness (meters)

Lower Member: Coarse-grained sandstones with lenses of conglomerates, subordinate shales/clays and a few thin bands of coal. Talchir

350

Fine-grained sandstones, splintery green clays/shales, chocolate coloured clays, pebble beds and tillite. - - - - - - - - - - - - - - - - - - Unconformity- - - - - - - - - - - - - - - - - -

? Upper Proterozoic

Sullavai

545

Medium to coarse grained, white to brick red sandstones, at places quartzitic and mottled shales.

Lower Proterozoic

Pakhal

3335

Grayish white to buff quartzites, grey shales, phyllites and marble.

- - - - - - - - - - - - - - - - - Unconformity- - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - Unconformity- - - - - - - - - - - - - - - - - Precambrian

–

–

–

Granites, banded gneisses, biotite gneisses, hornblende gneisses, quartz magnetite schists, biotite schists, quartz and pegmatite veins. JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016

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Fig.1. Geological details and location map of Bore-hole Nos. 616 and 618 (Courtesy, SCCL, Kothagudem, Telangana).

moulds have been used for coal pellet preparation. Before pouring adequate amount of the crushed coal samples the moulds were coated with a thin film of releasing agent. An instantly made mixture of resin and hardener in 5:1 was added to the moulds containing samples and mixed properly avoiding bubble formation. The pellets were numbered and allowed to dry and settle for a day at room temperature. The hardened pellets were removed, ground and polished as per the recommendations of ICCP (1971, 1975, 1998) and Stach et al., (2001). The quantitative micro-constitutional observations have been done using Leica DM4500P, version 2.35 of petroglite. However, random vitrinite reflectance (Ro mean %) has been measured through Microscopephotometry System (PMT III) and Software 200 and photomicrographs were taken using software tool Leica applications. DESCRIPTION OF MACERALS

The microscopic entities of the coal are termed as coal macerals, which can be identified by their distinct morphological features, reflectivity as well as fluorescence property (Stopes, 1930). JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016

Vitrinite: The macerals of this group have mostly shown predominance over inertinite group of macerals. However, some of the coal seams have also recorded internite dominance. The vitrinite group of macerals exists in banded forms (both thick and thin) with dark or light grey colouration. Collotelinite (Plate 1, Fig. 1 & 2) can easily be distinguished from telinite which have darker colour than collotelinite. Exudatinite (Plate 1. Fig. 3 & 5) expulsion is also witnessed from the micro-cracks of the collotelinite (Plate 1. Fig. 4). Collotelinite is most frequently observed than the telinite in these coals. The cell lumens and fissures of the collotelinite and the telinite are sometimes occupied by gelinite and also by different mineral matter. Vitrodetrinite is recorded as fine fragmented form and displays variation in shape and size. Liptinite: Microspores particularly the thin walled microsporinites (tenuispores) are abundantly recorded in these coals with spindle shape or thread like appearance and dark grey or blackish colouration. They are either seen randomly distributed in the inertodetrinite fraction or in linearly arranged rows (Plate 1. Fig. 9 & 10), in the vitrinitic groundmass. Megaspores are rarely noticed they

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are also not well preserved. Large vitrinite and inertinite bands one above the other are also frequently observed. (Palate 1. Fig. 11). Fusinite also show cellular compression and disintegration (Plate 1. Fig. 12 & 13). Semifusinite has higher reflectance than the vitrinite and lower than the fusinite, its colour also varies between light grey and white. Funginite is the name given to the fungal remains found among the other coal constituents, they mainly includes, single and multi-cellular dark black coloured fungal spores, hyphae, mycelia or sclerotia generally interspersed with inertinite or inertodetrinite fraction. Similarly, Secretinite with spherical or oval shape (Plate 1. Fig. 14) is also frequently observed. Mineral Matter: The coal macerals are invariably found associated with mater matter. Clay minerals are most commonly noticed and display black colour and fine grained (Plate 1, Fig.15). Mostly they exist as groundmass, as well are seen embedded in the cracks and fissures of the other coal macerals. Similarly, carbonate minerals are recorded from cracks and fissures of the vitrinite and inertinite macerals. Pyrite (Plate 1. Fig. 4) is recorded as isolated bodies as well as in framboidal forms mostly from the vitrinite, inertinite and inertodetrinite. MACERAL CONSTITUTION

Fig.2. Litholog of Bore-hole 616 and 618 showing the location of coal seams.

have ornamented body, large in size, dark blackish colour and distinct lumen. Cutinites show serrated margins and darker grey colour than the sporinite. Thick walled crassi-sporinites, with well defined cuticular ledges are occasionally seen (Plate 1. Fig 6, 7 & 8). Similarly, sporangium containing spores are also found in these coals. Oval or spherical resinites are also noticed displaying dark grey or black colour. Leptodetrinite exists in fragmentary form with wide range of variation in shape and size. Inertinite: Fusinite is most abundantly noticed as highly reflecting cellular bodies. Their yellowish colour is due to high carbon contents. The fusinites with yellowish colour and well defined cell preservation are termed as pyrofusinites whereas, degradofusinite show white colour and the cells

The topmost IA, I, top part of III, and basal parts of IV and V seams have shown the dominance of vitrinite group of macerals (38% to 58%) along with inertinite (14% to 33%). Both the vitrinite and inertinite in IA seam have shown increasing trend of frequency distribution towards the bottom part. However, liptinite (25% to 9%) and mineral matter (23% and 14%) have depicted reverse trend of distribution. Predominance of inertinite (40% to 48%) with invariable association of vitrinite (17% to 31%) and liptinite (14% to 20%) is depicted from the coals of II, IIIA, bottom part of III, IVA, top of IV and Index below IV seams. Mineral matter association in these seams is recorded between 9% and 18%, barring seam IVA, which contains 24 per cent mineral matter. Index below II seam differs from rest as it contains equal proportions of liptinite (34%) and inertinite (34%), besides quite low vitrinite (13%) and mineral matter (9%) distribution. Similarly, IIIB seam is also characterized by the presence of almost same proportion of the vitrinite and inertinite (35%- 36%) maceral groups, along with low liptinite (8%) association. Mineral matter has been recorded to be 21 per cent (Table 2, Fig. 3). REFLECTANCE STUDY

The top of III, basal part of IV and the entire Index below IV seam has shown random vitrinite reflectance (Ro mean JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016

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Plate 1. Fig. 1 & 2. Collotelinite bands, 3 & 5. Exudatinite, 4. Telinite containing framboidal pyrites and hydrocarbon expulsion, 6, 7 and 8. Cutinite disbursed in vitrinitic and inertinitic ground mass respectively, 9 & 10. Linearly arranged microspores. 11. Large bands of vitrinite and fusinite, 12 & 13. Fusinite, showing cellular compression. 14. Secretinite, 15. Mineral matter. JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016

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OMPRAKASH S. SARATE Table 2. ithological details of the coal seams intersected in Bore-hole Nos. 616 and 618 and their maceral constitution and reflectance (Ro mean %) analysis, from Bhupalpalli area of the Godavari Valley Coalfield Sr. No.

Pellet No.

Depth (in meter)

Coal Seam

Vitrinite %

Liptinite %

Inertinite %

Mineral Matter %

Reflectance ( Ro mean %)

1. 2. 3. 4. 5. 6. 7. 8. 9, 10. 11. 12. 13. 14. 15. 16. 17

618-1 618-2 618-6 618-7 618-8 618-9 618-10 618-11 618-12 618-13 618-14 618-15 618-16 618-17 618-18 618-19 616-1

106.18-107.01 107.01-107.84 136.95-137.95 177.10-179.20 190.37-191.04 217.78-218.88 236.75-237.15 248.24-249.24 249.24-250.24 250.24-251.24 251.24-252.24 266.00-267.35 289.15-289.95 289.95-290.75 299.15-299.75 299.75-300.35 445.65-446.45

IA IA I II Index below II III B III A III III III III IV A IV IV Index below IV Index below IV V

38 (49) 58 (67) 38 (44) 31 (34) 13 (16) 35 (44) 28 (32) 37 (42) 58 (63) 31 (35) 31 (35) 17 (22) 25 (31) 41 (45) 18 (22) 26 (30) 52 (57)

25 (33) 9 (11) 17 (19) 20 (22) 34 (42) 8 (10) 17 (19) 20 (22) 13 (14) 16 (18) 19 (21) 14 (19) 15 (18) 17 (19) 18 (22) 17 (20) 17 (19)

14 (18) 19 (22) 32 (37) 40 (44) 34 (42) 36 (46) 43 (49) 32 (36) 21 (23) 42 (47) 40 (44) 45 (59) 42 (51) 33 (36) 48 (56) 43 (50) 22 (24)

23 14 13 9 19 21 12 11 8 11 10 24 18 9 16 14 9

0.58 0.56 0.55 0.50 0.49 0.61 0.53 0.67 0.53 0.60 0.50 0.53 0.59 0.66 0.66 0.51 0.49

Note : The values given in the bracket indicates the mineral matter free (m.m.f.) percentage.

%) variation between 0.66-0.67%, thus attained high volatile bituminous B stage. IA, I, IIB, middle portion of III and the top of IV seam has vitrinite reflectance variability from 0.550.61%. Similarly, quite low reflectance of 0.49-0.53% is recorded from II, Index below II, IIIA, some parts of III, IVA, bottom of Index below IV and V seams, hence, they have reached high volatile bituminous C rank (Fig. 5). DISCUSSION AND CONCLUSIONS

The deposition of vegetal matter in the study area has

Fig.3. Maceral constitution of the coal seams intersected in Borehole Nos. 616 & 618, Godavari Valley Coalfield.

been initiated during cold and humid climate as evidenced by the formation of vitrinite rich coal constitution of the basal most IV seam. Gradually the climate shifted to warm and oxidizing conditions as suggested by the inertinite rich coal constitution of the Index below IV seam. Again the climate changed to cold condition when the basal part of the IV seam was being deposited and reversed to warm and oxidizing conditions during the deposition of the top part of the IV seam and continued during the deposition of the IVA seam.III seam has witnessed cold climatic conditions during the early stages of its deposition which change to warm and

Fig.4. Ternary mineral matter free (m.m.f.) maceral constitution of the coal seams intersected in Bore-hole Nos. 616 & 618 Godavari Valley Coalfield. JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016

PETROGRAPHIC CHARACTERISTICS OF SUB-SURFACE COAL SEAMS OF BHUPALPALLI AND GOLAPALLI AREAS

Fig.5. Reflectance (Ro mean %) analysis of the coal seams intersected in Bore-hole Nos. 616 & 618, Godavari Valley Coalfield.

oxidizing stage during later stages as indicated by the presence of vitric coal at the base and fusic coal at its top. IIA seam, however has been deposited during warm and oxidizing condition as reflected by fusic nature of the coal seam. The climate became moderate during the deposition of the IIB and Index below I seam as suggested by formation of mixed type of coal. A distinct change from moderate to oxidizing condition has been observed when the II seam was being deposited. Whereas, cold climatic conditions prevailed during the deposition of the I and the topmost IA seams. The ternary mineral matter free (m.m.f.) plotting has shown that the lowermost V seam contains vitric type of coal and the seam IVA is represented by fusic coal type. Whereas, the seams I, II, Index below II, IIIB, IIIA and IV contain mixed type of coal. Seams IA and III are characterized by both the vitric and mixed coal types and Index below II seam is found containing fusic and mixed coal types (Fig. 4). The facies diagram (Fig. 6) drawn for interpretations based upon maceral contents, the depositional environment of different coal seams of the study area has indicated that the IA seam has been deposited during the prevalence of

159

Fig.6. Diagram showing depositional environment of the coal seams intersected in Bore-hole Nos. 616 & 618, Godavari Valley Coalfield (Singh and Singh, 1996).

alternate oxic and anoxic moor conditions and also witnessed wet moor with intermittent moderate to high flooding. All the other seams however, were exposed to alternate oxic and anoxic moor conditions (Singh and Singh, 1996). Thus, the entire coal seam succession of the study has been deposited during the prevalence of cold and humid conditions with alternate dry and oxidizing spells (Kraüsel, 1961) as indicated by the vitric and fusic nature of the coal. The existence of mixed type of coal however, demonstrates the prevalence of moderate climate during the deposition of IIB and Index below II seams. Similar climate has been predicted by King (1958, 1961), Plumsted (1961) and Chandra and Chandra (1987) during Gondwana period. Acknowledgements: I am beholden to Prof. Sunil Bajpai, Director of the Institute, for his permission to publish the data. Similarly, I wish to express my gratitude to the authorities of the Exploration Division of the Singareni Collieries Company Limited, Kothagudem, Telangana, for their permission to collect the bore-hole samples and also for providing relevant details. I am also thankful to Mr. V.P. Singh, Technical Officer for his help in plotting the Textfigures.

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(Received: 23 December 2013; Revised form accepted:15 October 2015 )

JOUR.GEOL.SOC.INDIA, VOL.87, FEB. 2016