1 Introduction

The Mand–Raigarh Coalfield is located in the central part of the Upper Mahanadi Gondwana Master Basin (figure 1) and extends over a vast stretch from Sambalpur district of Orissa in the southeast, to the Surguja district of Chhattisgarh in the northwest. The Gondwana sediments here have been subdivided into different coalfields, e.g., Ib-River, Mand–Raigarh, Korba and Hasdo-Arand. The state boundary between Chhattisgarh and Orissa is generally considered to mark the southeastern limit of Mand–Raigarh Coalfield. This coalfield actually covers the areal extents of three initially assigned coalfields, the North Raigarh, South Raigarh, and Mand River coalfields (Raja Rao 1983). Later, on the basis of tectonic and lithostratigraphic modelling, Chakraborti (2001) revised the geology of Mand Coalfield.

Figure 1
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Map showing the study area and principal Gondwana basins of India.

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The north and western parts of the Mand–Raigarh Coalfield have been referred to Mand sub-basin. It is separated from the Raigarh and Ib river basin in the east by a N–S to NNE–SSW trending lineament passing the Konkori–Gersa–Sirsinga area. On the west, it is separated from the Korba–Basin by the NW–SE trending Mauhari–Machida lineament, and from the Hasdo-Arand basin in the north by the well defined E–W trending Dhirpada–Kedma-Chornai shear zone. Within these structural boundaries, the Mand sub-basin acquired NNW–SSE to NW–SE trending asymmetrical shape, with an aerial extent of about 2000 km2. The area is bounded by latitudes 22∘05′00″–22∘47′00′′N and longitudes 82∘55′00′′–83∘15′00′′E (figure 2).

Figure 2
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Geological map of Mand–Raigarh Coalfield showing location of borehole MBKW-3.

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Palaeobotanical data from this coalfield are meagre and scattered. Though different species of Glossopteris, Schizoneura, Vertebraria and Phyllotheca have been recorded by Raja Rao (1983), Chakraborti and Chakraborty (2001) have recorded Early and Middle Triassic plant megafossils from the Kamthi Formation. They also reported Alisporites, Falcisporites, Klausipollenites and Weylanditesfrom the Kamthi Formation, near the Baronakund area, Raigarh Coalfield, Chhatisgarh. In addition, Jana et al. (2002), Ram-Awatar (2007) and Chakraborti and Ram-Awatar (2006) have also recorded Early–Late Permian palynoflora from this coalfield. In the present investigation, Early and Late Permian palynofossils have been recorded from subsurface (MBKW-3) samples which have an important bearing on the correlation of coal seams in the area.

2 General geology

The Gondwana sediments of the Mand–Raigarh Coalfield are classified into the Talchir, Barakar, and Kamthi formations. The geology of the Mand–Raigarh Basin has undergone a major change when regional exploration and large scale mapping was carried out over a large part of the basin by Chakraborti et al. (2002). On the basis of lithological attributes, the total sedimentary package of the basin has been recategorized into Talchir, Barakar, Barren Measures, Raniganj, and Kamthi formations.

In the Mand Basin, Gondwana sediments are juxtaposed with quartzites of the Chandrapur Group (Chhattisgarh Supergroup) in the southwest, and metamorphic rocks of Raigarh–Sundargarh schist belt in the northwest. The contact between the Gondwana strata and the metamorphics is faulted in nature. The general stratigraphic succession in the Mand–Raigarh Coalfield is shown in table 1.

Table 1 Generalized lithostratigraphy of the Mand–Raigarh Coalfield, Chhattisgarh (after Chakraborti et al. 2002).
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3 Materials and methods

The samples for the present study were collected from borecore MBKW-3, located in the exploration blocks of Barpali–Karmitikra, in the northwestern part of the Mand Basin (figures 2 and 3). A total of 83 samples of varied lithofacies, comprising mudstones, silty shales, shales, coaly shales and coal horizons from the borecore MBKW-3 (41.95–640.00 m depth) were processed for spore-pollen study. Only 75 samples have yielded rich and diverse palynotaxa. For palynological preparations, 50 gm of sediments were crushed and treated with 40% hydrofluoric acid for 3–4 days to remove silica. This was followed by treatment with nitric acid for 5 days to digest the organic matter. The residue was treated with 10% potassium hydroxide to release the humus. After thorough wash with distilled water, the residues were mixed with polyvinyl alcohol, smeared over cover glasses and kept to dry at room temperature. After complete drying, the cover glasses were fixed to slides with Canada balsam. Five slides were prepared for each sample. Microscopic observation (Olympus BX61model) was done at species level for microfloral analysis.

Figure 3
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Lithologic column of borehole MBKW-3, Mand–Raigarh Coalfield showing individual lithofacies, and location of productive samples in the succession.

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4 Palynological observations

The preservation of the palynomorphs is variable within the samples. Recovery is frequently very good, can be low to moderate. Specimens are yellowish–dark brown in colour, distorted, and broken to fairly well-preserved (Plates I and II; table 2). The relative occurrences of the taxa vary from rare (<1%), common (1–5%), fair (5–10%) to an abundance (11–25%) and dominant (>25%) in an assemblage, and based on changes in the palynomorphs of characteristic genera and species (tables 3 and 4), three palynoassemblage zones were identified in the 598.05 m thick strata of Permian successions of borecore MBKW-3. The species identified herein are listed in table 5.

PLATE I
figure 4

1. Lacinitriletes badamensis Venkatachala and Kar emend. Tiwari and Singh (1981). 2. Microbaculispora barakarensis Tiwari emend. Tiwari and Singh (1981). 3. Microbaculispora indica Tiwari emend. Tiwari and Singh (1981). 4. Didecitriletes horridus Venkatachala and Kar emend. Tiwari and Singh (1981). 5. Microfoveolatispora foveolata Tiwari emend. Tiwari and Singh (1981). 6. Acantotriletes filiformis (Balme and Hennelly) Tiwari (1965). 7. Gondisporites raniganjensis Bharadwaj (1962). 8. Lundbladispora warti Tiwari and Rana (1981). 9. Lundbladispora raniganjensis Tiwari and Rana (1981). 10. Lundbladispora willmotti Balme emend. Playford (1965). 11. Gondisporites sp. 12. Goubinispora morondavensis (Goubin) Tiwari and Rana (1981). 13. Goubinispora indica Tiwari and Rana (1981). 14. Parasaccites obscures Tiwari (1965). 15. Potonieisporites sp. 16. Potonieisporites neglectus Potonie and Lele (1961). 17. Striomonosaccites ovatus Bharadwaj (1962). 18. Faunipollenites varius Bharadwaj emend. Tiwari et al. (1989). 19. Faunipollenites singrauliensis Sinha (1972). 20. Striatites levistriatus Bharadwaj and Tiwari (1977). 21. Striatopodocarpites magnificus Bharadwaj and Tiwari (1964). 22. Striatopodocarpites antiques (Leschik) Soritschewa and Sedova (1954).

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PLATE II
figure 5

1. Crescentipollenites fuscus Bharadwaj, Tiwari and Kar (1974). 2. Verticipollenites gibbosus Bharadwaj (1962). 3. Arcuatipollenites asansoliensis (Tiwari and Rana) Tiwari and Vijaya (1995). 4. Arcuatipollenites pellucidus (Goubin) Tiwari and Vijaya (1995). 5. Arcuatipollenites paliensis (Tiwari and Ram-Awatar) Tiwari and Viajaya (1995). 6. Arcuatipollenites tethysensis (Vijaya and Tiwari) Tiwari and Vijaya (1995). 7. Scheuringipollenites tentulus Tiwari ememd. Tiwari (1973). 8. Scheuringipollenites maximus (Hart) Tiwari (1973). 9. Scheuringipollenites barakarensis Tiwari ememd. Tiwari (1973). 10. Alisporites ovalis Kumar (1973). 11. Alisporites plicatus Kar et al. (1972). 12. Falcisporites zapfei Leschick emend. Klaus (1963). 13. Klausipollenites schaubergeri Potonie and Klaus emend. Jansonius (1962). 14 and 15. Guttulapollenites hannonicus Goubin (1965). 16. Guttulapollenites sp. 17. Dicappipollenites crassus (Sinha) Tiwari and Vijaya (1995). 18. Cf. Maculatisporites sp. 19. Lueckisporites virkkiae Potonie and Klaus in Leschic (1956). 20 and 21. Qudrisporites horridus Hennelly emend. Potonie and Lele (1961).

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Table 2 Details of lithofacies and spore-pollen content and composition of dispersed organic matter at different depths in Borehole MBKW-3, Mand–Raigarh Coalfield.
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Table 3 Composition of palynoassemblages identified in borehole MBKW-3, Mand–Raigarh Coalfield, Chhattisgarh.
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Table 4 Palynologic dating in Borehole MBKW-3 (41.95–640.00 m depth), Mand–Raigarh Coalfield.
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Table 5 List of the palynomorph taxa identified in present study, arranged under probable plant groups.
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4.1 Palynoassemblage-I; Depth 41.95–98.35 m (table 4)

Dominant: Striatopodocarpites

Subdominant: Gondisporites

The assemblage recovered from the shales, carbonaceous shales, and coal in 242.94-m thick strata is characterised by a dominance of Striatopodocarpites and Gondisporites,along with fair occurrence of Faunipollenites spp., Guttulapollenites hannonicus, Arcuatipollenitess spp., Lundbladispora micorconata, Goubinispora indica, Alisporites opii and Klausipollenites spp. Some palynomorphs, such as Microbaculispora, Microfoveolatispora, Crescentipollenites, Weylandites, Distriatites, Didecitriletes and Scheuringipollenites are rare in occurrence. The FADs of Arcuatipollenites pellucidus, Guttulapollenites hannonicus, Lundbladispora microconata and Klausipollenitessp. at 41.95 m are significant, because they represent the terminal phase of Late Permian sedimentation on the Indian peninsula (Vijaya and Tiwari 1987; Tiwari and Tripathi 1992).

This composition of palynoassemblage-1 is very similar to the known palynoflora from the upper part of the Raniganj Formation in Damodar Basin in having an abundance of Gondisporites, Striatopodocarpites, and Faunipollenites. Hence, palynoassemblage-I is placed in the Gondisporites raniganjensisassemblage zone of Tiwari and Tripathi (1992), dated as Late Permian in age.

Palynodating: Late Permian (Raniganj Formation).

4.2 Palynoassemblage-II; Depth 135.55–284.89 m (table 4)

Dominance: Faunipollenites

Subdominance: Scheuringipollenites

Palynomorphs were recovered from mudstones, micaceous siltstones, shales, coaly shales and coal horizons in 149.34-m thick strata of the Barakar Formation. The striate bisaccate pollen grain Faunipollenites was dominant in the assemblage, while nonstriate bisaccate pollen, e.g., Scheuringipollenites was subdominant in this assemblage zone. Moderate to low occurrence of striate bisaccate palynomorphs like Verticipollenites, Rhizomaspora, Dicappipollenites, Platysaccus, Striasulcites, Tiwariasporis, Weylandites, Parasaccites, Striamonosaccitessp., Guttulapollenitessp., Barakaritessp., Potonieisporitessp., and nonstriate bisaccates is also recorded. Trilete spores are infrequent but are represented by Microfeveolatispora, Microbaculispora, Brevitriletes and Horriditriletes.

Palynoassemblage-II correlates with the generic acme-zone of the Faunipollenites–Scheuringipollenites zone in the Barakar Formation of the Damodar Basin which is late Early Permian in age (Tiwari and Tripathi 1988, 1992).

Palynodating: late Early Permian (Upper Barakar Formation).

4.3 Palynoassemblage-III; Depth 287.15–640.00 m (table 4)

Dominant: Scheuringipollenites Subdominant: Faunipollenites

The siltstones, shales, coaly shales, and coal horizons of the Barakar Formation yielded abundant and qualitatively diversified spore-pollen assemblages. Nonstriate bisaccate pollen taxon Scheuringipollenites was most abundant, followed by Faunipollenitesspp., Striatopodocarpitesand Horriditriletespalynotaxa recorded between the depths 287.15–337.72 m. Less common monosaccate taxa include Parasaccitesspp. Other stratigraphically significant taxa in this assemblage are Microbaculispora indica, Micorbaculispora tentula, Microfoveolatispora foeveolata, Verticipollenitessp., Tiwariasporis gondwanensis, Rizomaspora indica, Crescentipollenitessp., and Weylanditessp.

The spore/pollen composition of palynoassemblage-III correlates with the Scheuringipollenites barakarensis palynozone of Barakar Formation, Damodar Basin, which is of Early Permian age (Tiwari and Tripathi 1988, 1992).

Strata between 358.55 and 640.00 m depths, which include shales, silty shales, siltstones, coaly shales, and coal, had poor spore and pollen yields (especially, Scheuringipollenites and radial monosaccates). Macerations contained an abundance of black woody splinters, plant tissues, and amorphous matter.

Palynodating: Late Early Permian (Lower Barakar Formation).

5 Discussion

The 598.05-m thick interval of Barakar Formation strata encountered in Borecore MBKW-3, Barpali-Karmitikra block, Mand–Raigarh Coalfield was investigated palynologically. In this litho-succession, three palynozones were identified based upon the dominance, and sub dominance of palynotaxa, stratigraphic importance of key taxa, and their relative occurrence along with other associated significant species. Based on these palynozones, the biostratigraphic status, age and phytogeographical provincialisms of the palynoflora are discussed (table 6).

Table 6 Distribution of stratigraphically significant and geographically restricted palynotaxa during Late Permian time within the Guttulapollenites showing palaeophytogeograhic province in the central part of Gondwana.
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In the younger part (41.95–98.35 m) of the borecore, abundant striate bisaccate pollen taxa with zonate spores, such as Gondisporites(79.10–98.35 m depth) are common .These elements indicate a younger age for this part of the borecore than that of the Barakar Formation. The introduction of Arcuatipollenites pellucidus, A. ovatus, Guttulapollenites hannonicus, and Lundbladispora microconataat 41.95, 45.90, 98.35 m, and Alisporites opii, Klausipollenitessp., and Goubinispora indica at 41.95 m, indicate the closing phase of Permian, as presence of these key species mark a transition from Permian to the Lower Triassic.

The strata at 135.55–284.89 m had yielded very low spore and pollen grain and abundant woody and amorphous organic matters (table 2). Variants of striate and nonstriate bisaccate pollen taxa within this 149.34 m are placed in the Faunipollenites and Scheuringipollenitespalynozones. This association correlates with the Barakar Formation of the Damodar Basin, which is late Early Permian in age (Tiwari and Tripathi 1992).

The lower part of the core between 287.15 and 640.00 m yielded predominantly nonstriate bisaccate Scheuringipollenites and striate bisaccate Faunipollenites. Based on the abundance of these pollen taxa this interval is placed in the Scheuringipollenites–Faunipollenites palynozone and is comparable with the Lower Barakar Formation of Damodar Basin of late Early Permian age (Tiwari and Tripathi 1992). In general, the specimens are poorly preserved with an abundance of vegetal matter and dark broken wood debris (table 2).

The cyclic sequence of siltstones, mudstones, shales, coaly shales, and coal facies of the Barakar Formation (41.95–640.00 m) is not consistently productive palynologically. Previously, this lithosuccession was considered to be Early Permian in age (GSI, table 1 and figure 2).

The infrequent occurrence of Scheuringipollenites, Faunipollenites, Striatopodocarpites and radial monosaccates, along with abundance of plant remains and amorphous matter between 358.55 and 640.00 m is indicative of the Barakar Formation.

6 Phytogeographic provincialism

It is well documented that the palynotaxa Guttulapollenites is known from most, if not all, of the Gondwana continents (India, Australia, Madagascar, Africa, Antarctica and Salt Range). In the Assemblage Zone-I (Gondisporites ranigangensis), a large number of striate bisaccate and taeniate pollen were recorded in association with Guttulapollenites. This genus was first reported by Goubin (1965), and later emended by Venkatachala et al. (1967). To date, only two species are known; Guttulapollenites hannonicus and G. gondwanensis were recorded by Goubin (1965). In addition, Guttulapollenites is known from all the Gondwanan continents (table 6, figure 4).

Figure 4
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Distribution of stratigraphically significant and geographically restricted palynotaxa during Late Permian time in the Guttulapollenites palaeophytogeographic province (after Jha 2006).

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Outside former Gondwanaland,Guttulapollenites has also been recorded from the Triassic sediments in the Netherlands by Visscher (1966). The occurrence of Guttulapollenitesin the Netherlands may be due to migration along the southern Tethys coast into Europe (Bharadwaj 1976).

It is generally believed that two phytogeographic provinces: an Africa/West Gondwanaland and an Australia/East Gondwanaland existed (Truswell 1980). Within the accepted model of the supercontinent Gondwanaland, it is opined that it contained two segments; the west Gondwanaland province that includes Africa and South America and the east Gondwanaland province consisting Antractica, Australia and India. Recently, Jha (2006) suggested based on palynology that there were three palaeophytogeographcal provinces during Late Permian period. They are the East Gondwana Floral Province (Australia and part of Antractica, N–E part of India, viz., Arunachal Pradesh); West Gondwana Floral Province (South America and western half of Africa); and Central Gondwana Floral Province (Antarctica, southern part of Africa, Madagascar, India and Pakistan (figure 4)).

During the Late Permian time, India and southeastern Africa (Kenya, Tanzania, Zimbabwe and South Africa) were located in the same latitudinal position, approximately 40 ∘–60 ∘ south of the equator (Bharadwaj 1976). It is possible that during Permian time both continents (India and Africa) were connected, which has been suggested by an earlier study (Medlicot and Blanford 1879). On the Gondwana supercontinent Guttulapollenites is the only taxon that has been recorded from India, Pakistan (Salt Range), Malagasy, Africa and Antarctica constituting a distinct phytogeographic province. The occurrence of abundant Guttulapollenites from the Mand–Raigarh Coalfield indicates that same phytogeographic province existed in India and South Africa.

7 Conclusions

  • Three palynoassemblages have been identified from borecore MBKW-3 in the Mand–Raigarh Coalfield and are indicative of Early to Late Permian age.

  • The Raniganj Formation was intersected between 41.95 and 98.35 m depth. The Lower Barakar and Upper Barakar Formation were identified between 135.55–284.89 and 287.15–640 m, respectively.

  • The occurrence of abundant Guttulapollenites in the assemblages, attests to the existence of phytogeographic provincialism in the Gondwana supercontinent.