1 Introduction

South Karanpura Coalfield is located in the western part of the Damodar valley, situated between latitudes 23 ∘38’–23∘45’N and longitudes 85∘05’–85∘28’E in the Ramgarh district of Jharkhand state. It covers an area of 194 km2 (figure 1). Palynological work has been done in this coalfield, namely by Bhattacharya et al. (1957); Khan (1962, 1964); Bharadwaj and Tiwari (1968); Bharadwaj and Anand Prakash (1972); Lele and Chandra (1977); Lele and Kulkarni (1969); Bharadwaj and Tripathi (1978); Bharadwaj and Dwivdi (1981) and Bandyopadhyay (1984). Most of the work is on the coal bearing Barakar Formation.

Figure 1
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(a) Map showing coalfields in extrapeninsular India; (b) some coalfields in Damodar Koel River Valley, and (c) geologicalmap of South Karanpura Coalfield showing location of borehole SKB-1 (after Raja Rao 1987).

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Binja Block of this coalfield is situated in the southwestern part of the South Karanpura Coalfield where the rocks of the Barren Measures and Raniganj formations are exposed on the surface (figure 1). The main objective of the present analysis is to determine the palynological dating of the borecore SKB-1 at Binja Block, South Karanpura Coalfield. The taphonomic study on the same material is also attempted to understand the depositional environment.

2 General geology

This east–west trending elongated coalfield, occurring within Damodar–Koel River Valley Basins is bounded by metamorphic basement rocks to the north and south. The rocks of the Talchir Formation are mostly exposed in patches in lenticular fashion in the fringe areas along the northern, southern, and eastern margins of the coalfield. A continuous succession from Talchir to Raniganj formations is preserved in this basin. Major parts of this basin are occupied by Barakar Formation, which lies unconformably over the basement in large areas. To the east and northeast, Barakar Formation conformably overlies the older rocks whereas in the southern parts, it is faulted against the basement. In totality, this coalfield contains 42 regional Barakar coal seams within a thick pile of lower coal measure, though not all the seams are developed in any single block. The outcrops of Barren Measures and Raniganj are exposed at the central part (Raja Rao 1987).

Lamprophyre and dolerite dykes and sills are reported to occur at different stratigraphic levels within the Barakar, Barren Measures, and Raniganj formations.

Based on available literatures and unpublished Progress Reports of GSI, the generalized stratigraphic succession in the South Karanpura Coalfield (modified after Raja Rao 1987) is given in table 1.

Table 1 General stratigraphic succession in South Karanpura Coalfield (modified after Raja Rao 1987).
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3 Materials and methods

The study is based on the material from bore core SKB-1, total depth in the borecore is approximately 538.00 m (13.80–552.00 m). The borecore intersected through Raniganj, Barren Measures, and Barakar formations. The formational contact–Raniganj/Barren Measures is marked at 37.70 m and Barren Measures/Barakar at 429.15 m (table 2 and figure 2). In all 73 rock samples that were collected for palynological study, 42 samples yielded palynomorphs. Sediments are processed by standard maceration technique. For each sample, 50 gm of sediments were taken and crushed, were first treated with 40% hydrofluoric acid for 3–4 days to remove silica material, and then followed by nitric acid for 5 days for digestion of humic matter. Then they were treated with 10% potassium hydroxide to release the humus. The maceral were mounted in polyvinyl alcohol and Canada balsam. Five slides from each sample were prepared and pollen-spores were observed under the transmitted light microscope.

Figure 2
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Lithocolumn in borehole SKB-1, to show different levels of occurrence of palynomorphs assemblage zone identified and their stratigraphic status.

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Table 2 Lithostratigraphic succession in the borecore SKB-1.
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4 Palynological observation

Borehole SKB-1 (13.80–552.00 m depth) from Binja Block of South Karanpura Coalfield has been worked out for the dating of the intersected strata. The samples comprise diverse lithofacies and recovery of spores and pollen is average and varies from poor to fair (Plates I and II). Besides, an abundance of wood shreds, plant tissues and organic matter were also observed. For details, see figure 2.

Plate I
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1. Cyclogranisporites triletes Kar (1970); 2. Horriditriletes curvibaculus Bharadwaj and Salujha (1964); 3. Microbaculispora tentula Tiwari (1965); 4. Microfoveolatispora foveolata Tiwari (1965); 5. Gondisporites reticulates Tiwari and Ram-Awatar (1988); 6. Indotriradites korbaensis Tiwari (1964); 7. Gondisporites sp.; 8. Parasaccites obscurus Tiwari (1965); 9. Barakarites crassus Bharadwaj and Tiwari (1964); 10. Striamonosaccites ovatus Bharadwaj (1962); 11. Distriasulcites ovatus Venkatachala and Kar (1968); 12. Densipollenites magnicorpus Tiwari and Rana (1981); 13. Densipollenites invisus Bharadwaj and Salujha (1964); 14. Densipollenites densus Bharadwaj and Srivastava (1969); 15. Goubinispora sp.; 16.Goubinispora morondavensis (Goubin) and Rana (1981); 17. Guttulapollenites gondwanensis Goubin (1965); 18. Guttulapollenites hannonicus Goubin (1965); 19. Playfordiaspora cancellosa Maheshwari and Banerji emend. Vijaya (1995); 20. Kamthisaccites kamthiensis Srivastava and Jha (1986).

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Plate II
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1. Faunipollenites varius Bharadwaj (1962); 2. Striatites varius Kar (1968); 3. Striatopodocarpites magnificus Bharadwaj and Salujha (1964); 4. Verticipollenites gibbosus Bharadwaj (1962); 5. Crescentipollenites fuscus (Bharadwaj) Bharadwaj, Tiwari and Kar (1974); 6. Crescentipollenites sp.; 7. Platysaccus densicorpus Anand-Prakash (1972); 8. Rhizamospora triassica Tiwari and Rana (1981); 9. Distriatites bilateris Bharadwaj (1962); 10. Arcuatipollenites pellucidus (Goubin) Tiwari and Vijaya (1995); 11. Arcuatipollenites sp.; 12. Arcuatipollenites damudicus (Tiwari and Rana) Tiwari and Vijaya (1995); 13. Scheuringipollenites tentulus Tiwari (1973); 14. Scheuringipollenites barakarensis Tiwari (1973); 15. Scheuringipollenites maximus Tiwari (1973); 16. Krempipollenites sp.; 17. Alisporites ovalis Kumar (1973); 18. Alisporites sp.; 19. Satsangisaccites nidpurensis Bharadwaj and Srivastava 1969; 20. Krempipollenites indicus Tiwari and Vijaya (1995).

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The overall composition of spore-pollen, i.e., diversity in their relative abundances along with the presence of significant age marker taxa (tables 3 and 4) at different depth intervals in the borehole SKB-1 are discussed here. Here two palynoassemblages are identified (figure 2 and table 3).

Table 3 Palynodating in Borehole SKB-1 (13.80–552.00 m depth), South Karanpura Coalfield.
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Table 4 List of spore–pollen species identified in Borehole SKB-1, South Karanpura Coalfield.
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4.1 Palynoassemblage-I

Depth: 552.00–53.20 m; carbonaceous shales, micaceous shales, mudstones, fine-to-medium grained sandstones with charcoal, coaly shales, and coals (figure 2 and table 3).

In the strata between 53.20 and 552.00 m depth in borehole SKB-1 the assemblage contains dominance of species of Striatopodocarpites followed by Crescentipollenites, Faunipollenites and Scheuringipollenites genera. Characteristic age marker species recovered in this assemblage are Gondisporites raniganjensis, G. reticulates, Guttulapollenites hannonicus, Distriomonosaccites ovalis, Verticipollenites oblongus and Distriatites bilateris. Other associated taxa are Microbaculispora barakarensis, Microfoveolatispora foveolata, Cyclogranisporites sp., Cyclobaculisporites sp., Didecitriletes horridus, Horridirtiletes curvibaculosus, Tiwarisporis gondwanensis, Rhizomaspora indica, R. monosulcata, Faunipollenites varius, Platysaccus sp., Striasulcites tectus, Bharadwajiapollis striatus, Schizopollis sp., Vestigisporites sp., Striomonosaccites ovatus, Densipollenites indicus, D. invisus, Weylandities indicus and Verticipollenites oblongus.

Remarks: By the significant quantitative presentation of Gondisporites raniganjensis, G. reticulatus in the population of striate bisaccate pollen taxa, this assemblage is comparable to the Gondisporites raniganjensis, established in the Raniganj Formation of the Damodar Basin (Tiwari and Tripathi 1992) which is dated as Late Permian in age.

4.1.1 Palynoassemblage–II

Depth: 39.50–13.80 m; siltstones, micaceous shales, and mudstones (figure 2 and table 3).

Palynoassemblage recovered in the interval of 13.80–39.50 m depth in borehole SKB-1 shows dominance of striated bisaccate pollen Striatopodocarpites spp. with increased frequency of enveloping monosaccate pollen Densipollenites (D. invisus and D. magnicorpus). The palynoassemblage is much diversified in having abundant striate bisaccate pollen – Faunipollenites varius, Striatites sp., Verticipollenites oblongus, Distriatites bilateris, Crescentipollenites fuscus, C. gondwanensis, Primuspollenites sp. and Sahnites sp. The trilete spores are very rare and represented by Leiotriletes sp. and Cyclobaculisporites indicus. FADs of Arcuatipollenites pellucidus, Krempipollenites sp., Falcisporites sp., and Alisporites sp. are recorded in this interval.

Remarks: Palynoassemblage-II, compares with the Densipollenites magnicorpus palynoassemblage of Tiwari and Tripathi (1992) in having relatively fair occurrence of D. magnicorpus and this composition suggests the Latest Permian in age. The FADs of Arcuatipollenites pellucidus, Playfordiaspora cancellosa, Krempipollenites indicus, Falcisporites sp., and Alisporites sp .observed at 13.80, 14.90 and 39.50 m depths mark the transition from Permian to Triassic period.

5 Discussion

The recovery of palynomorphs in approximately 538.00 m (13.80–552.00 m) thick Gondwana strata is observed with both palynomorphs and palynodebris in equal proportion (figure 2). The palynodebris consists of lumps of organic matter and plant tissues that includes dark to brown woody splinters, amorphous matter (figure 2). This infers high energy flow regime during the deposition of the present studied material. Lithologically the formation intersected in the borecore are Raniganj, Barren Measures, and Barakar formations The formational contacts–Raniganj and Barren Measures formations is delimited at 37.70 m depth, and Barren Measures and Barakar formations at 429.15 m depth (table 2). The palynological investigation reveals presence of two palynoassemblages. The vertical placement of the two palynoassamblages (I–II) identified, is based upon the stratigraphical importance of the age marker taxa and their relative occurrences along with other associated significant marker species (tables 3, 5, 6, and figure 3). On the basis of the standard palynozonation schemes established for the Permian successions in India (Tiwari and Tripathi 1992), the identified palynoassemblages are used to date the studied litho-succession in borehole SKB-1.

Figure 3
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Distribution of important palynotaxa in the borecore SKB-1, South Karanpura Coalfield.

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Table 5 Relative occurrence of spore-pollen taxa in the Raniganj, Barren Measures and Barakar formations in the borehole SKB-1, South Karanpura Coalfield; R: Rare (< 1%), C: Common (2–5%), F: Fair (5–10%), A: Abundant (11–25%) and D: Dominant (> 25%).
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Table 6 Palynocomposition of palynoassemblages identified in borehole SKB-1, South Karanpura Coalfield.
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The palynoassemblage-I recorded in strata between 552.00 and 53.20 m depth in borehole is lithologically delimited as Raniganj, Barren Measures, and Barakar formations, contain a prolific palynoassemblage of striate bisaccate pollen taxa with fair presence of Gondisporites raniganjensis, G. reticulates and Densipollenites magnicorpus at 192.25 and 270.80 m depth and FADs of Guttulapollenites spp. at 415.90, 504.70, and 526.70 m; Goubinospora sp. at 415.90 m; Alisporites ovalis, and Arcuatipollenites sp. are at 552.00 m depth. This kind of composition correlates with Gondisporites raniganjensis palynoassemblage of Raniganj Formation, Damodar Basin which was considered Late Permian by Tiwari and Tripathi (1992).

In palynoassemblage-II, the significant record of enveloping monosaccate pollen Densipollenites and striate bisaccate pollen Stiatopodocarpites and Crescentipollenites, between 13.80 and 39.50 m depth, corroborate this part with the Raniganj Formation of Latest Permian age (Tiwari and Tripathi 1992). FADs of Early Triassic palynomorphs, viz., Arcuatipollenites pellucidus, Playfordiaspora cancellosa, Krempipollenites indicus, Alisporites sp., and Falcisporites sp. mark these sediments to span Permian to Early Triassic transition.

6 Conclusion

The palynological study done in approximately 538.00 m thick Gondwana strata in the Borehole SKB-1, South Karanpura Coalfield revealed that:

  • The strata between 552.00 and 53.20 m depths are lithologically identified as Barren Measures and Barakar formations. The palynoassemblage here contain an abundance of Striatopodocarpites spp., Crescentipollenites sp.,Faunipollenites varius, Densipollenites magnicorpus, Gondipollenites raniganjensis, and Scheuringipollenites spp. The FAD of Guttulapollenites hannonicus at 504.00, 526.70 m are observed. This composition compares well with the Raniganj Formation of Late Permian in age.

  • Lithological strata between 39.50 and 13.80 m depths are of Raniganj Formation. Palynological dating also indicates Latest Permian age by the presence of stratigraphic age marker species Densipollenites magnicorpus. The occurrence of Early Triassic palynomorphs likeArcuatipollenites pellucidus, Playfordiaspora cancellosa, Krempipollenites sp., Falcisporites sp. and Alisporites sp., suggest that these strata mark the transition from Permian into Lower Triassic period.

  • The FAD of Arcuatipollenites pellucidus at 13.00, 39.50, 552.00 m; Playfordiaspora cancellosa at 13.00, 39.50 m; Gondisporites raniganjensis, G. reticulates, and Densipollenites magnicorpus at 13.00, 43.00, 192.25, and 270.80 m and Guttulapollenites spp. at 415.90, 504.70 and 526.70 m; and Goubinispora sp. at 415.90 m depth records the Late Permian (Raniganj Formation) age for the complete succession of the borehole SKB-1.

  • The complete strata of borecore SKB-1 is dated as Late Permian in age.