1 Introduction

The sedimentary sequences comprising the Permian and Triassic deposits in the Singrauli Gondwana Basin are intersected in number of borecores, and these deposits are widely scattered (figures 1, 2). Previous spores-pollen studies carried out in the subsurface deposits in this basin (Bharadwaj and Sinha 1969a, b; Sinha 1972; Tiwari and Srivastava 1984; Tripathi et al. 2005) have documented the existence of Upper Permian and Upper Triassic strata punctuated within many hiatus levels.

Figure 1
figure 1

Map of Singrauli Gondwana Basin to show the Majhauli block, and the location of three borehols – SMJS-2, 3, and SMBS-1.

Full size image
Figure 2
figure 2

Part of Singrauli Gondwana Basin to show the Mahuli–Mahersop block, and the location of two boreholes SSM-1 and SSM-2.

Full size image

Present study includes the dating of subsurface strata in boreholes SMJS-2, 3, and SMBS-1, in the Singrauli main sub-basin. Beside this, the spores-pollen data from the Moher sub-basin (boreholes SSM-1 and 2 in Tripathi et al. 2005) has also been included herein to built-up the palynostratigraphy in the Singrauli Gondwana Basin. The spores-pollen studies done in these five borecores are interpreted for age correlation of the sedimentary sequences from that earliest Permian through Late Triassic.

2 Geology

The Singrauli Gondwana Basin (figures 1, 2) is the northernmost part of the Son-Mahanadi master Gondwana Basin, and is situated in the drainage area of Son and Rihand rivers. In the heart of peninsular India, it occupies the north-western zone between NW–SE trending rift zone of Son/Mahanadi Valley Basin and east–west trending Tatapani–Koel–Damodar Basin. As the Gondwana sediments in Singrauli Gondwana Basin were deposited through fluvial network, it contains a predominance of sandstone dominated cycle. This character is typical of the Son Valley Basin belt (Mukhopadhyay and Mukhopadhyay 1999).

The Singrauli Gondwana Basin has been considered to be comprised of two tectono-sedimentary sub-basins: (i) the Moher sub-basin in the northeastern flank and (ii) the Singrauli main sub-basin to the west (figures 1, 2). Demarcation between these two sub-basins is not possible in the field, as all the formations in the Lower Gondwana are continuously exposed (without any structural break) within these two so called sub-basins. Only major difference between the two is in the coal resource potentiality and its developmental pattern. The Moher sub-basin contains more coal resources as compared to the main sub-basin.

In general, the Singrauli main sub-basin of about 1900 km2, is dissected into flat-topped plateau of Upper Gondwana rocks. Lower Gondwana rocks are exposed particularly in the east and central parts of the main sub-basin, whereas the outcrops of Upper Gondwana occurred predominantly towards the western and southern portions. The Gondwana rocks are juxtaposed against the metamorphics of Mahakoshal Group in the north along mostly an east–west trending shear zone.

Majhauli (S) block, under present study, forms the eastern part of the Singrauli main sub-basin (figure 1). During sub-surface exploration, a sedimentary sequence from Talchir to Raniganj formations has been encountered. Strata belonging to Barren Measures and Raniganj formations also occur as outcrops here, whereas of Barakar and Talchir formations are encountered as subsurface strata.

In Mahuli-Mahersop block of the Moher sub-basin (figure 2), the Parsora Formation is intersected in two boreholes – SSM-1 and SSM-2, and that is mainly represented by medium-to-coarse grained sandstone facies. The most significant finding within the Parsora Formation is the occurrence of palaeosol bed in borehole SSM-2 at 509.00 m (figure 4).

Based on the surface and sub-surface data acquired so far, the generalized stratigraphic sequences developed in the Singrauli Gondwana Basin are given in table 1.

Table 1
Full size table

3 Materials

The materials for present spores-pollen study includes the subsurface sediments explored in the two sub-basins of that Singrauli Gondwana Basin (figures 1, 2). Details about the facies in each borehole are given in figures 3, 4.

  1. (i)

    Boreholes SSM-1 and SSM-2, Moher sub-basin (in Tripathi et al. 2005).

  2. (ii)

    Boreholes SMJS-2, SMJS-3, and SMBS-1, Singrauli main sub-basin (present study).

Figure 3
figure 3

Sedimentary sequences in boreholes – SMJS-2, 3 and SMBS-1 (Majhauli block), Singrauli Gondwana Basin, U.P. and Chattisgarh.

Full size image
Figure 4
figure 4

Sedimentary sequences in boreholes – SSM-1 and SSM-2 (Mahuli–Mahersop block), Singrauli Gondwana Basin, U.P. and Chattisgarh.

Full size image

The rock samples are processed with the standard method using the chemicals – HF and HCL, for the recovery of spores-pollen. The slides prepared for microscopic observations are stored in the repository of the Museum of Birbal Sahni Institute of Palaeobotany, Lucknow.

4 Palynological observations

The sedimentary successions encounterd in the three boreholes SMJS-2 (depth 5.70–631.50 m), SMJS-3 (depth 15.50–319.50 m) and SMBS-1 (depth 12.00–681.50 m; figures 3, 4) are analysed for their spore-pollen contents. In general, well preserved, unaltered organic matter, including the spores-pollen are recovered (figures 5, 6), but at different depth intervals, the strata have yielded mainly the amorphous plant matter.

Figure 5
figure 5

Characteristic spores-pollen species identified in the Permian succession intersected in these boreholes – SMJS-2, SMJS-3 and SMBS-1 from study area. A. Jayantisporites pseudozonatus Lele and Makada (1972), B. Lacinitriletes badamensis Venkatachala and Kar emend. Tiwari and Singh (1986), C. Jayantisporites conatus Lele and Makada (1972), D. Jayantisporites indicus Lele and Makada (1972), E. Callumispora barakarensis Bharadwaj and Srivastava (1969), F. Horriditriletes novus Tiwari (1965), G. Dentatispora gondwanensis Tiwari (1965), H. Cyclogranisporites gondwanensis Bharadwaj and Salujha (1964), I. Quadrisporites horridus Potonie and Lele (1961), J. Crucisaccites latisulcatus Lele and Maithy (1964), K. Crescentipollenites fuscus (Bharadwaj) Bharadwaj, Tiwari and Kar (1974), L. Circumstriatites talchirensis Lele and Makada (1972), M. Striatopodocarpites magnificus Bharadwaj and Salujha (1964), N. Striomonosaccites ovatus Bharadwaj (1962), O. Dicapipollenites nykaendensis (Hart) Tiwari and Vijaya (1995), P. Bharadwajiapollis striatus Kar (1969), Q. Faunipollenites perexiguus Bharadwaj and Salujha (1964), R. Verticipollenites gibbosus Bharadwaj (1962), S. Arcuatipollenites ovatus (Goubin) Tiwari and Vijaya (1995), T. Densipollenites invisus Bharadwaj and Salujha (1964), U. Potoniesporites sp., V. Sahnites jayantiensis (Lele and Makada) Tiwari and Singh (1984), W. Stellapollenite talchirensis Lele (1965), X. Densipollenites magnicorpus Tiwari and Rana (1981), Y. Plicatipollenites indicus Lele (1964), Z. Crucisaccites monoletus Srivastava (1970), AA. Plicatipollenites gondwanensis (Balme and Hennelly) Lele (1964), AB. Densipollenites indicus Bharadwaj (1962), AC. Goubinispora indica Tiwari and Rana (1981), AD. Parasaccites densicorpus Lele (1975).

Full size image
Figure 6
figure 6

Characteristic spores-pollen species identified in the Parsora Formation intersected in these boreholes – SSM-1, and SSM-2 from the study area. A. Carnisporites mesozoicus (Klaus) Mädler (1964), B. Camerozonosporites rudis (Leschik) Klaus (1960), C. Anapiculatisporites telephorus Pautsch (1958), D. Uvaesporites verrucosus Helby in de Jersey (1971), E. Dictyotosporites filosus Dettmann (1963), F. Clavatisporites hammenii (Herbst) de Jersey (1971), G. Lundbladispora warti Tiwari and Rana (1981), H. Polycingulatisporites crenulatus Playford and Dettmann (1965), I. Lundbladispora baculata Bharadwaj and Tiwari (1977), J. Carnisporites raniganjensis Tiwari and Rana (1980), K. Klukisporites variegates Couper (1958), L. Tigrisporites hallienis Klaus (1960), M. Circulisporites parvus de Jersey (1962), N. Tikisporites balmei Kumaran in Kumaran and Maheshwari (1980), O. Tethysispora playfordii Vijaya and Tiwari in Vijaya et al. (1988), P. Minutosaccus crenulatus Dolby and Balme (1976), Q. Cingutriletes sp cf. C. clavus (Balme) Dettmann (1963), R. Grebespora concentrica Jansonius (1962), S. Cadargasporites baculatus de Jersey and Paten (1964), T. Striatopodocarpites dubrajpurensis Tripathi et al. (1990), U. Kamthisaccites ringus Vijaya and Tripathi (2008), V. Playfordiaspora cancellosa (Maheshwari and Banerji) Vijaya (1995), W. Plicatisaccus badius Partsch (1971), X. Arcuatipollenites tethysensis (Vijaya and Tiwari) Tiwari and Vijaya (1995), Y. Arcuatipollenites ovatus (Goubin) Tiwari and Vijaya (1995).

Full size image

Based on the quantitative occurrences, and diversity of spores and pollen species (figures 7, 8), the assemblages identified within each borecore are described below. Besides, the data published earlier (Tripathi et al. 2005) has also been included here, to built-up the palynostratigraphy in the two blocks of Singrauli Gondwana Basin (figure 9). Furthermore, these assemblages are compared with the Palynozones already established for the Permian and Triassic sequences on Indian peninsula (see in Tripathi et al. 2005); and Australia (Helby et al. 1987; Backhouse 1993).

  1. (i)

    Borehole SMJS-2: depth 5.70–631.50 m; five assemblages

  2. (ii)

    Borehole SMJS-3: depth 15.50–319.10 m; three assemblages

  3. (iii)

    Borehole SMBS-1: depth 12.00–681.50 m; three assemblages

  4. (iv)

    Borehole SSM-1: depth 00.7–18.00 m; two assemblages

  5. (v)

    Borehole SSM-2: depth 00. 6–10.65 m; four assemblages

Figure 7
figure 7

Palynostratigraphy of the Permain succession in boreholes SMJS-2, 3, and SMBS-1 Majhauli block, Singrauli Gondwana Basin, Chattisgarh.

Full size image
Figure 8
figure 8

Relative occurrences of characteristic species in each assemblage identified in the Permian and Triassic sequences in the five boreholes from two blocks of Singrauli Gondwana Basin, U.P. and Chattisgarh.

Full size image
Figure 9
figure 9

A summary of the assemblages identified in the two blocks – (1) Majhauli, boreholes SMJS-1 and 2 (present study), and (2) Mahuli–Mahershop, boreholes SSM-1 and 2 (Tripathi et al. 2005) in Singrauli Gondwana Basin, U.P. and Chattisgarh.

Full size image

4.1 Talchir Formation

Borehole SMJS-2, depth 621.60–631.50 m, figure 3

Assemblage I:

Depth 625.50, 627.65, 631.50 m; figures 7, 8; fine grained greenish sandstones with specks of carbonaceous matter

Monosaccate pollen taxa (Parasaccites-Plicatipollenites) abundance associated with these spores Callumispora and Jayantisporites characterize this assemblage. The diversity among spores-pollen contents is shown by the occurrences of Potoieisporites magnus, Tuberisaccites tuberculatus, Crucisaccites sp., Microbaculispora tentula, Lacinitriletes minutus, Brevitriletes unicus, Circumstriatites spp., Faunipollenites sp., Striatopodocarpites sp.,Crescentipollenites fuscus, Tiwariasporis sp., Platysaccus sp., and the alete forms Tetraporina, Maculatasporites.

This assemblage is comparable with the Parasaccites korbaensis Palynozone in Tiwari and Tripathi (1992), which is dated earliest Permian in age (figure 7).

4.2 Barakar Formation

Boreholes SMJS-2, depth 251.66–621.60 m; SMJS-3, depth 286.40–319.10 m; and SMBS-1, depth 351.75–547.50 m; figure 3

Assemblage II:

Borehole SMJS-2, depth 512.80, 532.60, 583.50 m; figures 7, 8; fine-to-medium grained sandstones with alternate laminations of carbonaceous shales.

A much diversified spores-pollen assemblage is obtained in approximately 71.00 m thick strata. Here, an abundance of Parasaccites and Callumispora is associated with good frequency of Plicatipollenites, Circumstriatites. Further, these pollen taxa Striatopodocarpites, Faunipollenites, Diverisaccus and Crucisaccites are added along with a group of species. Rare occurrences Jayantisporites spp., Brevitriletes unicus, Imparitriletes korbaensis, Verrucosisporites donarii, Sahnites thomasi, Cuneatisporites sp., Potonieisporites spp., Tuberisaccites spp., and Cycadopites sp. are also observed. And, the vegetal matter do occur fairly along with hyaline mineral particles.

This assemblage is correlatable with the Crucisaccites monoletes Palynozone in Tiwari and Tripathi (1992), which suggests the presence of Karharbari Formation, a formational unit in the Lower Permian (figure 7).

Assemblage III:

Borehole SMJS-2, depths 428.00, 436.25, 452.50, 470.40 m; figures 7, 8; fine-to-coarse grained sandstones with specks of carbonaceous shales and coal intermittently.

At 470.40 and 452.50 m depth, the assemblage contains an admixture of these pollen taxa Scheuringipollenites, Faunipollenites, Striatopodocarpites and Parasaccites followed by a spore genus Callumispora. The relative occurrences of the four taxa along with these species – Indotriradites korbaensis, Microbaculispora indica, Microfoveolatispora foveolata, Sahnites thomasi, Cyclogranisporites gondwanensis, Verrucosisporites distinctus, Jayantisporites pseudozonatus, Horriditriletes spp., Rhizomaspora spp., Platysacus densus, Crescentipollenites spp., Densipollenites indicus, D. invisus, and Distriamonocolpites ovalis, have shown the gradual changes in the spores-pollen contents from that Karharbari Formation into the basalmost Barakar Formation. This composition is similar with that of Scheuringipollenites barakarensis Palynozone in Tiwari and Tripathi (1992), and that is dated Early Permian in age (figure 7).

Assemblage IV:

Boreholes SMJS-2 and 309.50; and SMBS-1, depth 270.00, 351.75 and 407.50; figures 7, 8; intercalated fine-to-coarse grained sandstones and carbonaceous shales

The assemblage recovered at these depths, has an abundance of striate bisaccate pollen taxa (Striatopodocarpites, Faunipollenites) along with Scheuringipollenites. At 260.80 m depth are present Densipollenites indicus, D. invisus and Crescentipollenites spp. in fair numbers. Other commonly found elements are Microbaculispora spp., Microfoveolatispora foveolata, Potonieitriradites barakarensis, Circumstriatites spp., Parasaccites spp., Platysaccus spp., Sahnites spp., Rhizomaspora spp. In very low counts are present Microfoveolatispora bokaroensis, Cyclobaculisporites minutus, Indotriradites sparsus, Lacinitriletes badamensis, Insignisporites barakarensis, Thymospora sp., Crucisaccites spp., Distriamonocolpites ovalis, Platysaccus ovatus, and Cuneatisporites spp.

At these depths 251.66, 256.80 and 260.80 m in borehole SMJ-2 and 287.50 m in borehole SMJS-3, admixture of striate bisaccate along with a monosaccate (Densipollenites indicus, D. densus) pollen taxa is noted. This shows a gradational change in the composition of assemblage, which suggests the transition from the proximity of the Barakar Formation into the Barren Measures Formation.

Other notable feature observed is the increased frequency of Parasaccites at 428.00 and 436.25 m depths in the studied strata from borehole SMJS-2, that might be in continuity from that with the older assemblage. Otherwise, this assemblage compares with Faunipollenites varius Palynozone in Tiwari and Tripathi (1992), that is dated younger part of the Early Permian (figures 7, 8).

4.3 Barren Measures Formation

Boreholes SMJS-2, depth 5.70–251.66   m; SMJS-3, depth 36.27–286.40 m; and SMBS-1, 132.60-351.75 m; figure 3

The sediments mainly comprise medium-to-coarse grained sandstone facies, which have low presentation of the spores-pollen. In borehole SMBS-1, the sediments are mainly black and hard silty shales. Hyaline to blackish amorphous granular mass of organic matter is present in high quantity. Yellowish-brown to grey, broken pieces of plant matter are commonly observed.

Assemblage V:

Boreholes SMJS-2, depth 144.20, 170.40, 187.20 m; SMJS-3, depth 147.15, 221.50, 227.90, 262.00, 277.00 m; and SMBS-1, depth 144.00, 216.60, 223.40, 258.70, 266.00 m; figures 7, 8; fine grained sandstones with shale, siltstones and greenish grey carbonaceous shales

The spores-pollen are recovered at the interval depths in the studied strata. Dominance of striate bisaccate pollen taxa along with fair occurrence of Densipollenites (D. indicus, D. invisus, and D. densus) is observed here. Other common elements are Crescentipollenites fuscus, C. bengalensis, Rhizomaspora singula, R. monosulcata, R. indica, Korbapollenites sp., Cuneatisporites spp., and Parasaccites korbaensis, P. diffusus. Besides, a group of species Insignisporites barakarensis, Verrucosisporites distinctus, Cyclobaculisporites sp., Horriditriletes novus, Microbaculisporites barakarensis, M. indica, Didecitriletes horridus, Barakarites spp., Dicapipollenites crassus, Guttulapollenites hannonicus, Distriatites bilaterais, Striomonosaccites sp., Crucisaccites latisulcatus,Tiwariasporis flavatus, Vittatina sp., Maculatasporites gondwananensis, and Cycadopites follicularis although counts very low, but their occurrences add much diversity to this assemblage.

The assemblage at 256.80 to 187.20 m depth in borehole SMJS-2, is suggestive of the transition from that Barakar Formation into the basalmost Barren Measures. This assemblage is correlatable with the Densipollenites indicus Palynozone in Tiwari and Tripathi (1992), and that is dated to be of early Late Permian in age (figure 7).

Here, the bisaccate pollen dominates the scenario. The unproductive strata in between 144.20–187.20 m in borehole SMJS-2; 147.15–277.00 m in borehole SMJS-3 and 144.00–266.00 m in borehole SMBS-1, is rich in elongated wood shreds and plant tissues in the Barren Measures Formation, which mainly comprises of medium-to-coarse grained sandstone facies (figure 3).

4.4 Raniganj Formation

Borehole SMJS-3, depth 00.00–36.27 m; and SMBS-1, depth 00.00–132.60, figure 3

Assemblage VI:

Boreholes SMJS-3, depth 15.50, 17.00, 20.20, 32.00, 35.50 m; SMBS-1, depth 25.65, 40.50, 45.00, 69.80 m; figures 7, 8; carbonaceous silty shales intercalated with medium-to-coarse grained sandstones

In between the above given depths, recovery of spores-pollen do occur at varied depths. Abundance of Densipollenites along with striate bisaccate pollen taxa – Striatopodocarpites and Faunipollenites is observed within the studied strata.

Relatively fair in quantitative occurrences are Rhizomaspora spp., Barakarites spp., Crescentipollenites spp., Distriatites spp., Weylandites spp. Rare occurrences of these elements – Horriditriletes curvibaculosus, H. novus, Cyclobaculisporites sp., Potonieitriradites barakarensis, Guttulapollenites hannonicus, Tiwariasporis flavatus, Striapollenites spp., Striomonosaccites spp., Gondisporites raniganjensis, Distriomonocolpites ovatus, Dicapipollenites crassus, Marsupipollenites spp., are observed herein. Presence of Trabeculosporites gopadensis, Arcuatipollenites pellucidus, Kamthisaccites kamthiensis and Goubinispora sp., along with fair number of Densipollenites magnicorpus suggests the comparision of this assemblage with Densipollenites magnicorpus Palynozone (Tiwari and Tripathi 1992), and that is dated latest Late Permian in age (figure 7).

4.5 Parsora Formation

Boreholes SSM-1, depth 00–718.00 m; SSM-2, depth 00–509.00 m; figure 4

In the studied sedimentary sequences of Parsora Formation, four assemblages (SSM-1/Assemblages A and B; SSM-2/Assemblages II, IIIa and IIIB in Tripathi et al. 2005) are identified.

Borehole SSM-2, depth 514.00–537.00 m; figures 4, 9; dark grey fine grained shaly sandstones with carbonaceous pieces

Assemblage II in borehole SSM-2, the oldest one, contain the dominance of Striatopodocarpites and Satsangisaccites. Other significant species in this assemblage are Arcuatipollenites spp., Ringosporites fossulatus, Verrucosisporites triassicus and Indotriradites mammilatus. This composition is correlatable with the Krempipollenites indicus palynozone in Tiwari and Tripathi (1992), that equates this part of the Parsora Formation with the Lower Triassic Panchet Formation in Damodar Basin (Vijaya and Tiwari 1987).

Borehole SSM-1, depth 716.00–696.90 m; Borehole SSM-2, depth 508.50–261.75 m; figures 4, 9; fine grained sandstones, intercalated with mudstones, shaly sandstone and carbonaceous shales.

In this part of the Parasora Formation, these two pollen taxa – Striatopodocarpites and Arcuatipollenites are in abundance with their changing relative counts. Besides, a diverse group of species Striatopodocarpites dubrajpurensis, Arcuatipollenites tethysensis, Infernopollenites claustratus, Staurosacites spp., Plicatisaccus badius, Enzonalasporites vigens, Tethysipora playfordii, Camerosporites verrucosus, Cadargasporites spp., Verrucosisporites morulae, Lycopodiacites rugulatus, Grandispora spinosa, Grebespora concentrica do occur, and this correlates the assemblage with the known Upper Triassic palynoflora in India (see in Tripathi et al. 2005).

In the younger part of Parsora Formation (borehole SSM-1 at 152.56 m; and borehole SSM-2 at 261.75 m), first occurrences of Callialasporites turbatus and Classopollis spp., are suggestive of the Rhaetic age (Helby et al. 1987; Tripathi 2000). From the above given data, it is for certain that the studied part of the Parsora Formation represents the Lower and Upper Triassic strata with a hiatus of Middle Triassic (figures 8, 9).

5 Discussion

The spores-pollen studies done in two blocks of the Singrauli Gondwana Basin (figures 1, 2), include five boreholes – SMJS-2/5.30–631.50 m and SMJS-3/5.50–319.10 m in Majhauli block; borehole SMBS-1/12.00–681.50 m near to this block, and boreholes SSM-1/00–718.00 m, SSM-2/00-610.65 m in Mahuli–Moher block (figures 3, 4). This sedimentary sequence includes the deposits from that earliest Permian (Talchir Formation through Barakar Formation) into Late Triassic (Parasora Formation) in the study area. And thus obtained data have been assessed here to built-up the palynostratigraphy of these two formational units – Barakar, and Parsora in particular (figures 9, 10).

Figure 10
figure 10

Suggested age correlation of the assemblages identified in the two blocks of Singrauli Gondwana Basin with the Palynozones established in India (Tiwari and Tripathi 1992) and Australia (Helby et al. 1987; Backhouse 1993)

Full size image

The rock samples in boreholes SMJS-2, SMJS-3 and SMBS-1 (tables 2–4) have yielded in varied frequency and diversity of plant matter. And, the spores-pollen that could be well preserved specimens or hyaline, distorted to amorphous mass. Relative occurrences of key taxa and species are the main features of each assemblage discussed herein (figure 9).

Table 2 List of samples from borehole SMJS-2, Majhauli block, Singrauli main sub-basin, U.P. and Chattisgarh.
Full size table
Table 3 List of samples from borehole SMJS-3, Majhauli block, Singrauli main sub-basin, U.P. and Chattisgarh.
Full size table
Table 4
Full size table

Part of the Talchir Formation (borehole SMJS-2/621.60–631.50 m, figure 3) consists mainly of fine grained sandstone/siltstone facies with few specks of greenish shales. These sediments are considered to be distal and periglacial origin (GSI, unpublished report). Present study infers an earlist Permian age for these strata (Tiwari and Tripathi 1992), which is in accordance with the stratigraphic delimitation (figure 11).

Figure 11
figure 11

Showing the stratigraphic status of the horizons identified in the Permian and Triassic sequences (boreholes SMJS-2, 3 and SMBS-1, Singrauli main sub-basin; and boreholes SSM-1 and 2 Moher sub-basin) in Singrauli Gondwana Basin, U.P. and Chattisgarh.

Full size image

Above the Talchir Formation (621.60 m in borehole SMJS-2), an alternate bands of medium-to-coarse grained sandstones with silty shales, carbonaceous shales and very thin bands of coal comprise the Barakar Formation in the Permian sequence. Inbetween 583.50–512.80 m depth in borehole SMJS-2, the assemblage identified in the basalmost part in the Barakar Formation suggests the existence of strata that is equitable with the Karharbari Formation (figure 11). This formational unit is not delimited in the studied sedimentary sequence (figure 3).

Within 631.50–512.80 m depths in borehole SMJS-2, the occurrences of these three taxa Parasaccites, Plicatipollenites and Callumispora in the sandstones dominated facies with carbonaceous streaks at places, is suggestive of gymnospermous community that had survived in approximately 119.00 m thick strata.

In borehole SMBS-1, intrusion of basic rock in between 578.70–547.50 m depths is the notable feature. This encounters the hiatus level within the coal horizon and non-availability of the coal bands (figure 3). Herein, the impact of heat on the then vegetation had resulted in the poor recovery of spores-pollen.

The major part of the strata in the Barakar Formation is represented by coarser sandstone facies and comprises irregular alternations of fine-grained sandstones, siltstones, grey to carbonaceous shales (figure 3). This nature of sediments had resulted into no recovery of spores-pollen within the Barakar Formation, and also discontinuity from the older into younger assemblages (621.60–251.66 m in SMJS-2; 286.40–319.00 m in SMJS-3; 407.50–351.75 m in SMBS-1; figures 11, 12).

Figure 12
figure 12

The varied levels of hiatuses identified in the five formational units (approx. 1400.00 m thick) intersected in the Permian (approx. 650.00 m thick, Majhauli block) and Triassic (approx. 720.00 m thick, Mahuli–Mahersop block) sequences in two blocks from Singrauli Master Basin. (not to scale).

Full size image

At certain depths in this sedimentary succession of the Barakar Formation, the assemblages obtained are quite rich and diversified in their spores-pollen composition. An assemblage having mixed population of Parasaccites, Callumispora, Scheuringipollenites and Faunipollenites at 470.40–452.50 m depths in borehole SMJS-2, allows a transition from that Karharbari Formation into the basalmost Barakar Formation within 18.00 m thick strata (figure 11). These biostratigraphic precisions are not recognisable in the sedimentary sequence (figure 3). An abundance of Faunipollenites, Scheuringipollenites and Striatopodocarpites within 436.25–428.00 and 353.85–345.70 m depths in borehole SMJS-2, corroborates with the Barakar Formation.

The Barakar Formation, including about 370.00 m thick strata in borehole SMJS-2, 33.00 m in SMJS-3, and 116.00 m in SMBS-1 has many levels of the palyniferous and non-palyniferous matter. Although, the sedimentary facies in this strata include the coal bands of varied thickness at intervals and fine-to-medium grained sandstones intercalated with silty carbonaceous shales (figure 3). The most significant finding is the identification of the Karharbari Formation, in basalmost part of the Barakar Formation (583.50–512.80 m, borehole SMJS-2), while the overlying strata (470.40–260.80 m) conforms with that Barakar Formation. The other two features observed within the Barakar Formation by the mixed population of spores-pollen at 470.40 and 260.80 m depths in borehole SMJS-2, favour the Karharbari–Barakar and Barakar–Barren Measures formational transition respectively (figure 11).

At the very base of the Barren Measures Formation (251.66–144.20 m, borehole SMJS-2; 277.00–147.15 m, borehole SMJS-3, and 266.00–144.00 m, borehole SMBS-1), an increased frequency of Densipollenites in association of striate bisaccate pollen is observed in the medium-to-fine grained sandstone facies, carbonaceous silty shales intercalated with very thin layers of coal. This part in the Barren Measures corresponds to earliest Late Permian in age (figure 4). At 144.20 m depth, genus Densipollenites attains an abundance, with an unproductive strata of 144.00 m in thick medium-to-coarse sandstone facies intermittentily in borehole SMJS-2 (figure 11).

Regarding the Raniganj Formation, not much spores-pollen study is available in the explored strata (figure 3). Moreover, the assemblages recovered in boreholes SMJS-3 (15.00–35.00 m), SMBS-1(25.65–69.80 m) and SSM-2 (542.00–547.00 m) are suggestive of the deposits of that latest Late Permian (figure 11).

In the total run of studied Permian succession (approximately 650.00 m thick) in boreholes SMJS-2, SMJS-3 and 679.00 m SMBS-1 (figures 3, 4), the unproductive strata encountered is of varied thickness (figure 12). From drastically low to high productivity of spores-pollen, it is derived that depositional set-up might not be favourable to the preservation of the plant matter. And, the levels of unproductive strata possibly had resulted into the condensed sedimentary sequence from that earliest Permian (Talchir Formation) to Latest Permian (Raniganj Formation) in Majhauli(s) block of Singrauli Gondwana Basin.

In and around the Mahuli–Mahersop block, the sedimentary facies encountered as the Parasora Formation in boreholes SSM-1 and SSM-2, lies between these depths in boreholes – SSM-1/00.00–718.00 m; SSM-2/00.00–509.00 m. This is represented mainly by medium-to-coarser sandstone facies, rich in micaceous and ferruginous components (figure 3). The assemblages identified in the studied part of the Parasora Formation (figure 9) suggest the deposits of earliest Triassic and Late Triassic age, and display a sharp turnover through the Parasora Formation (figure 11).

The carbonaceous grey facies intercalated with medium-to-coarse grained sandstones of the Raniganj Formation trangresses into the ferugenous facies of the Parsora Formation with a record of palaesol beds (in borehole SSM-2 at 509.00 m depth). This evidences the major regional unconformity in sequence (figure 3).

This study has shown a consistent microfloral change through these sedimentary sequences (figures 11, 12). Several geo-physical and bio-factors have likely contributed to this change within the period of deposition from that glacial to fully arid facies in approximately 1400.00 m thick strata. The coal deposition has its existence from the minimum 00.34 m to the maximum thickness of 9.35 m in the studied sequence (boreholes SMJS-2; SMJS-3; and SSM-2; figure 3).The varied magnitude of hiatuses (figure 12) from that Talchir Formation (earliest Permian) into Parsora Formation (Late Triassic), might be either due to the low presentation of the vegetation or by the silty to sandy alternating layers within a predominantly sandstone facies.

The occurrences of basic rocks that had introduced in the distant areas of these two sub-basins (figures 1, 2) are noteworthy. In Singrauli master sub-basin, the outburst of the basic rock seems to have happened during the deposition of Barakar Formation as noted in borehole SMBS-1 (578.70–529.50 m depth). Apart from this, in the northeastern part of the Singrauli Gondwana Basin (Moher sub-basin), the basic rock intrusion is noted in the younger part of the Upper Triassic (Parsora Formation, 398.00–531.90 m in borehole SSM-1). High degree of heating impact can be seen in the sediments that comprise hard, brittle and dark grey to blackish siltstones intercalated with silty shales and medium-to-fine grained sandstone facies. That is also visible from the exinal surface pattern and the colour of spores-pollen specimens along with vegetal matter, which had become translucent and darkened (table 5).

Table 5 List of spore-pollen species identified in the Permian Succession from boreholes SMJS-2,3 and SMBS-1 Singrauli Master Basin, U.P. and Chattisgarh.
Full size table

The assemblages recognized here in the two blocks in Singrauli Gondwana Basin (figure 9) have been correlated with the Palynozones established in the Permian and Triassic sequences in Australia for their possible age correlation (figure 10).

6 Conclusions

Present study suggests the below given palynostratigraphy and age correlation among the formational units intersected in subsurface strata within the two sub-basins in Singrauli Gondwana Basin (figures 9, 10, 11):

  • Fluvial sediments of Talchir Formation in borehole SMJS-2 (631.50–621.50 m) contain spores-pollen that infers earliest Permian age.

  • Strata in between 583.50–512.80 m, a part of the Barakar Formation in borehole SMJS-2, is equitable with that Karharbari Formation of Early Permian in age (figure 11).

  • The Barakar Formation intersected in boreholes – SMJS-2 (251.66-470.40 m), SMJS-3 (286.40–309.50 m) and SMBS-1 (351.75–407.50 m) contains the assemblages which conform the early Permian age of the strata.

  • The Barren Measures Formation delimited in boreholes SMJS-2 (5.70-251.66 m), SMJS-3 (36.27–286.40 m) and SMBS-1 (132.60–351.75 m) conforms to the age derived from its spores-pollen content.

  • The Raniganj Formation within borehole SMJS-3 (approx. 37.00 m), SMBS-1 (100.00 m), and SSM-2 (102.00 m) in both the sub-basins (figures 3, 4), represents the latest Permian level. FAD’s of Arcuatipollenites pellucidus, Kamthisaccites kamthiensis and Goubinispora sp. certainly evidence the Permian and Triassic transition in the upper part (figures 11, 12).

  • Occurrence of palaeosol horizon at 509.50 m in borehole SSM-2 is significant as one of the sedimentary feature to demarcate the P/Tr level (figure 11).

  • The Parasora Formation intersected in the Mahuli–Mahersop block (boreholes SSM-1, 2) represents the Lower and Upper Triassic level with a hiatus of Middle Triassic deposits, as derived from spores-pollen study (figure 11).

  • Strata devoid spores-pollen are identified at many intervals in the sedimentary sequences in the study area (figure 12).

  • Occurrences of the basic rock intrusions in the Barakar Formation (SMBS-1, figure 3), and Parsora Formation (SSM-1, figure 4) might be inferred the out-brusting of heat flow through the sedimentary rocks irrespective of the geological time.