Palaeoenvironmental Reconstruction and Evidence of Marine

International Journal of Coal Geology 224 (2020) 103485

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International Journal of Coal Geology

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Palaeoenvironmental reconstruction and evidence of marine influence in Permian coal-bearing sequence from Lalmatia Coal mine (Rajmahal Basin), T Jharkhand, India: A multi-proxy approach

⁎ Runcie P. Mathews , S. Suresh K. Pillai, M.C. Manoj, Shailesh Agrawal

Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow 226007, India

ARTICLE INFO ABSTRACT

Keywords: Lalmatia coal-bearing sequences belong to the Barakar Formation (Permian) of Lower Gondwana. The well- Permian coal-bearing sequence developed coal-bearing sequences (approx. 52 m) exposed along the mine section have been studied to un- Glossopteris derstand the depositional environment. Along with this, a cuticle study was performed to understand the pa- Biomarkers laeoclimate with the help of the stomatal index. The distribution of n–alkanes (n–C15 to n–C31) suggests major Stable carbon isotope higher plant and algal dominant source input, although variations are seen in the relative input. Steranes Stomatal index identified include C regular sterane and 4-Methylsteranes. The Pr/Ph ratio varied from 0.43 to 4.26. Warm Palaeoclimate 29 temperate to subtropical palaeoclimate with fresh to brackish water bodies, and reducing oxygen-poor environment were inferred from the Rb/Sr, Sr/Cu, Th/U, Sr/Ba, V/(V+Ni). Mean δ13C value measured is −23.0‰ ± 0.60‰ for coal and −22.6‰ for shale. These values are well correlated with typical δ13C values of the Permian coal and shale. The stomatal index of Glossopteris leaves (280 million years) was taken into account,

and it showed a value of 10.7 that assumes a higher level of atmospheric CO2 during the Barakar Formation

(Artinskian age). The result also shows that Permian taxon Glossopteris can be used for CO2–proxy during Permian age. The geochemical evidence suggests that towards the middle part (middle coal seam) of the studied section, the depositional milieu was under a marine-influenced marginal condition. The geochemical studies and carbon isotopic ratios unequivocally suggest that fluctuating climatic conditions existed during the deposition of the Lalmatia coal-bearing sequence.

1. Introduction degradation, biomarkers provide highly convincing signatures re- flecting past environments than other proxies (Zhang et al., 2014, Climate is the supreme factor controlling the floral composition as 2016a). Besides this, inorganic geochemical parameters also provide plant families respond to the change in environmental factors. The highly useful information regarding past environmental shifts. Ac- dominance or absence of plant communities is directly related to the cordingly, various methods are applied to differentiate past sedimen- temperature and moisture conditions and thus to the climatic varia- tary realms. Elemental composition is an important parameter that can tions. Hence, the determination of palaeofloral composition can provide provide indications of geodynamic and palaeoclimatic conditions (Fu clues to the change in environmental factors that occurred during se- et al., 2018). However, quantitative analysis of major and trace ele- dimentation (Hautevelle et al., 2006). The latest developments in the ments is the most commonly accepted and applied method across basins macromolecular analysis of organic matter demonstrated the im- (Liu and Zhou, 2007; Dai et al., 2016; Zhang et al., 2016b; Wang et al., portance of biomarker compounds in the palaeoclimate reconstruction 2017; Fu et al., 2018). Consequently, the occurrence and composition of (Castañeda and Schouten, 2011). Although, the OM is affected by trace elements in coal have been studied extensively (Dai et al., 2015, various alterations after the deposition causing transformations in the 2016, 2017, 2018). Similarly, one of the robust proxies which can re- C=H bonds and functional groups, the carbon skeletal structures of flect the variation of the carbon cycle in local to regional levelhe ist biomarker compounds are indestructible. Hence, in the sedimentary stable carbon isotopic ratio (δ13C) (Chen et al., 2014; Aggarwal et al., record, these compounds are well upheld for geological ages (Peterson 2019). Considering the morphological aspects, various studies have et al., 2007). Due to this source specificity and resistance to shown that the quantitative estimation of the stomatal number of fossil

⁎ Corresponding author. E-mail address: [email protected] (R.P. Mathews). https://doi.org/10.1016/j.coal.2020.103485 Received 18 December 2019; Received in revised form 12 April 2020; Accepted 12 April 2020

Fig. 1. The transgression of Tethys through Khemgaon of Sikkim till Northern Bihar and present day Jharkhand (after Chatterjee and Hotton, 1986; Moore and Scotese, 2012). plant leaves (i.e, the stomatal index and density analysis) can be effi- magmatism during the Gondwana period and beneath the trap lays the caciously correlated to the palaeoatmospheric fluctuationsMcElwain, ( unclassified Triassic sediments underlain by Barakar and Talchir for- 1998; Wagner et al., 2005). Thus, in addition to the geochemical mations. The N–S aligned lower Gondwana exposures are encountered parameters microscopic investigation of cuticles is also considered as an extensively covering Bengal Basin, North Bengal, and Purnea. The essential tool to decipher past climates (Stace, 1965; Cutler, 1982; sampling is done in the Lalmatia Coal mine, Boarijor Tehsil, Godda Kovach and Dilcher, 1984; Upchurch Jr., 1995). District, Jharkhand State, India. Lalmatia Coalfield/mine (Earlier called Several studies have been done on the coal-bearing sequences of the as Rajmahal Open Cast Mine) occupies around 15 sq. km and is ex- Rajmahal Basin particularly on the morpho-taxonomical (Feistmantel, plored by the Central Mine Planning and Design Institute. The block is 1880; Singh et al., 1987; Bajpai and Maheshwari, 1991; Maheshwari located between latitudes 25° 1' 12" and 25° 3' 15" N and Longitude 87° and Bajpai, 1992; Srivastava and Pant, 2002), palynology (Tripathi and 21' 0" and 87° 24' 0" E (Fig. 2a). Hura, Pachwara, Chuperbita, Brahmani Ray, 2005; Tripathi et al., 2010), petrological (Roy et al., 1983; and Mahuagarhi are the five coal fields of the Rajmahal Gondwana Madabhushi, 1990; Singh, 1992), molecular composition and hydro- Basin. Towards the northern part of the Rajmahal Basin coal seams of carbon potential (Tewari et al., 2016, 2017) aspects. Earlier studies approximately 78 m thickness are encountered in the Lalmatia Coal have shown possible marine influences at various localities in the lower mine (Hura Coal-field). The age of this sedimentary sequence is as- Gondwana basins of India as given in Fig. 1 (e.g. Shah and Sastry, 1975; signed as Artinskian (280 Ma). Intercalated shales yielding plant fossils Chatterjee and Hotton, 1986; Venkatachala and Tiwari, 1988; Ahmad (Maheshwari and Bajpai, 1992) are very thick in some places and divide and Khan, 1993). Reports of marine incursions during Gondwana are the seam into three parts: referred to as seams L−I, L−II, and L−III based on Eurydesma–Productus–Conularia. Apart from this, reports of (Raja Rao, 1987). A total of eight workable coal seams are present in marine incursions are reported from Daltonganj (Dutta, 1965), Umaria the Lalmatia coal mine. The seams are bottom to top as seam I, II marine beds (Sinor, 1923), Subansiri (Sahni and Dutta, 1959), Ma- (bottom), II (top), III, IV, IX, X and VI. Seams II (bottom), II (top) and III hendragardh (Ghosh, 1954), Badhaura of Western Rajasthan (Mishra merge and split within the area to form various combinations. Max- et al., 1961; Shah, 1963) in India. The other evidence of marine in- imum coal reserves (95%) are found in seam II (bottom), II (top) and III cursion during Permian is from sedimentary nodules, invertebrate (95%). Towards the western periphery of the basin, the sedimentary faunas, Acritarch (Leiosphaerid and Foveofusa), coastal–marine, and rocks of Talchir Formation are encountered. Karharbari Formation Cruzianaichno–facies (Seilacher, 1964). Recently, Goswami (2008) has succeeds above encompass conglomerates, grits and carbonaceous pointed out marine incursions in Mahanadi Basin from trace fossils sandstones. In most of the areas, Archean rocks form the basement and wave ripples and acritarchs. In the present study, multi–proxy analyses it is overlain by the coal-bearing formation (Barakar). The general have been done to know the OM source, depositional conditions, pa- stratigraphical succession exposed in the Rajmahal area, eastern laeoclimatic scenario and its variations during the period of formation Jharkhand is given in Table 1 (after Ball, 1877; Raja Rao, 1987; of Permian Lalmatia coal–bearing sequences. More importantly, this is Sengupta, 1988; Tiwari and Tripathi, 1995; Ghose et al., 1996; Tripathi the first attempt from the Indian context to study palaeoenvironment et al., 2013). The litholog of the studied section from the Lalmatia coal and marine influence based on multiple proxies (biomarker, plant fos- mine showing three coal seams (upper, middle and bottom) is given in sils, stable carbon isotope, and geochemical records) of Gondwana se- Fig. 2b. diments along with the stomatal index of Glossopteris leaves.

2. Geology of the area

The Rajmahal Basin is considered to be evolved from tholeiitic

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Fig. 2. (a) Location map and geology of Lalmatia, Damodar Basin, Jharkhand state. (b) Litholog of the studied mine section showing lithounits and samples.

3. Methodology spectrometer (MS). Fused silica capillary column (HP−5MS: 30m×0.25mm i.d., 0.25μm film thickness), and helium (carrier gas: 1 3.1. Gas chromatography−mass spectrometry ml/min flow rate) was used. In GC, 80°C was maintained initially, for 5 min subsequently increased to 300°C (4°C/min) and maintained for 5 Thirteen samples were subjected to biomarker analysis from min finally. Full scanm/z ( 50–550) 70 eV mass spectra were acquired Lalmatia coal mine. The samples were powdered and extracted initially with a source temperature of 300°C. Data processing and analysis were with dichloromethane: methanol (9:1, v:v) by 30 min ultrasonication. done by software (Chemstation) and published literature. Asphaltenes were removed subsequently by precipitation using n- hexane in excess. Different fractions were separated later on using the column chromatographic method using activated silica gel. Hexane and 3.2. Inductively coupled plasma–mass spectrometry mixture of dichloromethane–hexane (1:4) were successively eluted for saturated for aromatic fractions, respectively. The instrument used was Open acid digestion of powdered sediment samples using 10 ml of Agilent 7890A gas chromatograph (GC) connected with a 5975C mass HF (3 ml), HNO3 (7ml) and HClO4 (1ml) acid mixture was done in clean PTFE Teflon® beakers for 8–9 hrs or until complete digestion (Xiong

Table 1 The general geological succession in the Rajmahal area, Jharkhand, India (after Raja Rao, 1987; Singh and Singh, 1996).

Age Formation Lithology Thickness

Recent to sub-recent Alluvium Loose soil, silt and clay Up to 80 m

Unconformity Early Cretaceous to Early Jurassic RajmahaTraps and Inter-trappeans Flows of basalt, pitchstone and lnter-trappean beds (sandstone shale and ash) 600 m

Unconformity Late Triassic Dubrajpur Pebbly sandstone, Coarse to medium grained sandstone, red siltstone 60-250 m

Unconformity Early Permian Barakar Coarse to medium grained sandstone, pebbly sandstone, gray shales, clay and coal seams 250–550 m Karharbari Grits, conglomerates and carbonaceous sandstones Talchir Tillite, fine to medium grained sandstones, olive green shale

Unconformity Archean Basic rocks, amphibolites, bands of quartzite, limestone, gneisses and granite

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clumps. Packed (in tin capsules) samples were introduced into Ele- mental Analyzer (Flash EA 2000 HT) and measured carbon isotopic

composition of CO2 gas produced during the combustion with the help of Continuous Flow Isotope Ratio Mass Spectrometer (CFIRMS, MAT

253) coupled with the Con–Flow IV interface. The reference CO2 gas was calibrated using IAEA standard CH3 and data has been reported against VPDB. International standards (IAEA CH3 and CH6) as well as internal standards (Sulfanilamide) were run to check the accuracy for

the CO2 measurements with an external precision of ± 0.1‰ (1σ). Total organic carbon (TOC) was calculated from the peak area obtained from the sum of the integrated m/z 44, 45 and 46 signal measured in the CFIRMS (Jensen, 1991). For total nitrogen (TN) measurement in coal and shale, we have used powdered bulk samples. The known amount of powdered bulk samples were packed into tin capsules and introduced into Elemental Analyzer (Flash EA 2000 HT) through an

auto sampler. Through the combustion, N2 gas was produced and introduced into Continuous Flow Isotope Ratio Mass Spectrometer (CFIRMS, MAT 253) coupled with Con-Flow IV interface. Towards this, the peak area obtained from the sum of the integrated m/z 28 and 29 signal measured in the CFIRMS is used (Jensen, 1991).

3.4. Stomatal index analysis

The plant fossils and cuticles were retrieved from the shale band between seams L–III and L–II as shown in Fig. 2b. The fossils yielded are impressions and compressions of grey coloured shale. Cuticle study was carried out for ten compressed Glossopteris leaves. The cuticles were

prepared by cellulose acetate pulls in concentrated nitric acid (HNO3) for a few days. A pinch of potassium chlorate (KClO3) was added to increase the rate of reaction. The cuticles were repeatedly washed in water and the acid was removed as it turned from black to brown colour. The cuticles were treated in 5% of KOH to separate the lower and upper epidermis. They were washed in water several times, and kept in hydrogen peroxide solution overnight. After washing them in water several times they were stained in saffranine, dried in polyvinyl alcohol and mounted with Canada balsam. They were photographed in transmitted light under a high power microscope (Olympus Vanox AHBS3) and the structural features were studied. Few Glossopteris cuticles were dried and dispersed on a smooth, clean glass plate. The glass plate with dispersed Glossopteris cuticles were mounted on the copper stub with the help of double sided adhesive carbon tape. The mounted stubs were then coated with Jeol JEC–3000 PC auto fine coater. The coating was done for seventy seconds using gold palladium alloy target. The coated stubs were observed under FESEM JEOL 7610f Field Fig. 3. The n-alkane distribution according to SIM m/z 57 of the Lalmatia Emission Electron Microscope. The images were recorded with the samples. Numbers correspond to carbons in the n-alkane chain. desired magnification. A total of ten slides were prepared by extracting cuticles that were counted based on 20X magnification. The epidermal and stomatal cells et al., 2012). The residue was dissolved in 2% HNO3 in the Teflon beaker and after cooling to the room temperature, the volume was were counted manually under the microscope. The number of stomata made upto 50 ml and stored in polypropylene bottles. Trace and rare was used to calculate the stomatal density and stomatal index earth elements were measured using an Inductively Coupled Plasma–- (Salisbury, 1927). The following equation was used for calculating the Mass Spectrometry (Agilent 7700 series) hosted at Birbal Sahni Institute stomatal index. of Palaeosciences (BSIP), Lucknow. Rhodium (Rh) was used as an in- S Stomatal Index (SI) = × 100 ternal standard for the collection of matrix effect and machine drift. ES+ Standard reference materials such as SGR1b and SCO1 have analyzed Where, S is the number of stomata and E is the number of epidermal along with the samples to measure the accuracy of the ICP–MS result, cells respectively in the unit area. and the precision was better than 5%.

4. Results 3.3. Total organic carbon (TOC) and carbon isotope (δ13C) analysis 4.1. Biomarker composition The sample preparation procedures given by Agrawal et al. (2015, 2017) have been followed for carbon isotopic analysis. In short, pow- In the present study, main emphasis has been done on the deposi- dered samples i.e. coal and shale were treated with 5% HCl solution and tional environment. Therefore, normal (n–) alkanes, various alkane washed with Milli–Q water to remove the acid and soluble salts. The de- parameters and sterane distribution have been discussed. The range of carbonated samples were dried and again pulverized to lose any n–alkanes begins with n–C15 continuing up to n–C31, comprising of uni–

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Table 2 4.3. Total organic carbon (TOC) and carbon isotope (δ13C) analysis Various n-alkane parameters, stable carbon isotopic ratios and TOC of the studied Lalmatia samples. In LRJ coal samples, the TOC content ranges from 24% to 64% and the shale unit is characterized by relatively lower TOC content (~ 8%). Sample Pr/Ph Pr/n-C17 Ph/n-C18 TAR TMD δ13C TOC TN The content of TN ranges from 0.45% to 1.5% and the lowest is ob- LRJ–13 1.00 0.43 0.37 1.28 1.56 -22.7 24 0.45 served in shale (0.42%). Overall, the TN content is well correlated with LRJ –12 0.94 0.39 0.36 1.56 1.70 -22.7 38 0.69 TOC. The TOC/TN ratio varies from 20 to 80 in the profile, and the LRJ–11 0.35 0.32 0.42 0.19 0.24 -22.6 8 0.42 lowest values are observed in the shale. LRJ–10 0.79 0.34 0.36 0.77 0.99 -22.6 52 1.03 13 LRJ–9 0.80 0.38 0.41 0.31 0.57 -23.1 55 1.09 The δ C values of samples vary from –24.0 ‰ to –22.2 ‰ (range ~ LRJ–8 0.60 0.29 0.39 0.20 0.34 -22.8 44 0.53 2.2 ‰; Table 2). In Lalmatia samples, −23.0 ± 0.60‰ and −22.6 ‰ LRJ–7 0.80 0.38 0.45 0.32 0.56 -23.2 48 0.98 are the mean value for δ13C for coal and shale respectively. A pro- LRJ–6 0.75 0.30 0.37 0.30 0.38 -23.3 37 0.65 gressive decrease followed by a gradually increasing trend in the LRJ–5 1.16 1.23 0.61 3.27 1.98 -24.0 57 1.12 δ13Cvalues has been observed. Overall, the δ13C values of the present LRJ–4 0.75 0.32 0.27 0.93 0.81 -22.4 38 1.01 13 LRJ–3 1.44 1.98 0.71 2.18 1.14 -23.7 62 1.18 study show a distinct depth trend. At the bottom levels, the highest δ C LRJ–2 0.91 0.18 0.13 1.43 1.02 -22.2 31 0.72 value (–22.2 ‰) is observed while it decreased gradually in the upper LRJ–1 4.23 1.93 0.28 0.92 0.58 -22.2 61 1.46 part and the lowest δ13C value (–24.0 ‰) is observed in the LRJ–5 sample. Following this, the δ13C values are observed to increase to the and bimodal distributions (Fig. 3). In majority of the studied samples, top of the studied profile. n–C25 and n–C18 are the prominent peaks with usual occurrence of pristane (Pr) and phytane (Ph). The abundance of these compounds 4.4. Stomatal index varies between samples and their ratio (Pr/Ph) ranges from 0.43 to The cuticles with well–preserved stomata were retrieved for 4.26. The Pr/n–C17 ratio range from 0.23 to 2.00, whereas the Ph/n–C18 ratio ranges from 0.14 to 3.29. The terrigenous/aquatic ratio (TAR) studying the stomatal index. There are no published records to calculate varies from 0.19 to 3.16. The terrestrial-marine discriminant (TMD) palaeoatmospheric CO2 using Glossopteris leaf as there is no NLR to varies from 0.24 to 1.98 (Table 2). Sterane distribution is identified study the PCO2. Hence, a comparative study was carried out for from the mass ion chromatogram (m/z 217). Steranes are identified in a Glossopteris communis from two sedimentary formations of the same relatively low abundance in Lalmatia samples. In most of the samples, basin by Schmidt et al. (2011) to test the possible relationship of the stomatal index and the modeled global changes in Phanerozoic atmo- C29 regular sterane is identified, while C27 and C28 steranes are absent. Besides, in sample LRJ–7, 4–methylsteranes are also identified. spheric CO2 from Paraná Basin, Brazil (Lower Permian shales). Since, there is no direct approach to calculate pCO2, we tried to find the stomatal index based on cuticles (Fig. 5) to calculate PCO2. The minimum 4.2. Trace and REE elements and maximum stomatal index for the studied samples is 0.8 and 16.2 respectively. The calculated mean stomatal index is 10.7 (Table 5). The The trace–elements and REE concentrations from average global variation of the stomatal index in the studied sample is given in Fig. 6. hard coal value and their comparison with the Lalmatia samples are listed in Tables 3 and 4 (Ketris and Yudovich, 2009). In the Lalmatia 5. Discussion coals, enrichment in most of the trace elements is observed. Ge shows concentration coefficient (CC) values > 10 and other elements with 5.1. Source of OM and depositional environment such as Sn and Cr shows values ranging 5–10. The elements like Ti, Th, Nb, Se, Ga, Cs, Ta, Zn, V, Pb, Cu, Zr, Ni, and Hf shows slight enrichment Biomarker compounds are regarded as excellent indicators of the in coal (CC = 2–5). The CC values ranging from 0.5 to 2 for the ele- depositional environment. Owing to its specificity of the source, ments like Ba, Co, Rb, U, Mn, Cd, Sb, Sr and Mo are nearer to the structural stability and diversity, biomarker compounds are proved to average global values. Remaining elements like As and Tl showed de- be one of the most efficient tools in the characterization of sedimentary pletion (CC < 0.5) in the coal samples. The close relationship between OM in various realms such as marine (e.g., Wakeham and Canuel, 1988; most of the trace elements with Al suggests its associations with alu- Eglinton and Eglinton, 2008), coastal deposits (Prahl et al., 1994; Boon minosilicate or clay minerals (Chen and Selvaraj, 2008). According to et al., 1999), estuaries (Yunker et al., 1995; Mudge and Norris, 1997), Banerjee et al. (2000), volatile elements (Ge, Ga, Cd, Sb, Sn, Pb, etc.) in lacustrine (Wang et al., 2013; Wang et al., 2014), lagoonal (Elias et al., Indian coals show decreasing concentration with higher concentrations 1997; Zink et al., 2004), etc. The pattern of n–alkane distribution and of V, Cr, Mn, Zn, Na, K, etc. In this study, many elements (Cu, Mg, Rb, their abundance indicate variety in OM source/s in the sedimentary Ni, Ga, Sn, Zr, Hf, Ta, Cd, Nb, U, Th, and Tl showed a positive corre- systems (Moldowan et al., 1985). In the studied samples both unimodal lation with the Al and Ti, suggesting primarily aluminosilicate affi- and bimodal patterns are observed. Short-chain n–alkanes indicate the nities. The Upper Continental Crust (UCC)–normalized REE patterns are input of microbially derived OM (Cranwell, 1977). The odd n–alkane shown in Fig. 4 and followed the classification by Seredin and Dai chains (n–C15 to n–C25) shows aquatic inputs with algal and macrophyte (2012). The total REE (Ʃ REE) concentrations vary between 89.68 and inputs indicated by shorter chains and longer chains respectively 536.98 mg/kg, with an average of 215.84 mg/kg. The Lalmatia coal (Ficken et al., 2000, 2002). Those n–alkanes with odd long-chain samples shows high concentrations of LREE (ranging from 78.45 to (> 25) suggest higher plant contributions (Egllinton and Hamilton, 464.80 mg/kg) and LRJ–6 and LRJ–7 show the highest. Correlation 1967). The incidences of unimodal and bimodal patterns suggest the coefficients have been used to examine the modes of occurrence for variation in the OM source during the formation of this sequence. trace elements. The elemental affinity derived from the concentrations However, more evidently a pattern is observed showing higher plant of trace elements and TOC, TN indicated their provenance and en- dominant source at the bottom part (LRJ–1 to LRJ–5), then a microbial vironmental settings of coal samples for this study. Most of the trace source including algae dominant middle part (LRJ–6 to LRJ–11) and elements have positive correlations with the terrigenous elements like higher plant dominance towards the top part (LRJ–13 to LRJ–14) of the Al, Ti, and Fe, and REE elements are correlated with each other and studied mine section. This is well supported by the terrigenous aquatic have a good correlation with V, Mo, Cr, As and Se. ratio. During the late Carboniferous–early Permian, the rifting of Gondwanaland led to the formation of many intracratonic rift basins

5 ..Mtes tal. et Mathews, R.P. Table 3 The Trace elemental composition (ppm) in the studied Lalmatia samples.

Sample B Na Mg Al P S K Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga

LRJ–13 26.91 542.71 2350.28 51932.2 40.9 727.98 4566.19 9312.31 4816.12 53.81 71.93 64.88 5594.51 7.1 33.72 34.42 60.52 20.91 LRJ–12 25.67 452.33 1402.15 42693.1 121.35 532.38 2127.09 4294.32 4359.53 46.63 55.82 60.81 5308.01 3.72 18 28.02 46.83 16.91 LRJ–11 26.2 809.88 5296.82 94829.5 121.25 774.57 11112.4 1392.99 7311.2 155.8 190.2 206.29 21612.6 14.3 77.29 115.97 116.82 38.09 LRJ–10 10.57 394.14 1545.32 23269.3 749.31 422.19 1336.47 5032.37 3263.74 46.75 82.15 49.99 5656.58 8.68 23.46 45.73 46.24 19.66 LRJ–9 59.34 388.83 1650.95 19796.6 4197.98 – 1362.51 15195 2523.07 33.69 64.51 243.08 20312.1 11.63 24.15 32.32 95.99 19.38 LRJ–8 10.17 384.44 1550.72 43632.9 255.39 399.32 2228.74 4932.53 4001.56 37.43 55.06 46.34 4322.15 2.15 14.59 18.76 20.08 16.61 LRJ–7 9.78 376.11 992.35 37301.9 997.72 350.7 1473.88 2848.69 2126.87 309.1 262.3 42.59 3577.91 14.02 41.9 30.6 90.33 28.02 LRJ–6 – – – – – – – – – 49.74 93.51 219.1 – 3.13 18.68 34.54 48.1 – LRJ–5 10.89 427.01 1271.41 20002.6 115.5 753.94 1641.09 4912.09 3365.32 40.06 54.97 291.25 21245.5 21.01 28.24 44.17 92.56 14.34 LRJ–4 14.78 441.31 1324.32 58932.3 633.11 952.36 2016.16 6009.16 3816.64 47.67 86.2 44.28 4337.07 1.4 15.73 26.02 46 21.22 LRJ–3 48.18 362.13 961.92 12105.3 221.56 431.98 833.47 2561.09 1849.88 29.04 36.4 205.47 17264.4 13.59 20.44 21.25 102.74 11.45 LRJ–2 5.11 491.46 1343.23 73949.1 100.29 525.1 3001.73 4153.09 5488.61 65.7 88.44 48.74 4327.22 1.82 26.5 42.33 106.64 23.38 LRJ–1 – 379.01 1248.04 17798.2 183.71 673.8 710.05 4573.57 2358.86 20.95 38.96 153.33 9014.76 4.09 19.87 29.93 42.31 8.77

Sample Ge As Se Rb Sr Zr Nb Mo Cd Sn Sb Cs Ba Hf Ta Tl Pb Th U

LRJ–13 42.4 0.86 4.11 35.99 45.4 117.57 19.78 1.62 0.31 9.05 0.58 5.01 201.85 3.25 1.21 0.05 30.33 16.89 4.62 LRJ–12 20.88 1.26 0 28.56 18.78 96.06 19.18 1.91 0.35 11.44 0.73 5.6 101.06 2.72 1.14 0.05 16.77 14.43 4.12 LRJ–11 31.11 1.16 6.9 62.4 23.48 141.23 34.65 1.09 0.39 13.42 0.07 2.98 350.16 3.52 1.83 0.1 34.62 35.03 5.9 LRJ–10 13.6 1.46 7 15.6 107.8 82.07 11.93 1.9 0.32 9.13 0.97 2.35 263.97 2.48 0.8 0.03 29.18 12.68 5.46 LRJ–9 10.97 1.49 3.79 12 283.04 58.96 8.08 1.86 0.26 6.97 0.57 2.78 399.85 1.67 0.58 0.02 19.95 9.06 3.65 LRJ–8 23.48 1.73 1.32 24.27 24.18 72.59 16.57 1.94 0.15 7.15 0.52 5.05 121.23 2.02 0.91 0.02 7.75 14.35 2.77 LRJ–7 133.57 6.44 17.45 17.75 208.85 62 9.32 2.85 0.19 9.17 0.99 3.36 550.93 1.82 0.49 0.04 27.25 9.78 2.68 LRJ–6 – – – 23.73 33.76 118.77 – 1.77 0.21 – – – 162.12 3.55 – – 27.75 24.83 4.41 6 LRJ–5 71.28 1.54 4.13 17.8 79.64 69.79 12.84 1.53 0.15 7.92 1.22 4.12 221.75 1.97 0.8 0.03 14.73 10.32 2.72 LRJ–4 18.71 1.59 2.6 19.02 112.13 97.22 15.43 1.11 0.22 7.15 0.72 2.89 589.72 2.8 0.72 0.02 19.57 17.87 3.42 LRJ–3 153.14 1.84 3.7 5.98 68.83 45.88 7.35 1.85 0.29 7.01 1.06 1.1 160.52 1.16 0.33 0.03 14.22 5.34 1.47 LRJ–2 16.68 1.57 6.79 32.98 19.81 130.2 24.51 1.27 0.66 9.56 0.44 4.25 123.05 3.98 1.38 0.02 16.29 19.56 3.76 LRJ–1 44.88 1.7 2.85 4.48 16.59 55.66 10.5 1 0.15 6.74 0.74 0.48 55.95 1.61 0.6 0.01 37 8.14 1.95 International Journal of Coal Geology 224 Geology Coal (2020) of 103485 Journal International R.P. Mathews, et al. International Journal of Coal Geology 224 (2020) 103485

Table 4 The REE composition (ppm) in the studied Lalmatia samples.

Sample La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

LRJ-13 59.43 121.9 12.64 45.76 8.26 1.89 9.02 1.29 6.88 1.34 3.93 0.5 3.29 0.49 LRJ-12 63.6 118.45 11.86 40 7.72 1.23 7.25 0.98 4.7 0.95 2.56 0.35 2.18 0.3 LRJ-11 48.67 83.93 10.3 36.28 7.39 1.49 6.78 1 4.53 0.89 2.35 0.35 2.23 0.38 LRJ-10 40.1 68.37 6.93 22.99 5.3 1.11 5.39 0.91 4.2 0.77 1.96 0.26 1.41 0.21 LRJ-9 31.43 63.79 6.93 23.03 4.5 1.05 6.05 0.96 4.57 0.75 2.03 0.26 1.51 0.2 LRJ-8 36.26 81.22 9.72 39.01 7.61 1.58 7.75 1.13 5.46 0.98 2.81 0.37 2.18 0.35 LRJ-7 106.4 207.11 28.85 106.85 15.58 4.85 19.52 3.54 18.85 3.74 10.75 1.41 8.34 1.18 LRJ-6 69.94 163.62 21.4 92.28 21.12 3.54 22.7 3.1 19.55 3.72 9.82 1.25 7.73 1.08 LRJ-5 32.19 58.26 6.41 20.96 4.14 0.74 3.84 0.53 3.07 0.64 1.58 0.21 1.35 0.21 LRJ-4 58.87 112.88 10.79 33.99 5.24 1.08 6.31 0.93 4.5 0.86 2.2 0.31 1.9 0.25 LRJ-3 36.2 59.8 5.72 19.43 3.33 0.58 3.38 0.47 2.21 0.46 1.01 0.16 0.77 0.12 LRJ-2 46.7 89.18 9.85 34.59 6.65 1.35 7.09 0.95 4.7 0.83 2.51 0.33 1.82 0.29 LRJ-1 18.83 37.65 4.03 15.3 3.24 0.57 3.49 0.53 2.72 0.51 1.38 0.19 1.17 0.2

and the ratio of Sr to Ba can define sedimentary realms indirectly (Ye et al., 2008; Xiong and Xiao, 2011; Wang et al., 2005; Wang et al., 2011; Fu et al., 2017, 2018). The Sr/Ba of Lamatia coal sample ranges between 0.07 and 0.71, and the average value is 0.30. Except for the LRJ–9 sample, all the other samples show values less than 0.5, which indicates a freshwater environment (Fig. 7). Previous studies report that the values ranging from 0.19 to 0.69 indicate terrestrial, freshwater environment (Zhang et al., 2006, 2008; Fu et al., 2018). However, Th/U results are contradicted with Sr/Ba values. Th/U of Lalmatia coal samples are distributed between 2.32 and 5.93 with an average of 4.06 and all values greater than 2 indicates that this group of the section was terrestrial freshwater–brackish deposit (Zhang et al., 2008). Thus, the present study shows that the margin waters of the basin are saline (marginally), as indicated by the Th/U values in the middle coal seam. Accordingly, in the Th/U vs. Sr/Ba plot (Fig. 8) also, the distribution of samples in the brackish area suggests a marine-influenced setting.

Generally, the C15,C17 and C19n–alkanes are predominant compounds in marine planktons like cyanobacteria and algae (Brassel et al., 1978). In the middle coal seam samples, an increase in the algal input in ob- Fig. 4. The Upper Continental Crust (UCC)-normalized REE distribution pat- served supporting marine influence (Fig. 3). In the present study, terns of the Lalmatia coal samples. samples LRJ–1, LRJ–6, LRJ–7, LRJ–8, LRJ–9 and LRJ–11 showed low TMD values. The TMD is used to differentiate the organic matter input as it delineates the dominant contributions from vascular plants and packed with continental clastic deposits. However, these basins also phytoplankton (Syakti et al., 2013; Azis et al., 2016). Studies show that witnessed minor marine incursions during the early phase (Mazumder values > 1 indicate dominant terrestrial input while, values < 0.5 et al., 2017). Records of early Permian marine sedimentation is re- suggests marine contributions (Syakti et al., 2013). The low TMD values ported from different places which were once part of Gondwana super- mainly in the middle coal seam suggest marine-influenced conditions continent such as Africa (Wescott and Diggens, 1998; Schandelmeier during the deposition. Further, Pr/n–C vs. Ph/n–C plot (Fig. 9) also et al., 2004; Uys, 2007; Nyathi, 2014), Arabia (Al-Aswad, 1997; 17 18 supports this observation. Pollastro, 1999), Pakisthan (Khan and Afzal, 2005; Ezaki, 2006; Jan The steroidal composition in a sedimentary deposit is highly es- et al., 2009; Ghazi et al., 2012; Aadil et al., 2013; Iqbal et al., 2013), sential in recognition of the OM source and depositional environment India (Shah and Mehrotra, 1985; Shellnutt et al., 2012; Kulkarni and (eg., Mello et al., 1988; Aboglila et al., 2010; Araújo and Azevedo, Bokar, 2014), etc. Early Permian Gondwana Basins were inundated by 2016). The relative abundances of C ,C , and C regular steranes sea due to the continued subsidence. Goswami (2008) in his review 27 28 29 indicate marine phytoplankton, lacustrine algal and terrestrial organic mentioned marine incursions in Indian Gondwana sediments. Marine matter source input respectively (Huang and Meinschein, 1979). inundation in the Rajmahal is related to the incursion of Tethys in 4–methylsteranes are also considered to be important markers of the Subansiri (Arunachal Pradesh), Rajhara and Daltonganj coalfields depositional environment with varying source than that of regular (Damodar Basin), Manendragarh Coalfield (Rewa Basin) and Umaria steranes. One major 4–methylsterane compound is the dinosterane Coalfield (Rewa Basin). Analysis of the sediments from the Gondwana derived mostly from dinoflagellates (Boon et al., 1979; De Leeuw et al., deposits in Arunachal Pradesh points to the transgression of Tethys and 1983; Summons et al., 1987). It is also reported to have bacterial (Bird subsequent formation of lagoons and wet-lands, while the volcanism et al., 1971; Summons et al., 1987; Huang et al., 1994) and diatom resulted in the regression (Singh, 1973). The route of inception of the (Volkman et al., 1993) source of this compound. However, the 4–me- marine incursion was earlier reconstructed based on the fauna and thylsteranes identified in the studied samples do not match with the palaeogeography (Fox, 1931; Sastry and Shah, 1964; Ahmad, 1964; dinosterane configuration; rather it is more comparable to 4–methyl- Ghosh and Bandopadhyay, 1969). Due to the close resemblance of the steranes reported from Chinese (Pearl River Mouth Basin) lacustrine Eurysdema faunas with Khemgaon of Sikkim, the marine transgression sediments (Goodwin et al., 1988). This compound is widespread in salt was considered to have occurred from the eastern Himalayan region lake, brackish, fresh lacustrine sediments and corresponding oils in (Shah and Sastry, 1975) and incursion was up to northern Bihar and Pearl River Mouth Basin (Fu et al., 1993). From the Lalmatia samples, present-day Jharkhand (Chatterjee and Hotton, 1986)(Fig. 1). Con- other proxies and parameters collectively suggest a brackish condition sidering the trace elements, the higher solubility of Sr than Ba in water

7 R.P. Mathews, et al. International Journal of Coal Geology 224 (2020) 103485

Fig. 5. Representative images of Glossopteris cuticles under high-power microscope: (1) distribution of stomata, (2-5) opened stomata with guard cells and subsidiary cells, (6) dome-shaped papillae, (7) stomata and trichomes, and under SEM: (8) distribution of stomata (9-10) closed stomata with guard cells, (11-12) opened stomata with guard cells, (13-14) trichomes, (15) distribution of papillae.

Table 5 condition towards the middle part of the sequence. Calculated epidermal cell density (ED), stomatal density (SD) and stomatal A prime factor controlling the development of organic-rich sedi- index (SI) for ments is the redox conditions present in the depositional milieu. This significantly controls the abundance of OM preserved in sediments Epidermal cell Stomatal density Stomatal index density(ED) (SD) (SI) (Jomes and Manning, 1994). The pristane/phytane (Pr/Ph) ratio is a reliable and widely used redox indicator. Earlier, Powell and McKirdy Mean 427 43.5 10.7 (1973) used this ratio initially to delineate redox conditions in sedi- Minimum 80 13 8 mentary deposits. According to Didyk et al. (1978), redox conditions Maximum 820 66 16.2 are represented by Pr/Ph ratios < 1 (anoxic), 1–3 (dysaerobic) and > 3 Standard deviation 224.52 22 2.5 (Oxic). However, this ratio must be used with caution as the generation of these compounds depends on the OM sources (Goossens et al., 1984; of the depositional milieu during the deposition of the middle part of Volkman and Maxwell, 1986; ten Haven et al., 1987). Likewise, the the studied Lalmatia section. Hence, the presence of C29 regular sterane thermal maturity of sediments also affects this ratioTissot ( and Welte, and 4–methylsteranes suggests that the source of the organic matter 1984). Redox sensitive trace elements like V, Cd, Cr, Co, Cu, U, Fe, Cu, was largely of terrestrial source possibly deposited in a brackish and Zn are used to reconstruct the environmental condition of the

8 R.P. Mathews, et al. International Journal of Coal Geology 224 (2020) 103485

Fig. 6. Bar diagram representing the epidermal cell density, stomatal density and stomatal index from Lalmatia Glossopteris leaf cuticles Fig. 8. The Th/U vs. Sr/Ba plot indicating the depositional conditions of the Lalmatia samples. basins (Hatch and Leventhal, 1992; Jomes and Manning, 1994; Arthur and Sageman, 1994; Li et al., 2008). In Lalmatia samples, large varia- milieu. 13 tion in the Pr/Ph ratio is noticeable suggesting varying redox condi- The δ C of OM associated with any sedimentary sequence is mainly 13 tions. The bottom-most sample showed the highest value of 4.26 sug- governed by in-situ vegetation. Therefore, δ C values of OM are highly 13 gesting oxic conditions in the depositional milieu. However, the ratio significant in tracing the palaeovegetation history of the area.e Th δ C then dips to dysoxic-anoxic conditions later on throughout the deposi- value of C3 plants is mainly affected by environmental changes like tion of the sequence. The V/(V+Ni) ratio ranging from 0.51 to 0.88 water availability, temperature, humidity, and atmospheric CO2 con- 13 (avg. 0.67), also reflects reducing oxygen-poor environmentRimmer, ( centration. Besides, δ C values of OM associated with the sedimentary 2004). The ratio of Th to U ranges from 2.32 to 5.93 (avg. 4.06). All the rocks can also be altered through diagenesis. In the present study, values are higher than 2.0, further suggesting a brackish sedimentary dominance of odd-long-chain alkanes (C27,C29) with high CPI value environment with weak oxidation causing uranium dissolution (Zhang indicates that the significant OM source was from higher plants. The et al., 2008; Xie et al., 2018). A reason for this could be the rise in the very high TOC/TN ratio further indicates the significant higher terres- 13 water column or an increased input of sediments into the depositional trial plant input. The δ C values (–24.0 to –22.2 ‰) also support this

Fig. 7. The Plot showing variation of the ratios calculated from the trace element composition in the Lalmatia samples.

9 R.P. Mathews, et al. International Journal of Coal Geology 224 (2020) 103485

Cenozoic flora with the help of the nearest living relatives (NLR) (Chen et al., 2001a; Royer et al., 2001; Taylor et al., 2009). Here in this study, there are no close living species with which we can compare Glossopteris leaves as in cases of Mesozoic and Cenozoic floras i.e. no NLR is present in the fossils of Permian age. Recently, the study of the stomatal index from fossil leaves has come up as a significant proxy to estimate the

palaeo CO2 (pCO2) levels. In the Indian Gondwana scenario, few in- itiatives have been carried out for the cuticular study, especially for deducing the taxonomic characters of Glossopteris leaves (Srivastava, 1956; Pant and Verma, 1963; Pant and Gupta, 1971; Maheshwari and

Tewari, 1992; Srivastava et al., 2010). Nevertheless, cuticle based pCO2 analysis has not been applied yet on fossil leaves from Gondwana sediments of India. A constraint in this study was that there are no living

fossils present for determining the exact pCO2 of the fossils of Permian age. An attempt was made by Schmidt et al. (2011) from Parana Basin, Brazil (Lower Permian shales) based on the compressed Glossopteris Fig. 9. The Pristane/n-C17 versus phytane/n-C18 plot of the studied Lalmatia communis leaves to calculate the stomatal density and index and to find samples. out atmospheric CO2 during Phanerozoic. It was confirmed that early Permian is characterized by a low level of atmospheric CO2 as shown by view and suggest that the OM is originated from terrestrial higher C3 the modeled curve (Berner, 1991, 1994; Berner and Kothavala, 2001). plants. The range of δ13C values corresponds well with the typical va- It was observed that towards the end of the deposition of coal interval, lues of the Permian coal, usually varying between –26.0 and –22.0 ‰ the stomatal numbers detected were low (Faxinal Coalfield, Sakmarian) all along the basins of Gondwana (Aggarwal et al., 2019). de Wit et al. while it was high during younger intervals (Figueira Coalfield, Artins- 13 (2002) and Singh et al. (2012) have reported the δ C values from the kian) showing high atmospheric CO2 levels throughout Sakmarian. The Permian of Pranhita–Godawari Basin (borehole samples) and Sattupalli stomatal index and density variation corroborate well with the analysis Coalfield. In the present study, the values match well with the pre- done by Schmidt et al. (2011). The mean value of the stomatal index viously reported δ13C values. The lowest TOC/TN ratio (20.0) in the from Lalmatia Coalfield (Artinskian, 290 million years) and Faxinal shale unit suggests that the dominant input of organic matter is from Coalfield (Sakmarian, 295 million years) were compared to deduce the 13 aquatic plants. During this time the δ C values were reasonably stable. changes in atmospheric CO2 during Permian. The minimum stomatal index of Lalmatia Coalmine is 8.0, whereas in Faxinal Coalfield (Paraná 5.2. Palaeoclimate Basin) it is 12.6 (difference: 4.6). The maximum stomatal index from Lalmatia Coalfield is 16.2 and from Faxinal Coalfield is 18.75 (differ- In recent sediments, various lipid biomarker ratios are successfully ence: 2.55). The mean stomatal index of Lalmatia is 10.7, whereas the applied for the reconstruction of palaeoclimate (e.g., Nott et al., 2000; mean stomatal index from Faxinal Coalfield (Paraná Basin) is 15.7 Xie et al., 2004; Zheng et al., 2007; Andersson et al., 2011). However, in (difference: 5). Hence, we can infer that the cuticles of Glossopteris sp. ancient deposits such as Permian coal-bearing sequences, studies sig- from Lalmatia Coalfield (Artinskian) have lower stomatal index than nifying palaeoclimate have rarely been carried out (e.g., Izart et al., that of Faxinal Coalfield (Sakmarian) and this indicates a relatively

2012, 2015). Similarly, the environmental settings directly affect the higher level of atmospheric CO2 during Artinskian (younger Lalmatia trace element concentrations in sediments and subsequently, the cli- Coalfield) in comparison to Sakmarian (older Faxinal Coalfield) in- matic conditions are recorded. The ratio of elements Rb, Cu (wet–type) dicating that more warm conditions were experienced during the Bar- and Sr (dry–type) are often used to analyze the palaeoclimate char- akar sedimentation. acteristics (Lerman, 1978; Liu and Zhou, 2007; Xiong and Xiao, 2011). In the present study, the δ13C values show a significant depth trend Cuticles of fossil leaf have been regarded as immensely significant due and such a distinct difference in δ13C values of the LRJ profile points to to their application in taxonomy, biostratigraphy, interpretation of change in palaeoclimate and depositional conditions. It has been ob- palaeoclimate and reconstruction of palaeoenvironments (Kovach and served that plants narrow their stomatal opening leading to a reduction

Dilcher, 1984). Cuticular features are sensitive to climate based on of CO2 concentration with the stomata to evade water loss during water various size natures of anticlinal and lateral walls, which vary from stress conditions, resulting in an increase in δ13C and vice–versa. It is straight to arched, presence of striations and papillae, frequency of also supported by recent studies suggest that the δ13C of sedimentary stomata and amphistomatic nature of cuticles. The xerophytic plants OM as well as modern C3 plants respond principally to rainfall varia- have a straight lateral cell wall, small cell size, thickened cutinized cell tions (Kohn, 2010; Basu et al., 2015; Rao et al., 2017). Thus, it indicates 13 wall, papillate subsidiary cells, amphistomatic nature, overhanging that the δ C values of sedimentary OM archives derived from C3 ve- stomata, and rough and scabrate surface walls. The mesophytic plants getation will potentially reflect moisture availability. The Sr/Cu widely (damp, shaded and humid conditions) have characters like large cell varies from 0.2 to 8.75, with an average of 2.65 which suggests a warm size, low stomatal frequency. Plants adapt striations to prevent over- and humid climate. The high values in LRJ–7 and LRJ–9 point towards heating and scattering and reflection of heat, which also indicates light a dry climate. Considering trace elements, the stability of Rb is higher intensity. Dispersed cuticles, also provide a link with leaf megafossils than Sr during weathering (Chen et al., 2001b). During warm climate (Upchurch Jr., 1995) and an understanding of the history of an extant with high precipitation, intense weathering induces leaching of Sr re- taxon (Kovach and Dilcher, 1984). sulting in an increase in Rb/Sr value. Here in the present study, the Rb/ Woodward (1987) considered the inverse correlation of stomatal Sr and Sr/Cu values correspond and the values averaging 0.72 indicates frequency and atmospheric CO2. According to many workers, en- warm to dry climate transition (Fig. 7). Srivastava et al. (2010) studied vironmental factors including temperature and humidity is directly Glossopteris stenoneura Feistmantel cuticles collected from Churulia area proportional to the stomatal density (Salisbury, 1927; Tichá, 1982; (Barakar Formation) of Raniganj Coalfield and inferred warm and Roth-Nebelsick, 2005) and stomatal index is the direct effect of the humid climatic conditions. Consequently, this study demonstrates that atmospheric pCO2 (McElwain, 2003; Beerling et al., 2009). Conse- during the by and large warm and humid climatic settings in the Per- quently, many studies have been performed on the Mesozoic and mian, intermittent drier conditions also existed although it was not

10 R.P. Mathews, et al. International Journal of Coal Geology 224 (2020) 103485

Fig. 10. The comparative plot of various ratios indicating the depositional environment of the Lalmatia samples. the Lalmatia Coalfield (Artinskian age). extreme (Fig. 10). brackish water bodies, and reducing oxygen-poor environment. Although not a direct proxy for palaeoclimate interpretation, there 3. The hypostomatic nature of Glossopteris cuticles suggests heavy is an evident variation in the Pr/Ph, Pr/n–C17, and TAR across the precipitation. The climate can be deduced as humid and warm. The section. It is evident from Izart et al. (2012) that there is a noticeable comparative study of the stomatal index from Faxinal Coalfield difference in the Pr/n–C17 values of samples from humid tropical (tro- (Sakamarian) and Lalmatia Coalfield (Artinskian), shows a low pical wet climate) and humid dry climatic zones (tropical wet and dry stomatal index inferring a higher level of atmospheric CO2 during climate). Most of the samples from humid tropical regions show higher Barakar Formation (Artinskian age). values (avg. ~ 6), while the samples from humid dry tropical climates 4. The deposition of this sedimentary sequence took place in terres- show low values (avg. ~ 2). A Similar trend of Pr/n–C17is also observed trial–marginal conditions with marine influence during the deposi- in an earlier study (Izart et al., 2015). In Lalmatia samples, the values tion, probably due to the continued subsidence of the early Permian range from 0.45 to 2, which are similar to the values observed during Gondwana Basin. humid dry tropical climate. However, the change is not as pronounced 5. All the proxies are complementary to each other and unequivocally as in Izart et al. (2012), suggesting that the variation was not drastic. suggest variations in the climatic conditions. Although the climate The Pr/Ph ratio also showed similar tends along the studied section. was warm and humid, intermittent dry conditions were also ex- The terrigenous aquatic ratio (TAR) is used to distinguish OM according perienced in the setting. The inorganic and organic study reveals to the autochthonous or allochthonous nature (Bourbonniere and marine influence, but no biosignature was traced. Meyers, 1996). Higher terrestrial OM contribution leads to TAR > 1 and in eutrophic systems having largely autochthonous OM sources, Declaration of competing interest TAR is usually higher than 1 (Bourbonniere and Meyers, 1996; Meyers, 1997). As TAR is sensitive to vascular plant-derived OM contributions, None. changes in floral composition affect the TAR significantlySilliman ( et al., 1996). The study also shows that cooler climates lead to low TAR Acknowledgments values while higher values are related to the relatively warmer condition (Wang et al., 2014). The variation of TAR is matching with the The authors express sincere thanks to the Director, Birbal Sahni change in Pr/n–C17 and Pr/Ph ratio in the studied samples and suggests Institute of Palaeosciences, Lucknow, for her continuous support and that climate change is also recorded in the OM source input. As per the permission (BSIP/RDCC/Publication no.42/2019–20). The authors are previous reports, the coal-bearing Permian Gondwana sediments of the also grateful to Dr. Paul Mathew for critically going through the article Rajmahal Basin were formed under humid climatic conditions. The and giving valuable suggestions. We are also highly grateful to the present study demonstrates that during the by and large warm and administrators of the Eastern Coalfield Limited for giving necessary humid climatic settings in the Permian, intervening drier conditions permission and facilitating sample collection. also existed during the deposition of this coal-bearing sequence. References 6. Conclusions Aadil, N., Qasim, M., Hussain, A., 2013. Microfacies and diagenetic analysis of Amb 1. Biomarker and isotopic data suggest higher plants as the primary Formation, western part of Central Salt Range, Pakistan. Pak. J. Sci. 65, 503–510. sources of these deposits, mainly formed from the conifer and the Aboglila, S., Grice, K., Trinajstic, K., Dawson, D., Williford, K.H., 2010. Use of biomarker distributions and compound specific isotopes of carbon and hydrogen to delineate prominent Glossopteris flora. hydrocarbon characteristics in the East Sirte Basin (Libya). Org. Geochem. 41, 2. From the comprehensive geochemical data, it is evident that the 1249–1258. palaeoclimate was warm temperate to subtropical with fresh to Aggarwal, N., Agarwal, S., Thakur, B., 2019. Palynofloral, palynofacies and carbon

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