Search

A rich Glossopteris dominated plant fossils assemblage is recovered from the Barakar Formation of Lalmatia coal mine, Hura coalfield of Rajmahal Basin, Godda district, Jharkhand, India. The assemblage includes Glossopteris, Gangamopteris and Noeggerathiopsis (leaf forms) along with Vertebraria (root form). There are 4 genera and 14 species of megafossils in the collection, which includes 10 species of Glossopteris, two species of Gangamopteris and one species of Noeggerathiopsis and Vertebraria each. The flora, although similar to that of the Barakar Formation of the Damodar Basin complex, exhibit unique characteristics and is of Artinskian to Kungurian in age. The palynoassemblage recovered in the section reveals the dominance of genus Scheuringipollenites and sub-dominance of Faunipollenites (=Protohaploxypinus) along with Parasaccites, Potonieisporites, Barakarites, Plicatipollenites, Striomonosaccites, Striatopodocarpites, Crescentipollenites, Verticipollenites, Rhizomaspora, Distriatites, Primuspollenites, Striasulcites, Lunatisporites, Guttulapollenites, Platysaccus, Microfoveolatispora, Microbaculispora, Horriditriletes, Tiwariasporis and Weylandites, which demonstrates an early Permian age (Artinskian). The palynoassemblage indicates that the sediments belong to the lower part of the Barakar Formation. Biomarker analysis suggests varying organic matter input during the deposition of the studied sequence. Diterpane compounds and megafossil evidences suggest Glossopteris were the dominant flora along with conifers. Bacterial alteration of the organic matter is inferred from the hopane compounds. The δ13C value of organic matter associated with the carbonaceous shale directly corroborates with the typical δ13C values of the Permian time and is suggestive of warm and humid climatic conditions.

This study performed a stable isotope and redox-sensitive trace-element investigation on the Gotan Limestone and Pondlo Dolomite of the Bilara Group, Marwar Supergroup to decipher the palaeodepositional redox condition. A multivariate-statistical analysis of geochemical data set (δ13C-carb, δ18O-carb, δ13C-org, TOC, V, Ni, Cu, Zn, Mo, Pb, and U) reveals that limestone and dolomite units of the Bilara Group were deposited under two different redox regimes. Dolomite has an average δ13C-org values ~ − 30.0 ‰ and shows a statistically significant negative correlation with δ13C-carb which indicates an oxygen-depleted closed palaeodepositional environment. Dolomite δ13C-carb also shows a statistically significant negative correlation with redox-sensitive trace elements V, Ce, Pb, and U which infer higher secondary productivity during the dolomite deposition. The limestone has an average δ13C-org values ~ − 28.9 ‰ and δ13C-carb shows a significant positive correlation with δ18O-carb and Sr, whereas δ13C-carb shows a significant negative correlation with V and U. These statistical relationships among the geochemical parameter are indicative of suboxic-to-oxic water column with a relatively higher depth that received a significant input of water discharge from the terrestrial region. This discharge may have brought nutrients and other weathering-derived ions into the basin.

Results of a robust high-resolution carbon and oxygen stable isotope studies conducted on the Ediacaran Bilara carbonate sequence of the Marwar Supergroup, Rajasthan, India are presented. The δ13C-carb and δ18O-carb in the Bilara Group vary from −9.0 to 4.1‰ and from −10.7 to 8.3‰ respectively. Overall, 457 analyzed samples have δ18O-carb significantly above −10‰, below which carbonates are considered diagenetically altered. The results are compared with well-dated established high amplitude negative carbon isotope excursions sites in other parts of the world recorded from the Ediacaran successions. The Bilara δ13C-carb pattern is closely similar to that of the Yangtze Gorges platform, South China, where the Ediacaran δ13C-carb variation profile revealed four negatives (EN1, EN2, EN3, EN4) and three positive excursions (EP1, EP2, EP3). Similarities of δ13C-carb pattern demonstrate that carbonate succession of the Bilara Group is likely time equivalent to Yangtze Gorges succession.

Lalmatia coal-bearing sequences belong to the Barakar Formation (Permian) of Lower Gondwana. The well-developed coal-bearing sequences (approx. 52 m) exposed along the mine section have been studied to understand the depositional environment. Along with this, a cuticle study was performed to understand the palaeoclimate with the help of the stomatal index. The distribution of n–alkanes (n–C15 to n–C31) suggests major higher plant and algal dominant source input, although variations are seen in the relative input. Steranes identified include C29 regular sterane and 4-Methylsteranes. The Pr/Ph ratio varied from 0.43 to 4.26. Warm 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.

This study performed a redox sensitive trace element (RSTE) and organic carbon isotope investigation on the shallow section of ~1.2 Ga Bijaigarh Shale, Kaimur Group, Vindhyan Supergroup. The results demonstrate that unlike the coeval deeper section, in which Mo and Ni concentrations are several-folds higher compared to the upper continental crust (UCC), the shallow section contains Mo and Ni equivalent to the upper continental crust (UCC). This spatially heterogeneous burial of Mo and Ni is very similar to the modern stratified basins i.e., Black Sea and Cariaco Basin, where Ni and Mo composition of the sediments underlying a shallow oxic water column is comparable to the UCC however, the deeper sediments underlying the anoxic/euxinic contains several folds-higher Mo and Ni compared to the UCC. Bulk precipitation of Mo in a hydrosphere is mainly controlled by sulphide present in the anoxic/euxinic layers of the water column, on the other hand, Ni precipitation is generally controlled by oxygenic primary productivity. Though the shallow section of the Bijaigarh Shale is depleted in Ni, a significant correlation between Ni and TOC is still relevant and indicates an oxygen-rich surface water layer for the respective palaeohydrosphere. Furthermore, δ13C-org values (between −32.0 and −30.4‰) from the shallow section suggests that the organic carbon exported into the sediments during the Bijaigarh Shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers.

Palynological studies of the present Permian sediments play a vital role in biostratigraphic and palaeoecological interpretations. Additionally, the palynofacies analysis, Total Organic Carbon (TOC) content and δ13C value in the present study focus largely for the palaeoenvironmental and palaeoclimatic reconstruction and also provides information about processes responsible for sedimentary deposits along with their lithological counter parts. The palynological investigation of 306 m deep borehole (MSM-25) from the Somavaram area of the Godavari Valley Coalfield has led to infer five distinct palynofloral assemblages. The Artinskian (Palynofloral assemblage-I and II), Guadalupian (Palynofloral assemblage-III and IV), and Lopingian (Palynofloral assemblage-V) ages have been assigned to the palynofloral assemblages based on the palynofloral evidence. The distinct stable carbon isotope ratios also comprehend these ages with extreme climatic events. The Artinskian age (−22.4‰) is characterized by relatively higher average δ13C values, whereas lowest average δ13C values are observed at the Lopingian age (−24.0‰) with intermediate average δ13C value (−23.2‰) during Guadalupian age. In the present study, the Permian-Triassic (P-T) transition is marked by the distinct negative carbon-isotope excursion followed by a distinct recovery during the early Triassic time period. The relative variability of palynofacies components, such as palynomorphs, structured terrestrial phytoclasts, opaque phytoclasts, degraded organic matter (OM) and amorphous OM, is related to hydrodynamic perturbations during the deposition time. Based on the dominance and sub-dominance of the palynofacies, three distinct depositional phases have been identified, representing differential environmental settings. The palynomorphs and structured terrestrial phytoclasts dominate the Palynofacies assemblage A suggesting forest swamp environment, while in the Palynofacies assemblage B the dominance of degraded OM and amorphous OM characterize Reed marshes/lakeshore setting and the abundance of opaque phytoclasts in the Palynofacies assemblage C indicate oxidized swamp environment.

Present study aims at reconstructing the paleomonsoonal rainfall, paleovegetation and provenance change during the late Quaternary. Towards this, Bhognipur core, collected from the southern Ganga Plain, have been sampled for soil carbonate (SC) and soil. The δ 18O values of SC (δ 18OSC) range from −7.6 to −4.9‰. The variations in δ 18OSC values suggest that during the late Quaternary, the monsoon intensified during MIS 3 and MIS 1 and the maximum lowering of rainfall intensity is observed during MIS 2. The δ 13C value of SC (δ 13CSC), organic matter dispersed in the soil (δ 13CSOM) and occluded in the carbonate nodules (δ 13CNOM) ranges from −4.1 to +1.4‰, −25.6 to −16.3‰, and −27.7 to −25.0‰, respectively, implies mixed C3–C4 vegetation over the Ganga Plain. Variations in δ 13CSOM and δ 13CNOM values at same depth imply preservation problem of pristine organic matter signature. Therefore, it is important to assess the preservation of residual organic matter before using it for paleovegetational reconstruction. The monsoon-vegetation relationship indicates that relative abundances of C3–C4 vegetation were mainly driven by variations in monsoonal rainfall intensity. Using 87Sr/86Sr in SC, we show that the Himalayan river was supplying sediments in the southern part of the Ganga Plain during MIS 3.

Temporal analysis of Sr isotopes in soil carbonates and Sr and Nd isotopes in silicate fractions has been carried out in a sedimentary core (Kalpi core; 50 m long) raised from the southern bank of the Yamuna river, Ganga Plain, India. The aim of the study is to constrain sediment provenance through comparison with the modern Himalayan and peninsular river systems' water and bank sediments. Sr isotopic data in soil carbonates (0.71874 to 0.71410) and Sr Nd isotopic data in silicate (0.72865 to 0.74544 and − 13.9 to − 17.2, respectively) vary significantly with depth and are indicative of both Himalayan and peninsular sources for sediments in the southern Ganga Plain. The positive correlation between 87Sr/86Sr ratio and 1/Sr in soil carbonate and the negative correlation between 87Sr/86Sr and eNd in silicate confirm mixing of sediments from these sources. Variations of 87Sr/86Sr ratios in soil carbonates show that at ~ 80 and 45 ka the Himalaya acted as the major source of sediments in the southern part of the Ganga Plain. The gradual decrease in 87Sr/86Sr ratios after 80 and 45 ka indicates change in source to peninsular India which is also supported by limited Sr and Nd isotope data in silicates. The change in sediment provenance corresponds well with the available climatic record and is suggestive of strong climatic control in sediment supply with high supply from the Himalaya during the interglacial period and peninsular sediments during glacial period.

The carbon isotope composition of graphite and carbon and oxygen isotope composition of associated calcite from different locations of the Eastern Ghats Mobile Belt (EGMB) of Orissa have been measured in order to understand the origin of graphite. The δ13C values of graphite range from −2.4‰ to −26.6‰. Forty-four of sixty-one samples have δ13C values less than −20‰. Most of these low δ13C values graphite corresponds to schists and disseminations in khondalite and calc-silicate granulites, thus indicating graphitization of organic matter. The remaining light-carbon–graphite occurs as veins which is the result of graphitization of transported organic matter. The graphite with intermediate δ13C value (−13‰ to −19‰) indicates carbon contributions from both organic and carbonates sources and/or mantle sources. The higher δ13C values graphite (−2.4‰ to −8.8‰) represent mantle carbon and/or carbonate sources without significant contribution from organic carbon. The temperatures of metamorphism have been estimated using carbon isotope ratios of graphite and associated calcite of calc-silicate granulites, where typical cation exchange thermometer assemblages are lacking and significant mineral reaction textures used to calculate pressure–temperature of metamorphic events are absent. Metamorphic temperatures obtained 945 °C are close to the ultrahigh-temperature reported from the EGMB. The minimum temperature estimated using the graphite–carbonate carbon isotope ratio is 90 °C. The lower estimates of temperatures probably indicate changes in the carbon isotope ratio of calcite by decarbonation reaction or armoring of carbonaceous matter in silicates during metamorphism preventing continuous exchange with calcite.