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Summer Research Fellowship Programme of India's Science Academies

Nuances of geochemical techniques used in

provenance/palaeoclimatic studies

Nikhil Sarwadnya

1st MSc Applied Geology, Department of Earth and Atmospheric Sciences, National Institute of Technology, Rourkela, Odisha State 769008

Dr. Anupam Sharma

Scientist F, Birbal Sahni Institute of Palaeosciences, Lucknow, Uttar Pradesh 226007

Abstract

To learn geochemical techniques used in provenance and palaeoclimatic studies late Paleocene-early Eocene sedimentary rock samples from Kapurdi Lignite mine were studied by textural and mineralogical analysis. Grain size analysis was carried out by International Pipette Method as well as by using Particle Size Analyzer instrument. Mineralogical analysis was performed by X-ray Diffraction technique, Trace and REE analysis was carried out by ICP-MS. Loss on ignition method followed to find the inorganic and organic content. Results indicate that the reducing conditions were prevailing during deposition of most part of the sequence and a climatic condition was warm and humid.

Keywords: Barmer basin, Akli Formation, clay mineral analysis

Abbreviations

Abbreviations
 ICP-MS Inductively Coupled Plasma Mass Spectrometer 
 XRD X-ray Diffraction 
 XRF X-ray Fluorescence 
REE Rare Earth Elements
LOI Loss On Ignition

INTRODUCTION

Background

Provenance and Palaeoclimatic studies involve textural, geochemical and mineralogical analysis of sediments or sedimentary rock. The word provenance has its origin in latin verb "Provenire", meaning to come forth or to originate. Provenance studies involve interpretation of source of sediments or sedimentary rock. Provenance studies are generally easy for coarser clastic sediments, because the cobbles and pebbles can be easily examined and based on texture of individual clast the provenance can be identified. In such cases heavy mineral analysis is carried out. In case of finer sediments (sand, silt and clay) or sedimentary rocks it becomes difficult to determine the provenance due to mixing of sediments. In such cases geochemical approach is preferred in determining provenance. Major and trace element geochemistry of sedimentary rocks provide information about the type of source rock, palaeoweathering conditions and hydraulic sorting. Certain clay minerals form as a result of weathering of particular bed rock types. Clay mineral analysis is one of the reliable method to investigate provenance. Sedimentary rock samples from Akli Formation of Barmer basin, Rajasthan were chosen for geochemical analysis. There is very less available literature about the provenance study of the Akli Formation of Barmer basin. The main objective of this study is to infer about provenance of sediments of Akli Formation and prevailing palaeoclimatic conditions by geochemical techniques.

Geology of Rajasthan

The state is located within 23º03’-30º12’ N and 69º29’-78º29’-78º17’E and bounded on west and northwest by Pakistan, on the north and northeast by Haryana and Uttar Pradesh and on the southwest and south-southeast by Gujarat and Madhya-Pradesh states respectively. The north western part of the state is occupied by the Thar Desert covering one third of the total area. The Aravalli hill range extends from Delhi in the north-east to the north of Gujarat in the south-west divides the State into two unequal parts. Archaean Banded Gneissic Complex is grey coloured gneissic rocks over which rocks of Meso-Neo Proterozoic Aravalli and Delhi fold belts were deposited and are located in the north and central region of the state. Towards the eastern part of the state occurs the Vindhyan Supergroup of rocks which range from Neo-Proterozoic to lower Cambrian. In south eastern part the state is partly covered by Deccan lava flows. In the north western part occurs Malani felsic igneous suite and the younger Mesozoic Cenozoic sedimentary basins viz, Barmer basin, Jaiselmer basin, Bikaner-Nagaur basin. Most of the area is now covered by windblown sand.

Geology of Barmer basin

The Barmer basin is a narrow N-S trending graben and it is a northern extension of Cambay basin. It is located in the western part of Rajasthan. It is a tectonic graben bound by the Barmer–Birmania high on the west, Jodhpur high on the east, northern boundary by Fatehgarh fault and Malani igneous suite on the south. Sisodia and Singh (2000) have classified the sediments of the basin as- i) Pre-rift sediments ii) Syn-rift sediments and iii) Post-rift sediments. The sediments are deposited on Late Proterozoic Malani Igneous suit.

The pre-rift sediments are represented by siliceous facies, comprising shale, sandstone and orthoquartzite belonging to Randha Formation; Calcareous facies comprising limestone phosphorites and dolomudstones of Birmania formation; fining upward sand bodies of Sarnu Formation; Medium to coarse grained sand with plant fossils of Lathi Formation.

The syn-rift sediments are consisting of sandstone and clast supported conglomerate of Barmer hill Formation and Fatehgarh Formation. The siliceous earth forming base of Mataji ka Dungar formation and underlain by Fatehgarh Formation is also a part of syn-rift sediments.

The post-rift sediment comprises sedimentary rocks of Mataji ka Dungar Formation and Akli Formation. The Akli formation overlies the Mataji ka Dungar Formation and is made up of sandpoor claystone and lignites.

Akli formation

The Akli Formation is consisting of bentonitic claystone, grey bituminous claystone and light yellow coloured claystone. Akli Formation occurs in the central part of the basin. Sisodia and Singh (2000) have divided Akli Formation into two members Thumbli Shale member and Kapurdi Fullers earth member.

The Thumbli member comprising grey sand poor bituminous claystone as host deposit enclosing channel fill lignite deposit. These beds are arranged in cycle which commence with bentonite followed by bituminous claystone and ends up in lignite. The Kapurdi member is clay rich deposit.

Barmer stratigraphy_1.PNG
    Stratigraphy of Barmer Basin after Sisodia and Singh (2000) and Tripathi et al (2009).

    Depositional environment

    The Akli Formation shows channel fill sedimentation, fining upward nature of the sediments indicates the flood plain deposition (Sisodia and Singh 2000). The dominent occurrence of claystone and fullers earth type claystone facies represent low energy shallow basinal sedimentation. The thin sandstone beds and claystone within the claystone show that the basin was periodically interrupted by flood events. Occurrence of Mangroove plant pollens such as Nypa sp. indicate deltaic environment (Tripathi et al 2003, Tripathi et al 2009).

    Age

    The age for Akli Formation is Middle to Late Palaeogene as suggested by Sisodia and Singh (2000). Palynological and palynofloral studies indicate that the age of the Akli Formation is Thanestian to Ypresian (A. Sahni et al., 2004 ; S. K. N. Tripathi et al., 2009).

    Study area

    Kapurdi lignite mine (25°94'86"06N 71°34'72"10E) is located in the Indian state of Rajasthan. The lignite mine is an open cast mine. The rock samples are collected from the mine faces from the depth of 57 m up to the topmost horizon. The collected samples consist of clay, siltstone, shale and sandstone.

    LITERATURE REVIEW

    The depositional environment and recent stratigraphy of the Barmer basin is given by Sisodia and Singh (2000). They have classified the rock succession into Pre-rift, Syn-rift and Post-rift sedimentary rock units. The depositional environment for the Paleogene succession is near shore flood plain as indicated by fining upward nature of lignite cycle. Palynological work on Akli formation by A. Sahni et al., (2004) and S. K. M. Tripathi et al., (2009) concluded that the Akli Formation was deposited in a palaeoshoreline with extensive swamp fringed by abundant mangrove Nypa palm. The abundance of biodegraded terrestrial and amorphous organic matter throughout the sequence shows the dominance of anoxic conditions after burial of organic matter. The study on microforaminiferal linings from the Akli Formation conducted by Morteza Tabaei and Ram Yash Singh (2002) suggests shallow sea conditionand the occurrence of microforaminiferal lining in pollen dominated assemblages indicates high influence of terrestrial sediments thus the area was very close to the ancient shore line.

    METHODOLOGY

    There are two types of analytical techniques; Qualitative analytical techniques and Quantitative analytical techniques. Qualitative analytical techniques are those by which the one can infer the chemical composition of the sample. Quantitative analytical techniques are used to determine the amount or quantity of chemical compounds present in the sample.

    Qualitative analytical techniques include X-ray Diffraction (XRD), Flame spectroscopy, etc while the quantitative analytical techniques include X-ray Fluorescence Spectrometry (XRF), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Isotope Ratio Mass Spectrometry (IR-MS) etc.

    Textural Analysis

    Textural analysis is carried out to determine grain size of the sediments. Grain size analysis is carried out by International Pipette Method and Laser Diffraction Particle Size Analyzer.

    Grain size analysis by international pipette method

    In this method concentration of suspension is measured from known volume of liquid. This method follows Stroke’s law, according to which,

    The terminal (Vt) velocity of a spherical particle settling under influence of gravity is directly proportional to square of its radius (r).

    Vt α r2

    The salts, amorphous organic content and amorphous iron oxide coating over the sediment grains can act as cementing agent. To obtain errorless data for the grain size analysis, the sediment samples are made free from salts, organic content and free metal ions. Following protocols are followed for 10 gm of sediment sample.

    1)  To remove water soluble salts from the sediments, 50 ml of 1N NaOAc (Sodium acetate) solution having pH-5 is added and samples are heated on the water bath for an hour. The samples are then centrifuged for three times and supernatant is discarded.

    2)  To remove organic matter 10 ml of 30% H2O2 (Hydrogen peroxide) is added in each sample. Samples are then placed on water bath for an hour and left overnight for the completion of the reaction. Hydrogen peroxide is thermodynamically unstable and decomposes to O2 and H2O as shown in the following reaction.

    H2O2 + H2O2 → 2H2O + O2

    The Oxygen molecule then reacts with organic matter present in the soil and produce carbon dioxide.

    Organic matter (C) + O2 → CO2 ↑+ H2O

    The reaction completes when the CO2 bubbles disappear. Except the sandstone samples, the rest samples have taken more time for completion of the reaction, this indicates their higher organic content. Samples are then centrifuged thrice and decanted in order to remove the supernatant.

    3)  To remove amorphous coating and crystals of free iron oxides (particularly Hematite and Goethite), 40 ml of 0.3M Na-Citrate and 60ml of 1N NaHCO3 (Sodium bicarbonate) is added in each sample. After heating on water bath for 20 minutes at 75˚-80˚C temperature, 1 gm Na2S2O4 (Sodium dithionite) is added in each sample and placed on water bath for half an hour. The samples then centrifuged three times and supernatant is removed. Here sodium citrate serves as chelating agent, while sodium bicarbonate buffers the solution and sodium dithionite reduces free iron. The iron oxide removal reaction requires reducing agent having high oxidation potential. The oxidation potential of sodium dithionite system increases with increasing pH. Sodium bicarbonate provides required OH- ions (O. P. Mehra and M. L. Jackson (1960)).

    Now the samples were anlyzed by International Pipette method or Particle size analyzer.

    4)  Separating sand, silt and clay: - The Sand particles are separated by using 63µ sieve. The centrifuged bottle is emptied on the sieve, with the help of water jet spray, sand particles remaining on the sieve are collected in a 100 ml beaker and kept in oven at 110˚C for drying.

    The fine fraction collected in the bottom is transferred to 1 liter polypropylene bottle. Required amount of distilled water is added to make up the volume of the suspension. Then 2 ml of 2% NaCO3 is added to disperse the particles and to raise the pH of the solution to 9.5. The bottle is now placed on water bath for half an hour for heating.

    The suspension is allowed to cool and then transferred to a 1 liter cylinder. The bottom sediment is dislodged using plunger. Immediately after removing the plunger the time and the temperature is recorded. The Cylinder is left undisturbed until the sediment is settled down. For clay at 25˚C temperature the suspension is left undisturbed for 6 hours and 51 minutes; then suspension from 10 cm distance from the 1000 ml mark is transferred to the polythene bottle. The separated clay in the bottle is recovered after centrifuge and mounted on glass slide for XRD analysis. The remaining fraction of clay is kept in the oven for drying and stored for further analysis.

    Laser diffraction particle size analyzer

    The grain size analysis of the sediment is carried out using Beckman Coulter LS-13 320 Laser diffraction Particle Size Analyzer available at BSIP’s Geochemistry lab. The instrument measures the size distribution of particles suspended either in a liquid or in dry powder form by using the principles of light scattering. Scattering of light is a natural phenomenon, it occurs when a light wave or energy wave is deflected off its rectilinear path when it passes through an imperfect medium or heterogeneous medium.

    IMG_20190606_152628.jpg
      Beckman Coulter LS 13 320 Partical Size Analyzer

      Procedure

      A single drop of sample (representative of whole sample) is introduced in to the sample chamber then the instrument starts analyzing the particle size after manually receiving the command from the operator. The density of the sample drop must be in an average range for accurate measurement; otherwise obtained data will be inaccurate. The working of the instrument is explained below.

      Working

      The instrument measures particle size distributions by measuring the pattern of light scattered by the particles in the sample. The scattering pattern is result of light intensity as function of scattering angle. Each particle's scattering pattern is characteristic of its size. The pattern measured by the instrument is the sum of the patterns scattered by each constituent particle in the sample. A Fourier lens is situated in between the sample and detector and light source (Fig 5). Fourier lens serves two functions, it focuses the incident beam to avoid its interference with the scattered light and it transforms the angularly scattered light into a function of location on the detection plane. The most important feature of Fourier optics is that the scattered light of any particle at a specific angle will be refracted by the lens so as to fall onto a particular detector, regardless of the particle's position in the beam.

      LS13 320.PNG
        Fourier optics after Beckman Coulter (2011)

        The connected computer yields the resultant data in the form of differential volume percentage versus the particle diameter (Fig 4).

        Grainsizegraph.PNG
          Differential Volume percentage versus particle diameter graph plot.

          Elemental and Minerological Analysis

          For Trace element & REE analysis samples were analyzed using ICP-MS. Clay and bulk samples mineral analysis was done using XRD. Total moisture, organic and inorganic carbon content was determined by LOI method.

          The rock samples were powdered using RETSCH Vibratory Disc Mill / Retsch RS200. The sample powdering involves, taking approx. 20 gm sample in the pot made of Tungsten Carbide along with a cylindrical block of same material and then fixing it in the disc mill. After receiving the command, the disc mill evenly powders the sample.

          Inductively coupled plasma- mass spectrometry

          What is mass spectrometer?

          A mass spectrometer generates multiple ions from the sample under investigation; it then separates them according to their specific mass-to-charge ratio (m/z), and then records the relative abundance of each ion type.

          Sample Preparation/Acid digestion: - For a sample to be processed efficiently in the plasma, it must be in either gas or vapor (aerosol) form. Therefore the typical protocol is to digest rock samples in strong and hot acid.

          1) Step 1 - Approximately 30 mg of the rock sample is taken in a clean and dry Teflon vial. 2 ml of HF (hydrofluoric acid), 1 ml of concentrated distilled HNO3 (nitric acid) (2:1) and 1 ml of HClO4 (perchloric acid) is added. The lead tight vial is then placed on a hot plate at 120˚C for nearly 8 hrs; further heated by opening the cap till every drop of acid solution evaporates and solid residue develops.

          2) Step 2 - Again 1 ml of HF (hydrofluoric acid), 2 ml of HNO3 (nitric acid) (1:2) and 1 ml of HClO4 (perchloric acid) is added and lead tight Teflon vial is heated at 120˚C for 8 hours on a hotplate. After 8 hrs of heating, the cap is removed and the sample is again heated till all the acid solution evaporates and whitish yellow residue is obtained. The residue is soluble in nitric acid. The residue dissolved in 50 ml of 2-5% nitric acid. Thus the solid rock sample is now converted to a solution.

          For cleaning and washing the vials and in acid dilution Milli-Q/ultrapure/deionized water is used. In acid digestion and also in cleaning, HNO3 (nitric acid) is preferred over HCl or H2SO4 because it forms water soluble salts and thus ensures maximum purity. Nitric acid is a strong mineral acid that produces soluble salts, useful for keeping the elements of interest in solution until they reach the plasma of the ICP-MS. Nitric acid, also an oxidizing agent, additionally breaking down the organic components better than other acids.

          The role of HF (Hydrofluoric) acid is to dissolve the silicates to access free metal ions enclosed in silicates.

          ·         SiO2(s) + HF(aq) → SiF4(g) + H2O(l)

          HClO4 (Perchloric acid) being a powerful oxidising agent at higher temperature, break the metal bonding between the chemical constituents of the sample, for better reaction of sample’s constituents with the acids and reagents. It has the capacity to explosively react with organic matter. Nitric acid is used to avoid this violent reaction, Nitric acid reacts with organic matter at comparatively lower temperature.

          IMG_20190524_132736.jpg
            Vials kept on hotplate in acid digestion unit.

            ICP-MS working

            The ICP-MS requires 15˚C to 30˚C temperature and non condensing 20 to 80% humidity for its operation. Before running the samples, ICP-MS is calibrated using multi-element calibration standard solutions and are prepared using single and multi-element primary solutions. Rhodium is used as an internal reference standard. USGS (United States Geological Survey), NIST (National Institute of Standard and Technology) and IAEA (International Atomic Energy Agency) rock standards are used before running the samples. The ICP-MS is operated on Helium mode to overcome the interference.

             

            The robotic arm of SPS-4 Auto sampler unit which is operated by computer software, moves its probe into the desired sample. The pump passes the sample solution into the nebulizer. The nebulizer disperses the sample solution with the gas stream which results in the formation of mist. The double spray chamber separates the larger droplets from the fine droplets of aerosol.

            The separated fine sample aerosol passes into the horizontal injector tube. The injector tube is mounted horizontally on the ICP torch. The ICP torch consists of three concentric quartz tubes. The quartz tubes carry plasma gas, makeup or auxiliary gas and carrier or nebulizer gas. The radio frequency coil is situated at the end of the torch, radio frequency current passes through it as a result of intense RF field, plasma is generated. The plasma has temperature range of 8000K to 10000K. The carrier gas which flows through the innermost tube delivers sample aerosol to the plasma. At such a high temperature the sample aerosol is instantaneously desolvated and ionised. The ions are then passed through sampling and skimmer cone before converting to narrow beam by two conical extraction lenses. The beam then enters into the ORL which is an octopole ion guide. This unit is pressurised with He gas and it reduces spectral interferences. The beam then enters into the quadrupole. The quadrupole consist of parallely arranged four metal rods. These rods are applied with RF and DC voltages. At any combination of applied voltages these rods allow only specific mass to charge ratios to pass through the center. While other masses are unstable get destroyed after colliding with the rods. The quadrupole cannot resolve polyatomic and isobaric interferences and thus it is limited to the unit mass resolution. The ion signals are measured by the electron multiplier detector. The data is then entered into the connected computer and the concentrations of the elements in ppm are obtained.

            IMG_20190711_162407.jpg
              ICP-MS facility at Geochemistry lab, BSIP.

              icp.jpg
                ICP-MS working.

                (Source- Agilent Technologies ICP-MS 7700x Hardware Maintenance Manual)

                X-ray diffraction

                Principle: When x-rays are scattered from a crystal lattice, peaks of scattered intensity are observed which correspond to the following conditions:

                1.      The angle of incidence = angle of scattering

                2.      The pathlength difference is equal to an integer number of wavelengths.

                Bragg’s Law equation

                nλ=2dsinθ

                Bragg dada_1.PNG
                  Diffraction of X-rays from different crystal planes (Martin Ermrich and Detlef Opper, 2011).

                  In the crystal x-rays are scattered from different layers of atoms. Some travel longer optical path (here in the above figure wave II) for a radiation with defined wavelength. The criterion of Bragg’s law is met at a certain angle and all scattered beams are at the same plane which means that constructive interference takes place.

                  XRD_Defractometer.PNG
                    X-ray diffractometer basic elements, (Martin Ermrich and Detlef Opper,, 2011). 

                    Procedure

                    Take few gram of the sample (~2-3 gm) and put it in the sample holder provided for sample analysis.

                    Spread the sample evenly in the form of thin film with smooth top surface with the help of a glass slide.

                    Now place the sample holder in the socket in the XRD machine.

                    The x-ray of fixed wavelength ( Cu Kα1 1.540598 A°) produced by the x-ray tube irradiates the powder sample. The x-ray gets diffracted by the different phases present in the sample, and enters into the detector. By varying the diffraction angle (2θ) through movement of the tube or sample and detector intensities are recorded to create diffractogram. Diffractogram consists of intensity in counts per second v/s 2θ values. The atomic spacing is specific for a specific mineral crystal. Conversion of diffraction peaks to d-spacing allows identification of the mineral because each mineral has set of unique d-spacing. X-ray diffraction is performed for bulk powder samples and dry clay samples.

                    Diffractogram

                    diffractogram.PNG
                      Diffractogram for Clay showing major peaks at 12.01° and 24.80°.

                      As a mineral has specific d spacing values, different minerals show peaks at different 2θ angle. The angle is dependent on wavelength of the x-ray beam. ­­The ‘d’ values for each peaks were calculated using the Bragg’s equation and the values were matched with the reference d values. Thus the minerals present in the sample were inferred.

                      Loss on ignition

                      Loss on ignition is an analytical process which involves heating of the bulk powdered samples at different temperature in a furnace and then estimating the moisture, organic and inorganic carbon content of the rock sample.

                      The method is based on differential thermal analysis and following facts:

                      Moisture content of the sample gets depleted above 100˚C. Organic matter begins to ignite at about 200 °C and is completely depleted at about 550 °C. Most carbonate minerals are destroyed at higher temperatures (calcite between 800 and 850 °C, dolomite between 700 and 750 °C).

                      Procedure

                      At first empty crucibles are weighed and samples are placed in them and again weighed, the crucibles are then separately heated in furnace at 110˚C for 12 hours and for 2 hours at 550˚C & 950˚C. After heating, every time the crucibles are weighed and loss in percentage is determined. Following formulae are used to calculate weight loss percentage.

                      Moisture% = (Weight loss after 110°C ÷ Sample Weight) × 100

                      Organic Carbon/matter% = (Weight loss at 550°C ÷ Sample Weight after 110°C) × 100

                      Inorganic Carbon/Carbonate% = (Weight loss at 950°C ÷ Sample Weight after 550°C) × 1.36

                      LOI data is used to cross-check XRF analysis data. The summation of total oxides in the sample and total LOI should not exceed 100.

                      XRF

                      X-ray Fluorescence Spectrometry is used to determmine major oxides present in the sample.

                      Basic principle

                      According to Neil Bohr’s Shell model, an atom consists of a nucleus with positively charged protons and neutral neutrons. The nucleus is surrounded by electrons grouped in shells or orbitals. The innermost shell is called the ‘K’ shell followed by surrounding ‘L’ shell, ‘M’ shell and ‘N’ shell and so on. The maximum numbers of electrons in the principal shell are 2 for ‘K’, 8 for L and 18 for M shell. The energy of electron depends on the shell and on the proton number.

                      When an atom get irradiated by the x-ray radiation with sufficient energy an electron can be expelled from the atom. The emission of an electron can produces a void in a shell. This excites the atom and puts it on higher energy state. The atom restores its original configuration by transferring the electron from the outer shell to the void in the inner shell. The outer shell electron has higher energy than the inner shell electron. The excess of energy is emitted in the form of x-ray photon or wave with characteristic wavelength.

                      XRF-Electron.PNG
                        X-ray Fluorescence

                        Sample Preparation

                        The XRF machine requires solid sample pellet. The 6 gm of bulk powder sample was weighed along with 4 gm of boric acid on the Electrical Weighing Machine. The sample and boric acid mixed together till a homogenous mixture is formed. Without binder, fine powder particles may fall off or scatter from the pellet surface cause contamination of the spectrometer’s sample chamber in vaccum mode. Binder is added for easy pelletization of samples whose powdered form cant be easily pressed into pellet form. The binder must not have the elements which are to be analysed. Accurate weighing & complete mixing is essential to minimize the analysis error. Here boric acid is used as binding agent because it is cheap and used universally.

                        The Sample mixture was added in the Pellet making machine. The die applies around 20-25 tonnes of weight; it takes 4-5 minutes to make one pellet.

                        IMG_20190713_130226.jpg
                          Pellets

                          Working

                          The samples are first placed in the sample holders. The robotic arm which is operated by the computer, picks up the target sample and places it in the analyzing unit/X-ray cup. The analyzing unit/X-ray cup is made up of lead metal to check the X-ray radiation. The primary X-rays hits the sample in vacuum and the resultant secondary radiation is detected by the detectors according to their wavelength. The resultant data is then entered into the connected computer.

                          *Due to unavailability of standard sedimentary samples, major oxide analysis could not be performed.

                          RESULTS AND DISCUSSION

                          Grain Size Analysis

                          Grain size analysis results indicate that except four sandstone beds, rest sequence is sand poor. The average sand and mud (silt and clay) percentage for sequence determined by International Pipette method is 46.6% and 53.4% respectively. The values obtained by Particle Size Analyzer are 40.08% for sand and 59.92% for mud (silt 41.81% and clay 18.11%). The result is plotted in triangular diagram in (Fig13). The grain size variations are plotted against the litholog (Fig14). Brown coloured amorphous organic matter in variable proportion is recovered from most of the samples along with the sand.

                          Grain Ternary_1.PNG
                            Ternary plot for grain size analysis.
                            My samples Grain.jpg
                              Grain size varitions against litholog.

                              LOI

                              The average moisture content for the sequence is 1.67%, organic carbon content is 7.44% and inorganic carbon content is 0.05%. In the graph, LOI values are plotted against litholog (Fig15), moisture and organic carbon curves are showing similar trends. The organic and inorganic carbon curves have relatively inverse relation. The clay bed at 7.44 m in the litholog has highest inorganic carbon content (five fold than the average).

                              My samples_LOI.jpg
                                LOI data against litholog.

                                Mineralogy

                                Bulk XRD data shows dominance of quartz (3.34 A˚, 4.25 A°, 1.81 A°, 2.28 A°, 2.45 A°) in sandstone beds (Fig 16). Feldspar is absent in all analyzed sandstone samples. Dry clay mineral analysis reveals kaolinite (7.15 A˚, 3.58 A˚) is the dominant mineral in the clay fraction (Fig 17). Along with kaolinite, vermiculite (2.38 A˚), Illite (10.04 A˚), chlorite, smectite and quartz are also present in the clay fraction. Both chlorite and kaolinite have d spacing at 7.04-7.15A˚ and 3.58A˚, but the absence of feldspar in the sandstone beds suggest that the feldspar has been converted to kaolinite.

                                KD-17_1.PNG
                                  Diffractogram of sandstone sample.

                                  KD-02.PNG
                                    Difrractogram of separated dry clay, sample code KD-02.

                                    CONCLUSION AND RECOMMENDATIONS

                                    Conclusion

                                    1.      Occurrence of intermittent sandstone layers indicate that either regression could have occurred during their deposition or high meteoric precipitation was responsible for high sedimentation.

                                    2.      The presence of amorphous organic matter in clay-silt beds and high organic carbon LOI values, indicate that anoxic conditions were prevailing during deposition of most part of this sedimentary sequence. (S. K. M. Tripathi et al., 2009)

                                    3.      The sequence is showing fluctuating trend due to intermittent reducing and oxidizing conditions. Higher inorganic carbon content of the clay bed at 7.44 m in the litholog indicate the prevailing oxidizing conditions during its deposition. The overlying sequence is again showing higher organic content, a signature of reducing environment and may be a result of fluctuating water column depth.

                                    4.      Dominance of Kaolinite in clay fraction and absence of feldspar in sandstone beds indicate that the sediment is chemically highly mature wherein all the mobile elements are flushed out from the primary (feldspar) minerals, probably a function of warm and humid climatic conditions. Presence of quartz in clay fraction indicates that sediments have covered long distance before deposition.

                                    5.      The catchment area lithology could be granitic as quartz is present in large amount in sandstone and silt beds.

                                    The conclusions are preliminarily based on the grain size, LOI and XRD data. Further elemental analysis results will shed more light on the provenance of the studied sediments and palaeoclimatic conditions prevailing during their deposition.

                                    Recommendation

                                    Detailed geochemical analysis of the entire sedimentary sequence of the Kapurdi lignite mine, its petrography, heavy mineral analysis and radiogenic isotope dating will give more information about the provenance and palaeoenvironmental conditions as well as the age of the sediments. Similarly, different chemical and thermal treatment of Glycolated clay fraction XRD analysis will help us to differentiate various clay minerals present in the sediments at different intervals, which may further help us to ascertain the depositional environmental conditions experienced by the sediments.

                                    REFERENCES

                                    1) Sisodia, M.S., Singh, U.K. (2000). Depositional environment and hydrocarbon prospects of Barmer Basin, Rajasthan, India. North American Free Trade Association, 9, 309-326.

                                    2) Tripathi, S. K. M., Kumar M., Shrivastava, D. (2009). Palynology of Lower Paleocene (Thanetian-Ypresian) coastal deposits from the Barmer Basin (Akli Formation, Western Rajasthan, India): Palaeoenvironmental and palaeoclimatic implications. Geologica Acta, 7(1-2).147-160.

                                    3) Tripathi, S. K. M., Singh, U. K., Sisodia, M. S. (2003). Palynological investigation and environmental interpretation on Akli Formation (Late Paleocene) from Barmer Basin, western Rajasthan, India. Palaeobotanist, 52,87-95.

                                    4) Tabaei, M., Singh, R. Y. (2002). Paleoenvironment and Paleoecological Significance of Microforaminiferal Linings in the Akli Lignite, Barmer Basin, Rajasthan, India. Iranian Int. J. Sci. 3(2), 263-277.

                                    5) Singer, A. (1980). The Palaeoclimatic Interpretation of Clay Minerals in Soils and Weathering Profiles. Earth Science Reviews, 15, 303-326.

                                    6) Singer, A. (1984). Palaeoclimatic Interpretation of Clay Minerals in Sediments-A Review. Earth Science Reviews, 21, 251-293.

                                    7) Mehra, O. P., Jackson, M. L. (1960). Iron Oxide Removal from Soils and Clays by a Dithionite-Citrate System Buffered with Sodium Bicarbonate. Clays and Clay minerals, 7(1), 317-327.

                                    8) Pal, D. K., Tarafdar, J. C., Sahoo, A. K. (2004). Analysis of Soil for Soil Survey and Mapping. Chapter 7, Techniques to Analyse Soil Samples. (Online pdf from www.researchgate.net).

                                    9) Sahni, A., Rana, R. S., Loral, R. S., Saraswati, P. K., Mathur, S. K., Rose, K. D., Tripathi, S. K. M., Garg, R., (2004), Western Margi Paleocene-Lower Eocene lignite: Biostratigraphic and palaeoecological constrains. Proceedings of 2nd APG Conference cum Exhibition, Khajuraho, 1-22.

                                    10) Agilent Technologies 7700x Hardware Maintenance Manual (2014).

                                    11) LS 13 320 Laser Diffraction Particle Size Analyzer Instructions. (2011).

                                    12)  Martin Ermrich and Detlef Opper, (2011) XRD for the analyst Getting acquainted with the principles, Panalytical..

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                                    Websites-

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                                    ACKNOWLEDGEMENTS

                                    I would like to show my sincere gratitude to Indian Academy of Sciences, Bengaluru; National Science Academy, New Delhi; The National Academy of Sciences, Prayagraj and Birbal Sahni Institute of Palaeosciences, Lucknow for providing me this summer training at BSIP.

                                    I would like to devote my sincere thanks and gratitude to Dr. Mukund Sharma, Director (Additional Charge) and Dr. Vandana Prasad, Director BSIP, for giving me opportunity to undergo summer training in one of the leading research institution of the country.

                                    I would like to thanks my guide Scientist Dr. Anupam Sharma and my geochemistry professor Dr. Sk. Md. Equeenuddin, Technical Officer Mr. Ishwar Chandra Rahi, Research Scholars Ms. Harshita and Mr. Mukesh for providing guidance and supporting me at every step of the internship.

                                     

                                    References

                                    • O. P. Mehra, 1958, Iron Oxide Removal from Soils and Clays by a Dithionite-Citrate System Buffered with Sodium Bicarbonate, Clays and Clay Minerals, vol. 7, no. 1, pp. 317-327

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