Browsing by Author "Ratnayake, A.S."
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Item Depositional Characteristics and Accumulation Model of Peaty Sediments in the Southwest Coast of Sri Lanka(Uva Wellassa University of Sri Lanka, 2019) Senanayake, N.D.M.S.; Ratnayake, A.S.Tropical peat lands are a major terrestrial carbon sink during the Holocene, but there is considerable uncertainty in the accumulation of carbon in a changing climate. In this study, our objective was to measure baseline carbon cycling data for understanding depositional mechanism and peat accumulates in the southwest coast of Sri Lanka. Sedimentary facies were identified using a representative peat core sample (54 cm in depth) at Telwatta. Geochemical characteristics of peaty sediments were determined using proximate, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), atomic absorption spectroscopy (AAS) analyses. Chronology was determined using accelerated mass spectrometry (AMS) 14C data for a coral sample at International Chemical Analysis Inc laboratory, USA. Core log data indicate mainly clayey peat deposit under minerogenic sediments and coral fragments, suggesting an ancient buried peat land. Temporal variations of moisture (range from 1.55 to 16.89%), ash (range from 88.66 to 99.43%), and volatile (range from 6.27 to 14.03%) contents show an irregular distribution with depth. However, total organic carbon values drastically increase in the upper sedimentary succession (0-30 cm in depth, range from 2.40 to 3.58%, average = 5.23% ± 0.01) compared to lower sedimentary succession (range from 3.69 to 4.14%, average = 4.10% ± 0.01), suggesting that reduction of microbial activity and decomposition rates with the depth. The calculated humification index based on FTIR peak intensities suggests that sapric humus condition in the upper sedimentary succession (Humification IndexH1) due to plant remain easily identifiable and no amorphous material. XRD analysis indicates the calcite (26.8⁰) and aragonite (20.9⁰) phases in coral samples. Fe range from 65.24 to 212.50 ppm) element distributions in core samples suggest the development of the anoxic and acidic condition of core samples. Radiometric dating of the inland coral fragment at 23 cm in depth is 3435 cal yr B.P., reflecting inland coral formation during the middle Holocene sea-level rise over the southwest coast. In summary, southwest coast of Sri Lanka was characterized by long-term carbon sequestration after middle Holocene seawater invasion, at the rate of 0.07 mm per year under the warmest climate regimes.Item Determination of the Regional and Residual Gravity Anomalies in the Cauvery Basin, Sri Lanka(Uva Wellassa University of Sri Lanka, 2019) Bandara, M.A.A.S.; Weerasinghe, D.A.; Ratnayake, A.S.The measured gravity field of the Earth contains two main components of shortwavelength residual anomalies and long-wavelength regional anomalies. In the petroleum industry, the most important component is the residual anomalies which correlate with shallow density variations such as sedimentary basins. The regional anomalies are caused by deeper density contrasts in the lithospheric mantle and the Asthenosphere. Usually, the residual anomalies are obtained by filtering out the regional anomalies mathematically. This study is focused to determine residual gravity of the Cauvery Basin, as the basement data is known up to a reasonable accuracy. In this study, a depth structure map of the basement in the Cauvery Basin was prepared initially using a two-way-travel time map and velocity data obtained from eight exploration wells. Depth data from selected 2D sections were used as input data for a Mathematica® program which was based on an iterative algorithm, developed to calculate the residual gravity anomaly caused by a 2D polygonal body having a density contrast with the surrounding. The difference of the calculated and the observed gravity was then used to obtain the regional gravity along the lines. A regional gravity map was created by interpolating the above data. A variation of -50 mGal to 71 mGal of the regional gravity was observed and a relatively high gravity anomaly was also observed in the central part of the basin. This may have been caused due to the crustal thinning process which occurred during the rifting phase of the basin. The residual gravity anomaly varies from about -60 mGal to 20 mGal in the region and follows the horst and graben structures. In conclusion, the authors identified undiscovered sub-basins which are related to the separations of Sri Lanka from the Gondwana supercontinent.Item Geochemical Exploration of Negombo Lagoon Sediments in Western Coast of Sri Lanka(Uva Wellassa University of Sri Lanka, 2019) Wijesinghe, U.M.P.; Ratnayake, A.S.Negombo Lagoon is one of the largest lagoons in Sri Lanka, and it is surrounded by Muthurajawela peat deposit. Geochemical characteristics of sediments were examined using proximate, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), atomic absorption spectroscopy (AAS) analyses. Chronology was determined using accelerated mass spectrometry (AMS) 14C data for undamaged two shells at International Chemical Analysis Inc laboratory, USA. Stratigraphic observation suggests deposition of dark color sandy/silty clays. Moisture, volatile, ash and organic matter contents show homogeneous distribution with depth. XRD analysis identified mainly peaks of Quartz, Calcite, Feldspar, Beryllium Carbide (Be2C), Lanthanum Palladium, suggesting that different provenances for the source materials. FTIR analysis identifies mainly functional groups of C-H, O-H, C=C, C=O, Si-O and C-O probably from carboxylic acid, alcohol, aliphatic hydrocarbons and polysaccharides, suggesting that the early stage diagenesis in this natural system. Fe (range from 30.98 ppm to 31.79 ppm), Cr (range from 0.055 ppm to 1.381 ppm) and Rb (range from 0 ppm to 0.323 ppm) elements distributions in core samples suggest the increment of the anoxic and acidic conditions. Therefore, organic matter preservation can be enhanced by slow decomposition rates in deeper anoxic layer. According to radiometric dating, the undamaged shells at 45 cm and 57 cm in depth were deposited after 1950. Therefore, it suggests that higher short-term carbon accumulation rates (sedimentation rate > 8.4 mm per year) in this estuary. Finally, Negombo Lagoon can be identified as represent important carbon stores, and are important archives of past climatic and ecological information.Item Geochemical Variations of Prospective Heavy Mineral Deposits Bordering the Coastline of Sri Lanka(Uva Wellassa University of Sri Lanka, 2021) Subasinghe, H.C.S.; Ratnayake, A.S.; Wijewardhana, T.D.U.; Sameera, K.A.G.Heavy minerals with a specific gravity greater than 2.9 g/cm3 such as ilmenite (FeTiO3), rutile (TiO2), leucoxene (altered ilmenite), zircon (ZrSiO4), monazite ((Ce,La,Nd,Th)PO4), garnet ((Ca,Mg,Fe,Mn)3(Al,Fe,Mn,V,Cr)2(SiO4)3), sillimanite (Al2SiO5), and magnetite (Fe3O4) have gained global attention as a result of modern technological advances. In this regard, the mining and processing of these heavy minerals are a timely requirement to uplift the mineral industry and the economy of Sri Lanka. Therefore, the objective of this study is to investigate the geochemical variations of prospective heavy mineral deposits along the coastline in order to identify locations with economically significant concentrations of heavy minerals. Field excursions were carried out to identify the potential of heavy mineral placers in Sri Lanka. Sediment samples were collected from ten locations covering both the shoreline and raised beaches. X-ray fluorescence (XRF) analysis was used to determine the major and trace element compositions of sediments. When compared to average Upper Continental Crust (UCC) values, major and trace element variations show the enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th, and V. The abundance of TiO2, Fe2O3, and Zr, and visual examination of samples suggest the presence of higher concentrations of heavy minerals such as ilmenite, rutile, and zircon in the prospective locations. Moreover, the abundance of trace elements such as La, Ce, and Th implies the presence of rare earth elements (REEs) bearing heavy minerals such as monazite and zircon. In contrast, major elements (Al2O3, Na2O, and K2O) and large- ion lithophile elements (Ba and Rb) were significantly depleted compared to UCC values. Based on the XRF data and visual examination, it can be concluded that all the studied locations such as Verugal, Dickwella, Kosgoda, Payagala, Beruwala, Kalutara, Dharga Town, and Aruwakkalu can be identified as potential sites for heavy mineral placers. Finally, proper quantification is required to estimate economic grade and to determine mining feasibility. Keywords: Heavy minerals; Geochemical variation; Economic concentrations; Coastline of Sri LankaItem Geochemistry of Petroleum Potential Source Rocks in Barracuda Well of Mannar Basin, Sri Lanka(Uva Wellassa University of Sri Lanka, 2020) Ratnayake, A.S.; Bogahawatte, M.V.Four exploration wells (Dorado North, Dorado, Barracuda, and Wallago) were drilled in the deep-water Mannar Basin during the second phase of hydrocarbon exploration. The Barracuda well was confirmed as gas potential due to presence of 85 wt% methane in the Upper Cretaceous sediments. Therefore, the current study focused to evaluate geochemistry of core sediments (depth from 2139–4741 m) in Barracuda well using XRay Diffraction (XRD) and stable isotopes analyses. The upstream petroleum industry prefers such supportive geochemical data at the development stage. Stable carbon (δ 13 C) isotopic values (–33.86 ‰ to – 24.88 ‰) and C/N ratios (17.3–158.8) suggest a considerable supply of terrestrial plants organic matter (gas prone Type III kerogen) to sediment. XRD results identified several paleoclimatic chronozones based on dominant clay mineral assemblages. The Early Campanian age consists of montmorillonite dominant sediments suggesting that arid climate. Kaolinite dominant Late Campanian to Late Maastrichtian sediments indicates the warmer/wetter paleoclimatic condition. However, montmorillonite dominant sediments in the Late Maastrichtian can be controlled by short-term global cooling events and/or volcanogenic sediments followed by Deccan-Reunion basalt volcanism. The Early-Late Paleocene sediments in the Barracuda well suggest arid (mock aridity) climate in the Indian Ocean. The Late Paleocene to Middle-Late Eocene age is composed of kaolinite dominant sediments that correlate warmer and wetter greenhouse paleoclimate in the Indian Ocean. The EarlyMiddle Oligocene to Miocene sedimentary succession of the Barracuda well also contains kaolinite dominant clay mineral assemblage. This wet climate characteristic is linked to the sharp decline of atmospheric CO2 concentration followed by the growth of Antarctica ice sheets after the Eocene-Oligocene climate transition (ca. 34 Ma) and development of present-day South Asian monsoon system. Keywords: Paleoclimate, Sediments, Clay mineralogyItem Preliminary Investigations of Geochemical Characterization in Murunkan Clay Deposit, Sri Lanka(Uva Wellassa University of Sri Lanka, 2020) Subasinghe, H.C.S.; Gayashini, K.Y.; Ratnayake, A.S.; Wijewardhana, D.T.U.; Pitawala, H.M.J.C.; Attanayake, A.M.A.N.B.Clay minerals are categorised into several groups as kaolin group, smectite group, illite group, chlorite group and 2:1 clays such as attapulgite and sepiolite. Over other clays, smectites are far more valuable due to their advanced application potential. Smectites exhibit excellent swell properties and the highest cation exchange capacity (CEC). Smectites can be used as adsorbents, filler material, drilling mud, excipients, and plasticisers. Montmorillonite is a layered alumino silicate with a higher specific surface area. It is also the most abundant of the smectite clays. The main objective of the current study is to identify spatial and temporal variations in geochemical characteristics of the Murunkan clay deposit. In this on-going project, two boreholes were drilled nearly 1 km distance each other in the Murunkan Basin. One borehole reached a depth of 6.5 feet while the other just passed a depth of 4.0 feet. Samples were cut into 5 inches of each core. Geochemical characteristics of the Murunkan clay deposit were evaluated for 15 clay samples and a Sigma Aldrich montmorillonite sample (reference material) using Xray fluorescence (XRF), X-ray diffraction (XRD) and Fourier Transform Infra-Red (FTIR) analyses. XRF results indicate ~57% SiO2, ~19% Na2O, ~10% Al2O3, ~5% Fe2O3, ~2% CaO, ~2% MgO, ~1.5% K2O, and ~1% TiO2. FTIR spectra of analysed clay samples show transmittance bands matching with the standard data of kaolinite and montmorillonite. Similarly, XRD analysis also suggests the occurrence of clay minerals such as montmorillonite, illite, kaolinite, chlorite, muscovite and cookeite. Quartz and feldspar can also be detected as the major impurities in the Murunkan clay samples. However, no considerable spatial and temporal geochemical variations can be observed in this deposit. Therefore, the Murunkan clay deposit can be identified as a prospective area for further exploration. The future research works would focus to demarcate the boundary of clay deposit and quantify the volumetric estimation. Besides, value additional potential such as purification and possible industrial applications would be examined. Keywords: Murunkan clay, Montmorillonite, Value addition potentialItem Selective Removal of Iron Oxide in Sri Lankan Laterite(Uva Wellassa University of Sri Lanka, 2019) Goonetilleke, W.A.I.A.T.; Jayawardana, D.T.; Ratnayake, A.S.Fe-rich laterite uses as the main alumina source in cement manufacturing process. The high iron content in laterite increases the limestone consumption. Therefore, this study is focused to investigate the effect of pH, temperature and sonication time for Fe removal. The Fe removal from laterite was examined along with Cd and Mn. The loss of mass on ignition (LOI), moisture, pH, elemental and mineralogical characterization of raw and treated laterite were determined by using Atomic absorption spectroscopy, X-ray diffraction (XRD) and Fourier-transform infrared instruments. The particle size (63 µm) and the solid-to-liquid ratio (1:10) were constant, for the whole experiment. The pH range was prepared using HCl acid and NaOH at 300 K for 1800 s, while the temperature and sonication time were examined with 313, 333, 353 and 373 K for 3600 s and 600, 900, 1800, 2700 and 3600 s at 300 K, respectively. The pH, moisture, and LOI of raw laterite were 5.69, 15.80% and 16.56%, separately. The Fe and Mn removal efficiencies were increased when the pH from 5 to 1 and the efficiency was negligible when pH 6-10. Cd removal efficiency was increased when pH 1-10. All elements removal efficiencies were increased 313-373 K. Fe and Mn got high efficiency at 900 s and Cd was recovered within a short time with sonication. XRD results revealed goethite, hematite and magnetite are main Fe-rich minerals. The effective pH for Fe, Cd and Mn were 1 (17.6 ppm), 7 (0.18 ppm) and 1 (2.05 ppm), respectively. The Fe and Mn removal efficiencies were greatly influenced by hydrogen ion concentration and Cd removal was influenced by hydroxyl ion concentration. The optimal condition of Fe for industrial applications is pH 1 with 333 K temperature or pH 1 with 900 s sonication time. The optimal condition for Mn is pH 1 with 900 s sonication time and Cd can dissolve effectively with basic pH conditions under high temperatures.Item Shoreline Change Analysis along the East Coast of Sri Lanka: A Remote sensing- Based Approach(Uva Wellassa University of Sri Lanka, 2021) Weerasingha, W.A.D.B.; Ratnayake, A.S.The changes along the eastern coastlines of Sri Lanka have been investigated for short- and long-term natural and anthropogenic processes. Such coastal changes can be classified as either negative (coastal erosion, seawater intrusion) or positive (coastal accretion) impacts. The understanding of such impacts can directly be applied to coastal conservation/management and the designing of coastal engineering structures. In this study, the authors examined Landsat 5, 7, and 8 sun-synchronized earth resources satellite data for understanding coastal changes since 2000. These Landsat series have advanced sensors (e.g., thematic mapper (TM), enhanced thematic mapper plus (ETM+), operational land imager (OLI)) for data acquisition. Data selection, pre-processing, and processing were carried out using a geographic information system (GIS). Besides, the authors developed a new model known as “Jargon’s script” for data preprocessing and processing. Modified Normalized Difference Water Index (MNDWI) is the important algorithm of Jargon’s script models that helps to extract water and land features. The threshold value for the MNDWI to get maximum contrast of objects was identified as 0.13. Furthermore, the current study covered nearly 1043 km coastline along major coastal zones such as Jaffna, Mullaitivu-Trincomalee, Batticaloa-Hambantota, Matara, etc. Long- term and short-term coastal changes were then determined using Digital Shoreline Analysis System (DSAS) software linked to ArcMap 10.6. Results identified five major parameters such as net shoreline movement (NSM), shoreline change envelope (SCE), endpoint rate (EPR), linear regression rate (LRR), and weighted linear regression rate (WLR). In this study, coastal geomorphological changes were classified into eight classes based on the annual variation of EPR values, such as extreme erosion (>-10 m/year), high erosion (-10 to -5 m/year), moderate erosion (-5 m/y to -2.5 m/year), low erosion (-2.5 to 0 m/year), low accretion (0 to +2.5 m/year), moderate accretion (+2.5 to +5.0 m/year), high accretion (+5.0 m/y to +10 m/y), and extreme accretion (> +10 m/year). Those parameters can be used to visualize spatial and temporal variations of geomorphological changes along this coastline, and such variations can be used to correlate natural (monsoon, sea-level rising) and anthropogenic activities. According to the EPR results of Karainagar east, Kalido beach has the highest coastal erosion compared to other coastal areas. Keywords: Shoreline change rate; Satellite images; Coastal geomorphology; Sediment dynamics; East coast of Sri LankaItem Upgrading of Sri Lankan Ilmenite by Ball Milling Induced Carbothermic Reduction(Uva Wellassa University of Sri Lanka, 2019) Wijewardhana, T.D.U.; Ratnayake, A.S.Ilmenite (FeTiO3) and rutile (TiO2) are titanium bearing heavy minerals. The existence of ilmenite percentage (70-72%) is much higher than rutile percentage (8%) in the northeastern coastal area of Sri Lanka. The value of rutile is higher than ilmenite. Though there are many chemical methods for upgrading ilmenite, physical method is cost effective for Sri Lanka. This research was carried out to analyze the optimum temperature under specific conditions for upgrading ilmenite using physical method. Upgrading was carried out using magnetically separated ilmenite sample from Lanka Mineral Sands, Pulmoddai. Mixture of ilmenite and activated carbon samples were milled using planetary ball mill for one to four hour separately. Subsequently milled samples were treated with activated carbon and heated for two hours at temperature of 800 °C, 900 °C, 1000 °C, 1100 °C and 1200 °C. Crystallinity and functional groups of the treated samples were determined using X-ray diffractometer (XRD) and Fourier transform infrared (FTIR), respectively. Particle sizes of the treated samples were determined using dry sieving method. Intensity, broadness and number of titanium dioxide (TiO2) XRD peaks in treated samples were increased with the time during the studied four hours. FTIR analysis indicates initial ilmenite contains Fe=O, Fe-O and Fe-OH stretching vibrations. The upgraded ilmenite sample contains Ti-O stretching vibrations with more broadness instead of Fe=O and Fe-OH stretching vibrations. Particle size of the four hour milled samples was laid in between 44 to 74 microns. Characterization results show that the amount of TiO2 and their crystallinity were increased. The annealing temperature can be reduced up to 1000 °C during the studied four hours. Therefore, Sri Lankan ilmenite can be upgraded by ball milling induced carbothermic reduction.