Browsing by Author "Ranasinghe, P. N."

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    Stream Sediment Geochemistry and Mineral Potential of Lower Walawe and Mau Ara Basins
    (Uva Wellassa University of Sri Lanka, 2013) Marasinghe, H.P; Ranasinghe, P. N.
    Regional geochemical maps are considered to be a national asset for resource evaluation and environmental management. This project covered a considerable portion of the lower Walawe Ganga and Mau Ara which represent the geologically and environmentally important Highland - Vijayanlithotectonic boundary of Sri Lanka Stream sediments remain the dominant sampling medium in regional geochemical exploration, in areas where relief permits development of distinct drainage systems (Fletcher, 1997). In addition, human activity can often strongly influence the stream sediment composition that can be used to identify pollution sources. In this study, distribution of selected major, trace and rare earth elements (REE) were studied to identify potential mineral enrichments in the Lower Walawe Basin. Methodology 44 sample locations were selected within lower Walawe and Mau Ara streams. Chemical components were analyzed using various analytical methods. Element concentrations in stream sediments were measured in powdered using hand held X-ray Fluorescence Absorption Spectrophotometer (AAS) (Ranasinghe et al, 2008). Stream sediment geochemical maps were prepared using Arc-GIS 9 software and data analysis was done using SPSS 13 software. Results and Discussions A comparison of special element concentrations in studied area with upper crustal and mean stream sediment values are given in Table 1. Results show that Cr, Ni Y, Zr and Pb at some sampling locations are well above the upper crustal values and mean sediment levels while other elements are below the above global average values. When examined the individual distribution maps of above elevated elements, UWG 18 and UWG 20 locations are enriched with respect to Zr, Y and Cr, Ni elements (Figure 1). However, enrichment of Zr and Y at UWG 18 is mainly due to hydro dynamical heavy mineral accumulation in the area. UWG 20 location is a confluence point of two streams and enriched Cr and Ni concentrations indicate potential metallic mineral source upstream of above location., Elevated Pb concentrations at UWG 5-1, UWG 6, LWG 1 and LWG 2 locations could be due to natural sources because there is very low potential for anthropogenic Pb pollution in the area. Also these locations are situated at the vicinity of gem and gold mining areas. Conclusions This study reveals the enrichment of Cr, Ni and Pb in several locations in the lower catchment of the Walawe and Mau Ara basins. Analysis of geographical and geological features of the locations suggests that these elevated levels could be due to natural sources rather than anthropogenic or hydrodynamic enrichments. Therefore, detailed high resolution sampling around these localities is suggested to identify potential mineralization.
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    A Study on Evolution of Koggala Lagoon during the Holocene
    (Uva Wellassa University of Sri Lanka, 2013) Kopalakrishnan, K.; Ranasinghe, P. N.
    Climate change will have significant impacts on the oceans and on the coastal zone at a global scale. It will introduce new hazards and increase existing hazard potential, both with respect to magnitude and frequency of occurrence, in coastal regions. The hazards would be sea level rise, storm and tsunami events. Sea level rise is one of the major problems experienced by many nations including Sri Lanka Sediment entrainment in the coastal environment is changed according to the climate changes. So their sedimentation rates also change, depending on the type and its magnitude. Therefore, the past depositional environments of sediments and their provenance can be identified by studying the physical, chemical, biological and textural properties of sediments preserved in coastal environments. This helps to understand the past environmental changes, which can also be expressed as “studying the paleo-coastal environmental evolution”. Indeed this evolutionary history can be used to interpret past and future environmental aspects in order to build a more comprehensive framework to understand the behavior of the natural system. This study attempts modeling the evolution of the Koggala Lagoon in Southern Sri Lanka in the said context. Methodology Two continuous sediment cores KG 1 and KG 2 were extracted from the Koggala Lagoon. KG 1 was extracted closer to the sea side (1100 m) and KG 2 further 1900m inland from the sea. Both cores were logged and photographed. Organic matter content was analyzed by Loss on Ignition (LOI) method and dry sand percentage was calculated by wet sieving with 63 μm sieve. Geochemical variation of sediment cores was analyzed using handheld X-ray fluorescence analyzer (Bruker S1). Gamma ray intensity and concentration were analyzed using gamma ray spectrometer for the two cores. Sub-samples taken from different depositional environments and recognized events were identified through the binocular polarized microscope. Data were plotted using Pan Plot software. The ages for the boundaries of mid-Holocene sea level variations and recognized events were approximately calculated using the published regional age models equation (Ranasingheet al., 2013.).