Geosciences Research

Number 4, 2018

9
A Note on the Chemical Composition and Origin of Peridot from the Harrat Kishb, Saudi Arabia

Authors: Adel A. Surour

Abstract

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Zabarjad (peridot in Arabic) is a common gemstone of valuable importance used in jewelry. It is the mineral olivine that has some gemological characters that classify it as peridot or gem olivine. Although it is not found in huge quantities in Saudi Arabia, there are some mining activities to extract peridot from the Harrat Kishb where the mineral is found scattered in alkali basalt or in the scree and wadi deposits. The basaltic flows at the Harrat Kishb include this gem olivine in the form of mantle xenoliths that comprise both dunite and peridotite. The size of collected peridot lies in the range of 0.4-0.8 cm and it occurs either as free olivine or in the form of cluster with components of host basalt. The collected crystals are transparent olive-green after washing and screening. Using the modern technique of analysis by the electron microprobe, the accurate chemical composition of peridot crystals was obtained. The studied peridot is a Mg-rich end-member of the foresterite (Mg) and fayalite (Fe) solid solution series where the forsterite content is Fo90.35-92.31. Such composition of olivine is similar to majority of olivine in the ultramafic mantle beneath the western Arabian Peninsula. The present work uses the concentrations of some elements such as Mn, Ni and Ca in addition to the forsterite content to characterize the Saudi peridot. It is typically terrsterial when compared to extraterrestrial (pallastic) olivine, and mostly xenocrystic and rarely magmatic. The forsterite content (Fo>90) suggests transition from a residual to cumulate origin

14
Investigating Rainfall Trend and Monitoring Meteorological Drought in a Himalayan Watershed of India

Authors: Alok Kumar Mishra, Anil Kumar

Abstract

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Assessment of rainfall trend and monitoring meteorological drought and wet conditions are very important in dealing with agricultural planning and water resources management under the influence of changing climate in the Himalayan region. This study was conducted to assess rainfall trend and monitor the drought and wet pattern at four stations, namely Naula, Kedar, Chaukhutia and Mehalchauri, located in the upper Ramganga River catchment in Uttarakhand state of India in the central Himalayan region. Rainfall trend analysis at these stations was carried out using Mann-Kendall test and Sen’s slope estimator. Standardized Precipitation Index (SPI) at multiple time scales of 1-, 3-, 6-, 9-, 12- and 24-months was used to assess meteorological drought and wet pattern at Naula station. Results have indicated a significantly downward trend in December and post-monsoon season and an upward trend in September at Naula station. Significantly downward trend was also observed in July, December and monsoon season at Kedar station, and in June, July, August, monsoon and annual data series at Chaukhutia station. No significant trend was observed at Mehalchauri station. Study also revealed that there are more chances of occurrences of mild drought and wet conditions and only meager chances of moderate drought and wet conditions during monsoon season. However, the chances of severe and extreme drought and wet conditions are almost negligible. Therefore, efforts must be made to harvest the excess water during the wet periods and utilize the same during the periods of mild and moderate drought for drinking, household activities and irrigation purposes.

22
Younger Granites and Associated Pegmatites of Gabal El Fereyid – Wadi Rahaba Area, South Eastern Desert, Egypt: Geological and Geochemical Characteristics

Authors: Maher I. Dawoud, Gehad M. Saleh, Hassan A. Shahin, Farrage M. Khaleal, Bahaa M. Emad

Abstract

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Lithologically, the rock types of G. El Fereyid - W. Rahaba area are dominantly granites associated with pegmatites. The granitic rocks comprise tonalite and monzogranite with (minor acidic dykes), quartz and pegmatites occur as a vein type (granitic and perthitic pegmatites) hosted within the monzogranite. Structural analysis shows the presence of a prominent set of folds with axes striking WNW to NW and a less prominent set with pronounced ENE and NNW trends. Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as post orogenic granites (POG). Geochemically, monzogranite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Ba, Sr) and high field strength elements (HFSE; Y, Zr, Nd,) and depletion (troughs) of K, P and Ti. Pegmatite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Sr) and high field strength elements (HFSE; Y, Zr, Th, U, Nb) and depletion (troughs) of K, P and Ti. They exhibit high K-calc alkaline magma and peraluminous characteristics and considered as post orogenic granites (POG). The monzogranite reveal small to moderate negative Eu anomaly, while the pegmatites reveal moderate to large negative Eu anomaly. The pegmatite displays clear W-type tetrad effect of the REE while, the studied monzogranite do not show tetrad effect.

Number 3, 2018

7
Landslide Disaster Risk Reduction Strategies and Present Achievements in Sri Lanka

Authors: R.M.S Bandara, Pathmakumara Jayasingha

Abstract

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A significant impact on the economy and the social context of Sri Lanka has been caused by hydro-meteorologically induced landslides. Though many organizations are working on landslide studies, National Building Research Organization (NBRO) is the key organization that involves in landslide research and risk reduction programs in Sri Lanka. This paper discusses about the present strategies set to reduce the landslide risk and the present achievements. Landslide risk reduction process has been strategized in number of ways which follow basic guidelines of disaster management. The strategic plan developed by NBRO includes following main components/activities; such as identification, awareness, early warning, mitigation and low enforcement. Implementation of those strategies have resulted Landslide Hazard Zonation Maps through Landslide Hazard Zonation Mapping Program, establishment of real time early warning system, declaring landslide prone areas and introducing land clearance process and successful completion of landslide mitigation projects with improvement of technological knowledge.

Number 2, 2018

12
Impacts of El Nino on Rainfall and Its AgrocltmaticIncidences in the Zanzan Region: North-East of Cote d’Ivoire

Authors: Kouakou Bernard DJE, Abé Delfin OCHOU, Zilé Alex KOUADIO3, Kolotioloma Alama COULIBALY

Abstract

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The aim of this study is to analyze the manifestation of rainfall variability in the district of Zanzan level during El Niño episodes and to evaluate its agro-climatic impacts. SODEXAM climate data and Sea Surface Temperature (SST) of El Niño 3.4 area were used. The composite analysis made it possible to evaluate the impacts of the El Niño phenomenon on rainfall. INSTAT+ v3.30 software was used for the analysis of agro-climatic events. The results indicated average rainfall deficits from 10 to 44% in the district from October to April. Rainfall patterns are disrupted in the El Niño year. Crops seasons are late and end early in Bondoukou, Bouna and Tanda. This disturbance affects agro-climatic events by shortening the growing season in the Zanzan on average 21 days in El Niño year.

Number 1, 2018

8
Status of Wildlife Habitats in Ramnagar Forest Division, Terai-Arc Landscape, Uttarakhand, India

Authors: Tanveer Ahmed, Harendra Singh Bargali, Neha Verma, Afifullah Khan

Abstract

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The Terai-Arc Landscape in the foothills of Himalaya supports a mosaic of wildlife habitats that sustains an amazing biodiversity. The high human pressure coupled with developmental activities, not only degrade wildlife habitats but restrict the dispersal of wild animals particularly in multiple-use managed forest. We determined the status of wildlife habitats in Ramnagar Forest Division classifying Landsat 8 OLI/TIRS image acquired on April 2015. Landsat Aster GDEM data of 17 October 2011 was used to assess slope, aspect and elevation of the study area. Sal forest was the dominant class and it was followed by sal mixed forest, mixed forest, human habitation and barren land. The elevation ranges between 307m and 1892m amsl with sizable area having gentle slope (50 to 100 ). Most of the region was south facing. Importance of these habitats for mammals of western Terai-Arc Landscape has been discussed. The current information is expected to serve as baseline information for planning future management strategies and determining changes in wildlife habitats.