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    Geochemical, mineralogical and isotopic signatures of the Semikan, West KasrA±k Turkish phosphorites from the Derik-MazA±dagA±-Mardin area, SE Anatolia
    (Springer, 2009) Imamoglu, M. Sefik; Nathan, Yaacov; Coban, Hakan; Soudry, David; Glenn, Craig
    The geochemistry and mineralogy of a condensed section, similar to 6 m thick of the West Kasrik member (Coniacian-Santonian) near the uplifted northern flank of the Mardin-Derik anticline (south-eastern Turkey) was studied. The only deposit exploited in Turkey is found in this area. The sediment textures as well as the mineralogical and the geochemical results collectively suggest that these recycled phosphorites accumulated in areas of intensive very early diagenesis of the sediments in highly oxic bottom waters, and almost no detrital apport. The total concentration of redox-sensitive trace metals is very low (< 600 mu g/g); in addition the structural CO2 and F/P2O5 are unusually high (similar to 5 wt % and 0.14, respectively). REE distribution shows a clear seawater pattern with a strongly negative Ce-anomaly (0.20 +/- A 0.02) and heavy REE enrichment (Lu-N/La-N = 1.50 +/- A 0.12), however their total concentration is very low. The low REE contents, quite unexpected in recycled phosphorites, are explained by the scarcity of terrigenous components which leads to minimal incorporation of REEs from detrital clastic phases in the CFA fraction. Weathering previously suggested as responsible for the high P enrichment of the Mazidagi phosphorites is rather improbable in the samples we studied, in view of their high structural CO2, high F/P2O5, high (La/Nd)(N) and (La/Sm)(N) ratios, and high Sr/P and Ca/P of separated CFA fractions that all negate post-depositional weathering. More likely, the high P enrichment of some rocks (P2O5 content reaches 34%) was produced by sedimentary and early diagenetic processes acting in oxygenated areas of starved sedimentation on and around tectonic highs.
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    Öğe
    Investigation of a methane flare during the excavation of the Silvan irrigation tunnel, Turkey
    (Springer Heidelberg, 2019) Ayhan, Mustafa; Aydin, Deniz; Imamoglu, M. Sefik; Cogalan, Mustafa; Karakus, Askeri
    Mechanized methods are being increasingly used in tunnel excavations to such an extent that to ensure safe construction and the economic viability of projects the need for design-stage geotechnical studies has considerably increased. However, unexpected problems, such as gas inflow, can be experienced during excavation when the geological conditions are insufficiently investigated. In fact, even if construction is taking place in a known oil-natural gas basin or coal-bearing strata, the possibility of methane flare/explosion events can be minimized if a suitable excavation method and equipment are used. However, little published literature is available on this topic, resulting in the potential problem of encounters with sources of methane during construction that have not been considered in the planning of the tunneling operations. We have studied a methane (natural gas) flare incident that occurred in 2015 during the excavation by full-face hard rock tunnel boring machine of the Silvan irrigation tunnel, south-eastern Turkey. During the planning and pre-construction stages no consideration was given to the fact that the tunnel passes through a natural gas basin and, consequently, the selection of excavation method and machine equipment was made without taking into account the high possibility of natural gas being present. During excavation a significant methane gas flare occurred, resulting in 13 workers being injured and abandonment of the project. Subsequent investigations revealed that the proposed route of the tunnel passed through a natural gas basin and that Turkish Petroleum Corporation (TPAO) had carried out natural gas exploration in the area. Here we provide details on the geological background and the flare incident itself and come to the conclusion that the pre-construction ground investigations for this project were grossly inadequate. We also suggest that in order to facilitate economical and safe tunnel construction, consideration should always be given to the possible presence of methane and other gases at the ground investigation stages of tunneling projects and that all previous geological and technical studies related to the study area should be taken into consideration during the pre-construction stage.