Biogenic Accumulations of Uranium in Recent Seas

The objective of this study is to determine the geochemical role of molluscs in the distribution of uranium in the marine ecosystem. Biogeochemical studies are carried out on recent mollusc shells from the Caspian Sea, Sea of Japan, Sea of Marmara, Aegean Sea, Black Sea, Mediterranean Sea, Baltic Sea, and Indian Ocean, which differ from each other in terms of physical, chemical, geographic, and geochemical characteristics. In this study, nine Gastropoda and fifty-four Pelecypoda shells of different species are analyzed to document variations of uranium in seasonal layers, which were formed by the seasonal carbonate-organic phase of molluscs during their entire lives. Shell used in this study principally comprises three layers: upper (outer) prismatic, middle prismatic, and inner (mother-of-pearl) layers. In addition, when possible, the head, the middle, and the lower parts of the shells are used for analyses separately. Also, the biological accumulation rate values for each different mollusc species rel

Factors Controlling Low Uranium and Thorium Concentrations in the Cayirhan Bituminous Shales(CBS)in the Beypazari(Ankara)Area,Turkey

In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The H rka formation which hosts bituminous shale deposits is a volcanosedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of BS（1.83/2.62 ppm） are much lower than averages of UC, NASK and PAAS（uranium： 2.70/2.66/3.10 ppm; thorium： 8.50/12.30/14.60 ppm）. Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of BS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites（e.g. gneiss, schist） which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals（e.g. autunite, torbernite） which occur in granite, gneiss and schist. BS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma-Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements.

Taxonomical and Biogeochemical Investigation of Elements in Holocene Mollusk Shells in the South and Southwestern Marmara Basin,Turkey

Concentrations of some heavy metals and trace elements such as Cr, Ga, Ni, Zn, Mo, Cu, Pb, Yb, Y, Nb, Ti, Sr, Ba, Mn, Sc, Co, V, Zr, Fe, Al, W, Se, Bi, Sb, As, Cd in recent mollusk shells and factors affecting their distribution and deposits collected from various depths in the southern and southwestern parts of the Marmara Sea are investigated. The distribution of the elements in the shells is categorized into four groups. Of these, concentrations of 12 elements （As, Bi, Cd, Co, Ga, Mo, Nb, Sb, Se, Sc, W and Yb） are below zero [（0.053-0.79）×10^-6]; concentrations of seven elements （Cr, Ni, Pb, V, Y, Zr and Cu） are （1.0-6.0）×10^-6; concentrations of four elements （Ti, Mn, Ba and Zn） are 10- 20×10^-6; and concentrations of five elements （Si, Al, Fe, Mg and Sr） are （47.44-268.11）×10^-6. The taxonomic characteristics of the 29 elements were studied separately in mollusk shells such as Chamalea gallina （Linn6）, Pitar rudis （Poli）, Nassarius reticulatus （Linn6）, Venerupis senescens （Coocconi）, Mytilus galloprovincialis （Lamarck）, Mytilaster lineatus （Gemelin in Linne） and Chlamys glabra. It was found that, in mollusk taxonomy, the elements have unique values. In other words, element concentrations in various mollusk shells depend mainly on the taxonomic characteristics of mollusks. In various bionomic environments different element distributions of the same species are attributed to the different geochemical characters of the each environment. Data obtained in this study indicate that the organisms are the most active and deterministic factors of the environment.

土耳其Beysehir-Konyan地区西南Tepearasi组中白云岩的微细结构特征和成因

块状白云岩的成因和地史分布称为“白云岩问题”。本文作者从微观岩相分析入手并采用扫描电镜分析和能量色谱分析等方法把分布在土耳其Beysehir- Konyan地区西南Tepearasi组中的白云岩分为三种类型;均质白云岩、杂色(或鞍状结晶)白云岩和裂隙充填白云岩,并认为第一种为早期产物,后两种为成岩晚期产物。

Organic Material and Trace Elements of Bituminous Rocks in the Ozank(?)y Field,Ankara,Turkey

Bituminous rocks in the Ozankoey （Ankara） field are different from those of the Paleocene- Eocene Mengen and Giineytepe （Bolu） regions in metal enrichment levels. Organic carbon （Corg） content of organic material-rich rocks in the Ozankoey （Ankara） field is 3.66-40.72% wt averaging 14.34%. The dominant organic materials are algae/amorphous accompanied by minor amount of herbaceous material （The dominant kerogen type is Type-I with a limited amount of Type-Ⅱ kerogen.）. The bituminous rocks in the Ozankoey field are enriched in heavy metals such as Ni, Mn, As and Cr. In comparison with the average enrichment values of dements, Ni, Mn, As and Cr in bituminous shales of the Ozankoey field are as about 4.38, 14.93, 10.90 and 5.58 times as average values. The average concentrations of these heavy metals are also as high as 215× 10^-6, 828 × 10^-6, 58.54 × 10^-6, and 148 × 10^-6 respectively. In addition, sorption properties of day and organic materials are also important for metal enrichments in the bituminous shales.

Microtextural Characteristics and Origin of Dolomites in the Tepearasi Formation, SW of Beysehir-Konya, Turkey

The Tepearasi Formation of the autochthonous Geyikdagi Group in the CentralTauride Belt, SE of Beysehir, is Dogger in age and consists dominantly of massive limestones andgreyish dolomites occurring within the middle to upper sections. The total thickness of thedolomitic levels ranges from 100-300 m and laterally extends 500-700 m. Three types of dolomite weredistinguished through petrographic analyses: homogeneous, mottled (saddle-crystalline) andjoint-filling dolomite, which were interpreted to have formed in two different stages, earlydiagenetic and late diagenetic. The homogeneous dolomite of the early diagenetic stage islight-coloured and monotonous-textured and shows the form of a dolosparite mosaic. The mottleddolomite formed in the late diagenetic stage is light- to dark-coloured and coarsely granularidiomorphic. The other type of late diagenetic dolomite, described as the joint-filling type,presents a crystal growth pattern from the joint walls towards the centre of the joint space. It isassociated with coarse calcite crystals as well as primary dolomite crystal clasts which were formedin the early diagenetic stage. In addition to these characteristics, cataclastic texture indicatingthe influence of tectonism is also observed. Microtexture-oriented scanning electron microscopy(SEM) studies indicate that mottled dolomites show zonal structures and contain secondarydissolution vugs. SEM studies also revealed the existence of some remains (calcite, clay etc.) injoint-filling dolomites. Analyses by energy dispersive spectrometry (EDS) indicate the existence ofclay minerals (likely to be illite) in the pores of dolomite. Isotope studies conducted to shedlight onto the origin of the dolomites of the Tepearasi Formation yielded the results of delta^18O=-2.48 to - 3.87 per thousand and delta^13C=0.93 to l.12 per thousand for the early diagenetichomogeneous dolomites. Mottled and joint-filling type dolomites of the late diagenetic stage, on theother hand, gave the results of delta^18O = -5.42 to -7.12 per thousand, and delta^13C= -2.29 and-5.70 respectively. X-Ray diffractometry (XRD) and energy dispersive analysis X-Ray (EDAX), atomicabsorption spectrometry (AAS) analyses, results of petrographic data, and delta^18O and delta^13Cvalues suggest that the early diagenetic dolomitization in the Tepearasi Formation occurred underthe control of hypersaline (rich in Mg) and fresh water mixing zone. The late diagenetic dolomitespartly developed under the control of tectonic thrusting.

Study of Oxidation Kinetics in Air of Zircaloy-4 by <i>in Situ</i>X-Ray Diffraction

The zircaloy-4 is an alloy of zirconium, which has a very weak thermal neutron absorption, satisfactory mechanical properties and good corrosion resistance at high temperature. For these reasons, zircaloy-4 is used as a material of cladding fuel rod of nuclear reactors. In this environment, it is submitted to different severe conditions of temperature and pressure. The objective of this work is to study the oxidation kinetics of zircaloy-4 in air by the X-ray diffraction technique. The experiments were realized in a “HTK1200” furnace installed as a sample holder in the diffractometer at different temperatures;25°C, 350°C, 500°C, 830°C and 1000°C. The results show that the monoclinic and the tetragonal phases are formed at 350°C temperature. The volume fraction of these phases increased with the temperature until 1000°C where the α phase disappears completely. For simulating the case of loss-of-coolant-accident (LOCA), we have done x-ray diffraction of Zry-4 samples water quenched at 1050°C with different ageing times at this temperature. At 10 seconds and more, there is an important evolution of monoclinic and tetragonal zirconias, which leads to the degradation of zircaloy-4 properties.

Effect of Quantum Interference from Incoherent Pumping Field and Spontaneous Emission on Controlling the Optical Bistability and Multi-Stability

Optical bistability (OB) and optical multi-stability (OM) of a four-level Λ-type atomic system with two fold lower levels inside a unidirectional ring cavity is investigated. The effect of quantum interference arising from spontaneous emission and incoherent pumping on OB and OM is discussed. It is found that the threshold of OB and OM can be controlled by quantum interference mechanisms. In addition intensity of coupling field and the rate of an incoherent pumping field on behavior of OB and OM are then discussed.