Search results for "PET"
showing 10 items of 12749 documents
Carbonate stromatolites from a Messinian hypersaline setting in the Caltanissetta Basin, Sicily: petrographic evidence of microbial activity and rela…
2010
Lower Messinian stromatolites of the Calcare di Base Formation at Sutera in Sicily record periods of low sea-level, strong evaporation and elevated salinity, thought to be associated with the onset of the Messinian Salinity Crisis. Overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions, occasionally influenced by an influx of meteoric water. Evidence of bacterial involvement in carbonate formation is recorded in three dolomite-rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre-scale lamination and small fenestrae. The dominant microfabrics are: (i) peloidal and clotted dolomicrite with c…
Partial high-pressure aragonitization of micritic limestones in an accretionary complex, Tavşanlı Zone, NW Turkey
2006
Pelagic micritic limestones within an upper Cretaceous accretionary complex in the Tavsanli Zone, NW Turkey, preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite, representing the only known example of this type. Aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite. Micrite is very fine grained (<0.003 mm) and contains radiolaria, foraminifera and thin shell fragments. Aragonite forms large crystals, up to 3 cm across, with straight grain boundaries and c-axis mostly subparallel to the carbonate beds. Relict micritic portions are devoid of …
The influence of natural trace element distribution on the mobility of radionuclides. The exemple of nickel in a clay-rock
2015
International audience; The natural distribution of nickel (Ni) in the Callovian–Oxfordian clay-rich rock of Bure (France) was investigated, together with that of cobalt (Co), zinc (Zn) and lead (Pb). The most Ni-enriched phases are pyrite (∼400 × 10−6 g g−1 Ni), sphalerite (∼300 × 10−6 g g−1), chlorite (∼285 × 10−6 g g−1), organic matter (∼300 × 10−6 g g−1), muscovite (100–200 × 10−6 g g−1) and possibly carbonate minerals (mainly calcite and minor dolomite, ∼10 × 10−6 g g−1). Despite their high abundance (up to ∼80% in the upper part of the formation), carbonate minerals are quantitatively a minor Ni reservoir; most of the Ni is borne by chlorite and pyrite, which are minor mineral phases.…
Textural, chemical and isotopic variations induced by hydrothermal fluids on mesozoic limestones in northwestern Sicily
1984
The results are given of textural and compositional investigations carried out on carbonate materials outcropping in various localities in northwestern Sicily where fluorite, barite and calcite mineralizations of hydrothermal origin occur. Observation of the textural features indicate variations in the degree of calcite recrystallization and silicification that appear to be more marked in rocks that show more evident effects of mineralization. The geochemical behaviour of the minor elements indicate variations in chemical composition (increase of Mn, Fe, and Sr and removal of Mg) as a result of interactions between mineralizing fluids and host-rocks. Comparison between the isotopic composit…
A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol
2006
The aim of this study is to characterize the pedogenic clay minerals by using simple approach: Mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD ana…
Zirconium and hafnium fractionation and distribution of Rare Earth Elements in neutral–alkaline waters: Case study of Lake Van hydrothermal system, T…
2021
International audience; We investigated the distribution of Zr, Hf, and rare earth elements (REE) as the sum of lanthanides plus Y in the hydrothermal system in the Lake Van area of south-eastern Turkey. This system is characterised by water with variable pH in alkaline conditions resulting from hydrothermal CO2 upraise and neoformation of calcite minerals in near equilibrium with the interacting waters. Zr, Hf, and REE determinations were carried out for aqueous phases and suspended solids in lake water and surrounding thermal springs. We found that dissolved Hf is partitioned relative to Zr during calcite formation and that such fractionation is a function of the Ca2+ activity in warm wat…
Microbially-induced Fe and Mn oxides in condensed pelagic sediments (Middle -Upper Jurassic, Western Sicily)
2011
Abstract This article presents a petrographic comparison of the Rosso Ammonitico facies of Western Sicily and the original Rosso Ammonitico Veronese of Northern Italy based on a total of 27 sections. The Rosso Ammonitico has been the subject of numerous controversies that range from bathyal to shallow-water platform sedimentation. Therefore it seemed interesting to verify if the term Rosso Ammonitico has the same geologic connotation from region to region. The Middle-Upper Jurassic Rosso Ammonitico of Western Sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the Ionian Ocean. Slope-to-basin or pelagic carbonate deposi…
Refining the temperature dependence of the oxygen and clumped isotopic compositions of structurally bound carbonate in apatite
2019
Abstract Clumped isotope data from carbonated apatite from in vivo and in vitro samples are presented to refine the relationship between mineral growth temperature and carbonate clumped isotopic composition (Δ47). Δ47, δ18O and δ13C data were obtained from phosphoric acid digestion (T = 110 °C) of chemically untreated teeth from an African elephant, Greenland sharks, sand tiger sharks and synthetic apatites. These data cover a temperature range between 1 °C and 80 °C and enlarge the calibration dataset presented in Wacker et al. (2016) by a factor of five. Taxon-specific analyses of tooth enamel(oid) and dentine reveal that both tissues show identical Δ47 values even though the content of o…
Chemical evolution of dissolved inorganic carbon species flowing in thin water films and its implications for (rapid) degassing of CO2 during speleot…
2013
Abstract Rapid degassing of CO2 from a thin film of drip water on the surface of stalagmites is often considered to have a large effect on both speleothem growth and stable isotope values and is offered as an explanation for higher δ13C and δ18O values than expected under conditions of stable isotope equilibrium. However, the time constant for degassing of CO2 from the solution only depends on film thickness and the coefficient of molecular diffusion for CO2. Thus, for thin films, the time for degassing of CO2 is much shorter than the time for subsequent equilibration of the dissolved carbon species and precipitation of CaCO3. In this context, degassing of CO2 is always fast. Here we presen…
Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction
2021
We report Li measurements from cave-analogue carbonate-precipitation experiments in order to: i) assess the expected isotope fractionation factors applicable to speleothem growth, and ii) contribute to the wider understanding of lithium incorporation in carbonates. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2 degassing, low ionic strength solution, thin solution film) but within a laboratory setting that allows for controlled growth conditions (temperature, pCO2, drip rate, carbonate saturation index and the composition of the initial solution). For the main batch of calcite growth experiments our average 1000lnαcalcite-solution is -8.5&plu…