Search results for "Rite"
showing 10 items of 2726 documents
Microbial-mediated pre-salt carbonate deposition during the Messinian salinity crisis (Calcare di Base fm., Southern Italy)
2017
Abstract A multi-scale analysis of sedimentary carbonate facies and post-sedimentary diagenetic features of the Calcare di Base Formation, the precursor to evaporites in Upper Messinian successions of Northern Calabria and Central Sicily, has revealed their microbial bio-mediated origin. Massive to laminated microbial boundstones represent the most common sedimentary facies forming flat to low relief cm to m scale stromatolitic and thrombolitic bodies. The fabric of the micrite varies from peloidal to aphanitic, and almost always preserves filamentous bacteria which characterized the original microbial mat. The mat was dominated by sulphur-oxidizing bacteria belonging to the Thiotrichaceae,…
Carbonate deposits from the ancient aqueduct of Béziers, France — A high-resolution palaeoenvironmental archive for the Roman Empire
2016
Abstract Carbonate deposits from a Roman aqueduct in Beziers, southern France, record environmental conditions during the late first century C.E. These deposits formed in a steep section of the aqueduct with a high flow velocity, which caused rapid deposition of up to 11 mm of calcite per year over a period of 22–24 years. The microstructure, trace element and stable isotope composition show that regular deposition was interrupted by high-discharge events, probably in response to heavy rainfall during autumn and winter, transporting colloidally- and particle-bound elements and depositing calcite with elevated δ 18 O values. Individual autumn high-discharge events coincide with abrupt decrea…
Influence of a major exposure surface on the development of microporous micritic limestones - Example of the Upper Mishrif Formation (Cenomanian) of …
2017
18 pages; International audience; Microporous platform top limestones of the Cenomanian Mishrif Formation (offshore Qatar) were studied in order to investigate the diagenetic processes associated with the top-Mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates. Petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the Mishrif Formation, including pervasive dissolution and meteoric cementation, as well as neomorphism of the micritic matrix. Micrites at the top of the Mishrif Formation are coarse (i.e. > 2 μm), sub-rounded and very dull luminescent under cathodoluminesc…
The aqueduct of Gerasa – Intra-annual palaeoenvironmental data from Roman Jordan using carbonate deposits
2021
Abstract Calcium carbonate (CaCO3) deposits from Roman aqueducts are an innovative archive to obtain local high-resolution palaeoenvironmental and archaeological data in interdisciplinary studies. Deposits from one of the aqueducts of the Roman city of Gerasa provide a record of 59 years during the 1st to 3rd centuries CE, divided into three sequences separated by plaster layers. Annual carbonate layers show an alternation of sparite, formed in winter, and micrite, formed in summer. Brown bands at the base of many sparite layers probably correspond to large rainstorms in early winter. A fine lamination present in the brown bands may be diurnal in origin. Stable isotope and trace element dat…
Spherulites in Calcrete Laminar Crusts: Biogenic CACO3 Precipitation as a Major Contributor to Crust Formation
1995
ABSTRACT Spherulites (calcitic fibro-radial spherulitic polycrystals) are a major component of calcite layers in Quaternary calcrete laminar crusts. To explain the formation of spherulites, petrographic and chemical studies were performed on Pleistocene calcrete laminar crusts, Holocene biological crusts, and laboratory (in vitro) cultures of cyanobacterial strains. Spherulites were found to be formed of acicular and radiating crystals, either smooth and regular-edged, or twisted and irregular-edged. Spherulites were composed of low-Mg calcite, the concentration of Mg in the spherulites increasing from nucleus to periphery. The shape and chemistry of the in vitro spherulites and laminar cru…
Structural Behavior of Natural Silicate–Carbonate Spurrite Mineral, Ca5(SiO4)2(CO3), under High-Pressure, High-Temperature Conditions
2017
We report on high-pressure and high-temperature angle-dispersive synchrotron X-ray diffraction and high-pressure Raman data up to 27 GPa and 700 K for natural silicate carbonate Ca5(SiO4)2(CO3) spurrite mineral. No phase transition was found in the studied P–T range. The room-temperature bulk modulus of spurrite using Ne as the pressure-transmitting medium is B0 = 77(1) GPa with a first-pressure derivative of B0′ = 5.9(2). The structure compression is highly anisotropic, the b axis being approximately 30% more compressible than the a and c axes. The volumetric thermal expansivity value around 8 GPa was estimated to be 4.1(3) × 10–5 K–1. A comparison with intimately related minerals CaCO3 ca…
Burial dissolution of micrite in Middle East carbonate reservoirs (Jurassic–Cretaceous): keys for recognition and timing.
2006
14 pages; International audience; This paper discusses burial diagenesis and especially a burial dissolution phase and its effects on micrite microtexture in reservoirs in the Middle East. Three microporous reservoirs were selected: the Cenomanian Mishrif Formation in Iraq; the Kimmeridgian–Tithonian Arab D and the Barremian Kharaib Formations, both in Abu Dhabi. Staining, cathodoluminescence and scanning electron microscopy were used for petrographic observations. In the selected reservoirs, three typical micrite microtextures are distinguished: micro-rhombic, compact anhedral, and rounded. The chronology of diagenesis, based on petrographic observations, shows that mineralogical stabilisa…
Mercaptophenol-Protected Gold Colloids as Nuclei for the Crystallization of Inorganic Minerals: Templated Crystallization on Curved Surfaces
1999
The self-assembly of monolayers of thiols on gold(111) surfaces yields substrates that are able to template in a controlled manner, the nucleation and growth of crystals of calcium carbonate from solution. In the absence of additives, various factors such as the nature of the thiol, the temperature, and the pH are now established as influencing the nature and relative amounts of the different CaCO3 phases (calcite, vaterite, and aragonite). Recently, we have been able to extend the use of thiol/gold self-assembled monolayers as templates for the growth of inorganic crystals by utilizing protected gold colloids instead of flat gold surfaces. The thiol monolayers that protect the colloids pro…
HYDROTHERMAL CARBONATES OF THE SCHWARZWALD ORE DISTRICT, SOUTHWESTERN GERMANY: CARBON SOURCE AND CONDITIONS OF FORMATION USING 18O, 13C, 87Sr/86Sr,…
2012
Diagenetic carbonates, metamorphic carbonates, primary hydrothermal carbonates, and secondary remobilized carbonates (including sinters) from the Schwarzwald ore district in SW Germany formed in various tectonic settings and hydrothermal environments over a period of almost 300 Ma. They were investigated in order to define sources of carbon, dispersion of carbon during fluid-rock interaction processes and, where possible, to specify geochemical fingerprints for carbonates formed during different processes and in different geochemical and tectonic environments. For this purpose, 335 samples of calcite, ankerite, dolomite, siderite, and strontianite from 92 localities in 46 mining areas in th…
Transition from marine to hypersaline conditions in the Messinian Tripoli Formation from the marginal areas of the central Sicilian Basin
2001
Abstract Three sections of the early Messinian Tripoli Formation from the northern and southern margins of the central Sicilian Basin (Serra Pirciata, Torrente Vaccarizzo, and Marianopoli) have been studied with the aim to reconstruct the sedimentary and environmental changes which occurred during the transition between marine conditions and the evaporitic events of the Salinity Crisis recorded in the overlying Calcare di Base Formation. A detailed biostratigraphic and cyclostratigraphic study provided the opportunity of cycle-by-cycle correlations between the marginal sections and the reference section of Falconara. The main paleoenvironmental changes are recorded by: (1) the evolution of …