نتایج جستجو برای: diagenetic origin
تعداد نتایج: 200395 فیلتر نتایج به سال:
The Mozduran One Formation (Middle Jura~!;ic ) in NE Ma!;hhad is mainly composed o f dolomite and limestone. Based on texture (size and fabri c), dolomites were divided into 5 diITerent types with a crystal size which ranges from 10 to 1200 microns. Type one is very fine tn fine subhedral to euhedral crystals. while type two is fine to medium euhedral with poikilotopic texture. Type three...
Measurements of natural cosmogenic Si (t1/2 ~ 140 years) in tropical deltaic sediments demonstrate for the first time that most Si is present in rapidly formed authigenic clays and not biogenic opaline silica (bSi). The burial of bSi in deltaic and continental margin sediments has likely been greatly underestimated because of diagenetic alteration of bSi to clay, little of which dissolves in th...
Polycyclic aromatic hydrocarbons (PAH) in lake sediments and nearby soils of two European high mountain regions, Pyrenees and Tatra, have been studied. Similar mixtures of parent PAH were observed in all cases, indicating predominance of airborne transported combustion products. Nevertheless, the composition of these atmospherically long-range transported PAH was better preserved in the superfi...
I\itrogen and carbon isotope ratios were studied in a stratified deposit of guano of ivlexican Free-tailed bats in Eagle Creek Cave. Arizona. U.S.A. Little diagenetic change was observed over the 25-year time span of the guano deposit. High aridity and reduced circulation of air in the cave are hypothesized to have slowed the normally rapid decomposition of the excreta and the subsequent escape...
Sequential extraction of Hg was performed in a core collected from intertidal area in Ulhas Estuary in order to characterize the downward distribution and diagenetic behavior of Hg in a polluted estuary. Concentration of total Hg ranged between 0.46 and 6.40 microg g(-1) with significant decrease in surficial sediment as a result of closing of two Hg-cell based chlor-alkali plants. Results of s...
Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicate...
The rare earth elements and yttrium (REY)-enriched phosphorites in the Zhijin region, southwest China, have attracted much attention, yet its origin has not been sufficiently addressed. geology, mineralogy geochemistry of samples from four sections early Cambrian age region were studied to attain redox condition REY. Data situ analysis show that REY are mainly contained francolite, two types fr...
The Silurian Pelplin Formation is a part of thick, mud-prone distal fill the Caledonian foredeep, which stretches along western margin East European Craton. consists organic carbon-rich mudstones that have recently been target intensive investigations, as they represent potential source shale gas. host numerous calcite concretions containing authigenic pyrite and barite. Mineralogical and petro...
A brief account of the representative and workable industrial minerals namely magnesite, talc and barite in Lesser Himalaya, is presented here emphasizing their genesis. Deposits of magnesite and talc are found associated with Neoproterozoic, plateform type, shelf-slope limestone-dolomite host rocks from inner Lesser Himalayan sequences. Field, textural, geochemical signatures and fluid inclusi...
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