نتایج جستجو برای: sedimentary structure
تعداد نتایج: 1577589 فیلتر نتایج به سال:
The isotope record of sedimentary sulfides can help resolve the history of oxygen accumulation into the atmosphere. We measured sulfur isotopic fractionation during microbial sulfate reduction up to 88 degrees C and show how sulfate reduction rate influences the preservation of biological fractionations in sediments. The sedimentary sulfur isotope record suggests low concentrations of seawater ...
The western segment of the Churchill Province of Canada, west of Hudson Bay, was divided by Hoffman (1988) into the Archean Rae and Hearne domains separated by the Snowbird Tectonic Zone (STZ) (Fig. 1), defined on the basis of potential field data. The Hearne domain has been further subdivided into the northern Hearne and southern Hearne subdomains (Davis et al., this volume). There is little d...
Reservoirs in the southern Pennines have been investigated to determine their potential for reconstructing a history of atmospheric pollution. A selection procedure has been used to identify sites with the best chance of obtaining a usable sedimentary record prior to sample collection. Five reservoirs were selected for core collection and sediment analysis using magnetic susceptibility (%if), p...
We use a method based on a statistical geomagnetic field model to recognize and correct for inclination error in sedimentary rocks from early Mesozoic rift basins in North America, Greenland, and Europe. The congruence of the corrected sedimentary results and independent data from igneous rocks on a regional scale indicates that a geocentric axial dipole field operated in the Late Triassic. The...
Definition and interpretation of sedimentary facies often involves examination of well logs to assess values, trends, cycles, and sudden changes. The procedure, which often includes visual inspection of the logs, could be improved by using recently developed signal analysis and feature extraction techniques. In particular, wavelet analysis of logs provides an easily interpretable visual represe...
Two hundred and seven weaned foals aging 6 to 12 months from small farms in the Lublin region were examined in the years 2005 to 2007. The investigations were carried out using flotation and sedimentary flotation methods, and McMaster’s quantitative method modified by Wetzel. Eimeria leuckarti oocysts were found in 19 (9.18%) of the foals. The horses demonstrated occasionally clinical signs (fo...
Diverse microbial communities and numerous energy-yielding activities occur in deeply buried sediments of the eastern Pacific Ocean. Distributions of metabolic activities often deviate from the standard model. Rates of activities, cell concentrations, and populations of cultured bacteria vary consistently from one subseafloor environment to another. Net rates of major activities principally rel...
Flame structures found in sedimentary rocks may have formed from liquefaction and gravitational instability when the sediments were still unconsolidated and were subject to shaking caused by earthquakes. However, the details of the process that leads to the formation of the flame structure, and the conditions required for the instability to initiate and grow remain unclear. Here, we conduct a s...
The outcropping Cretaceous siliciclastic sediments in the Al Bauga area in Northern Sudan reach a maximum thickness of about 30 meter. They rest with angular unconformity on tilted Precambrian basement rocks and are capped by Tertiary-Quaternary basalts forming a type of nonconformity. The sedimentary sequence was subdivided into three major units separated by two disconformities. The lower uni...
Geobotanical assessment of taxa with a high percentage of richness and endemism plays an important role on conservation plans. South-West Asia is one of the main biodiversity centers of the genus Onosma (Boraginaceae) comprising a high rate of species richness and endemism in Iran. Due to existing threatened factors to habitats and lack of sufficient data on conservation and distribution patter...
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