323 resultados para Classification and description of nets


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Anhydrite occurs in veins in hydrothermally altered basalts recovered from Hole 504B during Leg 83 of the Deep Sea Drilling Project. Sulfur isotopic data indicate that the anhydrites formed from fluids with sulfur isotopic compositions similar to seawater sulfate. Anhydrite probably formed as a pulse of relatively unreacted seawater was heated when it entered a relatively hot hydrothermal system containing evolved fluids. Reheating and continued evolution of the system followed anhydrite deposition. Preservation of anhydrite in Hole 504B was probably favored by the high temperatures and by the low permeability that resulted from the sealing of cracks with secondary minerals. Evidence also indicates that anhydrite was partly replaced by laumontite and prehnite at relatively high temperatures, and possibly by calcite at lower temperatures.

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The results of the International Permafrost Association's International Polar Year Thermal State of Permafrost (TSP) project are presented based on field measurements from Russia during the IPY years (2007-09) and collected historical data. Most ground temperatures measured in existing and new boreholes show a substantial warming during the last 20 to 30 years. The magnitude of the warming varied with location, but was typically from 0.5°C to 2°C at the depth of zero annual amplitude. Thawing of Little Ice Age permafrost is ongoing at many locations. There are some indications that the late Holocene permafrost has begun to thaw at some undisturbed locations in northeastern Europe and northwest Siberia. Thawing of permafrost is most noticeable within the discontinuous permafrost domain. However, permafrost in Russia is also starting to thaw at some limited locations in the continuous permafrost zone. As a result, a northward displacement of the boundary between continuous and discontinuous permafrost zones was observed. This data set will serve as a baseline against which to measure changes of near-surface permafrost temperatures and permafrost boundaries, to validate climate model scenarios, and for temperature reanalysis.

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This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

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A detailed analysis of the texture, matrix, and elements of the microfacies from the carbonate sequence recovered in ODP Hole 639D resulted in a typological classification of 10 major microfacies types and their variants. The variations in distribution and succession of type microfacies allowed us to divide the carbonate sequence into 12 facies-defined subunits. Based on the analyzed characteristics and their relations, we also propose a paleoenvironmental interpretation involving a mixed carbonate/terrigenous ramp model instead of the previous, classical zoned carbonate platform.