975 resultados para Ore deposits.


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The cores described in this report were taken on AMPHITRITE Expedition in Decenber 1963 - February 1964 by Scripps Institution of Oceanography from, the R/V Argo. A total of 148 cores were recovered and are available at Scripps for sampling and study. The coring sites, all in the tropical central Pacific. The AMPHITRITE cores are here briefly described to identify visually distinct units based on lithology, color, texture, or other characteristic unique to an interval of sediment. For determination of lithology, the slides prepared from samples of the cores were examined microscopically in conjuction with the visual examination.

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A sediment core obtained from the northeastern Philippine Sea Basin was analyzed for 232Th, 230Th, 226Ra and 210Pb. Three sheets of Ferro-manganese oxide in a matrix of red clay were included in the 73 m core. Although the concentration of 232Th of land origin is normal as compared with that of the usual red clay or of the sediment obtained at the neighboring station, the concentration of radiogenic 230Th is extremely low and does not decrease with increasing depth. The radioactivity of rather soluble 226Ra at the station is not less than that of 230Th in the surface sediment, showing a tendency different from that observed in usual cores. Some enrichment in the comparatively short-lived 210Pb activity relative to 226Ra activity was found in the top sediment and in the first ferro-manganese sheet at the station. If the excess 210Pb in the ferro-manganese sheet is not due to contamination of the surface sediment, lead should migrate through the sheet. These facts suggest that the core has not been accumulating during the past few hundred thousand years or more.

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In this volume, Agassiz gives a detailed account of the results of the cruise the steamer "Amra" chartered from the British India Steam Navigation Company. The cruise covered the attols of the Maldives archipelago. The deep sea formations are described in detail.

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The Danish Expedition of the "Galathea II" around the world brought important results concerning the marine organisms in the deep sea. The "Galathea II" showed not only different organisms of the Abyssal but for the first time of the deepest trenches of the western Pacific. Anton Bruun coined the term Hadal for the region below the Abyssal under 6000 m. Although the "Galathea II" aimed to investigate new deep sea regions beside the routes of former expeditions and to widen the horizon of knowledge relating marine organisms the technical equipment and the methodological approach had partly been developed earlier. The expedition of the "Galathea II" is part of a long tradition of cruises such as that of the British "Challenger", the German "Valdivia" and the Swedish "Albatross" and especially the Danish cruises of the "Dana I" and "Dana II" which happened some years before.

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The McMurdo Dry Valleys, Antarctica (MDV) are among the oldest landscapes on Earth, and some landforms there present an intriguing apparent contradiction such that millions of years old surface deposits maintain their meter-scale morphology despite the fact that measured erosion rates are 0.1-4 m/Ma. We analyzed the concentration of cosmic ray-produced 10Be and 26Al in quartz sands from regolith directly above and below two well-documented ash deposits in the MDV, the Arena Valley ash (40Ar/39Ar age of 4.33 Ma) and the Hart ash (K-Ar age of 3.9 Ma). Measured concentrations of 10Be and 26Al are significantly less than expected given the age of the in situ air fall ashes and are best interpreted as reflecting the degradation rate of the overlying sediments. The erosion rate of the material above the Arena Valley ash that best explains the observed isotope profiles is 3.5 ± 0.41 x 10**-5 g/cm**2/yr (~0.19 m/Ma) for the past ~4 Ma. For the Hart ash, the erosion rate is 4.8 ± 0.21 x 10**-4 g/cm**2/yr (~2.6 m/Ma) for the past ~1 Ma. The concentration profiles do not show signs of mixing, creep, or deflation caused by sublimation of ground ice. These results indicate that the slow, steady lowering of the surface without vertical mixing may allow landforms to maintain their meter-scale morphology even though they are actively eroding.

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The cores and dredges described in this report were taken on the DODO Expedition in May 1964 until December 1964 by the Scripps Institution of Oceanography from the R/V Argo. A total of 290 cores and dredges were recovered and are available at Scripps for sampling and study.