440 resultados para Mounds


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In the nineties, cold-water coral mounds were discovered in the Porcupine Seabight (NE Atlantic, west of Ireland). A decade later, this discovery led to the drilling of the entire Challenger cold-water coral mound (Eastern slope, Porcupine Seabight) during IODP Expedition 307. As more than 50% of the sediment within Challenger Mound consists of terrigenous material, the terrigenous component is equally important for the build-up of the mound as the framework-building corals. Moreover, the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development. In this study, the first in-depth investigation of the terrigenous sediment fraction of a cold-water coral mound is performed, combining clay mineralogy, sedimentology, petrography and Sr-Nd-isotopic analysis on a gravity core (MD01-2451G) collected at the top of Challenger Mound. Sr- and Nd-isotopic fingerprinting identifies Ireland as the main contributor of terrigenous material in Challenger Mound. Besides this, a variable input of volcanic material from the northern volcanic provinces (Iceland and/or the NW British Isles) is recognized in most of the samples. This volcanic material was most likely transported to Challenger Mound during cold climatic stages. In three samples, the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on Greenland, Scandinavia or Canada. The grain-size distributions of glacial sediments demonstrate that ice-rafted debris was deposited with little or no sorting, indicating a slow bottom-current regime. In contrast, interglacial intervals contain strongly current-sorted sediments, including reworked glacio-marine grains. The micro textures of the quartz-sand grains confirm the presence of grains transported by icebergs in interglacial intervals. These observations highlight the role of ice-rafting as an important transport mechanism of terrigenous material towards the mound during the Late Quaternary. Furthermore, elevated smectite content in the siliciclastic, glaciomarine sediment intervals is linked to the deglaciation history of the British-Irish Ice Sheet (BIIS). The increase of smectite is attributed to the initial stage of chemical weathering processes, which became activated following glacial retreat and the onset of warmer climatic conditions. During these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed. Therefore, we postulate that the deglaciation of the BIIS has an important effect on mound growth. It can seriously alter the hydrography, nutrient supply and sedimentation processes, thereby affecting both sediment input and coral growth and hence, coral mound development.

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Termites are the most important soil ecosystem engineers of semi-arid and arid habitats. They enhance decomposition processes as well as the subsequent mineralisation of nutrients by bacteria and fungi. Through their construction of galleries, nests and mounds, they promote soil turnover and influence the distribution of nutrients and also alter texture and hydrological properties of soils, thereby affecting the heterogeneity of their ecosystem. The main aim of the present thesis was to define the impact of termites on ecosys-tem functioning in a semi-arid ecosystem. In a baseline study, I assessed the diversity of termite taxa in relation to the amount of precipitation, the vegetation patterns and the land use systems at several sites in Namibia. Subsequently, I focussed on a species that is highly abundant in many African savannas, the fungus growing and mound building species Macro-termes michaelseni (Sjöstedt, 1914). I asked how this species influences the spatial hetero-geneity of soil and vegetation patterns. From repeated samplings at 13 sites in Namibia, I obtained 17 termite taxa of 15 genera. While the type of land use seems to have a minor effect on the termite fauna, the mean annual precipitation explained 96% and the Simpson index of vascular plant diversity 81% of the variation in taxa diversity. The number of termite taxa increased with both of these explanation variables. In contrast to former studies on Macrotermes mounds in several regions of Africa that I reviewed, soil analyses from M. michaelseni mounds in the central Namibian savanna revealed that they contain much higher nitrogen contents when compared to their parent material. Further analyses revealed that nitrate forms a major component of the nitrogen content in termite mounds. As nitrate solves easily in water, evaporation processes are most probably responsible for the transport of solved nitrates to the mound surface and their accumulation there. The analysed mounds in central Namibia contained higher sand propor-tions compared to the mounds of the former studies. Through the higher percentage of coarse and middle sized pores, water moves more easily in sandy soils compared to more clayey soils. In consequence, evaporation-driven nitrate accumulation can occur in the studied mounds at high rates. ff...

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Clay minerals recovered from the Galapagos hydrothermal mounds (Holes 506C, 507D, and 509B) are mainly iron-rich nontronite-like minerals enriched in potassium. Nontronites from Hole 509B show a distinct tendency to become micaceous toward the lower beds of clay sediments. Mn-crusts consist mainly of todorokite or a mixture of todorokite and nontronite. Minerals of clay and Mnrich sediments in the mounds originated from hydrothermal solutions of uncertain origin. Pelagic oozes from hydrothermal mounds and from areas between mounds (Hole 506D) consist mainly of calcite. In the carbonate beds on or near the hydrothermal mounds an admixture of smectite is often found.

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"Reprint from the Journal of the Academy of natural sciences of Philadelphia, vol. XVI."

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Summary in French.

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Oriental research and the Bible, by J. F. McCurdy.--The mounds of Palestine, by F. J. Bliss.--Explorations in Babylonia, by H. V. Hilprecht.--Research in Egypt, by A. H. Sayce.--Discoveries and researches in Arabia, by F. Hommel.--The Hittites, by W. H. Ward.--Early Greek manuscripts from Egypt, by J. P. Mahaffy.--New light on the Book of Acts, by W. M. Ramsay.--Indexes.

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Principally a reply to statements in H.W. Henshaw's Animal carvings from mounds in the Mississippi Valley, published in the 2nd annual report of the Bureau of American Ethnology, Washington, 1883.

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W.C. Mills, curator and librarian.

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The Native Americans and Nature in Illinois activity book from the Illinois Department of Natural Resources (IDNR) is designed to supplement your curriculum in a variety of ways. The information and activities contained in this publication are targeted to grades kindergarten through three and can help you meet the following Illinois Learning Standards: 16.A.1a; 16.C.1a (U.S.).

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Includes bibliographical references (p. 407-419).