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Sediments of Chatham Rise
Norris, R.M. (1964). Sediments of Chatham Rise. NIWA Biodiversity Memoir, 26. New Zealand Oceanographic Institute: [s.l.]. 9-38 + 3 Pl. pp.
Deel van: New Zealand Oceanographic Institute Memoir. New Zealand Department of Scientific and Industrial Research: Wellington. ISSN 0083-7903
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| Abstract |
The Chatham Rise is a broad, elongate submarine ridge extending about 500 miles east of South Island, New Zealand. It includes three banks, two of which may have been Pleistocene islands. Little is known of the structure or bedrock composition of the Rise except at the Chatham Islands near its eastern extremity where schists similar to those of Otago occur and are overlain by Cretaceous to Oligocene and Pleistocene to Recent sedimentary and volcanic rocks. Mernoo Bank near the western end of the Rise is probably developed on Permo-Jurassic greywacke. Greywacke, plutonic igneous rocks and fine-grained sedimentary rocks occur as scattered ice and tree-rafted erratics on all parts of the Rise. Sediments of the Rise include shell gravels on Mernoo and Yeryan Banks and concentrated greensands on Reserve Bank. Foraminiferal oozes cover most of the rest of the area shallower than about 500 m, and silty and clayey sediments, including abundant faecal pellets, blanket the deeper slopes into the adjacent basins. Sediments near the Chatham Islands and Banks Peninsula are mostly land-derived and differ mineralogically from the balance of Rise sediment. Volcanic glass, believed derived from the Taupo rhyolitic eruptions of North Island on the basis of the associated suite of minerals, is widely disseminated throughout the sediments, being present even in depth as shown by ash horizons in the cores. Most of this glass was wind transported from its source. Glauconite comprises up to about 80 per cent of some samples and occurs mainly as discrete sand-size grains. It is believed to be forming at the present time in sheltered, slightly reducing environments where illite clays occur and iron compounds are made available by bacterial destruction of organic colloids. Similarity of recent glauconitic sediments on Chatham Rise and Tertiary calcareous greensands of New Zealand provides a strong basis for reconstructing the Tertiary paleogeography of parts of New Zealand. Phosphatised Miocene foraminiferal oozes in nodular form are widely distributed on the surface of the Rise suggesting a continuously marine environment since Miocene time at least, in which organic carbonates have been dissolved about as fast as they were deposited. Sediments, rocks exposed in the Chatham Islands, and what is known of the bedrock structure of the Rise suggest a schist undermass outlined structurally about the beginning of the Tertiary and persisting in more or less the same form to the present time with occasional volcanic activity at the eastern and western ends. Phosphate nodules, glauconite, and the calcareous organic components of the sediment may be of future economic value to New Zealand as a substitute for phosphates and potash presently imported to maintain the fertility of grazing lands. |
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