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- Boström, Kurt, et al.
(författare)
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Biological matter as a source of authigenic matter in pelagic sediments
- 1978
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 23:1-4, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- Pelagic sediments are rich in components that appear to have formed from seawater, so-called authigenic deposits. Such authigenic components are commonly well oxidized and are rich in many metals such as Cu, Co and Ni. On the other hand, most of these metals have restricted solubilities and very short residence times in seawater. True authigenesis can therefore only account for little of the "authigenic"-looking matter in the deep sea.Conservative mixing models, using average terrigenous matter, average marine biological matter, average volcanic matter (East Pacific Rise-emanation) and average basaltic matter, produce model sediments that are strikingly similar to real sediments.In the model sediments several of the trace-element abundances for instance those for Cu, Ni and Ba can only be explained by a large admixture of biological matter. Several of these elements are enriched in the authigenic phases in deep-sea sediments. This implies that most components that generally have been considered as authigenic are rearranged decay products of biological material.
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- Boström, Kurt, et al.
(författare)
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Geochemical behavior of U and Th during exhalative sedimentary processes
- 1978
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Ingår i: Genesis of the manganese nodules. - : Centre National de la Recherche Scientifique, CNRS. ; , s. 151-166
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Konferensbidrag (refereegranskat)abstract
- Exhalative sediments are formed on a large scale on spreading (or active) ridges. Such sediments on the crest of the East Pacific Rise (EPR) are on the average rich in U (38 ppm) and poor in Th (2.4 ppm), contrary to other pelagic sediments that contan 3-6 ppm U and 3-11 ppm Th in the non-biogenic fraction. Most U in active ridge deposits is absorbed from sea water but some derives from different volcanic sources: (a) Shallow hydrothermal leaching of basalts form solutions with high SUP-234 U/SUP-238 U values; (b) Deep seated sources deliver solutions which are very rich in U but with radiochemical equilibrium between SUP-234 U and SUP-238 U; (c) Hydrothermal leaching of sediments is possibly an additional process. Bottom waters over the EPR show normal sea-water values for SUP-234 U/SUP-238 U, suggesting that volcanic U is delivered intemittently. Terrigenous matter delivers most of the Th, whereas biological matter probably is of negligible importance on active ridges as a source for Th. Volcanic processes are negligible sources of U in deposits formed far from spreading centers, such as the bauer Deep sediments and manganese nodules, since any adsorbed U is redissolved during diagenesis. Metamorphic alterations of U rich exhalative deposits could give them the reappearance of vein deposits; a detailed study of such deposits will probably reveal that many of them originally were sedimentary deposits.
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- Boström, Kurt, et al.
(författare)
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Geochemistry and origin of ferromanganese concretions in the Gulf of Bothnia
- 1982
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Ingår i: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 50:1-2, s. 1-24
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Tidskriftsartikel (refereegranskat)abstract
- Ferromanganese concretions cover large areas of the Gulf of Bothnia. They are flat to well-rounded, the rounded ones being richer in oxyhydroxides of iron and manganese. Rounded and ellipsoidal nodules, particularly those in the northern Gulf of Bothnia, are richest in Mn, Ni, Ba and Cu, which probably coexist in a Mn oxyhydroxide phase. Flat nodules are enriched in Fe, P, rare earths and As, probably associated with an Fe oxy-hydroxide component. Aluminum, V, Cr and Ti occur in still another phase. The sediments of the gulf generally consist of a 10-50 mm-thick layer of oxidized surface sediment, enriched in Mn, Ba, P and Ni lying on top of reduced sediments which are diagenetically depleted in these elements. The remobilized elements have redeposited in the nodules, but this process cannot explain the origin of all the nodular material. Some released Mn, Ba and Ni furthermore enter into suspended phases, which eventually leave the Baltic Sea. The economic value of the nodules in the Gulf of Bothnia is probably limited at present.
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- Boström, Kurt, et al.
(författare)
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Geochemistry, mineralogy and origin of the sediments in the Gulf of Bothnia
- 1978
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Ingår i: Proceedings of the Finnish-Swedish seminar on the Gulf of Bothnia. - : Merentutkimuslaito. - 9514636430 ; , s. 8-35
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Konferensbidrag (refereegranskat)abstract
- and DWD at larger depths, but DWD does also occur in some protected depressions where bottom depths may be 20-30 meters or less. DWD represents Postglacial deposits, whereas SWD represents more or less reworked tills. SWD largely consist of little altered rock detritus and are rich in silty, sandy or coarser fractions. DWD contains much clay sized material, but silts and sand may occur occasionally. In general SWD are rich in quartz and feldspars, whereas the DWD are poor in these minerals, but instead show higher contents of X-ray amorphus (background producing) matter, and clay-minerals. The relation Quartz-Feldspar also varies latitudinally, the feldspar-richest sediments occurring towards the North. DWD are enriched in Ti, Fe, Mn, Ba and probably some trace elements (e.g. Cu, Cr) whereas SWD are relatively rich in Si. Al, Ca, Na, and some traces occur in the same concentrations in both sediment types. DWD are identical to average shale in composition and SWD to average granite. This is probably due to a mechanical action, the panning of sediments by waves, bottom currents etc. preferentially moving clay and mica minerals into the deep basins, whereas coarse weathering residues, rich in quartz and feldspar, remain in shallow waters. Iron-manganese concretions occur extensively on the bottom areas that are protected from excessive abrasion and rapid accumulation. The nodules in the Bothnian Bay, are richer in Mn, Cu, Ni and Co than in other parts of Gulf of Bothnia. It is concluded that, in addition to organic matter, hydroxides and other fines may be important adsorbers of pollutants in sediments
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