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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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| 4. |
- 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, 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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- Boström, K., et al.
(författare)
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Langban - Exhalative Sedimentary Deposit
- 1979
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 74:5, s. 1002-1011
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Tidskriftsartikel (refereegranskat)abstract
- Chemical, mineralogical, and isotope analyses of hausmannite, braunite, and hematite ores from Laangban, Sweden, show that the precursor of this deposit has several similarities in its mineralogy, chemistry, and oxidation state with many deposits of Devonian and Recent ages, such as some deposits in Kazakhstan, in the Red Sea hot brine depressions, and in the East Pacific Rise. Possibly Rammelsberg, Meggen, Franklin Furnace, and Sterling Hill also belong to this type of deposit, for which an exhalative-sedimentary origin is proposed.
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| 7. |
- Boström, Kurt
(författare)
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Particulate and dissolved matter as sources for pelagic sediments
- 1976
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Ingår i: Stockholm Contributions in Geology. - 0585-3532. ; 30, s. 15-79
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Tidskriftsartikel (refereegranskat)abstract
- Compositional data for pelagic sediments, for denudation products from the continents and for marine biological matter can explain how much material is deposited on the ocean floor in dissolved and particulate form. Geochemical mixing models demonstrate that only 2 particulate phases, namely average biological matter and average continental matter, have to be mixed in various proportions to reproduce most pelagic sediments in regard to the elements Si, Al, Ti, Zr, V, Cu, Ni, Zn, Fe, and Cr. CaCO SUB-3 , B, Mn and to some extent Ba usually do not fit the models, since these elements partake in redissolution and migration processes. These latter processes to a large extent occur in hemipelagic and shelf areas. It is probable that such 'hemipelagic pumping' of elements over to the pelagic domain also affects constituents like Cu, P SUB-2 0 SUB-5 , and probably also Ni, Y, La and Co, but the effects are too small to show up in the mixing models. Improved mixing models are produced if a volcanic phase also is involved; the volcanic phase containing Fe, Mn, V and Ba, and possibly additional trace elements in proportions similar to those found in the East Pacific Rise deposits. The models suggest that continental detritus delivers most of the Al, Ti, Zr, Fe, Mn and V, and that biological detritus delivers the main fraction of the Ca, Sr, Cu, Pb, B, Ba, Ni, and Zn to the sediments. In most areas the main fraction of the SiO SUB-2 is terrigenous
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| 8. |
- Boström, Kurt, et al.
(författare)
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Plankton: Its chemical composition and its significance as a source of pelagic sediments
- 1974
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 14:4, s. 255-271
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Tidskriftsartikel (refereegranskat)abstract
- The absolute concentrations of minor and trace elements vary considerably in plankton. However, normalization of elemental abundances versus the minor elements Fe, Al and Zn (instead of the commonly used normalization versus seawater concentrations) demonstrates that these elements show remarkably constant proportions vis à vis each other. Thus, Ti, Fe, Al, Mn, V, and Zr occur in marine lower organisms in the same proportions as in the average shale, whereas Ba, Cr, Cu, Ni, Cd, Pb, Zn and B are enriched relative to the shale abundances, as are also Ca, Mg, Na, K, and Sr. These patterns appear to suggest that marine plankton are rich in lithogenic matter, but this is probably not the normal case.Contrary to the uniformity of plankton, sediments from the Pacific vary considerably in composition. Under the Equatorial high-productivity region the sediments show striking similarities with a mixture of average shale and average plankton mass, as could be expected, whereas sediments from the East Pacific Rise differ considerably from such mixtures. An iron-manganese phase (of deep-seated origin?), mixed with biological matter, on the other hand, yields model sediments with remarkable similarities to the East Pacific Rise deposits. It is therefore likely that biological processes account for a considerable fraction of some elements such as Cu, Ni, Zn and Ba also in the East Pacific Rise metalliferous sediments.
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| 9. |
- Brown, James R.
(författare)
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Microearthquakes and seismic risk
- 1978
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 100:3, s. 307-13
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Tidskriftsartikel (refereegranskat)abstract
- This paper is presented in the nature of a review of the potential of microearthquake surveys in seismotectonic studies, particularly seismic-risk analyses. Microearthquakes are generally considered as shocks with magnitude less than 3. They radiate, in general, higher frequencies than larger earthquakes and therefore microearthquake seismographs must be sensitive to frequencies typically up to 30 or 40 Hz. Mircroearthquakes are useful in seismotectonic studies because: (1) a greater number of small than large shocks occur in the same time, (2) extension to lower magnitudes of frequency-of-occurrence curves can yield more reliable seismic-risk statistics, (3) due to the reduced scale, both in space and time, very precise focal location is possible, often enabling mapping of fracture surfaces, (4) focal-mechanism solutions can further determine the fault surface and, in addition, the direction of slip, and (S) continuous monitoring of seismic activity is possible through the means of a permanent network of microearthquake systems.
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| 10. |
- Brown, R.J., et al.
(författare)
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Weighted vertical stacking in crustal seismic reflection studies on the Canadian shield
- 1977
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Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 25:2, s. 251-268
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Tidskriftsartikel (refereegranskat)abstract
- Seismic reflection methods are being developed at the University of Manitoba to aid in determining fine crustal structures in the Precambrian of Manitoba and northwestern Ontario. Present-day environmental concern as well as mineshaft conditions necessitate the detonation of several smaller charges repeated, say, I times and followed by ''vertical'' stacking. To obtain the familiar ..sqrt..I improvement in signal-to-noise (S : N) amplitude ratio applying the straight-sum (SS) method, one assumes, among other things, that both S : N ratio and signal variance are the same on all traces. Dropping these assumptions, as we must for our data, it becomes necessary to apply weighting coefficients to optimize the S : N ratio of the stacked trace. We still assume the signal shapes to be the same for repeated shots, so for the jth trace on the record of the ith shot we model the time series as: t/sub ij/ = a/sub i/(s/sub j/ + n/sub ij/); where a/sub i/ is a scaling factor. The proper weights w/sub i/ are then shown to be proportional to sigma/sub si//sigma/sup 2//sub ni/ where sigma/sup 2/ is variance, or to ..gamma../sub i//a/sub i/ where ..gamma../sub i/ is S : N power ratio. Applying the weighted-stack (WS) method gives S : N amplitude ratios which are, on average, 55% of the optimal ratios expected from WS theory compared with only 24% for the SS method. The 45% shortfall in WS performance is ascribed mainly to trace-alignment (or time-delay) errors. Varying noise levels on individual traces, slight dissimilarity of signal shape, and correlated noise may also contribute to a lesser extent (in decreasing order of significance). This WS method appears to strike a good practical balance between S : N improvement and processing efficiency.
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