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Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans
Oceanographic Abstracts
1029
BISCAYE PIERRE E., 1964. Mineralogy and sedimentation o f recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. GeoL Soc., Am. Bull., 76 (7): 803-832. Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 ~- and 2-20 ~-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite (?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, reid-spars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis o f the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety ofpedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea are mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator. BLANCHARD RICHARD L., 1965. U 234/U 238 ratios in coastal marine waters and calcium carbonates. J. geophys. Res., 70 (16): 4055--4061. Water and live molluscan shell samples were collected simultaneously at seven locations on the seacoast of the United States. Samples of silt, water, and shells from an estuary were also included in the study. The water samples were analyzed for U 2~8, Ll~aa, calcium, and salinity; the shell samples were analyzed for U zaa, U zaa, calcium, and crystal structure. All water samples, regardless of salinity or total uranium content, were found to have uranium activity ratios, AvZ2a/Av 23s, within the experimental uncertainty o f the 1-15 value accepted for an oceanic environment. The results indicate that the normally higher uranium activity ratio of rivers does not increase the ratio o f coastal waters above the 1-15 oceanic value. The activity ratios of all except two shell samples analyzed were similar to those o f the surrounding seawater and to the oceanic I. 15 value. The application of the results of the study to the determination o f geologic age via uranium-uranium daughter equilibrium is discussed. BOOTH E., 1965. The manurial value o f seaweed. Botanica Marina, 8 (1): 138-143. The use of seaweed products as manure is discussed with reference to nutrient content, the presence of compounds known to affect plant growth or the physical condition of the soil and the effect of algal chemicals on plant diseases. The recent discovery that chitin, laminarin and seaweed have a mycolytic effect o n certain phytopathogenic fungi, together with the failure of analytical methods to explain the nutritional value of organic manures, has revived interest in the biochemical study of the traditional manures. Certain agricultural research which appears to be related to some of the research on seaweed is also included. Boar M. H. P., 1965. Formation of oceanic ridges. Nature, Lond. 207 (4999): 840-843. The low-density underlying rocks causing the uplift of the oceanic ridges and the western United States lie in the upper mantle, and substantially result from partial fusion, although other causes such as serpentinization may contribute. The evidence leading to this conclusion comes from a combination o f geological, geophysical and geochemical discoveries of recent years, and particularly the present burst o f oceanographical research. When pieced together, this evidence suggests rejection of other hypotheses such as crust-mantle mix and solid-solid phase changes as the major cause on the assumption that a single mechanism is of prime importance throughout the whole system of ocean ridges. The hypothesis of partial fusion, however, seems to be consistent with all the lines of evidence. The only mechanism known for causing magma generation on such a large scale depends on the reduction of confining pressure in an upwelling convection current in the mantle. Such convection currents appear to rise beneath the oceanic ridges, causing their volcanism and uplift.
1029
BISCAYE PIERRE E., 1964. Mineralogy and sedimentation o f recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. GeoL Soc., Am. Bull., 76 (7): 803-832. Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 ~- and 2-20 ~-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite (?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, reid-spars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis o f the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety ofpedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea are mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator. BLANCHARD RICHARD L., 1965. U 234/U 238 ratios in coastal marine waters and calcium carbonates. J. geophys. Res., 70 (16): 4055--4061. Water and live molluscan shell samples were collected simultaneously at seven locations on the seacoast of the United States. Samples of silt, water, and shells from an estuary were also included in the study. The water samples were analyzed for U 2~8, Ll~aa, calcium, and salinity; the shell samples were analyzed for U zaa, U zaa, calcium, and crystal structure. All water samples, regardless of salinity or total uranium content, were found to have uranium activity ratios, AvZ2a/Av 23s, within the experimental uncertainty o f the 1-15 value accepted for an oceanic environment. The results indicate that the normally higher uranium activity ratio of rivers does not increase the ratio o f coastal waters above the 1-15 oceanic value. The activity ratios of all except two shell samples analyzed were similar to those o f the surrounding seawater and to the oceanic I. 15 value. The application of the results of the study to the determination o f geologic age via uranium-uranium daughter equilibrium is discussed. BOOTH E., 1965. The manurial value o f seaweed. Botanica Marina, 8 (1): 138-143. The use of seaweed products as manure is discussed with reference to nutrient content, the presence of compounds known to affect plant growth or the physical condition of the soil and the effect of algal chemicals on plant diseases. The recent discovery that chitin, laminarin and seaweed have a mycolytic effect o n certain phytopathogenic fungi, together with the failure of analytical methods to explain the nutritional value of organic manures, has revived interest in the biochemical study of the traditional manures. Certain agricultural research which appears to be related to some of the research on seaweed is also included. Boar M. H. P., 1965. Formation of oceanic ridges. Nature, Lond. 207 (4999): 840-843. The low-density underlying rocks causing the uplift of the oceanic ridges and the western United States lie in the upper mantle, and substantially result from partial fusion, although other causes such as serpentinization may contribute. The evidence leading to this conclusion comes from a combination o f geological, geophysical and geochemical discoveries of recent years, and particularly the present burst o f oceanographical research. When pieced together, this evidence suggests rejection of other hypotheses such as crust-mantle mix and solid-solid phase changes as the major cause on the assumption that a single mechanism is of prime importance throughout the whole system of ocean ridges. The hypothesis of partial fusion, however, seems to be consistent with all the lines of evidence. The only mechanism known for causing magma generation on such a large scale depends on the reduction of confining pressure in an upwelling convection current in the mantle. Such convection currents appear to rise beneath the oceanic ridges, causing their volcanism and uplift.