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1.
George R. Helz Scott A. Sinex Kenneth L. Ferri Maynard Nichols 《Estuarine, Coastal and Shelf Science》1985,21(1):1-16
The dominant physical and chemical processes that control Fe, Mn and Zn are explored by comparing the compositions of sediments and their sources. The and ratios in sediment are found to be largely unaffected by local hydraulic sorting (unlike the actual concentrations of Fe, Mn and Zn) and thus are useful indicators of origin. The sediments in northern Chesapeake Bay have markedly lower and ratios than those found in the Susquehanna River (dissolved plus suspended) under ordinary flow, but not under high flow conditions. Since high flow conditions dominate sediment transport, seaward loss of a major fraction of the river-derived Mn and Zn need not be invoked to reconcile sediment and river compositions. Sediments in the seaward end of the northern bay have higher and ratios than their principal external source, the eroding shore deposits. The excess Zn appears to be derived from the atmosphere; the required depositional flux of Zn is consistent with measurements of the total atmospheric flux. The excess Mn can be explained by remobilization of roughly 5% of the river-borne Mn from sediments in the landward part of the northern bay. Because rare floods influence sediment composition markedly, comparing suspended particles in the river at ordinary stages with resuspended sediment in the estuary would lead to the false interpretation that Mn and Zn were being desorbed in the saltwater. 相似文献
2.
Deep-sea nodules from the Southeast Pacific (northern sector of the Nazca Plate) have been studied regarding their metal content, shapes, and sedimentary environment. The area investigated lies in the southern boundary region of the equatorial zone of high biological productivity. The nodules accumulate by two different growth processes: (1) early diagenetic growth by supply from pore water and (2) hydrogenetic growth by supply from near-bottom sea-water. These growth processes lead to different genetic types of nodules. Considering the ratio, the examined basin can clearly be divided in three ferromanganese facies. The quotient increases generally from south to north, whereas Ni and Cu concentrations show a distinct maximum in the mid facies at a ratio of about 5. Computing the correlation of quotient versus (Ni+Cu), hyperbolic regressions show the best coefficients of correlation and separate the quantity of nodules in two groups. The ascending and the descending hyperbola represent two geochemical ranges which are controlled by different accumulation mechanisms. 相似文献
3.
Bulk composition of ferromanganese nodules from the pelagic environment of the Pacific Ocean is apparently related to nodule-growth rate, sediment-accumulation rate, and biologic productivity in the overlying seawater. Nodules with a high ratio and high Ni and Cu concentrations tend to occur in areas where primary productivity in the surface layer of the ocean is high and the sediment-accumulation rate low. Nodules with a low ratio and low Ni and Cu concentrations occur in areas either where sediment-accumulation rate is high or biologic productivity is low. They may have a ratio as low as one and accrete at rates as low as . Nodules with a larger ratio apparently have growth rates that are greater by as much as a factor of 10. 相似文献
4.
Bobb Carson 《Marine Geology》1977,24(4):289-307
Convergent motion of the North American and Juan de Fuca plates has resulted in deformation of Cascadia Basin sediments and accretion of these deposits to the North American continental margin. The accreted deposits, which occur as anticlinal ridges and thrust blocks, constitute the lower continental slope or borderland off Washington and northern Oregon. Over the past 2.0 m.y., approximately 30 km of this deformed material has been added to the lower slope, removing undeformed deposits from Cascadia Basin at a rate of 2.3–2.9 cm/yr.Near-surface sediments involved in this accretionary process are mechanically consolidated: muds?tones dredged from the lower slope exhibit physical properties (water contents, 20–47%; void ratios, 0.4–1.2; preconsolidation pressures, 0.8–8.2 MPa) which differ significantly from properties of similar, but undeformed sediments (water contents, 50–250%; void ratios, 1.1–1.9). While some consolidation may be attributable to prior burial () or carbonate precipitation, neither mechanism can wholly account for the values observed. It appears that most of the consolidation has occurred in response to tectonically induced overpressures.Initial consolidation occurs rapidly across a narrow () front, defined by the base of the continental slope. Further consolidation and dewatering appears to take place, at a much reduced rate, over the entire width of the lower slope.Development of foliation is nearly ubiquitous in the deformed mudstones. This property limits the strength of the deposits (shear strengths, 90–416 kPa) and movement along these planes probably accommodates much of the strain after initial consolidation.The physical properties characteristic of Washington—Oregon deformed sediments may represent limiting values for mechanical consolidation of near-surface terrigenous sediments under horizontal stress. 相似文献
5.
To understand the behavior of manganese in diagenetic processes in sediments of an enclosed bay which is similar to those
of an estuary, chemical analyses have been carried out on both sediment and interstitial water of a core sample collected
from Tokyo Bay. The results suggest that redistribution of manganese takes place within the sediment as a result of the dissolution
of buried manganese oxides and hydroxides under reducing condition, the downward diffusion of Mn2+ through the interstitial water toward lower layers and then the precipitation of carbonate. The carbonate formed in the sediment
contains managanese carbonate probably as a solid solution between calcitic calcium carbonate and manganese carbonate. 相似文献
6.
Natural abundances of 15N as a source indicator for near-shore marine sedimentary and dissolved nitrogen 总被引：1，自引：0，他引：1
Because organic matter originating in the euphotic zone of the ocean may have a distinctive nitrogen isotope composition (15N/14N), as compared to organic matter originating in terrestrial soils, it may be used to evaluate the relative nitrogen contribution to marine and estuarine sediment. The nitrogen isotope ratios of 42 sediment samples of total nitrogen and 38 dissolved pore-water ammonium samples from Santa Barbara Basin sediment cores were measured. The range of δ15N values for total nitrogen was with a mean of and for pore water ammonium, with a mean of 10.2‰.The results suggest that the dissolved ammonium in the pore water is produced from bacterial degradation of marine organic matter. The range of δ15N values for total nitrogen in the sediment is interpreted as resulting from an admixture of nitrogen derived from marine () and terrestrial (+2‰ marines. The marine component of this mixture, composed principally of calcium carbonate with smaller amounts of opal and organic matter, contains ～ 1.0% nitrogen. The terrestrial component, which comprises over 80% of the sediment, contains ～ 0.1% organically bound nitrogen and accounts for > 25% of the total nitrogen in Santa Barbara Basin sediment. 相似文献
7.
The distribution of iodine and bromine was examined in sediments which receive inputs of marine and terrigenous organic matter. The I and Br concentrations are directly related to the content of ‘marine’ organic matter defined using carbon/nitrogen ratios. In the Etive sediments both Br and I may be used as an indicator of ‘marine’ organic matter; Br is of general application as the ratio (180 × 10?4) is similar to ratios in other sedimentary environments but the use of I is restricted as the ratio is unlike those in other sediments. Experimental study of iodine sorption clearly shows the importance of decaying marine organic matter and oxygenated conditions in the incorporation of iodine by sediments. This suggests that the mechanism of incorporation of iodine by seston previously proposed is probably an important pathway to sediments. The similarity of Br association with marine organic matter suggests that Br sorption as opposed to residual enrichment may be important for sediment Br accumulation. 相似文献
8.
Five fresh, two weathered, and two metamorphosed basalt pillows with a presently or originally glassy outermost layer, together with a weathered and a metamorphosed basalt fragment without an originally glassy layer, all from the Mid-Atlantic Ridge, were investigated in detail. Fresh pillows usually show only very slight compositional heterogeneity, except for the glassy outermost layer where the total iron and MgO contents are higher and the K2O content and the ratio are lower than the interior. In particular, the K2O content of the glassy outermost layer is only about a half of that of the core in some pillows. In weathered pillows the surface layer shows higher total iron, TiO2, P2O5 and H2O contents and a higher ratio and a much lower CaO content than the interior. Most of the compositional heterogeneity observed in metamorphosed pillows may be ascribed to chemical migration during weathering, though metamorphism also may cause considerable heterogeneity. 相似文献
9.
Pavements of manganese nodules and crusts and outcrops of Miocene limestones were observed on the flanks and flat top of the Tenpo Seamount during three Shinkai 2000 dives. The pre‐Miocene volcano supplied nuclei of volcanic rocks and hydrothermal manganese deposits, and subsequent slow or no sedimentation promoted deposition of abundant hydrogenetic nodules and crusts, mainly on the upper flank of the seamount. Nodule pavements generally cover calcareous sand surface sediments, while crusts cover hard outcrops composed probably of volcanic rocks. The fields of crusts and nodules are sparsely distributed with each other on scales of meters to tens of meters. The on‐site observation suggests the deposits have encountered tectonic and/or mass movements that resulted in unusual occurrences of densely stacked nodules and occasionally the nodules resting directly on crusts or hard substrates. Mineralogical and chemical compositions reveal that for nodules and crusts the encrusting manganese layers of around 1 cm thickness are composed of hydrogenetic vernadite, and diagenetic influence is negligible. 相似文献
10.
The major elements and the minor elements cadmium, chromium and vanadium in 12 samples of shallow-water deposits collected
in Tokyo Bay were studied. Average silica content of the deposits is 53.93%, which is approximate to the average of 54.15%
of red clay. Iron (av. 5.67% Fe2O3), titanium (av. 0.71% TiO2), especially manganese (av. 0.87% MnO), are more abundant in the deposits than in the deposits along the entire sea-coasts
of Honshu and of Nanao Bay, Japan. The deposits show higher contents of cadmium (av. 0.61 ppm), the chromium (av. 86 ppm)
and vanadium (av. 79ppm). About 3 to 17 times cadmium and manganese contents compared with those in the deposits along the
sea-coasts of Honshu and of Nanao Bay, Japan was found. Such accumulation, of cadmium and manganese in the deposits is probably
caused by artificial contamination rather than of natural origin. No relation was found between the contents of cadmium, chromium
and vanadium and those of major elements. 相似文献
11.
Organic matter in four Quaternary sediment cores from the Gulf of Mexico and one core from the Washington State coast have been analyzed for lignin and stable carbon isotope compositions. Holocene sequences of all five cores contain organic matter with high relative abundances of 13C () and low lignin concentrations, both of which are consistent with a marine origin. Distinctly lower 13C concentrations () occur in underlying glacial-age sequences from four of the five cores, including the core from the Washington coast where such trends are previously unreported. Although the carbon isotopic compositions of these Pleistocene sediments are typical of predominantly land-derived organic matter, they contain only about 5% of the lignin found in modern sediments of similar from adjacent continental shelves. The lignin-poor organic matter in the glacial-age deposits appears to be either marine-derived or terrigenous material that likely was depleted in vascular plant debris at the time of deposition. 相似文献
12.
13.
H. Elderfield 《Marine Chemistry》1976,4(2):103-132
Application of a simple model describing regional variations in the contents of manganese and associated minor metals in deep-sea sediments suggests that solid manganese phases are being removed from the <0.5 μm fraction of seawater at ～1–7 · 1012g yr?1 in excess of the rate of stream-supplied manganese. This flux is consistent with: (1) the relative rates of sediment accumulation in the Atlantic and Pacific Oceans; (2) the contrast between the oceanic residence time of manganese calculated from stream-supply data (14 · 103 yr) and from the flux of manganese precipitating in marine sediments or as manganese nodules (0.38–2.4 · 103 yr); (3) the surplus mass of manganese revealed by geochemical balance calculations (22.9 · 102g). On this basis excess manganese is accumulating in deep-sea sediments at 0.2–2.0 · 10?6 g cm?2yr?1. Manganese supplied to the upper layers of marine sediments by diagenesis has been evaluated with the aid of vertical advection—diffusion—reaction models. The calculated diagenetic flux of manganese at the sediment surface in a near-shore environment is in agreement with the known accretion rate of manganese deposits (1.7 · 10?2 g cm?2 10?3 yr?1) and the regionally variable flux over the area assessed is consistent with the presence or absence of manganese nodules at or near the water-sediment interface. The diagenetic flux at the surface of deep-sea sediments has been calculated at 0.7 · 10?4 g cm?2 10?3 yr?1 when the upper, oxic, zone of the sediment is ～20 cm thick. A limiting factor on the in situ production flux of dissolved manganese in deep-sea sediments appears to be the availability of reducing agents for manganese dissolution rather than the rate of downward transport of manganese-rich sediment to a reaction boundary where dissolution takes place. Various estimates of the rate of upward-migrating manganese suggest that manganese precipitates in the oxic zone with a rate constant of ～10?7 sec?1 with the result that diagenetic processes cannot supply the flux of excess manganese through more than ～0.25 m of oxic sediment. However, estimates of the flux of manganese to the oceans by submarine volcanic processes (0.79–1.1 · 1012g yr?1) are similar to the surplus mass of manganese detected by geochemical balance calculations (0.7 · 1012g yr?1). If submarine hydrothermal solutions provide only 10% of this excess then their computed discharge rate (39 g cm?2 yr?1) and residence time in the upper layer of oceanic crust (130,000 yr) agree well with these parameters for continental thermal springs. 相似文献
14.
Dissolved and total dissolvable manganese concentrations have been measured at four stations in the western North Atlantic Ocean. Total dissolvable manganese concentrations are high in surface waters, decrease to uniformly low levels throughout the bulk of the water column, and increase in the bottom nepheloid layer. Dissolved Mn (Mnd) concentrations follow the total dissolvable concentrations throughout the surface and deep waters but do not increase in the near-bottom waters.Deep water concentrations of Mnd decrease from 30 ng l?1 in the Newfoundland Basin to 20 ng l?1 in the Sargasso Sea. This change and other features of the deep water distribution of dissolved manganese could be associated with the slow oxidation of Mn2+ to MnO2. There is also evidence at one station of scavenging of manganese from the dissolved phase in the near-bottom layer which may again be related to the kinetics of manganese oxidation. 相似文献
15.
Several diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ18O, δ13C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky calcite cements, and their connection with fracturation events. Four generations of blocky calcite (Cal1–Cal4) are identified. Cal1 and Cal2 are widespread in the dominantly grain-supported facies of the Middle Jurassic limestones (about 90% of the cementation), whereas they are limited in the Oxfordian because grain-supported facies are restricted to certain stratigraphic levels. Cal1 and Cal2 blocky spars precipitated during burial in a reducing environment from mixed marine-meteoric waters and/or buffered meteoric waters. The meteoric waters probably entered aquifers during the Late Cimmerian (Jurassic/Cretaceous boundary) and Late Aptian (Early Cretaceous) unconformities. The amount of Cal2 cement is thought to be linked to the intensity of burial pressure dissolution, which in turn was partly controlled by the clay content of the host rocks. Cal3 and Cal4 are associated with telogenetic fracturing phases. The succession of Cal3 and Cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water/rock ratios. These meteoric fluids circulated along Pyrenean, Oligocene and Alpine fractures and generated both dissolution and subsequent cementation in Oxfordian vugs in mud-supported facies and in poorly stylolitized grainstones. However, these cements filled only the residual porosity in Middle Jurassic limestones. In addition to fluorine inputs, fracturation also permitted inputs of sulphur possibly due to weathering of Triassic or Purbeckian evaporites or H2S input during Paleogene times. 相似文献
16.
Various types of rocks consisting of plagioclase basalts, olivine basalts, pyroxene basalts, picritic basalts and volcanoclastics were found in the Rift Valley between 36°52′N and 36°47′N in the Atlantic Ocean. Palagonite and manganese are the main coating materials encountered on the chilled margins of the pillow-lava fragments. Palagonite is often associated with montmorillonite and chlorite. The thickness of palagonite coating the chilled margins increases in the fragments found from the innerfloor axis towards the walls of the Rift Valley. There is a linear correlation between the thickness of palagonite and that of the manganese encrustation. Considering a rate of manganese and palagonite accumulation of about year it is speculated that the age of a hill located near the axis of the inner floor near 36°50′N is between 3,000 and 12,000 years. The relative age of the inner floor near the intersection of the Rift Valley walls is less than 120,000 years. The specimens having a thicker manganese and palagonite crust located at 4–6 km away from the inner floor axis are 130,000–482,000 years old. 相似文献
17.
1985年12月至1986年4月对西太平洋锰结核进行了调查并对所获沉积物样品进行了分析,研完了锰结核区域沉积物中Fe,Mn,Al和CaCO_3的含量分布特征及其相关关系,说明沉积物中Fe,Mn,Al和caCO_3的含量分布特征主要受水深的制约。 相似文献
18.
19.
Peter R. Payne 《Ocean Engineering》1982,9(6):515-545
Virtual mass solutions (Payne, 1974, 1980a) for the normal force on a flat planing plate gave good agreement with experiments for wetted length to beam ratios in excess of unity. In an article by Payne (1981a), the region below was faired into the known two-dimensional solution (infinite aspect ratio) by means of a bridging function. A subsequent study (Payne, 1980c) of the virtual mass of a rectangular plate led to another bridging function which seemed to be more fundamental, and might give better agreement between theory and experiment below than was the case in the work by Payne (1981a). In the present note this is shown to be so. And although the lift curve slope of a wing and a planing plate (when the cavity lift contribution is neglected) are identical for slender planforms and in the two dimensional flow the plate is found to have a higher lift curve slope in between. There is no relationship between the pitching moment of a planing plate and an aerofoil.This subsequent work has also resulted in a more elegant version of the basic equations, and the new version is presented for both normal force and moment. For slender flat plates the non-dimensional center of pressure of the “virtual mass” force is close to the stagnation line and moves aft with increasing τ and . It is rarely further aft than 10% of the wetted length. The theoretical prediction is compared with the measurements of Sottorf and found to be within the scatter of the data. In contrast, for a chines dry prismatic hull, and for a wing or hydrofoil.The theory enables the effect of camber and rocker to be studied. Using simplified approximations to the general theory it is shown that camber reduces pressure drag (by as much as half) and the bow-up pitching moment; the latter by so much that a cambered planing surface can become unstable. (This was already known theoretically for two-dimensional flow, from the work of Wagner (1932a,b), Cumberbatch (1958), Wu and Whitney (1972), Doctors (1974), Wellicome and Jahangeer (1978). It was known for slender planing surfaces from the work of Maruo (1967) and Tulin (1957). It was also known experimentally for finite aspect ratios from the work of Sottorf (1932, 1934), Clements (1964) and Moore (1967). Rocker, on the other hand, gives a large bow-up couple, and results in increased pressure drag. Presumably this large bow-up moment is why rocker is almost invariably employed with planing sailing dinghies and surfboards, despite the resistance penalty. 相似文献
20.
Wave-induced setup/setdown and longshore currents are examined theoretically for non-planar, concave-up beaches. A beach profile in which the still-water-depth is proportional to the horizontal distance offshore raised to the power is examined in detail. The total mean-water-depth, which includes the sum of the still-water-depth for this power beach profile plus the wave-induced setup/setdown, may be approximated shoreward of the breaker line in a best least-squares sense by a profile that is proportional to the horizontal distance offshore raised to the power. The longshore current profile for this non-planar beach is found to differ significantly from that predicted analytically for a planar beach. The longshore current velocity does not vanish at the shoreline as in the planar beach case. In addition, the peak velocities and the total longshore transport of water are found to be less than for the corresponding planar beach cases. For a given concave-up beach profile, the influence of the lateral mixing increases as the wave height decreases. 相似文献