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1.
Mineralogical, geochemical and grain‐size composition of soil and pore‐water chemistry parameters were characterized on both eroded (south‐facing) and non‐eroded (north‐facing) clayey‐silt slopes in the Basilicata region (southern Italy). Only a few grain‐size parameters and clay mineralogy discriminate eroded from non‐eroded substrates. Compared with the latter, the former have fractions of over 63 µm and 1–4 µm lower and fractions 4–63 µm higher. Grain‐size characters of crusts did not discriminate with respect to substrate. Bulk rock mineralogy was not distinctive, but the clay mineral assemblage shows that the eroded slope is enriched in kaolinite, mixed layers (illite–smectite) and chlorite, whereas illite decreases, although overlaps are common. Chemical data enable discrimination between eroded and non‐eroded slopes. pH, SAR (sodium adsorption ratio), TDS (total dissolved salts) and PS (percentage of sodium) are distinctive parameters for both eroded and non‐eroded slopes. TDS increases in depth in the non‐eroded slope, whereas the maximum TDS is just below the crust in the eroded one. On average, eroded substrates are higher in pH, SAR and PS than non‐eroded ones. The ESP (exchangeable sodium percentage) of the eroded slope has a higher value than the non‐eroded one. Crusts are less dispersive than eroded substrates, and non‐eroded substrates behave as crusts. This suggests that the portion of the slope most severely exposed to weathering tends to stabilize, due to strong decreases in SAR, PS and ESP. Several diagrams reported in the literature show similarly anomalous crust samples on eroded slopes, compared with other samples coming from greater depths on eroded slopes. In the present case study, the exchangeable form of Na characterizes crusts more than the soluble form. This study describes the erosional mechanism, which involves morphological and geographic exposure and climatic elements, as well as grain size, mineralogy, chemistry and exchangeable processes of soils. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

2.
Samples dredged from the sediment mounds have a unique chemistry and mineralogy which reveals details of the hydrothermal processes that produce these deposits. The mounds form primarily by deposition of Fe, Mn and Si from hydrothermal fluids which circulate through the basalt crust and the overlying sediments. The Mn, Fe and Si are strongly fractionated in the process; the Fe and Si precipitate within the mounds under slightly reducing conditions as nontronite, while the Mn is deposited as Mn oxyhydroxides at the seawater-sediment interface. The nontronite is exceptionally well crystallized, and contains less than 200 ppm Al. The Mn minerals, todorokite and birnessite, also have exceptional crystallinity and the distribution of trace elements Cu, Ni, Zn, Co, Ca and Ba in these phases agrees with predictions made on the basis of models of their crystal structure. The environment of deposition which produces this suite of minerals — slow percolation of hydrothermal fluids through pelagic sediments — may not be unique to the Galapagos Rift, as the same suite of minerals has been found in similar setting in the Gulf of Aden and on the Mid-Atlantic Ridge.  相似文献   

3.
Analyses have been made of the REE contents of a suite of hydrogenous δMnO2-rich ferromanganese encrustations obtained from a variety of depths (1000–4700 m) on the Line Islands Archipelago. The crusts form a coherent sample group, the REE contents of which are distinctly higher than those of diagenetic nodules. Crusts from 1 to 2 km depth exhibit higher Mn/Fe ratios and are approximately 50% REE depleted with respect to crusts below ～ 2 km. Furthermore, the shale-normalised patterns of the REE fall into the same depth-related categories. Crusts from depths greater than 2000–2500 m exhibit slight heavy REE depletion relative to intermediate REE whilst crusts from above that level exhibit more fractionated, heavy-REE-enriched patterns.To explain these depth-related processes, it is proposed that Mn and Fe oxides exhibit distinct behaviour with respect to REE scavenging. Between ～ 1 and 2 km, higher Mn/Fe ratios in the crusts are considered to be caused by an enhanced supply of Mn2+ —by diffusion and advection from nearshore sediments—which is adsorbed by and occludes existing oxide flocs. At these depths, oxides therefore tend to exhibit predominantly Mn oxide adsorptive properties. Consideration of the REE patterns shows that Fe oxides must be enriched overall in REE relative to Mn oxides and exhibit a flat shale-normalised REE pattern, whilst Mn oxide exhibits a heavy-REE-enriched pattern.Comparison of dissolved REE depth profiles with the crust data enables a qualitative appraisal of the application of scavenging models to the oxide-REE system. The data are not simply described by either equilibrium or irreversible adsorption models alone. It is concluded that whilst oxides may play a general role in creating the LREE depleted seawater pattern, they have little effect on individual vertical profiles, except close to points where fresh oxides precipitate.  相似文献   

4.
Ferromanganese nodules from the Bauer Basin of the south equatorial Pacific are unlike virtually all oceanic nodules so far analyzed in showing negative Ce anomalies in their REE abundance patterns. In comparison with similarly Cu-Ni-enriched nodules from the north equatorial Pacific they are depleted in REE by 50–80% and are heavy REE enriched relative to intermediate REE. The REE patterns can be accounted for by the input of hydrothermal iron oxyhydroxides and associated REE to the Bauer Basin and the transfer of the REE to the nodules because of diagenetic reactions in the sediment. The excess iron input also is reflected in lower Cu/Ni ratios in the nodules as compared with nodules from the north equatorial zone, apparently because of the larger proportions of a residual Fe phase in the nodules relative to todorokite. Cerium anomalies of the Bauer Basin nodules range from ?0.17 to ?0.29 as compared with +0.33 to +0.07 in the north equatorial Pacific but show a parallel sensitivity of Ce anomaly to Mn/Fe ratios of the nodules. Nodules with the more positive anomalies within each group have the smallest Mn/Fe ratios and have been subjected to the greatest seawater influence whereas nodules with the more negative anomalies have the largest Mn/Fe ratios and have been subjected to the greatest diagenetic influence.  相似文献   

5.
During DSDP Leg 70, a 1.60 m thick manganese oxide layer was sampled in hole 509B. This deposit is formed of alternating layers of hard plates of pure todorokite, about 2 mm thick, and of a more powdery material deeply impregnated with manganese oxide, about 3 mm thick. A SEM study of the plates and the associated powder shows that the powdery material is a transformation of a pre-existing sediment, while the plates are a direct precipitation from a hydrothermal solution.The uranium series disequilibrium method was used to determine the ages of the plates. They are found to be in good chronological sequence and in accordance with the sedimentation rate of the area (4.9 cm/103 years) which implies that they have been formed at the sediment-seawater interface during a pulsed injection of hydrothermal solution. The powder presents systematically an “older age” which is explained by a slowing down of the injection while the normal sediment settles; the older age is due to the230Th excess of the sediment.  相似文献   

6.
186Os enrichments in volcanic rocks and peridotite-derived iridosmine grains have been attributed to contributions from Earth’s outer core to the mantle, and apparently constrain the scale of mantle convection and an early timing for inner–outer core segregation more than 3.5 Gyr ago. Here, we highlight that marine ferromanganese crusts and nodules are characterised by high Pt/Os ratios and Pt–Os contents that develop much larger 186Os excesses over geological time (≥0.2%/Gyr) than those hypothesised for Earth’s outer core (<0.005–0.01%/Gyr). 187Os/188Os ratios in ferromanganese crusts are radiogenic due to sequestering of continental Os from seawater. Similarly, ancient ferromanganese materials may have had 186Os excesses (>0.1%) as a result of high Pt/Os ratios in continental crust, even prior to in-growth of 186Os after formation due to their high Pt/Os ratios. Past recycling of small amounts of these materials into the Earth’s mantle will produce coupled 187Os–186Os excesses and little change in Re and platinum-group-element concentrations, as observed in Hawaiian picrites, and in contrast to the predicted result of outer core addition to the mantle. 187Os and 186Os enrichments in the Hawaiian mantle source are potentially consistent with it comprising recycled oceanic lithosphere, pelagic sediments and ferromanganese materials, and questions the notion that Os isotopes can be used to uniquely identify core–mantle interactions and the depth at which mantle sources for volcanism originate.  相似文献   

7.
Chemical and mineralogical data are presented for a suite of 59 sediment samples collected from the P8 and Speedwell cave systems (and mineralogical data are presented for a further six surface sediments) in the Castleton karst catchment, Derbyshire, England. Sediments are grouped according to age and depositional environment and these groups show distinctive mineralogical and chemical characteristics. Clay mineralogy is effective at distinguishing different sediment sources for ancient and modern sediments which are derived from pre-Devensian tills and Devensian solifluction deposits, respectively. Major element chemistry reflects these differences in clay mineral content, while trace elements demonstrate the importance of abrasion of ore minerals in conduits in the aquifer which follow mineral veins, even under natural, pre-mining conditions. Clay minerals are confirmed as the host for uranium in uranium-rich ancient sediments. Consideration of organic carbon and hydrogen concentrations shows that plant material is the dominant source of organic material in the modern sediments. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

8.
Abstract   Hydrogenetic ferromanganese crusts are widespread on the floor of the northwestern Pacific Ocean, south and east of the Japanese Islands, despite vigorous tectonic activity, such as subduction and back-arc spreading, since at least the Mid-Paleogene over the Philippine Sea Plate region and nearby. The crusts occur mainly at water depths shallower than 3000 m, but also at greater depths of up to 6000 m. Fine-scale 10Be/9Be dating was undertaken on several 5–10 cm thick hydrogenetic ferromanganese crusts sampled from different geological environments, including inactive submarine volcanoes, tectonic escarpments and abandoned rifts. The results indicate that the crusts have grown at relatively constant rates of 4–7 mm/my without any significant time breaks. These uniform and constant growth rates suggest that the basins have been exposed constantly to oxygenated bottom waters since their formation in the Middle Miocene ( ca 15 Ma) or earlier. Local geological or oceanographic environmental changes might have slowed or increased some of the growth rates resulting in correlation of some internal structures. The Philippine Sea Plate region could have economic potential in areas of thick hydrogenetic ferromanganese crusts over a wide range of water depths.  相似文献   

9.
The Pulmoddai placer sands in Sri Lanka(9°3’23.65’’-8°51’38.83’’N and 80°55’22.91’’-81°3’32.65’’E) is considered to be one of the major rare earth element(REE) prospects world-wide. This deposit has a global significance in terms of strategic economic resources and can provide valuable insight for resource estimation and for its economic use. A detailed study of the geochemical, mineralogical, and textural properties of the heavy minerals of this region is undertaken applying the scanning electr...  相似文献   

10.
The metal composition of oceanic ferromanganese deposits occurring in seamount regions (Line Islands chain and Mid-Pacific Mountains) varies with water depth and age. The results of metal determinations of carbonate plankton samples suggest that carbonate dissolution in the water column might have an important influence on the accretion and composition of hydrogenetic precipitates. Two ferromanganese crust generations of different age have been observed The precipitation of the older crust took probably place during early Oligocene, the younger crust began to form during middle Miocene. Between the two crust generations periods of carbonate sedimentation and of phosphorite deposition occur. The hydrogenetic formation of the crusts is controlled by the metal supply from the water column, according to the laws of colloidal surface chemistry.Dissolution experiments with carbonate plankton samples show that the main Fe source for the hydrogenetic crust formation are colloidal Fe-hydroxide particles being released in the water column from the dissolution of carbonate plankton skeletons. In the case of Mn, maximum dissolved Mn occurs in the oxygen minimum zone as the result of in-situ break-down of organic matter and the in-situ reduction of Mn-bearing solid phases. Closely beneath the oxygen minimum zone a Fe supply, mobilized within the oxygen minimum zone, has also to be taken into account. In the water column below the oxygen minimum zone, a mixture of colloidal particles of MnFe-oxyhydroxide and colloidal AlFe-silicate, precipitate together on the surface of substratum rocks. The mixing ratio of these colloidal phases controlling the metal composition of the ferromanganese precipitates, is depth-dependent and shows also temporal variations. In general, Mn/Fe ratio, Ni, and Co contents decrease with depth down to the calcite compensation depth.The most probable mechanism for the ultimate removal of Co and Ni from the water column might be a surface reaction. δ-MnO2 is specifically able to absorb hydrous Co2+ and Ni2+ ions. Because of the surface enrichment of Co and the strong electrical field of Mn(IV), a subsequent oxidation of Co2+ to Co3+ takes place leading to higher enrichment of Co in comparison to Ni. The most important factor governing the high Co enrichment in the ferromanganese crusts is the growth rate: the lower the growth rate, the higher the Co content. Maximum values of up to 2% Co occurring in samples from water depths between 1500 and 1100 m [1] are related to lower carbonate dissolution rates and corresponding lower Fe supply.The metal supply from the water column is strongly related to distinct environmental factors such as bio-productivity, range of lysocline and calcite compensation depth, rate of carbonate dissolution, and activity of the Antarctic bottom water. Thus, our model shows that the growth periods and the metal composition of hydrogenetic seamount crusts are controlled by changes in the paleoceanography and reflect distinct environmental conditions.  相似文献   

11.
Using a fluorescence microscope and EPMA, abundant microbe ”bodies“ and clear microbic fluorescent microstructure are determined in the ferromanganese nodules recently collected from the East Pacific deep sea floor. The microbic fluorescent structure shows a close relation to the formation of the ferromanganese nodules. According to their morphological features, the microbes are classified into two types: one is named clumpy microbe, which takes a bar-shaped manganese mineral as a pillar and grows like fasciculate coral, resulting in irregular cauliflorate nodules with rough surfaces; the other is called filamentous microbe, which grows in very thin arcuate and/or concentric circular laminae composed of a microbe layer and a metal (manganese and iron)-rich layer, leading to potato-shaped nodules with relatively smooth surfaces. It also can be seen that the two types of microbes are intergrown together, resulting in nodules complicated in compositions and shapes.  相似文献   

12.
A microprobe study of metalliferous sediment components   总被引：1，自引：0，他引：1  
Smectite aggregates, Fe-Mn micronodules, and fish debris from the coarse fraction of a metalliferous sediment sample from the Bauer Basin have been analyzed by microprobe. Both X-ray diffraction and bulk chemical analyses reveal that the smectite, an iron-rich and aluminum-poor nontronite, is the dominant phase. A linear programming solution to a series of mass balance equations indicates that the bulk sample is 70% smectite, 4% todorokite, 13% microlaminated material, and 1% fish debris. Two episodes of micronodule development are indicated by the presence of overgrowths of microlaminated iron-rich material over a homogeneous dense todorokite core. The two micronodule compositions can be explained by reaction of hydrothermally produced amorphous Fe-Mn oxyhydroxides with biogenous opal to form the calculated phase composition. The rare earth elements in the bulk sample can be explained by a similar diagenetic process which distributes rare earth elements of a seawater origin between cerium-enriched micronodules and cerium-depleted fish debris.  相似文献   

13.
《Journal of Hydrology》1999,214(1-4):165-178
Karst aquifers are capable of transporting and discharging large quantities of suspended sediment, which can have an important impact on water quality. Here we present the results of intensive monitoring of sediment discharging from a karst spring in response to two storm events, one following a wet season and the other following a dry season; we describe temporal changes in total suspended solids (TSS), mineralogy, and particle size distribution. Peak concentrations of suspended sediment coincided with changes in aqueous chemistry indicating arrival of surface water, suggesting that much of the discharging sediment had an allochthonous origin. Concentrations of suspended sediment peaked 14–16 h after rainfall, and the bulk of the sediment (approximately 1 metric ton in response to each storm) discharged within 24 h after rainfall. Filtered material included brightly colored fibers and organic matter. Suspended sediments consisted of dolomite, calcite, quartz, and clay. Proportions of each mineral constituent changed as the aquifer response to the storm progressed, indicating varying input from different sediment sources. The hydraulic response of the aquifer to precipitation was well described by changes in parameters obtained from the particle size distribution function, and corresponded to changes seen in TSS and mineralogy. Differences between storms in the quantity and mineralogy of sediment transported suggest that seasonal effects on surface sediment supply may be important. The quantity of sediment discharging and its potential to sorb and transport contaminants indicates that a mobile solid phase should be included in contaminant monitoring and contaminant transport models of karst. Temporal changes in sediment quantity and characteristics and differences between responses to the two storms, however, demonstrate that the process is not easily generalized.  相似文献   

14.
海底富钴结壳富含多种金属,是海底极为重要的矿产资源.在实验室里对用拖网采集的天然富钴结壳的湿密度、干密度、含水率、P波速度和抗压强度等物理特性进行了研究.研究表明:富钴结壳的湿密度或干密度的大小与孔隙率、含水量有关;富钴结壳的抗压强度与温密度、P波速度有较强的相关性,湿密度、P波速度越高,其抗压强度也相应越大.所以富钴结壳的物理特性与抗压强度之间的相互关系,为富钴结壳的资源评价、采选冶研究提供参考.  相似文献   

15.
Todorokite is a common manganese oxide in soils, sediments, and marine manganese nodules. The MnO6 octahedrons share edges within chains and share cor-ners between chains to form a 3×3 tunnel framework of todorokite. Octahedral molecular sieves with struc-ture of todorokite exhibit superior characteristics in ion exchange, specific surface area, thermal stability and molecule-sized tunnels[1]. Todorokite plays an important role in cleaning up natural water and con-trolling concentration of h…  相似文献   

16.
The response of runoff and erosion to soil crusts has been extensively investigated in recent decades. However, there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes. Here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi‐arid Loess Plateau region. Soil boxes (1.5 m long × 0.2 m wide) were set to a slope of 17.6% (10°) and simulated rainfall of 120 mm h?1 (60 minutes). The runoff generation and erosion rates were determined for three crust area ratios (depositional crust for 20%, 33%, and 50% of the total slope) and five spatial distribution patterns (depositional crust on the lower, lower‐middle, middle, mid‐upper, and upper slope) of soil crusts. The reduction in sediment loss (‘sediment reduction’) was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion. Sediment yield was influenced by the area ratio and spatial position of different soil crusts. The runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration. Sediment yield was controlled by detachment limitation and then transport limitation under rainfall. The shifting time of erosion from a transport to detachment‐limiting regime decreased with increasing area of depositional crust. No significant differences were observed in the total runoff among treatments, while the total sediment yield varied under different spatial distributions. At the same area ratio, total sediment yield was the largest when the depositional crust was on the upper slope, and it was smallest when the crust was deposited on the lower slope. The sediment reduction of structural crust (42.5–66.5%) was greater than that of depositional crust (16.7–34.3%). These results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
Manganese-rich rock coatings are widespread in Iceland, especially in fractures in basalt lavas. Three common types of coating are described. A thick subsurface coating is found on whaleback forms on high plateaux. The most common type is thinner and occurs in hydrothermal clay-filled fracture systems which are especially well developed in tholeiite lavas. A third type occurs in younger rocks and is associated with tephra-rich, loessic sediment which fills open fractures and vesicles. There are differences in the chemistry, morphology, and mineralogy of these coatings which are interpreted as being due to the different microenvironments in which they form. The fracture microenvironment is regarded as being of much more importance to coating thickness and chemistry than simple age and in this respect the hydrothermal clays seem to favour rapid manganese concentration. On the other hand, there are variations in coating type, both laterally and vertically through the lava succession, which are related to regional distribution of hydrothermal alteration and rock type. The regional patterns are the result of Iceland's lateral drift and as a result there is an incidental connection between coating type and rock age. There is some evidence to suggest that the manganese coatings may be both forming and being degraded rapidly in the present environment.  相似文献   

18.
Interiors of manganese nodules from siliceous ooze beneath the Pacific equatorial high-productivity region, when examined by scanning electron microscopy (SEM) and electron microprobe, display post-depositional recrystallization textures and metalliferous oxide bands (diameter 1–10 μm, 30–40 wt.% Mn, 4–5% Ni, 3–4% Cu). SEM has revealed biogenic siliceous matter in all stages of degradation and dissolution within nodule interiors, creating cavities and voids. Often these miniature vugs contain authigenic phillipsite crystallites which are coated with delicate clusters of crystalline Mn-Fe oxides (todorokite) containing significant amounts of Ni and Cu. We postulate the following diagenetic processes and mechanism of uptake of transition metals inside manganese nodules: (1) palagonite + biogenic silica + pelagic clay → phillipsite + montmorillonite; (2) biogenic matter + amorphous FeOOH or δ-MnO2 → Feaq2+ and/or MnIIMnIV oxide (todorokite); (3) aerated seawater or δ-MnO2 + Feaq2+ → FeOOH and/or todorokite (deposited on phillipsite); (4) (NiII and CuII) organic chelates (adsorbed on clays, etc.) + amorphous FeOOH or δ-MnO2 → Ni-Cu-todorokite + phillipsite, etc.This mechanism explains the well-known positive Mn-Ni-Cu and negative Fe-Ni, Fe-Cu correlations in nodules. By analogy with terrestrial todorokites, which require about 8 wt.% Mn to be in the divalent state to stabilize the crystal structure, as much as 8 wt.% (Ni + Cu) could be accommodated in todorokite-bearing deep-sea manganese nodules. However, although such nodules beneficiate Ni and Cu with respect to marine sediments and seawater, they remain undersaturated in these divalent cations.  相似文献   

19.
A hydrothermal deposit from explorer ridge in the northeast Pacific Ocean   总被引：1，自引：0，他引：1  
Crusts composed of nontronite and ferromanganese oxides were recovered from Explorer Ridge, a spreading ridge segment in the northeastern Pacific Ocean located off the west coast of Canada. The chemical and mineralogical composition of the crusts closely resembles that of the mound-like hydrothermal deposits recently discovered at the FAMOUS site on the Mid-Atlantic Ridge and on the Galapagos spreading centre. Compositional anomalies suggest that the crusts are precipitates of hydrothermal vent solutions which were ejected discontinuously and subsequently mixed with seawater.  相似文献   

20.
The clay and silt mineralogy of the Cretaceous bedrocks of the Rother drainage basin is restricted to seven minerals. The mineralogy of soils and alluvium is similar to the bedrock upon which they are developed although minor variations can be found. The mineralogy of bedrock, soils and alluvium is reflected to some extent in the suspended sediment of rivers draining over them, and three different mineral assemblage zones are identified. Subtle controls of mineralogical variation in suspended sediment may include the ratio of groundwater/surface runoff contribution to river flow, rate of reaction of soil and bedrock to precipitation, preferential settling of non-platy grains in quieter stretches of water, and the precipitation of material from solution as waters equilibriate with the atmosphere.  相似文献   

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