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121.
Michel Durand-Delga Silvia Gardin Manuel Esteras Hélène Paquet 《Comptes Rendus Geoscience》2005,337(8):787-798
The Lias–Dogger successions of the Tariquide units in the Gibraltar Arc differ from the series of tectonically adjacent units, the Penibetic (Iberia margin) and the Limestone ‘Dorsale’ (Alboran Domain). Lower Lias limestones are eroded and covered by the Domerian, which starts by deposits of open sea, continuous up to the Dogger (J. Musa-type successions), and elsewhere (Los Pastores-type successions) by a thin series (Upper Lias to Upper Dogger), starting by a manganesiferous episode (Ras Leona) and including marls deposited into three episodes, dated by calcareous nannofossils. Faulting events occurred before the Domerian and during the Late Toarcian (Los Pastores). To cite this article: M. Durand-Delga et al., C. R. Geoscience 337 (2005). 相似文献
122.
Nagireddi Srinivasa Rao 《Environmental Geology》2007,52(8):1455-1465
With the progradation of Godavari delta in the east coast of India, increase in iron (Fe) concentrations in the groundwater
was observed. High concentrations of Fe (>10 mg/l) were observed in khondalite and charnockite formations. A lower portion
of the Godavari river basin, viz. East Godavari district was chosen for the study of the distribution of iron with special
reference to the existing geological formations and the geomorphology of the area. The concentration of iron was observed
to vary from below detection limit to 69 mg/l in the groundwater while it was less than 1 mg Fe/l in river and spring waters.
The Fe of river water was reduced due to seawater mixing and the electrical conductivity (EC) was increased approximately
to half of the seawater conductivity. Unlike the mixing of seawater at the surface, the same seawater mixing with groundwater
yielded a water having similar order of EC with relatively high Fe. Fe was inversely related with nitrate in the groundwater.
Fe was found to correlate considerably better with manganese in fluvial and coastal alluvium zones. The locations having higher
Fe in delta are suspected to be related to palaeo channels. The association between Fe and Mn and their negative association
with NO3 may be due to the possible autotrophic denitrification that might have taken place in the subsurface. 相似文献
123.
Stable and radiogenic isotope composition of stratiform Cu–Co–Zn mineralization and associated sedimentary rocks within the Boléo district of the Miocene Santa Rosalía basin, Baja California Sur, constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition. Stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column. Near-shore limestone at the base of the Boléo Formation is characterized by modified marine carbon (δ
13CPDB=−6.0 to +4.4‰) and oxygen (δ
18OSMOW=+19.5 to +26.2‰) isotope composition due to the influx of 13C- and 18O-depleted fluvial water. Sulfate sulfur isotope composition (δ
34SCDT=+17.21 to +22.3‰ and δ
18OSMOW=+10.7 to +13.1‰) for basal evaporite and claystone facies are similar to Miocene seawater. Strontium isotopes are less radiogenic than expected for Miocene seawater due to interaction with volcanic rocks. Low S/C ratios, high Mn contents and sedimentological evidence indicate the basin water column was oxidizing. The oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore-space filling by Cu–Co–Zn sulfides to produce disseminated sulfides. Quartz–Mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118°C. Sulfur isotopes indicate the following sources of sulfide: (1) bacterial sulfate reduction within the sedimentary pile produced negative δ
34S values (<−20‰) in framboidal pyrite; and (2) bacterial sulfate reduction at high temperature (80–118°C) within the sedimentary pile during the infiltration of the metal-bearing brines produced Cu–Co–Zn sulfides with negative, but close to 0‰, δ
34S values. Isotope modeling of fluid-rock reaction and fluid mixing indicates: (1) sedimentary and marine carbonates (δ
13C=−11.6 to −3.2‰ and δ
18O=+19.0 to +21.8‰) precipitated from basin seawater/pore water that variably mixed with isotopically depleted meteoric waters; and (2) hydrothermal calcite (δ
13C=−7.9 to +4.3‰ and δ
18O=+22.1 to +25.8‰) formed by dissolution and replacement of authigenic marine calcite by downward-infiltrating metalliferous brine and brine-sediment exchange, that prior to reaction with calcite, had mixed with isotopically depleted pore water. The downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of Cu sulfides along the upper contact of pyrite-bearing laminae. The co-existence and textural relationships among framboidal pyrite, base metal sulfides, carbonate and Mn–Fe oxides (including magnetite) within mineralized units are consistent with carbonate replacement and high-temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions. 相似文献
124.
The quantitative separation of As(III) from a water sample containing As(III) and As(V) in the presence of Fe and Mn in an ion exchange resin (AG1 X8) column for the speciation of arsenic is described. Individual and combined effects of Fe and Mn on the separation of As(III) from the solution have been studied separately. In absence of Fe and Mn, the ratio between the As(T) concentration in the eluent and the As(III) concentration in the original sample has been found to be 0.9717 under optimum process conditions. The presence of Fe(II) in the water sample increased the As(T) concentration in the eluent whereas Mn(II) decreased it. Combined effects of Fe and Mn on the percentage increment in the eluent arsenic concentration have been expressed by additive and interactive models. The interactive model has been developed by a statistical software with a 95 % confidence level. In most of the cases the error on the determination of the As(III) concentration had a minimum when using the interactive model. 相似文献
125.
Hydrothermal Manganese Deposits from the Tonga-Kermadec Ridge and Lau Basin Region,Southwest Pacific
T. D. S. Rogers R. A. Hodkinson D. S. Cronan 《Marine Georesources & Geotechnology》2013,31(4):245-268
Hydrothermal Mn-oxide deposits from the Tonga-Kermadec Ridge and the Valu Fa Ridge back-arc spreading center in the Lau Basin have been studied mineralogically and by bulk and partition geochemical techniques. The Mn-oxides are present as three main morphological types; of these, a dense, grey submetallic material is most common. Common lamination of this material suggests an intermittent rate of formation. Mineralogically, the crusts comprise variable proportions of 10Å and 7Å manganite. Concentrations of some trace elements, including Li, Mo, and Zn are generally significantly higher than those observed in Mn-crusts of hydrogenous origin, suggesting that the observed trace element enrichments are due to a hydrothermal source. Both temporal and geographical controls are seen to affect these trace element concentrations. Although most of the hydrothermally enriched elements are associated with the Mn-oxide phases, Li appears to reflect either a surficial adsorption or the presence of a separate Li-rich phase. Observed variations in deposit composition could reflect differences in the geochemistry of the basement rocks from which the elements have been leached, the proximity of high-temperature sulphide deposits and temporal variability in the hydrothermal systems. 相似文献
126.
Terence J. Hirst 《Marine Georesources & Geotechnology》2013,31(4):371-373
Ocean Floor Mining by John S. Pearson. Noyes Data Corporation, Park Ridge, New Jersey, 1975. 201 pp., $24.00. Offshore Drilling Technology by Frank R. Carmichael. Noyes Data Corporation, Park Ridge, New Jersey, 1975. 392 pp., $36.00. 相似文献
127.
128.
1998 Compilation of Analytical Data for Five GSJ Geochemical Reference Samples: The "Instrumental Analysis Series" 总被引:1,自引:0,他引:1
Noboru Imai Shigeru Terashima Shiro Itoh Atsushi Ando 《Geostandards and Geoanalytical Research》1999,23(2):223-250
Analytical data for five GSJ (Geological Survey of Japan) reference samples, the "Instrumental analysis series" received by October 1998, are compiled. The data reported in publications and personal communications were evaluated statistically, taking into account the analytical method and sample preparation. Based on the selected available data, recommended and preferred values for fourteen major and fifty one minor and trace elements are proposed. 相似文献