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191.
Understanding the dynamics and contamination of an urban aquifer system using groundwater age (14C, 3H,CFCs) and chemistry 下载免费PDF全文
Jürgen Mahlknecht Arturo Hernández‐Antonio Christopher J. Eastoe Carol Tamez‐Meléndez Rogelio Ledesma‐Ruiz José A. Ramos‐Leal Nancy Ornelas‐Soto 《水文研究》2017,31(13):2365-2380
The quality of the groundwater supplying drinking water to the Guadalajara metropolitan area has deteriorated due to both endogenic and exogenic processes. Previous studies of this complex neotectonic volcanic environment suggest that the sources of contamination here are underground fluids derived from an active volcanic center and surface wastewater derived from regional land‐use intensification. This study uses isotopic, gaseous, and chemical signatures to more comprehensively characterize this groundwater flow and its contamination paths. Groundwater is mainly recharged at the La Primavera Caldera to the west and is discharged into the Santiago River to the east. The exception to this trend is the Toluquilla area, where groundwater most likely represents rainfall originating from outside the basin limits. Evaporation affects groundwater in these areas, especially waters that have been affected by recycling below urban areas in the Atejamac area and by intensive agricultural activity in the Toluquilla area. Additionally, we present evidence that groundwater flow through alluvial sediments and tuffs in deeper wells mixes with a lower aquifer unit in basaltic‐andesitic rocks, which are in contact with hydrothermal fluids. Groundwater ages range from postbomb in the western and northwestern regions of the study area (i.e., the Atemajac aquifer unit) to Late Pleistocene in the southern and southeastern regions (i.e., the Toluquilla aquifer unit). Recently recharged water records little mixing and is located mostly in or near the La Primavera volcanic system. As groundwater undergoes gravitational flow towards discharge areas, it mixes with older water components. Chloride and sodium concentrations above natural background levels are primarily related to volcanic activity, nitrate is associated with human activities, and sulfate originates from both anthropogenic sources and water–rock interactions. Nitrate originating from land‐use activities (such as sewers, septic tanks, landfills, and agricultural fields) that is introduced into the deeper part of the groundwater system is expected to travel with the groundwater to the discharge areas because oxidizing conditions will prevent microbial reduction. See Supplementary Information. 相似文献
192.
Yu. D. Zakharov S. P. Pletnev M. E. Mel’nikov O. P. Smyshlyaeva V. D. Khudik G. A. Evseev T. A. Punina P. P. Safronov A. M. Popov 《Russian Journal of Pacific Geology》2007,1(1):29-41
The occurrence of belemnites in Mesozoic sediments of the Pacific guyots is established for the first time (rostra Dimitobelidae gen. et sp. indet. from the late Campanian-Maastrichtian detrital limestone of the DVGI Guyot, Belemnitella? sp. from oolitic limestone of the Gelendzhik Guyot, which are presumably of the Santonian-Maastrichtian age, and Belemnitidae? gen. et sp. indet. from the Maastrichtian oolitic limestone of the Butakov Guyot, the Magellan Rise). In recent years, fossil cephalopods important in stratigraphic and paleobiogeographic aspects have been found at five guyots of that rise. New data on fossil invertebrates from the study region suggest breaks in the sedimentation here at the terminal Maastrichtian, Paleogene, and initial Neogene time. Possible limits of vertical migration in the tropical Pacific are estimated for the Late Cretaceous belemnites based on preliminary results of the oxygen isotope analysis. 相似文献
193.
Rudolph Scherreiks Dan Bosence Marcelle BouDagher-Fadel Guillermo Meléndez Peter O. Baumgartner 《International Journal of Earth Sciences》2010,99(6):1317-1334
The Late Triassic and Jurassic platform and the oceanic complexes in Evvoia, Greece, share a complementary plate-tectonic
evolution. Shallow marine carbonate deposition responded to changing rates of subsidence and uplift, whilst the adjacent ocean
underwent spreading, and then convergence, collision and finally obduction over the platform complex. Late Triassic ocean
spreading correlated with platform subsidence and the formation of a long-persisting peritidal passive-margin platform. Incipient
drowning occurred from the Sinemurian to the late Middle Jurassic. This subsidence correlated with intra-oceanic subduction
and plate convergence that led to supra-subduction calc-alkaline magmatism and the formation of a primitive volcanic arc.
During the Middle Jurassic, plate collision caused arc uplift above the carbonate compensation depth (CCD) in the oceanic
realm, and related thrust-faulting, on the platform, led to sub-aerial exposures. Patch-reefs developed there during the Late
Oxfordian to Kimmeridgian. Advanced oceanic nappe-loading caused platform drowning below the CCD during the Tithonian, which
is documented by intercalations of reefal turbidites with non-carbonate radiolarites. Radiolarites and bypass-turbidites,
consisting of siliciclastic greywacke, terminate the platform succession beneath the emplaced oceanic nappe during late Tithonian
to Valanginian time. 相似文献
194.
G. V. Novikov M. E. Mel’nikov O. Yu. Bogdanova I. V. Vikent’ev 《Lithology and Mineral Resources》2014,49(1):1-22
Communication 1 of the present paper is devoted to various aspects of the hydrogenic ferromanganese crusts in the western and eastern clusters of the Magellan Seamounts in the Pacific. It was revealed that crusts are developed on guyots as a continuous sheet of Fe-Mn minerals on exposures of primary rocks. They commonly make up ring-shaped deposits along the periphery of the summit surface and in the upper sectors of slopes. Thickness of the crust varies from n to ~18 cm and shows irregular variations in separate layers. Irrespective of the geographic position, crusts are composed of four layers—two lower phosphatized (I-1 and I-2) and two upper nonphosphatized (II and III) layers. The crusts differ in terms of structure and texture, but they are sufficiently similar within separate layers (I-1, I-2, and others). The major ore minerals in crusts are commonly represented by poorly crystallized and low-ordered minerals (Fe-vernadite and Mn-feroxyhyte); the subordinate mineral, by the well-crystallized and ordered vernadite. It has been established that heavy and rare metal cations are concentrated extremely irregularly in ore minerals of the crusts, suggesting a pulsating mode of their input during different geological epochs. 相似文献
195.
The paper represents results of a comprehensive geochemical and isotopic-geochemical (SIMS) study of eclogites from the northwestern
part of the Belomorian Belt (Salma eclogites). A detailed fieldwork was carried out at the quarry of the Kuru-Vaara deposit
of ceramic pegmatite in the northwestern part of the study area, in which tonalite-trondhjemite gneisses include bodies and
blocks of eclogite and Grt-Aug eclogite-like clinopyroxenite and are cut across by numerous pegmatite veins. The least altered types of the Grt-Cpx rocks selected for our further research included: (1) widespread massive homogeneous fine-grained Grt-Omp eclogite that replaced gabbro and contained symplectites of Pl + low-Na-Cpx around omphacite and Pl-Hbl kelyphite rims around Grt; and (2) coarse-grained eclogite-like Grt-Hbl-Aug clinopyroxenite beds up to 20 cm thick in the central parts of high-Mg metaultrabasites, which are mostly tremolite-actinolite
schists. The REE patterns of garnet, clinopyroxene, and amphibole from the eclogites confirm that they crystallized simultaneously,
under a high pressure, and in the absence of plagioclase. Local U-Pb dates of the zircons and their geochemistry are at variance
with the earlier hypothesis that the eclogite metamorphism occurred in the Archean. The eclogites and Grt-Hbl-Aug clinopyroxenite were determined to contain zircons of Svecofennian age (approximately 1900 Ma), which show all geochemical
characteristics of classic eclogitic zircons and occur either as individual crystals or as rims around Archean magmatic zircons
from the primary gabbroids. 相似文献
196.
L. P. Ogorodova I. A. Kiseleva M. F. Vigasina L. V. Mel’chakova D. A. Ksenofontov I. A. Bryzgalov 《Geochemistry International》2017,55(7):669-673
The paper presents data on the thermochemical study (high-temperature melt calorimetry in a Tian–Calvet microcalorometer) of two natural Mg–Fe amphiboles: anthophyllite Mg2.0(Mg4.8Fe0.2 2+)[Si8.0O22](OH)2 from Kukh-i-Lal, southwestern Pamirs, Tajikistan, and gedrite Na0.4Mg2.0(Mg1.7Fe0.2 2+Al1.3)[Si6.3Al1.7O22](OH)2 from the Kola Peninsula, Russia. The enthalpy of formation from elements is obtained as–12021 ± 20 kJ/mol for anthophyllite and as–11545 ± 12 kJ/mol for gedrite. The standard entropy, enthalpy, and Gibbs energy of formation are evaluated for Mg–Fe amphiboles of theoretical composition. 相似文献