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51.
Peter Bauer-Gottwein Bibi R. N. Gondwe Guillaume Charvet Luis E. Mar��n Mario Rebolledo-Vieyra Gonzalo Merediz-Alonso 《Hydrogeology Journal》2011,19(3):507-524
The Yucatán Peninsula karst aquifer is one of the most extensive and spectacular karst aquifer systems on the planet. This transboundary aquifer system extends over an area of approximately 165,000? km2 in México, Guatemala and Belize. The Triassic to Holocene Yucatán limestone platform is located in the vicinity of the North American/Caribbean plate boundary and has been reshaped by a series of tectonic events over its long geologic history. At the end of the Cretaceous period, the Yucatán Peninsula was hit by a large asteroid, which formed the Chicxulub impact crater. The Yucatán Peninsula karst aquifer hosts large amounts of groundwater resources which maintain highly diverse groundwater-dependent ecosystems. Large parts of the aquifer are affected by seawater intrusion. Anthropogenic pollution of the aquifer has been increasing over the past few decades, owing to relentless economic development and population growth on the Peninsula. This review summarizes the state of knowledge on the Yucatán Peninsula karst aquifer and outlines the main challenges for hydrologic research and practical groundwater-resources management on the Peninsula. 相似文献
52.
Efforts are being made to improve the irrigation efficiency in the Murray-Darling River Basin, Australia, to deal with predicted rainfall decline and to reduce the incidence of secondary soil and water salinization. The latter commonly occurs as a result of locating water reservoirs upon relic drainage channels. To better manage irrigation, information is required about the spatial distribution of soil type and the stratigraphic features capable of redistributing deep-draining water. In previous research, electromagnetic (EM) induction instruments (e.g. EM38 and EM34) have been used to map the distribution of soil type, hydrological processes (e.g. deep drainage) and vadose-zone features. The aim of this research is to demonstrate how a joint inversion of EM38 and EM34 data, using a one-dimensional spatially constrained algorithm for quasi three-dimensional (quasi-3D) electrical conductivity imaging, can be used to infer the areal distribution of soil types and physiographic and hydrogeological units. The quasi-3D modeling of true electrical conductivity provides a framework for future environmental monitoring and management to mitigate the hydrological processes that drive localized secondary salinization in the study area. 相似文献
53.
Amy Gartman Mustafa Y��cel Andrew S. Madison David W. Chu Shufen Ma Christopher P. Janzen Erin L. Becker Roxanne A. Beinart Peter R. Girguis George W. Luther III 《Aquatic Geochemistry》2011,17(4-5):583-601
The sulfide (H2S/HS?) that is emitted from hydrothermal vents begins to oxidize abiotically with oxygen upon contact with ambient bottom water, but the reaction kinetics are slow. Here, using in situ voltammetry, we report detection of the intermediate sulfur oxidation products polysulfides [ $ {\text{S}}_{\text{x}}^{2 - } $ ] and thiosulfate [ $ {\text{S}}_{ 2} {\text{O}}_{ 3}^{ 2- } $ ], along with contextual data on sulfide, oxygen, and temperature. At Lau Basin in 2006, thiosulfate was identified in less than one percent of approximately 10,500 scans and no polysulfides were detected. Only five percent of 11,000 voltammetric scans taken at four vent sites at Lau Basin in May 2009 show either thiosulfate or polysulfides. These in situ data indicate that abiotic sulfide oxidation does not readily occur as H2S contacts oxic bottom waters. Calculated abiotic potential sulfide oxidation rates are <10?3 ??M/min and are consistent with slow oxidation and the observed lack of sulfur oxidation intermediates. It is known that the thermodynamics for the first electron transfer step for sulfide and oxygen during sulfide oxidation in these systems are unfavorable, and that the kinetics for two electron transfers are not rapid. Here, we suggest that different metal catalyzed and/or biotic reaction pathways can readily produce sulfur oxidation intermediates. Via shipboard high-pressure incubation experiments, we show that snails with chemosynthetic endosymbionts do release polysulfides and may be responsible for our field observations of polysulfides. 相似文献
54.
Rainfall-induced landslide event of May 2010 in the eastern part of the Czech Republic 总被引：3，自引：2，他引：1
Tom��? P��nek Rudolf Br��zdil Jan Klime? Veronika Smolkov�� Jan Hradecky Pavel Zahradn��?ek 《Landslides》2011,8(4):507-516
More than 150 landslides originated in the eastern part of the Czech Republic (region of the Flysch Outer Western Carpathians—hereinafter,
OWC) due to soil saturation caused by antecedent precipitation and long lasting and intensive rainfalls on 16–18 May 2010
(>300 mm as measured by some stations). As a consequence, a multitude of small failures originated 88% of which was smaller
than 104 m2. Most landslides are characterised as shallow (<10 m) or middle–deep (10–30 m) incipient (rather short travel) landslides,
debris slides and soil slips spatially clustered to a geological domain underlain by rather weak thin-bedded flysch and unconsolidated
Quaternary deposits. An exception to this is represented by a kilometre-long rockslide (∼2–3 mil m3) affecting tectonically weakened and weathered claystone/mudstone-dominated flysch on the southern slope of Mt. Girová (the
Beskydy Mountains). The rockslide is one of the largest long runout landslides in the territory of the Czech Republic activated
over the past few decades as it reaches the dimensions of the largest documented Holocene long runout landslides in the Czech
part of the OWC. A majority of the May 2010 landslide events developed inside older (Holocene or historic) landslide terrains,
which points to their spatial persistency and recurrent nature. In spite of the fact that the May 2010 landslide event was
not as destructive as some previous landslide activisation in the OWC region (e.g. July 1997 event), it left many slope failures
at the initial stage of their potential future reactivation. 相似文献
55.
The Sea to Sky Corridor has experienced hundreds of historic and prehistoric landslides. The most common types of historical
landslides are rock falls and debris flows, which are relatively small in volume but can be damaging. These types of failures
are more common in the southern part of the corridor, between Horseshoe Bay and Porteau, where infrastructure has been built
in close proximity to steep slopes. Farther north, fewer landslides have been reported historically, but those that have been
recorded are usually large and date to prehistoric time (e.g., Cheekye fan and Mystery Creek rock avalanche). As part of a
Geological Survey of Canada surficial geology and landslide inventory mapping study, Mystery Creek rock avalanche, near Whistler,
British Columbia, was sampled for 36Cl dating. Samples were collected from three large flat boulders of quartz diorite in the rock avalanche deposit to test a
correlation with the previously reported radiocarbon age of 800 ± 100 years BP on charcoal. One sample revealed a mean age
of 2,400 years and the other two, 4,300 and 4,800 years, respectively. These new results point to four possible interpretations:
(1) Mystery Creek landslide is about 800 years old; (2) Based on the overlapping 2σ uncertainties, the rock avalanche took
place between 2,200 and 3,600 years ago; (3) The rock avalanche deposit is 2,400 years old and the other two blocks are too
old; and (4) The rock avalanche is between 4,300 and 4,800 years old. Although there is strength in numbers and it is likely
that the age varies between 4,300 and 4,800 years, we favor the second interpretation where the age range is broader and statistically
significant for all three samples. Moreover, at this time, we favor discounting the radiocarbon age based on a greater number
of samples analyzed for 36Cl analysis and lack of detailed information on the charcoal sampling. The causes and triggers of the Mystery Creek rock avalanche
remain unknown, but direct glacial debuttressing can be ruled out. Some of the causes are likely a combination of the regional
tectonic setting which produced preferential planes of weakness reflected in the trend of major faults, headscarp, and reverse
scarps. Yearly cycles of freezing and thawing are considered a plausible cause based on present-day climate records. Finally,
a large earthquake still remains a possible trigger because of the active tectonic setting and the presence of potentially
contemporaneous landslides in the same area. Mystery Creek rock avalanche and other historic and pre-historic landslides contributed
to validation of a heuristic rock fall/rock slide/rock avalanche susceptibility mapping study, in which their headscarps correlated
well with medium-high to high susceptibility zones. In terms of hazard assessment, Mystery Creek rock avalanche, although
pre-historic in age, occurred in present-day climatic and geological conditions. This poses a threat to infrastructure such
as the Sea to Sky Highway, railway, and power line. 相似文献
56.
The material of Hispanomys decedens (Rodentia, Cricetodontinae) from La Grive-Saint Alban (France) is described in detail for the first time. H. decedens, which is one of the oldest species of the genus, shows the primitive character states that are typical of the Aragonian congeneric species, such as the mesolophs and labial cingula surrounding the upper molar valleys. The detailed examination of the teeth of H. decedens shows that this taxon is a good candidate ancestor for H. aragonensis. 相似文献
57.
The oceanic anoxic event at the Cenomanian?CTuronian transition (OAE-2) is a worldwide phenomenon related with variations in atmosphere?Cocean dynamics. This event coincides with significant changes in the palaeoenvironment determining marine mass extinction affecting numerous groups of organisms. Ichnological analysis of the Cenomanian?CTuronian boundary interval has been conducted in three selected sections from different ecological and depositional settings in the western Tethys. Indeed, a brief overview of existing knowledge in this domain highlights increasing recognition of the usefulness of trace fossils in the characterization of even minor-scale deep-sea environmental changes linked to sea-level dynamics. At the study sites, variations in ichnological features, including trace fossil composition, tiering patterns and ichnofabrics, can be related to fluctuations in bottom- and pore-water oxygenation during the Cenomanian?CTuronian interval. In the Barnasiówka section (Polish Outer Carpathians), changes between oxic/dysoxic??characterized by Chondrites, Planolites and even Thalassinoides??and euxinic conditions, without trace fossils or only with Chondrites, can be explained by variations in gravity flows influencing the benthic habitat. In the El Chorro and Hedionda sections (Betic Cordillera), longer anoxic intervals during the OAE-2, characterized by the absence of trace fossils, are interrupted by shorter dysaerobic and aerobic sub-events associated with Chondrites, Palaeophycus, Planolites, Thalassinoides, Trichichnus and Zoophycos, but showing significant differences between these two sections related to the palaeogeographically differentiated influence of upwelling conditions. 相似文献
58.
The rocky coastline of the Sultanate of Oman between Fins and Sur is decorated by a number of large blocks and boulder accumulations forming ramparts. The blocks occur as individual rocks of up to 40 tons, as imbricated sets and as ??boulder trains.?? Landward, the deposits change into a sand/boulder mixture and distal into sands. The coast is made up of Tertiary folded limestones and beach rock of Quaternary age, both also constitute the megaclasts. The transport distance from the fractured seaward platform of 6?C10?m above mean sea level varies between 20?m and more than 50?m. We found individual blocks of recent corals and overturned blocks with attached oysters and rock pools. Terrestrial laser scanning was used to analyze geomorphologic features as well as for volumetric estimates of the block weights. Tropical cyclones such as Gonu in 2007 or Phet in 2010 are known to have affected Oman??s coastline in the past. The coastal changes during recent cyclones were minor; therefore, we interpret the block deposits as tsunamigenic. However, this interpretation is not unambiguous. The most likely source area for a tsunami is seen in the Makran Subduction Zone situated in the northern Indian Ocean. Here, at least 4?C5 tsunamigenic earthquakes are documented. 相似文献
59.
Evangelos Moulas Stefan M. Schmalholz Yury Podladchikov Lucie Taj
manov Dimitrios Kostopoulos Lukas Baumgartner 《Journal of Metamorphic Geology》2019,37(1):1-14
Pressure is one of the most important parameters to be quantified in geological problems. However, in metamorphic systems the pressure is usually calculated with two different approaches. One pressure calculation is based on petrological phase equilibria and this pressure is often termed thermodynamic pressure. The other calculation is based on continuum mechanics, which provides a mean stress that is commonly used to estimate the thermodynamic pressure. Both thermodynamic pressure calculations can be justified by the accuracy and applicability of the results. Here, we consider systems with low‐differential stress (<1 kbar) and no irreversible volumetric deformation, and refer to them as conventional systems. We investigate the relationship between mean stress and thermodynamic pressure. We discuss the meaning of thermodynamic pressure and its calculation for irreversible processes such as viscous deformation and heat conduction, which exhibit entropy production. Moreover, it is demonstrated that the mean stress for incompressible viscous deformation is essentially equal to the mean stress for the corresponding viscous deformation with elastic compressibility, if the characteristic time of deformation is five times longer than the Maxwell viscoelastic relaxation time that is equal to the ratio of shear viscosity to bulk modulus. For typical lithospheric rocks, this Maxwell time is smaller than c. 10,000 years. Therefore, numerical simulations of long‐term (>10 kyr) geodynamic processes, employing incompressible deformation, provide mean stress values that are close to the mean‐stress value associated with elastic compressibility. Finally, we show that for conventional systems the mean stress is essentially equal to the thermodynamic pressure. However, mean stress and, hence, thermodynamic pressure can be significantly different from the lithostatic pressure. 相似文献
60.
D. Parcerisa M��dard Thiry J. M. Schmitt 《International Journal of Earth Sciences》2010,99(3):527-544
The Carboniferous Morvan Massif, in the northern part of the French Massif Central, consists of granite and some rhyolite.
A Triassic erosional unconformity has developed on the massif which is covered by Mesozoic sediments of the Paris Basin. The
igneous rocks of the Morvan Massif show a strong alteration with pseudomorphic replacement of the primary plagioclases into
albite, pseudomorphic replacement of primary biotite into chlorite and minor precipitation of neogenic minerals like albite,
chlorite, apatite, haematite, calcite and titanite. The geometry and arrangement of these alterations give significant constraints
about their development. Some of the altered facies develop in a pervasive manner; others are restricted to centimetric to
metric-wide joints that imply fluid-flow phenomena. Moreover, the alteration facies are arranged in a clear succession with
strongly altered facies at the top and weakly altered facies towards the depth, which point to a genetic relationship with
the Triassic unconformity. Regional distribution of the alterations, which affect the Carboniferous igneous and volcanic formations
beneath the Jurassic sedimentary cover, also leads to associate these alterations with the Triassic unconformity. Dating of
the alterations provides even a further constraint, alterations are of Triassic age, that means the same age as the unconformity.
Taking into account all these geological constraints, it is proposed that albitisation of the Morvan Massif was developed
under low temperature subsurface conditions in relation to the Triassic palaeosurface. 相似文献