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131.
The future exploration of Mars is likely to utilize resources that can be extracted in situ. An overview of the geology of Mars has been presented and several mechanisms that could result in the formation of ore deposits have been identified. These include deposits caused by hydrothermal fluids resulting from volcanic activity, large igneous province formation and impact craters. Surface enrichment of mineral sand deposits is also discussed. Where appropriate, terrestrial analogues of these mechanisms have been discussed and supporting evidence from observations of Mars undertaken to date presented. Types of deposits that are unlikely to be found on Mars are also listed. 相似文献
132.
Michael D. West Jonathan D.A. Clarke Matilda Thomas Malcolm R. Walter 《Planetary and Space Science》2010,58(4):447-458
Australia has numerous landforms and features, some unique, that provide a useful reference for interpreting the results of spacecraft orbiting Mars and exploring the martian surface. Examples of desert landforms, impact structures, relief inversion, long-term landscape evolution and hydrothermal systems that are relevant to Mars are outlined and the relevant literature reviewed. The Mars analogue value of Australia's acid lakes, hypersaline embayments and mound spring complexes is highlighted along with the Pilbara region, where the oldest convincing evidence of life guides exploration for early life on Mars. The distinctive characteristics of the Arkaroola Mars Analogue Region are also assessed and opportunities for future work in Australia are outlined. 相似文献
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Wooyong Um Jonathan P. Icenhower R. Jeffery Serne Cleveland J. Dodge Arokiasamy J. Francis 《Geochimica et cosmochimica acta》2010,74(4):1363-6031
The concentration and distribution of uranium (U) in sediment samples from three boreholes recovered near radioactive waste storage tanks at Hanford, Washington, USA, were determined in detail using bulk and micro-analytical techniques. The source of contamination was a plume that contained an estimated 7000 kg of dissolved U that seeped into the subsurface as a result of an accident that occurred during filling of tank BX-102. The desorption character and kinetics of U were also determined by experiment in order to assess the mobility of U in the vadose zone. Most samples contained too little moisture to obtain quantitative information on pore water compositions. Concentrations of U (and contaminant phosphate—P) in pore waters were therefore estimated by performing 1:1 sediment-to-water extractions and the data indicated concentrations of these elements were above that of uncontaminated “background” sediments. Further extraction of U by 8 N nitric acid indicated that a significant fraction of the total U is relatively immobile and may be sequestered in mobilization-resistant phases. Fine- and coarse-grained samples in sharp contact with one another were sub-sampled for further scrutiny and identification of U reservoirs. Segregation of the samples into their constituent size fractions coupled with microwave-assisted digestion of bulk samples showed that most of the U contamination was sequestered within the fine-grained fraction. Isotope exchange (233U) tests revealed that ∼51% to 63% of the U is labile, indicating that the remaining fund of U is locked up in mobilization-resistant phases. Analysis by Micro-X-ray Fluorescence and Micro-X-ray Absorption Near-Edge Spectroscopy (μ-XRF and μ-XANES) showed that U is primarily associated with Ca and is predominately U(VI). The spectra obtained on U-enriched “hot spots” using Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLIFS) provide strong evidence for uranophane-type [Ca(UO2)2(SiO3OH)2(H2O)5] and uranyl phosphate [Ca(UO2)2(PO4)2(H2O)10-12] phases. These data show that disseminated micro-precipitates can form in narrow pore spaces within the finer-grained matrix and that these objects are likely not restricted to lithic fragment environments. Uranium mobility may therefore be curtailed by precipitation of uranyl silicate and phosphate phases, with additional possible influence exerted by capillary barriers. Consequently, equilibrium-based desorption models that predict the concentrations and mobility of U in the subsurface matrix at Hanford are unnecessarily conservative. 相似文献
135.
Paulo C. Boggiani Claudio Gaucher Alcides N. Sial Marly Babinski Cynthia M. Simon Claudio Riccomini Valderez P. Ferreira Thomas R. Fairchild 《Precambrian Research》2010
The Corumbá Group, cropping out in the southern Paraguay Belt in Brazil, is one of the most complete Ediacaran sedimentary archives of palaeogeographic, climatic, biogeochemical and biotic evolution in southwestern Gondwana. The unit hosts a rich fossil record, including acritarchs, vendotaenids (Vendotaenia, Eoholynia), soft-bodied metazoans (Corumbella) and skeletal fossils (Cloudina, Titanotheca). The Tamengo Formation, made up mainly of limestones and marls, provides a rich bio- and chemostratigraphic record. Several outcrops, formerly assigned to the Cuiabá Group, are here included in the Tamengo Formation on the basis of lithological and chemostratigraphical criteria. High-resolution carbon isotopic analyses are reported for the Tamengo Formation, showing (from base to top): (1) a positive δ13C excursion to +4‰ PDB above post-glacial negative values, (2) a negative excursion to −3.5‰ associated with a marked regression and subsequent transgression, (3) a positive excursion to +5.5‰, and (4) a plateau characterized by δ13C around +3‰. A U-Pb SHRIMP zircon age of an ash bed interbedded in the upper part of the δ13C positive plateau yielded 543 ± 3 Ma, which is considered as the depositional age ( Babinski et al., 2008a). The positive plateau in the upper Tamengo Formation and the preceding positive excursion are ubiquitous features in several successions worldwide, including the Nama Group (Namibia), the Dengying Formation (South China) and the Nafun and Ara groups (Oman). This plateau is constrained between 542 and 551 Ma, thus consistent with the age of the upper Tamengo Formation. The negative excursion of the lower Tamengo Formation may be correlated to the Shuram–Wonoka negative anomaly, although δ13C values do not fall beyond −3.5‰ in the Brazilian sections. Sedimentary breccias occur just beneath this negative excursion in the lower Tamengo Formation. One possible interpretation of the origin of these breccias is a glacioeustatic sea-level fall, but a tectonic interpretation cannot be completely ruled out. 相似文献
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139.
Pradeep Adhikari Yang Hong Kimberly R. Douglas Dalia Bach Kirschbaum Jonathan Gourley Robert Adler G. Robert Brakenridge 《Natural Hazards》2010,55(2):405-422
Floods have profound impacts on populations worldwide in terms of both loss of life and property. A global inventory of floods
is an important tool for quantifying the spatial and temporal distribution of floods and for evaluating global flood prediction
models. Several global hazard inventories currently exist; however, their utility for spatiotemporal analysis of global floods
is limited. The existing flood catalogs either fail to record the geospatial area over which the flood impacted or restrict
the types of flood events included in the database according to a set of criteria, limiting the scope of the inventory. To
improve upon existing databases, and make it more comprehensive, we have compiled a digitized Global Flood Inventory (GFI)
for the period 1998–2008 which also geo-references each flood event by latitude and longitude. This technical report presents
the methodology used to compile the GFI and preliminary findings on the spatial and temporal distributions of the flooding
events that are contained in the inventory. 相似文献
140.
Jonathan J. Liberda Jeroen W. Thompson W. Jack Rink Federico Bernaldo de Quirs Rohit Jayaraman Kailash Selvaretinam Kerry Chancellor‐Maddison Vito Volterra 《Geoarchaeology》2010,25(4):467-474
Nine faunal teeth from layer 20 of El Castillo cave in Cantabrian Spain were dated using electron spin resonance (ESR). Two teeth were rejected due to inconsistent subsample ages, while the remaining teeth yielded a mean age that is consistent with the stratigraphic expectations: 42.7±3.5. Uncertainty in the external γ dose rate results in a potential systematic uncertainty of±6.4ka that should affect all samples equally. The results provide independent confirmation of previously reported 14C ages for layer 20. © 2010 Wiley Periodicals, Inc. 相似文献