(U–Th)/He dating of fluorite: application to the La Azul fluorspar deposit in the Taxco mining district, Mexico     

Teresa Pi  Jesús Solé  Yuri Taran 《Mineralium Deposita》2005,39(8):976-982

The (U–Th)/He dating method was applied to fluorite of the La Azul fluorspar deposit, Taxco mining district, Mexico. Ages of ten U-rich (4–94 g/g) samples range from 30 to 33 Ma (mean 32±2 Ma, 1). This age range is interpreted as the time of primary fluorite precipitation and is close to the K/Ar age of sericite from a small fluorspar deposit (Los Tréboles) in the same area, and the K/Ar age of the nearby volcanic succession, which is thought to be the main source of fluorine in both deposits. This age is also in concordance with the very few published ages of epithermal deposits in southern Mexico. The dating of fluorite by other methods, particularly for young samples, is a difficult task. We believe that the (U–Th)/He method, which has been applied before to thermochronological studies of apatite, zircon, titanite and hematite, can be used as a tool for direct dating of fluorite with microgram per gram levels of uranium and thorium.Editorial handling: B. Lehmann  相似文献   

Benefits and organization of cooperative research for fisheries management     

Johnson  Teresa R.; van Densen  Wim L. T. 《ICES Journal of Marine Science》2007,64(4):834-840

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Rationalizing tax increment financing in Chicago   总被引：1，自引：1，他引：0  

Benjamin F. Teresa 《Urban geography》2017,38(2):199-220

A central problem in planning is how planners can be both technical experts and political actors sensitive to the moral consequences of planning. Rationality refers to the reasons for choosing a means to achieve an end; a rationality that considers the morality of means and ends is value rationality, and one that does not is instrumental rationality. Through the case of using Tax Increment Financing (TIF) to subsidize corporate headquarters relocation in Chicago, I follow City follows planners’ struggle with TIF policy and their engagement with instrumental and value rationality within a state that exercised an entrepreneurial planning strategy. This position meant that planners were constrained from acting value-rationally to consider and then take action on questions about the moral content of TIF projects. Nonetheless, planning staff developed an instrumentally-rational planning and policy exercise, which they performed as a way to channel their value-rational concerns about the assumption that every economic development project is an unambiguously valuable goal.  相似文献   

Trawl-induced bottom disturbances off the south coast of Portugal: direct observations by the 'Delta' manned-submersible on the Submarine Canyon of Portimão     

Paulo Morais  Teresa C. Borges  Vera Carnall  Pedro Terrinha  Christopher Cooper  & Richard Cooper 《Marine Ecology》2007,28(S1):112-122

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Effect of Hydrocarbons and Decontaminating Substances on Bacterial Flora of Coastal Sediments     

Ermanno Crisafi  Renata Zaccone  Lucrezia Genovese  Rosabruna La Ferla  Teresa Luciana Maugeri 《Marine Ecology》1989,10(4):365-375

Abstract. Seventy six samples of coastal sediments collected in the Straits of Messina were studied in order to evaluate the effects of an oil spill and the consequent "clean-up" operations on heterotrophic acrobic bacteria.
In addition, in vitro tests were carried out to estimate the effects of five dispersants on the growth and oil degrading capacity of marine strains isolated from the same sediments.  相似文献   

Assessment of Sulfate Concentrations in Water Used During Chemical Stabilization and Its Potential Impact on Sulfate Induced Heave     

Douglas Mohn  Teresa J. Cutright  John Senko  Ala Abbas 《Geotechnical and Geological Engineering》2016,34(1):285-296

The occurrence of sulfate-induced heave of roadways that were chemically stabilized with either lime or cement can require expensive road repairs. Previous research attributed the heave to the formation of an expansive mineral named ettringite. However, not all chemically stabilized soils will exhibit heave. The overall goal of this research was to determine if the sulfate concentration in water can contribute to, or even cause, sulfate induced heave. Two soils, one with a soluble sulfate level below 3000 mg/kg and one with >8000 mg/kg sulfate, were stabilized with either lime or cement and subjected to a capillary soak with distilled water or saturated sulfate water. The low sulfate soils did not swell above the accepted limit of 1.5 %. The high sulfate soils swelled significantly (p < 0.05) above accepted level regardless of the stabilizer used. Overall, stabilized soils subjected to a capillary soak with saturated sulfate water swelled more than soils soaked with distilled water. The results found in this study demonstrated that cement will increase the axial load capacity of the soil, but the soil will still have the potential to heave excessively if sulfate and aluminum are present above the stoichiometric requirements to from ettringite.  相似文献   

Origin and Formation of Sulfate in Soils from Three Ohio Counties     

Kevin?Freese  Kenneth?Jambor  Ala?R.?Abbas  John?M.?Senko  Teresa?J.?CutrightEmail author 《Geotechnical and Geological Engineering》2016,34(5):1327-1343

Sulfate induced heave has been attributed to ettringite, which can form when there is an elevated pH as well as sufficient amounts of aluminum, sulfate, calcium and water present. The primary objective of this project was to study the origin and formation of sulfate in Ohio soils in order to assist with selecting appropriate soil stabilization strategies for future roadway construction. Three roadway construction project areas were evaluated: State Route 2 in Lake (LAK) County, US Highway 24 in Paulding and Defiance Counties and Interstate-71 in Morrow (MRW) County. Defiance County had the most soil samples with sulfate concentrations above acceptable risk level (3000 mg/kg SO₄). Morrow County had the next highest number of unacceptable sulfate levels. Of the 42 Lake County soils analyzed, 11 contained sulfate above acceptable risk level. The soils surrounding the road construction activities along State Route 2 and US-24 had similar geological characteristics. A potential source of sulfate in Paulding and Defiance Counties was attributed to the direct deposition of gypsum as a soil amendment for farmlands. The most likely sources of soil sulfate in Morrow County were deposition of gypsum for farmland activities and the oxidative weathering of pyrite.  相似文献   

Rainfall thresholds for the possible landslide occurrence in Sicily (Southern Italy) based on the automatic reconstruction of rainfall events   总被引：1，自引：1，他引：0  

Massimo Melillo  Maria Teresa Brunetti  Silvia Peruccacci  Stefano Luigi Gariano  Fausto Guzzetti 《Landslides》2016,13(1):165-172

Review of the literature on the reconstruction of the rainfall responsible for slope failures reveals that criteria for the identification of rainfall events are lacking or somewhat subjective. To overcome this problem, we developed an algorithm for the objective and reproducible reconstruction of rainfall events and of rainfall conditions responsible for landslides. The algorithm consists of three distinct modules for (i) the reconstruction of distinct rainfall events, in terms of duration (D, in h) and cumulated event rainfall (E, in mm), (ii) the identification of multiple ED rainfall conditions responsible for the documented landslides, and (iii) the definition of critical rainfall thresholds for possible landslide occurrences. The algorithm uses pre-defined parameters to account for different seasonal and climatic settings. We applied the algorithm in Sicily, southern Italy, using rainfall measurements obtained from a network of 169 rain gauges, and information on 229 rainfall-induced landslides occurred between July 2002 and December 2012. The algorithm identified 29,270 rainfall events and reconstructed 472 ED rainfall conditions as possible triggers of the observed landslides. The algorithm exploited the multiple rainfall conditions to define objective and reproducible empirical rainfall thresholds for the possible initiation of landslide in Sicily. The calculated thresholds may be implemented in an operational early warning system for shallow landslide forecasting.  相似文献   

Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron     

Encarni Montoya  Valenti Rull  Nathan D. Stansell  Broxton W. Bird  Sandra Nogué  Teresa Vegas‐vilarrúbia  Mark B. Abbott  Wilmer A. Díaz 《第四纪科学杂志》2011,26(2):207-218

The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 °N, 61.0157 °W, 884 m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from ～15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200 m elevation above the lake, suggesting a cooling‐driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The 1.5-ka varved record of Lake Montcortès (southern Pyrenees,NE Spain)     

Juan Pablo Corella  Achim Brauer  Clara Mangili  Valentí Rull  Teresa Vegas‐Vilarrúbia  Mario Morellón  Blas L. Valero‐Garcés 《Quaternary Research》2012,78(2):323-332

The karstic Lake Montcortès sedimentary sequence spanning the last 1548 yr constitutes the first continuous, high-resolution, multi-proxy varved record in northern Spain. Sediments consist of biogenic varves composed of calcite, organic matter and detrital laminae and turbidite layers. Calcite layer thickness and internal sub-layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability. Higher temperatures occurred in Lake Montcortès in AD 555–738, 825–875, 1010–1322 and 1874–present. Lower temperatures and prolonged winter conditions were recorded in AD 1446–1598, 1663–1711 and 1759–1819. Extreme and multiple precipitation events dominated in AD 571–593, 848–922, 987–1086, 1168–1196, 1217–1249, 1444–1457, 1728–1741 and 1840–1875, indicating complex hydrological variability in NE Spain since AD 463. The sedimentary record of Lake Montcortès reveals a short-term relation between rainfall variability and the detrital influx, pronounced during extended periods of reduced anthropogenic influences. In pre-industrial times, during warm climate episodes, population and land use increased in the area. After the onset of the industrialization, the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio‐economic factors.  相似文献