1,721,042 research outputs found
L'evoluzione geomorfologica del F.Volturno (Campania) durante il tardo Quaternario (Pleistocene medio superiore - Olocene)
No full textAn unsuccessful attempt at U/Th dating of soil calcretes from the Doukkali area (western Morocco) and environmental implications
No full textA large number of calcrete samples from topsoils of the Doukkaˆ li area, western Morocco, were studied by U-disequilibrium series methods. The 230Th/234U ages are rather uniformly distributed between4350 and 2 ka BP. Homologous samples for occurrence and structure display quite different ages, the 230Th/234U ages are considered apparent. This is explained by repeated deposition of secondary calcite in the calcrete pores, which caused lowering of the original ages. However, the apparent ages may be considered minimum ages of the calcrete formation, indicating that calcium carbonate mobilization and deposition has been taking place repeatedly since 4350 ka. The age range obtained is quite comparable with that of calcretes from southern Spain, suggesting similar conditions for the calcrete formation in the two areas
L'evoluzione geomorfologica del F.Volturno (Campania) durante il tardo Quaternario (Pleistocene medio superiore - Olocene)
No full textUsing 222-Radon as tracer for areal and vertical distribution of hydrocarbon contaminations
No full textNon-aqueous Phase Liquids (NAPLs), including crude oil and its refined products, produce a long lasting
impact on the enviroment due to unwilling releases. Storage sites of fuel and pump stations are often involved
in unwilling NAPL spills in the subsoil and/or groundwater. The non-polar nature of these contaminants
confers them a slight solubility in water, causing a reduced efficency of the most common remediation
techniques. These limitations result in long-term remediation activities with high related costs. Unconventional
characterization methods like the Radon (222Rn)-deficit technique are meant to supplement and optimize the
conventional approach by providing dense spatial information in quasi-real time, and at a reasonable cost
(De Miguel et al., 2020). Schubert (2015) presented a comprehensive review of the use of 222Rn as a natural
tracer to assess subsurface NAPL contamination. In the present work Radon deficit technique was applied to
determine the vertical distribution of Rn in groundwater inside a gasoline contaminated area. Twelve passive
accumulators PDMS-AC (polydimethylsiloxane mixed with activated carbon) were inserted at different depth
inside fenestrated piezometers and left for two weeks to maximize the Rn accumulation. Then they were
measured by high resolution gamma spectometry. PDMS-AC are characterized by a high permeability to Rn
and impermeability to water (Voltaggio & Spadoni, 2013). The obtained results suggest the possible application
of Radon deficit to find not only the areal but also the vertical distribution of a NAPL contamination in the
saturated level. This datum could offer interesting applications to estimate initial and residual volumes of the
contaminant during remediation procedures
Uranium Series Disequilibrium Dating in volcanic areas
No full textDisequilibrium existing within the uranium series radioactive family (the so called ‘U-Th’ or ‘230Th’ method) can be used for chronological purposes in volcanic areas. It can be applied to volcanic rocks as well as to travertines connected to volcanic events, provided that the age of these materials (volcanics or travertines) is younger than ∼300 ka. Many problems, capable of seriously affecting the reliability of the method, arise. This paper is intended for people who deal with chronology in volcanic areas but lack the specific knowledge necessary to assess critically the dating procedures performed by scientists with different backgrounds.
Direct dating of volcanics can be affected by (a) the similar and low partition coefficients for uranium and thorium shown by many major constituents of volcanic rocks, (b) the occlusion, within the major minerals, of minor ones particularly enriched in uranium and thorium, (c) uranium loss caused by alteration, (d) the various phases used to draw the isochrone being of different ages, (e) problems connected to isotopic homogeneity of magma. The main difficulties that arise when dating travertine derive from the presence of a non-carbonate phase containing 230Th that has not been generated within the travertine post-depositionally.
These troublesome occurrences are discussed and methods of assessing them are suggested
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