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421.
Veronica Rossi Giulia Barbieri Stefano Claudio Vaiani Marco Cacciari Luigi Bruno Bruno Campo Marco Marchesini Silvia Marvelli Alessandro Amorosi 《第四纪科学杂志》2021,36(6):961-979
Framed into a robust stratigraphic context, multivariate analyses on the Holocene palaeobiological record (pollen, benthic foraminifers, ostracods) of the Po coastal plain (NE Italy) allowed the investigation of microtidal ecosystems variability and driving parameters along a 35-km-long land–sea transect. Millennial-scale ecosystem shifts are documented by coeval changes in the meiofauna, reflecting variations in organic matter–water depth (shallow-marine environments) and degree of confinement-salinity (back-barrier settings). In-phase shifts of vegetation communities track unsteady water-table levels and river dynamics in freshwater palustrine areas. Five environmental–ecological stages followed one another crossing four tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. At the culmination of Mediterranean RSL rise, after the 8200 event, remarkable growth of peatlands took place in the Po estuary, while low accumulation rates typified the shelf. At the transgressive–regressive turnaround (~7000 cal a bp ), the estuary turned into a delta plain with tidally influenced interdistributary embayments. River flow regime oscillations after the Climate Optimum (post-5000 cal a bp ) favoured isolation of the bays and the development of brackish wetlands surrounded by wooded peatlands. The youngest threshold (~800 cal a bp ), which led to the establishment of the modern delta, reflects a major avulsion of the Po River. 相似文献
422.
Rodrigo Valdés-Pineda Roberto Pizarro Juan B. Valdés Jorge F. Carrasco Pablo García-Chevesich Claudio Olivares 《水文科学杂志》2013,58(11):2110-2132
ABSTRACTPrecipitation is the most critical climatic element that directly affects the availability of water resources. The objective of this study was to describe and discuss spatio-temporal patterns of annual precipitation, its aggressiveness, and its concentration along the southwest coast of South America (36°–49°S) from 1930 to 2006. An annual and multi-decadal analysis was applied to 107 sampling stations distributed throughout this region, using the Mann-Kendall test (MK), and the Sampling Uncertainty Analysis (SUA) coupled with Gumbel probability density function (SUA-Gumbel). The analysis revealed positive but not significant trends in annual precipitation and aggressiveness for the region between 36° and 44°S, at least during the last 50 years of the analysed period. However, a significant decrease in annual precipitation and aggressiveness was observed between 44° and 49°S during the same period. The annual concentration of precipitation became slightly more seasonal in the last 50 years within the entire study area. 相似文献
423.
Stefano Calcaterra Claudio Cesi Caterina Di Maio Piera Gambino Katia Merli Margherita Vallario Roberto Vassallo 《Natural Hazards》2012,61(1):257-266
This paper reports experimental data on surface and deep displacements evaluated by means of GPS stations and inclinometers
in two rototranslational deep landslides in a clayey slope of the Italian Southern Apennines. The displacements of the landslides
cause continuous damage to buildings and infrastructures. To study these phenomena and control their effects, the local public
administration provided financial support for a geotechnical investigation that started in 2004. Laboratory tests, in situ
pore pressure and inclinometer measurements were carried out. In July 2006, systems of fixed-in-place inclinometer probes
with continuous data acquisition were installed in two of the eleven guide casings, in correspondence to the slip surfaces
detected by previous periodical measurements. In the meanwhile, a GPS network was installed, consisting in six permanent stations
and ten non-permanent ones. Among the latter, five were installed on the top of five inclinometer casings. The experimental
results show that, in the case under study, the surface displacements evaluated by means of the GPS stations are consistent
with the surface displacements evaluated by means of the inclinometer measurements. This implies mutual data validation, availability
of considerable amount of continuous data, as well as monitoring continuity when, for some reason, one of the instruments
goes out of use. 相似文献
424.
Miguel Tupinambá Monica Heilbron Claudio Valeriano Rubem Porto Júnior Fátima Blanco de Dios Nuno Machado Luiz Guilherme do Eirado Silva Júlio Cesar Horta de Almeida 《Gondwana Research》2012,21(2-3):422-438
The ca. 790–600 Ma Rio Negro Complex (RNC) of the Ribeira belt (Brazil) consists of a plutonic portion of a magmatic arc built by the E-vergent subduction of the ESE border of the São Francisco paleoplate during the amalgamation of Western Gondwana.The plutonic series comprises low- to medium-K granitoids (ca. 790–620 Ma) and high-K granitoids and shoshonite rocks (ca. 610–605). The age span of 185 m.y. is suggestive of a long history of arc-related magmatism, continuously or not in time. The Nd isotopic signatures of the RNC consist of εNd(t) ratios from ? 3 to + 5 for the medium-K series shoshonite series and from ? 14 to ? 3 for the younger high-K group. This time-dependent trend of Nd isotopes is indicative of progressive maturity of the arc over time. The same evolution is indicated by Sr data, as the medium-K rocks have 87Sr/86Sr initial ratios < 0.705 while the high-K rocks yield values between 0.705 and 0.710. The predominance of intermediate rocks over mafic ones suggests an initial intra-oceanic to transitional stage, possibly developed in a distal portion of a passive margin, such as the Japanese arc, evolving to a more developed, differentiated felsic rock associations.The role of transform fault zones, such as the Luanda shear zone, is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of Western Gondwana. 相似文献
425.
426.
The Mw 7.7 earthquake that struck SE Pakistan on 24 September 2013 at 11.29.48 UTC was a sinistral strike-slip event on a branch of the Ornach-Nal-Chaman fault system which hereabouts separates the Eurasian Plate from the Indian Plate. Although the focus was at a depth of 15 km and 400 km inland the earthquake was accompanied by the emergence of an island off the Makran coast and the generation of a tsunami with a peak amplitude of 27 cm at Muscat (Oman) and 20 cm at Chah Bahar (Iran). At DART marine buoy 23228 in the Indian Ocean 500 km to the south a series of seismic Rayleigh waves about 4 min after the main shock was followed 54 min later by a tsunami with a peak amplitude of 1 cm. The Rayleigh series is here attributed to seafloor vibration during accelerated subduction of the Arabian Plate beneath the Eurasian Plate, and the tsunami to the development or reactivation of one or more reverse faults on the seaward portion of the Makran imbricate fan. As in the 2010.2.27 Mw 8.8 Maule (Chile), the 2004.12.26 Mw 9.2 Sumatra–Andaman, the 2005.3.28 Mw 8.7 Nias (Indonesia) and the 2011.3.11 Mw 9.0 Tohoku (Japan) earthquakes, the link between tsunami generation and slip on the megathrust is thus very indirect, to the detriment of attempts to mitigate coastal hazards using teleseismic data when nearshore seafloor monitoring would probably prove more effective. 相似文献
427.
Stefano Conti Daniela Fontana Claudio Corrado Lucente Gian Andrea Pini 《International Journal of Earth Sciences》2014,103(1):281-295
The Montardone mélange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle–Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, characterized by negative values of δ13C (from ?18.22 to ?39.05 ‰ PDB) and chemosynthetic benthic fauna (lucinid and vesicomyid bivalves). In this paper, we propose that the Mm is a mud volcano originated by the post-depositional reactivation and rising of a stratigraphically lower mud-rich mass transport body (Canossa–Val Tiepido sedimentary mélange or olistostrome) triggered by fluid overpressure. We base our conclusion on (1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa–Val Tiepido mélange; (2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; (3) the systematic presence of large-scale (lateral extension 300–400 m) seep-carbonates associated with the mélange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; (4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids. The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary mélange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed. 相似文献
428.
Brian D. Smerdon Laura A. Smith Glenn A. Harrington W. Payton Gardner Claudio Delle Piane Joel Sarout 《Hydrogeology Journal》2014,22(8):1875-1887
A workflow is described to estimate specific storage (S s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S s and K were, respectively, 8.8?×?10?6 to 1.2?×?10?5 m?1 and 2?×?10?12 m s?1 for a claystone/siltstone, and 4.3?×?10?6 to 9.6?×?10?6 m?1 and 1?×?10?12 to 5?×?10?12 m s?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale. 相似文献
429.
The stability in the Lyapunov sense of an equilibrium position in a periodic Hamiltonian system with one degree of freedom is studied. It is assumed that the equilibrium is stable in the first approximation and that there exists an even resonance of order $k$ k , arbitrary. The critical case is considered, i.e., when the system of parameters is such that, in order to draw rigorous conclusions about the stability of the equilibrium position in the Lypaunov sense, terms or order higher than three in the series expansion of the Hamiltonian function must be taken into account. Sufficient conditions are derived for stability and instability. 相似文献
430.
Sandra Donnici Rossana Serandrei‐Barbero Claudio Bini Maurizio Bonardi Alberto Lezziero 《Geoarchaeology》2011,26(4):514-543
As rising sea level threatens Venice, there is a need to construct a historical framework for interpreting modern environmental changes. Environmental conditions that would later help support Venice's urbanization were established during the Late Glacial period when calcic soils began to develop in the Venetian alluvial paleoplain. A calcic paleosol, buried by Middle to Late Holocene marine transgressive deposits, represents a subsurface layer long known in the Venice area as “caranto.” Referenced in the ancient chronicles of architects and builders, the caranto exhibits relatively high compressive and shear strength, making it an important substrate for supporting building foundations, some dating back to the Gothic era (12th–15th centuries A.D.). Hence, the caranto paleosol documents local post‐glacial environmental changes while playing an important role in Venetian building construction and human settlement. Here we provide geochemical, sedimentological, paleoecological, and chronological analyses of the caranto paleosol and related deposits based on recent coring of the Venetian Lagoon. © 2011 Wiley Periodicals, Inc. 相似文献