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171.
Neoproterozoic peritidal phosphorite from the Sete Lagoas Formation (Brazil) and the Precambrian phosphorus cycle 总被引:1,自引:0,他引:1 下载免费PDF全文
Justin B. R. Drummond Peir K. Pufahl Claudio G. Porto Mariana Carvalho 《Sedimentology》2015,62(7):1978-2008
The Neoproterozoic Sete Lagoas Formation (ca 610 Ma) of the São Francisco Basin, Brazil, is a succession of siltstone, limestone and phosphorite. Phosphorite forms part of a previously unrecognized 150 to 200 m thick, unconformity bounded depositional sequence. Lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences. These shallowing‐upward cycles record the progradation of phosphate‐rich intertidal flats over shallow subtidal deposits as accommodation filled. The presence of mudcracks, authigenic chert nodules, lack of coarse terrigenous clastics and the abundance of silt with fine, abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input. Delivery of phosphorus adsorbed on aeolian Fe‐(oxyhydr)oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments. Lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast, which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite. As in other Precambrian phosphatic systems, nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus. In more distal, anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column, which cycled phosphorus in sea water rather than at the sediment–water interface. Such shallow‐water phosphorite is unlike larger, younger Neoproterozoic–Phanerozoic phosphatic deposits inferred to have formed in deeper‐upwelling related environments. The increasing size of phosphatic deposits through the latest Precambrian is interpreted as reflecting the progressive ventilation of the oceans during the Neoproterozoic Oxygenation Event, and resultant expansion of phosphogenic environments into distal settings. The widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants, but may have also been an important precondition for the evolution of multicellular animals. 相似文献
172.
Tiziano Boschetti Lorenzo Toscani Orfan Shouakar-Stash Paola Iacumin Giampiero Venturelli Claudio Mucchino Shaun K. Frape 《Aquatic Geochemistry》2011,17(1):71-108
The salt waters from the Emilia-Romagna sector of the Northern Apennine Foredeep have been investigated using major and trace
element and stable isotope (δ2H, δ18O, δ37Cl, δ81Br and 87Sr/86Sr ratio). Ca, Mg, Na, K, Sr, Li, B, I, Br and SO4 vs. Cl diagrams suggest the subaerial evaporation of seawater beyond gypsum and before halite precipitation as primary process
to explain the brine’s salinity, whereas saline to brackish waters were formed by mixing of evaporated seawater and water
of meteoric origin. A diagenetic end-member may be a third component for mud volcanoes and some brackish waters. Salinization
by dissolution of (Triassic) evaporites has been detected only in samples from the Tuscan side of the Apennines and/or interacting
with the Tuscan Nappe. In comparison with the seawater evaporation path, Ca–Sr enrichment and Na–K–Mg depletion of the foredeep
waters reveal the presence of secondary processes such as dolomitization–chloritization, zeolitization–albitization and illitization.
Sulfate concentration, formerly buffered by gypsum-anhydrite deposition, is heavily lowered by bacterial and locally by thermochemical
reduction during burial diagenesis. From an isotopic point of view, data of the water molecule confirm mixing between seawater
and meteoric end-members. Local 18O-shift up to +11‰ at Salsomaggiore is related to water–rock interaction at high temperature (≈150°C) as confirmed by chemical
(Mg, Li, Ca distribution) and isotopic (SO4–H2O) geothermometers. 37Cl/35Cl and 81Br/79Br ratios corroborate the marine origin of the brines and evidence the diffusion of halogens from the deepest and most saline
aquifers toward the surface. The 87Sr/86Sr ratio suggests a Miocene origin of Sr and rule out the hypothesis of a Triassic provenance of the dissolved components
for the analyzed waters issuing from the Emilia-Romagna sector of the foredeep. Waters issuing from the Tuscan side of the
Apennines and from the Marche sector of the foredeep show higher 87Sr/86Sr ratios because of the interaction with siliciclastic rocks. 相似文献
173.
A New Ionosphere Monitoring Technology Based on GPS 总被引:1,自引:0,他引:1
Claudio Brunini Amalia Meza Francisco Azpilicueta María Andrea Van Zele Mauricio Gende Alejandro Díaz 《Astrophysics and Space Science》2004,290(3-4):415-429
Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper. 相似文献
174.
the Neapolitan Yellow Tuff (NYT) (12 ka BP) is considered to be the product of a single eruption. Two different members (A and B) have been identified and can be correlated around the whole of Campi Flegrei. Member A is made up of at least 6 fall units including both ash and lapilli horizons. The basal stratified ash unit (A1) is interpreted to be a phreatoplinian fall deposit, since it shows a widespread dispersal (>1000 km2) and a constant thickness over considerable topography. The absence of many lapilli fall units in proximal and medial areas testifies to the erosive power of the intervening pyroclastic surges. The overlying member B was formed by many pyroclastic flows, radially distributed around Campi Flegrei, that varied widely in their eruptive and emplacement mechanisms. In some of the most proximal exposures coarse scoria and lithic-rich deposits, sometimes welded, have been identified at the base of member B. Isopach and isopleth maps of fall-units, combined with the distribution of the coarse proximal facies, indicate that the eruptive vent was located in the NE area of Campi Flegrei. It is considered that the NYT eruption produced collapse of a caldera approximately 10 km diameter within Campi Flegrei. The caldera rim, located by geological and borehole evidence, is now largely buried by the products of more recent eruptions. Initiation of caldera collapse may have been contemporaneous with the start of the second phase (member B). It is suggested that there was a single vent throughout the eruption rather than the development of multiple or ring vents. Chemical data indicate that different levels of a zoned trachyte-phonolite magma chamber were tapped during the eruption. The minimum volume of the NYT is calculated to be about 50 km3 (DRE), of which 35 km3 (70%) occurs within the caldera. 相似文献
175.
The distribution of C2 S and NH3 in two Bok globules at different evolutionary stages: CB246 and CB34
Claudio Codella & Flavio Scappini 《Monthly notices of the Royal Astronomical Society》1998,298(4):1092-1096
Two Bok globules, L1253 (CB246) and CB34, have been mapped in the C2 S (21 –10 ) transition and in the NH3 (1, 1) and NH3 (2, 2) inversion transitions, respectively. By comparing the C2 S map of L1253 (CB246) with the NH3 map of the same globule from Lemme et al., a clumped onion structure results as a consequence of the chemical and dynamical evolution of the object. From the derived parameters it appears that both L1253 (CB246) and CB34 are close to virial equilibrium. 相似文献
176.
Neotectonic data may indicate whether stored elastic energy will be dissipated or released destructively. The Hengchun Peninsula of Taiwan is the southern extremity of the Central Range of Taiwan and thus an emergent part of the accretionary wedge resulting from subduction of Eurasia beneath the Philippine Sea plate at the Manila Trench. Radiocarbon dating of fossil shorelines on the peninsula shows that it has been uplifted at an average rate of 3.8 mm/yr during the Holocene. About of the uplift is due to deformation along the Hengchun reverse fault but, in contrast with the Chelungpu and other low angle reverse faults west of the Central Range, it accommodates strain principally by aseismic creep. To cite this article: C. Vita-Finzi, J.-C. Lin, C. R. Geoscience 337 (2005). 相似文献
177.
Daniele?Borghesi Davide?Vione Valter?Maurino Claudio?MineroEmail author 《Journal of Atmospheric Chemistry》2005,52(3):259-281
This paper reports the results of a study on the transformation of benzene in the presence of solid nitrate salts (NaNO3, NH4NO3) under irradiation in a gas-solid photoreactor. Sodium and ammonium nitrate have been chosen as representative of the composition
of atmospheric particulate, benzene as a model aromatic molecule. The purpose is to simulate the transformations that aromatic
compounds undergo on the surface of dispersed particles in the atmosphere. Irradiation of sodium nitrate causes hydroxylation
and nitration of benzene, yielding phenol and nitrobenzene. This is most likely due to the generation of •OH and •NO2 radicals upon nitrate photolysis, with •OH + O2 leading to the formation of phenol and •OH + •NO2 yielding nitrobenzene. The percentage of oxygen in the reaction environment influences the transformation pathways, with
phenol formation being favoured and nitrobenzene formation depressed by high O2 concentration. In the presence of hematite (α-Fe2O3, another component of atmospheric particulate) very relevant formation of nitrobenzene takes place even with 21% oxygen (simulated
air), indicating that the interaction between hematite and nitrate can lead to the formation of aromatic nitroderivatives
on the surface of atmospheric particulate. The effect of hematite is possibly due to protonation of peroxynitrite, formed
upon nitrate photoisomerisation, to peroxynitrous acid, a powerful nitrating agent. A similar effect leads to relevant formation
of nitrobenzene under atmospheric conditions upon irradiation of the acid salt ammonium nitrate. 相似文献
178.
In this paper, the modelling of strong parametric resonance in head seas is investigated. Non-linear equations of ship motions in waves describing the couplings between heave, roll and pitch are contemplated. A third-order mathematical model is introduced, aimed at describing strong parametric excitation associated with cyclic changes of the ship restoring characteristics. A derivative model is employed to describe the coupled restoring actions up to third order. Non-linear coupling coefficients are analytically derived in terms of hull form characteristics.The main theoretical aspects of the new model are discussed. Numerical simulations obtained from the derived third-order non-linear mathematical model are compared to experimental results, corresponding to excessive motions of the model of a transom stern fishing vessel in head seas. It is shown that this enhanced model gives very realistic results and a much better comparison with the experiments than a second-order model. 相似文献
179.
The land surface processes play an important role in weather and climate systems through its regulation of radiation, heat, water and momentum fluxes. Soil temperature (ST) is one of the most important parameters in the land surface processes; however, there are few extensive measurements of ST with a long time series in the world. According to the CLImatology of Parameters at the Surface (CLIPS) methodology, the output of a trusted Soil-Vegetation- Atmosphere Transfer (SVAT) scheme can be utilized instead of observations to investigate the regional climate of interest. In this study, ST in South Korea is estimated in a view of future climate using the output from a trusted SVAT scheme — the University of TOrino model of land Process Interaction with Atmosphere (UTOPIA), which is driven by a regional climate model. Here characteristic changes in ST are analyzed under the IPCC A2 future climate for 2046-2055 and 2091-2100, and are compared with those under the reference climate for 1996-2005. The UTOPIA results were validated using the observed ST in the reference climate, and the model proved to produce reasonable ST in South Korea. The UTOPIA simulations indicate that ST increases due to environmental change, especially in air temperature (AT), in the future climate. The increment of ST is proportional to that of AT except for winter. In wintertime, the ST variations are different from region to region mainly due to variations in snow cover, which keeps ST from significant changes by the climate change. 相似文献
180.
Jay Quade Jason A. Rech Claudio Latorre Barbra Quade Timothy Fisher 《Quaternary Research》2008,69(3):343-360
Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?-9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900-13,800 and 12,700-9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions). 相似文献