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131.
P. J. Statham S. Leclercq V. Hart M. Batt Y. Auger M. Wartel J. Cheftel 《Continental Shelf Research》1999,19(15-16)
Measurements of dissolved Cd, Co, Cu, Mn, Ni, Pb, and Zn have been made on a seasonal basis at five stations on a north–south transect across the central English Channel between Cherbourg and the Isle of Wight. Vertical and horizontal distributions of dissolved Cd, Pb, Cu and Zn are relatively uniform except for sampling sites near the English coast. Dissolved Mn and Co show increased concentrations in the English coastal waters, and for Mn the seasonal trend in concentration follows the pattern seen in the Strait of Dover with higher values in the late summer. Ni and Cu are higher in concentration on the English side, which reflects mainly riverine sources. Measurements were also made of particulate forms of the metals above plus particulate Al, Ca, Fe, Mg, Sr and Ti. Water column concentrations of particulate metals broadly follow the distribution of suspended particulate matter, with highest concentrations near the UK coast. Trace metal concentrations have been integrated with modelled data on fluxes of water to provide estimates of fluxes for these elements into the eastern Channel, and an initial comparison is made with data for fluxes of metals through the Strait of Dover obtained during an earlier study. A major influence on the fluxes of particulate metals through the Isle of Wight-Cherbourg transect is the gyre system to the South east to the Isle of Wight, which has important east to west as well as west to east transport components. For those elements where the dissolved form of the metal dominates, the large flow of water in the central Channel waters leads to major fluxes of the metals towards the east and the Strait of Dover. However, the high suspended particulate matter loadings in the coastal waters and impact of the gyre system lead to net east to west fluxes of particulate Al, Fe, Mn and Ti. Comparison of these fluxes with data on the net west to east transport of these materials through the Strait of Dover infers that there must be a significant supply of these particulate metals to the eastern Channel. 相似文献
132.
Jane Wigforss‐Lange Vivi Vajda Adriana Ocampo 《Meteoritics & planetary science》2007,42(11):1871-1882
Abstract— Four exposures of Chicxulub impact ejecta along the Mexico‐Belize border have been sampled and analyzed for major and trace element abundances. The ejecta deposits consist of a lower spheroid bed, containing clay and dolomite spheroids, and an upper diamictite bed with boulders and clasts of limestone and dolomite. The matrix of both beds is composed of clay and micritic dolomite. The rare earth element (REE) compositions in the matrix of both units show strong similarities in concentrations and pattern. Furthermore, the Zr/TiO2 scatter plot shows a linear correlation indicating one source. These results indicate that the basal spheroid bed has the same source and was generated during the same event as the overlying diamictite bed, which lends support to a single‐impact scenario for the Albion Formation ejecta deposits. The elevated concentrations of non‐meteoritic elements such as Sb, As, U, and Zn in the matrix of the lower spheroid bed are regarded to have been derived from the sedimentary target rocks at the Chicxulub impact site. The positive Eu and Ce anomalies in clay concretion and in the matrix of the lower part of the spheroid bed in Albion Island quarry is probably related to processes involved in the impact, such as high temperature and oxidizing conditions. Analogous trace element anomalies have been reported from the distal Cretaceous‐Paleogene (K/T) boundary clay layer at different sites. Thus, the trace element signals, reported herein, are regarded to support a genetic link between the Chicxulub impact, the ejecta deposits along the Mexico‐Belize border, and the global K/T boundary layer. 相似文献
133.
Annibal Hetem Jr Jane Gregorio-Hetem 《Monthly notices of the Royal Astronomical Society》2007,382(4):1707-1718
The protoplanetary discs of T Tauri and Herbig Ae/Be stars have previously been studied using geometric disc models to fit their spectral energy distribution (SED). The simulations provide a means to reproduce the signatures of various circumstellar structures, which are related to different levels of infrared excess. With the aim of improving our previous model, which assumed a simple flat-disc configuration, we adopt here a reprocessing flared-disc model that assumes hydrostatic, radiative equilibrium. We have developed a method to optimize the parameter estimation based on genetic algorithms (GAs). This paper describes the implementation of the new code, which has been applied to Herbig stars from the Pico dos Dias Survey catalogue, in order to illustrate the quality of the fitting for a variety of SED shapes. The star AB Aur was used as a test of the GA parameter estimation, and demonstrates that the new code reproduces successfully a canonical example of the flared-disc model. The GA method gives a good quality of fit, but the range of input parameters must be chosen with caution, as unrealistic disc parameters can be derived. It is confirmed that the flared-disc model fits the flattened SEDs typical of Herbig stars; however, embedded objects (increasing SED slope) and debris discs (steeply decreasing SED slope) are not well fitted with this configuration. Even considering the limitation of the derived parameters, the automatic process of SED fitting provides an interesting tool for the statistical analysis of the circumstellar luminosity of large samples of young stars. 相似文献
134.
135.
Jane Dove 《Geology Today》2016,32(2):70-74
Postage stamps are useful in promoting geological heritage. This concept is explored through an analysis of British and New Zealand stamps, which portray a variety of different types of geological heritage. Coastal, glacial, fluvial and limestone scenery all feature, together with volcanic landforms such as the Giant's Causeway. Other stamps celebrate the work of historically significant figures who have contributed to geology, such as Charles Darwin. The field of palaeontology is represented in stamps, for example, featuring dinosaurs. Others portray economic activities and engineering achievements associated with geology such as oil and gas exploration. Industrial heritage is depicted by stamps featuring, for example, abandoned tin mines, while building stones are represented in stamps of ancient monuments, bridges, cathedrals and domestic architecture. Perhaps subjects for future stamp issues in the UK might draw upon the recently published 100 top geosites list. 相似文献
136.
Jian Bai Alok Porwal Craig Hart Arianne Ford Le Yu 《Journal of Geochemical Exploration》2010,104(1-2):1-11
Most conventional statistical methods aiming at defining geochemical concentration thresholds for separating anomalies from background have limited effectiveness in areas with complex geological settings. This paper uses multifractal analysis to combine the characteristics of geochemical frequency distribution and spatial dispersion in order to map geochemical singularities instead of using conventional statistically derived concentration thresholds. The model, termed radius–areal Productivity (r–P) model, employs a stable measure and a scale-increasing method to estimate geochemical singularities spatially on geochemical landscape for delineating potential anomalies. The model is applied to geochemical data of regional stream sediments from the Funin Sheet, Yunnan, China. 相似文献
137.
Emily M. White David J. Kieber Jane Sherrard William L. Miller Kenneth Mopper 《Marine Chemistry》2010,118(1-2):11-21
Photochemical mineralization of dissolved organic matter (DOM) plays an important role in the cycling of carbon in estuarine systems. A key to modeling this process is knowledge of apparent quantum yields (AQYs) for the photochemical products. Here we determined spectral AQYs for carbon dioxide (CO2) and carbon monoxide (CO), the main products of DOM photomineralization, along the main axis of the Delaware Estuary. Apparent quantum yields for CO2 photoproduction were determined shipboard using a multi-spectral irradiation system. Carbon monoxide AQYs were determined in stored samples by employing a narrow band spectral irradiation system. A single AQY spectrum described carbon dioxide photochemical production within the estuary whereas CO AQY spectra varied with salinity, suggesting different precursors and mechanisms for the production of these two species. CO2 AQYs were used along with shipboard measurements of DOM absorbance and solar irradiance to calculate photoproduction rates. Calculated CO2 photoproduction rates agreed with directly measured rates (2 to 4 μM CO2 d? 1) within experimental error, supporting the further development and use of AQYs to calculate regional-scale photochemical fluxes. 相似文献
138.
Experimental cpx/melt partitioning of 24 trace elements 总被引:46,自引:13,他引:46
Cpx/melt partition coefficients have been determined by ion probe for 24 trace elements at natural levels in an alkali basalt experimentally equilibrated at 1,380°C and 3 GPa. One goal was to intercompare Ds for both high-field-strength elements and rare earth elements (REE) in a single experiment. Relative to the REE spidergram, Hf and Ti show virtually no anomaly, whereas Zr exhibits a major negative anomaly. Other incompatible elements (Ba, K, Nb) fall in the range of published values, as do elements such as Sr, Y, Sc, Cr and V. Pb shows a value intermediate between La and Ce. Values for Be, Li and Ga are reported for the first time, and show that Be is as incompatible as the light REEs whereas Li and Ga are somewhat more compatible than the heavy REE. 相似文献
139.
Noble gas data are reported for 12 E-chondrites. Combined with literature data, they show that K-Ar ages are >4 Æ for 14 out of 18 meteorites, yet U, Th-He ages are often shorter, perhaps due to late, mild reheating. Cosmic-ray exposure ages differ systematically between types 4 and 6, with E4's mostly below 16 Myr and E6's above 30 Myr. This may mean that the E-chondrite parent body contains predominantly a single petrologic type on the (~ 1 km) scale of individual impacts, in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites.The heavy noble gases consist of at least two primordial components: the usual planetary component () and a less fractionated, ‘subsolar’ component (). The latter is found in highest concentration in the E4 chondrite South Oman (36Ar = 760 × 10?8cc/g, ). The isotopic compositions of both components are similar to typical planetary values, indicating that some factor other than mass controlled the noble gas elemental ratios. The heavy Xe isotopes occasionally show some of the lowest and ratios measured in bulk chondrites, suggestive of nearly fission-free Xe (e.g. ). Amounts of planetary gas in E4 E6 chondrites fall in the range for ordinary chondrites of types 4–6, but, in contrast to the ordinary chondrites. fail to correlate with petrologic type or volatile trace element contents. Another unusual feature of E-chondrites is that primordial Ne is present even in most 4's and 5's (20Nep ~ 1 to 7 × 10?8cc/g). with an isotopic composition consistent with planetary Ne.Analyses of mineral separates show that the planetary gases are concentrated in an HF- and HCl-insoluble mineral similar to phase Q, the poorly characterized, HNO3-soluble carrier of primordial gases in carbonaceous and ordinary chondrites. The subsolar gases, on the other hand, are located in an HCl- and HNO3-resistant phase, possibly enstatite or a minor phase included in enstatite. Much of the 129Xer (50% for E4's, > 70% for E6's) is in HCl-resistant but HF-soluble sites, suggestive of a silicate.A similar subsolar component may be responsible for the high ratios of some C3's, unequilibrated ordinary chondrites, and the unique aubrite Shallowater. The planet Venus also has a high ratio, well above the planetary range, and hence may have acquired its noble gases from an E-chondrite-like material, similar to South Oman. 相似文献
140.
R. Paul Philp Trevor D. Gilbert Jane Friedrich 《Geochimica et cosmochimica acta》1981,45(7):1173-1180
Bicyclanes previously reported only in heavily biodegraded Texas Gulf Coast crudes have been found to be ubiquitous in Australian crude oils of non-marine origin from four different basins. The compounds are present in oils, thought to be derived from the same or similar sources, that have undergone varying degrees of biodegradation. They are also found to be present in oils of different geological age. In addition a series of tricyclic diterpenoid hydrocarbons was common to four oils from the Gippsland Basin. Four of these compounds had the molecular formula C20H34 and mass spectral fragmentation patterns suggested they were mono-unsaturated diterpenoids. The presence of unsaturated diterpenoids in crude oils appears to be a unique observation. It is proposed that the diterpenoids may be the source of the bicyclanes also observed in these oils. 相似文献