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41.
A detailed geochemical study on river waters of the Australian Victorian Alps was carried out to determine: (i) the relative significance of silicate, carbonate, evaporite and sulfide weathering in controlling the major ion composition and; (ii) the factors regulating seasonal and spatial variations of CO2 consumption via silicate weathering in the catchments. Major ion chemistry implies that solutes are largely derived from evaporation of precipitation and chemical weathering of carbonate and silicate lithologies. The input of solutes from rock weathering was determined by calculating the contribution of halite dissolution and atmospheric inputs using local rain and snow samples. Despite the lack of carbonate outcrops in the study area and waters being undersaturated with respect to calcite, the dissolution of vein calcite accounts for up to 67% of the total dissolved cations, generating up to 90% of dissolved Ca and 97% of Mg. Dissolved sulfate has δ34S values of 16 to 20‰CDT, indicating that it is derived predominantly from atmospheric deposition and minor gypsum weathering and not from bacterial reduction of FeS2. This militates against sulphuric acid weathering in Victorian rivers. Ratios of Si vs. the atmospheric corrected Na and K concentrations range from ~ 1.1 to ~ 4.3, suggesting incongruent weathering from plagioclase to smectite, kaolinite and gibbsite.Estimated long-term average CO2 fluxes from silicate weathering range from ~ 0.012 × 106 to 0.039 × 106 mol/km2/yr with the highest values in rivers draining the basement outcrops rather than sedimentary rocks. This is about one order of magnitude below the global average which is due to low relief, and the arid climate in that region. Time series measurements show that exposure to lithology, high physical erosion and long water–rock contact times dominate CO2 consumption fluxes via silicate weathering, while variations in water temperature are not overriding parameters controlling chemical weathering. Because the atmospheric corrected concentrations of Na, K and Mg act non-conservative in Victorian rivers the parameterizations of weathering processes, and net CO2 consumption rates in particular, based on major ion abundances, should be treated with skepticism. 相似文献
42.
Birgit Nabbefeld Kliti Grice Roger E. Summons Lindsay E. Hays Changqun Cao 《Applied Geochemistry》2010
In this study the abundances of several polycyclic aromatic hydrocarbons (PAHs Table 1, I–XXI) have been measured throughout three Permian/Triassic (P/Tr) sections from Meishan (South China), Kap Stosch area (East Greenland) and Peace River Basin (Western Canada). Dibenzothiophene (I) and dibenzofuran (II) were found to decrease in abundance just before or shortly after the P/Tr transition in all three sections while perylene (III) was observed to increase in abundance at the onset of the main extinction horizon (bed 25) in Meishan. Perylene has been attributed to a wood degrading fungal source and, therefore, it seems possible these phenomena are related to the demise of land plants. Further, distinct patterns of various combustion-derived PAHs occurring in each section imply that forest fire events occurred within the Late Permian and Early Triassic. In the Meishan section high amounts of combustion-derived PAHs [pyrene (IV), fluoranthene (V), benzo[a]anthracene (VI), benzofluoranthenes (sum, i.e. VII), benzo[a]pyrene (VIII), benzo[e]pyrene (IX) and coronene (X)] occur within bed 25, also containing ash attributed to the fallout from massive volcanic eruptions in Siberia and/or China. 相似文献
43.
Gabor Tari Rudi Dellmour Emma Rodgers Chloe Asmar Peter Hagedorn Adel Salman 《Arabian Journal of Geosciences》2016,9(10):570
A variety of distinct salt tectonic features are present in the Sab’atayn Basin of western Yemen. Based on the interpretation of regional 2D seismic reflection data and exploration wells in the central part of the basin, an Upper Jurassic evaporite formation produced numerous salt rollers, salt pillows, reactive, flip-flop, and falling diapirs. Due to regional extension, halokinetics began as soon as the early Cretaceous, within just a few million years after the deposition of the Tithonian Sab’atayn evaporite sequence, by formation of salt rollers. The salt locally formed salt pillows which evolved to reactive and active salt diapirs and diapiric salt walls as the result of renewed, but low-strain extension in the basin. Some of the diapiric walls further evolved into falling diapirs due to ongoing extension. As the result of a prominent extensional episode at the end of the Cretaceous, many of the diapiric walls in the basin are controlled by large normal faults on their updip flanks. As the post-Cretaceous sedimentary cover is largely missing in the study area, the assumed reactivation of salt structures during the Cenozoic remains poorly constrained. The interpreted changes in the style of salt tectonics in the Sab’atayn Basin offer a better understanding of the regional-scale tectonic development of the Arabian plate during the late Jurassic and Cretaceous. 相似文献
44.
Birgit Scheibner Gerhard Wörner Lucia Civetta Heinz-Günter Stosch Klaus Simon Andreas Kronz 《Contributions to Mineralogy and Petrology》2007,154(1):55-74
Igneous garnets have the potential to strongly fractionate rare earth elements (REE). Yet informations on partition coefficients
are very scant, and criteria for distinguishing between hydrothermal and magmatic garnets are ambiguous. To fill this gap,
we present trace element and isotopic data for two types of Ca-rich garnets from phonolites (Mt. Somma-Vesuvius). Both Ca-garnet
populations are different in their style and dynamics of fractionation: one population is progressively strongly depleted
in HREE from core to rim, reflecting REE fractionation in the host phonolite via earlier-crystallized garnets. Such examples
for extreme changes in HREE in garnets are only known for hydrothermal grandites by REE-bearing fluids. The second garnet
population is homogeneous and formed in a closed system. Near-flat patterns between Sm and Lu confirm experimental data indicating
lower D(Sm)/D(Lu) for Ca-rich garnets than for e.g. pyrope-rich garnets. It follows: D
Grt/PhMelt for La = 0.5, Sm = 48 and Yb = 110. 相似文献
45.
The orientation of the maximum horizontal stress SH is obtained from the analysis of borehole breakouts, covering a depth range from 300 to 3415 m (below sea level) in twelve offshore exploration wells in the northwestern Valencia Trough. The orientation of SH is roughly coincident with the strike of major extensional structures. From N to S it changes counterclockwise from a NE–SW orientation to a N–S orientation. Estimates of the tectonic regimes indicate that the area is characterised predominantly by normal-faulting with a strike-slip component. Both the stress orientations and the tectonic regimes are consistent with neotectonic studies in the nearby Catalan Coastal Ranges. An established method of estimating the tectonic regime by Moos and Zoback (1990) was modified by the inclusion of a nontrivial cohesion, but this changes the results insignificantly. 相似文献
46.
The analysis of hydrographic time series from moored sensors from the eastern end of the Sargasso Sea has shown that in the late 1980s the Subtropical Mode Water was dominated by high temperatures. The 18 Degree Water observed during this period was warmer and saltier than the definition given by Worthington, with an increase in values over the observation period. Although severe winter conditions in 1988 led to the formation of colder types of 18 Degree Water at the eastern part of the Sargasso Sea, they were not incorporated in the subtropical gyre. Simultaneous current meter measurements indicated eastward flow within the “southern recirculation gyre” during spring that might have been responsible for the fact that these cold Mode Water types have not been entrained into the gyre. The meteorological forcing fields show considerable interannual variability that is, in part, mimicked by changes in the 18 Degree Water properties. Due to the strong influence of the advection field on the 18 Degree Water properties, the relationship between the surface forcing and 18 Degree Water properties remains qualitative. The continuing influence of further mild winters after 1989, however, is manifested in rising temperatures within the Mode Water range. 相似文献
47.
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49.
The aim of this study is to investigate tide–surge interaction in narrow channels with complex and relatively shallow topography. A high-resolution depth-integrated tidal and storm surge model has been implemented for the Tjeldsund channel which is an important sailing lane in northern Norway. A horizontal grid resolution down to 50 m is applied in order to represent the complex bottom topography and the formation of jets and small-scale eddies. Two typically storm surge events in December 2004 have been examined in detail. The tide–surge interaction is found to influence the generation of higher harmonics and the formation of eddies in the current field. In some cases, the magnitude of storm surge currents may reach the same magnitude as the tidal currents enhancing the formation of jets and eddies. 相似文献
50.
Clara Mangili Achim Brauer Birgit Plessen Peter Dulski Andrea Moscariello Rudolf Naumann 《第四纪科学杂志》2010,25(2):135-145
Contamination with detrital matter is a well‐known bias in δ18O records from lake carbonates but quantitative information of this effect is yet lacking. Therefore, we developed a new methodological approach combining isotope analyses with microfacies, X‐ray diffraction and micro‐X‐ray fluorescence data and applied this in a case study for the Piànico interglacial lake record in order to provide a quantitative estimate of the effect of detrital carbonate on stable δ18O and δ13C data. The Piànico record contains a long series of distinct and well‐preserved calcite varves and is correlated to Marine Isotope Stage 11. Intercalated in the varve sequence are detrital layers triggered by surface erosion events. These detrital layers are mainly composed of dolomite, thus reflecting the mineralogical signature of the catchment. Microfacies analyses of a 9350 varve year interval allows the identification of detrital layers down to sub‐millimetre scale and a precise selection of three different types of samples for isotope analyses: (1) pure endogenic calcite varves (five varves per sample) without detrital contamination; (2) individual detrital layers; and (3) ‘mixed’ samples including five calcite varves and up to four thin detrital layers. Detrital samples show the isotopic signature of the catchment dolomite and are up to 5.7‰ enriched in δ18O values with respect to endogenic calcite samples. In mixed samples, the degree of isotopic enrichment is directly related to the amount of detrital contamination; δ18O of bulk carbonates is significantly biased when the detrital component amounts to more than 5% of the sample. It is also shown that samples containing detrital material have an influence on the calculation of the covariance between δ13C and δ18O. Covariance is high (r = 0.76) when the correlation coefficient is calculated on the base of all samples, but absent (r = ?0.43) when samples containing detrital dolomite are excluded. It has been demonstrated that microfacies analysis is a quick tool to avoid or reduce detrital contamination in bulk carbonate samples during sample selection. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献