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71.
72.
H.I. Petersen N. Sherwood A. Mathiesen M.B.W. Fyhn N.T. Dau N. Russell J.A. Bojesen-Koefoed L.H. Nielsen 《Marine and Petroleum Geology》2009
Several exploration wells have intersected a Cenozoic coal-bearing, fluvial-deltaic mudstone and sandstone succession in the northeastern Vietnamese part of the Malay Basin, and have successfully tested seismically identified direct hydrocarbon indicators (DHIs). The oil and gas/condensate discovery well 46-CN-1x encountered a ∼55 m thick section of lacustrine mudstones having considerable potential as an oil source. Vitrinite reflectance (VR) measurements from these alginite-bearing rocks introduce several problems in thermal maturity evaluation, including associated VR suppression and delineation of cavings and bitumens. Reliable thermal maturity gradients, however, may be established using a combination of conventional VR measurements and ‘equivalent VR’ (EqVR) values derived from the fluorescence alteration of multiple macerals (FAMM) technique. These measurements, performed on dispersed organic matter (DOM) in cuttings from 46-CN-1x, allow separation of low-reflecting bitumens and vitrinite in cavings from indigenous vitrinite and the FAMM results indicate VR suppression of 0.14% in an alginite-bearing mudstone with a high Hydrogen Index value. On the basis of available ‘raw’ VR data, a highly irregular maturity trend is determined, with the deepest sample (2675–2680 m) having a VR of ∼0.4%Ro. The EqVR value, however, for the deepest sample is 0.70%. The maturity trend determined from the FAMM data (and VR data, omitting samples having suppressed VR) indicates that the top of the oil window (VR of 0.75%Ro) is located at about 2800 m depth. Modelling the geothermal gradient using the EASY%Ro algorithm yields ∼40 °C/km for both of the two maturity profiles; this is in the low end of the range for the Malay Basin. Modelled temperature histories indicate onset of hydrocarbon generation for the uppermost Oligocene source rocks between 2 Ma and present-day, which post-dates trap formation. Seismic facies patterns suggest that lacustrine oil-prone units are in the oil window in the same graben complex a few km NW of the investigated well, and these rocks are likely to be the source of the hydrocarbons found in the well. A more widespread occurrence of hydrocarbons sourced from this kitchen is indicated by other discoveries and mapping of DHIs in the area. 相似文献
73.
Abstract A distributed eco-hydrological model based on soil—vegetation—atmosphere transfer processes is applied to estimate actual evapotranspiration (ET) and gross primary production (GPP) over the Wuding River basin, Loess Plateau, China, based on digital elevation model, vegetation and soil information between 2000 and 2003 over three grid sizes: 250 m, 1 km and 8 km. The spatial patterns of annual ET and GPP are related to precipitation variability and land-use/cover conditions. The grid size is shown to affect the spatial patterns of annual ET and GPP, the effect on GPP being more significant than that on ET. Geostatistical and regression analyses demonstrate that precipitation and vegetation influence the scaling effect of ET and GPP in a complex way. When precipitation is high, the scaling effect of ET is more dependent on precipitation. The scaling effect of ET and GPP from 1-km to 8-km grid size is much larger than that from 250-m to 1-km grid size, showing the 1-km grid size to be a feasible choice for simulation of their spatial patterns. Although the annual GPP is more sensitive to the grid size than annual ET, both daily ET and daily GPP averaged over the whole basin seem to be insensitive to the grid size, illustrating that the coarse grid size can be used to simulate spatially-averaged variables without losing much accuracy. 相似文献
74.
Experiments were carried out on an intermittent estuary during its closed (summer) and open (winter) states to identify the physical processes responsible for vertical mixing across the halocline, and to quantify vertical fluxes of oxygen and salt between water layers. During the blocked phase a two-layer structure was observed, with a brackish surface layer overlying old seawater. Within a deep basin the wind-driven turbulent mixing was consistent with the measured surface-layer turbulent dissipation, but the dissipation in the bottom layer appeared to be driven by internal seiching. In the shallow regions of the estuary vertical fluxes of dissolved oxygen were indicative of oxygen demand by respiration and remineralization of organic material in bottom water and sediments. During the estuary's open phase a three-layer structure was observed, having a fresh, river-derived surface layer, a middle layer of new seawater, and a bottom layer of old seawater. In the shallower regions surface-layer turbulent diffusion was consistent with the strong, gusty winds experienced at the time. The dissolved oxygen of the incoming seawater decreased to very low values by the time it reached the upstream deep basin as a result of the low cross-pycnocline oxygen flux being unable to compensate for the oxygen utilization. At least 50 % of the cross-pycnocline salt fluxes in the shallow reaches of the open estuary are suggested to be driven by Holmboe instabilities.
Responsible Editor: Hans Burchard 相似文献
75.
Steven Sherwood 《Climatic change》2007,80(3-4):205-212
76.
F. Ghassemzadeh J. Sherwood M. C. Geddes W. D. Williams 《International Journal of Salt Lake Research》1997,6(3):269-278
The analysis of nitrate in seawater and hypersaline waters should take account of a significant “salt effect”. Procedures
developed for fresh water and marine waters must be applied cautiously to highly saline waters. The most widely used standard
method for the determination of nitrate-nitrogen (NO3-N) in fresh and marine waters involves the quantitative reduction of nitrate by the Cd column technique followed by colorimetric
procedures. In our study, three approaches to estimate NO3-N in highly saline waters were examined. The first involved dilution. This approach overcame the salt effect but dilution
limited the detection of low concentrations of nitrate in highly saline waters. The second involved the use of standard nitrate
solutions in saline water. This method is not recommended because of nitrate impurities in AR grade salts. The third- and
preferred approach-involved the use of standard additions. “Spikes” of a known volume of NO3-N standard solution were added to natural saline waters. Nitrate values estimated by the stadard addition method were used
to calculate an equation for salt error correction at different salinities applicable to waters with the same relative ionic
composition as seawater. This could then be used to correct nitrate determinations in highly saline waters where standards
made in distilled water were used for calibration. Many previously published data for NO3-N in saline water used methods of analysis which do not take account of salt error and are therefore probably in error. 相似文献
77.
Adakite-like Lavas from Antisana Volcano (Ecuador): Evidence for Slab Melt Metasomatism Beneath Andean Northern Volcanic Zone 总被引:6,自引:1,他引:6
BOURDON ERWAN; EISSEN JEAN-PHILIPPE; MONZIER MICHEL; ROBIN CLAUDE; MARTIN HERVE; COTTEN JOSEPH; HALL MINARD L. 《Journal of Petrology》2002,43(2):199-217
Extensive sampling of the Antisana volcano in Ecuador (NorthernVolcanic Zone of the Andes) has revealed the presence of adakite-likerocks throughout the edifice, i.e. rocks with geochemical characteristicsclose, but not identical, to those of slab melts. Two main volcanicgroups have been distinguished, characterized by two distinctevolutionary trends. The AND group, mostly composed of andesites,shows the clearest adakitic characteristics such as high La/Yband Sr/Y ratios and low heavy rare earth element (HREE) contents.The CAK group, composed of high-K andesites and dacites, displaysless pronounced adakitic-like characteristics. Although themore basic rocks of each group are difficult to distinguishon many geochemical diagrams, a geochemical study shows thatthe evolution of the AND and CAK groups is dominated by differentpetrogenetic processes. The isotopic characteristics of theCAK rocks suggest that evolution of this group is dominatedby a limited assimilationfractional crystallization processwithin the granitic continental basement of the cordillera.In the AND group, the abundances of incompatible elements, suchas Nb or HREE, suggest that the series was produced by a partialmelting process in a mantle rich in garnet, amphibole and/orclinopyroxene. Such a mantle source has been demonstrated (experimentallyand by exhumed mantle xenoliths) to be produced in subductionzones where slab melts react with and metasomatize the mantlewedge. In Ecuador, magmas erupted in the Western Cordillera(trenchward relative to Antisana volcano) are true adakites,suggesting that slab melts can be responsible for the metasomatismof the mantle wedge beneath the NVZ in Ecuador. If mantle convectioncan drag down this modified mantle beneath Antisana volcano,destabilization of metasomatic amphibole at appropriate pressuresin this modified garnetiferous mantle can adequately explainthe formation and the geochemical features of Antisana lavas. KEY WORDS: subduction; adakite; metasomatism; Ecuador; AFC; Sr and Nd isotopes 相似文献
78.
MAHONEY J. J.; GRAHAM D. W.; CHRISTIE D. M.; JOHNSON K. T. M.; HALL L. S.; VONDERHAAR D. L. 《Journal of Petrology》2002,43(7):1155-1176
Glasses from a 2600 km section of the Southeast Indian Ridgewest of the AustralianAntarctic Discordance all possessNdPbSr isotopic signatures typical of Indian Oceanridge basalt. The boundary between Pacific- and Indian-Ocean-typeridge basalt within the Discordance thus marks the westernmostextent of shallow Pacific-type asthenosphere beneath the ridge.Along-axis He, Nd, Pb, and Sr isotopic patterns are largelyindependent of ridge segmentation, but a weak tendency is evidentfor the most strongly Indian-Ocean-type mantle to be relativelyfusible and for shallower asthenosphere to have lower 3He/4He.On average, 相似文献
79.
80.
Stable isotope analysis of some representative fish and invertebrates of the Newfoundland and Labrador continental shelf food web 总被引:3,自引:1,他引:3
We examined stable carbon and nitrogen isotopic signatures of 17 fish and 16 invertebrate taxa common to the Newfoundland and Labrador (NL) continental shelf food web. Particular sampling emphasis was placed on Atlantic cod (Gadus morhua) and related prey species (e.g. shrimp, Pandalus borealis, and capelin, Mallotus villosus). We found highly significant (p < 0.0001) differences between near-shore (bays) and offshore (shelf edge) δ15N signatures for cod, ‘other fish’ (pooled) and invertebrates (pooled). In contrast, there were only minor differences in δ13C signatures of ‘other fish’ (p < 0.05) and no difference for cod and invertebrates among the two habitats. We sampled at two times of the year (January and June) and found no systematic effect of season on both δ13C and δ15N in cod, ‘other fish’ and invertebrates. We calculated isotopic fractionation factors for cod from the entire shelf (mixed diet) and for cod with diets composed mainly of capelin or shrimp. These values ranged between 2.2‰ and 3.9‰ for δ15N and −0.4‰ and 0.8‰ for δ13C and, for δ15N, may reflect diet-related differences in bioenergetic status. We discuss potential mechanisms for near-shore versus offshore enrichment of δ15N signatures, and demonstrate the implications of this spatial variation on δ15N-derived trophic position estimates. 相似文献