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131.
A roughly 30 km 2D section across the Faja Plegada y Corrida del Agrio in the Neuquen Basin, Argentina, is the basis for a petroleum systems study, including structural restoration through time, deposition and erosion, pressure, temperature and migration modeling. Integrating tectonic and petroleum systems modeling proved critical to properly evaluate sub-thrust plays. Multi-dimensional modeling of dynamic processes allows accurate assessment and prediction of the potential of petroleum systems in tectonically complex areas such as the Neuquen Basin.  相似文献   
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Mathematical Geosciences - Recent advances in satellite technologies, statistical and mathematical models, and computational resources have paved the way for operational use of satellite data in...  相似文献   
135.
We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H2O (ΔFMQ = ??0.21 to ??1.01), employing a double-capsule setting. Fluids, binary H2O–CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite?+?enstatite solubility in H2O–CO2 fluids is higher compared to pure water, both in terms of dissolved silica (mSiO2?=?1.24 mol/kgH2O versus mSiO2?=?0.22 mol/kgH2O at P?=?1 GPa, T?=?800 °C) and magnesia (mMgO?=?1.08 mol/kgH2O versus mMgO?=?0.28 mol/kgH2O) probably due to the formation of organic C–Mg–Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H2O–CO2 fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high PT conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle.  相似文献   
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Surficial sediments of three northern Egyptian lakes (Manzala, Burullus and Edku) show differences in diatom assemblages deposited in different sites of these lakes. A total of 172 species and varieties belonging to 58 genera were identified and counted from 62 samples. Of these, 163 diatom taxa were recorded from Manzala Lake sediments, 147 taxa were found in Burullus Lake sediments, and 117 taxa were identified in Edku Lake sediments. The considerable variation in the composition and distribution of the diatom assemblages among these lakes was mainly related to differences in the water quality, salinity, the concentration of nutrients and climatic changes. The planktonic diatom Cyclotella meneghiniana was dominant in the majority of the samples from Manzala Lake, but dominant in only a few samples from the middle parts of Burullus and Edku lakes. The non-planktonic epiphytic taxa Cocconeis placentula and Epithemia sorex were the subdominant species in the surface sediments, especially in shallow and marginal parts of the lakes. Multivariate statistical techniques (hierarchical ascending clustering and canonical correspondence analysis) were used to identify ecological groups of diatoms and to investigate which environmental variables were important in explaining the variation between these groups. Eight ecological groups containing distinctive diatom assemblages reflect current environmental conditions; especially saltwater intrusion in the north and nutrient-rich freshwater in the south.  相似文献   
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Fossil invertebrates from cores collected in Lake Tanganyika provide a record of probable nearshore ecological response to recent watershed deforestation and sediment erosion in several East African watersheds. We compared paleoecological profiles (primarily from ostracodes) from watersheds spanning a range of sizes and present-day deforestation disturbance levels to understand the timing and magnitude of faunal changes, and their relationship in time to terrestrially-derived disturbance indicators. Profiles from the Lubulungu and Nyasanga/Kahama Rivers (Tanzania) provide a record of faunal variability in watersheds that are currently undisturbed with respect to deforestation. These records indicate continuous faunal turnover through time. However, this pattern of turnover is accompanied by relatively high levels of diversity throughout the record, with no wholesale extinction events. Ostracode taphonomic data and other fossil abundance data from the Lubulungu area provide strong evidence in support of at least two episodes of lower lake levels, associated with episodes of Late Holocene aridity. Records from deltas of disturbed watersheds at the Kabesi River (Tanzania) and those of Northern Burundi all show a combination of profound and abrupt faunal turnover, in some cases accompanied by local extinction and establishment of a few dominant taxa. At the Mwamgongo River delta, fed from a very small, disturbed watershed, species turnover was subtler. In disturbed watershed cores showing abrupt faunal changes the transitions mostly occurred in the late 19th to early 20th centuries, predating the major mid-20th century increase in sediment mass accumulation rates, with the latter only correlated with changing fossil abundance and flux. However, the earlier faunal community changes are contemporaneous with both palynological and geochemical changes in the core profiles indicative of changing land-use patterns. This suggests that lacustrine ecosystem response to deforestation was a two-stage process, with an earlier phase of response to changing quality of sediments or dissolved matter being discharged from the watershed, and a subsequent phase responding to increased quantity of sediment.  相似文献   
138.
Two types of dispersive seismic waves have been acquired in different geological settings to investigate the potential to reveal the elastic parameters of the shallow marine subsurface. Scholte waves as well as acoustic guided waves are excited by a near-surface towed airgun, and recorded using two acquisition methods: (1) the towed-acquisition system using a hydrophone streamer towed close to the sea floor, and (2) the stationary-receiver method using Ocean-Bottom Seismometers and/or Hydrophones (OBS/OBH). Our diverse data sets reveal that the spatial sampling of the wavefield required to avoid aliasing may vary significantly for different geological settings. Scholte waves are characterised by a few distinct modes observed at low frequencies and low phase velocities. Their dispersion is mainly controlled by the depth profile of the shear-wave velocity. Acoustic guided waves show profound amplitude variations of numerous higher modes over a broad frequency range. These are sensitive to shear-wave velocity, but more sensitive to compressional-wave velocity than Scholte waves are. To avoid the identification of distinct modes we infer 1-D models of elastic parameters of the subsurface from the inversion of the full wavefield spectra of acoustic guided waves. In the Siberian Laptev Sea we infer the presence of a soft sediment layer (8–10 m) with a well resolved strong S-velocity gradient (150–450 m/s). In the Baltic Sea a low P-velocity layer with a strong vertical gradient (1250–1440 m/s) corresponding to a post-glacial gassy mud layer could be resolved, which agrees well with the sediment stratigraphy derived from a gravity core.  相似文献   
139.
The fishery for the edible sea urchin Paracentrotus lividus is of great importance to many European regions, although in some of them this species has shown a wide scale decline in recent years. This paper reports on direct (on P. lividus) and indirect (on the co-occurring but not fished echinoid, Arbacia lixula) effects of sea urchin harvesting in shallow rocky reefs in North-western Sardinia (Italy, central-western Mediterranean Sea), where this activity is intensively practised. Density, size (test diameter), and biomass of both species were assessed in autumn 2004 at two locations impacted by P. lividus fishery, and at two controls within an adjacent Marine Protected Area. Density of P. lividus and A. lixula was significantly greater at the controls than at the exploited locations. The average test diameter of P. lividus was also significantly larger at the controls, where large-sized specimens (i.e. >5 cm) were notably more abundant. The average size of A. lixula did not significantly differ between the impacted locations and the controls. The average biomass of P. lividus was significantly greater at the controls than at the exploited locations, whereas no differences were detected for A. lixula. These results reveal the existence of a heavy fishing impact on P. lividus in North-western Sardinia and the need for regulation of its harvesting to prevent severe direct effects on its populations. Since no indirect effects on A. lixula have been detected, it could be hypothesized that this species did not benefit from P. lividus fishery due to an only moderate competition for habitat and resources between these two echinoids. Implications for management of edible sea urchin fishery are also discussed.  相似文献   
140.

The relationship of the hydrological variability of the Rio Negro in Manaus and the dominant large-scale climate variability patterns for the 1902–2007 period is investigated using the quantile method and composite analyses. Variations of the Rio Negro Level (RNL) during its 3-month high (May to July—MJJ) and low (October to December—OND) phases are examined separately. The El Niño (La Niña) related maximum warming (cooling) in the central tropical Pacific during its mature and decaying stages modulates the atmospheric circulation in the tropics and displaces the Walker circulation cell eastward (westward), so that its sinking (rising) branch occurs over western Amazon and causes negative (positive) precipitation anomalies in this region. These anomalous climate conditions occur before the Rio Negro high phase (MJJ) and contribute to reduce (increase) the RNL and lead to a very low (very high) event in the river. On the other hand, the SST variability modes in the tropical Atlantic mainly during the transition from wet to dry season modulate the precipitation variations over western Amazon in OND. The very high events are more frequent after the 1960’s decade and the very low events, before the 1930’s decade. Therefore, the occurrence of these events contains a multidecadal scale variability. The results also indicate that the variations in the rainfall in western Amazon occur up to 9 months in advance and modulate the RNL in Manaus. The results presented here might be useful for monitoring purposes of the RNL.

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