Closing and continentalization of the South Pyrenean foreland basin (NE Spain): magnetochronological constraints

This paper presents new magnetostratigraphic results from a 1100‐m‐thick composite section across the marine to continental sediments of the central part of the SE margin of the Ebro basin (NE Spain). Integration with existing marine and continental biochronological data allows a robust correlation with the geomagnetic polarity time scale. The resulting absolute chronology ranges from 36.3 to 31.1 Ma (Priabonian to Rupelian), and yields an interpolated age of ～36.0 Ma (within chron C16n.2n) for the youngest marine sediments of the eastern Ebro basin. This age is in concordance with a reinterpretation of earlier magnetostratigraphic data from the western South Pyrenean foreland basin, and indicates that continentalization of the basin occurred as a rapid and isochronous event. The basin continentalization, determined by the seaway closure that resulted from the uplift of the western Pyrenees, was probably coincident with a mid‐amplitude eustatic sea level low with a maximum at 36.2 Ma. The base level drop that followed the basin closure and desiccation does not appear associated to a significant sedimentary hiatus along the margins, suggesting a late Eocene shallow marine basin that rapidly refilled and raised its base level after the seaway closing. Rapid basin filling following continentalization predates the phase of rapid exhumation of the Central Pyrenean Axial Zone from 35.0 to 32.0 Ma, determined from the thermochronology data. It is possible then that sediment aggradation at the front of the fold‐and‐thrust belt could have contributed to a decrease in the taper angle, triggering growth of the inner orogenic wedge through break‐back thrusting and underplating. Contrasting sedimentation trends between the western and eastern sectors of the South Pyrenean foreland indicate that basin closing preferentially affected those areas subjected to sediment bypass towards the ocean domain. As a result, sediment ponding after basin closure is responsible for a two‐fold increase of sedimentation rates in the western sector, while changes of sedimentation rates are undetected in the more restricted scenario of the eastern Ebro basin.     

Transboundary flow modeling: the Zohor depression of Austria and the Slovak Republic

Estimation of available ground water is a basic aspect of ground water management. Mathematical modeling is one of the methods that can be effectively used to obtain such estimates. A numerical model was used to calculate available ground water in the Zohor depression-an aquifer transcending national boundaries between the Slovak Republic and Austria. The aquifer, formed by Quaternary sediments overlying Neogene sequences, is composed of various clays interbedded with layers of sand, gravel, sandstones, and conglomerates. The AQUA computer model package was used to simulate flow in the aquifer. For model compilation, the following data were used: (1) effective precipitation; (2) surface water levels in surface water gauging profiles; and (3) withdrawal amounts. Hydraulic parameters of the aquifer were estimated based on information from 86 wells located in the area. The model was verified using data on ground water levels from a monitoring network. The simulation of the aquifer system permitted the estimation of the available ground water in the study area, showing that an additional 587 L/s can be abstracted. Ground water inflows to the Morava River, which flows through the region, range from 745 to 3100 L/s.     

Cosmic-ray streaming and anisotropies

The principal result of this paper is the demonstration that in interplanetary space the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind. In addition there are diffusive currents and transverse gradient drift currents. With this interpretation direct reference to the interplanetary electric-field drifts is eliminated and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler. Following a discussion of our present knowledge of the diffusion coefficient in the interplanetary medium, the theory is applied to steady-state anisotropies near Earth in the kinetic energy (T) range 7.5 MeV<T<20 GeV. First the theory of the diurnal variation atT>-2 GeV is examined and it is suggested that the azimuthal streaming associated with the observations be regarded simply as proof that there is no significant net radial flow of cosmic rays at these energies. Second, it is predicted that, near Earth, the radial anisotropy will have a (+?+) variation with energy and this prediction is very insensitive to the precise values of the parameters used: intensity spectrum, solar wind speed, radial density gradient, and diffusion coefficient. Then, third, the small and radial steady-state anisotropies reported by Raoet al. (1967) in the intervals 7.5<T<45 MeV and 45<T<90 MeV are re-examined and it is found that the gradients and diffusion coefficients required to produce the reported anisotropies in 7.5<T<45 MeV are inconsistent with those expected from other data.     

The Impact of Herder Sedentarization on Natural Resource Access in Northeastern Ghana

The Fulani of West Africa have increasingly migrated to humid West Africa since the Sahelian droughts of the 1970s, drawing opposition from indigenous groups that are concerned about the deprivation of their livelihood and monopolization of resources for herders’ livestock. This research, which involved farmers, shepherds, and Fulani herders, addressed three issues: the nature of indigenous grazing and watering regimes, shepherd–herder relations, and herders’ impact on resource access for indigenes’ livestock. The research indicates that in-community and off-community platforms for resource access exist. The former has not been impacted by the herders; the latter has experienced changes insufficient to constitute an overhaul of resource access at the expense of indigenes’ livestock. Instead, a “shepherd–herder” category of resource access has emerged that is characterized by negotiation for resource space, opening avenues for addressing broader resource access issues, and typically tense indigene–herder relationships.     

The behavior of arsenic and antimony at Pezinok mining site,southwestern part of the Slovak Republic

Arsenic and antimony contamination is found at the Pezinok mining site in the southwest of the Slovak Republic. Investigation of this site included sampling and analysis of water, mineralogical analyses, sequential extraction, in addition to flow and geochemical modeling. The highest dissolved arsenic concentrations correspond to mine tailings (up to 90,000 μg/L) and the arsenic is present predominately as As(V). The primary source of the arsenic is the dissolution of arsenopyrite. Concentration of antimony reaches 7,500 μg/L and its primary source is the dissolution of stibnite. Pore water in mine tailings is well-buffered by the dissolution of carbonates (pH values between 6.6 and 7.0) and arsenopyrite grains are surrounded by reaction rims composed of ferric iron minerals. Based on sequential extraction results, most solid phase arsenic is in the reducible fraction (i.e. ferric oxyhydroxides), sulfidic fraction, and residual fraction. Distribution of antimony in the solid phase is similar, but contents are lower. The principal attenuation mechanism for As(V) is adsorption to ferric oxide and hydroxides, but the adsorption seems to be limited by the competition with Sb(V) produced by the oxidation of stibnite for adsorption sites. Water in mine tailings is at equilibrium with gypsum and calcite, but far from equilibrium with any arsenic and antimony minerals. The concentrations of arsenic and antimony in the surrounding aquifer are much lower, with maximum values of 215 and 426 μg/L, respectively. Arsenic and antimony are transported by ground water flow towards the Blatina Creek, but their loading from ground water to the creek is much lower compared with the input from the mine adits. In the Blatina Creek, arsenic and antimony are attenuated by dilution and by adsorption on ferric iron minerals in stream sediments with resulting respective concentrations of 93 and 45 μg/L at the site boundary south of mine tailing ponds.     

三个印度洋区域天然气水合物的产状和地下水文学对比研究

2006年度印度洋天然气水合物规划（NG—HP）的目标是调查控制印度近海天然气水合物分布及其特征的地质因素,以便最终评价作为潜在能源的天然气水合物的开采可能性。海洋中聚集的天然气水合物的总量是巨大的,大约25000～10000亿t。     

A 3.5 ka record of paleoenvironments and human occupation at Angkor Borei,Mekong Delta,southern Cambodia

Microfossil and sedimentological data from a 3.1 m core extracted from a reservoir (baray) at the ancient Cambodian settlement of Angkor Borei in the Mekong Delta have provided a continuous record of sedimentation and paleoenvironments dating from about 2000 cal yr B.C. Palynological data indicate that for much of the cal. 1st and 2nd millennia B.C. mangroves dominated the regional vegetation, while extensively and regularly burnt grasslands dominated the local vegetation. Turbid, nutrient‐rich standing water characterized the core locality, perhaps suggesting a connection with rivers in the area. An abrupt change during the cal. 5th to 6th centuries A.D. involved a dramatic reduction in grasslands and the expansion of secondary forest or re‐growth taxa. These changes are synchronous with an abrupt decline in the concentration of microscopic charcoal particles in the sediments, and the colonization of the core locality by swamp forest plants. These changes are taken to indicate a shift in land‐use strategies or, possibly, a period of land abandonment. The age for the construction of the baray is interpreted to be in the 17th–19th centuries, but this dating remains speculative. Construction of the Angkor Borei baray exploited a preexisting body of standing water, so its construction was fundamentally different from the methods used at the Angkorian capital in northern Cambodia. © 2003 Wiley Periodicals, Inc.