Unexpected phase assemblages in inclusions with ternary H2O-salt fluids at low temperatures

Phase assemblages and temperatures of phase changes provide important information about the bulk properties of fluid inclusions, and are typically obtained by microthermometry. Inclusions are synthesized in natural quartz containing an aqueous fluid with a composition in the ternary systems of H₂O-NaCl₂-CaCl₂, H₂O-NaCl-MgCl₂, and H₂O-CaCl₂-MgCl₂. This study reveals that these fluid inclusions may behave highly unpredictably at low temperatures due to the formation of metastable phase assemblages. Eutectic temperatures cannot be detected in most of the fluid inclusions containing these ternary systems. Nucleation of a variety of solid ice and salt-hydrate phases in single fluid inclusions is often partly inhibited. Raman spectroscopy at low temperatures provides an important tool for interpreting and understanding microthermometric experiments, and visualizing stable and metastable phase assemblages. Final dissolution temperatures of ice, salt-hydrates, and salt must be treated with care, as they can only be interpreted by purely empirical or thermodynamic models at stable conditions.     

A model for the bite mechanics in the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae)

Although the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae) is a well-described Late Jurassic taxon, little is known about the feeding habits and biomechanics of its homodont dentition. The presence of a rhamphotheca has been suggested, but it is still unknown how much such structure would have participated in the foraging behaviour of Stegosaurus. To better understand the feeding mechanism of this taxon, three-dimensional models of a Stegosaurus tooth were created, using the software ZBrush^®. One model was simple and lacked serrations, whereas the other model included serrations. Those models were then transferred to the software Strand7^®, where finite element analyses took place. The models were given material properties of enamel, based on studies done with crocodilian and mammalian teeth. In addition to that, bite forces were calculated for Stegosaurus, based on skull proportions. The results show little difference between the force distributions on the serrated and non-serrated models, indicating an efficient mechanism of stress dissipation that avoids high stresses being transferred to the jaw bones during biting. Digital plant models were also created to test the calculated bite forces in Stegosaurus, which suggests this animal was capable of biting through smaller branches. Computer modelling and analyses provide additional information about feeding habits and plant preferences for Stegosaurus, and can be adapted for studying other comparable herbivorous taxa.     

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.