Shock temperatures in anorthite glass

Summary. Temperatures of CaAl₂Si₂O₈ (anorthite glass) shocked to pressures between 48 and 117 GPa have been measured in the range from 2500 to 5600 K, using optical pyrometry techniques. The pressure dependence of the shock temperatures deviates significantly from predictions based on a single high-pressure phase. Either a variable specific heat, or the existence of three phase transitions, at pressures of about 55, 85 and 100 GPa and with transition energies of about 0.5 MJ kg⁻¹ each (∼ 1.5 MJ kg⁻¹ total) can explain the shock-temperature data. The proposed phase transition at 100 GPa can possibly be identified with the stishovite melting transition. Theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations, indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases. Observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm⁻¹ to greater than 24 mm⁻¹– an increasing function of shock pressure. The assumption that the shocked material radiates as a black body is supported by the theoretical model, and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength.     

Structure and evolution of mass transport deposits in the South Caspian Basin,Azerbaijan

The Quaternary to late Pliocene sedimentary succession along the margin of the South Caspian Basin contains numerous kilometre‐scale submarine slope failures, which were sourced along the basin slope and from the inclined flanks of contemporaneous anticlines. This study uses three‐dimensional (3D) seismic reflection data to visualise the internal structure of 27 mass transport deposits and catalogues the syndepositional structures contained within them. These are used to interpret emplacement processes occurring during submarine slope failure. The deposits consist of three linked structural domains: extensional, translational and compressive, each containing characteristic structures. Novel features are present within the mass transport deposits: (1) a diverging retrogression of the headwall scarp; (2) the absence of a conventional headwall scarp around growth stratal pinch outs; (3) restraining bends in the lateral margin; (4) a downslope increase in the throw of thrust faults. The results of this study shed light on the deformation that occurred during submarine slope failure, and highlight an important geological process in the evolution of the South Caspian Basin margin.     

Efficiency of heavy liquid separation to concentrate magnetic particles

Low-temperature rock magnetic measurements have distinct diagnostic value. However, in most bulk marine sediments the concentration of ferrimagnetic and antiferromagnetic minerals is extremely low, so even sensitive instrumentation often responds to the paramagnetic contribution of the silicate matrix in the residual field of the magnetometer. Analysis of magnetic extracts is usually performed to solve the problems raised by low magnetic concentrations. Additionally magnetic extracts can be used for several other analyses, for example electron microscopy or X-ray diffraction. The magnetic extraction technique is generally sufficient for sediments dominated by magnetite. In this study however, we show that high-coercivity components are rather underrepresented in magnetic extracts of sediments with a more complex magnetic mineralogy. We test heavy liquid separation, using hydrophilic sodium polytungstenate solution Na₆[H₂W₁₂O₄₀], to demonstrate the efficiencies of both concentration techniques. Low-temperature cycling of zero-field-cooled, field-cooled and saturation isothermal remanent magnetization acquired at room temperature was performed on dry bulk sediments, magnetic extracts, and heavy liquid separates of clay-rich pelagic sediments originating from the Equatorial Atlantic. The results of the thermomagnetic measurements clarify that magnetic extraction favours components with high spontaneous magnetization, such as magnetite and titanomagnetite. The heavy liquid separation is unbiased with respect to high- and low-coercive minerals, thus it represents the entire magnetic assemblage.     

Progress in isotope paleohydrology using lake sediment cellulose

Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced by studies conducted over the past 15 years that span Holocene and pre-historical timescales.     

Occurrence of juvenile Atlantic sturgeon,Acipenser oxyrhynchus,in the upper tidal Delaware River

Eighty-nine juvenile Atlantic sturgeon,Acipenser oxyrhynchus oxyrhynchus, including 10 recaptures, were collected, tagged and released in the upper tidal Delaware River between July 1981 and December 1984. All were captured in the river channel between Roebling and Trenton, New Jersey, using bottom-set experimental gill nets during daylight hours. The species was present from July through December and collected in increased numbers in the past two years. The fork lengths ranged from 284 to 862 mm (mean±SD = 516 mm±106 mm) and the weights from 140 to 4,250 g (mean±SD = 1,369 g±815 g). Ten juvenile Atlantic sturgeon were recaptured between September 1983 and December 1984 and were at large from one to 418 d. Recapture data suggest that these sturgeon utilize this area annually from July through December, possibly as a nursery. Juvenile Atlantic sturgeon appear to utilize the upper tidal portion of the Delaware River for a much longer period of time and at lower temperatures than in other river systems.     

Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Although methane is the dominant absorber in Titan's reflection spectrum, the amount of methane in the atmosphere has only been determined to an order of magnitude. We analyzed spectra from the Space Telescope Imaging Spectrograph, looking at both a bright surface region (700-km radius) and a dark surface region. The difference between the spectra of the two regions is attributed to light that has scattered off the surface, and therefore made a round-trip through all of Titan's methane. Considering only absorption, the shape of the difference spectrum provides an upper limit on methane abundance of 3.5 km-am. Modeling the multiple scattering in the atmosphere further constrains the methane abundance to 2.63±0.17 km-am. In the absence of supersaturation and with a simplified methane vertical profile, this corresponds to a surface methane-mole fraction near 3.8% and a relative humidity of 0.32. With supersaturation near the tropopause, the surface methane mole fraction could be as low as 3%.