Aeolian system sediment state: theory and Mojave Desert Kelso dune field example

The sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply, sediment availability and the transport capacity of the wind. The sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system. Numerous factors impact the susceptibility of grains on a surface to transport, but these are cumulatively manifested by the actual transport rate, which serves as a proxy for sediment availability. Transport capacity is the potential sediment transport rate of the wind. Because the three aspects of sediment state can be given as a volumetric rate, they are directly comparable. Plotted simultaneously against time, the generated curves define nine possible classes of sediment state. Sediment supply that is stored occurs because it is transport or availability limited, or generated at a rate greater than the potential or actual transport rates respectively. Contemporaneous or lagged influx to an aeolian system may be limited by sediment availability, but cannot exceed the transport capacity of the wind. For the Kelso dune field in the Mojave Desert of California, a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system. The sediment supply was generated during the latest Pleistocene and earliest Holocene during humid periods of enhanced discharge by the Mojave River to form the Lake Mojave fan delta or terminal fan, and has been calculated over time from the sedimentation rate and the frequency of floods. Estimation of transport capacity over time was based upon modern wind data, with an allowance for greater winds during the Pleistocene based upon climatic models. Sediment availability was approximated by calculation of a modern dune mobility index, with variation over time based upon climatic inferences. While quantifying the Kelso or any natural system is subject to numerous uncertainties, the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at Kelso, as well as illuminating questions for future research.     

Seismic Reflection and Vibracoring Studies of the Continental Shelf Offshore Central and Western Long Island, New York

The ridge-and-swale topography on the continental shelf south of Fire Island, New York, is characterized by northeast-trending linear shoals that are shore attached and shore oblique on the inner shelf and isolated and shore parallel on the middle shelf. High-resolution seismic reflection profiles show that the ridges and swales occur independent of, and are not controlled by, the presence of internal structures (for example, filled tidal inlet channels, paleobarrier strata) or underlying structure (for example, high-relief Cretaceous unconformity). Grab samples of surficial sediments on the shelf south of Fire Island average 98 % sand. Locally, benthic fauna increase silt and clay content through fecal pellet production or increase the content of gravel-size material by contribution of their fragmented shell remains. Surficial sand on the ridges is unimodal at 0.33 mm (medium sand, about 50 mesh), and surficial sand in troughs is bimodal at 0.33 mm and 0.15 mm (fine sand, about 100 mesh). In addition to seismic studies, 26 vibracores were recovered from the continental shelf in state and federal waters from south of Rockaway and Long Beaches, Long Island, New York. Stratigraphic and sedimentological data gleaned from these cores were used to outline the geologic framework in the study area. A variety of sedimentary features were noted in the cores, including burrow-mottled sections of sand in a finer silty-sand, rhythmic lamination of sand and silty-sand that reflect cyclic changes in sediment transport, layers of shell hash and shells that probably represent tempestites, and changes from dark color to light color in the sediments that probably represent changes in the oxidation reduction conditions in the area with time. The stratigraphic units identified are an upper, generally oxidized,nearshore facies, an underlying fine-to medium-sand and silty-clay unit considered to be an estuarine facies, and a lower, coarse-grained, deeply oxidized, cross-laminated preHolocene unit. Grain-size analysis shows that medium-to fine-grained sand makes up most (68-99 %) of the surficial sediments. Gravel exists in trace amounts up to 19 %. Silt ranges between 3 % and 42 %, and clay ranges from 1 % to 10 %.     

Graphical representation of particle shape using triangular diagrams: an Excel spreadsheet method

Analysis of the shape of sedimentary particles can provide information about their transport history and aid facies differentiation and the characterization of depositional environments. Triangular (Sneed and Folk) diagrams, employing ratios of the three orthogonal particle axes, have been advocated as the most appropriate method for unbiased presentation of primary particle shape data. A spreadsheet method for the production of these diagrams is described. Clast data‐sets from a range of environments are presented using this method. An alternative use of the spreadsheet for the presentation of sedimentary fabric shape is suggested. Copyright © 2000 John Wiley & Sons, Ltd.     

羊鲍(Haliotis ovina)和耳鲍(H.asinina)MtDNA COⅠ和COⅡ基因片段序列的比较研究

采用基因测序的方法,对我国海南产的羊鲍和耳鲍两个自然种群的COⅠ和COⅡ基因片段进行了PCR扩增和测序。结果表明,羊鲍和耳鲍COⅠ基因片段的核苷酸序列均为193bp,4种碱基组成非常相似,且其A T的含量也非常相似,分别为45.08%和45.60%。羊鲍和耳鲍COⅠ基因片段的核苷酸序列之间有29bp的差异,其中有8处发生碱基颠换,21处发生碱基转换,差异为15.03%,同源性为84.97%;羊鲍和耳鲍COⅡ基因片段的核苷酸序列均为157bp,羊鲍和耳鲍4种碱基组成差异较大,且其A T的含量也不同,分别为59.24%和55.41%。羊鲍和耳鲍COⅡ基因片段的核苷酸序列之间有19bp的差异,其中3处发生碱基颠换,16处发生碱基转换,达到12.10%的差异,同源性为87.90%。分子变异分析表明羊鲍和耳鲍物种间的变异组成为0.50,变异百分数为100.00,羊鲍和耳鲍物种间的遗传分化显著(FST=1,P<0.001)。     

A weight-of-evidence approach to assessing the ecological impact of organotin pollution in Dutch marine and brackish waters; combining risk prognosis and field monitoring using common periwinkles (Littorina littorea)

In the present study an integrated ecological risk assessment based on multiple lines of evidence (LOEs) was evaluated in order to better assess the risk from TBT in Dutch harbours and open coastal waters. On the basis of spatial distributions of measured tributyltin (TBT) concentrations in sediments and suspended matter, predictions of the intersex index (ISI) in Littorina littorea and the ecological risk expressed as the Potentially Affected Fraction (PAF) of species were made. The results were compared to actual ISI measurements and presence of L. littorea in the field. The PAF calculated on the basis of TBT levels for open coastal waters ranged from 4.2% to 15.3%; for harbours it ranged from 3.5% to 26.9%. Significant intersex levels were observed only in waters where the risk was calculated above 10% PAF. This study suggests that the absence of L. littorea from some harbours with high ecological risk values can be explained by high TBT concentrations. A call is made for the use of integrated approaches like weight-of-evidence (WOE) to help practitioners improve ecological risk assessment.     

Improving the calibration of Type Ia supernovae using late-time light curves

The use of Type Ia supernovae (SNe Ia) as cosmological standard candles is a key to solving the mystery of dark energy. Improving the calibration of SNe Ia increases their power as cosmological standard candles. We find tentative evidence for a correlation between the late-time light-curve slope and the peak luminosity of SNe Ia in the B band; brighter SNe Ia seem to have shallower light-curve slopes between 100 and 150 d from maximum light. Using a Markov Chain Monte Carlo (MCMC) analysis in calibrating SNe Ia, we are able to simultaneously take into consideration the effect of dust extinction, the luminosity and light-curve width correlation (parametrized by  Δ m ₁₅  ), and the luminosity and late-time light-curve slope correlation. For the available sample of 11 SNe Ia with well-measured late-time light curves, we find that correcting for the correlation between luminosity and late-time light-curve slope of the SNe Ia leads to an intrinsic dispersion of 0.12 mag in the Hubble diagram. Our results have significant implications for future supernova surveys aimed to illuminate the nature of dark energy.     

Lightning activity related to satellite and radar observations of a mesoscale convective system over Texas on 7–8 April 2002

A multi-sensor study of the leading-line, trailing-stratiform (LLTS) mesoscale convective system (MCS) that developed over Texas in the afternoon of 7 April 2002 is presented. The analysis relies mainly on operationally available data sources such as GOES East satellite imagery, WSR-88D radar data and NLDN cloud-to-ground flash data. In addition, total lightning information in three dimensions from the LDAR II network in the Dallas–Ft. Worth region is used.GOES East satellite imagery revealed several ring-like cloud top structures with a diameter of about 100 km during MCS formation. The Throckmorton tornadic supercell, which had formed just ahead of the developing linear MCS, was characterized by a high CG+ percentage below a V-shaped cloud top overshoot north of the tornado swath. There were indications of the presence of a tilted electrical dipole in this storm. Also this supercell had low average CG− first stroke currents and flash multiplicities. Interestingly, especially the average CG+ flash multiplicity in the Throckmorton storm showed oscillations with an estimated period of about 15 min.Later on, in the mature LLTS MCS, the radar versus lightning activity comparison revealed two dominant discharge regions at the back of the convective leading edge and a gentle descent of the upper intracloud lightning region into the trailing stratiform region, apparently coupled to hydrometeor sedimentation. There was evidence for an inverted dipole in the stratiform region of the LLTS MCS, and CG+ flashes from the stratiform region had high first return stroke peak currents.     

The skill of atmospheric linear inverse models in hindcasting the Madden–Julian Oscillation

A suite of statistical atmosphere-only linear inverse models of varying complexity are used to hindcast recent MJO events from the Year of Tropical Convection and the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden–Julian Oscillation mission periods, as well as over the 2000–2009 time period. Skill exists for over two weeks, competitive with the skill of some numerical models in both bivariate correlation and root-mean-squared-error scores during both observational mission periods. Skill is higher during mature Madden–Julian Oscillation conditions, as opposed to during growth phases, suggesting that growth dynamics may be more complex or non-linear since they are not as well captured by a linear model. There is little prediction skill gained by including non-leading modes of variability.     

Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district,South China Block

The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U–Pb and apatite fission‐track thermochronology. The pitchblende U–Pb results indicate that uranium mineralization occurred at ~801–759 Ma. Fractionation of uranium and lead at ~374–295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission‐track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.     

Determination of Trace Elements in Selected Geological Reference Materials by Instrumental Neutron Activation Analysis

Data are presented for eight rare earth elements and ten other elements in 22 reference samples recently distributed by the University of Liege (Belgian sedimentary rock reference samples), the Geological and Mining Service (Suriname), the Geological Survey of Japan and the Venezuelan laterite. Determinations were made using a well characterised, high precision, neutron activation analysis technique.