Shock features in iron-nickel metal and troilite of L-group ordinary chondrites

Abstract— Shock metamorphic features in opaque minerals (FeNi metal and troilite) of 22 L chondrites have been studied petrographically and geochemically in an attempt to establish a connection between the present silicate-based shock classification scheme (Stöffler et al., 1991) and the peak-shock and postshock thermal history recorded in these minerals. Unshocked to weakly shocked (S1–S3) L chondrites contain FeNi metal and troilite that display textures related to normal, slow cooling. They may also contain rare disequilibrium shock features, which suggest localized departures from equilibrium shock conditions. Above shock stage S3, selected melting of FeNi metal and troilite produces melt droplets whose composition and abundance correspond to the maximum equilibrium shock state achieved by the sample. At these higher shock levels, the abundance of other shock-induced features, such as polycrystalline kamacite, sheared and fizzed troilite, coarse-grained pearlitic plessite, polycrystalline troilite, and polymineralic melt veins serve as textural criteria that can be used to establish peak-shock conditions. Minimum postshock temperatures obtained from analyses of plessite components show a systematic increase in temperature with an increase in shock stage, thereby providing additional information about the postshock thermal histories of L chondrites. At the highest shock levels recorded in L chondrites (S6 and above), melting and chemical homogenization of FeNi metal produces flattened Ni profiles that may partially to completely obscure any evidence for an earlier, slow-cooling history. All of these features serve as aids for shock classifying L chondrites as well as for quantifying minimum peak temperatures that resulted during shock metamorphism.     

Measurement of partition coefficients of phenol and cresols in gas-charged crude oil/water systems

An instrument has been constructed for monitoring the partition coefficients of phenol and cresols between crude oil and water under sub-surface conditions. The device has the capacity for introducing methane gas into crude oil, thereby allowing measurements under live oil (solution gas-containing) conditions. The partition coefficients of phenol and cresols have been measured in crude oil: water substrates under “live” oil and “dead” oil (without solution gas) conditions over a temperature range 25–150 °C. Over the range investigated it is seen that the introduction of gas (crude oil saturated at 100 bar with methane) into the system resulted in an approximate doubling of partition coefficients compared to the equivalent dead oil: brine systems. The partition coefficient data obtained using the device may be employed in a number of petroleum exploration and production activities such as the determination of residual oil saturation of a water-flooded petroleum reservoir. Partition coefficient measurements may help in predicting toxic organic solute loadings in oilfield discharge waters.     

210Pb activities in and fluxes to sediments of the Washington continental slope and shelf

Surface sediments of the Washington coast have ²¹⁰Pb activites which average 104 ± 48dpm/g for submarine canyon and slope regimes and 18 ± 12dpm/g for the continental shelf regime. ²¹⁰Pb sedimentary fluxes are also higher in canyons, averaging 18 ± 13dpm/cm² per yr, compared to 5.2 ± 3.1 dpm/cm² per yr for slope and 4.8 ± 1.8dpm/cm² per year for shelf regions. These ²¹⁰Pb activities and fluxes are 2–7 times greater than those reported for other coastal regions. Inputs from the atmosphere and the Columbia River are not sufficient to supply the ²¹⁰Pb, but advection of seawater containing dissolved ²¹⁰Pb produced in situ from ²²⁶Ra provides an input several times larger than the sedimentary fluxes. The sedimentary ²¹⁰Pb flux is limited by scavenging reactions rather than by supply of dissolved ²¹⁰Pb.Calculations of maximum biological uptake and fluxes of ²¹⁰Pb and ‘selective’ chemical leaching experiments all show that the primary scavenging processes are due to hydrous Mn and Fe oxides rather than biological phases. The pattern of higher ²¹⁰Pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved ²¹⁰Pb near the sea floor, rather than by processes operating throughout the water column. Relatively rapid removal of dissolved ²¹⁰Pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer.     

Asset Management and Safety Assessment of Levees and Earthen Dams Through Comprehensive Real-Time Field Monitoring

Assessing the health of and maintaining civil infrastructure has been an increased concern in the wake of natural disasters such as Hurricane Katrina in 2005 and the summer 2007 flood events in the UK. The variability of properties within geotechnical systems makes predictions of soil behavior extremely difficult, especially when soil models are not calibrated with field-measured performance. Unfortunately the current state of the art in geotechnical system health assessment is either based on very expensive monitoring systems for real-time information or on periodic measurement of ground surface displacements. Accordingly, a need has arisen for a system capable of in situ, real-time monitoring of levees, embankments, and other earthen structures. The work presented herein highlights the development of novel, affordable sensing technologies for use in a framework to monitor, manage and ensure the safety of geotechnical infrastructure. MEMS (micro-electro-mechanical systems)-based in-place inclinometer system, Measurand’s ShapeAccelArray (SAA), is now established as a sensing tool for simultaneous measurement of 3D soil acceleration and 3D ground deformation up to a depth of one hundred meters, with an accuracy of ±1.5 mm per 30 m. Each sensor array is connected to a wireless sensor node to enable real-time monitoring as well as remote sensor configuration. This system is now being further developed to include digitally integrated pore pressure measurement in the form of vibrating wire piezometers equipped with microprocessors (called SAAPs). The SAAPs are able to convert vibrating wire data to digital data downhole, and they integrate easily into the SAA system. In situ testing was conducted in a levee in England subjected to significant tidal loading (up to 6 m of fluctuation during spring tides) through collaboration with the European Union’s UrbanFlood project. In addition to the SAAs and SAAPs installed in three sections of the levee, the site was also instrumented with other sensors from Alert Solutions and TenCate, providing values for comparison. The likelihood of this levee to experience deformation and the density of instrumentation installed in the bank made this the ideal location to test the new SAAP system. The additional insight into subsurface behavior provided by the SAAPs is integral in the development of a comprehensive system for monitoring and management of civil infrastructure. The preliminary testing indicates the suitability of this new multi-parameter system for inclusion in a multi-scale monitoring and health assessment framework, which will be implemented in New Orleans, LA in 2012.     

Exploring the Solution Space of Semi-structured Geographical Problems Using Genetic Algorithms

Semi-structured geographical problems are often addressed by groups of decision-makers. Each group member is likely to have a specific set of objectives that they wish to address and a unique perspective on the way in which the problem should be solved. The solution to such problems often requires consensus building and compromise among decision-makers as they attempt to optimize their own criteria. The set of criteria adopted by a particular decision-maker constrains the set of solutions he/she will deem acceptable. Compromise among multiple decision-makers can occur at the intersection of these constrained solution sets. Knowledge about the criteria space, the solution space, and the relation between the two is often incomplete for semi-structured problems. New tools are needed to explore, analyze, and visualize the solution space of a problem with respect to multiple analytical models and criteria. In this research we explore the utility of genetic algorithms as an effective means to: (1) search the solution space of geographical problems; (2) visualize the spatial ramifications of alternative criteria spaces; and (3) identify compromise solutions.     

The uranium and thorium decay series nuclides in Mt. St. Helens effusives

The concentrations of the radionuclides²³⁸U,²³⁰Th,²²⁶Ra,²¹⁰Pb,²¹⁰Po,²³²Th,²²⁸Ra and²²⁸Th and the abundances of major elements were determined in samples from all major eruptions of Mt. St. Helens from May 18, 1980 through June 21, 1981. During this time the effusives changed from plagioclase-phyric dacite to a more andesitic composition but the concentrations of U and Th series nuclides were measurably invariant. The average²³²Th/²³⁸U weight ratio in the rocks is 2.4 and the²³⁰Th/²³²Th activity ratio equals the²³⁸U/²³²Th activity ratio indicating no fractionation of U from Th during magma genesis.²²⁶Ra activity is in excess (～40% on average) of its parent²³⁰Th whereas²²⁸Ra is in radioactive equilibrium with its parent²³²Th, constraining the time of magma formation between 30 and 10⁴ years prior to eruption. The²¹⁰Pb/²²⁶Ra activity ratios in the samples average 1.0, with a 20% scatter on either side, but allowing for volatile²¹⁰Pb loss at time of eruption excess²¹⁰Pb over²²⁶Ra is inferred, indicating that the time of magma formation was within the last 150 years.²¹⁰Po was virtually absent in the samples immediately after eruption, indicating its total loss by volatilization during eruption. The quantity of²¹⁰Po volatilized during the May 18, 1980 event is estimated to be in the range of 300 Ci from the effusives and as much as 5000 Ci total including losses from heated slide material. The²²²Rn activity volatilized should have been comparable to the²¹⁰Po activity released.