AÏOUN EL ATROUSS: A NEW HYPERSTHENE ACHONDRITE WITH EUCRITIC INCLUSIONS

Preliminary investigations have been made on two separate pieces from the Aïoun el Atrouss meteorite that fell on April 17, 1974 in southeast Mauritania. The major portion of the meteorite is a brecciated hypersthene achondrite with orthopyroxene (En₇₄) as the major phase. Clasts of eucrite, up to 7 percent in volume within a single slice, occur within the hypersthene achondrite host. No evidence has been found of reaction between the two meteorite types, nor of the presence of any materials intermediate in composition.     

THE KRAMER CREEK,COLORADO METEORITE: A NEW L4 CHONDRITE

The Kramer Creek, Colorado, chondrite was found in 1966 and identified as a meteorite in 1972. Bulk chemical analysis, particularly the total iron content (20.36%) and the ratio of Fe_total/SiO₂ (0.52), as well as the compositions of olivine (Fa_21.7) and orthopyroxene (Fs_18.3) place the meteorite into the L-group of chondrites. The well-defined chondritic texture of the meteorite, the presence of igneous glass in the chondrules and of low-Ca clinopyroxene, as well as the slight variations in FeO contents of olivine (2.4% MD) and orthopyroxene (5.6% MD) indicate that the chondrite belongs to the type 4 petrologic class.     

The formation of weathering products on the LEW 85320 ordinary chondrite: Evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites

Abstract— Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the δ¹³C and δ¹⁸O values of the two generations of bicarbonate (Antarctic and Texas) are different: δ¹³C = +7.9‰ and +4.2‰; δ¹⁸O = +17.9‰ and + 12.1‰ respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at ?2 ± 4 °C (Antarctic) and +16 ± 4 °C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapour or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar δ¹³C values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.     

Comparing single-phase,non-Newtonian approaches with experimental results: Validating flume-scale mud and debris flow in HEC-RAS

Post-fire debris flows and tailing impoundment failures destroy lives and property. These geologic hazards – and other similar processes – fall on a continuum between classic Newtonian flood analyses and geotechnical stability analyses. The US Army Corps of Engineers (USACE) is developing a non-Newtonian library (DebrisLib) that includes a suite of rheological and clastic approaches to hyper-concentrated, mudflow and debris flow dynamics. The Hydrologic Engineering Center (HEC) has implemented these non-Newtonian methods into the widely used, public-domain open-channel hydraulics and morphodynamic software, HEC-RAS (river analysis system). This work presents part of the verification and validation of these non-Newtonian approaches, applying several rheological equations to published laboratory results high-concentration flume experiments. This study tested the linear Bingham model as well as the turbulent and Bagnold quadratic terms of the O'Brien equation. HEC-RAS also includes the non-linear Herschel–Bulkley (HB) approach, which quantifies shear-thickening or shear-thinning processes. The study used these non-Newtonian models in HEC-RAS to simulate 10 of Parsons et al.’s (2001) flume experiments, which measured the snout and plug velocity of fluids with high solid concentrations (C_v = 68–74%) and a broad range of material gradations (d₅₀ = 0.05–1 mm, d₁₅ = 0.006–0.1 mm). The experiments also measured and back-calculated Bingham and HB parameters of the materials, finding HB powers between 0.45 and 1.25 (i.e. fluids that are dilatant, pseudo-plastic and visco-plastic). The rheological models incorporated into DebrisLib and implemented in HEC-RAS reproduce experimental data well for most experiments. The Bingham model generated a plug velocity root-mean-square error (RMSE) of 0.21 m/s using standard flow parameters and Parsons et al.’s calibrated parameters, a substantial improvement over the unmodified shallow water flow equations (RMSE 0.77 m/s). Experiments with strong snout effects tended to generate higher residuals, especially in the snout velocity. The RMSE associated with the O'Brien equation was larger with the Parsons et al. fit parameters, but similar (0.23 m/s) with measured parameters. The turbulent parameter was the largest (often the dominant) parameter in most O'Brien simulations, with the dispersive stress only proving significant for the coarsest material. DebrisLib had to use a modified version of the dispersive term to simulate these concentrations. Both the 2D depth-averaged shallow water equation (SWE) and diffusion wave equation were used to simulate the experiments. The best results were obtained with the SWE with horizontal mixing.     

Hillslope erosion in a grassland environment: Calibration and evaluation of the SIBERIA landscape evolution model

Field measurement and modelling of soil erosion provides insights into landscape systems as well as the potential for enhanced landscape management. There are a number of field and numerical methods by which soil erosion and deposition can be quantified. Here we examine the capability of the SIBERIA landscape evolution model to quantify short-term erosion and deposition on a well-managed cattle grazing landscape on the east coast of Australia. The model is calibrated by two methods (1) a geomorphological approach using a site digital elevation model (DEM) and soil data and (2) a laboratory-scale flume. The two calibration processes resulted in similar model input parameters and estimated erosion rates of 3.1 t ha⁻¹ year⁻¹ and 4.4 t ha⁻¹ year⁻¹, respectively. These were found to closely match erosion rates estimated using the environmental tracer ¹³⁷Cs (2.7–4.8 t ha⁻¹ year⁻¹). However, erosion and deposition estimated at individual points along the hillslope was not well correlated with ¹³⁷Cs at the same position due to the temporal averaging of the model and microtopography. Sensitivity analysis showed the model was more sensitive to parameterisation than sub-DEM-scale topography. This places confidence in the model's ability to estimate erosion and deposition across an entire hillslope and catchment on decadal time scales. We also highlight the robustness and flexibility of the calibration methods.     

The Global Context of Solar Activity During the Whole Heliosphere Interval Campaign

The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected ??heliophysical?? system during this solar minimum, centered on Carrington Rotation 2068, March 20??C?April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. But during the first half of CR 2068 three solar active regions flanked by two opposite-polarity, low-latitude coronal holes were present. These departures from the quiet Sun led to both eruptive activity and solar wind structure. Most of the eruptive activity, i.e., flares, filament eruptions and coronal mass ejections (CMEs), occurred during this first, active half of the interval. We determined the source locations of the CMEs and the type of associated region, such as active region, or quiet sun or active region prominence. To analyze the evolution of the events in the context of the global solar magnetic field and its evolution during the three rotations centered on CR 2068, we plotted the CME source locations onto synoptic maps of the photospheric magnetic field, of the magnetic and chromospheric structure, of the white light corona, and of helioseismological subsurface flows. Most of the CME sources were associated with the three dominant active regions on CR 2068, particularly AR 10989. Most of the other sources on all three CRs appear to have been associated with either isolated filaments or filaments in the north polar crown filament channel. Although calculations of the flux balance and helicity of the surface magnetic features did not clearly identify a dominance of one region over the others, helioseismological subsurface flows beneath these active regions did reveal a pronounced difference among them. These preliminary results suggest that the ??twistedness?? (i.e., vorticity and helicity) of subsurface flows and its temporal variation might be related to the CME productivity of active regions, similar to the relationship between flares and subsurface flows.     

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.     

A Queer Country? A case study of the politics of gay/lesbian belonging in an Australian country town

The present paper examines the complex politics of gay/lesbian belonging through a case study of Daylesford, Victoria, an Australian country town. It contributes to two research bodies: gay/lesbian rural geographies and the politics of belonging. Daylesford hosts ChillOut, Australia's largest rural gay/lesbian festival, which provides a telling context for investigating gay/lesbian belonging in rural Australia. We use qualitative data from the 2006 ChillOut Festival, including interviews with local residents, newspaper commentaries, and visitors’ surveys, to explore how Daylesford has been constructed, imagined, and experienced as a ‘unique’ site of gay/lesbian belonging in rural Australia. We find that ChillOut crucially contributes to its wider reputation as a gay-friendly country town, but also, we argue, to the contested nature of gay/lesbian belonging. This was most powerfully demonstrated by the local council's refusal to fly the gay-identified rainbow flag on the Town Hall during the 2006 Festival and its subsequent banning of the display of all festival flags from that key public building. Because ChillOut was the catalyst for this protocol, the resolution was viewed as homophobic. Indeed, the homophobic and heterosexist rhetoric that ensued in the Letters to the Editor section of the local newspaper revealed some residents’ underlying antagonism towards ChillOut and the local gay/lesbian community. Moreover, appealing to a shared ‘Australian identity’ and associated normative ‘family values’, these letter writers deployed a multi-scalar politics of belonging, where a sense of gay/lesbian belonging to Daylesford at the local scale was contested by the assertion of a ‘more meaningful’ national scale of allegiance fashioned by heteronormativity.     

Petrographic and geochemical evidence for an allochthonous, possibly impact melt, origin of pseudotachylite from the Vredefort Dome, South Africa

Hypotheses proposed to explain the origin of pseudotachylite bodies formed during impact cratering include: (1) frictional heating, (2) shock loading, (3) decompression or (4) drainage of impact melt into target rocks. In order to differentiate among these processes, we conducted detailed geochemical and petrographic analysis of the matrices in pseudotachylitic veins and dikes and of their respective wall rocks. Our analyses indicate that the chemical compositions of matrices locally deviate significantly from their immediate wall rocks and that assimilation of wall rock has substantially modified the pseudotachylite matrix compositions in places. Variable magnitudes of assimilation can be explained by the surface area of wall rock or its fragments in contact with melt, as well as the initial temperature and cooling rate of the pseudotachylitic melt. Chemical trends observed can be explained either by admixture of an exotic melt component with immediate wall rock or by mixing of melts derived from local lithologies. Trends in the compositional deviation of centimetre to metre-wide pseudotachylite dikes from their immediate wall rocks are consistent with the presence of a primary melt component having granitoid composition akin to the average composition of Vredefort Granophyre dikes. Within veins, melt transport can be geochemically and petrographically traced for distances of centimetres to metres, with the direction of melt transport from larger pseudotachylite veins toward smaller ones and into apophyses. Sulphide and silicate mineralogy indicates that the initial temperature of pseudotachylitic melt must have been at least 1200-1700 °C. Collectively, these characteristics point to an allochthonous origin of pseudotachylitic melt. We advocate the possibility that impact melt from the initially superheated impact melt sheet contributed to the formation of pseudotachylite bodies at Vredefort.     

Richter magnitudes and site corrections using vertical component seismograms

The definition of the Richter Ml magnitude scale is in terms of seismic wave horizontal components recorded on Wood‐Anderson seismographs. However, at many seismograph sites only the vertical component is available, and at sedimentary sites horizontal components are usually significantly amplified, causing complications in the assignment of a magnitude to an earthquake. Because each earthquake can be recorded at a different subset of sites, each subset having a different combination of site amplifications, the assignment of a magnitude is dependent upon the seismograph site combination that records a particular earthquake. Although there is some amplification of the vertical component at sedimentary foundation sites, it is shown that a reduced spread of values of Ml magnitude, consistent with low amplification (bedrock) site magnitudes, can be achieved using the vertical component to compute the magnitude and adding 0.2 to adjust to the Ml magnitude scale (defined in terms of the horizontal components). This presupposes that the sites used by Richter were on bedrock; however, even if this is incorrect, it appears to be a necessary precondition for the world‐wide unification of the Richter scale along with defining the true gain of Wood‐Anderson seismographs rather than accepting the design gain of 2800. Site corrections would be smaller than those established using the horizontal components. Taking into account the use of only the vertical component in the calculation of Ml and including the 0.2 adjustment to the equivalent horizontal component derived magnitude, the expression for the calculation of magnitudes in the Victoria region becomes:

Ml = logA_z ‐ logS_z + 0.9 + logR + 0.0056Re^‐0.0013R

where A_z is the equivalent Wood‐Anderson seismograph displacement amplitude, S_z is the site amplification (vertical component) and R is the hypocentral distance.