Sediment magnetic properties reveal holocene climate change along the Minnesota prairie-forest ecotone

We propose a model that explains variations in magnetic parameters of lake sediments as a record of Holocene climate change. Our model is based on records from 4 lakes and incorporates the effects of erosion, dust deposition, and the authigenesis and diagenesis of the magnetic component of the sediment. Once checked against high resolution multi proxy climate records, which are currently being established for some of our study sites, it will allow us to use magnetic proxies to establish high-resolution climate reconstructions on a regional scale.Our model utilizes a combination of concentration-dependent parameters (magnetic susceptibility, IRM) and grain-size-dependent parameters (ARM/IRM, hysteresis parameters). Magnetic mineralogy is characterized by a combination of low-temperature measurements and S-ratios, and our magnetic measurements are complemented by XRD, LOI and smearslide analyses.During periods of forest growth within the watershed, deposition of terrigenous material is low and the sediment magnetic properties are characterized by low concentrations of mainly authigenic minerals (low values of IRM, high ratios of ARM/IRM). During the early to mid-Holocene dry period, deposition of terrigenous material increased due to intensified dust deposition and the erosion of lake margins caused by lowered water levels. Concentration of magnetic minerals increases (high IRM, ) and so does the grain-size of the magnetic fraction (low ARM/IRM). During the late-Holocene, sediment magnetic properties depend on the varied position of the site with respect to the prairie–forest ecotone.     

Identification of perylene in sediments: Occurrence and diagenetic evolution

Perylene and penta-aromatic hydrocarbons were determined in sediments as part of a study that was dedicated to the aquatic ecosystem of Elelenwo Creek (Southern Nigeria) in order to carry out a critical corroboration of occurrence and diagenetic evolution of perylene in the sediments of the creek. The results show that the annual mean levels of Benzo [g, h, i] Perylene ranged from 209.00–245.28 ?g/kg dry weight at the various stations sampled. Meanwhile, Station 3 recorded the highest mean level of 245.28 ?g/kg dry weight. The observed values for total penta-aromatic hydrocarbons were high (787.00–1154.36?g/kg dry weight) in all the stations sampled. In addition, the highest mean value of 1154.36?g/kg dry weight was again recorded at station 3 for the penta-aromatic hydrocarbons. One origin index or concentration ratio of Ip/Ip+BghiP was also used to evaluate the suitability of the penta-aromatic hydrocarbons as a tracer to distinguish between contaminations arising from different sources. The values for the sampling stations therefore ranged from 0.41 to 0.43. A critical appraisal of the PAH index, consequently, suggested that petroleum combustion is the major penta-aromatic hydrocarbon source in sediments of the creek. The PAH group profile shows that perylene was high in the sediments and would pose apparent effects in fauna. The high concentration of perylene in the sediments was also indicative of an in situ biogenic derivation. Furthermore, a concentration of perylene > 10 % of total penta-aromatic hydrocarbons established a credible diagenetic origin.     

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation.     

Space, place and pollbooks: incorporating a neglected electoral geography

Summary This paper calls for the incorporation of pre-1872 (and especially early Victorian) elections into the electoral geography research agenda. It argues that early Victorian elections provide a rare opportunity to examine actual voting behaviour at the individual level and also constitute a valid focus of enquiry in their own right. The paper concludes by discussing some of the principal methodological implications of an historical electoral geography.     

Shocked quartz in polymict impact breccia from the Upper Cretaceous Yallalie impact structure in Western Australia

Yallalie is a ~12 km diameter circular structure located ~200 km north of Perth, Australia. Previous studies have proposed that the buried structure is a complex impact crater based on geophysical data. Allochthonous breccia exposed near the structure has previously been interpreted as proximal impact ejecta; however, no diagnostic indicators of shock metamorphism have been found. Here we report multiple (27) shocked quartz grains containing planar fractures (PFs) and planar deformation features (PDFs) in the breccia. The PFs occur in up to five sets per grain, while the PDFs occur in up to four sets per grain. Universal stage measurements of all 27 shocked quartz grains confirms that the planar microstructures occur in known crystallographic orientations in quartz corresponding to shock compression from 5 to 20 GPa. Proximity to the buried structure (~4 km) and occurrence of shocked quartz indicates that the breccia represents either primary or reworked ejecta. Ejecta distribution simulated using iSALE hydrocode predicts the same distribution of shock levels at the site as those found in the breccia, which supports a primary ejecta interpretation, although local reworking cannot be excluded. The Yallalie impact event is stratigraphically constrained to have occurred in the interval from 89.8 to 83.6 Ma based on the occurrence of Coniacian clasts in the breccia and undisturbed overlying Santonian to Campanian sedimentary rocks. Yallalie is thus the first confirmed Upper Cretaceous impact structure in Australia.     

Precipitation of heavy metals in produced water: influence on contaminant transport and toxicity

Produced water undergoes changes in its physical chemistry including precipitation of heavy metals after being discharged and mixed with ambient seawater. Potential impacts of the precipitation of heavy metals on their transport and toxicity were studied using samples from offshore oil production sites on the Scotian Shelf off eastern Canada. Concentrations of aluminum, cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel and zinc were measured in total, particulate and dissolved fractions together with Microtox tests for assessment of toxicity. Heavy metals in produced water were transformed from dissolved to particulate phase in a period of hours under oxygenated conditions, and aggregated to larger particles that settle rapidly (>100 m/day) over a few days. In addition, there was production of buoyant particles comprised of heavy metal precipitates sequestered onto oil droplets that were transported to the surface. The particulate fraction was generally more toxic than the dissolved fraction. This was evident at the mixing interface between produced water and seawater where elevated particulate and toxicity levels were observed. Laboratory studies suggest an increase in the toxicity of discharged produced water over time. Time-series experiments showed a sustained toxic response for more than a week following the oxidation of freshly discharged produced water that initially elicited little or no toxic response in the Microtox test. Chemical processes identified in this study, namely precipitation of heavy metals and consequent settling and rising fluxes of particles, will influence the toxicity, the fate and the transport of potential contaminants in the produced water. Therefore, these processes need to be considered in assessment of the environmental impact associated with offshore oil and gas operations.     

Measuring Urban Sustainability: the potential and pitfalls of city rankings

Measuring the sustainability of a city, and ranking the city against other cities, is increasingly seen as a way to achieve urban sustainability. A number of studies have highlighted how Sydney is unsustainable, with two recent ranking exercises appearing to confirm these findings by placing Sydney below many other Australian cities for urban sustainability. These two exercises are situated within international moves towards ranking cities. The article explores the assumptions and criteria used by Mercer in its Eco-City Index and the Australian Conservation Foundation in its Sustainable Cities Index. The conclusion discusses how Sydney could become more sustainable, and identifies why normative urban sustainability rankings should be recognised for their potential while simultaneously being treated with caution.     

Is C/O enhanced in NGC 253?

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.