Luminescence dating of sediments from two sites near Anuradhapura, Sri Lanka

Previous Optical Stimulated Luminescence (OSL) investigations of irrigation features and archaeological sites in the hinterland around Anuradhapura, Sri Lanka, had observed highly heterogeneous dose distributions and apparent ages older than expected for bunds and similar constructions. These observations are consistent with utilising older sedimentary materials, which did not have their luminescence signals reset during construction. The work reported here consists of OSL measurements from two sites in the Anuradhapura region. The first is a modern bund, sampled to examine the degree of heterogeneity of the dose distributions from a control structure. Two samples were taken from within this bund, one near the top and the other just above the land surface the bund was built upon. These show dose distributions that are highly heterogeneous with apparent ages in excess of 1500 years. The third sample from this site is from the truncated land surface beneath the bund, and gives a luminescence age of 150 ± 40 years with just one much older aliquot. The second site in this work is an abandoned red-earth platform site, covered by an extensive layer of cultural deposits. A sample from the overlying deposits just above the constructed platform gives a luminescence age of 540 ± 70 years, with a homogenous dose distribution. A sample from near the top of the constructed platform gives a heterogeneous dose distribution and apparent ages up to 4000 years. The results support the inferences from earlier sampling, providing clear confirmation that platform sites contain unbleached, re-deposited sediments, with significant residual OSL ages. The OSL results from the underlying land surfaces, and from slowly accumulated abandonment layers, appear to be consistent with external age control where available and thus are to be preferred as targets for OSL dating in such geo-archaeological investigations

Evidence for an impact-induced biosphere from the δ34S signature of sulphides in the Rochechouart impact structure, France

The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralization. The sulphides can be divided into four types on the basis of their mineralogy and host rock. They range from pyrites and chalcopyrite in the underlying coherent crystalline basement to pyrites hosted in the impactites. Sulphur isotopic results show that δ34S values vary over a wide range, from -35.8‰ to +0.4‰. The highest values, δ34S -3.7‰ to +0.4‰, are recorded in the coherent basement, and likely represent a primary terrestrial sulphur reservoir. Sulphides with the lowest values, δ34S -35.8‰ to -5.2‰, are hosted within locally brecciated and displaced parautochthonous and autochthonous impactites. Intermediate δ34S values of -10.7‰ to -1.2‰ are recorded in the semi-continuous monomict lithic breccia unit, differing between carbonate-hosted sulphides and intraclastic and clastic matrix-hosted sulphides. Such variable isotope values are consistent with a biological origin, via bacterial sulphate reduction, for sulphides in the parautochthonous and autochthonous units; these minerals formed in the shallow subsurface and are probably related to the post impact hydrothermal system. The source of the sulphate is likely to have been seawater, penecontemporaneous to the impact, as inferred from the marginal marine paleogeography of the structure. In other eroded impact craters that show evidence for impact-induced hydrothermal circulation, indirect evidence for life may be sought isotopically within late-stage (≤120°C) secondary sulphides and within the shocked and brecciated basement immediately beneath the transient crater floor

Stable Isotope Studies of the Rochechouart Impact Structure: Sources of Secondary Carbonates and Sulphides within Allochthonous and Parautochthonous Impactites

Hypervelocity impacts are among the most ubiquitous processes to affect solid bodies within our solar system [1, 2]. Although they are notoriously devastating, citing responsibility for mass extinction events and global climate perturbations, impacts can also create temporary environments which are favorable for life to thrive, if there is enough water present in the target, and sufficient energy is released as heat [1, 2]. One-third of impact structures on Earth contain fossil impact-initiated hydrothermal systems, and they are therefore being explored as potential “cradles of life” on other solid planets and satellites in our solar system [1].<p></p> We are presenting a case for the evaluation of the Mesozoic Rochechouart impact structure in France as a once-habitable environment. Initial δ 13C, δ18O and δ 34S isotope data collected in 2014 from hydrothermal carbonates and sulphides within monomict lithic impact breccia, collected from a site located 7.5km from the center of the structure at Champagnac quarry, supports our hypothesis of a warm, wet environment; we also found evidence for metabolically reduced sulphate [3]. Similar mineral assemblages can be found throughout the structure, including allochthonous breccias and low to unshocked target material. In order to explore our hypothesis further, a larger sample set was collected from various lithologies within the Champagnac site containing sulphide and carbonate mineralization for δ 13C, δ18O and δ34S isotope analysis in January 2015. These results will allow us to determine the relationships between the many hydrothermal mineral assemblages within this area of the structure, and ask whether the isotopic compositions recorded in secondary sulphides and carbonates of the impactites are inherited from the target, or possibly represent colonization by thermophilic microbes during the post-impact hydrothermal period.<p></p&gt

Science, religion and sustainability in schools: outlining a teacher learning community approach.

Sustainability is a large and growing field in educational research. Existing research has explored conceptually how the science/religion dialogue might inform sustainability education. This has the potential to enrich sustainability education by acknowledging difference and better engaging students across different religions and worldviews. Fostering a multidisciplinary approach to sustainability education in schools can help create connections between science, RE, geography, economics, and history, as these all contribute to critical thinking and inform compassionate action that supports social justice. Epistemically insightful approaches to teaching and learning have the potential to support this vital dialogue and push back against compartmentalization. In this presentation, we will discuss preliminary work and findings for our pilot study with ECTs, funded by the International Network for Science and Belief in Society. Our project will assess the potential of a cross-national (England and Pakistan) teacher research community model for co-creating resources and approaches that address the above issues of the conflict model, compartmentalization and lack of understanding/confidence in the delivery of sustainability education across different curriculum subjects

Stable isotope studies of post impact hydrothermal deposits within the sub-crater environment of the Rochechouart structure

No abstract available

Stable isotope studies of post impact hydrothermal deposits within the sub-crater environment of the Rochechouart structure

No abstract available

Insights into the composition of recalcitrant organic matter from estuarine sediments using NMR spectroscopy

peer-reviewedThe full text of this article will not be available on ULIR until the embargo expires on the 24/05/2018Sediment cores (ca. 6 m) from an estuarine environment gave insights into the composition and preservation of recalcitrant organic carbon (OC) in the environment. The coring locations provided organic matter (OM) of terrestrial origin and of marine origin. Our study specifically focused on the humin (HU), the OM fraction that is most difficult to isolate and to characterize. HU fractions were compared with the total OM recovered after removal of the associated mineral colloids. Solid state and multiphase (nuclear magnetic resonance) NMR experiments were carried out on dried and swollen samples to obtain comparative information about the whole samples and the fractionated samples. The total OM associated with the clay-size fraction provided a standard that allowed differences between the fractions to be observed. The NMR data provided new insights into the molecular structures that become part of the long term C sink in sediments. The recalcitrant OC in the sediments is composed mainly of aliphatic hydrocarbon material that may be protected from, or otherwise unavailable for, degradation. Microbial peptides and carbohydrates were also shown to be important contributors to the C sink and these biomolecules may be from living biomass or preserved necromass. Lignin residues formed only a small part of the OM in the surface sediments but made a greater contribution at depth. Highly ordered components in HU (that resists swelling by dimethylsulfoxide, DMSO) play a major role in C sequestration

Temperature Dependence of Low-Lying Electronic Excitations of LaMnO_3

We report on the optical properties of undoped single crystal LaMnO_3, the parent compound of the colossal magneto-resistive manganites. Near-Normal incidence reflectance measurements are reported in the frequency range of 20-50,000 cm-1 and in the temperature range 10-300 K. The optical conductivity, s_1(w), is derived by performing a Kramers-Kronig analysis of the reflectance data. The far-infrared spectrum of s_1(w) displays the infrared active optical phonons. We observe a shift of several of the phonon to high frequencies as the temperature is lowered through the Neel temperature of the sample (T_N = 137 K). The high-frequency s_1(w) is characterized by the onset of absorption near 1.5 eV. This energy has been identified as the threshold for optical transitions across the Jahn-Teller split e_g levels. The spectral weight of this feature increases in the low-temperature state. This implies a transfer of spectral weight from the UV to the visible associated with the paramagnetic to antiferromagnetic state. We discuss the results in terms of the double exchange processes that affect the optical processes in this magnetic material.Comment: 7 pages, 5 figure

Role of Orbital Degeneracy in Double Exchange Systems

We investigate the role of orbital degeneracy in the double exchange (DE) model. In the $J_{H}\to\infty$ limit, an effective generalized ``Hubbard'' model incorporating orbital pseudospin degrees of freedom is derived. The model possesses an exact solution in one- and in infinite dimensions. In 1D, the metallic phase off ``half-filling'' is a Luttinger liquid with pseudospin-charge separation. Using the $d=\infty$ solution for our effective model, we show how many experimental observations for the well-doped ($x\simeq 0.3$) three-dimensional manganites $La_{1-x}Sr_{x}MnO_{3}$ can be qualitatively explained by invoking the role of orbital degeneracy in the DE model.Comment: 8 pages, 2 figures, submitted to Phys. Rev.