A case study of the internal structures of gossans and weathering processes in the Iberian Pyrite Belt using magnetic fabrics and paleomagnetic dating

In the Rio Tinto district of the Iberian Pryrite Belt of South Spain, the weathering of massive sulfide bodies form iron caps, i.e., true gossans and their subsequent alteration and re-sedimentation has resulted in iron terraces, i.e., displaced gossans. To study the stucture and evolution of both types of gossans, magnetic investigations have been carried out with two foci: (1) the characterisation and spatial distribution of magnetic fabrics in different mineralised settings, including massive sulfides, gossans, and terraces, and (2) paleomagnetic dating. Hematite has been identified as the suceptibility carrier in all sites and magnetic fabric investigation of four gossans reveals a vertical variation from top to bottom, with: (1) a horizontal foliation refered to as “mature” fabric in the uppermost part of the primary gossans, (2) highly inclined or vertical foliation interpreted as “immature” fabric between the uppermost and lowermost parts, and (3) a vertical foliation interpreted to be inherited from Hercynian deformation in the lowermost part of the profiles. In terraces, a horizontal foliation dominates and is interpreted to be a “sedimentary” fabric. Rock magnetic studies of gossan samples have identified goethite as the magnetic remanence carrier for the low-temperature component, showing either a single direction close to the present Earth field (PEF) direction or random directions. Maghemite, hematite, and occasionally magnetite are the remanence carriers for the stable high-temperature component that is characterized by non PEF directions with both normal and reversed magnetic polarities. No reliable conclusion can be yet be drawn on the timing of terrace magnetization due to the small number of samples. In gossans, the polarity is reversed in the upper part and normal in the lower part. This vertical distribution with a negative reversal test suggests remanence formation during two distinct periods. Remanence in the upper parts of the gossans is older than in the lower parts, indicating that the alteration proceeded from top to bottom of the profiles. In the upper part, the older age and the horizontal “mature” fabric is interpreted to be a high maturation stage of massive sulfides’ alteration. In the lower part, the age is younger and the inherited “imature” vertical Hercynian fabric indicates a weak maturation stage. These two distinct periods may reflect changes of paleoclimate, erosion, and/or tectonic motion.     

Modelling grazed grassland systems: wether sheep grazing perennial ryegrass

A simple model or a lowland sheep flock grazing a ryegrass sward is described, which incorporates herbage growth and deterioration; the mechanics of grazing, herbage intake and animal production. The model takes into account the effects of climate, the availability of water and nitrogen and the frequency and intensity of defoliation on herbage production; diet selection by the grazing animal; the effects of herbage digestibility and animal body weight on intake; and the fate of the organic matter ingested by the ruminant. Preliminary results comparing continuous and rotational grazing systems and different levels of nitrogen fertilizer application are discussed. Some possible areas for further applied research are also outlined.     

A luminescence‐based chronology for the Harletz loess sequence,Bulgaria

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.     

A photohabitable zone in the martian snowpack? A laboratory and radiative-transfer study of dusty water-ice snow

Dusty water-ice snowpacks on Mars may provide a habitable zone for DNA based photosynthetic life. Previous work has over estimated the depths and thicknesses of such photohabitable zones by not considering the effect of red dust within the snowpack. For the summer solar solstice, at 80°N and a surface albedo of 0.45, there is a calculated photohabitable zone in the snowpack between depths of 5.5 and 7.5 cm. For an albedo of 0.62, there is a calculated photohabitable zone in the snowpack between depths of 8 and 11 cm. A coupled atmosphere-snow radiative-transfer model was set to model the Photosynthetic Active Radiation and DNA dose rates through water-ice snow at the north polar region of Mars. The optical properties of the polar caps were determined by creating a laboratory analogue to the Mars north polar deposits, and directly measuring light penetration and albedo. It is important for future exobiology missions to the polar regions of Mars to consider the implications of these findings, as drilling to depths of ∼11 cm should be sufficient to determine whether life exists within the martian snows, whether it is photosynthetic or otherwise, as at this depth the snow cover will provide a permanent protection from DNA damaging UV radiation.     

The Cosmic Origins Spectrograph: on-orbit instrument performance

The Cosmic Origins Spectrograph (COS) was installed in the Hubble Space Telescope in May, 2009 as part of Servicing Mission 4 to provide high sensitivity, medium and low resolution spectroscopy at far- and near-ultraviolet wavelengths (FUV, NUV). COS is the most sensitive FUV/NUV spectrograph flown to date, spanning the wavelength range from 900 Å to 3200 Å with peak effective area approaching 3000 cm². This paper describes instrument design, the results of the Servicing Mission Orbital Verification (SMOV), and the ongoing performance monitoring program.     

Fish recruitment into a South African temporarily open/closed temperate estuary during three different hydrological mouth phases

Quantitative recruitment of ichthyofauna into a South African temporarily open/closed estuary (TOCE) was investigated during three distinct hydrological phases: closed overwash, open outflow and tidal mouth conditions. Maximum recruitment densities occurred during outflow conditions and declined when the system became tidally inundated. Recruitment densities were lowest during overwash events. Selective diel variation was evident, with higher night-time densities for each phase. This study highlights the importance of seasonal timing and duration of open conditions and overwash events for structuring ichthyofaunal community composition of southern African TOCEs.     

华南、华北地块中生代构造演化与超高压变质岩的折返机制

本文在讨论中国东部现有构造演化模式基础上，着重从华北与华南地块之间板块尺度的动力学过程剖析秦岭－大别中生代造山带构造演化，以及大别－苏鲁超高压变质地体的形成和折返过程。晚二叠世－中三叠世华南地块向华北地块持续挤压，陆壳大规模俯冲导致超高压变质作用的产生，而华北地块在晚三叠世至早侏罗世发生快速逆时针旋转，使得这一地区上地幔深度的超高压变质地体快速折返至下地壳。由于超高压变质地体侵位后，地壳结构、构造的差异，在南北地块的进一步挤压下，造成中国东部晚侏罗世－早白垩世郯庐断裂带的巨大左行剪切。     

The geology of ordovician rocks at Balbriggan,County Dublin,Eire

A thick series of Caradocian volcanics is described. The volcanics are basic-intermediate and it is own that they have a number of characteristics which are peculiar to emplacement in a subaqueous environment. A new interpretation of the stratigraphy results from a consideration of the folding of the succession.