Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

The sulphur content of coal is an important consideration when developing reserves for exploitation, driven by emission limits from power stations becoming more stringent. Variations in the sulphur content of Westphalian A and B coals from the predominantly freshwater Northumberland Coalfield, Northeast England, were studied according to their regional, stratigraphic and in-seam location. The observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas, with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine-influenced. A model of basinal surface water and groundwater flow driven by post-depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal. However, the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the North Pennine Orefield along the southern margin of the coalfield, suggesting an additional potential source of secondary sulphur, as sulphur-rich fluids were expelled northwards through the coal measures during early Permian Variscan transpression from the south. The Westphalian A and B are interpreted as third-order depositional sequences, defined by third-order maximum flooding surfaces. Each sequence is made up of several coal-bearing fourth-order parasequences, which tend to be more brackish to marine in character, on either side of the third-order maximum flooding surfaces when base level was relatively high. The lowest sulphur coals are confined to the lower to middle, relative low stand part of the Westphalian A third-order base level curve and the lowest part of the Westphalian B third-order base level curve. This difference is attributed to a more rapid rise of base level in the Westphalian B. The stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations.     

The use of ultra-sound in the preparation of carbonate and clay sediments for chironomid analysis

Initial investigations of Holocene carbonate sediment from Hawes Water, Northwest England, yielded lower numbers of chironomid head capsules than anticipated. Standard techniques used to prepare sediment for chironomid analysis were ineffective in breaking up the coarse crystalline sediment structure sufficiently. This led to large amounts of sediment being retained and increased sample processing times. The low yield of head capsules also meant that more sediment was needed to produce adequate numbers of head capsules for analysis. The use of ultra-sound as part of the sediment processing was investigated. This technique reduced the amount of sediment left for sorting and yielded significantly more head capsules which were of equivalent structural condition and cleaner than those produced by conventional methods. The technique was extended to clay samples where similar results were obtained although shorter treatment times are recommended. The proportion of Tanytarsini and Tanypodinae heads increased significantly in carbonate and clay samples, respectively; both sediment types showed a significant decline in the proportion of Chironomini. The results indicate that ultra-sonic preparation of samples will yield a more accurate representation of chironomid assemblages in sediments leading to greater sensitivity and reliability in analysing past environmental conditions.     

Metamorphic consequences of crustal eclogite production in overthrust orogenic zones

Continental collision can produce crust of much greater than normal thickness in whose lower part eclogite facies conditions may pertain. The resulting density increase of ca. 0.3 Mg m^?3 greatly decreases the buoyancy forces normally regarded as inhibiting the subduction of continental material. The high-density phase may persist for tens of millions of years giving anomalously low surface elevation of the thickened continent and inhibiting erosion.Temperature relaxation in the overthrust pile produces regional metamorphism. The conditions of metamorphism are analysed in terms of varying initial thermal gradient, erosion rate constant and the presence or absence of the eclogite transition. The suite of recorded metamorphic P-T conditions, called the piezothermic array has a slope which is insensitive to the variable conditions. High-temperature metamorphic rocks can be produced either by high initial thermal gradient or by relatively slow erosion of eclogite-weighted crust: to distinguish these causes, details of the chronology of metamorphic recrystallization are required.     

Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites

In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolated olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.     

Apparent stress and stress drop for intraplate earthquakes and tectonic stress in the plates

The magnitude of shear stress in the lithosphere is bounded from below by the apparent stress and stress drop during intraplate earthquakes. Apparent stresses and stress drops for a number of mid-plate earthquakes are calculated from the earthquake magnitude, SH wave amplitude spectra, and estimates of the length of the fault zone. Apparent stresses vary between 0.1 and 2 bars, ifm _b is used as a measure of seismic energy, and stress drops lie between 2 and 70 bars. There is no systematic difference in either apparent stress or stress drop between these intraplate events and typical plate boundary earthquakes. These bounds on intraplate shear stresses are consistent with the inference from current models of plate tectonic driving forces that regional stress differences in the plates are typically on the order of 100 bars. The highest stress drops measured for midplate earthquakes under this model represent nearly total release of local tectonic stress.     

Rotation of the Iberian arc: Palaeomagnetic results from North Spain

NRM directions measured from 32 sites in Middle Cambrian, Upper Silurian/Lower Devonian and Lower Carboniferous redbeds follow the trend of the Variscan arc in North Spain. Thermal demagnetisation does not significantly alter this pattern. Fold tests show that the NRM is earlier than the ?₁ folds which form the arc; consistency of angle between bedding and the tilt-corrected NRM inclination (22–28°), similarity of the corresponding palaeolatitudes to Carboniferous values and microscopic evidence of Variscan redistribution of hematite indicates that the magnetisation is post-Lower Carboniferous. A statistical plot of the orientation of ?₁ fold traces against angle between ?₁ fold traces and declination of NRM shows that where these folds curve through 165° the NRM has been rotated through 110°: the arc is an orocline. Restoration of this rotation, and that needed to close the Bay of Biscay, brings the calculated mean palaeomagnetic pole reasonably close to the Upper Carboniferous part of the apparent polar wander path for Europe.     

Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin

The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre‐drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO₃^?] < 0.5 mg/L; [SO₄^2?] < 2.5 mg/L). However, no significant relationship exists between methane and iron [Fe(II)], which is traditionally considered an indicator of conditions that have progressed through iron reduction. As shown in previous studies, water type is significantly correlated with natural methane concentrations, where sodium (Na) ‐rich waters exhibit significantly higher (p<0.001) natural methane concentrations than calcium (Ca)‐rich waters. For water wells exhibiting Na‐rich waters and/or low nitrate and low sulfate conditions, valley locations are associated with higher methane concentrations than upland topography. Consequently, we identify three factors (“Low NO₃^? & SO₄^2?” redox condition, Na‐rich water type, and valley location), which, in combination, offer strong predictive power regarding the natural occurrence of high methane concentrations. Samples exhibiting these three factors have a median methane concentration of 10,000 µg/L. These heuristic relationships may facilitate the design of pre‐drill monitoring programs and the subsequent evaluation of post‐drill monitoring results to help distinguish between naturally occurring methane and methane originating from anthropogenic sources or migration pathways.     

The use of selected genotoxicity assays in green-lipped mussels (Perna viridis): a validation study in Hong Kong coastal waters

In Hong Kong, discharges of domestic and industrial wastewaters and disposal of contaminated muds into coastal waters have resulted in high levels of persistent organic contaminants in the water column, biota and bottom sediments. Although the acute toxicity of effluents has been tested by government regulators using mortality-based bioassays, the sublethal effects of many of the pollutants, including environmental carcinogens, have not been well studied. The objective of the present work was to examine the efficiency and efficacy of using: (1) DNA strand breaks (comet assay and alkaline agarose gel electrophoresis assay); (2) oxidative DNA damage (levels of 8-hydroxy-2-deoxyguanosine in cellular DNA) and (3) micronuclei (MN) formation as early warning toxicological indicators of potential environmental carcinogen exposure. Green-lipped mussels (Perna viridis) were transplanted to study sites and retrieved after 4, 8, 12, 16 and 30 days. The bioaccumulation of organic pollutants, including the polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OC pesticides) and polychlorinated biphenyls (PCBs) was observed, and compared with biomarker assays. Some significant dose- and time-dependent inductions of the genotoxic biomarkers, including 8-OHdG, DNA strand breaks and micronuclei were observed. In particular, several very strong (r>0.9) and significantly positive relationships were found at all sites during days 0-12. In addition, significant strong relationships between certain organic contaminants (carcinogenic PAHs and 4 common OC pesticides) and micronuclei were detected at the polluted sites, Tsim Sha Tsui and Sai Wan Ho. The results suggest that the use of micronuclei as a biomarker is potentially effective, especially at the more polluted sites. Nonetheless, further research is required to validate their effectiveness under varying field conditions, especially to elucidate responses under lower contaminant loads, interactions between the environmental and physiological factors affecting organisms in differing coastal environments, and changes in biotransformation and DNA repair enzymes in test organisms.