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Publication History View all

  • Curator: The Museum Journal. 05/2010; 18(2):140 - 147.
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    ABSTRACT: Palaeospinax (Lower Jurassic) is the oldest euselachian known from articulated remains, and has certain structural similarities with ctenacanths. Euselachians may therefore have evolved from ctenacanth fishes and not from hybodonts. Nemacanthus Agassiz 1837 (Triassic), known only from finspines, is closely allied to Palaeospinax and may represent an immediate ancestor.
    Zoological Journal of the Linnean Society 06/2008; 60(3):259 - 273.
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    ABSTRACT: Detailed sampling of two sections of Turonian-aged Chalk from southeast England for foraminifera has revealed that cyclical abundance changes in many species and genera were mediated by orbitally induced climatic cycles. These cycles can be used for high-resolution stratigraphic correlation of the two sections and as a possible means of re-estimating the duration of the Turonian period.
    Terra Nova 06/2007; 1(5):426 - 431.
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    ABSTRACT: There is a correlation between variations in the clay mineral assemblages of the Crackington Formation (Upper Carboniferous) shales in parts of Devon, and the soil series mapped in the same areas. The differences in soil-forming characteristics of the shales are not due to mineralogy alone, but to various states of diagenetic induration which they have achieved. Brown earths (Dunsford series) are formed on steeper slopes of more durable, illite-chlorite dominated shales, whereas clayey soils (Tedburn and Halstow series) are typical of flatter, more poorly drained slopes of weaker illite and illite-kaolinite clay mineral assemblages. This result adds the geological component to earlier views that the different soil series are simply a consequence of physiographic and hydrologic position.
    European Journal of Soil Science 07/2006; 35(4):599 - 606.
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    ABSTRACT: The Carnmenellis granite is one of seven Variscan plutons exposed in SW England which intrude a folded and thrusted succession of metasedimentary and metavolcanic rocks of Devonian and Carboniferous age. The granite contains higher than average radionuclide concentrations which give rise to enhanced heat flow and fracture-controlled, low enthalpy hydrothermal circulation. Measurements of4He in soil gas have been made at 91 sites over the pluton and the surrounding host rocks, in order to assess variation of4He emanation in relation to the distribution of radionuclides and the groundwater circulation system. The pattern of variation obtained shows little correlation with the results of an airborne total gamma-ray activity survey, but agrees well with the distribution of4He in spring waters. Because the occurrence of zones of high4He concentration in these spring waters shows a significant correlation with local variations of heat flow within the pluton, it is believed that the distribution of upwelling limbs of groundwater circulation cells controls the groundwater4He flux. The spatial association of high values of4He in soil gas with high values in spring waters thus suggests that fracture-controlled groundwater circulation systems can be mapped using the soil gas method, even in the absence of springs. However, the variation of4He concentrations in soil gas is more complex than that given by spring waters. This is due to variation in soil moisture content affecting the pore space concentration of4He. Nevertheless, resolution of this effect is possible by statistical analysis of the4He distribution.
    Applied Geochemistry. 01/1987;
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    ABSTRACT: Most grabs and corers are inadequate for sampling the sediment-water surface, yet this is a key area for the study of fine-grained sediment and meiofauna. This device was designed specifically to sample the top 1 cm of sediment. The sampling mechanism comprises a scoop which cuts 1 cm deep over an area of 100 cm2 and then seals itself against a closure plate. There is no loss of material through washing during the passage of the sampler to the deck of the ship. It weighs 70 kg, can be used from small boats or research ships, operates in all depths of water, and under wind conditions up to force 9.
    Marine Geology - MAR GEOLOGY. 01/1987; 76:313-317.
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    ABSTRACT: Techniques established as most successful in the examination of widely variable but mainly oxidised geological materials require separation and isolation of components prior to analysis. These methods reduce the number of variables involved in the production of clastic debris and enable conclusions to be drawn from a practical reversal of rock manufacture. Alkali metals prove successful as indicators of the surficial processes operative during Permo-Triassic times. They demonstrate enrichment by igneous material during early breccia production, and subsequent dilution by wider sedimentation in basins to the east of Cornubia, England.Alkalis in Recent soils, river, estuarine and beach sediments of southwest England are concentrated in the fine-grained (< 2 μm) fraction. Soils developed over Permo-Triassic bedrock, modern river, estuarine sediments, and beach sands, all show anomalous enrichment of trace alkali metals. They reflect the abundance of Li, Rb and Cs in parent material.Geochemical analyses of clays from deep boreholes in the Wessex and Central Somerset Basins enable inter-basin comparisons with the high-alkali deposits of Devon. Absolute trace alkali levels are broadly similar to those of correlated beds at outcrop. Concentrations of Cs prove higher in the Upper Permian than in the Triassic of the Wessex Basin, whilst values show Devonian (Old Red Sandstone) sediments to be un-enriched in Li and Cs. Enrichment of Li over Rb in Triassic Mercia Mudstones of the south Devon coast suggests some Li capture from sabkha brines by clays during evaporite production.
    Chemical Geology. 07/1986;
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    ABSTRACT: To investigate the control on small-scale variation of He in soil gas exercised by minor fracturing, shallow surveys have been carried out over a cave system formed along an approximately orthogonal set of fractures in Devonian limestone in southwest England. The possibilities that He variation could be related to deep-seated, major fractures or hidden mineralisation, and that other soil gases may also be affected by minor fracturing were assessed by contemporary surveys for CO2 and O2. Comparisons of soil gas values with variations in electrical apparent resistivity were also carried out. Location of fractures with direct connection to the cave system was determined by spiking the cave atmosphere with He and then resurveying after equilibration.The results for CO2 and O2 show anomalies of low magnitude (with respect to atmospheric concentrations), and although they display an antithetic relationship, this is generally poor. There is also no strong correlation with the results of the He surveys either before or after spiking, or with the apparent resistivity values. Moreover, anomalies in CO2 + O2 do not support the pattern of variation shown by the individual gases. These negative results suggest the absence of deep-seated fractures or hidden mineralisation, and show that CO2 and O2 values are independent of minor fracturing. The origin of the variation is attributed to bacteriological productivity.He soil gas concentrations were obtained as disequilibrium values relative to Field Atmospheric Air (ΔHe/ppb-FAA). Positive ΔHe values were generally found to correlate with areas of thin, dry soil cover, enhancement occurring along fracture lines. Negative ΔHe values were also found to correlate with fracture lines, but in these areas the fractures are overlain by a thick soil cover with a high moisture content. It is considered that distinctions can be drawn between water-conducting and dry fractures, and that negative ΔHe values are likely only to be encountered with shallow soil gas samples. Results of spiking with He show a clear distribution of enhanced values along the set of orthogonal fractures, irrespective of the sign of the natural He anomaly. It is considered, therefore, that major deep-seated fractures may result in positive He anomalies superimposed upon negative ΔHe values. This implies that He anomalies must always be related to a local datum value. It is concluded that resolution of interacting variables in the interpretation of soil gas data is facilitated by integrated soil gas surveys.
    Journal of Geochemical Exploration - J GEOCHEM EXPLOR. 01/1985; 24(1):29-49.
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    ABSTRACT: Interpretation of textures of lithium-mica granites in the Cornubian batholith based upon the inclusion principle and instances where one mineral clearly invests another leads to a chronology of textural evolution as follows. (1) Magmatic crystallization of small quartz grains followed by two alkali feldspars and, in some instances, by lepidolite. (2) Late magmatic growth of feldspars, especially K-feldspar, leading into post-magmatic growth and inclusion of marginal quartz and albite, along with almost complete exsolution of both feldspars. These events are believed to result from water-rock interaction. (3) Post-magmatic growth of zinnwaldite (often by the replacement of feldspar), tourmaline and topaz. Topaz growth along grain boundaries between feldspars and feldspar and quartz is related to F release which is associated with the removal of alkali from the granites and marked local alkali and F metasomatism in the pelitic contact hornfelses. These textures of ‘fresh’ granites grade into those associated with greisenization and it is suggested that there may be a complete continuum between magma and magmatic crystallization on the one hand and the evolution of a saline hydrothermal fluid that initiated an early stage of greisenization on the other.
    Proceedings of the Geologists Association 01/1984; 95(1):29-41.
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    ABSTRACT: The plateau deposits of East Devon contain a variety of residual deposits including non-indurated kaolinitic weathering profiles and silcretes. These reflect a complex pedological, diagenetic and geomorphological history which began with the emergence of the post-Chalk land surface at the end of the Cretaceous. During the Palaeocene, lateritic weathering of the Chalk led to the formation of kaolinitic residual flint gravels which are up to 10 m thick over much of the East Devon tableland. These deposits show a variety of deep weathering profile morphology, but well differentiated lateritic weathering profiles are preserved in irregular deep pockets on Chalk. Where resting directly on Albian sediments the residual gravels are thought to represent the response of earlier profiles developed on Chalk to continued pedogenesis and diagenesis once the Chalk had been completely removed. Locally, late silicification of the weathering profile formed silicretes. Cenomanian-Albian calcarenites and arenites have been decalcified and kaolinised to considerable depths beneath the gravels where a protective Chalk capping is absent.In areas adjacent to the Sticklepath-Lustleigh Fault Zone destruction of the Palaeocene weathering mantle was accomplished by late Middle Eocene times when new weathering profiles were established on newly exposed Upper Palaeozoic rocks. These younger profiles were subsequently eroded and redeposited in deep tectonic basins along major wrench fault zones. This phase of erosion and sedimentation was accompanied by a climatic change which is reflected by changes in profile morphology and clay mineralogy with time. The oldest Palaeocene profiles are mature, took >107 years to form and developed in a tropical climate, whereas profiles dating from the Lower Eocene onwards are immature, took ≈106 years to form and developed in a sub-tropical to temperate climate.
    Proceedings of the Geologists' Association. 01/1983;
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