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21.
Appalachian Deep Core Hole 2 (ADCOH-2) penetrated part of one of the most persistent and important tectonostratigraphic belts in the southern Appalachians—the Brevard-Chauga belt in South Carolina. The Brevard-Chauga belt is a subdivision of the Inner Piedmont and it includes the Brevard fault zone. The 307 m core contains four imbricated slices of Early Ordovician Henderson Gneiss and metasedimentary rocks of the Chauga River Formation. Aqueous (NaCl–CaCl2) inclusions and CO2–CH4-rich inclusions present in syntectonic quartz veins in the metasedimentary units, together with garnet-biotite geothermometry, provide information on the P-T conditions during uplift. Garnet-biotite geothermometry in the Brevard metasiltstone indicates a crystallization temperature of 466±52 °C, which together with published 40Ar/39Ar hornblende data from the Chauga belt, are interpreted as a Neoacadian (late Devonian) garnet crystallization age. High-density CO2-rich fluid inclusion isochores indicate a pressure of 4.5 kbar at 466±52 °C at this time. A Rb–Sr muscovite model age of 302 Ma in retrograde mylonitic Henderson Gneiss is interpreted as an Alleghanian recrystallization age. Fluid inclusions record a 2.5 kbar decompression event at this time, consistent with thrust assembly of the tectonostratigraphic units in the core. 相似文献
22.
Kieran F. Mulchrone 《Mathematical Geology》2007,39(7):647-655
Geological materials are largely heterogeneous and are typically comprised of approximately ellipsoidal objects immersed in
a matrix with different physical properties. Methodologies for the identification of ancient regional tectonic patterns may
be developed based on an understanding of the behaviour of heterogeneous materials. In this contribution, the differential
equation governing the rotation of a deformable ellipse immersed in a viscous fluid is considered and is found to contain
a singularity when the ellipse becomes circular in shape. This problem is avoided by reformulating the equations using the
standard algebraic representation of an ellipse. Thus, the equations can be numerically solved without difficulty. 相似文献
23.
Yaser A. Hafez Rod D. Davies Richard J. Davis Clive Dickinson Elia S. Battistelli Francisco Blanco Kieran Cleary Thomas Franzen Ricardo Genova-Santos Keith Grainge Michael P. Hobson Michael E. Jones Katy Lancaster Anthony N. Lasenby Carmen P. Padilla-Torres José Alberto Rubiño-Martin Rafael Rebolo Richard D. E. Saunders Paul F. Scott Angela C. Taylor David Titterington Marco Tucci Robert A. Watson 《Monthly notices of the Royal Astronomical Society》2008,388(4):1775-1786
Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr−1 over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr−1 . A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr−1 over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°. 相似文献
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr
24.
We present early to Mid‐Holocene paleo‐geographic reconstructions for the Ramore Head area (Northern Ireland). This coastal area is characterized by Mesolithic occupation (c. 10–6 ka) and preserved early–Mid‐Holocene peats both on‐ and offshore. This paper improves on previous reconstructions by employing a backstripping methodology, which removes accumulated recent deposits from identified buried paleo‐landsurfaces instead of using modern topography as an analogue to the past landscape. Paleo‐landsurfaces are identified offshore from seismic profiles supplemented by cores, and onshore through legacy borehole records. The paleo‐landsurface can be traced offshore to depths of −2 to −19 m and is buried by <5 m of modern sediment. It extends onshore under the coastal town of Portrush and is buried <2.5–10 m below modern ground level. The identified paleo‐landsurface is combined with sea‐level curves from recent Glacio‐Isostatic‐Adjustment models to reconstruct marine transgression during the early–Mid‐Holocene. Comparison is also made with reconstructions based on modern topography. Together, the identified paleo‐landsurfaces and revised reconstructions can assist future site prospection on‐ and offshore and delimit high‐potential areas for heritage management. Revised reconstructions also allow placement of extant archaeology into a more accurate context of landscape change and help develop insights into local‐scale site location patterns. 相似文献
25.
Soumyajit Mukherjee Kieran F. Mulchrone 《International Journal of Earth Sciences》2012,101(7):1929-1947
The Tso Morari crystalline (TMC) gneiss dome in the Indian Himalaya extruded from a depth of?~120?km through an inclined subduction channel of sub-elliptical cross-section at the leading edge of the Indian plate. The velocity profile of this gneiss dome is derived after (1) presuming its incompressible Newtonian rheology, (2) finding the “best fit” of the outcrop of the gneiss dome to an ellipse, (3) taking into account different lithologies to have existed at the top of the extruding gneiss body, (4) considering the extrusion to have been driven by the buoyant push of the denser mantle beneath the lighter gneiss, and (5) assigning a range of plausible densities for different litho-units. Fitting the known rates of extrusion—from a few centimetres up to about one-hundredth of a millimetre per year—from?~53?Ma onwards of this gneiss dome to its velocity profile constrains its maximum possible viscosity to?~7.5?×?1022 Pa?s. This magnitude is?102–104 times higher than previous estimates for gneisses and granites. Alternative explanations of our data are the following: (1) There was a fall in extrusion rates of the TMC gneiss from 53?to?<30?Ma because of an increase in the estimated maximum viscosity from 6.2?×?1020 to 7.5?×?1022 Pa?s, possibly indicating a fall in temperature and/or compositional change of the TMC gneiss. (2) Lower the extrusion rates, higher are the estimated viscosities. (3) The TMC gneiss was more viscous probably due to its eclogite content. (4) The estimated maximum viscosity is?~102 times higher than that in collision zones and?102–104 times than that in the Tibetan lower crust, but broadly conforms to that for the crustal channel, and average lithospheric and asthenospheric values. The high magnitude of maximum possible Prandtl number of?~1028 of the TMC gneiss might be related to isothermal decompression of the gneiss during its extrusion. 相似文献
26.
Kieran M. Baker Simon H. Bottrell Steven F. Thornton Kate E. Peel Michael J. Spence 《Applied Geochemistry》2012
The availability of dissolved O2 can limit biodegradation of organic compounds in aquifers. Where O2 is depleted, biodegradation proceeds via anaerobic processes, including NO3-, Mn(IV)-, Fe(III)- and SO4-reduction and fermentation/methanogenesis. The environmental controls on these anaerobic processes must be understood to support implementation of management strategies such as monitored natural attenuation (MNA). In this study stable isotope analysis is used to show that the relative significance of two key anaerobic biodegradation processes (bacterial SO4 reduction (BSR) and methanogenesis) in a phenol-contaminated sandstone aquifer is sensitive to spatial and temporal changes in total dissolved phenols concentration (TPC) (= phenol + cresols + dimethylphenols) over a 5-a period. In general, 34SO4-enrichment (characteristic of bacterial SO4 reduction) is restricted spatially to locations where TPC < 2000 mg L−1. In contrast, 13C-depleted CH4 and 13C-enriched CO2 isotope compositions (characteristic of methanogenesis) were measured at TPC up to 8000 mg L−1. This is consistent with previous studies that demonstrate suppression of BSR at TPC of >500 mg L−1, and suggests that methanogenic microorganisms may have a higher tolerance for TPC in this contaminant plume. It is concluded that isotopic enrichment trends can be used to identify conditions under which in situ biodegradation may be limited by the properties of the biodegradation substrate (in this case TPC). Such data may be used to deduce the performance of MNA for contaminated groundwater in similar settings. 相似文献
27.
28.
Lauren A. Michel Thomas Lehmann Kieran P. Mcnulty Steven G. Driese Holly Dunsworth David L. Fox William E.H. Harcourt-Smith Kirsten Jenkins Daniel J. Peppe 《Sedimentology》2020,67(7):3567-3594
Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin-spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up-section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up-section, the uppermost palaeosol layer contains abundant root traces and tree-stump casts, previously reported as evidence of a closed-canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time-averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well-preserved fossil primates. 相似文献
29.
Travis G. Gerwing Kieran Cox Alyssa M. Allen Gerwing Charmaine N. Carr-Harris Sarah E. Dudas Francis Juanes 《国际泥沙研究》2018,33(2):149-156
The usefulness of the apparent redox potential discontinuity (aRPD) in assessments of marine benthic habitat quality was explored at two intertidal mudflats along the north Pacific coast of Canada. Two transects were established at each intertidal site, with three sediment biogeochemistry cores collected from each transect four times over the summer of 2016. Measurements of the sediment pore water dissolved oxygen (DO) content and redox (Eh) conditions were taken at the surface of the core (measured vertically), as well as at increasing depths (1 cm between readings) into the sediment (measured horizontally through predrilled holes in the biogeochemistry corer). While oxic, anoxic, oxidized, and reduced sediment pore water was observed above and below the aRPD, in general, sediment above the aRPD had higher DO content, and higher Eh values than sediment below the aRPD. Therefore, the aRPD depth can be used as a relative indicator of sediment pore water DO and Eh conditions: sediment with a deeper aRPD depth has more available DO, and the pore water has higher Eh values (more oxidized or less reduced) than sediment with a shallower aRPD depth. As such, the aRPD depth is a useful parameter to include in models that assess the quality of marine benthic habitats. 相似文献
30.
Diamondoids are hydrocarbons with a carbon skeleton that is superimposable on the diamond lattice. Adamantane is the cage-shaped primary unit of diamondoids and occurs widely in sediments and petroleum. The first report of adamantane isolated from petroleum extends back seven decades, but the precursors and reaction mechanisms for the formation of adamantane and related diamondoids in sediments has remained unclear. We report the formation of alkyl adamantanes by heating β-ionone with activated carbon in closed system pyrolysis experiments in the range 170-320 °C. In addition, hydrogen exchange, demethylation, methyl transfer and isomerisation reactions were observed when the model compounds adamantane and 1,3-dimethyladamantane were heated at moderate temperature with activated carbon. A reaction pathway for the formation and reactions of alkyl adamantanes is proposed on the basis of ring isomerisation of adamantane to protoadamantane on the activated carbon surface. The carbonaceous surface reactions described help account for the occurrence and distribution of alkyl adamantanes in petroleum basins, as evidenced by the strong linear relationships between compound pairs related by isomerisation and demethylation for a set of crude oils from the Carnarvon Basin, Western Australia. 相似文献