Origin of light volatile hydrocarbon gases in mud volcano fluids, Gulf of Cadiz — Evidence for multiple sources and transport mechanisms in active sedimentary wedges     

Marianne Nuzzo  Edward R.C. Hornibrook  Fiona Gill  Christian Hensen  Richard D. Pancost  Matthias Haeckel  Anja Reitz  Florian Scholz  Vitor H. Magalhes  Warner Brückmann  Luis M. Pinheiro 《Chemical Geology》2009,266(3-4):359-372

Widespread mud volcanism across the thick (≤ 14 km) seismically active sedimentary prism of the Gulf of Cadiz is driven by tectonic activity along extensive strike–slip faults and thrusts associated with the accommodation of the Africa–Eurasia convergence and building of the Arc of Gibraltar, respectively. An investigation of eleven active sites located on the Moroccan Margin and in deeper waters across the wedge showed that light volatile hydrocarbon gases vented at the mud volcanoes (MVs) have distinct, mainly thermogenic, origins. Gases of higher and lower thermal maturities are mixed at Ginsburg and Mercator MVs on the Moroccan Margin, probably because high maturity gases that are trapped beneath evaporite deposits are transported upwards at the MVs and mixed with shallower, less mature, thermogenic gases during migration. At all other sites except for the westernmost Porto MV, δ¹³C–CH₄ and δ²H–CH₄ values of ~ − 50‰ and − 200‰, respectively, suggest a common origin for methane; however, the ratio of CH₄/(C₂H₆ + C₃H₈) varies from ~ 10 to > 7000 between sites. Mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply-buried sediments, possibly associated with biodegradation of C₂₊ homologues and secondary methane production at Captain Arutyunov and Carlos Ribeiro MVs. At the deep-water Bonjardim, Olenin and Carlos Ribeiro MVs, generation of C₂₊-enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge. At Porto MV, gases are highly enriched in CH₄ having δ¹³C–CH₄ ~ − 50‰, as at most sites, but markedly lower δ²H–CH₄ values < − 250‰, suggesting that it is not generated by thermal cracking of n-alkanes but rather that it has a deep Archaeal origin. The presence of petroleum-type hydrocarbons is consistent with a thermogenic origin, and at sites where CH₄ is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments ~ 2–4 km deep. These fluids then migrate into shallower, thermally immature muds, driving their mobilization and extrusion at the seafloor. At Porto MV, the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of CH₄.  相似文献   

A late Pleistocene steppe bison (Bison priscus) partial carcass from Tsiigehtchic, Northwest Territories, Canada     

Grant D. Zazula  Glen MacKay  Thomas D. Andrews  Beth Shapiro  Brandon Letts  Fiona Brock 《Quaternary Science Reviews》2009,28(25-26):2734-2742

A partial steppe bison (Bison priscus) carcass was recovered at Tsiigehtchic, near the confluence of the Arctic Red and Mackenzie Rivers, Northwest Territories, Canada in September of 2007. The carcass includes a complete cranium with horn cores and sheaths, several complete post-cranial elements (many of which have some mummified soft tissue), intestines and a large piece of hide. A piece of metacarpal bone was subsampled and yielded an AMS radiocarbon age of 11,830 ± 45 ¹⁴C yr BP (OxA-18549). Mitochondrial DNA sequenced from a hair sample confirms that Tsiigehtchic steppe bison (Bison priscus) did not belong to the lineage that eventually gave rise to modern bison (Bison bison). This is the first radiocarbon dated Bison priscus in the Mackenzie River valley, and to our knowledge, the first reported Pleistocene mammal soft tissue remains from the glaciated regions of northern Canada. Investigation of the recovery site indicates that the steppe bison was released from the permafrost during a landslide within unconsolidated glacial outwash gravel. These data indicate that the lower Mackenzie River valley was ice free and inhabited by steppe bison by 11,800 ¹⁴C years ago. This date is important for the deglacial chronology of the Laurentide Ice Sheet and the opening of the northern portal to the Ice Free Corridor. The presence of steppe bison raises further potential for the discovery of more late Pleistocene fauna, and possibly archaeological evidence, in the region.  相似文献   

Past major tsunamis and the level of tsunami risk on the Aitape coast of Papua New Guinea     

Davies  Hugh L.  Simeon  Oliver B.  Hope  Geoffrey  Petchey  Fiona  Davies  Jocelyn M. 《Natural Hazards》2019,96(3):1019-1040

Natural Hazards - This paper reports the results of an investigation into past major tsunamis on the Aitape coast of Papua New Guinea. The investigation was mounted to gather information to help...  相似文献   

Intensity and direction of lattice-preferred orientation of olivine: are electrical and seismic anisotropies of the Australian mantle reconcilable?     

Fiona Simpson 《Earth and Planetary Science Letters》2002,203(1):535-547

It has been hypothesised that seismic and electrical anisotropy at the base of the lithosphere are caused by strain-induced lattice-preferred orientation (LPO) of olivine [100] axes parallel to present-day plate motion. This would imply that seismic and electrical anisotropy observations can provide geodynamicists with fundamental information for characterising mantle flow. The qualitative agreement between the fast direction of SV-waves and direction of maximum electrical conductance modelled deeper than 150 km below the North Central craton of Australia appear to support a common alignment mechanism, and the observed, anisotropic electrical conductances can be generated by hydrogen diffusivity in a water-poor (<1000 ppm H/Si) olivine mantle. A quantitative test is proposed for the hypothesis that electrical anisotropy is generated by anisotropic hydrogen diffusion rates (D) in olivine. Electrical anisotropy factors are computed using random resistor network models assuming that D[100]≈20×D[010]≈40×D[001]. Electrical and seismic anisotropies calculated from olivine LPO angular distribution functions modelled for a range of shear strains under a simple shear deformation demonstrate that the intensity of olivine [100] alignments (and associated shear strains) that would be required to explain the electrical anisotropy in the mantle below central Australia are significantly greater than predicted by Rayleigh wave anisotropies. The poor agreement between the observed electrical anisotropies and the electrical anisotropies that would be predicted from the Rayleigh wave anisotropies indicates that either (i) electrical anisotropy in the upper mantle below central Australia is not generated by hydrogen diffusivity alone or (ii) the seismic anisotropy is underestimated. The orientation of the olivine [100] axes maxima is inferred to be ∼30° rotated relative to the direction of present-day absolute plate motion (APM) that is determined relative to the hotspot reference frame (HS2-NUVEL1). Both the APM direction that is determined relative to a reference frame defined by requiring no-net rotation of the lithosphere (NNR-NUVEL1) and GPS-derived plate motion vectors fit the geophysical observations of upper mantle anisotropy better. This may support the contention that hotspots are not stationary relative to the deep mantle.  相似文献   

The Role of non-timber forest products as safety-nets: A review of evidence with a focus on South Africa     

Fiona Paumgarten 《GeoJournal》2005,64(3):189-197

Poor, rural communities are vulnerable to adversity. To secure their livelihoods, people adopt multiple livelihood strategies, including using non-timber forest products (NTFPs). NTFPs have been identified as important to rural livelihoods, as an alternative land-use option as well as in fulfilling an important safety-net function although empirical evidence on the latter’s strength is limited. Whilst NTFPs may contribute towards alleviating poverty, this safety-net function needs more critical and quantitative investigation. This includes the establishment of an applicable definition so this function can be communicated to policy makers and taken into account in national poverty alleviation strategies and, in attempts to promote resource-conserving behaviour by highlighting the value of natural resources (including NTFPs) compared to alternative land-use options. Poverty in rural households is complex and households are vulnerable to a range of shocks. During adversity households can turn to a range of possible safety-nets. What determines the use of NTFPs as a safety-net, how this safety-net function manifests and the strength of this function is poorly understood and there is need for further investigation.  相似文献   

Challenging a place myth: New Zealand's clean green image meets the biotechnology revolution     

Fiona Coyle  John Fairweather 《Area》2005,37(2):148-158

The 'clean green image' of New Zealand is a well-known example of what has been called a 'place myth'. But more recently, emerging alongside this place myth is an image that the government is trying to co-create of New Zealand as an innovator in biotechnology. In nationwide focus groups, whilst a matter of pride, participants typically saw this clean green myth as a temporally distant utopia. However, when considered alongside the futures proposed by biotechnology, clean green New Zealand was mobilized into the present moment to defend a general reluctance to take up these practices. Alternately, some participants saw the possibility for co-evolution of the place myths, with biotechnology enabling the re-construction of a 'picture-perfect', clean green country.  相似文献   

A first detailed look at the Greenland lithosphere and upper mantle, using Rayleigh wave tomography   总被引：2，自引：1，他引：2  

Fiona A. Darbyshire  Tine B. Larsen  Klaus Mosegaard  Trine Dahl-Jensen  Ólafur Gudmundsson  Torben Bach  Søren Gregersen  Helle A. Pedersen  Winfried Hanka 《Geophysical Journal International》2004,158(1):267-286

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A Polygenetic Landform At Stígá, Öræfajökull, Southern Iceland     

Tim Harris  Fiona S. Tweed  Óskar Knudsen 《Geografiska Annaler: Series A, Physical Geography》2004,86(2):143-154

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Climatic Control of Hydraulic Conductivity of Bahamian Limestones   总被引：1，自引：0，他引：1  

Fiona F. Whitaker  Peter L. Smart 《Ground water》1997,35(5):859-868

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Reconceptualising local community: environment, identity and threat   总被引：1，自引：0，他引：1  

Simon Dalby  Fiona Mackenzie 《Area》1997,29(2):99-108

Summary Economic 'development' driven by global economic forces produces specific expressions of 'community' in places where large new economic projects are to be located. This paper draws on contemporary geopolitical literature to theorise community identity as partly formulated in response to external 'threats'. A comparative study of community mobilisation in response to proposals to locate coastal superquarries on the Isle of Harris, Outer Hebrides, Scotland, and Cape Breton, Nova Scotia, Canada, suggests the applicability of this theoretical framework for extending geographical analysis of community identity and the politics of place.  相似文献