Australian offshore natural hydrocarbon seepage studies,a review and re-evaluation   总被引：2，自引：0，他引：2  

Graham A. Logan  Andrew T. JonesJohn M. Kennard  Georgina J. RyanNadege Rollet 《Marine and Petroleum Geology》2010

Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Early studies of natural hydrocarbon seepage around the Australian margin were generally based on the geochemical analysis of stranded bitumens, water column geochemical ‘sniffer’ sampling, synthetic aperture radar or airborne laser fluorosensor. Later studies involved the integration of these remote sensing and geochemical techniques with multi-channel and shallow seismic. A review of these earlier studies indicates that many seepage interpretations need to be re-evaluated and that previous data sets, when placed in a global context, often represent normal background hydrocarbon levels. Low Recent burial and subsidence rates are not favourable for high rates of seepage. There are also difficulties in proving seepage on high energy, shallow carbonate shelves, where seabed features may be rapidly re-worked and modern marine signatures are overprinted on authigenic seep carbonates. Thus, the relatively few sites of proven natural hydrocarbon seepage in Australia's offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting. Active thermogenic methane seepage on the Yampi Shelf, the only proven documented occurrence in Australia, is driven by deposition of a thick Late Tertiary carbonate succession and Late Miocene tectonic reactivation. Therefore, to increase the success of detecting and correctly interpreting natural hydrocarbon seepage, data need to be analysed and integrated within the context of the local geological setting, and with an understanding of what is observed globally.  相似文献   

Coronate echinoderms from the Ordovician of the Llanddowror area,South Wales     

Patrick D. McDermott  Christopher R. C. Paul 《Geological Journal》2015,50(2):173-188

A large sample of coronates (over 90 specimens) from a narrow horizon in the Upper Ordovician, Sholeshook Limestone, at Talfan Farm, Llanddowror, South Wales allows assessment of variation and growth in a population of these rare Palaeozoic echinoderms. Variation is extensive and we synonymize two previously described species. This occurrence extends the stratigraphic range of Cupulocorona rugosa Donovan and Paul down to Cautleyan, Zone 2. Internal moulds reveal new morphological features, especially of the coronal canals. The flattened blade‐like and kite‐shaped portions support the idea that the coronal canals functioned in respiratory gas exchange by increasing the surface area. We suggest that internal currents flowed up the inner (adoral) canal and down the outer (aboral) canal. Quantitative estimates of flow rate suggest that a volume of coelomic fluid equivalent to the entire body cavity could be flushed through the coronal canals in 10 seconds at most. These coronates probably lived attached by a relatively long stem with a simple, conical holdfast and bent over in gentle currents. They seem to have been characteristic of relatively high‐energy environments and are not generally distributed in the Sholeshook Limestone of South Wales. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Locating benefits: Decision-spaces, resource access and equity in US community-based forestry   总被引：1，自引：0，他引：1  

Melanie Hughes McDermott 《Geoforum》2009,40(2):249-259

In the US, the Ford Foundation’s Community-based Forestry Demonstration Program (2000-2005) promoted an internationally prominent model of community forestry centered on the simultaneous, balanced pursuit of ecological, economic and social goals (often symbolized as the “three-legged stool,” or “triple bottom line”). This paper develops an alternative framework for analysis that emphasizes the causal precedence of shifts in power relations, specifically the devolution of resource access and decision-making authority, rather than environmental, social and economic outcomes. These outcomes are not necessarily beneficial, and any benefits realized seldom occur simultaneously. Rather, they can be envisioned as the floors of a house erected sequentially on a foundation of resource access and control. While no universal claim is made, the “house” model proves an apt fit for many community-based forestry initiatives, including the two case studies presented. Who among the differentiated social groups within a community gained access to resources and decision-making influence largely predicted who gained individually. Nonetheless, indirect benefits felt at community and higher scales were significant. The findings further indicate that community forestry generally will not advance social equity unless it specifically targets marginalized groups. Crucially, equity is understood to embrace not only distributional justice, but also capacity-building and empowerment.  相似文献   

Direct Fourier transform mass spectral analysis of natural waters with low dissolved organic matter     

Rachel L. Sleighter  Georgina A. McKee  Patrick G. Hatcher 《Organic Geochemistry》2009,40(1):119-125

A major obstacle for characterizing dissolved organic matter (DOM) with ultrahigh resolution mass spectrometry has been its low concentrations in natural waters. Many previous mass spectrometric studies of both terrestrial and marine DOM typically have isolated and concentrated the DOM using solid phase C₁₈ extraction disks, ultrafiltration, or XAD resins, all of which are known to discriminate against many different classes of compounds. We have, for the first time, developed an approach to directly analyze natural water samples with less than 6 mg/l DOC (dissolved organic carbon), using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). We demonstrate the sensitivity and ability of sequential selective ion accumulation (SSIA) to detect the thousands of components in a single freshwater DOM sample without any significant pretreatment. By utilizing SSIA, the baseline noise decreases while signal to noise ratios of the peaks increase, allowing for approximately 40% more formulas to be assigned to peaks in the mass spectra.  相似文献   

Dichotomy in host environments and signs of recycled active galactic nuclei     

Georgina V. Coldwell  Diego G. Lambas  Ilona K. Söchting  Sebastián Gurovich 《Monthly notices of the Royal Astronomical Society》2009,399(1):88-96

We analyse the relation between active galactic nuclei (AGN) host properties and large-scale environment for a representative red and blue AGN host galaxy sample selected from the Data Release 4 Sloan Digital Sky Survey. A comparison is made with two carefully constructed control samples of non-active galaxies, covering the same redshift range and colour baseline. The cross-correlation functions show that the density distribution of neighbours is almost identical for blue galaxies, either active or non-active. Although active red galaxies inhabit environments less dense compared to non-active red galaxies, both reside in environments considerably denser than those of blue hosts. Moreover, the radial density profile of AGN relative to galaxy group centres is less concentrated than galaxies. This is particularly evident when comparing red AGN and non-active galaxies.
The properties of the neighbouring galaxies of blue and red AGN and non active galaxies reflect this effect. While the neighbourhood of the blue samples is indistinguishable, the red AGN environs show an excess of blue-star-forming galaxies with respect to their non-active counterpart. On the other hand, the active and non-active blue systems have similar environments but markedly different morphological distributions, showing an excess of blue early-type AGN, which are argued to be late-stage mergers. This comparison reveals that the observable differences between active red and blue host galaxy properties including star formation history and AGN activity depends on the environment within which the galaxies form and evolve.  相似文献   

Market Linkage and Spatial Monopoly in New Zealand Manufacturing   总被引：1，自引：0，他引：1  

P. J. McDermott 《New Zealand geographer》1974,30(1):1-17

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Evolution of continental crust in southern Africa     

N.B.W. Harris  C.J. Hawkesworth  P. Van Calsteren  F. McDermott 《Earth and Planetary Science Letters》1987,83(1-4)

Nd isotopic data from the Zimbabwe and Kaapvaal cratons and the Limpopo, Kalahari, Namaqualand and Damara mobile belts imply that over 50% of present-day continental crust in this region had separated from the mantle by the end of the Archaean and that< 10% of continental crust of southern Africa has formed in the last 1.0 Ga. Such a growth rate implies that average erosion rates through geological time were high and that evolution of continental crust has been dominated by crustal growth prior to 1.4 Ga, and crustal reworking since that time. The evolution of average crust is not represented directly by clastic sediment samples but may be determined from sediment analyses if both the time of orogeneses and the average erosion rate are known. Both trace element data from southern Africa granitoids and the high erosion rates implied by the isotopic study suggest that growth of continental crust in the Archaean was by underplating rather than lateral accretion, but arc accretion was the dominant mechanism after 2.0 Ga.  相似文献   

Numerical modeling of stress-permeability coupling in rough fractures   总被引：2，自引：0，他引：2  

Robert Walsh  Chris McDermott  Olaf Kolditz 《Hydrogeology Journal》2008,16(4):613-627

A numerical model is described for coupled flow and mechanical deformation in fractured rock. The mechanical response of rock joints to changes in hydraulic pressure is strongly influenced by the geometric characteristics of the joint surfaces. The concept of this work is to combine straightforward finite element solutions with complex and realistic fracture surface geometry in order to reproduce the non-linear stress-deformation-permeability coupling that is commonly observed in fractures. Building on the numerous studies that have expanded the understanding of the key parameters needed to describe natural rough-walled fractures, new methods have been developed to generate a finite element mesh representing discrete fractures with realistic rough surface geometries embedded in a rock matrix. The finite element code GeoSys/Rockflow was then used to simulate the coupled effects of hydraulic stress, mechanical stress, and surface geometry on the evolving permeability of a single discrete fracture. The modeling concept was experimentally verified against examples from the literature. Modeling results were also compared to a simple interpenetration model.  相似文献   

The effect of the East Atlantic pattern on the precipitation δ18O-NAO relationship in Europe     

L. Comas-Bru  F. McDermott  M. Werner 《Climate Dynamics》2016,47(7-8):2059-2069

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A U-series study of lavas from Kamchatka and the Aleutians: constraints on source composition and melting processes   总被引：1，自引：0，他引：1  

Simon Turner  Frank McDermott  Chris Hawkesworth  Pavel Kepezhinskas 《Contributions to Mineralogy and Petrology》1998,133(3):217-234

New data are presented for lavas from the Kamchatka Peninsula and the Aleutian arc. Radiogenic isotopes are strikingly homogeneous in the Kamchatka lavas and although incompatible trace element ratios exhibit much greater variability, much of this appears to result from shallow level, crystal fractionation. The data reveal little systematic across-arc change in radiogenic isotopes or trace element ratios. The Nd and Pb isotope data overlap those for Pacific MORB and limit the amount of sediment that could be incorporated in the mantle source region to <1% which is insufficient to account for the observed La/Ta ratios (50–68) in the high-MgO lavas. The lack of a positive correlation between La/Ta and depth to the slab suggests that melt–wall rock interaction was not important in controlling this ratio. Instead it is inferred that La/Ta increased during partial melting and that D_La/D_Ta = 0.11–0.06, possibly due to residual amphibole. Ba, U, Sr and Pb were added to the source by an aqueous fluid from the subducting slab and its inferred isotopic composition indicates that this fluid was derived from the altered oceanic crust. The addition of U resulted in a large range of (²³⁸U/²³²Th) from 0.79–2.48 similar to that observed in the Mariana and Lesser Antilles island arcs. However, (²³⁰Th/²³²Th) = 0.79–2.34, and the majority of samples lie close to the equiline indicating that the time since U/Th fractionation is generally ≥150 thousand years. The large width of the volcanic zone is assumed to reflect protracted fluid release from the subducting slab over the depth interval 170–380 km possibly coupled with extension across the Central Kamchatka Depression. The data from the Aleutians contrast strongly with those from Kamchatka. Radiogenic isotope data indicate that the Aleutian lavas contain a significant recycled sedimentary component, consistent with elevated ¹⁰Be/⁹Be ratios. The Aleutian lavas have (²³⁰Th/²³²Th) = 0.79–2.34 and exhibit a significant range of U/Th disequilibria [(²³⁸U/²³⁰Th) = 0.75–1.01]. However, ¹⁰Be/⁹Be is positively correlated with (²³⁸U/²³⁰Th) suggesting that the ¹⁰Be signal was carried by the aqueous fluid from the slab. The U/Th disequilibria for the Aleutian lavas lie close to a 30 thousand year reference line suggesting that this fluid was released from the slab ∼30 thousand years ago similar to recent estimates from the Lesser Antilles, Marianas, and Tonga-Kermadec island arcs from which it is inferred that fluid addition was the trigger for partial melting. Given that the rate of convergence in Kamchatka is similar to that in the Aleutians, Marianas and Tonga-Kermadec the inferred greater time since␣fluid release in Kamchatka requires further investigation. Received: 24 September 1997 / Accepted: 7 July 1998  相似文献