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1.
Analysis was carried out of part of the northern North Sea to test what the presence and style of gas chimneys indicate about fluid pressure (Pf) within hydrocarbon reservoirs. Previous results suggest that broad chimneys above a trap and thin chimneys on the flanks indicate the presence of hydrocarbons, whilst thin chimneys in the crest suggest the hydrocarbons have escaped. Each type of gas chimney is usually associated with overpressure within Mesozoic reservoirs, but the water leg is hydrostatically-pressured in most Cenozoic reservoirs. This indicates: (a) gas leaking from a trap does not necessarily cause Pf to become hydrostatic; (b) overpressure may not be necessary for the expulsion of gasses through seal units to create the chimneys; (c) although gas chimneys indicate the existence of an active hydrocarbon system, their presence does not appear to indicate anything significant about present-day Pf.  相似文献   

2.
The recent moratorium on the commercial at-sea driftnet fishery for wild Irish Atlantic salmon (Salmo salar L.) attempts to halt the decline witnessed in these stocks over the past three decades. The research investigated stakeholder attitudes to the perceived effects on stock recovery, in Irish rivers and estuaries, of seal predation and seal culling. Structured interviews conducted with 10 key stakeholders during June 2007 revealed divisive attitudes and a feeling of powerlessness in relation to stock recovery, which are impeding successful management of salmon stocks. However, areas of common ground exist between stakeholders, which lay the foundation for a sustainable way forward.  相似文献   

3.
The roots of the Canadian harp seal hunt can be traced to the 16th Century. But in the mid-20th century, opposition to the commercial hunt became widespread after television images of seal pups being killed with clubs on the pack ice off the coast of Newfoundland were broadcast around the world. International conservation groups, animal welfare groups, animal rights groups, and foreign governments have been calling for the Canadian government to end the commercial seal hunt on the grounds that it is inhumane and that harvest levels are unsustainable. The Canadian government defends the traditional practices of hunting harp seals, argues that seal pelts are an important source of income for sealers, and insists that the killing methods are humane and that harvest levels are sustainable. Emotions run high on both sides of the debate. The purpose of this paper is to evaluate whether or not there is a purely economic argument for ending Canada's commercial seal hunt. The paper finds that the benefits of ending the commercial hunt exceed the costs, but not unequivocally. However, the paper argues there should be a higher criterion—the Pareto criterion—for ending the commercial hunt; that is the hunt should end only if winners compensate the losers. The paper goes on to argue that an effective way to satisfy this criterion is to introduce a system of individual transferable quotas (ITQs) and let the market reveal the value of the commercial seal hunt. In addition to many other advantages such as improving the safety and efficiency of the hunt, the ITQ market could provide a mechanism by which those willing to pay to end the hunt could do so directly to sealers thereby ensuring that the hunt is scaled back or ultimately ended only when it is economically efficient and unambiguously welfare-improving.  相似文献   

4.
In a recent article in this journal (Butterworth and Richardson. A review of animal welfare implications of the Canadian commercial seal hunt. Marine Policy 2013;38:457–469), the authors argued that “generally accepted principles of humane slaughter cannot be carried out effectively or consistently during the Canadian commercial seal hunt”. The present review purports to show that these authors' conclusions were incorrect because they were highly selective in their treatment of the information available and made no attempt to consider other perspectives. In addition, their reliance on anecdotal video sequences to support some of their points was seriously flawed since a vast proportion of these sequences failed to meet fundamental criteria of scientific rigor. The article by Butterworth and Richardson [5] failed to provide an unbiased presentation of the available data and therefore did not bring further clarity to the debate on the Canadian commercial seal hunt.  相似文献   

5.
Cap-rock seals can be divided genetically into those that fail by capillary leakage (membrane seals) and those whose capillary entry pressures are so high that seal failure preferentially occurs by fracturing and/or wedging open of faults (hydraulic seals). A given membrane seal can trap a larger oil column than gas column at shallow depths, but below a critical depth (interval), gas is more easily sealed than oil. This critical depth increases with lower API gravity, lower oil GOR and overpressured conditions (for the gas phase). These observations arise from a series of modelling studies of membrane sealing and can be conveniently represented using pressure/ depth (P/D) profiles through sealed hydrocarbon columns. P/D diagrams have been applied to the more complex situation of the membrane sealing of a gas cap underlain by an oil rim; at seal capacity, such a two-phase column will be always greater than if only oil or gas occurs below the seal.These conclusions contrast with those for hydraulic seals where the seal capacity to oil always exceeds that for gas. Moreover, a trapped two-phase column, at hydraulic seal capacity will be less than the maximum-allowed oil-only column, but more than the maximum gas-only column. Unlike membrane seals, hydraulic seal capacity should be directly related to cap-rock thickness, in addition to the magnitude of the minimum effective stress in the sealing layer and the degree of overpressure development in the sequence as a whole.Fault-related seals are effectively analogous to membrane cap-rocks which have been tilted to the angle of the fault plane. Consequently, all of the above conclusions derived for membrane cap-rocks apply to both sealing faults sensu stricto (fault plane itself seals) and juxtaposition faults (hydrocarbon trapped laterally against a juxtaposed sealing unit). The maximum-allowed two-phase column trapped by a sealing fault is greater than for equivalent oil-only and gas-only columns, but less than that predicted for a horizontal membrane cap-rock under similar conditions. Where a two-phase column is present on both sides of a sealing fault (which is at two-phase seal capacity), a deeper oil/water contact (OWC) in one fault block is associated with a deeper gas/oil contact (GOC) compared with the adjacent fault block. If the fault seal is discontinuous in the gas leg, however, the deeper OWC is accompanied by a shallower GOC, whereas a break in the fault seal in the oil leg results in a common OWC in both fault blocks, even though separate GOC's exist. Schematic P/D profiles are provided for each of the above situations from which a series of fundamental equations governing single- and two-phase cap-rock and fault seal capacities can be derived. These relationships may have significant implications for exploration prospect appraisal exercises where more meaningful estimates of differential seal capacities can be made.The membrane sealing theory developed herein assumes that all reservoirs and seals are water-wet and no hydrodynamic flow exists. The conclusions on membrane seal capacity place constraints on the migration efficiency of gas along low-permeabiligy paths at depth where fracturing, wedging open of faults and/or diffusion process may be more important. Contrary to previous assertions, it is speculated that leakage of hydrocarbons through membrane seals occurs in distinct pulses such that the seal is at or near the theoretically calculated seal capacity, once this has been initially attained.Finally, the developed seal theory and P/D profile concepts are applied to a series of development geological problems including the effects of differential depletion, and degree of aquifer support, on sealing fault leakage, and the evaluation of barriers to vertical cross-flow using RFT profiles through depleted reservoirs. It is shown that imbibition processes and dynamic effects related to active cross-flow across such barriers often preclude quantitative analysis and solution of these problems for which simulation studies are usually required.  相似文献   

6.
This study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern Barents Sea. The aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells, 7220/10-1 (Salina discovery) and 7122/7-3 (Goliat field). The washed and freeze-dried samples were characterized for grain size distributions, geochemical analyses, and mineralogical compositions. A total of 25 compaction tests (12 dry and 13 brine-saturated) were performed with a maximum effective vertical stress of 50 MPa. The laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation. The results show that the collected aggregates from Goliat field are compacted more compared to Salina discovery. The maximum and minimum compaction are measured in samples collected from Snadd and Fuglen formations, respectively. The final porosity of brine-saturated specimens varies between 5% and 22%. The ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values. The resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay. All compaction trends show higher porosity reduction than the silt fraction with 100% quartz. Comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area. A net exhumation of 950 m and 800 m is estimated at Salina and Goliat wells, respectively. The outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre-mature sedimentary basin in terms of exploration and production, and also for geological CO2 storage sites. The experimental results may provide information for well log and seismic interpretation, basin modeling and seal integrity of investigated horizons.  相似文献   

7.
Hybrid beds, the deposits of sediment gravity flows that show evidence for more than one flow regime (turbulent, transitional and/or laminar), have been recognized as important components of submarine lobe deposits. A wide range of hybrid bed types have been documented, however, quantitative analysis of the stratigraphic and geographic distribution of these enigmatic bed types is rare. Here, extensive exposures integrated with research borehole data from Unit A of the Laingsburg Formation and Fan 4 of the Skoorsteenberg Formation, Ecca Group, South Africa, provide the opportunity to examine geographical and stratigraphic patterns over a range of hierarchical scales.For this purpose, >23,000 individual beds have been evaluated for deposit type and bed thickness. On average, hybrid beds make up < 5% of all events and <10% of the cumulative thickness. Lobe complex 1 (LC1) of Fan 4,Skoorsteenberg Formation, preserves a prominent geographical trend of hybrid beds becoming more prevalent towards the frontal fringes of a lobe complex (up to 33.2% of beds), whereas their proportion in proximal and medial lobe complex settings is <10%.Data from Unit A, Laingsburg Formation, show hybrid beds are less common in the basal (A.1) and top (A.6) subunits compared to A.2-A.5 in both core data sets. The bases and tops of some lobe complexes (A.2, A.3 and A.5.7) are observed to be slightly enriched in hybrid beds, whereas others (A.5.1, A.5.5 and A.6.1) show no hybrid beds in their bases, which does not conform to expected allogenically-driven distributions that predict more hybrid beds during the initiation of lobe complexes. Instead, the occurrence and distribution of hybrid beds in lobe complexes are interpreted to be controlled by autogenic processes, including flow transformation processes on the basin-floor meaning enrichment in frontal lobe fringe settings. Therefore, the 1D distribution of hybrid beds in lobe complexes reflects the dominant stacking pattern of lobes within a lobe complex, with enrichment at the base and top of lobe complexes due to overall progradational to retrogradational stacking patterns. Individual lobes show a wide range of hybrid bed distributions, due to stacking patterns of the component lobe elements. These findings highlight the importance of autogenic processes rather than allogenic controls in the distribution of hybrid beds, which has implications for reservoir evaluation and the assessment of lobe stacking patterns in 1D core data sets.  相似文献   

8.
The sedimentary sequence in the Western Black Sea region of Turkey both onshore and offshore offers many possibilities for different hydrocarbon plays. This study presents a new play, which considers Carboniferous coals and shales as source beds, Cretaceous sandstones as reservoirs and Cretaceous shales and marls as seal rocks. The evaluation of this play is performed using the petroleum system approach. Results suggest that the coals and shales have a good to very good source rock potential for gas, that the Cretaceous synrift sandstones are good reservoirs. On the other hand, the sealing efficiency of respective Cretaceous units is assumed to be sufficient based on their lithological (shales and carbonaceous marls) characteristics. Stratigraphic traps, which formed by transgression and by onlap on paleohighs, were sealed and potentially available at 97 million years (ma) before present. Structural traps related to Early Cretaceous extension were also sealed around 97 ma. On the contrary, traps formed by folding and thrusting during the Alpine orogeny only formed during the last 50 ma. The timing of gas generation and migration was determined by one and two-dimensional basin modeling in one well and along a cross-section. The modeling results indicated that during the period between 90 and 42 ma, large volumes of gas were generated from the Carboniferous source rocks. Comparison with the age of stratigraphic and structural traps showed that stratigraphic and normal fault traps were potentially available for the entire volume of generated gas and that the other structural traps associated with Alpine orogeny were available only for gas generated and/or re-migrated during the last 50 ma. The evaluation of this new play results in the conclusion, that the Western Black Sea region is worthy of further exploration for conventional accumulations of thermogenic gas.  相似文献   

9.
The Canadian seal hunt is the world's largest commercial slaughter of marine mammals and, as such, has been the subject of veterinary scrutiny for half a century. In that time, veterinary experts have made multiple recommendations to improve welfare at the seal hunt, some of which have been included in Canadian sealing regulations. Yet analysis of video material and studies on the outcomes of the hunt suggest that the potential for suffering during the hunt continues, and may, in fact, be increasing. In the past decade, numerous countries have taken action to prohibit their trade in products of commercial seal hunts in response to public concerns about the welfare of the seals. With these actions now being examined at the World Trade Organization, it is important to determine if these concerns are warranted. This paper reviews relevant veterinary science, exploring the intrinsic elements of commercial sealing and unique physical adaptations of seals that prevent effective and consistent application of humane slaughter methods at the seal hunt. The review of available data indicates that generally accepted principles of humane slaughter cannot be carried out effectively or consistently in the commercial seal hunt.  相似文献   

10.
The surface areas of 12 subtidal seagrass Zostera muelleri beds at the islands and adjacent mainland shores of the eastern Bay of Islands (35° 12′ S, 174° 10′ E), New Zealand were estimated from aerial images. It appears that little subtidal seagrass existed until after the early-1950s, so significant beds here may be a relatively recent biome. Possible explanations for recent emergence of subtidal seagrass include that debilitating periods of turbid water and pulses of sedimentation associated with the land clearances of the late 1800s had worked through the marine ecosystem. An overall peak in seagrass-cover in the 1960s to 1980s was followed by declines in several beds in the 1990s to 2000s, with recovery since. The temporal presence of seagrass was well-correlated among the three mainland beds, and moderately well among the south-facing beds on the islands, consistent with mechanisms driving seagrass establishment and persistence operating at reasonably broad scales.  相似文献   

11.
Experimental erosion of North Pacific red clay   总被引：1，自引：0，他引：1  
Threshold erosion velocities for plane beds of pelagic red clay were established by ten experimental runs in a recirculating salt-water flume. Even with water content as high as 82%, observable erosion of the sediment required a velocity equivalent to a bottom current of about 30 cm/sec. Sediment beds to which manganese nodules were added, simulating an abyssal nodule field, were eroded by much slower flows (e.g., by the equivalent of a 12 cm/sec current at 84% water content). These experimentally derived values may be useful approximations of critical current speeds on the deep-sea floor, though very slow erosion may well occur there at lower speeds, especially in the presence of benthic fauna.  相似文献   

12.
Due to a lack of borehole data, reservoir and seal rock presence in frontier basins is typically inferred from seismic reflection data. However, analysis of the geometry and kinematic development of polygonal fault systems (PFS), which almost exclusively form within very fine-grained strata, provides another, largely untested method to infer reservoir and seal rock presence. We here use very high-quality 3D seismic reflection data from offshore Uruguay and a range of quantitative GIS-based techniques to document the planform and cross-sectional characteristics of a basin-scale (>6400 km2) PFS, and to investigate the role that stratigraphic variations in the Tertiary deep-water host-rock have on its geometrical variability and kinematic development. We demonstrate that a series of likely sandstone-rich deep-water deposits occur at the base of and within the main PFS tier. The geometric characteristics and throw distribution on individual polygonal faults suggest these sandstone-rich deep-water deposits represent a mechanical barrier to fault propagation, thus influencing fault height and areal density and, in some cases, strike. We argue that in largely unexplored, deep-to ultra-deep water basins, such as those characterizing offshore Uruguay, the distribution and geometric attributes of PFS can be used to delineate sandstone-rich reservoir bodies. Furthermore, these characteristics may help exploration geoscientists better understand seal heterogeneity and quality in data-poor basins.  相似文献   

13.
This study documents the stratigraphic and palaeogeographic distribution of hybrid event beds that comprise both debris-flow (cohesive) and turbidity current (non-cohesive) deposits. This is the first study of such beds in a submarine fan system to combine outcrop and research borehole control, and uses a dataset from the Skoorsteenberg Formation of the Tanqua depocentre in the Karoo Basin, South Africa. Three types of 0.1–1.0 m thick hybrid beds are observed, which have a basal weakly graded fine-grained sandstone turbidite division overlain by a division of variable composition that can comprise 1) poorly sorted carbonaceous-rich material supported by a mud-rich and micaceous sand-matrix; 2) poorly sorted mudstone clasts in a mud-rich sand-silt matrix; or 3) gravel-grade, rounded mudstone clasts in a well sorted (mud-poor) sandstone matrix. These upper divisions are interpreted respectively as: 1) the deposit of a debris-flow most likely derived from shelf-edge collapse; 2) the deposit of a debris flow, most likely developed through flow transformation from turbidity current that eroded a muddy substrate; and 3) from a turbidity current with mudstone clasts transported towards the rear of the flow. All three hybrid bed types are found concentrated at the fringes of lobes that were deposited during fan initiation and growth. The basinward stepping of successive lobes means that the hybrid beds are concentrated at the base of stratigraphic successions in medial and distal fan settings. Hybrid beds are absent in proximal fan positions, and rare and thin in landward-stepping lobes deposited during fan retreat. This distribution is interpreted to reflect the enhanced amounts of erosion and availability of mud along the transport route during early lowstands of sea level. Therefore, hybrid beds can be used to indicate a fan fringe setting, infer lobe stacking patterns, and have a sequence stratigraphic significance.  相似文献   

14.
Controversies over the origin of globally distributed Cretaceous red beds have mainly focused on climate vs. weathering with potential hydrothermal influence. In comparison to Cretaceous Oceanic Red Beds, Cretaceous lacustrine red beds exhibit chronological inconsistencies and their diverse tectonic settings suggest differing genetic mechanisms. In this paper, Early Cretaceous red beds in the North Yellow Sea Basin, one of Mesozoic rift basins in eastern China that are associated with multi-phase magmatic activities, was chosen to document potential hydrothermal impact. Geological and geochemical analyses show that these red beds were syndepositional products developed in shallow to moderately deep lacustrine environments and that they were influenced by hydrothermal activity. Major and trace elements, including enhanced Al2O3-normalized Fe2O3 and Fe2O3 (total) values, Al/(Al + Fe + Mn) and (Fe + Mn)/Ti ratios, Ni-Co-Zn and Fe-Mn-(Ni + Co + Cu)*10, ∑REE-La/Yb, the concentrations of hydrothermally-related ions, invalid redox indicators of trace elements, abnormally high Fe2O3 (total) content, positive Eu anomaly, correlation of Fe2O3 (total) and Eu anomaly, and vitrinite reflectance (Ro) vs. total organic carbon (TOC), all show strong hydrothermal fluid influence and heating effects. By integrating and comparing data from previous studies, we propose a hydrothermally affected sedimentation model for Cretaceous red beds and associated sediments in magma-activated lacustrine basins, and conclude that the enriched metallic ions introduced by the hydrothermal fluids may be the most significant reason for the deposition of the red beds, and the flushed ferric ions, accompanied by hydrothermal fluid, are the main ions that are hosted inside hematite causing the red sediment. This model can be applied to similar lacustrine basins that experience strong magmatic activity.  相似文献   

15.
Studies on migration pathways remain qualitative, albeit extensive quantification of migration forcing. In this study, hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the Third Member of Eocene Shahejie Formation in the Dongying Depression, Bohai Bay Basin, eastern China, on the basis of their lithofacies and physical properties, spatial relationships, and data availability; secondary migration conduits are then quantified. A carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals. The carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration. A method of quantifying sandstone carrier units using common physical properties is developed. First, a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes. Second, physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory. Third, the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit. Last, the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters. The results for sandstone carrier units in the Third Member of the Shahejie Formation are used in numerical models addressing Pleistocene secondary migration. The model results explain the discovered accumulation and hydrocarbon shows well; and the model predictions on exploration targets have been confirmed by drilling.  相似文献   

16.
The deposits of subaqueous sediment gravity flows can show evidence for abrupt and/or progressive changes in flow behaviour making them hard to ascribe to a single flow type (e.g. turbidity currents, debris flows). Those showing evidence for transformation from poorly cohesive and essentially turbulent flows to increasingly cohesive deposition with suppressed turbulence ‘at a point’ are particularly common. They are here grouped as hybrid sediment gravity flow deposits and are recognised as key components in the lateral and distal reaches of many deep-water fan and basin plain sheet systems. Hybrid event beds contain up to five internal divisions: argillaceous and commonly mud clast-bearing sandstones (linked debrite, H3) overlie either banded sandstones (transitional flow deposits, H2) and/or structureless sandstones (high-density turbidity currents, H1), recording longitudinal and/or lateral heterogeneity in flow structure and the development of turbulent, transitional and laminar flow behaviour in different parts of the same flow. Many hybrid event beds are capped by a relatively thin, well-structured and graded sand–mud couplet (trailing low-density turbulent cloud H4 and mud suspension fallout H5). Progressive bed aggradation results in the deposits of the different flow components stacked vertically in the final bed. Variable vertical bed character is related to the style of up-dip flow transformations, the distance over which the flows can evolve and partition into rheological distinct sections, the extent to which different flow components mutually interact, and the rate at which the flows decelerate, reflecting position (lateral versus distal) and gradient changes. Hybrid beds may inherit their structure from the original failure, with turbidity currents outpacing debris flows from which they formed via partial flow transformation. Alternatively, they may form where sand-bearing turbidity currents erode sufficient substrate to force transformation of a section of the current to form a linked debris flow. The incorporation of mud clasts, their segregation in near-bed layers and their disintegration to produce clays that can dampen turbulence are inferred to be key steps in the generation of many hybrid flow deposits. The occurrence of such beds may therefore identify the presence of non-equilibrium slopes up-dip that were steep enough to promote significant flow incision. Where hybrid event beds dominate the entire distal fan stratigraphy, this implies either the system was continually out of grade in order to freight the flows with mud clasts and clays, or the failure mechanism and transport path repeatedly allowed transmission of components of the initial slumps distally. Where hybrid beds are restricted to sections representing fan initiation, or occur more sporadically within the fan deposits, this could indicate shorter episodes of disequilibrium, due to an initial phase of slope re-adjustment, or intermittent tectonically or gravity-driven surface deformation or supply variations. Alternatively, changes between conventional and hybrid event beds may record changes in the flow generation mechanism through time. Thus the vertical distribution of hybrid event beds may be diagnostic of the wider evolution of the fan systems that host them.  相似文献   

17.
Piercement structures such as hydrothermal vent complexes, pockmarks, and mud volcanoes, are found in various geological settings but are often associated with faults or other fluid-focussing features. This article aims to investigate and understand the mechanisms responsible for the formation of piercement structures in sedimentary basins and the role of strike-slip faulting as a triggering mechanism for fluidization. For this purpose four different approaches were combined: fieldwork, analogue experiments, and mathematical modeling for brittle and ductile rheologies. The results of this study may be applied to several geological settings, including the newly formed Lusi mud volcano in Indonesia (Mazzini et al., 2007).  相似文献   

18.
Species differences in sensitivity to related planar halogenated aromatic hydrocarbons (PHAH) add significant uncertainty in assessing the ecological risk to aquatic mammals. To investigate mechanisms of PHAH sensitivity in aquatic mammals, we cloned and sequenced the cDNA of Baikal seal aryl hydrocarbon receptor (AHR), an intracellular protein that initiates PHAH-mediated effects. The Baikal seal AHR cDNA has an open reading frame of 843 amino acid residues with a predicted molecular mass of 94.6 kDa. Comparison of AHR amino acid sequences indicated a high degree of sequence conservation (98%) between Baikal and harbor seals. The high conservation of AHRs between Baikal and harbor seals indicates that these seals express AHR proteins closely related structurally. In our previous report (Kim & Hahn, 2002), the dioxin-binding affinity of the harbor seal AHR was at least as high as that of the AHR from a dioxin-sensitive strain of mice, suggesting that this seal species may be sensitive to PHAH effects. This implies that Baikal seal may also be sensitive to dioxin effects.  相似文献   

19.
Seven categories of event bed (1–7) are recognised in cores from hydrocarbon fields in the outer part of the Palaeocene Forties Fan, a large mixed sand-mud, deep-water fan system in the UK and Norwegian Central North Sea. Bed Types 1, 6 and 7 resemble conventional high-density turbidite, debrite and low-density turbidite, respectively. However the cores are dominated by distinctive hybrid event beds (Types 2–5; 81% by thickness) that comprise an erosively-based graded and structureless and/or banded sandstone overlain by an argillaceous sandstone or sandy-mudstone unit containing mudstone-clasts and common carbonaceous fragments. Many of the hybrid beds are capped by a thin laminated sandstone–mudstone couplet (the deposit of a dilute wake behind the head of the turbidity current). Different types of hybrid event bed Types are defined on the basis of the ratio of sandier lower part to upper argillaceous part of the bed, and the internal structure, particularly the presence of banding. Although the argillaceous and clast-rich upper divisions could reflect post-depositional mixing, sand injection or substrate deformation, they can be shown to be dominantly primary depositional features and record both a temporal (and by implication) spatial change from turbidite to debrite deposition beneath rheologically complex hybrid flows. Where banding occurs between lower sandy and upper argillaceous divisions, the flow may have passed through a transitional flow regime. Significantly, the often soft-sediment sheared and partly sand-injected argillaceous divisions are present in cores both close to and remote from salt diapirs and hence are not a local product of remobilisation around salt-cored topography. Lateral correlations between wells establish that sandy hybrid beds (Types 2, 3S) pass down-dip and laterally into packages dominated by muddier hybrid beds (Types 3M, 4) over relatively short distances (several km). Type 5 beds have minimal or no lower sandier divisions, implying that the debritic component outran the sandier component of the flow. The Forties hybrid beds are thought to record flow transformations affecting fluidal flows following erosion and bulking with mudstone clasts and clays that suppressed near-bed turbulence and induced a change to plastic flow. Hybrid beds dominate the muddier parts of sandying-upward, muddying-upward and sandying to muddying-upward successions, interpreted to record splay growth and abandonment, overall fan progradation, and local non-uniformity effects that either delayed or promoted the onset of flow transformations. The dominance of hybrid event beds in the outer Forties Fan may reflect very rapid delivery of sand to the basin, an uneven substrate that promoted flow non-uniformity, tilting as a consequence of source area uplift and extensive inner-fan erosion to create deep fan valleys. This combination of factors could have promoted erosion and bulking, and hence transformations leading to the predominance of hybrid beds in the outer parts of the fan.  相似文献   

20.
Canada's commercial seal hunt warrants close examination in that it is the largest kill of marine mammals on earth, it exists for commercial reasons, it targets deep diving seals with unique physical adaptations, and it is conducted in a particularly remote and uncontrolled environment amidst unstable sea ice and extreme weather conditions. For these reasons, commercial sealing in Canada has been the subject of regular veterinary scrutiny for more than five decades. In that time, despite repeated recommendations and some changes to the regulations, considerable evidence continues to be presented during each new season of poor welfare outcomes for seals.To add to the discussion we (Butterworth and Richardson) (2013) [1] reviewed multiple studies on commercial sealing, government reports, trade journal articles and recommendation reports, in an attempt to answer the question of why, despite the efforts of veterinary advisors and government to improve the situation, seals continue to die in inhumane ways. In examining the available evidence, the environment in which commercial sealing occurs, and the physical adaptations of seals, the authors concluded that generally accepted principles of humane slaughter cannot be implemented effectively and consistently in the context of commercial sealing.  相似文献   

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