71 research outputs found

    Gnosticism in Lawrence Durrell’s Monsieur: New Textual Evidence for Source Materials

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    Previous scholarship on source materials for Lawrence Durrell’s Gnostic themes in Monsieur are insufficient in light of his marginalia in Serge Hutin’s Les Gnostiques and his notebooks for the novel. We contend that archival evidence from the Bibliothèque Lawrence Durrell in Nanterre, France, necessitates a reevaluation of previous work in order to account for the combination of Hutin’s approach to Gnosticism and newspaper clippings in the notebook, which recast the nature of the Gnostic suicide cult that provides the impetus for the plot of the novel

    Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

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    Atmospheric methane from episodic gas hydrate (GH) destabilization, the "clathrate gun" hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ~0.9 km depth only ~1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ~290–300 m ~6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed >255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ~1.0 Myr ago and ~4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where IBP is sufficiently thick, both IBP and GHs persist even where inundated by a Holocene sea level rise and both are also expected to persist into the next glacial even if atmospheric CO<sub>2</sub> doubles. We do not address the "clathrate gun" hypothesis directly, but our models show that sub-IBP GHs respond to, rather than cause GST changes, due to both how GST changes propagates with depth and latent heat effects. Models show that many thick GH accumulations are prevented from contributing methane to the atmosphere, because they are almost certainly trapped below either ice-filled IBP or lithological barriers. Where permafrost is sufficiently thick, combinations of geological structure, thermal processes and material properties make sub-IBP GHs unlikely sources for significant atmospheric methane fluxes. Our sub-IBP GH model histories suggest that similar models applied to other GH settings could improve the understanding of GHs and their potential to affect climate

    Freshwater Seepage Into Sediments of the Shelf, Shelf Edge, and Continental Slope of the Canadian Beaufort Sea

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    Long‐term warming of the continental shelf of the Canadian Beaufort Sea caused by the transgression associated with the last deglaciation may be causing decomposition of relict offshore subsea permafrost and gas hydrates. To evaluate this possibility, pore waters from 118 sediment cores up to 7.3‐m long were taken on the shelf and slope and analyzed for chloride concentrations and δ180 and δD composition. We observed downcore decreases in pore waters Cl− concentration in sediments from all sites from the inner shelf (<20‐m water depth), from the shelf edge, from the outer slope (down to 1,000‐m water depths), and from localized shelf features such as midshelf pingo‐like features and inner shelf pockmarks. In contrast, pore water freshening is absent from all investigated cores of the Mackenzie Trough. Downcore pore waters Cl− concentration decreases indicate regional widespread freshwater seepage. Extrapolations to zero Cl− of pore water Cl− versus δ180 regression lines indicate that freshwaters in these environments carry different isotope signatures and thus are sourced from different reservoirs. These isotopic signatures indicate that freshening of shelf sediments pore waters is a result of downward infiltration of Mackenzie River water, freshening of shelf edge sediments is due to relict submarine permafrost degradation or gas hydrate decomposition under the shelf, and freshening of slope sediments is consistent with regional groundwater flow and submarine groundwater discharge as far as 150 km from shore. These results confirm ongoing decomposition of offshore permafrost and suggest extensive current groundwater discharge far from the coast

    A method of evaluating psychomotor tooth preparation skills in preclinical dental programs

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    Preclinical and clinical tooth important and significant aspect of preparation is an a dental student's education. The associated procedures rely heavily on the development of particular psychomotor skills. The most common format of instruction and evaluation in tooth preparation at many Dental Faculties, emphasizes the product (tooth preparation) and associates performance with characteristics of this product. This integrated study examines which skills should be developed and how a course of instruction can best be structured to develop the necessary skills. The skills which are identified are those necessary for tooth preparation are selected from a psychomotor taxonomy. The purpose of evaluating these skills is identified. Behavioral objectives are set for student performance and the advisability of establishing standards of performance is examined. After reviewing studies related to learning strategy for dental psychomotor the most suitable tasks as well as articles on instructor effectiveness a model is proposed. A pilot project at the University of Toronto, based on this proposed model is described. The paper concludes wi th a discussion of the implications of this proposed model

    Models of Talik, Permafrost and Gas Hydrate Histories—Beaufort Mackenzie Basin, Canada

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    Models of talik, permafrost and gas hydrate (GH) histories below shallow lakes are investigated and compared to models of Beaufort Mackenzie Basin (BMB) GH occurrences to describe lacustrine inundation effects, which are compared against factors controlling the variations among Mackenzie Delta (MD) permafrost, GH and talik occurrence. Models using a 2–4 °C boundary temperature range indicate that geological setting, specifically underlying lithology and porosity, are the primary controls in talik formation below lakes. Below a lake of any size, where the underlying lithology is sandy it is practically impossible to produce a pervasive talik or to completely degrade significant GH accumulations in response to the boundary condition thermal effects alone. Models predict that talik formation is, in such cases, restricted to the upper few tens of meters below the lake. Permafrost degradation appears common where porosities are &lt;40% and water bottom temperatures reach 2–4 °C, in both marine and lacustrine settings. Where porosities are higher a thin GH stability zone can persist, even where deep taliks have formed

    Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins

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    We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial) and anthropogenic (climate change) forcing. Our models focus on the interval beginning three million years ago (i.e., Late Pliocene-Holocene). They continue through the current interglacial and they are projected to its anticipated natural end. During the current interglacial the gas hydrate stability zone (GHSZ) thickness in each region responded uniquely as a function of changes in water depth and sea bottom temperature influenced by ocean currents. In general, the GHSZ in the deeper parts of the Pacific and Atlantic margins (≥1316 m) thinned primarily due to increased water bottom temperatures. The GHSZ is highly variable in the shallower settings on the same margins (~400–500 m). On the Pacific Margin shallow GH dissociated completely prior to nine thousand years ago but the effects of subsequent sea level rise reestablished a persistent, thin GHSZ. On the Atlantic Margin Scotian Shelf the warm Gulf Stream caused GHSZ to disappear completely, whereas in shallow water depths offshore Labrador the combination of the cool Labrador Current and sea level rise increased the GHSZ. If future ocean bottom temperatures remain constant, these general characteristics will persist until the current interglacial ends. If the sea bottom warms, possibly in response to global climate change, there could be a significant reduction to complete loss of GH stability, especially on the shallow parts of the continental shelf. The interglacial GH thinning rates constrain rates at which carbon can be transferred between the GH reservoir and the atmosphere-ocean system. Marine GH can destabilize much more quickly than sub-permafrost terrestrial GHs and this combined with the immense marine GH reservoir suggests that GH have the potential to affect the climate-ocean system. Our models show that GH stability reacts quickly to water column pressure effects but slowly to sea bottom temperature changes. Therefore it is likely that marine GH destabilization was rapid and progressive in response to the pressure effects of glacial eustatic sea level fall. This suggests against a catastrophic GH auto-cyclic control on glacial-interglacial climate intervals. It is computationally possible but, unfortunately in no way verifiably, to analyze the interactions and impacts that marine GHs had prior to the current interglacial because of uncertainties in temperature and pressure history constraints. Thus we have the capability, but no confidence that we can contribute currently to questions regarding the relationships among climate, glacio-eustatic sea level fluctuations and marine GH stability without improved local temperature and water column histories. We infer that the possibility for a GH control on climate or oceanic cycles is speculative, but qualitatively contrary to our model results

    An assessment of tight oil resource potential in Upper Cretaceous Cardium Formation, Western Canada Sedimentary Basin

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    The Cardium Formation “halo oil” occurs either in the fringe of, or between, existing conventional discrete sandstone reservoirs. It is commonly associated with conventional oil and gas pools in stratigraphic traps. This paper uses a geological model-based simulation approach to assess Cardium “halo oil” resource potential. The geological model-based approach consists of a geological model, a resource model and a stochastic modeling procedure that extracts essential information regarding the richness and spatial characteristics of oil resources from various data sources using statistical methods. It integrates them with the geological and resource models, respectively, to estimate the resource potential. This approach predicts not only the resource potential, but also the resource spatial distribution and the exploration risk. These outcomes provide critical information for exploration decision-making. Cardium “halo-oil” assessment results indicate a mean total oil in-place (conventional and unconventional) of 4.6×109 m3 and a mean undiscovered “halo oil” in-place of 2.9×109 m3. Using current technology and economic constraints the undiscovered recoverable “halo oil” in this tight formation is 0.11×109 m3. This represents <4% of the remaining in-place oil resource, but it accounts for 38% of the total recoverable Cardium oil. A comparison with resource estimates obtained using a well-performance approach that is based on production data extrapolations from stimulated horizontal wells suggests that the mean recoverable estimate obtained using the two different approaches are similar, suggesting that the geological model-based approach provides a reliable oil resource potential estimate. Key words: unconventional, Halo oil pool, stochastic simulation, resource assessmen
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