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71.
Jean-Philippe Clment Christelle Legendre Martial Caroff Herv Guillou Joseph Cotten Claire Bollinger Grard Guille 《Journal of Volcanology and Geothermal Research》2003,120(1-2):87-101
Occurrences of debris avalanche deposits newly identified in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago) are described and interpreted here. In both islands, the breccias are located within horseshoe-shaped residual calderas. In Tahiti, the epiclastic formations, up to 500 m thick, lie on the floor of the central depression and in the valley of the northwards running Papenoo River. In Ua Huka, the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast. Their thickness is ca. 100 m. A few clasts collected in the Tahitian breccias and some rocks forming their substratum have been dated (K–Ar datings) and analysed (major and trace elements, Sr–Nd isotopes) for this study. Using these data, we show that the debris avalanche(s) occurred in Tahiti Nui at the end of the growth of the shield volcano (between 570 000 and 390 000 years ago), maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera. In Ua Huka, the collapse took place nearly 3 Ma ago, between the construction of the shield volcano and that of the inner one. The southwards orientation of the caldera, like that of the neighbouring island Nuku Hiva, might reflect a preferential direction of weakness in the substratum of the central Marquesas. 相似文献
72.
Claire L. Beaney 《Quaternary International》2002,90(1)
Tunnel channels in southeast Alberta are attributed to erosion by channelized, subglacial meltwater flows. An anabranching tunnel channel network dissects the preglacial drainage divide of the ancestral Milk River. Channel morphology and landform associations are used to evaluate competing hypotheses of tunnel channel formation. Mechanisms that invoke subaerial channel incision, direct glacial erosion or steady state, time-transgressive erosion at the ice margin cannot explain convex-up longitudinal channel profiles, anabranching channel networks or confinement to the preglacial drainage divide. Results conclude that the tunnel channel network in southeast Alberta represents late-stage erosion by a channelised subglacial flow of catastrophic dimensions. Interpretations for this tunnel channel network are in agreement with conclusions obtained for the regional subglacial landform assemblage. 相似文献
73.
Jacq Kévin Ployon Estelle Rapuc William Blanchet Claire Pignol Cécile Coquin Didier Fanget Bernard 《Journal of Paleolimnology》2021,66(3):249-260
Journal of Paleolimnology - Images of sediment cores are often acquired to preserve primary color information, before such profiles are altered by subsequent sampling and destructive analyses. In... 相似文献
74.
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We present the first demonstration of hydraulic tomography (HT) to estimate the three-dimensional (3D) hydraulic conductivity (K) distribution of a fractured aquifer at high-resolution field scale (HRFS), including the fracture network and connectivity through it. We invert drawdown data collected from packer-isolated borehole intervals during 42 pumping tests in a wellfield at the former Naval Air Warfare Center, West Trenton, New Jersey, in the Newark Basin. Five additional tests were reserved for a quality check of HT results. We used an equivalent porous medium forward model and geostatistical inversion to estimate 3D K at high resolution (K blocks <1 m3), using no strict assumptions about K variability or fracture statistics. The resulting 3D K estimate ranges from approximately 0.1 (highest-K fractures) to approximately 10−13 m/s (unfractured mudstone). Important estimated features include: (1) a highly fractured zone (HFZ) consisting of a sequence of high-K bedding-plane fractures; (2) a low-K zone that disrupts the HFZ; (3) several secondary fractures of limited extent; and (4) regions of very low-K rock matrix. The 3D K estimate explains complex drawdown behavior observed in the field. Drawdown tracing and particle tracking simulations reveal a 3D fracture network within the estimated K distribution, and connectivity routes through the network. Model fit is best in the shallower part of the wellfield, with high density of observations and tests. The capabilities of HT demonstrated for 3D fractured aquifer characterization at HRFS may support improved in situ remediation for contaminant source zones, and applications in mining, repository assessment, or geotechnical engineering. 相似文献
76.
Catherine O. de Burgh-Day Claire M. Spillman Craig Stevens Oscar Alves Graham Rickard 《新西兰海洋与淡水研究杂志》2019,53(2):201-221
We present a first assessment of the Sea Surface Temperature (SST) and 300m Heat Content (HC) ensemble mean skill of the Australian Community Climate and Earth-System Simulator-Seasonal v1.0 (ACCESS-S1) around New Zealand on seasonal timescales, using a set of retrospective ensemble forecasts for 1990-2012. This was verified against Reynolds AVHRR analysis and Bluelink ReANalysis 3.5 (BRAN3.5). For inshore areas with depth <300m, the model shows skill forecasting for summer at a lead time of 0 months, with 66% and 65% of model grid cells having correlation coefficients exceeding 0.6 for SST and 300m HC respectively. Regions of lower skill seem to be associated with the model representation of the complex and variable frontal systems around New Zealand, and an overly-strong response to the El Niño Southern-Oscillation (ENSO). Nevertheless, the skill of ACCESS-S1 around New Zealand suggests there is potential for the development of useful seasonal forecast products for the region. 相似文献
77.
Geological surveys of Australia’s marine territory have revealed significant potential for development of a marine resource industry. As onshore mineral deposits become harder to find, less accessible to their market and more challenging to extract, seafloor exploration and mining becomes an economically viable option. However, evidence from industry and environmental literature suggests that social acceptance will be important in determining the future of this industry in Australia. This paper reports on findings from research investigating the social viability of seafloor mining in Australia. A combination of interviews and focus groups were used to explore industry and community reactions to the possible development of seafloor mining in Australia. Although stakeholders’ reactions were variable, the majority of the participants were reluctant to see development of seafloor mining in Australia, primarily because of concerns about the industry’s potential environmental impact. All stakeholders sought further information about the benefits and costs associated with the industry suggesting that they did not yet have a fixed attitude towards the industry. Stakeholders favoured a precautionary approach towards the industry, supported by rigorous scientific analysis of the potential environmental impacts, transparent and socially responsive management processes and meaningful engagement with stakeholders. 相似文献
78.
Claire Chaïrat Eric H. Oelkers Jacques Schott 《Geochimica et cosmochimica acta》2007,71(24):5888-5900
The surface chemistry of fluorapatite in aqueous solution was investigated using electrokinetic techniques, potentiometric titrations, solubility measurements, and attenuated total reflection infrared spectroscopy. All methods indicate the formation of Ca/F depleted, P enriched altered layer via exchange reactions between H+ and Ca2+, and OH− and F− at the fluorapatite (FAP) surface. Observations suggest that this leached layer has a di-calcium phosphate (CaHPO4) composition and that it controls the apparent solubility of FAP. Electrokinetic measurements yield an iso-electric point value of 1 ± 0.5 consistent with a negatively charged FAP surface at pH > 1. In contrast, surface titrations give an apparent pH of point of zero charge of ∼7.7, consistent with a positively charged surface at pH < 7.7. These differences are shown to stem from proton consumption by both proton exchange and dissolution reactions at the FAP surface. After taking account for these effects, FAP surface charge is shown to be negative to at least pH 4 by surface titration analysis. 相似文献
79.
Richard V. Lacouture Jacqueline M. Johnson Claire Buchanan Harold G. Marshall 《Estuaries and Coasts》2006,29(4):598-616
A Phytoplankton Index of Biotic Integrity (P-IBI) was developed from data collected during 18 yr 91985–2002) of the Chesapeake
Bay Water Quality Monitoring Program. Dissolved inorganic nitrogen (DIN), orthophosphate (PO4), and Secchi depth were used to characterize phytoplankton habitat conditions. Low DIN and PO4 concentrations and high Secchi depths characterized least-impaire conditions. Thirty-eight phytoplankton metrics were tested
for their ability to discriminate between impaired and least-impaired habitat conditions. Twelve discriminatory metrics were
chosen, and different combinations of these twelve metrics were scored and used to create phytoplankton community indexes
for spring and summer in the four salinity regimes in Chesapeake Bay. The scoring criteria for each metric were based on the
distribution of the metric’s values in least-impaired conditions relative to the distribution in impaired conditions. An independent
data set and jackknife validation procedure were used to examine P-IBI performance. The P-IBI correctly classified 70.0–84.4%
of the impaired and least-impaired samples, grouped by season and salinity, in the calibration data set. The P-IBI is a management
tool to assess phytoplankton community status relative to estuarine nutrient and light conditions. 相似文献
80.