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381.
Richard A. Watson Herbert E. Wright Jr. 《Boreas: An International Journal of Quaternary Research》1980,9(3):153-162
Formal Chronostratigraphic Units are defined in the International Stratigraphic Guide on the basis of boundary stratotypes and then extended globally as isochronous units. They are unrealistic for application to late-Quaternary history, which involves events that are demonstrably time-transgressive owing to measurable lags between the causative force and the geologic response. Natural geologic time units that are diachronous globally are preferred because they represent events identifiable in the stratigraphic record. A similar objection is raised against formal Chronostratigraphy for the pre-Quaternary: recognizable biostratigraphic or lithostratigraphic units on which the geologic time scale has been built are diachronous globally, for they depend on slow evolutionary or tectonic processes. The imposition of Chronostratigraphic Units that are unrecognizable stratigraphically at a distance away from the type locality introduces an unnecessary terminology in the efforts of stratigraphers to econstruct the geologic history. 相似文献
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383.
J. B. Wright 《Geophysical Journal International》1968,16(2):161-167
The correlation between reversed polarity in rocks and strong oxidation of magnetic minerals is briefly re-examined, with especial reference to a well-documented Columbia Plateau basalt suite, recently described in this journal. The correlation appears to vary in quality from place to place and some reasons for this are suggested. Attention is particularly drawn to recent studies which suggest that for palaeomagnetic purposes there may be two groups of lavas, divisible on the basis of whether their magnetic minerals became oxidized under high or low temperature conditions.
A sizable body of opinion now holds (not necessarily correctly) that self-reversals are a negligible factor in the correlation between oxidation and reversed polarity, and that some compositional effect is most probably involved. Virtually the only known petrographic criterion which can (statistically) distinguish reversely from normally magnetized rocks is their (statistically) higher oxidation states. An obvious implication is that the water content of magmas, and perhaps of high-grade metamorphic rocks, is somehow increased during episodes of reversed polarity, so that a slightly larger proportion of rocks is more strongly oxidized.
Since motions of the Earth's core, upper mantle processes, and field reversals are apparently all related, compositional changes originating in the upper mantle could well be also related to field reversals. Alternating linear zones of more and less altered baslat recently reported from one place near the mid-Atlantic ridge might have arisen in such a way.
The importance of relating palaeomagnetic measurements to detailed mineralogical studies of magnetic minerals is again stressed. 相似文献
A sizable body of opinion now holds (not necessarily correctly) that self-reversals are a negligible factor in the correlation between oxidation and reversed polarity, and that some compositional effect is most probably involved. Virtually the only known petrographic criterion which can (statistically) distinguish reversely from normally magnetized rocks is their (statistically) higher oxidation states. An obvious implication is that the water content of magmas, and perhaps of high-grade metamorphic rocks, is somehow increased during episodes of reversed polarity, so that a slightly larger proportion of rocks is more strongly oxidized.
Since motions of the Earth's core, upper mantle processes, and field reversals are apparently all related, compositional changes originating in the upper mantle could well be also related to field reversals. Alternating linear zones of more and less altered baslat recently reported from one place near the mid-Atlantic ridge might have arisen in such a way.
The importance of relating palaeomagnetic measurements to detailed mineralogical studies of magnetic minerals is again stressed. 相似文献
384.
C. A. Wright 《Australian Journal of Earth Sciences》2013,60(5-6):269-277
Micropalaeontological investigation of samples from Scott Reef No. 1 has revealed a thick Cainozoic carbonate sequence. Rich planktonic faunas have enabled the identification of Lower Miocene to Oligocene (N6 to P19) and Lower Eocene to Lower Palaeocene intervals (P6 to Pic). The remainder of the succession has been dated on benthonic evidence and spot age‐determinations on isolated planktonic occurrences. The palaeoenvironmental history of the Cainozoic sequence appears to be regressive from a bathyal situation in the Palaeocene through indeterminate marine Eocene, bathyal to inner shelf Oligocene to Middle Miocene, to reefal conditions which have persisted from the Middle Miocene to the present day. 相似文献
385.
The purpose of this study was to assess the environmental impacts of forest fires on part of the Mediterranean basin. The study area is on the Kassandra peninsula, prefecture of Halkidiki, Greece. A maximum likelihood supervised classification was applied to a post-fire Landsat TM image for mapping the exact burned area. Land-cover types that had been affected by fire were identified with the aid of a CORINE land-cover type layer. Results showed an overall classification accuracy of 95%, and 83% of the total burned area was ‘forest areas’. A normalized difference vegetation index threshold technique was applied to a post-fire Quickbird image which had been recorded six years after the fire event to assess the vegetation recovery and to identify the vegetation species that were dominant in burned areas. Four classes were identified: ‘bare soil’, ‘sparse shrubs’, ‘dense shrubs’ and ‘tree and shrub communities’. Results showed that ‘shrublands’ is the main vegetation type which has prevailed (65%) and that vegetation recovery is homogeneous in burned areas. 相似文献
386.
The debate regarding geographic information systems (GIS) as tool, toolbox, or science still lingers in geography departments and among geographers. Analysis of geographic information is a vital component of decision making among business, governments, researchers, and academics. GIS users, geographers and nongeographers alike, use and benefit from problem-solving methods in numerous fields and contexts, making the use of GIS and the core competencies associated with using GIS a topic of intense debate. Complicating this ongoing discussion is the rise of data-centric approaches to research in geography that further expand the capabilities of spatial analysis and add to the expected knowledge of a GIS user and analyst. Building on a panel discussion at the 2016 American Association of Geographers (AAG) annual meeting, as well as informal dialogues on Twitter and other social media platforms that navigate this issue in academics and industry, this article explores how skills in research computing and programming operate in geography and GIS, especially given the rise of data-centric approaches to research in these realms. Some topics, like the costs and benefits of open and closed source software, are familiar from previous discussions in geography and GIS. Others, though, like the reward structures and recognition for computing skills or programming ability, have not been widely considered given the current landscape. 相似文献
387.
Matthew T. J. Brownlee Jeffrey C. Hallo DeWayne D. Moore Robert B. Powell Brett A. Wright 《社会与自然资源》2014,27(9):964-982
Areas affected by drought are increasing, and many lakes that provide potable water and recreation opportunities are located in drought-vulnerable areas. Understanding a population's attitudes toward conservation actions can improve communication initiatives, policy development, and education, which are all necessary for effective water resource management. However, little is known about stakeholders’ interactions with drought-influenced resources and the potential factors that form their water conservation attitudes. Using a mixed methods approach, we evaluated lake recreationists’ (n = 229) attitudes toward water conservation at a drought-impacted lake. We identified the relationships between two site-specific factors (place attachment and awareness of drought impacts), beliefs in climate change, concern for drought impacts, and water conservation attitudes. Results indicated concern for local drought impacts fully mediated the relationships between site-specific factors, beliefs in climate change, and attitudes toward water conservation behaviors. Implications for research, outreach, and water resource management are discussed. 相似文献
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390.
Abstract— Ten type 1 and 2 carbonaceous chondrites have been analysed by stepped combustion to determine the nature of their sulphur-bearing components. All samples show complex release patterns which, when combined with published petrographic observations, can be interpreted in terms of sulphur derived from a mixture of at least seven components (elemental sulphur, organic sulphur, sulphide, FESON or tochilinite and sulphates: gypsum, bloedite and epsomite). Estimated concentrations of individual components show that most of the sulphur in the meteorites exists in oxidised form. The concentrations of reduced and oxidised components can be used to derive approximate oxidised/reduced sulphur ratios for the meteorites. These ratios are indicators of the extent of aqueous alteration and increase in the order CM < CI. Formation of the different alteration products by aqueous processes active on the meteorite parent body appears to be the most likely origin. 相似文献