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91.
Tectonic evolution of China and adjacent crustal fragments 总被引:6,自引:6,他引:6
92.
Timothy B. Leduc 《Climatic change》2007,85(3-4):237-250
This research begins with the recognition that climate change researchers have become interested in Inuit ecological observations
because of the importance of northern changes on the global climate system, but this research often marginalizes Inuit understandings
of these climate-related changes. The direct translation of the Inuktitut term Sila in much of this research is a case study
in this methodological problem. In contrast to climate research translations of Sila as weather, ethnographies of Inuit conceive
of Sila as a spiritual power that is related to the weather. These diverging interpretations of Sila reflect the difficulty
of conducting cross-cultural research. To mitigate this difficulty a dialogue was engaged with Inuit concerning their experience
of climate change in relation to the different Inuit and Western understandings of Sila. The central goals of this paper are
to clearly define Sila so as to identify implications it may have for Western approaches in conducting cross-cultural climate
research, and, in the process, to begin a cross-cultural dialogue that aims at an agreed upon understanding of climate change
that is respectful of different knowledges. 相似文献
93.
Ignimbrites of the 13-ka Upper Laacher See Tephra were deposited from small, highly concentrated, moderately fluidized pyroclastic
flows. Their unconsolidated nature, and the prominence of accidental Devonian slate fragments, make these ignimbrites ideal
for clast fabric studies. The upper flow unit of ignimbrite M14 has characteristics typical of a type-2 ignimbrite. Layer
2a and the lower part of layer 2b of the flow unit have strong, upstream-inclined a[p] fabrics (a[p] means long particle axes
parallel to flow direction). Only clasts with a/b axial ratios of 2.5 or greater preserve good a[p] fabrics, whereas the a–b
planes of flat fragments dip upstream irrespective of axial ratio. The a-axis fabric becomes weaker, flatter, and more girdle-like
in the upper half of layer 2b. At one locality the a-axis fabric appears to rotate 40° up through the flow unit, suggesting
either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively
at its base. The existence of similarly strong a[p] fabrics in layer 2a and the lower half of layer 2b appears inconsistent
with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non-shearing material (layer
2b) on a thin shear layer (layer 2a), and that the entire flow freezes en masse to form the deposit. The data suggest that,
if the flow froze en masse, it was shearing pervasively through at least half its thickness. Another possibility is that the
flow unit aggraded progressively from the base up, and that the fabrics record the integrated history of shear directions
and intensities immediately above the bed throughout the duration of deposition.
Received: 13 February 1997 / Accepted: 4 April 1998 相似文献
94.
Amphibole zonation in metabasites as a guide to the evolution of metamorphic conditions 总被引:2,自引:0,他引:2
Timothy J. B. Holland Stephen W. Richardson 《Contributions to Mineralogy and Petrology》1979,70(2):143-148
In low grade metabasites the amphibole components tremolite, glaucophane, edenite and tschermakite have their activities controlled
by interactions with the excess components albite, clinozoisite, chlorite, quartz and H2O vapor. Three types of reaction are involved, (i) Those in which only components of condensed phases take part: isopleths
of equilibrium constant are straight lines in the P-T plane. (ii) Dehydration reactions in which entropy change due to change in Al coordination is of the same sign as that due
to dehydration: isopleths of constant K are positive at low pressure and negative at high pressure. (iii) Dehydration reactions
in which entropy change due to Al coordination change is opposite in sign to that of dehydration: isopleths of constant K
loop in the P-T plane with positive slopes at low and at high pressure.
Zonation in naturally occurring amphiboles records the evolution of metamorphic conditions in particular rocks. In an example
from the eastern Alps (Austria) early conditions calculated as 15 kb, 200 ° C evolve upgrade to 6 kb, 525 ° C implying concurrent
heating and erosion. The record of evolving conditions may span some 30 Ma of geological history. 相似文献
95.
Sediment samples from a variety of different environments were analyzed for organo-sulfur compounds (OSC) to provide the first characterization of the amounts and types of these compounds in sediments of the greater Puget Sound basin. A gas Chromatograph equipped with a sulfur specific flame photometric detector was used to quantify individual OSC. Compositions of OSC mixtures were essentially constant throughout the study area. Dibenzothiophene (DBT), its alkylated homologs, and an unknown compound were the predominant OSC in most samples. Concentrations of total OSC and DBT ranged from 4 to 60 and 0.4 to 2 μg/g organic carbon, respectively. The flux of OSC to the sediments at a station in central Puget Sound west of Seattle was approximately 140 ng/cm2/yr. The profile of total OSC concentration with depth showed three organic sulfur compounds that are apparently created in situ in the vicinity of where hydrogen sulfide production begins. The concentrations of the aromatic OSC were relatively constant with depth. Although several anthropogenic sources of OSC were identified, there was no evidence that OSC from these sources were accumulating in the sediments. The major source of the aromatic OSC in the sediments is apparently atmospheric input from natural sources such as forest fires. 相似文献
96.
97.
Recent studies have identified poverty reduction near parks and protected areas, findings that challenge an extensive literature on the social burdens associated with protected areas. These studies move the discussion on the social dynamics of conservation forward, however, they do not offer insight into the underlying mechanisms that shape household-level outcomes such as income and wealth. By focusing on protected areas as centers of uncertainty, upheaval, and disturbance, this study examines the character and incidence of livelihood diversification within communities near Tarangire National Park in northern Tanzania compared to communities far from the park. Livelihood diversification is well understood as a coping and/or risk mitigation strategy pursued in response to various types of shocks, and uncertainty more generally. This study draws on mixed methodologies to construct multivariate statistical models to estimate the effect of proximity to the park on measures of livelihood diversification. The results indicate that proximity to park is strongly correlated with livelihood diversification, suggesting that households near the park are adapting to opportunities and constraints and may be seeking to reduce variance in income and wealth in response to disturbances and uncertainty associated with the park. 相似文献
98.
99.
Timothy M. Shanahan Jonathan T. Overpeck W. E. Sharp Christopher A. Scholz Justice A. Arko 《水文研究》2007,21(13):1678-1691
Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment‐scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939–2004. Several commonly used models for computing evaporation in data‐sparse regions are compared, including the Penman, the energy budget, and the Priestley–Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy‐budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer‐term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
100.
Limonitic oncoliths from the Bajocian of Europe, widely known as ‘snuff-boxes’, grew by accretion of bundles of laminae on one side, followed by overturning and accretion of laminae on the other side. A diverse hard-substrate encrusting fauna grew interleaved with the ferruginous laminations. The palaeoecological preferences of this fauna indicate that its growth, and hence the accumulation of the laminations, took place on the gloomy undersides of the oncoliths. This upsidedown growth is supported by characteristics of the lamination bundles themselves, and by the predominant present-day orientations of the snuff-boxes. The abundance of the associated fauna and the lack of carbonate-dissolving macroborers cutting the laminae suggest an original ferric composition. Precipitation was probably under the control of non-photosynthetic microorganisms that inhabited the microenvironments represented by the oncoliths' lower surfaces. 相似文献