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LISA NAUGHTON-TREVES 《Geographical review》1997,87(1):27-46
ABSTRACT. Subsistence farmers near Kibale National Park, Uganda, fear and resent many wildlife species. In this article I compare records of crop damage by wildlife and livestock with local complaints about the worst animals and the most vulnerable crops. I discuss the concordance and discrepancies in complaints versus actual damage in light of physical parameters of risk and of social factors that shape perceptions and vulnerabilities. Crop losses were greatest at the edge of the forest, where immigrants are disproportionately represented. State proprietorship of wildlife amplifies local vulnerability and constrains traditional coping strategies, such as hunting. 相似文献
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SUZANNE E. GRENFELL WILLIAM N. ELLERY MICHAEL C. GRENFELL LISA F. RAMSAY TYREL J. FLÜGEL 《Sedimentology》2010,57(5):1159-1174
Blocked‐valley lakes are formed when tributaries are impounded by the relatively rapid aggradation of a large river and its floodplain. These features are common in the landscape, and have been identified in the floodplains of the Solimões‐Amazon (Brazil) and Fly‐Strickland Rivers (Papua New Guinea), for example, but their inaccessibility has resulted in studies being limited to remotely sensed image analysis. This paper documents the sedimentology and geomorphic evolution of a blocked‐valley lake, Lake Futululu on the Mfolozi River floodplain margin, in South Africa, while also offering a context for the formation of lakes and wetlands at tributary junctions. The study combines aerial photography, elevation data from orthophotographs and field survey, and longitudinal sedimentology determined from a series of cores, which were sub‐sampled for organic content and particle size analysis. Radiocarbon dating was used to gauge the rate and timing of peat accumulation. Results indicate that following the last glacial maximum, rising sea‐levels caused aggradation of the Mfolozi River floodplain. By 3980 years bp , aggradation on the floodplain had impounded the Futululu drainage line, creating conditions suitable for peat formation, which has since occurred at a constant average rate of 0·13 cm year?1. Continued aggradation on the Mfolozi River floodplain has raised the base level of the Futululu drainage line, resulting in a series of back‐stepping sedimentary facies with fluvially derived sand and silt episodically prograding over lacustrine peat deposits. Blocked‐valley lakes form where the trunk river has a much larger sediment load and catchment than the tributary stream. Similarly, when the relative difference in sediment loads is less, palustrine wetlands, rather than lakes, may be the result. In contrast, where tributaries drain a steep, well‐connected catchment, they may impound much larger trunk rivers, creating lakes or wetlands upstream. 相似文献
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DAVID B. FINKELSTEIN LISA M. PRATT TARA M. CURTIN† SIMON C. BRASSELL 《Sedimentology》2005,52(3):587-599
Lithostratigraphic and organic chemostratigraphic studies of fluvial/lacustrine sediments in the Late Cretaceous Fort Crittenden Formation in south-eastern Arizona USA, reveal changes in palaeoclimate and tectonics as well as associated fluctuations in lake level. The lower Fort Crittenden is dominated by marginal wetland to deep-water lake deposits, whereas the upper Fort Crittenden is characterized by wetland to deltaic deposits. Abundance of polycyclic aromatic hydrocarbons (PAH) and reflectance of fusinite substantiate the impact of wildfires within the watershed. Organic geochemical evidence of wildfires is linked with sedimentological indicators of seasonal aridity suggesting that wildfires were common occurrences. Sedimentological evidence for seasonal aridity includes mottles and pseudoslickensides on ped structures within wetland mudstones. Distinct variations in PAH assemblages, characterized by the number of aromatic rings, indicate that there were variations in the intensities of wildfires, assuming no variations in the types of fuel. Fusinite reflectance values are consistent with combustion temperatures from 470 to 550 °C observed in modern wildfires. 相似文献
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LISA M. CAMPBELL NOELLA J. GRAY ZOE A. MELETIS JAMES G. ABBOTT JENNIFER J. SILVER 《Geographical review》2006,96(1):97-121
ABSTRACT. This article contributes to a recent and growing body of literature exploring the nature of fieldwork in human geography. Specifically, we critically examine the role of gatekeepers in providing access to “the field,” based on existing conceptualizations of gatekeepers in the literature and on our own experiences with gatekeepers. We argue that the concept of gatekeepers has been oversimplified, in that relationships between researchers and gatekeepers are often assumed to be unidirectional—with gatekeepers controlling or providing access by researchers—and predominantly static in form and time. Although we accept the necessity and advantages of working through gatekeepers, our experiences suggest that relationships with them are highly complex and evolve over time, with sometimes unexpected implications for research. In gathering and analyzing data, researchers become gatekeepers themselves, what we are calling “keymasters.” Reconceptualizing the gatekeeper‐researcher relationship will contribute to ongoing efforts to more fully understand field‐workers as undertaking a practice inherently political, personal, and linked to the production of knowledge. 相似文献
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A high-resolution record of a palaeomagnetic reversal is documented in Miocene alluvial rocks of Pakistan. We examined lateral variability of lithostratigraphy and palaeomagnetic stratigraphy through the same palaeomagnetic reversal in six correlated sections. Each section contains one or more palaeomagnetic sites with directions between fully reversed and fully normal. The position of the reversal illustrates local relief in the study area and the time-transgressive nature of certain stratigraphic units. Variability in the thickness of the transitional interval indicates contemporaneous variability in sediment accumulation rates. Different characteristics of palaeomagnetic remanence are associated with the depositional and post-depositional history of these sediments. Variability in patterns of remanence behaviour is the basis for inferences about post-depositional processes. We discuss two magnetic parameters that express coherency of palaeomagnetic samples—the maximum angle of deviation and the circular standard deviation. Of particular interest are samples with incoherent palaeomagnetic signals. The incoherency of samples is inversely correlated with the thickness of the transitional interval. A low rate of sediment accumulation, suggested by a thin transitional interval, may facilitate a prolonged period of remagnetization through pedogenic or hydrological processes. Alternatively, transition intervals, denned by coherent magnetization, may be thin as a result of pedogenically induced incoherency. 相似文献
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Abstract— We address the origin of “dusty,” metal-bearing relict olivine grains in chondrules. It has been suggested previously that these grains may be either primitive condensates or derived from a previous generation of chondrules. In this paper, we infer the original composition of dusty olivine grains, before they were reduced, and examine the possibility that they were derived from a previous generation of chondrules. Original compositions of dusty grains, including their estimated initial FeO contents and their minor element contents, match closely with compositions of olivines from chondrules in unequilibrated chondrites. In addition, the cores of some dusty grains are unaltered, and the compositions of these cores are also consistent with a chondrule origin. Therefore, we conclude that a derivation from a previous generation of chondrules is a plausible origin for these relicts. Although alternative origins, such as condensates or interstellar grains, cannot be ruled out on the basis of the available data, chondrules are an obvious source, and we suggest that this is the most likely interpretation. If this is the case, it is additional evidence for the importance of recycling of chondrule material in the chondrule-forming region. 相似文献
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PATRICK MEISTER CAROLINA REYES WILL BEAUMONT MIGUEL RINCON LISA COLLINS WILLIAM BERELSON LOWELL STOTT FRANK CORSETTI KENNETH H. NEALSON 《Sedimentology》2011,58(7):1810-1830
Dolomite [Ca,Mg(CO3)2] precipitation from supersaturated ionic solutions at Earth surface temperatures is considered kinetically inhibited because of the difficulties experienced in experimentally reproducing such a process. Nevertheless, recent dolomite is observed to form in hypersaline and alkaline environments. Such recent dolomite precipitation is commonly attributed to microbial mediation because dolomite has been demonstrated to form in vitro in microbial cultures. The mechanism of microbially mediated dolomite precipitation is, however, poorly understood and it remains unclear what role microbial mediation plays in natural environments. In the study presented here, simple geochemical methods were used to assess the limitations and controls of dolomite formation in Deep Springs Lake, a highly alkaline playa lake in eastern California showing ongoing dolomite authigenesis. The sediments of Deep Springs Lake consist of unlithified, clay‐fraction dolomite ooze. Based on δ18O equilibria and textural observations, dolomite precipitates from oxygenated and agitated surface brine. The Na‐SO4‐dominated brine contains up to 500 mm dissolved inorganic carbon whereas Mg2+ and Ca2+ concentrations are ca 1 and 0·3 mm , respectively. Precipitation in the subsurface probably is not significant because of the lack of Ca2+ (below 0·01 mm ). Under such highly alkaline conditions, the effect of microbial metabolism on supersaturation by pH and alkalinity increase is negligible. A putative microbial effect could, however, support dolomite nucleation or support crystal growth by overcoming a kinetic barrier. An essential limitation on crystal growth rates imposed by the low Ca2+ and Mg2+ concentrations could favour the thermodynamically more stable carbonate phase (which is dolomite) to precipitate. This mode of unlithified dolomite ooze formation showing δ13C values near to equilibrium with atmospheric CO2 (ca 3‰) contrasts the formation of isotopically light (organically derived), hard‐lithified dolomite layers in the subsurface of some less alkaline environments. Inferred physicochemical controls on dolomite formation under highly alkaline conditions observed in Deep Springs Lake may shed light on conditions that favoured extensive dolomite formation in alkaline Precambrian oceans, as opposed to modern oceans where dolomites only form diagenetically in organic C‐rich sediments. 相似文献
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JOHN A. MATTHEWS SVEIN-OLAF DAHL MARK S. BERRISFORD ATLE NESJE P. QUENTIN DRESSER LISA DUMAYNE-PEATY 《第四纪科学杂志》1997,12(2):117-129
A stratigraphic succession of alternating peat and minerogenic sediments at the foot of a steep mountain slope provides the basis for the reconstruction of a preliminary colluvial history from the alpine zone of Jotunheimen, southern Norway. Layers of silty sand and sandy silt, typically 5–10 cm thick and interpreted as distal debris-flow facies, are separated by layers of peat that have been radiocarbon dated. Deposition from at least 7500 to about 3800 14C yr BP of predominantly minerogenic material suggests relatively infrequent but large-magnitude debris-flow events in an environment warmer and/or drier than today. Particularly low colluvial activity between about 6500 and 3900 14C yr BP was terminated by a succession of major debris-flow events between about 3800 and 3400 14C yr BP. Unhumified peats indicative of higher water tables, separate six debris-flows that occurred between about 3300 and 2300 14C yr BP and signify a continuing high frequency of colluvial activity. Uninterrupted peat accumulation between about 2400 and 1600 14C yr BP indicates reduced debris-flow activity; subsequent renewed activity appears to have culuminated in the ‘Little Ice Age’ after about 600 14C yr BP. This pattern of colluvial deposition demonstrates a long history of natural Holocene low-alpine landscape instability, suggests an increase first in the magnitude and then in the frequency of debris-flow activity coincident with late Holocene climatic deterioration, and points to the potential of debris-flow records as a unique source of palaeoclimatic information related to extreme rainfall events. © 1997 John Wiley & Sons, Ltd. 相似文献
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