Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin,Kenya          下载免费PDF全文

Emily J. Beverly  Steven G. Driese  Daniel J. Peppe  Cara R. Johnson  Lauren A. Michel  J. Tyler Faith  Christian A. Tryon  Warren D. Sharp 《Sedimentology》2015,62(6):1611-1635

The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age arte‐facts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U‐series dating analyses. Tufa is identified in four sites: Nyamita (94·0 ± 3·3 and 111·4 ± 4·2 ka); Kisaaka, Aringo (455 ± 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring‐fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with δ¹³C values of ca 10‰ indicative of C₃ plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C₃/C₄ signature consistent with a semi‐arid C₄ grassland surrounding these spring‐fed rivers. The δ¹⁸O values of tufa from Nyamita are on average ca 1‰ more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface‐collected artefacts indicate that early modern humans were utilizing these spring‐fed rivers. The presence of spring?fed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment.  相似文献   

The molar volume of FeO–MgO–Fe2O3–Cr2O3–Al2O3–TiO2 spinels     

Emily A. Hamecher  Paula M. Antoshechkina  Mark S. Ghiorso  Paul D. Asimow 《Contributions to Mineralogy and Petrology》2013,165(1):25-43

We define and calibrate a new model of molar volume as a function of pressure, temperature, ordering state, and composition for spinels in the supersystem (Mg, Fe²⁺)(Al, Cr, Fe³⁺)₂O₄ ? (Mg, Fe²⁺)₂TiO₄. We use 832 X-ray and neutron diffraction measurements performed on spinels at ambient and in situ high-P, T conditions to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg²⁺, Al³⁺, and Fe³⁺ site occupancy terms. We allow standard-state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of state of the various spinel end members are analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end-member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The preferred model has a total of 9 excess volume and order-dependent parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5 % in volume. The model is compared to the current MELTS spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure.  相似文献   

Comparisons of wetland and drainage lake influences on stream dissolved carbon concentrations and yields in a north temperate lake-rich region     

Noah R. Lottig  Ishi Buffam  Emily H. Stanley 《Aquatic Sciences - Research Across Boundaries》2013,75(4):619-630

Processes occurring at various scales interact to influence the export of organic carbon from watersheds to freshwater ecosystems and eventually the ocean. The goal of this study was to determine if and how differences in wetland extent and presence of lakes influenced dissolved organic carbon (DOC) concentrations and yields in streams. We monitored stream flow, DOC and dissolved inorganic carbon concentrations periodically for 2 years at four sites with forested watersheds, four sites with wetland watersheds, and four sites with wetland watersheds that also contained in-network lakes. As expected, the presence of wetlands resulted in higher DOC concentrations and yields, but the impact of lakes was less clear on the magnitude of DOC concentrations and yields. With respect to temporal dynamics, we found positive relationships between stream flow and DOC concentration (median r² = 0.89) in streams without upstream lakes. The relationships for forested sites are among the strongest reported in the literature, and suggest a clear shift in hydrologic flowpath from intersecting mineral soils at low flow, to organic soils at high flow. In streams with upstream lakes, the relationship between flow and concentration was non-significant for three of four sites unless time lags with flow were applied to the concentration data, after which the relationship was similar to the non-lake streams (median r² = 0.95). These findings suggest that lakes buffering temporal patterns in streams by hydrologically delaying pulses of carbon, but provide little support that in-line lakes have a net effect on carbon exports in this region.  相似文献   

Capital and conscience: poverty management and the financialization of good intentions in the San Francisco Bay Area     

Emily Rosenman 《Urban geography》2013,34(8):1124-1147

Social impact investing differentiates itself from traditional investing by claiming to create public social benefits alongside private profits. Globally, municipal governments are increasingly looking to this model to fund urban social services and poverty management. Through a case study of social impact investing in affordable housing in the San Francisco Bay Area, I deconstruct the financial and ideological underpinnings of this model to understand how private profits are drawn from local geographies of impoverishment. Analyzing social impact investing as a poverty politics reveals how it places preexisting, state-subsidized systems of poverty management into social impact investing portfolios, dividing impoverished spaces into new hierarchies of deservingness by incorporating private investors’ visions of what will help low-income tenants. But these processes also fail to subsume social life within housing financed in this manner, as tenant practices subverting those idealized by the state and investors persist alongside the generation of private profits.  相似文献   

Contrasting the effects of climatic, nutrient, and oxygen dynamics on subfossil chironomid assemblages: a paleolimnological experiment from eutrophic High Arctic ponds     

Emily M. Stewart  Neal Michelutti  Jules M. Blais  Mark L. Mallory  Marianne S. V. Douglas  John P. Smol 《Journal of Paleolimnology》2013,49(2):205-219

Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds.  相似文献   

Barrier dynamics for GIS: a design pattern for geospatial barriers     

Emily White  Kathleen Stewart 《International journal of geographical information science》2013,27(6):1007-1022

When separation between geospatial features is desired, an obstacle or barrier is used to maintain distance between the features. Barriers are used in a wide variety of domains, such as hazards, transportation, and public safety. Floodwalls, for example, prevent flooding rivers or lakes from inundating buildings. This work presents an ontology design pattern for barriers and barring events useful for GIS. In this ontology design pattern, active features (e.g., the water-body that is causing flooding) and target features (e.g., buildings requiring flood protection) are defined. Along with these key features, the ontology design pattern also captures certain barring events. These are the dynamics that arise from the placement of barriers and include Blocking, Enclosing, KeepingIn and KeepingOut, involving interactions among barriers, and active and target features. The set of classes that model these features and events as well as the relations between them are presented and formalized. This design pattern is ready for integration in a GIS to allow queries on barriers and barring events that do not currently have explicit support in most GIS.  相似文献   

Remote sensing methods to detect land‐use/cover changes in New Zealand's ‘indigenous’ grasslands     

Emily S. Weeks  Anne‐Gaelle E. Ausseil  James D. Shepherd  John R. Dymond 《New Zealand geographer》2013,69(1):1-13

We compared four remote sensing methods to detect changes in New Zealand's grasslands (image differencing, normalised difference vegetation index (NDVI) differencing post‐classification and visual interpretation). The visual interpretation resulted in the best classification results, with a 98% overall accuracy when compared with ground‐truthed data. The tests on automatic classification (image differencing, NDVI differencing) and post classification had much lower accuracies, ranging from 47% to 56%. In the New Zealand grassland landscape, automatic detection methods were not able to differentiate between variations of soil moisture and vegetation phenology from variations in land‐use change. This, in combination with topographic effects, which have hampered the automated mapping of vegetation, is the main reason why visual interpretation of high‐resolution imagery is still needed.  相似文献   

Sketch Maps and Qualitative GIS: Using Cartographies of Individual Spatial Narratives in Geographic Research   总被引：1，自引：0，他引：1  

E. Eric Boschmann  Emily Cubbon 《The Professional geographer》2013,65(2):236-248

Mental and sketch maps have a long tradition in modern geography. Little theoretical and methodological distinction has been made, however, between different hand mapping approaches. Mental maps emerged from behavioral geography of the spatial science tradition as a technique to understand human behaviors based on peoples’ perceptions of their spatial environment. More recently, sketch maps have been used in participatory and qualitative geographic information systems (QGIS) to develop cartographies of group and individual spatial narratives. They are a tool that helps achieve QGIS's objectives of collecting unique spatial data of individual experiences, visualizing socio-spatial processes, breaking down particular barriers of positionality in research, and developing new uses of GIS. Two case studies illustrate the use of sketch maps in research, including a project examining job accessibility among working poor individuals and a study of the experiences of fear and safety in public spaces among lesbian, gay, bisexual, and transgender community members. Sketch maps in QGIS have many methodological merits. They add an invaluable dimension to the qualitative interview process, offer countermapping perspectives, generate detailed spatial information of individuals, and facilitate data interpretation.  相似文献   

Land Use History and Site Formation Processes at the Punic Site of Pauli Stincus in West Central Sardinia     

Cristiano Nicosia  Roger Langohr  Pilar Carmona Gonzlez  Carlos Gmez Bellard  Emily B. Modrall  Jos Miguel Ruíz Prez  Peter van Dommelen 《Geoarchaeology》2013,28(4):373-393

The site of Pauli Stincus is located near the town of Terralba, on the inland shores of the Gulf of Oristano in west central Sardinia, Italy, and was occupied between the mid‐4th and the late 2nd century B.C. The site and its surroundings were the object of a joint archaeopedological and geomorphological study, which complemented the data from archaeological excavations. This study allowed us to evaluate the suitability of the different landscape and soil components for crop production in the Punic period. The discovery of a buried plow soil at the site's edge enabled us to identify a set of agricultural practices carried out by Punic farmers. These included the removal of sandy topsoil to cultivate deeper horizons enriched in illuvial clay, the use of a "sodbuster" or "rip ard," and the periodic burning of weeds, stubble, and other harvesting residues. The present study helped us to better understand the formation processes of the archaeological record at Pauli Stincus. Large quantities of allochtonous calcareous material were imported to the site from wet areas closer to the coast in order to produce earth‐based construction material, such as bricks and daub. © 2013 Wiley Periodicals, Inc.  相似文献   

Fumarolic pipes in the Tshirege Member of the Bandelier Tuff on the Pajarito Plateau, Jemez Mountains, New Mexico     

Florie A. Caporuscio  Jamie N. Gardner  Emily S. Schultz-Fellenz  Richard E. Kelley 《Bulletin of Volcanology》2012,74(5):1023-1037

The objective of this study is to demonstrate the relationships among devitrification, vapor phase alteration, localization of gas emanations into fumarolic pipes, and initial deformation of the ash flow sheet during cooling and lithification. Utilizing a unique and temporary exposure of the Tshirege Member of the Bandelier Tuff near Los Alamos, New Mexico, we identify several zones of distinctly preserved fossil fumarolic activity. The fumarolic zones vary in width from a few centimeters to more than a meter. Almost ubiquitously, these zones demonstrate fines-depletion, induration of the margins, upward-flaring geometries, and intense fracturing of overlying geologic units. The fumaroles were preferentially located on post welding, early formed cooling joints that vented to the surface after the vapor phase alteration stage. The pipes were regularly spaced at distances of approximately 4.5?m (N–S) to 7?m (E–W). In turn the pipes were covered by a surge deposit and overlying tuff which rapidly lithified. The overlying tuff was then brecciated during continued fumarolic pipe emissions. Geochemical evaluations confirm the presence of high-temperature mineral (scapolite) indicative of transport of hot volcanic gases through these zones. The pipe centers and walls are depleted in SiO₂, and enriched in Al₂O₃ and FeO. The overlying tuff breccia zones are enriched in Al₂O₃, FeO and MgO, and depleted in SiO₂, NaO, and K₂O. From comparison to other ignimbrite cooling histories, the fissures, fumaroles, and structures observed all likely formed in the first few decades after the deposition of the upper Tshirege subunits. This may have significant implications as to timing of initial cooling fractures and subsequent consolidation of gas emission pathways.  相似文献