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1.
Multiple concepts of time apply to archaeology—from analytical time used to organize and interpret the archaeological record to the time of lived experience of those individuals responsible for creation of the archaeological record. This paper demonstrates how these disparate concepts of time can be reconciled through a perception-based approach to time perspectivism, which invokes multiple analytical scales working from the minimum scale of the average human lifespan. This approach is demonstrated through a case study of hunter–gatherer demographic change in Yosemite Valley in the central Sierra Nevada of California.  相似文献   

2.
The application of chemical geothermometry to shallow groundwaters or spring discharge assumes that there is minimal mixing or re-equilibration of water as it travels from depth to the surface. In this study, we examine the potential for mixing and re-equilibration by examining heat and fluid flow along crustal-scale faults in tectonic geothermal systems. Numerical modeling results indicate that maximum in situ temperatures could be under-predicted by up to 30% due to mixing of fluids that enter the fault at different depths. This, coupled with the depression of isotherms by downward groundwater flow in the hanging wall, could cause underestimates of maximum circulation depth of greater than 80% in extreme cases. Kinetics does not favor re-equilibration in the shallower portions of faults due to low temperatures and higher fluid velocities. However, in areas of deeper circulation or higher heat flow such reactions are possible.  相似文献   

3.
Thermal springs are commonly thought to be an indicator of geothermal resource potential. However, there have been few analyses of the relationship between thermal springs and the underlying thermal regime. An examination of temperature and discharge rates for a large database of thermal springs in North America demonstrates that there is not a simple relationship between these measurements made at the surface and subsurface heat flow. Hydrogeological factors appear to exert strong controls on the temperature and discharge at these springs and should be carefully considered in geothermal resource assessments.  相似文献   

4.
The concept of the foraging radius is essential to understanding hunter–gatherer settlement, subsistence, and sociocultural complexity yet is notoriously difficult to reconstruct archaeologically. Late prehistoric Western Mono foraging radii in the southern Sierra Nevada were reconstructed using GIS analysis of least-cost path distances between dispersed caching features and centralized residential features. Mean distances from settlements to caches exhibit a bimodal distribution, with peaks between 0.5 and 5.0 km, and 6.0 and 8.5 km, the former representing a caching limit and the latter a foraging limit around major settlements. Combined, these data demarcate a two-part foraging radius predicated not only on sustaining winter group aggregations but also on facilitating spring and summer residential moves. These results show the efficacy of using features and simple GIS-based spatial analyses to reconstruct prehistoric foraging radii and provide the means to model the energetics of different foraging behaviors, these speaking strongly to the social and economic factors conditioning the development of complex hunter–gatherer societies.  相似文献   

5.
The onset of Little Ice Age conditions in California’s Sierra Nevada mountains resulted in increased temporal and spatial variability, and hence uncertainty regarding the distribution and production of resources targeted by its inhabitants, the Western Mono. The Mono responded with a risk-averse strategy composed of lowland winter population aggregation supported by logistical forays and seasonal residential dispersals to the high country, both ways of averaging variance in environmental productivity. These patterns were reconstructed using surface archaeology, GIS, and two straightforward spatial statistics, nearest-neighbor and variance-to-mean ratios, that combined provide a robust, objective picture of population aggregation and dispersal and the scale of these phenomena in different environments and seasons. These diverse strategies conform to expectations regarding the best ways for hunter–gatherers to cope with uncertainty, particularly in mountain environments. Despite this, the residentially mobile aspect of the pattern is rare in mountains and probably the result of historical connections between the Mono and Great Basin groups employing similar behaviors. Ultimately, this research suggests that climate change and environmental variability condition risk-averse, satisficing economic behaviors focused more on security than optimization, implying that pronounced environmental variability runs counter to economic intensification and its association with the evolution of more complex societies.  相似文献   

6.
7.
The elemental fluxes and heat flow associated with large aquifer systems can be significant both at local and at regional scales. In fact, large amounts of heat transported by regional groundwater flow can affect the subsurface thermal regime, and the amount of matter discharged towards the surface by large spring systems can be significant relative to the elemental fluxes of surface waters. The Narni‐Amelia regional aquifer system (Central Italy) discharges more than 13 m3 sec?1 of groundwater characterised by a slight thermal anomaly, high salinity and high pCO2. During circulation in the regional aquifer, groundwater reacts with the host rocks (dolostones, limestones and evaporites) and mixes with deep CO2‐rich fluids of mantle origin. These processes transfer large amounts of dissolved substances, in particular carbon dioxide, and a considerable amount of heat towards the surface. Because practically all the water circulating in the Narni‐Amelia system is discharged by few large springs (Stifone‐Montoro), the mass and energy balance of these springs can give a good estimation of the mass and heat transported from the entire system towards the surface. By means of a detailed mass and balance of the aquifer and considering the soil CO2 fluxes measured from the main gas emission of the region, we computed a total CO2 discharge of about 7.8 × 109 mol a?1 for the whole Narni‐Amelia system. Finally, considering the enthalpy difference between infiltrating water and water discharged by the springs, we computed an advective heat transfer related to groundwater flow of 410 ± 50 MW.  相似文献   

8.
Landscapes of the Ghost Dance: A Cartography of Numic Ritual   总被引:1,自引:0,他引:1  
Recent historical and ethnographic research indicates that the study of ritual behavior could be greatly enhanced by combining parameters of place and landscape use with interpretation of material culture. This strategy is especially useful for identifying the archaeological record of ritual among societies that incorporated topographic features and natural resources into their liturgical order. In this article we apply a behavioral framework to the study of Numic ritual technologies. By intergrating ethnographic and historic data on the geography, practice, and material culture of the nineteenth-century Nevada Ghost Dance, we demonstrate how this framework helps to determine the configuration of a ritual place and its position relative to other ritual and nonritual places.  相似文献   

9.
This article is based on a GOAL Global field study of street children in Freetown, Sierra Leone. It draws on narrative accounts given by street children who have migrated to Freetown from rural Sierra Leone. The study used the participatory ranking method to generate data about children’s street and hideout (a room, shack or part of a building where children live in groups) lives post-migration. These data contained much about children’s fears, and the article explores their experience of fearsome people and places, showing that fear is a dominant aspect of these children’s lives. Fear shapes their day-to-day choices and decisions: their agency. It also suggests that agency should be seen as complex, contingent and sometimes paradoxical. The article concludes by identifying implications for social policy and practice, suggesting that these necessarily entail risky engagement with fearsome people in the liminal spaces of children’s street and hideout lives.  相似文献   

10.
    
This paper engages with an arising interest in heritage as a ‘future-making’ project, arguing that in a context such as Sierra Leone heritage work may be better understood as a reflection of aspirations for a ‘common destiny’, than the articulation of common pasts. It questions the centrality with which modern anxiety continues to frame heritage temporalities, drawing on anthropological engagements with contexts of development and social transformation to propose a non-linear model for mapping the relationship between the past and the present. Drawing on a recent surge in heritage work in Sierra Leone, I suggest that heritage has efficacy beyond the provision of emotional security in a context of rapid change, indeed that it may be implicated in the process of instituting and shaping change itself.  相似文献   

11.
12.
Arctic hydrothermal springs at Bockfjorden, Svalbard, have isotope and trace element signatures indicative of derivation from glacial melt waters with minor contribution from seawater. Downstream gradients in water chemistry, isotopic composition and carbonate precipitation rates have been documented for the Troll spring and travertine terrace system. The main controls on the downstream evolution of these parameters are carbon dioxide degassing, calcite precipitation, evaporation and biological activity. The carbonate precipitation rates not only show an approximately parabolic dependence on the calcite supersaturation levels, but depend also on local hydrodynamics. Downstream loss of light isotopes of oxygen and hydrogen can be explained as an effect of evaporation, as estimated using chloride as a conservative marker. Biological activity affects nitrate and bromide concentrations and influences the morphology of calcite precipitates.  相似文献   

13.
    
Thermal springs commonly occur along faults because of the enhanced vertical permeability afforded by fracture zones. Field and laboratory studies of fault zone materials document substantial heterogeneities in fracture permeabilities. Modeling and field studies of springs suggest that spatial variations in permeability strongly influence spring locations, discharge rates and temperatures. The impact of heterogeneous permeability on spring geochemistry, however, is poorly documented. We present stable isotope and water chemistry data from a series of closely spaced thermal springs associated with the Hayward Fault, California. We suggest that substantial spatial variations observed in δ18O and chloride values reflect subsurface fluid transport through a poorly connected fracture network in which mixing of subsurface waters remains limited. Our measurements provide insight into the effect of fracture zone heterogeneities on spring geochemistry, offer an additional tool to intuit the nature of tectonically induced changes in fault zone plumbing, and highlight the need to consider local variations when characterizing fracture zone fluid geochemistry from spring systems with multiple discharge sites.  相似文献   

14.
    
ABSTRACT

In a number of low-income countries the fisheries sector has been shown to be instrumental in meeting key development goals, specifically in combating malnutrition, but the crucial contribution of women within this sector has been largely overlooked. This is particularly true in Sierra Leone, despite gender featuring prominently in the country's poverty reduction strategy. This article therefore examines the history of female involvement in the sector, how this involvement was transformed by the civil war, and assesses whether the various current initiatives to support women in the post-harvest sector offer a realistic ‘pathway out of poverty’.  相似文献   

15.
    
Ongoing (1996–present) volcanic unrest near South Sister, Oregon, is accompanied by a striking set of hydrothermal anomalies, including elevated temperatures, elevated major ion concentrations, and 3He/4He ratios as large as 8.6 RA in slightly thermal springs. These observations prompted the US Geological Survey to begin a systematic hydrothermal‐monitoring effort encompassing 25 sites and 10 of the highest‐risk volcanoes in the Cascade volcanic arc, from Mount Baker near the Canadian border to Lassen Peak in northern California. A concerted effort was made to develop hourly, multiyear records of temperature and/or hydrothermal solute flux, suitable for retrospective comparison with other continuous geophysical monitoring data. Targets included summit fumarole groups and springs/streams that show clear evidence of magmatic influence in the form of high 3He/4He ratios and/or anomalous fluxes of magmatic CO2 or heat. As of 2009–2012, summit fumarole temperatures in the Cascade Range were generally near or below the local pure water boiling point; the maximum observed superheat was <2.5°C at Mount Baker. Variability in ground temperature records from the summit fumarole sites is temperature‐dependent, with the hottest sites tending to show less variability. Seasonal variability in the hydrothermal solute flux from magmatically influenced springs varied from essentially undetectable to a factor of 5–10. This range of observed behavior owes mainly to the local climate regime, with strongly snowmelt‐influenced springs and streams exhibiting more variability. As of the end of the 2012 field season, there had been 87 occurrences of local seismic energy densities approximately ≥ 0.001 J/m3 during periods of hourly record. Hydrothermal responses to these small seismic stimuli were generally undetectable or ambiguous. Evaluation of multiyear to multidecadal trends indicates that whereas the hydrothermal system at Mount St. Helens is still fast‐evolving in response to the 1980–present eruptive cycle, there is no clear evidence of ongoing long‐term trends in hydrothermal activity at other Cascade Range volcanoes that have been active or restless during the past century (Baker, South Sister, and Lassen). Experience gained during the Cascade Range hydrothermal‐monitoring experiment informs ongoing efforts to capture entire unrest cycles at more active but generally less accessible volcanoes such as those in the Aleutian arc.  相似文献   

16.
Stratiform sediment‐hosted Zn–Pb–Ag mineral deposits constitute about 40% of the Earth's zinc resources ( Allen 2001 ), and in most cases their genesis involves the discharge of basinal brines near or on the seafloor through syndepositional faults ( Sangster 2002 ). From the point of view of base metal exploration, it is therefore essential to identify all possible faults that formerly carried the upwelling ore‐forming solutions during mineralising events. This paper presents a numerical investigation of the relative importance of various physical parameters in controlling fluid discharge, recharge and heat transport in faults. A two‐dimensional, free convection of pure water, hydrogeological model is developed for the McArthur basin in northern Australia based on the surface geology, known stratigraphic and structural relationships and regional geophysical interpretations. Numerical experiments and sensitivity analyses reveal that faults with strong initial heat input, due to depth of penetration or magmatic activity, are the most likely candidates to carry discharge fluids to the sites of metal precipitation. Deeper, wider and more permeable faults are more likely to behave as the fluid discharge pathways, whereas shallow, narrow or less permeable faults act as marine water recharge pathways. Compared with these fault‐related factors, aquifer physical properties are less important in determining fluid flow patterns and the geothermal regime. These results are an important step in understanding hydrothermal fluid flow in sedimentary basins in order to develop effective exploration criteria for the location of stratiform Zn–Pb–Ag deposits.  相似文献   

17.
Abstract

As in all African nations, football is very popular in Sierra Leone. While there is a constant lack of equipment and the fields are far from perfect, boys and girls are practising the game with great motivation and dedication. Training starts with warming up. This warming up is characterised by rhythmic exercises, done in perfect synchrony. These rhythmic activities need to be acquired by practice. Young boys watch the older football players and try to imitate them. Also for the amputee football team, rhythm is an important aspect of the warm-up. Football in Sierra Leone is more than just a game. Football can be seen as a tool for rehabilitation and reintegration. It makes the footballers forget about the war. For the amputee players, football also brought back their human dignity and sense of recognition, making them feel part of society again. The rhythmic aspects during the warm-up can intensify this effect, increasing a sense of belonging to a group.  相似文献   

18.
Abstract

KS043 is a stratified site associated with a complex of artesian springs. The archaeological remains, as well as a series of radiocarbon determinations, date the site to between 4800 and 4200 b.c. Our study suggests a connection between Saharan pastoralists, forced to move into oasis areas by increasing aridification, and the first Predynastic cultures of the Nile Valley. The site is the only well dated stratified settlement attributed to the Late Neolithic in the eastern Sahara that is characterized by Tasian cultural traditions.  相似文献   

19.
A. WILSON  C. RUPPEL 《Geofluids》2007,7(4):377-386
Thermohaline convection associated with salt domes has the potential to drive significant fluid flow and mass and heat transport in continental margins, but previous studies of fluid flow associated with salt structures have focused on continental settings or deep flow systems of importance to petroleum exploration. Motivated by recent geophysical and geochemical observations that suggest a convective pattern to near‐seafloor pore fluid flow in the northern Gulf of Mexico (GoMex), we devise numerical models that fully couple thermal and chemical processes to quantify the effects of salt geometry and seafloor relief on fluid flow beneath the seafloor. Steady‐state models that ignore halite dissolution demonstrate that seafloor relief plays an important role in the evolution of shallow geothermal convection cells and that salt at depth can contribute a thermal component to this convection. The inclusion of faults causes significant, but highly localized, increases in flow rates at seafloor discharge zones. Transient models that include halite dissolution show the evolution of flow during brine formation from early salt‐driven convection to later geothermal convection, characteristics of which are controlled by the interplay of seafloor relief and salt geometry. Predicted flow rates are on the order of a few millimeters per year or less for homogeneous sediments with a permeability of 10?15 m2, comparable to compaction‐driven flow rates. Sediment permeabilities likely fall below 10?15 m2 at depth in the GoMex basin, but such thermohaline convection can drive pervasive mass transport across the seafloor, affecting sediment diagenesis in shallow sediments. In more permeable settings, such flow could affect methane hydrate stability, seafloor chemosynthetic communities, and the longevity of fluid seeps.  相似文献   

20.
The origins of increased stream flow and spring discharge following earthquakes have been the subject of controversy, in large part because there are many models to explain observations and few measurements suitable for distinguishing between hypotheses. On October 30, 2007 a magnitude 5.5 earthquake occurred near the Alum Rock springs, California, USA. Within a day we documented a several‐fold increase in discharge. Over the following year, we have monitored a gradual return towards pre‐earthquake properties, but for the largest springs there appears to be a permanent increase in discharge. The Alum Rock springs discharge waters that are a mixture between modern (shallow) meteoric water and old (deep) connate waters expelled by regional transpression. After the earthquake, there was a small and temporary decrease in the fraction of connate water in the largest springs. Accompanying this geochemical change was a small (1–2°C) temperature decrease. Combined with the rapid response, this implies that the increased discharge has a shallow origin. Increased discharge at these springs occurs both for earthquakes that cause static volumetric expansion and for those that cause contraction, supporting models in which dynamic strains are responsible for the subsurface changes that cause flow to increase. We make a quantitative comparison between the observed changes and model predictions for three types of models: (i) a permanent increase in permeability; (ii) an increase in permeability followed by a gradual decrease to its pre‐earthquake value; and (iii) an increase of hydraulic head in the groundwater system discharging at the springs. We show that models in which the permeability of the fracture system feeding the springs increases after the earthquake are in general consistent with the changes in discharge. The postseismic decrease in discharge could either reflect the groundwater system adjusting to the new, higher permeability or a gradual return of permeability to pre‐earthquake values; the available data do not allow us to distinguish between these two scenarios. However, the response of these springs to another earthquake will provide critical constraints on the changes that occur in the subsurface and should permit a test of all three types of models.  相似文献   

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