Insights into syndepositional fault movement in a foreland basin; trends in seismites of the Upper Cretaceous,Wahweap Formation,Kaiparowits Basin,Utah, USA     

Hannah L. Hilbert‐Wolf  Edward L. Simpson  Wendy S. Simpson  Sarah E. Tindall  Michael C. Wizevich 《Basin Research》2009,21(6):856-871

The Upper Cretaceous Wahweap Formation accumulated in the active Cordilleran foreland basin of Utah. Soft‐sediment deformation structures are abundant in the capping sandstone member of the Wahweap Formation. By comparing with well‐established criteria, a seismogenic origin was determined for the majority of structures, which places these soft‐sediment deformation features in a class of sedimentary features referred to as seismites. A systematic study of the seismite trends included their vertical and horizontal distribution and a semi‐quantitative intensity analysis using a scale from 1 to 5 that is based on magnitude, sedimentary structure type, and the predominance of inferred process of hydroplastic deformation, liquefaction or fluidization. In addition, orientations of soft‐sediment fold axes were recorded. Construction of a northwest‐to‐southeast stratigraphic and seismite intensity cross‐section demonstrates: (1) reduction in stratigraphic thickness and percentage of conglomerates to the southeast, (2) the presence of lower seismite, middle nonseismite, and upper seismite zones within the capping sandstone (permitting subdivision of the capping sandstone member), and (3) elimination of the nonseismite zone and amalgamation of the lower and upper seismite zones to the southeast. Regional isoseismal contour maps generated from the semi‐quantitative analysis indicate a decrease in overall intensity from northwest to southeast in the upper and lower seismic zones and in sandstone within 5 m stratigraphically of the contact between the upper and capping sandstone members. In addition, cumulative seismite fold orientations support a west–northwest direction towards regional epicentres. Isoseismal maps are used to distinguish the effects of intrabasinal normal faulting from those of regional orogenic thrusting. Thus, this study demonstrates the utility of mapping seismites to separate the importance of regional vs. local tectonic activity influencing foreland basin sedimentation by identifying patterns that delineate palaeoepicentres associated with specific local intrabasinal normal faults vs. regional trends in soft‐sediment deformation related to Sevier belt earthquakes.  相似文献   

Tropical precipitation, SSTs and the surface energy budget: a zonally symmetric perspective   总被引：1，自引：1，他引：0  

Sarah M. Kang  Isaac M. Held 《Climate Dynamics》2012,38(9-10):1917-1924

The relative importance of sea surface temperatures (SSTs) and the surface energy budget to tropical precipitation is examined by comparing models with zonally symmetric climates, both fixed SST and coupled to a slab mixed layer ocean. Two models are considered with differing surface flux formulations and in each case solutions that are symmetric about the equator are perturbed to create interhemispheric asymmetry. When SSTs are prescribed in the two models with different flux formulations, the magnitude of tropical precipitation response to identical SST anomalies is significantly different, but the differences can be understood in terms of the altered surface fluxes. In contrast, when the net surface energy fluxes are constrained to be identical in mixed layer simulations of the two different models, the response of tropical precipitation to perturbations in the surface energy balance is very similar. Both perspectives predict qualitatively the same precipitation response, but the energy budget better predicts the magnitude of the precipitation response. Thus, we argue that the atmospheric energy budget, controlled in these experiments primarily by the surface energy budget, is more fundamental to the control of tropical precipitation than the SSTs, in these simulations with axisymmetric climates. We touch briefly on a complication in the interpretation of the model results due to the fact that fixed SST and slab-ocean versions of the model can produce different Hadley cell strengths for the same SSTs.  相似文献   

Climate change, adaptation and economic growth     

Alex Bowen  Sarah Cochrane  Samuel Fankhauser 《Climatic change》2012,113(2):95-106

This paper explores the links between economic growth and the impacts of climate change. Inclusive, pro-poor growth is central to the development of low-income countries. There is also a broad consensus that growth and development are important to reduce vulnerability to climate change. Growth does not automatically reduce vulnerability, only the right kind of growth does. The paper aims to develop a better understanding of what the ??right kind of growth?? may be. We find that many growth policies, such as investment in skills and access to finance, indeed reduce vulnerability to climate change. However, climate change calls for some adjustments in growth policy. In particular, investment in infrastructure and efforts to stimulate entrepreneurship and competitive markets must take more of a risk management perspective and recognise climate risks.  相似文献   

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence     

Francine McCarthy  Sarah Tiffin  Adam Sarvis  John McAndrews  Stephan Blasco 《Journal of Paleolimnology》2012,47(3):429-445

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.  相似文献   

Force–displacement response of in‐plane‐loaded URM walls with a dominating flexural mode          下载免费PDF全文

Sarah Petry  Katrin Beyer 《地震工程与结构动力学》2015,44(14):2551-2573

This article presents a new mechanical model for the non‐linear force–displacement response of unreinforced masonry (URM) walls developing a flexural rocking mode including their displacement capacity. The model is based on the plane‐section hypothesis and a constitutive law for the masonry with zero tensile strength and linear elastic behaviour in compression. It is assumed that only the compressed part of the wall contributes to the stiffness of the wall and therefore the model accounts for a softening of the response due the reduction of the effective area. Stress conditions for limit states are proposed that characterise the flexural failure. The new model allows therefore linking local performance levels to global displacement capacities. The limit states criteria describe the behaviour of modern URM walls with cement mortar of normal thickness and clay bricks. The model is validated through comparison of local and global engineering demand parameters with experimental results. It provides good prediction of the effective stiffness, the force capacity and the displacement capacity of URM walls at different limit states. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A meta‐analysis of reef island response to environmental change on the Great Barrier Reef          下载免费PDF全文

Sarah M. Hamylton  Marji Puotinen 《地球表面变化过程与地形》2015,40(8):1006-1016

Reef islands on the Great Barrier Reef are influenced by a range of environmental factors. A meta‐analysis of 103 islands is presented to express variation in island size (area and volume) as a function of latitudinal and cross shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and tropical cyclone frequency) and local physical factors (position on the shelf, area, length and depth of supporting reef platform, vegetative cover). Models performed well for unvegetated sandcays (R² = 0.89), vegetated sandcays (R² = 0·72) and low wooded islands (R² = 0.78), with a moderate level of variation explained when all islands were simultaneously regressed (R² = 0.58). Future island dynamics were simulated for anticipated changes in cyclone regime, wave activity and sea level. For 38 islands mapped on the 1973 Royal Society and Universities of Queensland Expedition to the Northern Great Barrier Reef, change over the same 22 year period (1973–1995) was determined and the relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis (Γ = 0.84 for unvegetated sandcays, Γ = 0.81 for vegetated sandcays). Simulations of island area or volume change from 2000 to 2100 indicated that under a 30% decrease in tropical cyclone activity, unvegetated sandcays continue to accrete at a lower rate, whereas all island types erode under a 38% increase in tropical cyclone activity. Vegetated sandcays initially accrete at higher levels of cyclone activity, entering an erosive state with a 60% increase in activity. Low wooded islands are unresponsive to environmental changes modelled. A sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode. Greatest sedimentary losses occur within the central band of high cyclone activity between Cooktown and Mackay. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

High‐frequency water quality monitoring in an urban catchment: hydrochemical dynamics,primary production and implications for the Water Framework Directive          下载免费PDF全文

Sarah J. Halliday  Richard A. Skeffington  Andrew J. Wade  Michael J. Bowes  Emma Gozzard  Jonathan R. Newman  Matthew Loewenthal  Elizabeth J. Palmer‐Felgate  Helen P. Jarvie 《水文研究》2015,29(15):3388-3407

This paper describes the hydrochemistry of a lowland, urbanised river‐system, The Cut in England, using in situ sub‐daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190 000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Although 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in‐stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic, and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk. © 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.  相似文献   

Elevation‐dependent responses of streamflow to climate warming          下载免费PDF全文

Christopher J. Tennant  Benjamin T. Crosby  Sarah E. Godsey 《水文研究》2015,29(6):991-1001

Warming will affect snowline elevation, potentially altering the timing and magnitude of streamflow from mountain landscapes. Presently, the assessment of potential elevation‐dependent responses is difficult because many gauged watersheds integrate drainage areas that are both snow and rain dominated. To predict the impact of snowline rise on streamflow, we mapped the current snowline (1980 m) for the Salmon River watershed (Idaho, USA) and projected its elevation after 3 °C warming (2440 m). This increase results in a 40% reduction in snow‐covered area during winter months. We expand this analysis by collecting streamflow records from a new, elevation‐stratified gauging network of watersheds contained within high (2250–3800 m), mid (1500–2250 m) and low (300–1500 m) elevations that isolate snow, mixed and rain‐dominated precipitation regimes. Results indicate that lags between percentiles of precipitation and streamflow are much shorter in low elevations than in mid‐ and high‐elevation watersheds. Low elevation annual percentiles (Q₂₅ and Q₇₅) of streamflow occur 30–50 days earlier than in higher elevation watersheds. Extreme events in low elevations are dominated by low‐ and no‐flow events whereas mid‐ and high‐elevation extreme events are primarily large magnitude floods. Only mid‐ and high‐elevation watersheds are strongly cross correlated with catchment‐wide flow of the Salmon River, suggesting that changes in contributions from low‐elevation catchments may be poorly represented using mainstem gauges. As snowline rises, mid‐elevation watersheds will likely exhibit behaviours currently observed only at lower elevations. Streamflow monitoring networks designed for operational decision making or change detection may require modification to capture elevation‐dependent responses of streamflow to warming. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Biofilm Detection in a Model Well‐Bore Environment Using Low‐Field NMR          下载免费PDF全文

Catherine M. Kirkland  Randy Hiebert  Adrienne Phillips  Elliot Grunewald  David O. Walsh  Joseph D. Seymour  Sarah L. Codd 《Ground Water Monitoring & Remediation》2015,35(4):36-44

This research addresses the challenges of the lack of non‐invasive methods and poor spatiotemporal resolution associated with monitoring biogeochemical activity central to bioremediation of subsurface contaminants. Remediation efforts often include growth of biofilm to contain or degrade chemical contaminants, such as nitrates, hydrocarbons, heavy metals, and some chlorinated solvents. Previous research indicates that nuclear magnetic resonance (NMR) is sensitive to the biogeochemical processes of biofilm accumulation. The current research focuses on developing methods to use low‐cost NMR technology to support in situ monitoring of biofilm growth and geochemical remediation processes in the subsurface. Biofilm was grown in a lab‐scale radial flow bioreactor designed to model the near wellbore subsurface environment. The Vista Clara Javelin NMR logging device, a slim down‐the‐borehole probe, collected NMR measurements over the course of eight days while biofilm was cultivated in the sand‐packed reactor. Measured NMR mean log T₂ relaxation times decreased from approximately 710 to 389 ms, indicating that the pore environment and bulk fluid properties were changing due to biofilm growth. Destructive sampling employing drop plate microbial population analysis and scanning electron and stereoscopic microscopy confirmed biofilm formation. Our findings demonstrate that the NMR logging tool can detect small to moderate changes in T₂ distribution associated with environmentally relevant quantities of biofilm in quartz sand.  相似文献   

Experimental test of a radiative transfer model of the optical effects of space weathering     

Paul G. Lucey  Sarah K. Noble 《Icarus》2008,197(1):348-353

We compare laboratory measurements of the optical effects of nanophase iron on near-IR reflectance spectra of transparent silica gel infused with small iron particles [Noble, S.K., Pieters, C.M., Keller, L.P., 2007. Icarus 192, 629-642] with a radiative transfer model of the process [Hapke, B., 2001. J. Geophys. Res. 106 (E5), 10039-10074]. We find that the measurements exhibit reddening and darkening effects of nanophase (<50 nm) iron particles, a darkening effect of somewhat larger particles (>50 nm) and mixing effects of silica gel particles of varying total iron abundance. The radiative transfer model reproduces the effects of nanophase iron within the experimental uncertainties.  相似文献