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31.
This paper presents an overview of some of the most significant, recent to ancient, littoral morpho-sedimentary structures and deposits from the Lake Turkana Basin. We highlight the importance of wave-related sedimentary processes in lakes, and more specifically in rift lakes. In the published literature, references to wave-dominated shorelines are mainly in regards to coastal marine environments. However, numerous modern lakes exhibit typical wave-dominated littoral landforms, and related sedimentary deposits are known from several paleolake successions in the geological record. Wave-related processes are often of relatively minor importance in depositional models for lacustrine environments. Classical models emphasize clastics transported by rivers, which are then distributed by fan-deltas and/or deltas into a water body of fluctuating depth, where reworking of clastics is limited in the littoral domain, and episodic in deep waters. Modern processes in Lake Turkana and the exposed paleolake deposits of the Turkana Basin demonstrate that this view is incomplete. Wave-dominated shorelines are evident (1) for modern Lake Turkana based on prominent and active littoral landforms (e.g., beach ridges, sand spits, washover fans, and arcuate-cuspate deltas); (2) for the Holocene (African Humid Period) climate-driven highstand of Megalake Turkana and its subsequent forced regression based on conspicuous raised beach ridges and spits; and (3) for the Pliocene–Pleistocene (Omo Group, Nachukui Formation) from typical nearshore sedimentary facies and stratigraphic architectures associated with paleolake Turkana. These examples from the Turkana Basin coupled with examples from other lacustrine settings, suggest that wave-dominated clastic shorelines represent significant portions of existing and ancient lake-shores. As this view contrasts with classic depositional models for lakes, notably for those found in rift setting, we also present examples of wave-influenced littoral landforms from other lakes of the East African Rift System. Identifying lacustrine paleoshorelines from typical clastic landforms and deposits is the key to the spatial reconstruction of lakes over time, and to determine transgressive–regressive cycles. Waves action is an important agent in lakes for the erosion, transport, and deposition of clastics at the basin-scale, an aspect that needs to be integrated in sedimentary models. 相似文献
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This editorial presents a special collection of papers addressing the concept of place and its use in geographical information science (GIScience). The concept of place is a topic of increasing interest among GIScience scholars. First attempts to formalise platial information have been made and it is increasingly held that user‐generated data sets in particular are often more platial than spatial in nature. At the same time, and especially when compared to geometric spatial concepts, the concept of place is ambiguous, complex and difficult to capture in formal and analytical terms, suggesting the need for interdisciplinary approaches. This collection presents articles covering a wide range of place‐related aspects, including both conceptual and more applied contributions. In the present editorial we summarise these and comment on their individual contributions, and hope that the readership of Transactions in GIS will find the special collection inspiring and informative. 相似文献
34.
A SX Phe-type pulsating variable KZ Hya (HD94033) was observed with CCD set attached to the 45-cm reflector at Asuncion Astronomical Observatory in Paraguay. In the present work, 12 maximum phases were covered. A new ephemeris has been obtained, and the result suggests a probable change of the pulsation period of KZ Hya. 相似文献
35.
How much does dry‐season fog matter? Quantifying fog contributions to water balance in a coastal California watershed
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The seasonally‐dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non‐rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed‐scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed‐scale estimates of fog water fluxes. Inputs from fog water throughfall (10–30 mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry‐season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially‐averaged fog fluxes into the water balance than traditional interpolation approaches. 相似文献
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Katherine E. Wright Stephen E. Grasby Charles Williamson John Spear Alexis S. Templeton 《Applied Geochemistry》2011
The authors are studying microbial sulfur redox metabolisms in a glacial environment. The energy available from sulfur redox reactions at this site has been calculated using geochemical data obtained from the site. DNA has been extracted from the same site and is being analyzed for the presence and relative quantities of sulfur redox genes, to determine whether bioenergetic calculations can predict the sulfur redox reactions that microbes are in fact utilizing. 相似文献
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Natural Hazards - The adverse impact of climate change-associated extreme weather events is becoming more significant globally, particularly the flood impact on coastal and low-lying areas such as... 相似文献
39.
CO2 injection into deep saline formations as a way to mitigate climate change raises concerns that leakage of saline waters from the injection formations will impact water quality of overlying aquifers, especially underground sources of drinking water (USDWs). This paper aims to characterize the geochemical composition of deep brines, with a focus on constituents that pose a human health risk and are regulated by the U.S. Environmental Protection Agency (USEPA). A statistical analysis of the NATCARB brine database, combined with simple mixing model calculations, show total dissolved solids and concentrations of chloride, boron, arsenic, sulfate, nitrate, iron and manganese may exceed plant tolerance or regulatory levels. Twelve agricultural crops evaluated for decreased productivity in the event of brine leakage would experience some yield reduction due to increased TDS at brine‐USDW ratios of < 0.1, and a 50% yield reduction at < 0.2 brine‐USDW ratio. A brine‐USDW ratio as low as 0.004 may result in yield reduction in the most sensitive crops. The USEPA TDS secondary standard is exceeded at a brine fraction of approximately 0.002. To our knowledge, this is the first study to consider agricultural impacts of brine leakage, even though agricultural withdrawals of groundwater in the United States are almost three times higher than public and domestic withdrawals. 相似文献
40.
Amaury?PourteauEmail author Romain?Bousquet Olivier?Vidal Alexis?Plunder Erik?Duesterhoeft Osman?Candan Roland?Oberh?nsli 《Contributions to Mineralogy and Petrology》2014,168(6):1090
We provide new insights into the prograde evolution of HP/LT metasedimentary rocks on the basis of detailed petrologic examination, element-partitioning analysis, and thermodynamic modelling of well-preserved Fe–Mg–carpholite- and Fe–Mg–chloritoid-bearing rocks from the Afyon Zone (Anatolia). We document continuous and discontinuous compositional (ferromagnesian substitution) zoning of carpholite (overall X Mg = 0.27–0.73) and chloritoid (overall X Mg = 0.07–0.30), as well as clear equilibrium and disequilibrium (i.e., reaction-related) textures involving carpholite and chloritoid, which consistently account for the consistent enrichment in Mg of both minerals through time, and the progressive replacement of carpholite by chloritoid. Mg/Fe distribution coefficients calculated between carpholite and chloritoid vary widely within samples (2.2–20.0). Among this range, only values of 7–11 correlate with equilibrium textures, in agreement with data from the literature. Equilibrium phase diagrams for metapelitic compositions are calculated using a newly modified thermodynamic dataset, including most recent data for carpholite, chloritoid, chlorite, and white mica, as well as further refinements for Fe–carpholite, and both chloritoid end-members, as required to reproduce accurately petrologic observations (phase relations, experimental constraints, Mg/Fe partitioning). Modelling reveals that Mg/Fe partitioning between carpholite and chloritoid is greatly sensitive to temperature and calls for a future evaluation of possible use as a thermometer. In addition, calculations show significant effective bulk composition changes during prograde metamorphism due to the fractionation of chloritoid formed at the expense of carpholite. We retrieve P–T conditions for several carpholite and chloritoid growth stages (1) during prograde stages using unfractionated, bulk-rock XRF analyses, and (2) at peak conditions using compositions fractionated for chloritoid. The P–T paths reconstructed for the Kütahya and Afyon areas shed light on contrasting temperature conditions for these areas during prograde and peak stages. 相似文献