Sedimentology of Quaternary perched springline and paludal tufas: criteria for recognition, with examples from Guadalajara Province, Spain   总被引：2，自引：0，他引：2  

Martyn Pedley  Juan Antonio González Martín†  Salvador Ordóñez Delgado‡  MªÁngeles García Del Cura§ 《Sedimentology》2003,50(1):23-44

Outcrop‐scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model. At the field scale, four end‐member models encompass the tufa continuum: (1) perched springline; (2) paludal; (3) fluvial; and (4) lacustrine tufas. Individual bed types can occur with variable dominance within several of these models, but one or more beds are characteristically dominant only within a single tufa model, so it can be differentiated from relatively isolated outcrop fragments. Two models (perched springline tufas and paludal tufas) are known in outline only in the literature despite being present within the Quaternary deposits of most karstic regions. Perched springline tufas generally form lobate, fan‐shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences. Mature deposits show a subhorizontal top and a steep face on the downflow side. The steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle. Tufa deposits lying downslope of the mounds are usually detrital in nature, especially if some dismantling of the mound has occurred. The relatively thin subhorizontal lobe‐top deposits commonly contain organic‐rich deposits. Paludal tufas develop predominantly in waterlogged valley bottom situations, where line‐sourced waters emerge from valley side and bottom aquifers. Lime mud precipitation predominates in these sites. Mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences. Tufa spring‐mounds may form where lesser volumes of water are involved. Individual tussocks (phytoherm cushions) of grasses and rushes are the most diagnostic feature of the model, but sapropels and peats may be intercalated. Diagenesis in both models is rapid. Lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation. The resulting highly porous and permeable fabrics remain fresh in Holocene tufas, but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits. Dissolution in many perched springline tufas is small scale. Many large cavities are primary, but with later coatings of speleothems. Early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction.  相似文献   

Distribution and abundance of the Pacific sardine (Sardinops sagax) in the Gulf of California and their relation with the environment   总被引：1，自引：0，他引：1  

Manuel O. Nevrez-Martínez  Daniel Lluch-Belda  Miguel A. Cisneros-Mata  J. Pablo Santos-Molina  Ma. De los Angeles Martínez-Zavala  Salvador E. Lluch-Cota 《Progress in Oceanography》2001,49(1-4)

In 1989–90 the small pelagic fishery of the Gulf of California began to show a very marked decline in the catch of its main component, the Pacific sardine (Sardinops sagax). The catch plummeted from 292,000 t in 1988–89 to 7000 t in 1991–92 and 1992–93. This caused a serious economic crisis in the local fishery fleet and industry, and resulted in the loss of 3000 jobs. In 1993–94 the fishery showed signs of recovery as the abundance of the Pacific sardine began to recover. The catch improved to 128,000 t in 1993–94 and further to 215,000 t in 1996–97. In trying to understand this great variability, we proposed the hypothesis that the distribution and the abundance of the Pacific sardine of the Gulf of California is determined by the wind patterns (upwelling) and the sea surface temperature. The results of analyzing data from 25 cruises showed the period of low relative abundance between 1990 and 1993 and one of high abundance between 1993 and 1996. The range of the sardine's distribution expanded as its abundance increased and contracted when abundances were low. The relationship between the abundances of the sardine and environmental variables proved to nonlinear and bell-shaped. The adjusted pattern explained 78.8% of the variability of the sardine abundance. The highest abundance are produced by moderate upwelling (13–18 m³s⁻¹ per 10 m of coastline) and sea surface temperatures of between 19°C and 25°C.  相似文献   

Spatiotemporal analysis of the atmospheric and surface urban heat islands of the Metropolitan Area of Toluca,Mexico     

Erika Rivera  Xanat Antonio-Némiga  Gabriel Origel-Gutiérrez  Pablo Sarricolea  Salvador Adame-Martínez 《Environmental Earth Sciences》2017,76(5):225

The dynamic of consolidation of urban areas in Latin America has allowed that almost 80% of the population concentrates in cities; this has produced changes in land covers and modified regional climate, propitiating the appearance of urban heat islands. The Metropolitan Area of Toluca, State of Mexico, Mexico, holds the fifth national place in population size and experiences this process, because of this, the objective is to analyze and compare the spatiotemporal characteristics of the atmospheric urban heat island obtained from data gathered from 12 urban and rural weather stations with the surface urban heat island obtained from the digital processing of four Landsat 8 images. Results show the year-round presence of night-time atmospheric urban heat islands, which reach a peak in autumn (up to 6 °C). Daytime atmospheric urban heat islands occur in summer and autumn with a maximum intensity of 4 °C. For their part, surface urban heat islands occur in spring, summer and autumn and reach maximums of 19 °C in intensity. A strong correlation was found between wetness and surface temperature (coefficient of determination, 0.8) in spring and winter. Soil wetness directly impacts the formation of weak urban heat islands in dry season, and intense ones in wet season, while the green areas and the winds affect the spatial distribution of the same.  相似文献   

Estimating parameters of the channel width–flow discharge relation using rill and gully channel junction data     

M. Pilar Salvador Sanchis  Dino Torri  Lorenzo Borselli  Rorke Bryan  Jean Poesen  Marta S. Yañez  Cati Cremer 《地球表面变化过程与地形》2009,34(15):2023-2030

Eroding channels can usually be characterized by a power relationship between channel width (W) and channel discharge (Q). This paper examines the WQ relation using a recently developed channel junction approach to extend the validity of the WQ relation and to develop a procedure for estimating the WQ exponent and proportionality coefficient. Rill and gully channel data from the literature, and new data collected in different badland areas and in a few forest mountain streams, are analysed. Analysis shows that the WQ relation for channel width collected in badlands and forests agrees with trends observed for cropland. The exponent increases with increasing channel width in a continuous fashion rather than in a step‐like way and tends to a maximum whose value ranges between 0·5 and 0·6. The proportionality coefficient can be split into two terms, one expressing the case in which an eroding channel can broaden, the other reflecting the difficulties in removing the less erodible clods or rock fragments from the channel bed. Its splitting allows the development of a more correct form of the WQ relation in agreement with modern approaches of channel geometry: one part has the dimension of a discharge and makes the power base dimensionless, while the other brings the dimension of a length, needed for the channel width, into the WQ relation. The interpretation of the two constants is supported by data collected in rainfall‐runoff simulation experiments conducted in the field. Values characterizing the two constants in some environments are also given. Nevertheless the approach is not sufficiently parameterized yet to be of practical use (e.g. in models or for estimating peak discharge in areas where rill channels have formed). Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Morphodynamics and seismostratigraphy of a deep hole at tidal channel confluence     

Silvia Susana Ginsberg  Salvador Aliotta  Guillermo O. Lizasoain   《Geomorphology》2009,104(3-4):253-261

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Analysis of housing price by means of STAR models with neighbourhood effects: a Bayesian approach     

Asuncion Beamonte  Pilar Gargallo  Manuel Salvador 《Journal of Geographical Systems》2010,12(2):227-240

In this paper, we extend the Bayesian methodology introduced by Beamonte et al. (Stat Modelling 8:285–311, 2008) for the estimation and comparison of spatio-temporal autoregressive models (STAR) with neighbourhood effects, providing a more general treatment that uses larger and denser nets for the number of spatial and temporal influential neighbours and continuous distributions for their smoothing weights. This new treatment also reduces the computational time and the RAM necessities of the estimation algorithm in Beamonte et al. (Stat Modelling 8:285–311, 2008). The procedure is illustrated by an application to the Zaragoza (Spain) real estate market, improving the goodness of fit and the outsampling behaviour of the model thanks to a more flexible estimation of the neighbourhood parameters.  相似文献   

Evidence of site amplification from ground motion of the last two large crustal earthquakes in central-western Argentina     

Alvarado  Patricia  Christiansen  Rodolfo  Gregori  Salvador Daniel  Saez  Mauro 《Natural Hazards》2020,102(3):1011-1031

Natural Hazards - The present study has investigated site amplification effects from the analysis of peak ground accelerations (PGA) and spectral accelerations (SA) of the last two major crustal...  相似文献   

Stock Evaluation of Three Littoral Echinoid Species on the Catalan Coast North-Western Mediterranean   总被引：2，自引：0，他引：2  

Cruz  Palacín  Xavier  Turon  Manuel  Ballesteros  Gonzalo  Giribet Salvador  López 《Marine Ecology》1998,19(3):163-177

Abstract. We estimated the abundances of the three common littoral echinoid species Paracentrotus lividus, Arbacia lixula and Sphaerechinus granularis in a littoral zone between 0 and 10m depth on the Catalan shores NE Spain. Densities of each species were estimated from a total number of 11 571× 1 m² sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was estimated at the scale of the sampling unit 1 m² taking into account the fractal dimension of the shore. The stocks individuals > 2cm test diameter of these species for the whole Catalan shore ≅ 300 km, straight-line distance were estimated to be about 279.1 × 10⁶ individuals for P. lividus , 28.9 × 10⁶ individuals for A. lixula and 10.9 × 10⁶ individuals for S. granularis. These sea-urchins are key species in the regulation of algal communities and some of them P. lividus. S. granularis are of commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressures of human origin.  相似文献   

Storm Dispersal of Volcanogenic Sands from Buenos Aires, Where Heavy-Metal Concentrations Are Heavy-Mineral Segregations     

Federico I. Isla  Salvador Aliotta 《Marine Georesources & Geotechnology》1999,17(4):357-370

The southeastern beaches and inner shelf of the Buenos Aires coastline are dominated by storms coming from the south and southeast. Erosion is dominant at the coastal cliffs and abrasion platforms, while deposition is extended below the 9-m contour depth. In relation to sand abundance on the inner shelf, there is a northward transition between shelly sand sheets, a fine-sand ribbon field, and sand ridges with oblique megaripples. Side-scan records indicate the selective sorting processes that lead to grain size diminishing to the north, and heavy-mineral enrichment, either at the beach or on the shelf. These storm-induced effects should be considered when evaluating placers on the inner shelf or monitoring the heavy-metal content in sediments. Two-way analyses of variance (ANOVA) tests were used to establish the grain-size effects on heavy-metal analysis.  相似文献   

Evolution of a coastal alluvial deposit in response to the last Quaternary marine transgression, Bahía Blanca estuary, Argentina     

Darío Andrés Giagante  Salvador Aliotta  Silvia Susana Ginsberg  Laura Gabriela Vecchi  Jorge Osvaldo Spagnuolo 《Quaternary Research》2011,75(3):614-623

The purpose of this research is to analyze the seismostratigraphic and paleoenvironmental features of an ancient fluvial deposit characterized by the presence of paleochannels and sedimentary structures in Bahía Blanca estuary, Argentina. To this end, high-resolution seismic methods were used. Paleochannels exhibiting v-shaped cuts were found at different topographic positions at the base of this deposit. It was observed that channel silting is indicative of the relative change of river base level and the consequent migration of fluvial tributaries. This alluvial deposit is composed of low compacted fine sand and its middle–upper facies is characterized by the presence of horizontal and discontinuous wavy reflectors. The upper boundary of this deposit is an erosive discontinuity resulting from Holocene sea-level rise during which the mouth of old fluvial courses underwent changes. The deposit was subsequently buried by sandy and clayey silt sediments. The paleodrainage at subbottom indicates that this deposit is associated with an ancient river mouth. Based on the seismostratigraphic and lithological characteristics and the paleochannel structures found in the study area, it can be concluded that the deposit analyzed is an alluvial sequence formed in the period from the Middle-Late Pleistocene to Holocene marine transgression.  相似文献