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RAÚL DE LA HORRA Ma ISABEL BENITO JOSE LÓPEZ‐GÓMEZ ALFREDO ARCHE JOSÉ F. BARRENECHEA JAVIER LUQUE 《Sedimentology》2008,55(6):1849-1873
The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis. 相似文献
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EULOGIO PARDO‐IGÚZQUIZA ANTONIO PULIDO‐BOSCH MANUEL LÓPEZ‐CHICANO JUAN J. DURÁN 《Geografiska Annaler: Series A, Physical Geography》2016,98(3):247-263
Dolines are the most typical landform in karst landscapes. They play an important role in karst hydrogeology; they are effective sediment traps that provide information about past climates and karst evolution, and can also be indicators of tectonic activity. The morphometic analysis of those depressions can help in their study and interpretation. However, detailed identification and delineation of dolines becomes increasingly difficult when the study area is very large, of limited access or covered by vegetation. Here, we have used a method developed by the authors for automatic identification and delineation of karst depressions based on the use of a pit removal algorithm. Next a complete morphometric analysis of the karst depressions has been carried out. The main advantage of the methodology is that by delineating and identifying the depth of each doline from its rim, many morphometric statistics can be obtained, including the relation of doline depth and area with respect to altitude, the main doline orientations, doline density, the fractal dimension of doline area and frequency, and point field analysis, among others. The results are interpreted from a geomorphological point of view and the mapped dolines can be easily integrated into geomorphological mapping. A case study is presented from the large Sierra Gorda karst massif in southern Spain, where 3100 depressions have been identified. A strong structural control of doline shape and orientation is demonstrated; the main areas of doline density are highlighted and doline size is shown to follow a fractal law. 相似文献
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GUDRÚN LARSEN Bryndís G. Róbertsdóttir Bergrún A. Óladóttir JÓN EIRÍKSSON 《第四纪科学杂志》2020,35(1-2):143-154
Hekla volcano is a major producer of large, widespread silicic tephras. About 3000 years ago, the dominant eruption mode shifted from infrequent large (>1 km3) to more frequent moderate (<1 km3) eruptions. In the following two millennia ≥20 explosive silicic-to-intermediate eruptions occurred, and six or more basaltic. Three categories can be identified with dacite/andesite to basaltic andesite in the oldest eruptions through basaltic andesite to basalt in the youngest eruptions. Ten tephra layers of the first category have distinct field characteristics: a pale lower unit and a dark upper unit (two coloured or TC-layers). Colour separation is sharp indicating a stratified magma chamber origin. The lower unit is dominantly andesitic (61–63% SiO2), while the upper unit is basaltic andesite (53–57% SiO2). Volumes of the eight largest TC-layers range from 0.2 to 0.7 km3 as freshly fallen. Radiocarbon and soil accumulation rate dates constrain the TC-layers to between 3000 and 2200 years ago. Two of these (~2890 and ~2920 b2k) are likely to occur overseas. Low SiO2 in the last erupted tephra of the TC-layers is comparable to that of historical Hekla lavas, implying a final effusive phase. The Hekla edifice may, consequently, be younger than 3000 years. 相似文献
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The solute and suspended‐sediment load following five rainstorms (2005–2007) with varied intensities were studied at the Vernegà experimental watershed, north‐western Spain. Two land‐use areas are located within this watershed, the upstream one (forest) with 160 ha a 100% forested area, and the downstream one (agricultural) with 97 ha being 9 ha conventional agricultural field and 88 ha forest. This study investigates the capacity of each land‐use to yield water, suspended sediment concentration (SSC) and dissolved solid concentration (DSC). The hypothesis is that DSC and SSC from the agricultural area are greater than DSC and SSC of the forest area. Results showed that the agriculture area produced significantly greater mean DSC than in the forest area, the main contribution was the Ca2+ (24·68 ± 46·52 mg l?1) ion at the agricultural area. A long‐term sediment production rate at the agricultural outlet was calculated (69·1 tonnes per 100 years) based on the total sediment discharge (TSD) and the recurrence interval of the largest event of the five rainstorms (October 2005). Geographic information system (GIS) spatial data layers of the watershed were produced to determine the relation of tracks, landforms, slopes and forest management to SSC yield in the forest outlet (133·89 ± 308·14 mg l?1) during the five rainstorms. Agriculture practices are the main cause of soil erosion at the study area. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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DEFORMATIONAL BEHAVIOURS OF ALLUVIAL UNITS DETECTED BY ADVANCED RADAR INTERFEROMETRY IN THE VEGA MEDIA OF THE SEGURA RIVER,SOUTHEAST SPAIN 
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Anticlockwise P-T Path of Granulites from the Monte Castelo Gabbro (Ordenes Complex, NW Spain) 总被引：1，自引：0，他引：1
ABATI JACOBO; ARENAS RICARDO; MARTINEZ CATALAN JOSE RAMON; DIAZ GARCIA FLORENTINO 《Journal of Petrology》2003,44(2):305-327
The study of mafic and aluminous granulites from the Monte CasteloGabbro (Órdenes Complex, NW Spain) reveals an anticlockwiseP–T path that we interpret as related to the tectonothermalactivity in a magmatic arc, probably an island arc. The P–Tpath was obtained after a detailed study of the textural relationshipsand mineral assemblage succession in the aluminous granulites,and comparing these with an appropriate petrogenetic grid. Additionalthermobarometry was also performed. The granulites are highlyheterogeneous, with distinct compositional domains that mayalternate even at thin-section scale. Garnets are generallyidiomorphic to subidiomorphic, and in certain domains of thealuminous granulites they show overgrowths forming xenomorphiccoronas around a more or less idiomorphic core. Both types ofgarnets show significant Ca enrichment at the crystal rims,which, together with the other mineralogical and textural characteristics,is compatible with a pressure increase with low T variation.P–T estimations indicate a peak of T > 800°C andP 相似文献
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Exhumed channel sandstone networks within fluvial fan deposits from the Oligo-Miocene Caspe Formation, South-east Ebro Basin (North-east Spain) 总被引：1，自引：0，他引：1
JOSE L. CUEVAS MARTÍNEZ† LLUIS CABRERA PÉREZ† ALEX MARCUELLO‡ PAU ARBUÉS CAZO† MARIANO MARZO CARPIO† FABIA BELLMUNT‡ 《Sedimentology》2010,57(1):162-189
The Oligo‐Miocene Caspe Formation corresponds to the middle fluvial facies of the wider Guadalope‐Matarranya fluvial fan, located in the South‐east Ebro foreland basin (North‐east Spain). At the time of the Caspe Formation deposition, this sector of the Ebro basin underwent a very continuous, moderate sedimentation rate. Lithofacies comprise deposits from channellized and unchannellized flows. Channellized flow lithofacies form multi‐storey ribbon‐like sandstone bodies that crop out as extensive sandstone ridges belonging to exhumed channel networks. Width/thickness ratios of these channel‐fill bodies average close to six. Sinuosity is usually low (most common values around 1·1), although it can be high locally (up to 2). Thicknesses range from a few metres to 15 m. Unchannellized flow lithofacies form tabular bodies that can be ascribed to overbank deposits (levées, crevasse splays and fine‐grained floodplain deposits) and also to frontal lobes, although recognition of this last case requires exceptional outcrop conditions or geophysical subsurface studies. The unchannellized flow lithofacies proportion ranges from 75% to 97·8%. Methods applied to this study include detailed three‐dimensional architectural analysis in addition to sedimentological analysis. The architecture is characterized by an intricate network of highly interconnected ribbon‐like sandstone bodies. Such bodies are connected by three kinds of connections: convergences, divergences and cross‐cuttings. Although the Caspe Formation lithofacies and architecture resemble anastomosed channels (low topographic gradient, high preservation potential, moderate aggradation rate, high lateral stability of the channels, dominance of the ribbon‐like morphologies and high proportion of floodplain to channel‐fill sediments), an unambiguous interpretation of the channel networks as anastomosed or single threaded cannot be established. Instead, the observed architecture could be considered as the product of the complex evolution of a fluvial fan segment, where different network morphologies could develop. A facies model for aggrading ephemeral fluvial systems in tectonically active, endorheic basins is proposed. 相似文献