Palynological Evidence for Climatic Change and Human Activity during the Holocene on Minorca (Balearic Islands)     

Errikarta-Imanol Yll  Ramon Perez-Obiol  Jose Pantaleon-Cano  Joan Maria Roure 《Quaternary Research》1997,48(3):339-347

Four pollen diagrams from Minorca (Balearic Islands) have been correlated with other previously studied sequences from Majorca and Minorca to define a Holocene landscape sequence for the region from 8000 yr B.P. to the present. The lower part of the pollen diagrams reflects a climatic phase with more rain and less-marked seasonality than today. Significant quantities ofCorylus, Buxus,and mesophilous taxa are found. In the middle part, between 5000 and 4000 yr B.P., a strong change is recorded in composition and structure of the vegetational landscape, with vegetation appearing that was adapted to Mediterranean conditions. This episode coincided with the first human colonization of the island and also with a widespread climatic change in the western Mediterranean region. The change in taxa was complex and some sclerophyllous taxa suchOleaplayed an important role in the transformation of the landscape physiognomy from the mid-Holocene until the present. Although human activities have removed much of the Mediterranean vegetation on the Balearic Islands, it seems clear that the changes have been brought about, in part, by increasing dryness.  相似文献   

Applicability of a Backprojection Algorithm to Reconstruct Images of Subsurface Horizontal Planes for Laboratory Experiments in Electrical Resistance Tomography     

Josep Jordana  Ramon Pallàs-Areny 《Mathematical Geology》2004,36(1):127-141

This paper describes the use of a backprojection algorithm to reconstruct subsurface images of the electrical resistivity in horizontal planes parallel to the surface. The algorithm can be applied to detect buried objects such as tanks or pipes and possible leakages from them. Two imaging strategies are compared: juxtaposition of vertical planes, and 3D reconstruction from the sensitivity matrix corresponding to the entire volume whose surface is explored. The electrode arrays used for voltage measurement are the dipole–dipole array and a modified Schlumberger array. A personal computer controls current injection, electrode switching, and voltage detection. The system injects 1 kHz, 20 V peak-to-peak square waveforms, thus avoiding electrode polarization effects. Experimental laboratory measurements show that the algorithm detects localized objects such as an insulating sphere and a conductive cylinder immersed in water. Furthermore, covering half of the cylinder by a rubber sleeve to simulate a nonconductive leak, yields a distinct image for the leak. The backprojection algorithm does not need any regularization parameter and it is very fast in inverting the sensitivity matrix because it approximates the inverse matrix by its transposed. The dipole–dipole array usually yields a lower overall pixel error than the modified Schlumberger array but both allow the detection of simulated underground leaks.  相似文献   

Nature and evolution of the lithospheric mantle under an internal Variscan zone     

Ramon Capdevila 《Comptes Rendus Geoscience》2004,336(15):1321-1322

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Vegetation dynamics during the late Pleistocene in the Barreirinhas region, Maranhão State, northeastern Brazil, based on carbon isotopes in soil organic matter     

Luiz Carlos Ruiz Pessenda  Adauto de Souza Ribeiro  Ramon Aravena  José Albertino Bendassolli 《Quaternary Research》2004,62(2):183-193

The study place is in the Barreirinhas region, Maranhão State, northeastern Brazil. A vegetation transect of 78 km was studied among four vegetation types: Restinga (coastal vegetation), Cerrado (woody savanna), Cerradão (dense woody savanna), and Forest, as well as three forested sites around Lagoa do Caçó, located approximately 10 km of the transect. Soil profiles in this transect were sampled for δ¹³C analysis, as well as buried charcoal fragments were used for ¹⁴C dating. The data interpretation indicated that approximately between 15,000 and ∼9000 ¹⁴C yr B.P., arboreal vegetation prevailed in the whole transect, probably due to the presence of a humid climate. Approximately between ∼9000 and 4000-3000 ¹⁴C yr B.P., there was the expansion of the savanna, probably related to the presence of drier climate. From ∼4000-3000 ¹⁴C yr B.P. to the present, the results indicated an increase in the arboreal density in the area, due to the return to a more humid and probably similar climate to the present. The presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the Holocene. The vegetation dynamic inferred in this study for northeastern Brazil is in agreement with the results obtained in areas of Amazon region, based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter (SOM), implying than similar climatic conditions have affected these areas during the late Pleistocene until the present.  相似文献   

Hydrological characterization of dammed rivers in the NW Mediterranean region          下载免费PDF全文

Gemma Piqué  Ramon J. Batalla  Sergi Sabater 《水文研究》2016,30(11):1691-1707

Water scarcity and climatic variability in the Mediterranean region have traditionally required the construction of dams to guarantee water supply for irrigation, industrial and urban uses and hydropower production. Reservoirs affect the hydrology of the river downstream, but the magnitude and persistence of these effects are still poorly unknown. Understanding the magnitude of these effects is the objective of this paper, in which we analyse the flow regimes of twelve rivers located in the NW Mediterranean region. Different temporal scales (daily, monthly and annual) are used for the analysis and also to estimate flow variables associated with flow magnitude, frequency, duration and variability. It is shown that dams alter the hydrological regime of most of the studied rivers, with special influence on monthly flows and flood magnitude and frequency. The most altered rivers (Muga and Siurana, NE Iberian Peninsula) experience a complete overturn in their flow regime with, for instance, flood reduction reaching up to 76% for the 2‐year flood event. Other rivers showed lower changes in hydrology (e.g. Orb and Têt). Annual runoff showed a pattern of decrease in all the studied rivers (regulated and non‐regulated) indicating that besides dams (i.e. reservoir evaporation), other factors likely affect water yield. A general recovery downstream from dams is also observed at all temporal scales, mainly because of the inflow from tributaries. Although dams have a clear impact on the hydrology of Mediterranean rivers, water withdrawals and diversions for irrigation and other consumptive uses also affected the hydrological patterns. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Multi-temporal InSAR evidence of ground subsidence induced by groundwater withdrawal: the Montellano aquifer (SW Spain)     

Ana Ruiz-Constán  Antonio M. Ruiz-Armenteros  Francisco Lamas-Fernández  Sergio Martos-Rosillo  J. Manuel Delgado  David P. S. Bekaert  Joaquim João Sousa  Antonio J. Gil  Miguel Caro Cuenca  Ramon F. Hanssen  Jesús Galindo-Zaldívar  Carlos Sanz de Galdeano 《Environmental Earth Sciences》2016,75(3):242

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Deep seismic exploration of the Iberian Microplate     

Juvenal Andres  David Marti  Ignacio Marzan  Imma Palomeras  Puy Ayarz  Fernando Simancas  DavidMartinez-Poyatos  Antonio Azor  Francisco Gonzalez-Lodeiro?  Jordi Diaz  Ramon Carbonel 《《地质学报》英文版》2018,92(Z1):11-11

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Discussion of ‘The Azuara impact structure (Spain): new insights from geophysical and geological investigations’ by K. Ernston and J. Fiebag     

Marc Aurell  Ángle González  A. Pérez  Joan Guimerà  Albert Casas  Ramon Salas 《International Journal of Earth Sciences》1993,82(4):750-755

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D. Gajewski, W. Rabbel (eds.), Seismic Exploration of the Deep Continental Crust Methods and Concepts of DEKORP and Accompanying Projects, Pageoph Topical Volumes.     

Ramon Carbonell 《Surveys in Geophysics》2001,22(1):93-95

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Seismogenic destruction of the Kamenka medieval fortress, northern Issyk-Kul region, Tien Shan (Kyrgyzstan)     

Andrey M. Korjenkov  J. Ramon Arrowsmith  Christopher Crosby  Ernes Mamyrov  Lyubov A. Orlova  Irina E. Povolotskaya  Kubatbek Tabaldiev 《Journal of Seismology》2006,10(4):431-442

A paleoseismological study of the medieval Kamenka fortress in the northern part of the Issyk-Kul Lake depression, northern Tien Shan in Kyrgyzstan, revealed an oblique slip thrust fault scarp offsetting the fortification walls. This 700 m long scarp is not related to the 1911 Kebin Earthquake (Ms 8.2) fault scarps which are widespread in the region. As analysis of stratigraphy in a paleoseismic trench and archaeological evidence reveal, it can be assigned to a major twelfth century a.d. earthquake which produced up to 4 m of oblique slip thrusting antithetic to that of the nearby dominant faults. The inferred surface rupturing earthquake apparently caused the fortress destruction and was likely the primary reason for its abandonment, not the Mongolian–Tatar invasions as previously thought.  相似文献