Results 1 - 10 of 1275
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[en] The discovery of natural radioactivity and the applications of nuclear physics to the study of sediments and sediment content, allow for the delimitation of the chrono-stratigraphic and paleoclimatic framework of fossil Man. This chronology is based on the development of continental glacial phenomena and is specified through comparison with various methods: paleomagnetic inversion, the variation of oxygen isotopic composition of marine biogenic carbonates and the dating methods. Pleistocene and Holocene era are reviewed. (authors). 9 figs., 90 refs
[en] The circum-Mediterranean region is characterized by a strongly seasonal climate with rainy winters and intense summertime drought, steep topography, and a multi-millennial history of intensive human land use, all of which make its soils vulnerable to erosion. The historical and stratigraphic record documents severe and long-term soil erosion in several locations in the Mediterranean. A forest-to-scrub transition in Mediterranean vegetation between the mid-Holocene (6,000 yr BP) and the present is evident in the observational palaeorecord. Debate as to the causes of this shift is ongoing. This study seeks to test the sensitivity of large-scale vegetation patterns to changes in soil physical properties such as depth, content of coarse fragments, and organic matter content using the Mediterranean region as a case study. We find that simulated biomes are sensitive to changes in some soil physical properties at some locations, but that threshold values for soil change to affect vegetation are very high. Additional work is required to analyze the role that other soil physical properties, and climate change, played in influencing Holocene land cover change in the Mediterranean, and to improve model representations of relevant processes.
[en] The Marseille-Aubagne Basins, which extend from Marseille to Roquevaire, occupy more than fifty per cent of the Marseille-Aubagne geological map, with approximately one million people living in this area. Despite this geological importance they are still poorly known. The first synthetic view was delivered in the 1935 geological map. Studied by Bonifay, the Quaternary deposits have been included in the 1969 geological map. Nevertheless, the Oligocene formations remained unmodified until Nury, who provided a lot of very detailed stratigraphic data. New studies have been carried out in the frame of the third issue of the 1:50,000 geological map. These studies allow us to distinguish between three different basins: the ''Jarret basin'' in the northern part, the ''Prado basin'' in the southwestern part and the ''Aubagne basin'' in the eastern part. Each of them contains its own stratigraphic succession, including several formations from the Rupelian to the Chattian. Globally, the Lower to Upper Rupelian formations are tectonically deformed, whilst deposits from the Latest Rupelian to the Latest Chattian show only slight deformation. Thus, two main geodynamic stages have been distinguished: the first beginning with the Early Oligocene extensive regime leading to the opening of NNE-SSW troughs all over the European platform and, the second, beginning with a NNW-SSE extensive regime coeval with the Western Mediterranean rifting. The key point that separates these two stages from each other is a possible Late Rupelian compressive regime. To sum up, this basin can be considered as a natural archive for the Oligocene events. Therefore, these basins should be considered as master pieces for the Oligocene palaeogeographic and geodynamic reconstructions. (Author)
[en] Two quantitative methods were used to reconstruct paleoenvironments and vegetation in the Altai-Sayan mountains, Central Asia, during the Holocene. The 'biomization' method of Prentice et al (1996 Clim. Dyn. 12 185-96), applied to the surface pollen record, worked fairly well in the reconstructions of current vegetation. Applying this method to fossil pollen data, we reconstructed site paleovegetation. Our montane bioclimatic model, MontBioCliM, was used inversely to convert site paleovegetation into site paleoclimates. The differences between site paleo and current climates served as past climate change scenarios. The climatic anomalies for 2020, 2050, and 2080 derived from HadCM3 A1FI and B1 of the Hadley Centre, UK, served as climate change scenarios in the 21st century. MontBioCliM was applied directly to all climate scenarios through the Holocene to map past and future mountain vegetation over the Altai-Sayan mountains. Our results suggest that the early Holocene ca 10 000 BP was cold and dry; the period between 8000 and 5300 BP was warm and moist; and the time slice ca 3200 BP was cooler and drier than the present. Using kappa statistics, we showed that the vegetation at 8000 BP and 5300 BP was similar, as was the vegetation at 10 000 BP and 3200 BP, while future vegetation was predicted to be dissimilar to any of the paleovegetation reconstructions. The mid-Holocene is frequently hypothesized to be an analog of future climate warming; however, being known as warm and moist in Siberia, the mid-Holocene climate would likely impact terrestrial ecosystems differently from the projected warm and dry mid-century climate.
[en] The present field and GPR based investigations were carried out along the E–W trending Gedi Fault to precisely constrain the field location and shallow subsurface nature of the fault. The field investigations revealed the presence of thin Quaternary sedimentary cover, especially in the central and western part. Field examination of the scanty exposures showed that the fault trace marks the lithotectonic contact between Mesozoic rocks in the north and the Tertiary (Miocene) sediments to the south. Five sites were selected after field studies for GPR investigations of the Gedi Fault. The well-compacted Mesozoic rocks showed high amplitude returns while the softer and finer grained Tertiary sediments yielded low amplitude returns. The Quaternary sediments are reflected as consistent with wavy reflections in the upper parts of the profiles. The GPR data indicate that the Gedi Fault is a steep north dipping reverse fault which becomes vertical at depth. Since the fault does not displace the Quaternary deposits, we infer that the Gedi Fault has been characterized by low to moderate seismic activity under a compressive stress regime during the late Quaternary period. (paper)
[en] The products of bottom current circulation around the Iberian continental margin are characterised by large erosional and depositional features formed under a variety of geological and oceanographic contexts. The Iberian margins are influenced by several water masses that mainly interact along the upper and middle con- tinental slopes, as well as along the lower slope with the abyssal plains being influenced to a lesser extent. The main depositional features occur along the Ceuta Contourite Depositional System (CDS) within the SW Alboran Sea, in the Gulf of Cadiz (the most studied so far), the western margins of the Portugal/Galician mar- gin, the Ortegal Spur and the Le Danois Bank or Cachucho. Moreover, erosional contourite features have also been recently indentified, most notably terraces, abraded surfaces, channels, furrows and moats. The majority of these features are formed under the influence of the Mediterranean water masses, especially by the interaction of the Mediterranean Outflow Water (MOW) with the seafloor. The MOW is characterized as relatively warm (13 degree centigrade) and with a high salinity (∼36.5), giving it a high density relative to the surrounding water masses, hence constituting an important contribution to the global thermohaline circulation, making it one of the most studied water masses surrounding Iberia. The development of both depositional and ero- sional contourite features does not only depend on the bottom-current velocity but also on several other important controlling factors, including: 1) local margin morphology affected by recent tectonic activity; 2) multiple sources of sediment supply; 3) water-mass interphases interacting with the seafloor; and 4) glacioeustatic changes, especially during the Quaternary, when the increasing influence of the bottom cur- rent has been observed during the cold stages. The main objective of this special volume contribution is to provide a review and description of the regional along-slope processes and their sedimentary impact around the Iberian margin. Despite the numerous examples of bottom current processes recorded, there remains a number of challenges to understanding CDSs around the Iberian margin including: 1) evidencing their important scientific implications (stratigraphy, sedimentology, palaeoceanography and palaeoclimatology); assess- ing their geological hazard and their economic potential (for mineral and energy resources); and 3) using them to create conceptual models for CDS formation. There is a lack of complete knowledge about the different oceanographic processes that may drive bottom currents, and there is also the need to document the great variety of contourite features (processes and products) and facies models, along with their evolution over time and space. Therefore advances, both in new technologies and integrated studies (Geology, Physical Oceanography and Benthic/planktonic Biology), are anticipated. (Author)
[en] It is possible to analyse a diverse range of samples for environmental investigations. The main types are soil/sediments, vegetation, fauna, shellfish, waste and water. Each type of samples requires different storage and collection methods. Outlined here are the preferred methods of collection to ensure maximum sample integrity and reliability. (author).
[en] The present article gives an overview of climate development during the Holocene epoch. It discusses at different time scales certain methodological and substantive aspects that are relevant to the assessment of contemporary climate scenarios and therefore deserve greater consideration than they receive at present. A strong emphasis is placed on research projects on the historical perspective. After an excursion to the various data types and methods of Historical Climatology the authors present some regionally differentiated findings. This gives an idea of climate variability in an experential dimension that the human mind is able to grasp. Many of the slow climate fluctuations become particularly illuminating when considered, for example, in conjunction with the cold period between 1550 and 1850. Another point of interest are the numerous extreme periods and anomalous findings. Climate fluctuations and climate desasters, while differing in their temporal and spatial characteristics, have accompanied mankind throughout history. (orig.)
[de]Der vorliegende Beitrag gibt einen Ueberblick zur Klimaentwicklung im Holozaen. Dabei werden auf verschiedenen Zeitebenen einige methodische und inhaltliche Aspekte diskutiert, die fuer die Bewertung heutiger Klimaszenarien von Interesse sind und daher wieder staerker beruecksichtigt werden sollten. Besondere Gewichtung liegt auf den Forschungsarbeiten zur historischen Zeitebene. Nach einem Exkurs zu den unterschiedlichen Datentypen und Verfahren der historischen Klimatologie werden einige regional differenzierte Befunde vorgestellt. Sie machen die Variabilitaet des Klimas in einer, dem Erfahrungsbereich des Menschen nahe liegenden Dimension besonders deutlich. Bemerkenswert sind viele der langfristigen Klimafluktuationen beispielsweise im Zusammenhang mit der Kleinen Eiszeit ebenso wie die zahlreichen Extremereignisse und Anomalien. Klimafluktuationen und Klimakatastrophen waren in unterschiedlicher raum-zeitlicher Auspraegung und Intensitaet ein staendiger Begleiter des Menschen. (orig.)
[en] Geoarchaeological research carried out in NE Spain have focused on the study of Holocene geoarchaeological records linked with settlement areas from Neolithic to Middle Age and Little Ice Age. The dynamic of geomorphological processes, characteristic of these drylands, allow us to obtain fast and identifiable answers in the way of sedimentary records. These records are the consequence of slight changes in the slope stability and the operation of river systems. In this paper we present a synthesis of the information provided by slopes, rock shelters, valley bottoms, and alluvial fans. A succession of evolutionary stages was obtained on each environment identifying its origin according to Holocene climate fluctuations and human intervention over territory. The results of this research are of great interest when applied to archaeological prospection, the knowledge of past settlements, and the paleo-environmental reconstruction of NE Spain, where the strong erosion complicates the conservation of many archeological sites.
[es]Los trabajos geoarqueológicos realizados en el NE de España se han centrado en el estudio de registros sedimentarios holocenos relacionados con áreas de ocupación que abarcan desde el Neolítico hasta Época Medieval y la Pequeña Edad del Hielo. El dinamismo de los procesos geomorfológicos en estos ambientes semiáridos permite obtener respuestas rápidas e Identificables en forma de registros sedimentarios como consecuencia de pequeños cambios en la estabilidad de las laderas y en el funcionamiento de los sistemas fluviales. En este trabajo se sintetiza la información aportada por el análisis de laderas, abrigos rocosos, fondos de valle y conos aluviales. Se ha obtenido una sucesión de etapas evolutivas en cada uno de estos ambientes a partir de los cuales se intenta discriminar su génesis en relación con las fluctuaciones climáticas del Holoceno y con la intervención humana sobre el territorio. Los resultados de estos trabajos son de gran interés aplicado para la prospección arqueológica, para el conocimiento del poblamiento en épocas pasadas y para la reconstrucción paleoambiental en el NE de España, donde la fuerte erosión ha dificultado la conservación de numerosos yacimientos.