23 research outputs found

    Quaternary glacial history of the Mediterranean mountains

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    Glacial and periglacial landforms are widespread in the mountains of the Mediterranean region. The evidence for glacial and periglacial activity has been studied for over 120 years and it is possible to identify three phases of development in this area of research. First, a pioneer phase characterized by initial descriptive observations of glacial landforms; second, a mapping phase whereby the detailed distribution of glacial landforms and sediments have been depicted on geomorphological maps; and, third, an advanced phase characterized by detailed understanding of the geochronology of glacial sequences using radiometric dating alongside detailed sedimentological and stratigraphical analyses. It is only relatively recently that studies of glaciated mountain terrains in the Mediterranean region have reached an advanced phase and it is now clear from radiometric dating programmes that the Mediterranean mountains have been glaciated during multiple glacial cycles. The most extensive phases of glaciation appear to have occurred during the Middle Pleistocene. This represents a major shift from earlier work whereby many glacial sequences were assumed to have formed during the last cold stage. Glacial and periglacial deposits from multiple Quaternary cold stages constitute a valuable palaeoclimatic record. This is especially so in the Mediterranean mountains, since mountain glaciers in this latitudinal zone would have been particularly sensitive to changes in the global climate system. © 2006 Edward Arnold (Publishers) Ltd

    Low-sea-level emplacement of a very large Late Pleistocene 'megaturbidite' in the western Mediterranean Sea

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    Large-volume turbidites, termed 'megaturbidites' or 'megabeds', result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea. Such large sediment failures can generate tsunamis and, in terrains underlain by gas hydrates (clathrates), may be associated with the release of substantial amounts of the greenhouse gas methane. It has been proposed that the megaturbidite events may be triggered by seismic activity, or may result from gas hydrate release itself, caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level. Previous conclusions on the significance of sea-level change, however, have been conditional because of the lack of absolute times of turbidite emplacement. Here we use accelerator-mass-spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large-volume (500 km3) bed in the Balearic Basin of the western Mediterranean. This turbidite is exceptional in its magnitude and represents the main sedimentation event in the Balearic Basin over the past 100 kyr. Our data provide an estimate of 22,000 calendar years before present for emplacement of the megabed, a time when sea level stood at its lowest level during the Last Glacial Maximum. The coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level, although other triggering mechanisms, such as seismic shock, cannot be ruled out
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