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Accelerated fluvial aggradation during the Pleistocene in response to karst dissolution (Ebro-Gállego river system, NE Spain). In: Long term river evolution and fluvial dynamics,

AuthorsBenito, Gerardo ; Sancho, Carlos; Peña, José Luis; Machado, María José ; Rhodes, Edward J.
Issue Date2010
AbstractThe evolution and morpho-sedimentary features of some of the most important river systems of the Iberian Peninsula, such as the Ebro-Gállego system, have been controlled by the karstification of evaporitic bedrock. Along the lower Gállego river, evaporitic dissolution and volume loss underneath the alluvial cover gave rise to a solution-induced depositional basin 30 km-long by 8 km-wide infilled by up to 110 m of alluvial deposits (Benito et al., 1998, 2000). A detailed morpho-sedimentary analysis of these alluvial deposits supported with OSL dating has revealed that paleokarst subsidence and accelerated fluvial aggradation occurred at discrete time periods. An older, long-lasting period started in the Early Pleistocene and affected terrace levels T2, T3 and T4. A subsequent shorter-term Middle Pleistocene period affected terrace level T9 dated at 140-155 kyr (end of MIS 6). Subsidence not only affected stream terraces but also the extensive contemporaneous alluvial fans. The most important source of water enhancing surface-groundwater interaction and flushing a large volume of salts was provided by the Gállego headwaters. Correlation of the alluvial deposits affected by subsidence at the lower Gállego (140-150 kyr) with fluvio-glacial deposits within the upper catchment (156±10 and 155±24 kyr) provide evidence of prevailing cold conditions, large outwash discharges and high sediment yields associated with solution induced subsidence in the lower reach. This Middle Pleistocene subsidence episode also correlates with hydrological proxies indicating a prolonged (149 to 141 kyr) salinity drop at the Mediterranean Iberian margin interpreted previously as related to a Heinrich event (Martrat et al. 2004), but may instead reflect an anomalously long-lasting period of high river discharge enhanced by seasonal melting from glaciated mountains.
Appears in Collections:(MNCN) Comunicaciones congresos
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