Sandstone-body structure and river process in the Ebro Basin of Aragón, Spain.

The Miocene fluvial sediments of the Aragon part of the Ebro basin, northern Spain, provide remarkable exposuresof sandstone bodies.Three different types of sandstonebodies can be distinguished in terms of the form of their externalmorphology: ribbons, sheetsand amalgamatedcomplexes.Ihe internal structuresof the ribbon sandstonebodiesshow that theyresultedfrom at leastonechannelincision event, followed by the plugging of the channel, sometimesachieved only after a whole seriesof incísion and plugging cycles. In contrast, the sheetsandstonebodies may haveresultedfrom eitherchannelisedor unchannejisedf]ow. Wherechanneiswere involved, they slrnw evidence of migration by lateral bank erosion, either involving a single phase of progressivemigration, or involving complexreworking of íhe earlier phasesof channel deposits.Amalgamationoccurredwhen the erosion that precededribbon or sheetsandstonedepositioncut into an earlier sandstonebody. Whenthis createda complexgeometry,we distinguish a separatetype. Ribbon bodies will tend to result from eptemeral river f]ow or periodic uplift of the alluvial surface.Amalgamationwill tend to result from changesof hydrology, local alluvial uplift or tectonic tilting,