The impact of a major Quaternary river capture on the alluvial sediments of a beheaded river system, the Rio Alias SE Spain

The Rio Alias is a transverse river system developed within the Sorbas and Almeria Neogene sedimentary basins within the Internal Zone of the Betic Cordillera, southeast Spain. Headwaters of the Rio Alias rise in the southern margins of the Sorbas basin following a superimposed transverse course across the Sierra Alhamilla/Cabrera and its associated boundary faults. A major river capture event within the Sorbas Basin (c.70 ka) created a situation whereby the Rio Alias abruptly lost c. 70% of its drainage area. Such an extensive loss of drainage area led to significant modification of the fluvial system in both upstream and downstream zones on the capturing stream, and downstream on the beheaded system. On the beheaded Rio Alias, a combination of terrace mapping, clast identification/analysis, field descriptions of pedological development and mineral magnetic analysis allows the relative timing of the capture event to be confirmed. Examination of the fluvial architecture of the Quaternary terrace deposits reveals significant changes in bedform geometry, involving a reduction in bedform height, degree of channelisation and maximum clast size in the post-capture sediment assemblage. The post-capture evolution of the Rio Alias has been heavily influenced by the river capture event, highlighting the need for further analysis of beheaded drainage systems and their influence on developing landform assemblages.