Vertical and lateral building of river sandstone bodies, Ebro Basin, Spain

Six examples of river sandstone bodies are described from well exposed sections of Oligocene and Miocene age in the Ebro Basin, northern Spain. Three of these are of ribbon form, varying in cross-section from 10 m wide × 2 m high to 20 m wide × 9 m high. In plan these ribbons vary from straight to highly sinuous. The sandstone bodies, in two cases, are multi-storey, clearly demonstrating a series of vertical building episodes. The fourth sandstone body may have a ribbon or sheet geometry, and is of special interest because it demonstrates lateral building by a laterally migrating channel, as well as some vertical building. The fifth and sixth sandstone bodies are of sheet geometry, and demonstrate lateral migration of channels and depositional surfaces. Factors that appear to be most important in determining whether a river migrates laterally or remains stable laterally are: (1) river mean flow strength, (2) bank strength, (3) flood periodicity and duration, (4) vertical movement of the alluvial area.