Influencia del substrato sobre la arquitectura y características texturales de los sistemas fluviales: Desarrollo de paleovalles y su relleno

Abstract

Oligocene sedimentation into SW border of Duero Basin (Spain) took place in a tectonically active basin margin. Close examination of these deposits and their relations to paleotopography reveals a strong interaction between the degree of valley incision, i.e. paleovalley development, and architecture of the deposits. Uplift of the margin basin coupled to differences in the erosionability of the substratum of (future) river valleys led to inhomogeneus response along the river beds that resulted in. paleotopographical constraints for the inciding sedimentary systems. Hard-rocks in the substratum conditioned the development of narrow, usually deeply-incised, paleovalleys. By contrast, cut areas where the substratum consisted of soft rocks allowed the development of wider, shallower valleys. The relativelly-narrow passageways cut into areas with hard substratum filled up with coarse sediments related to hyperconcentrated flows, whereas the wider valleys cut into softer terrains contain well- differentiated finer-grained channel-floodplain deposits. The close concordance between hydrological equations and field observations confirms that textural and architectural features are strongly dependent on the morphological setting