Interpreting the stratigraphic architecture of fluvial systems in internally drained basins

Abstract

Models for fluvial architecture tend to focus on the effects of sea-level oscillation and syndepositional tectonics in creating and removing accommodation space and determining the relative distribution of channel and overbank deposits in the stratigraphic record. However, in basins of internal drainage sea-level change does not exert any influence and in settings where basin centre lakes are very shallow, fluctuations in lake level have little impact on the fluvial system. If there is variation in tectonic subsidence across the area this will affect depositional patterns, but otherwise subsidence does not play a role in affecting sediment distribution in an endorheic setting. The Luna and Huesca Systems were deposited in the endorheic Ebro Basin at a time when deformation in the adjacent Pyrenees had largely ceased. Hundreds of metres of fluvial and lacustrine sediment accumulated, raising the level of the basin centre by stratigraphic aggradation and back-filling of hinterland valleys. During aggradation the systems appear to have maintained a constant slope across the fluvial profile. The resulting stratigraphic architecture is well displayed in the Ebro Basin and provides a case study of architectural patterns in endorheic settings, which is in marked contrast to those described from fluvial successions formed in externally draining systems.