Stratigraphic Architecture of Fluvial Distributive Systems in Basins of Internal Drainage

Abstract

Stratigraphic models of fluvial successions tend to focus on the ‘incised valley’ model, which assumes that a marine base level exerts a strong control on the distribution of sandstones deposited by river channels. However, not all rivers flow to the sea and in basins of internal drainage there is no control exerted on river profiles by fluctuations in marine base level. Internal drainage basins are the sites of approximately half of the actively depositing fluvial systems today, and during periods of continental amalgamation, there would have been significant accumulations of continental successions in these endorheic basins. In relatively humid endorheic basins a deep basin-centre lake may act as a partial downstream control on fluvial successions. However, in temperate through to arid settings, rivers terminate in a shallow, perhaps ephemeral lake, dry out on an alluvial plain or interfinger with aeolian environments. In these settings the level of the downstream termination is related to aggradation in the basin, which is itself determined by sediment supply via the rivers. The fluvial system, its depositional patterns and the stratigraphic architecture are hence controlled by just discharge and sediment supply. A distributive fluvial pattern seems to be dominant in modern and modern and ancient endorheic basins. The fluvial successions formed by these systems in endorheic basins have a fundamentally different architecture to the ‘incised valley fill’ model commonly used in fluvial stratigraphy. Case studies from Miocene strata in northern Spain illustrate the stratigraphic relationships between fluvial channel and overbank successions in an endorheic basin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015