River response to lateral ground tilting: a synthesis and some implications for the modelling of alluvial architecture in extensional basins

This paper reviews and synthesizes several Holocene field examples of river response to lateral ground tilting. Key aspects of alluvial architecture modelling in extensional basins are addressed, including the nature of gradual lateral migration, the spatial and temporal history of avulsive sequences, and the underlying controls that determine whether a river responds to lateral tilting through gradual migration or avulsion. A new conceptual model for gradual lateral migration is proposed that unifies previously disparate models. Tilt-induced avulsion in several field examples is associated with sequences that move towards and away from the locus of subsidence during active and quiescent tectonic periods, respectively. These avulsion sequences closely correspond to those produced by several 2D and 3D alluvial architecture models. The rate of lateral tilt appears to control the style of channel movement, with gradual migration occurring at low tilt rates, and avulsion at higher rates. This apparent dependence on tilt rate suggests the mode of channel movement, and also the avulsion frequency, may in part be a function of the imposed tectonic regime.