The Development of Incised Valleys in a Three-Dimensional Numerical Model of Deltaic Deposition

Emma Finch¹, Stuart Hardy², and Rob Gawthorpe^2
1 Manchester University, Manchester, United Kingdom
² Universitat de Barcelona, 08028 Barcelona, Spain

We apply a three-dimensional model of clastic sedimentation and erosion to investigate the effect of sea level change and sediment supply on the development of incised valleys in a deltaic environment. Sediment is introduced at a point source and allowed to deposit into the basin while a constant sea level is maintained, developing a major incised channel. Sea level is then varied according to a sinusoid with varying amplitudes. As sea level falls, incision occurs, resulting in a three-dimensional incised valley network developing across the delta front. Results generally illustrate two stages of network development, i) a proto-incised valley stage where many small valley networks distribute sediment relatively uniformly along the delta front and ii) a main incised valley stage where one or more valleys develop by headward erosion and capture most of the sediment supply. Sediment supplied from the main channel is continually deposited during this stage, but can be captured by the headward erosion of neighbouring channels causing avulsion, and redirection of sediment in the basin. There can therefore be a large along strike variability in the spatial distribution of these valleys and the associated amount of sediment deposited. The stratigraphy developed during sea level rise is strongly influenced by the incised valley system developed during the preceding fall. These models show that important controls on the nature of incised valleys are i) the initial dimension of the delta, ii) the rate of sediment supply and iii) the nature of relative sea level change.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005