Updrift sands form homogenous shoreface deposits. They may be derived from other distributaries of the same river but they may also be derived from indirect sources, such as reworked shelf sands. Downdrift, mud and sand is supplied directly by the river. Barrier-lagoons thus appear to be a characteristic component of prograding asymmetric deltas. They may be initiated by large floods and do not necessarily imply transgression as is commonly believed More detailed analysis of several of these large modern asymmetric deltas, as well as description of some ancient examples, will be required in order to determine the volumes and types of sediment that are trapped, as well as elucidating the facies architecture.
Process diagram for wave-influenced deltas.
Different delta shapes are shown to be a consequence of variations in river sediment transport rate versus longshore sediment transport rate. Waves become less oblique as they approach the river mouth resulting in deposition on the updrift side. Higher sediment supply and oblique wave approach results in asymmetric delta types with downdrift shifting of the river mouths over time. Figure based on an idea by John Bridge. The objective of the proposed research is to test the applicability of this asymmetric model to an ancient delta system.