Summary

A new facies model has emerged for the facies architecture of wave-influenced deltas based on several recent papers on modern deltas (Dominguez, 1996; Hamilton and Anderson, 1994) as well as an evaluation of the modern Danube delta. The model shows that these deltas show a distinct asymmetry related to longshore drift direction. Updrift the river acts as a baffle and sand moving alongshore is trapped and deposited as a series of accreting sandy shoreface deposits, producing relatively homogenous sheet sands. These sands may be derived from updrift distributary branches of the same river or from a completely different source unrelated to the river. Downdrift, sand supplied by the river is reworked into a barrier-spit system. The back barrier lagoonal area fills with bayhead river- and tide-influenced delta deposits. The Danube delta shows that this asymmetry is preserved in successive lobes as distributary channels avulse. Examples of wave-influenced deltas in which sediment supplied by the river is transported alonsghore in both directions away from the river mouth, are rare.

Wave-influenced deltas may be distinguished from wave-dominated prograding strandplains in having a significant portion of mud deposited within the lagoonal environment by bayhead deltas associated with the river. The lateral transition from thick sandy shoreface deposits into lagoonal facies, such as seen in some ancient successions, may indicate wave-influenced deltas rather than prograding strandplains.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah