External Morphology Versus Internal Facies Architecture of Deltas Challenge Tripartite Classification Scheme

M. Royhan Gani, Geosciences, U. of Texas at Dallas, P.O. Box 830688, FO 21, Richardson, TX 75083-0688, phone: 972-883-2449, fax: 972-883-2537, mrg013000@utdallas.edu and Janok P. Bhattacharya, Geosciences, U. of Texas at Dallas, P.O. Box 830688, FO 21, Richardson, 75083-0688.

The tripartite classification of deltas into wave-, tide- and fluvial-dominated end members was largely based on compilations about the plan-view morphology of modern deltas. The modern Brazos, Baram/Trusan, and Burdekin deltas show smooth-fronted plan view shapes indicating wave-dominated end members, but detailed internal facies analysis suggests dominance of river and tidal processes. Likewise, sandstone-isolith shape of delta lobes within the Cretaceous Wall Creek Member of the Frontier Formation in Wyoming suggest wave-dominance, but the internal facies architecture shows a dominance of river-flood splays and channels with significant local tidal and wave reworking. Although the tripartite classification continues to be used as a framework for understanding deltas, it is clear that the end-member types are not mutually exclusive in terms of delta building processes and facies. The plan-view morphology of any given modern delta reflects dominant surficial process but may not necessarily reflect the short-lived constructional processes of river floods that dominate the internal facies architecture. Plan-view morphology can also evolve from one end-member type to another during the lifetime of a single delta (e.g. Mekong delta). Therefore, it may be misleading to infer a specific internal facies distribution with its consequent control on reservoir quality based on plan-view morphology alone.

Clastic Shelf, Deltaic and Shoreline Systems II
2005 AAPG Annual Convention (June 19-22, 2005) Technical Program