Sedimentology and evolution of a mixed-energy deltaic system, upper Eocene Maadi Formation, north Eastern Desert, Egypt

Abstract Improved understanding of mixed-process deltaic systems and their stratigraphic architectures is important for predicting reservoir heterogeneity and coastal geomorphic changes. This study reveals that the lower part of the upper Eocene Maadi Formation in the north Eastern Desert (Egypt) includes stacked deposits of a mixed-energy, sand-dominated deltaic system. The succession consists of six main architectural elements: i) offshore muds, ii) prodelta, iii) delta front, iv) delta plain, v) tide-dominated estuary, and vi) transgressive storm beds. These elements accumulated in two high-frequency transgressive–regressive sequences; each consists of regressive prograding-delta-lobe deposits truncated by transgressive storm deposits. The prograding-delta lobes show mixed storm and tide influences. Storm action prevailed in the distal delta front and waned in the proximal delta front, in contrast to the tidal action that prevailed in the proximal-delta-front elements and the delta-plain elements. The tidal impact increased successively through the studied succession, probably due to tectonically derived tidal amplification. The drowning of the deltaic system with development of an estuary is attributed to fluvial avulsion or autogenic delta-lobe switching. The study introduces a model for variability of the interaction between river, tide, and storm processes and their products in a mixed-energy delta, and the evolution of the mixed storm- and tide-influenced deltaic system. It improves our understanding of the sedimentological parameters and stratigraphic architecture of mixed-energy coastal reservoirs and their heterogeneities.