Facies transition and depositional architecture of the Late Eocene tide-dominated delta in northern coast of Birket Qarun, Fayum, Egypt

• Architecture of the recognized facies associations (FA1 to FA4) indicates delta progradation into a shallow marine embayment.
• The suggested facies model represents a HST tide-dominated delta.
• This is evidenced by the absence of an incised valley or a regional subaerial unconformity below the progressive succession.
• Stratigraphic and depositional characteristics strongly resemble the modern tide-dominated deltaic systems.

Late Eocene successions in the Fayum Depression display notable facies transition from open-marine to brackish-marine realms. Stratigraphic and sedimentologic characteristics of the depositional facies are integrated with ichnological data for the recognition of four facies associations (FA1 to FA4). The transition from open-marine sandstones (FA1) to the brackish-marine deposits (FA2) heralds a transgressive – regressive dislocation. The shallowing- and coarsening-upward progradation from the basal prodelta mudstone-dominated facies (FA2a) to deltafront heterolithics (FA2b) and sandstone facies (FA2c) are overlain by finning-upward delta plain deposits which are expressed by the delta plain mudstone (FA2d) and erosive-based distributary channel fills (FA4). Prodelta/deltfront deposits of FA2 are arranged in thinning- and coarsening-upward parasequences which are stacked in a shallowing-upward progressive cycle. Shallow-marine fossiliferous sandstones (FA3) mark the basal part of each parasequence. Stratigraphic and depositional architectures reflect a tide-dominated delta rather than an estuarine and incised valley (IV) model. This can be evinced by the progressive facies architecture, absence of basal regional incision or a subaerial unconformity and the stratigraphic position above a maximum flooding surface (MFS), in addition to the presence of multiple tidally-influenced distributary channels. Stratigraphic and depositional characteristics of the suggested model resemble those of modern tide-dominated deltaic systems. Accordingly, this model contributes to our understanding of the depositional models for analogous brackish-marine environments, particularly tide-dominated deltas in the rock record.