Controls on Late Miocene to Early Quaternary continental sedimentation during the development of the Sohag basin, Nile Valley, Egypt

Abstract

Sohag Basin is a Late Cenozoic rift basin that follows the course of the River Nile and contains a sequence of Early Miocene to Quaternary times. The present study outlines the impact of the allocyclic factors controlling a sequence of a fluvio-lacustrine succession dated from the Late Miocene to the Early Pleistocene and is subdivided into Units II and III. Unit II is made mostly of fluvial siliciclastic sediments (FA1), interpreted as channels and floodplains. Unit III consists of alluvial conglomerates (FA2) followed upwards by lacustrine carbonates (FA3) covering the whole basin. These two units are arranged in two depositional sequences (DSQ-1 and DSQ-2), bounded by sequence boundaries. Both sequences are composed of the Low- and High-Accommodation System Tracts (LAST, HAST), and they are distinguished primarily by the facies associations and the nature of the contacts that separate them. Allogenic controls strongly influenced the general evolution of the fluvio-lacustrine system. Tectonics determined the variations in thickness and lithofacies of Units II and III, where the basin was affected by the reactivation of basin-bounding faults, and suggested that the basin physiography changed from the full-graben to half-graben stage. The variation in the lacustrine facies associations and the pedogenic features show the response to tectonics and local climate conditions. Provenance played a role in the drainage pattern evolution. Using the Facies architecture and sequence stratigraphic framework, a depositional model was constructed and strongly influenced by tectonic subsidence and uplift of the basin concurrent with the reactivation of the Gulf of Suez-Red Sea rifting.