An Alternative Model for the Plio-Pleistocene Channelised Sandstone Bodies Within the Framework of the Sedimentary and Tectonic Evolution of the Nile Delta Area (WDDM Concession, Nile Delta Offshore, Egypt)

By

 Marco Roveri¹, Axum Cotti¹, Emiliano Mutti¹, Paolo Dar˜², Francesco Federici², Alberto Sitta³

(1) Parma University, Parma, Italy (2) Edison Gas S.p.A, Milano, Italy (3) Edison Gas S.p.A. now at Rashid Petroleum Company, Cairo, Egypt

 Channelised sand belts encased by dominantly mudstone deposits, represent the main exploration target in the Plio-Pleistocene succession of the WDDM concession. Their origin, time and space distribution and facies characteristics largely depend on a close interaction between the tectonic and climatic evolution of the Nile Delta area. These deposits, characterized in amplitude maps by moderately to highly sinuous shapes like many modern deep-water examples developed along passive continental margins, were genetically linked to the paleo-Nile fluvio-deltaic system.

Reconstruction of a regional geologic- stratigraphic framework shows that sedimentation was essentially controlled by deltaic processes linking marginal wedges to low-gradient shelfal and slope regions lying at moderate water depths during the Pliocene, and gradually increasing due to the flexural subsidence affecting the area through time. Channelised sandstone belts only occur north of the Rosetta Fault and originated from (1) sediment failures along the seaward edge of prograding delta lobes and (2) hyperpycnal flows exiting river mouths during periods of severe flooding. Sediment failures were triggered by the complex interaction of the tectonic instability of the Rosetta fault zone, severe floods, and probable sealevel lowstand conditions. These failures generated flows which were accelerated on tectonically-steepened clinoform slopes and moved seaward as inertia-driven dense flows forming extensively channelized sand belts. Individual sandstone bodies show very complex facies associations and stacking patterns that can be described by an evolutionary model implying three stages of growth reflecting the continuous interplay between changes in flow volumes through time and an evolving sea-floor topography.