Pliocene-Lower Pleistocene high-resolution foraminiferal biostratigraphy of offshore eastern Nile Delta area, Egypt

Abstract

This study presents a high-resolution foraminiferal biostratigraphic analysis of three Pliocene-Lower Pleistocene successions encountered in the Andaleeb-1, Temsah-NW-10, and Barboni-NW-1 wells, drilled for gas exploration in the offshore eastern Nile Delta. The studied successions were divided into two rock units from base to top: The Kafr El-Sheikh Formation and the El-Wastani Formation. The studied successions are characterized by scarce planktonic foraminiferal records in most parts, while benthonic foraminifera are more abundant and diverse, particularly in the top portion of the investigated sections. The biostratigraphic analysis of the recorded foraminiferal assemblages suggests six planktonic foraminiferal zones and three benthonic foraminiferal zones based on marker species consistent with Mediterranean basin standards. The planktonic zones, in ascending order, are the NPP-1 (Nile Delta Pliocene Planktonic) Zone, NPP-2 Zone, NPP-3 Zone, NPP-4 Zone, NPSP-1 (Nile Delta Pleistocene Planktonic) Zone, and NPSP-2 Zone. The three benthonic zones, also in ascending order, are the NPB-1 (Nile Delta Pliocene Benthonic) Zone, NPB-2, and NPSB-1 (Nile Delta Pleistocene Benthonic) Zone. However, the reliability of some bioevents used to define the zonal boundaries was challenged by the scarcity and patchy distribution of certain marker species in the study area. The sphaeroidenellopsis acme, a key marker for the NPP-1 Zone, could only be tentatively recognized in one well because the bottom Pliocene is not encountered in the other two wells. The limited occurrences of Globorotalia bononiensis, the marker species for the subdivision of the standard Mediterranean MPL-5 Zone, complicated the correlation of the NPSP-1 Zone with the Mediterranean standard zonation. As a result of bio-zonation, an unconformity surface was recorded between the Lower Pliocene (Zanclean stage) and the Lower Pleistocene (Gelasian stage) due to totally or partially absence of Piacenzian stage. The onset of the Gelasian stage (Lower Pleistocene) is marked by the progradation of the Nile Delta, which led to the development of nutrient-rich, shallow marine environments, supporting a relatively diverse and abundant benthonic foraminiferal assemblage.