Biostratigraphy and sequence stratigraphy of the Oligocene succession, offshore Nile Delta, southeastern Mediterranean, Egypt, and its paleoenvironmental implications

Following recent hydrocarbon exploration activity, a new study has been carried out with the goal of defining the high-resolution biochronologic sequence stratigraphy of the Oligocene section in the offshore Nile Delta. A total of 98 samples were selected from 2 wells: Burullus 1 Memphis and Petrobel 1 Habbar. The study is based on a high-resolution microfossil biochronology including benthic and planktonic foraminifera and nannofossils as well as facies analysis and wire-line log calibration to investigate the evolution of Oligocene gas-bearing sequences in the southeastern Mediterranean region. The planktonic–benthic ratio, foraminiferal diversity, and upper depth limit of benthic foraminiferal taxa as well as the abundance of calcareous nannoplankton help in interpreting the depositional paleoenvironments of the Oligocene succession as fluvial, shallow-marine, middle- to outer-shelf, and bathyal domains. Six sequences were identified, three of which are lower Oligocene (Rupelian) (RuSeq1, RuSeq2, and RuSeq3), and the others are upper Oligocene (Chattian) (ChSeq4, ChSeq5, and ChSeq6). The sequence boundaries and flooding surfaces were correlated with the global eustatic sea-level models. Three major breaks—Eocene–Oligocene, lower–upper Oligocene, and upper Oligocene–lower Miocene boundaries—with intraformational breaks were well defined.