The Pliocene–Pleistocene sequences in the Nile Delta are of immense economic significance
due to their hydrocarbon potential. Hence, a better understanding of the timecalibrated
basinal palaeoenvironmental changes is essential to improve the hydrocarbon
recovery. A total of 182 sub‐surface samples from the Sapphire‐DC well in the offshore
north‐western part of the Nile Delta were analysed to reveal changes in
calcareous nannofossil assemblage composition and palaeoenvironments during the
late Miocene–Pleistocene (5.44–0.43 Ma). Sixteen marker bioevents and nine biozones
are identified for the first time. The absence of Ceratolithus acutus suggests a hiatus at
the Messinian–Zanclean (Miocene–Pliocene) boundary. The studied interval is marked
by the dominance of five species; Pseudoemiliania lacunosa (24%), small Gephyrocapsa
sp. (20%), Helicosphaera kamptneri (11%), Reticulofenestra minutula (10%) and Calcidiscus
leptoporus (6%). Based on their distribution patterns, six intervals (Intervals 0
to 5) are identified. Throughout the study interval, cooler waters (except during Interval
0; Messinian Salinity Crisis, MSC, 5.44–5.26 Ma) and eutrophic conditions persisted
within a shallow hemipelagic and near‐continental setting, marked by moderateto‐
high terrigenous input (more for Intervals 4 and 5; ~2.73–0.42). Additionally, low
species diversity and high species dominance are identified, suggesting a stressed environment.
Species diversity shows a gradually declining trend, up section, whereas species
dominance correspondingly increases. Interval 0 (MSC) is dominated by warm
water species of Sphenolithus abies and Helicosphaera kamptneri. The cool water species,
Reticulofenestra pseudoumbilica, and small Gephyrocapsa dominate in Interval 1;
small Gephyrocapsa dominates in Interval 2. Interval 3 is marked by the deepening of
the basin with a brief introduction of warm, somewhat oligotrophic and open‐ocean
waters. In the middle of this interval (at 3.73 Ma; the Early–Late Pliocene boundary),
an abrupt decrease in species diversity with a corresponding increase in species dominance
suggests deteriorating conditions. Interval 3 also encompasses the mid–late Pliocene
warming period, which in the Nile Delta is marked by cooler waters. Intervals 3–5
are dominated by P. lacunosa, suggesting a continuation of cool waters and eutrophic
conditions. Hence, throughout the study interval, cooler waters (except during the
MSC) and eutrophic conditions within in a shallow hemipelagic and near‐continental
setting are inferred with moderate‐to‐high terrigenous input and low species diversity
and higher species dominance, suggestive of stressed environmental conditions. |
