The Pliocene–Pleistocene sequences in the Nile Delta are of immense economic significance due to their hydrocarbon potential. Hence, a better understanding of the time-calibrated 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 moderate-to-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.

中文翻译：

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埃及尼罗河三角洲西北部高分辨率上新世-更新世钙质超微化石分布与古环境变化

尼罗河三角洲的上新世-更新世层序因其油气潜力而具有巨大的经济意义。因此，更好地了解经时间校准的盆地古环境变化对于提高油气采收率至关重要。对尼罗河三角洲西北部近海 Sapphire-DC 井的 182 个地下样品进行了分析，以揭示晚中新世-更新世（5.44-0.43 Ma）期间钙质超微化石组合组成和古环境的变化。首次确定了 16 个标记生物事件和 9 个生物区。Ceratolithus acutus的缺失表明在 Messinian-Zanclean（中新世-上新世）边界处存在中断。研究区间以五个物种的优势为标志；Pseudoemiliania lacunosa (24%)，小Gephyrocapsa sp。(20%), Helicosphaera kamptneri (11%), Reticulofenestra minutula (10%) 和Calcidiscus leptoporus(6%)。根据它们的分布模式，确定了六个区间（区间 0 到 5）。在整个研究区间内，较冷的水域（除区间 0 期间；Messinian 盐度危机，MSC，5.44-5.26 Ma）和富营养化条件持续存在于浅层半远洋和近大陆环境中，以中到高陆源输入为特征（更多区间 4 和 5；~2.73–0.42）。此外，确定了低物种多样性和高物种优势，表明环境压力。物种多样性呈逐渐下降的趋势，向上段，而物种优势度相应增加。区间 0 (MSC) 以 Sphenolithus abies和Helicosphaera kamptneri的温水物种为主。凉水品种，Reticulofenestra pseudoumbilica和小Gephyrocapsa在间隔 1 中占主导地位；小Gephyrocapsa在区间 2 中占主导地位。区间 3 的标志是盆地的加深，并简要介绍了温暖的、有点贫营养的和公海水域。在这个区间的中间（3.73 Ma；早-晚上新世边界），物种多样性的突然减少和物种优势的相应增加表明条件恶化。区间 3 还包括上新世中后期的变暖期，尼罗河三角洲以较冷的水域为标志。区间 3-5 以P. lacunosa为主，表明冷水和富营养化条件的延续。因此，在整个研究间隔期间，在浅海半远洋和近大陆环境中的较冷水域（除了在 MSC 期间）和富营养化条件被推断为具有中到高陆源输入和低物种多样性和更高的物种优势，暗示压力环境条件。