Ramadan M. El-Kahawy

This study updates the lithostratigraphic and chronostratigraphic framework of the marine carbonate-dominated Paleogene strata of northwestern Saudi Arabia within the Sirhan–Turayf Basin by integrating detailed field observations and high-resolution calcareous nannofossil biostratigraphy. Previous studies assigned these strata to the Middle–Upper Eocene Rashrashiyah Formation but lacked precise chronostratigraphic constraints. New biostratigraphic and lithostratigraphic data from three measured sections (Rash1–Rash3) reveal that these strata comprise two distinct formations: the Middle–Upper Eocene Rashrashiyah Formation and the newly defined Lower Oligocene Qurayyat Formation, separated by a prominent erosional disconformity at the Eocene–Oligocene boundary (EOB). The revised framework highlights the role of local tectonics, including block faulting and differential subsidence, in preserving the Oligocene strata. Calcareous nannofossil assemblages suggest that the Rashrashiyah Formation corresponds to Zones NP17–NP20, while the Qurayyat Formation is assigned to Zone NP21, collectively spanning the Bartonian–Rupelian interval. The documentation of marine Oligocene strata in NW Saudi Arabia for the first time, with erosional disconformity at the base, challenges previous interpretations of continuous sedimentation across the Eocene-Oligocene transition. The findings suggest that depositional architecture and stratal distribution in the study area are significantly controlled by regional tectonics and global sea-level fluctuations. The proposed lithostratigraphic scheme and chronostratigraphic constraints improve regional correlations across the Arabian Plate.

The reconstruction of detrital flux, paleoclimate, paleosalinity, paleo-primary productivity, paleohydrodynamic conditions, and paleo-water depth enhances understanding of sedimentary processes and their drivers during deep-time greenhouse-icehouse transitions, such as the Eocene–Oligocene transition. This study uses detailed geochemical analyses of major oxides and trace elements in sediment samples collected from the Beni Suef Formation (Bartonian–Priabonian) and the Maadi Formation (Priabonian) in the southern Tethys shelf (Egypt, northeastern Desert). Detrital proxies, including Si/Al, Ti/Al, and Zr/Al, indicate an enhanced influx of terrigenous sediments in the middle portion of the Qurn Member of the Beni Suef Formation, as further supported by noticeable facies variations, particularly the transition from shale to coarser silt- and sand-sized fractions. Paleoclimate indicators (Sr/Ba, Rb/Sr, K₂O/Al₂O₃, and Sr/Cu) point to a climatic shift from humid to arid conditions, consistent with the regional Late Eocene aridification across the Tethyan realm. Paleosalinity proxies (Sr/Ba, Ca/Al, and Mg/Al×100) suggest episodic intensification of open-marine influence and a reduction in freshwater input, with an upsection increase in Sr/Ba ratios, reflecting phases of enhanced marine water settings or decreased terrestrial runoff. Primary productivity was evaluated using multiple geochemical proxies, including P, Ni/Al, Cu/Al, P/Al, P/Ti, and Babio ratios. These collectively indicate generally low primary productivity interrupted by intervals of enhanced paleoproductivity or increased organic matter export to the sediments. This interpretation is further supported by the low total organic carbon (TOC) values. These results highlight the sensitivity of the southern Tethys shelf to Middle–Late Eocene climatic variability and the key role of prevailing paleoenvironmental conditions in controlling sediment supply, water chemistry, and biological productivity.

The reconstruction of detrital flux, paleoclimate, paleosalinity, paleo-primary productivity, paleohydrodynamic conditions, and paleo–water depth enhances the understanding of sedimentary processes and their drivers in deep-time greenhouse-icehouse transitions such as the Eocene to Oligocene times. This study uses detailed geochemical analyses of major oxides and trace elements in sediment samples collected from the Beni Suef Formation (Bartonian–Priabonian) and the Maadi Formation (Priabonian) in the southern Tethys shelf (Egypt, northeastern Desert). Detrital proxies, including Si/Al, Ti/Al, and Zr/Al, indicate an enhanced influx of terrigenous sediments in the middle portion of the Qurn Member of the Beni Suef Formation, as further supported by noticeable facies variations, particularly the transition from shale to coarser silt- and sand-sized fractions. Paleoclimate indicators (Sr/Ba, Rb/Sr, K₂O/Al₂O₃, and Sr/Cu) point to a climatic shift from humid to arid conditions, consistent with the regional Late Eocene aridification across the Tethyan realm. Paleosalinity proxies (Sr/Ba, Ca/Al, and Mg/Al*100) suggest episodic intensification of open marine influence and a reduction in freshwater input, with the upsection increase in Sr/Ba ratios, reflecting phases of enhanced marine water settings or decreased terrestrial runoff. Primary productivity was evaluated using multiple geochemical proxies such as P, Ni/Al, Cu/Al, P/Al, P/Ti, and Babio ratios, which collectively indicate generally low primary productivity interrupted by intervals of enhanced paleoproductivity or increased organic matter export to the sediments. This interpretation is further supported by the low total organic carbon (TOC) values. These results highlight the sensitivity of the southern Tethys shelf to Middle–Late Eocene climatic variability and the key role of prevailing paleoenvironmental conditions in controlling sediment supply, water chemistry, and biological productivity.

Coastal ecosystems are increasingly threatened by anthropogenic activities associated with tourism development and maritime traffic. This study evaluates the environmental quality of a coastal sector using an integrated approach combining sediment characteristics, heavy metal concentrations, and benthic foraminiferal assemblages. Nineteen surface sediments were collected and analyzed for trace metals using ICP-MS, while benthic foraminiferal assemblages were quantified, and ecological indices were calculated. Results reveal elevated concentrations of trace metals at coastal stations, closely associated with high TOM and fine-grained sediments, indicating significant anthropogenic inputs. These stations are characterized by low species richness, reduced Shannon diversity, high dominance, low living foraminiferal percentages, high malformed individuals, and markedly low FoRAM values, reflecting stressed environmental conditions. Opportunistic taxa such as Ammonia tepida dominate impacted sites, whereas sensitive carbonate-producing taxa (Quinqueloculina lamarckiana, Coscinospira hemprichii, Elphidium striatopunctatum, Elphidium crispum) prevail at less disturbed stations. Multivariate analyses clearly separate polluted coastal stations from relatively unimpacted offshore sites. The combined geochemical and biological evidence demonstrates that tourism-related activities and ship effluents exert a strong negative influence on benthic ecosystems. Benthic foraminifera, together with heavy metals, provide an effective and sensitive tool for assessing anthropogenic impacts and coral reef health for sustainable coastal management of Safaga Bay.

Sharm El-Luli, one of the most pristine embayments along Egypt’s Red Sea coast, is increasingly recognized as a sensitive sink for terrigenous inputs and emerging anthropogenic pressures. This study assesses the distribution, sources, and ecological and human health implications of heavy metals in bottom sediments collected throughout the lagoon. Concentrations of Fe, Mn, Zn, Cu, Pb, Ni, Cd, and Co were quantified and assessed using a suite of geochemical indicators and environmentally based indices. Sediment quality guidelines (SQGs; TEL–PEL and ERL–ERM) were applied to evaluate potential biological effects. Most metals exhibited background to minor enrichment, although localized elevations of Pb, Ni, and Zn suggest contributions from episodic wadi runoff and limited tourism-related inputs. I_geo and CF values generally indicated low to moderate contamination, while SQG comparisons showed that exceedances of TEL values occurred primarily for Ni and Pb, implying occasional risk for benthic organisms. Multivariate statistical analysis (PCA) separated metals into two principal components: a lithogenic component dominated by Fe, Mn, and Co, reflecting the influence of Precambrian source rocks; and an anthropogenic-mixed component (Pb, Zn, Cu, Ni) associated with terrigenous pulses and local human activity. Human health risk assessment (non-carcinogenic) showed hazard index (HI) values below unity for both adults and children, indicating negligible immediate health concerns, while potential carcinogenic risk raised in adults via ingestion for Cr followed by Cd and Ni than in children. The results highlight that while Sharm El-Luli remains relatively unimpacted, the lagoon’s geomorphology and low hydrodynamic energy promote metal retention, underscoring the need for continuous monitoring as coastal use intensifies.

Sharm El-Luli, located along the southern Red Sea coast of Egypt, is a semi-enclosed, shallow, mangrove-fringed lagoon characterized by limited hydrodynamic exchange, high salinity, and low terrigenous input. This study investigates the influence of sediment properties, hydrodynamic gradients, and mangrove-associated microhabitats on the spatial distribution of benthic ostracod assemblages within this lagoonal system. Eighteen surface sediment samples (W1–W18) were collected along an onshore–offshore gradient and analyzed for ostracod composition, sediment texture, carbonate and organic matter content, and water parameters including temperature, salinity, dissolved oxygen, pH, redox potential, and total dissolved solids. Thirty-four ostracod taxa were identified, revealing a pronounced inner–outer ecological partitioning across the lagoon. Redundancy analysis (RDA) demonstrates that ostracod distribution is primarily controlled by substrate heterogeneity, organic enrichment, salinity, and conductivity-related variables. The inner, low-energy mangrove margin is dominated by Aglaiocypris triebeli, Paranesidea fracticorallicola, and Hiltermannicythere rubrimaris, reflecting stressed, low-diversity conditions associated with organic-rich sediments and restricted circulation. In contrast, mid- and outer-lagoon stations host more diverse assemblages dominated by Xestoleberis spp., Neonesidea schulzi, Loxocorniculum ghardaquensis, and Jugosocythereis borchersi, indicative of better-flushed environments with higher carbonate content and stable marine salinity. These results demonstrate that benthic ostracods respond sensitively to fine-scale environmental gradients in mangrove-fringed lagoons, underscoring their value for assessing ecological health and sedimentary dynamics in semi-enclosed Red Sea coastal systems.

The Cretaceous-Paleogene (K/Pg) sequence offers a global perception of the paleoecological evolution in the southern Tethys realm. High-resolution calcareous nannofossil and dinoflagellate cyst analyses were conducted on subsurface Maastrichtian-Danian deposits in the Western Desert of Egypt, to characterize the paleo-conditions. The calcareous nannofossil analysis retrieved four main biostratigraphic zones (UC18-UC20, and NP4). A hiatus at the K/Pg boundary resulted in absence of most Danian nannofossil zones (NP1-NP3). The palynofacies assemblages discriminated three intervals of varying oxygen levels: dysoxic, proximal suboxic-anoxic shelf, and distal suboxic-anoxic basin incorporated by oligo-eutrophic conditions. The species diversity and relative abundance patterns of sensitive nannofossil indicators during this interval are attributed to significant climatic shifts. The surface waters during the Maastrichtian experienced a general cooling trend, interrupted by two warming episodes that may be correlated with the Deccan traps’ two phases (1&2). The biotic productivity indices and geochemical proxy (P, Sr/Al& P/Al) showed that during the earliest Maastrichtian high productivity prevailed, whereas during middle and late Maastrichtian a fluctuating pattern appeared. Statistically, multivariate techniques discriminated the retrieved taxa into five groups, each characterizing a depositional environment and climatic trend. Further, the palynomorphs analysis classified the Maastrichtian-Danian sequence into three offshore environments. A more refined understanding of climatic upheavals is essential for future studies to assess their potential role in driving biotic changes across the K/Pg boundary.

Twenty-nine sediment samples were collected from Hurghada Bay, a highly impacted coastal area along the Northern Red Sea of Egypt, to evaluate environmental quality and human-induced effects on benthic ostracods. As potential bioindicators, benthic ostracods are highly responsive to environmental disturbances, with pollution leading to reduced abundance, lower diversity, and increased opportunistic taxa. To investigate the link between ostracod assemblages and sediment contamination, we measured the concentrations of eight heavy metals (Cu, Cd, Zn, Pb, As, Cr, Ni, and Mn) using inductively coupled plasma–atomic emission spectrometry (ICP-AES). Multivariate statistical analyses identified three distinct ostracod assemblages distributed across three station groups with varying pollution levels. Group I, associated with offshore stations, exhibited low to moderate heavy metal (HM) concentrations and high ostracod abundance and was dominated by Moosella striata, Hiltermannicythere rubrimaris, Ruggieria danielopoli, Neonesidea schulzi, and Paranesidea fracticorallcola, where the water depth and sand content are the main controlling factors. In contrast, Group II, corresponding to stations with the highest HMs and total organic matter (TOM), was dominated by pollution-tolerant species Jugosocythereis borchersi, Cyprideis torosa, Alocopocythere reticulata, and, to a lesser extent, Ghardaglaia triebeli, with reduced ostracod density and diversity. Group III, characterized by stations influenced by the mud-controlling factor, had the lowest HMs and was dominated by pollution-sensitive species Xestoleberis rhomboidei, Paranesidea fortificata, and Loxocorniculum ghardaquensis. These findings highlight the ecological risks posed by HM pollution and emphasize the urgent need for pollution mitigation strategies and continued monitoring to preserve the Red Sea’s benthic biodiversity.

The middle–upper Eocene successions of northwest Fayum, Egypt, provide a crucial archive for reconstructing paleoenvironmental conditions and paleobiogeographical patterns of the southern Tethys realm. Stratigraphically, the investigated section is subdivided into three rock units: the Gehannam Formation (Bartonian-Priabonian), the Birket Qarun Formation, and the Qasr El Sagha Formation (Priabonian). A total of 101 benthic foraminiferal taxa, representing 31 genera, 23 families, 13 superfamilies, and four suborders, were identified. The middle–late Eocene age is primarily determined by the co-occurrence of index spinose planktonic foraminifera (Acarinina spp., Morozovelloides spp., and Globigerinatheka semiinvoluta) and benthic foraminiferal assemblages, further supported by the presence of the nannofossil marker Chiasmolithus oamaruensis. Four local benthic biozones are identified and correlated with coeval zones in nearby areas. Quantitative analyses of benthic foraminiferal individuals, diversity indices, ecological parameters, and the benthic foraminiferal oxygen index (BFOI) reveal distinct environmental shifts. The rock unit occupied by the late middle Eocene assemblages is diversified and dominated by calcareous infaunal taxa (e.g., Bolivina spp., Fursenkoina spp., and Nonionella spp.), indicative of low-oxygen outer neritic conditions associated with elevated organic influx. In contrast, the late Eocene Birket Qarun and Qasr El Sagha showed an increase in epifaunal forms and reduced diversity, suggesting a transition to dysoxic-oxic conditions. Paleobiogeographical analysis indicates a strong affinity with the Tethyan realm, with potential faunal exchange through the Trans-Saharan Seaway. These findings enhance our understanding of Paleogene marine connections between the Tethyan and Indo-Pacific realms, contributing to broader discussions on Eocene paleobiogeography and depositional dynamics in North Africa.