This study deals with the reconstruction of the paleoenvironment and the paleoclimate situation of the middle–upper Eocene sediments in the northwest Fayum area. The reconstruction is based on comprehensive stratigraphical and geochemical analyses of major oxides and trace elements for selected sediment samples from the Gehannam Formation (Bartonian–Priabonian), the Birket Qarun and the Qasr El Sagha formations (Priabonian). The sedimentological features coupled with paleo-redox trace elemental ratios (Ni/Co, V/Cr, U/Th, V/(V + Ni), and Cu/Zn), paleosalinity (Sr/Ba, Mg/Al ×100, Ca/Al), and paleowater depth (Fe/Mn) proxies, indicate that deposition took place in a shallow marine agitated environment with high oxygen levels. Paleoclimate indicators (Sr/Cu, Rb/Sr, K₂O₃/Al₂O₃, Ga/Rb, C-value, CIA, and CIW) suggest warm and prevailing arid climatic conditions, with minor humid periods at some intervals. The observed low values of the total organic carbon (TOC) are attributed to significant high sediment influx, predominant oxygenated conditions, and poor primary productivity, which is further confirmed by low values of paleoprimary productivity proxies (P, Ni/Al, Cu/Al, P/Al and P/Ti, and Ba_bio ratios). These findings enhance our understanding of the Eocene environments and provide insights into sedimentation processes during this period.

Foraminifera are single-celled protists which are important mediators of the marine carbon cycle. In our study, we explored the potential impact of polystyrene (PS) microplastic particles on two symbiont-bearing large benthic foraminifera species—Heterostegina depressa and Amphistegina lobifera—over a period of three weeks, employing three different approaches: investigating (1) stable isotope (SI) incorporation—via ¹³C- and ¹⁵N-labelled substrates—of the foraminifera to assess their metabolic activity, (2) photosynthetic efficiency of the symbiotic diatoms using imaging PAM fluorometry, and (3) microscopic enumeration of accumulation of PS microplastic particles inside the foraminiferal test. The active feeder A. lobifera incorporated significantly more PS particles inside the cytoplasm than the non-feeding H. depressa, the latter accumulating the beads on the test surface. Photosynthetic area of the symbionts tended to decrease in the presence of microplastic particles in both species, suggesting that the foraminiferal host cells started to digest their diatom symbionts. Compared to the control, the presence of microplastic particles lead to reduced SI uptake in A. lobifera, which indicates inhibition of inorganic carbon and nitrogen assimilation. Competition for particulate food uptake was demonstrated between algae and microplastic particles of similar size. Based on our results, both species seem to be sensitive to microplastic pollution, with non-feeding H. depressa being more strongly affected.

The Eocene deposits of Egypt provide a wide variety of shallow marine facies and fossil assemblages, allowing paleoenvironmental reconstructions in this warmhouse climate interval. Forty-three rock samples have been collected from two middle Eocene sections, exposed at southeast Beni-Suef area in northern Egypt. The studied outcrops are lithologicsally subdivided into two rock units named from base to top as follows: (1) the Qarara Formation (Lutetian) and (2) the El Fashn Formation (Bartonian). Most investigated rock samples showed richness in benthic foraminiferal assemblages and only rare occurrences of index planktonic foraminifera. They yielded 160 foraminifera species which belong to 4 suborders, 19 superfamilies, 34 families, and 59 genera. The stratigraphic distribution of the identified species allowed us to define four local benthic bio-ecozones: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone, (3) Nonion scaphum Lowest Occurrence Zone, and (4) Brizalina cookei/Nonionella insecta Concurrent-Range Zone (Bartonian). These biozones are described and discussed in detail and correlated to stratigraphic equivalents in Egypt. The rareness of index planktonic foraminifera through the studied sections does not allow a precise biostratigraphic and chronostratigraphic correlation. The shale samples show low TOC values, which may be related to low productivity, high sediment influx, and/or prevailing oxic conditions. Bulk rock geochemistry, consistent with the benthic foraminifera ecological preferences, indicated that the studied sections were deposited in moderate to high oxygen levels and warm climatic conditions in a typical shelf marine setting. The identified species showed strong similarities with nearby southern Tethys areas, reflecting migration via the trans-Sahara seaway, and minor similarities with those identified from the northwestern Tethys and the North Atlantic province attributed to the change in the environmental and climatic conditions, such as cooler, latitudinal zoned climatic conditions along the northwestern Tethys, which was unsuitable for their biological demands. The warming trend identified from Lutetian to Bartonian intervals corresponds to the onset of the Middle Eocene Climatic Optimum (MECO).

Foraminifera are protists primarily living in benthic marine and estuarine environments. We studied uptake of inorganic carbon (C) and nitrogen (N) of the photosymbiont-bearing benthic coral reef foraminifera Heterostegina depressa in the presence of heavy metals.

We studied metabolic activity of the symbiont-bearing large benthic foraminifer Heterostegina depressa under different light conditions. Besides the overall photosynthetic performance of the photosymbionts estimated by means of variable fluorescence, the isotope uptake (¹³C and ¹⁵N) of the specimens (= holobionts) was measured. Heterostegina depressa was either incubated in darkness over a period of 15 days or exposed to an 16:8 h light:dark cycle mimicking natural light conditions. We found photosynthetic performance to be highly related to light supply. The photosymbionts, however, survived prolonged darkness and could be reactivated after 15 days of darkness. The same pattern was found in the isotope uptake of the holobionts. Based on these results, we propose that ¹³C-carbonate and ¹⁵N-nitrate assimilation is mainly controlled by the photosymbionts, whereas ¹⁵N-ammonium and ¹³C-glucose utilization is regulated by both, the symbiont and the host cells.

The Krems Embayment contains the westernmost fully marine depositional environments of the Karpatian and Bade-nian transgressions in the Central Paratethys. Four drill cores were investigated to analyse the bio- and lithostratigraphic, and tectonic relations. The investigated core sections cover the Karpatian Laa Formation (bio-zones M4, NN4) and the Badenian Gaindorf Formation (M5b-M6, NN4-NN5). Important biostratigraphic indicators identified are Praeorbulina glomerosa glomerosa, Praeorbulina glomerosa circularis and Orbulina suturalis for the Gaindorf Formation. The Laa Formation is indicated by the absence of Praeorbulina , Orbulina and Globigerina falconensis , low numbers of Globorotalia bykovae , and a prominent peak in Helicosphaera ampliaperta abundance at the end of the Karpatian. Cibicidoides lopjanicus and Cassigerinella spp. occur with high percentages in Badenian samples and show much longer stratigraphic ranges than known from literature data. The depositional gap at the Karpatian-Badenian boundary has a minimum duration of 0.41 My in the Krems Embayment. The combination of bio- and lithostratigraphic data allows the correlation across major faults. The Diendorf-Boskovice Fault System played an important role during basin formation and was identified as very active during the early to middle Badenian Stage. The results of this study show the complex interaction of sedimentation, tectonic activity and paleobiological developments in this peripheral part of a marginal sea.