ORIGINAL PAPER Response of foraminiferal assemblages on the middle Eocene climatic optimum and following climatic transition in the shallow tropical sea (the south Fayoum area, Egypt) Sobhi Helal 1 & Katarína Holcová 2 Received: 16 March 2015 /Accepted: 26 December 2016 # Saudi Society for Geosciences 2017 Abstract Foraminiferal assemblages from 4 sections (total- ling 158 samples) were quantitatively analysed to reconstruct paleoenvironmental changes in inner to outer shelf, tropical epicontinental sea of the southern Peritethys area around the middle Eocene climatic optimum. In comparison with bathyal oceanic sites, shelf assemblages from Fayoum area are strong- ly influenced by climatically forced sea-level oscillations and aridification in cooling post-MECO interval. Pre-MECO in- terval can be characterized by gradual deepening and hypoxic, eutrophic bottom water. The maximal deepening during the temperature peak was associated with destruction of hypoxic bottom water. Sea-level fall, nutrient decrease and salinity increase in marginal part of basin due to decreased continental runoff caused by aridification was suggested for post-MECO cooling interval. Clastic-carbonate system of the warming pe- riod and thermal maximum was changed to only carbonate system of cooling post-MECO period. Keywords Foraminifera . Middle Eocene climatic optimum . Paleoecology . Egypt Introduction The middle Eocene is a pivotal interval in the evolution of Cenozoic climate to determining the processes through tran- sition from ‘greenhouse’ to ‘icehouse’. The middle Eocene climatic evolution seems to be characterized by at least one prominent warming event at ∼40 Ma, known as the middle Eocene climatic optimum (MECO). This event interrupted the cooling trend of the middle Eocene. The MECO in the oceanic record was identified firstly in the Southern Ocean deep-sea cores (Bohaty and Zachos 2003; Sexton et al. 2006; Bohaty et al. 2009). A 500-kyr-long duration for the MECO was char- acterized by increasing δ 13 C and decreasing δ 18 O, with min- imum δ 18 O values lasting ~40 kyr at 40.1 Ma coincident with a short-lived negative δ 13 C excursion. Southern Ocean deep- water temperatures warmed by up to 4 °Cand lasted for 500 kyrs before rapidly cooling. Increase in CaCO 3 mass accumu- lation rates followed the event (Bohaty et al. 2009). Reconstructed CO 2 concentrations are mainly between 700 to 1000 ppm with a secular decline to 450 ppm. The CO 2 decline is compatible with a rapid (<10 4 years) transition from warm, largely ice-free conditions to cooler climates with ice sheets (Doria et al. 2011). The appearance of these small Cenozoic ice sheets (Miller et al. 1991; Ehrmann and Mackensen 1992; Browning et al. 1996) preceded the large- scale ice sheet expansion in the earliest Oligocene (Zachos et al. 1996, 2001; Coxall et al. 2005). In low latitudes, the MECO can be well biostratigraphically correlated with interval from the FO (first occurrence) to the LO (last occurrence) of Orbulinoides beckmanni (Bohaty et al. 2009; Edgar et al. 2010). Publications dealing with effects of the MECO on micro- organisms were comprehensive summarized by Boscolo Galazzo et al. (2015), and showed different imprint of global warming to local paleoenvironmental changes. Studied * Sobhi Helal sah04@fayoum.edu.eg Katarína Holcová holcova@natur.cuni.cz 1 Faculty of Science, Geology Department, Fayoum University, Fayoum, Egypt 2 Institute of Geology and Paleontology, Charles University in Prague, Albertov 6, 128 43 Praha 2, Czech Republic Arab J Geosci (2017) 10:43 DOI 10.1007/s12517-016-2818-7