The Middle to Upper Eocene sequence is a part of the middle Paleocene–Eocene mega sequence AP10, characterized by lateral stratigraphic variations in bed thicknesses and facies changes across depositional basins due to the final phase of subduction and closure of the Neo-Tethys ocean. This led to an uplift along the NE margin of the Arabian plate with the formation of ridges and basins. The sequence composed of siliciclastic and carbonate deposits. The study areas are located in Erbil Governorate, northeastern Iraq, two sections have been chosen and sampled, both in the High Folded Zone. Sork mountain (the limb of Safin anticline), within the Shaqlawa district and Haibat Sultan mountain (Kosret anticline), within the Koysnjaq district. The thickness of the formations’ changes depending on the rate of tectonic, subsidence that happened within the basin. The lateral variation in thickness in these formations are clearly observed. The Middle -Upper Eocene where deposited in a steeply sinking foredeep basin, in which the Gercus Formation was deposited and the clastic sediment was supplied from the emergent uplift. The red-bed successions comprise alternating red and brown mudstones, red calcareous siltstone, fine-to coarse-grained pebbly sandstone and conglomerate. Finally, the basin was filled with carbonate deposits of the Pila Spi Formation and the carbonate bands of the Avanah Formation were interbedded with red clastic deposits. Avanah Formation is composed of dolomitized, fossiliferous, and marly limestone’s intercalated with thin layers of siltstone, and sandstone occurring at irregular intervals interbedding with Gercus Formation in the studied sections. In Avanah Formation three main microfacies were recognized, and eight sub-microfacies within which representing environmental stretch from the shoal. In Pila Spi Formation, three main microfacies recognized, with eight submicrofacies. Lithologically consists mainly of marly, crystalline, and dolomitic limestone. The distinguished lithofacies in both studied sections are divided into five lithofacies. The stratigraphic units in the studied areas are distributed along NE-SW structures resting directly on the Paleocene- Eocene Kolosh and Khurmala formations and overlain
unconformably by Middle Miocene Lower Fars Formation. consists of fine to medium-sized detrital grains derived from sedimentary rocks; (claystone, siltstone, and sandstone with rare conglomerate), in addition to carbonate rock fragment Some metamorphic and igneous rock fragments found some mud and clay rock fragments It is a reddish brown and yellowish color.. Carbonates petrographic components comprising grains and groundmass. The grains are divided into 1-skeletal and 2-nonskeletal grains. The skeletal grains in the studied rock samples mainly include foraminifers and dasycladacean green algae with some occurrence of ostracods in addition to a few bioclasts of bryozoans and pelecypods. Nonskeletal grains include peloids, Ooids, and some Oncoids. The groundmass is composed of micrite and is slightly affected by the dolomitization process, leading to the development of fine crystalline subhedral to euhedral dolomite crystals. The current study has concluded that the environment of the Gercus Formation was fluvial and deltaic of continental molasses facies with possibly some shallow marine sediments at its lower part of Avanah Formation was deposited in the shallow marine platform (inner-outer shelf zone) during the Eocene. The field studies of the Pila Spi Formation show, lithified limestone to marly limestone highly affected by dolomitization, generally consisting of lagoonal sediment. The result of 34 stable Carbone and oxygen isotopes of studied carbonate samples show that the sea water was warm with low salinity when the carbonate of Pila Spi Formation precipitated in the Shallow marine in the high folded zone. According to the sum of all petrographic, facies, and textural analysis, of the three Formations concluded that the depositional environment of Gercus Formation was fluvial and deltaic, Pila Spi Formation deposited in Shallow marine open lagoon environment. and Avanah Formation was deposited in a shallow marine platform (inner – outer shelf zone) repeated cycles of low-energy subtidal facies.