This research is based on (23) Samples selected from the Avanah Formation (Middle Eocene) in the Geli Bessri section in Dohuk to recognize the microfacies and depositional environments. The Avanah Formation consists of rocks of marly limestone and limestone containing Alveolina and thin layers of sandstone lithofacies found in the lower part of the Formation. The depositional environment was determined depending on skeletal and non- skeletal grains. The facies of the Avanah Formation were divided into four main microfacies and four submicrofacies based on skeletal and non- skeletal grains: The mudstone and wackestone, which is divided into benthic foraminifera wackestone and Rotaliids wackestone, the Formation also contains the packstone which is divided into the Rotaliid - Miliolid Lime packstone submicrofacies and benthic foraminifera lim packstone submicrofacies, in addition to the lime grainstone and also contains the Sandstone lithofacies located at the bottom of the Formation. The Avanah Formation in the middle and upper part is subjected to diagenesis process early dolomization and it is observed this through floating dolomite rohmb. According to the results of the facies analysis and the presence of foraminifera fossils, the Formation was deposited in open marine platform to restricted platform interior.   http://dx.doi.org/10.25130/tjps.25.2020.014

This work depends on detailed petrographic and diagenetic processes studies of collected cutting rock samples, from the Late Jurassic Naokelekan Formation from Ajil-8, Balad-1 and Baiji-1 wells. Based on the thin sections study, the formation contains various petrographic components represented by pelecypods, calcispheres, planktonic and benthonic foraminifera, in addition to the groundmass of micrite and microspars. Many diagenetic processes affected the rock successions such as, compaction, micritization, authigenic minerals (pyrite), cementation, neomorphism, dissolution, porosity, replacement and dolomitization. The detailed microfacies analysis reveals that the rock successions consist mainly of three microfacies including; lime mudstone, which is divided into non-fossiliferous lime mudstone, bioclastic lime mudstone and planktonic foraminiferal lime mudstone, lime wackestone which also divided into calcispheres lime wackestone, benthonic lime wackestone, and pelcypodal lime wackestone, and lime packstone include, bioclastic lime packstone, peloidal lime packstone, and calcispheres lime packestone. The overall characters of these microfacies indicate the formation was deposited in two different environments: (1) shallow marine subtidal environment at the lower and upper parts (2) outer shelf in an euxinic environment at its middle part

Seventeen samples of Hartha Formation in Balad (1) well, central Iraq, are studied on the basis of stratigraphic ranges of the recorded calcareous nannofossils for twenty species belonging to twelve genera. The studied section reveals three biozones arranged from oldest to youngest as follows; (1) Calculites ovalis Interval Biozone (CC19), (2) Ceratolithoides aculeus Interval  Biozone (CC20), (3) Quadrum  sissinghii Interval Biozone (CC21). These Biozones are correlated with other calcareous nannofossils biozones from both local and regional sections, leading to conclude the age of the Middle Campanian. Rerecorded eighteen ostracode species that belong to eleven genera are identified, all of which were previously recorded from Iraq and adjacent regions. The occurrence of these species leads to conclude a continental shelf environment, while they are typical of inner shelf-outer shelf depth.

The current study included a study of the microfacies and sequence stratigraphy of Saadi Formation in two subsurface sections within the Balad and Tikrit oilfields, the first represented (Ba-5) with a thickness of (120) m, and the second section (TK-6) the thickness of this formation (270))m. The formation under study consisted of chalk limestone sequences with the layers of marley limestone, the study showed that the lower bounder is compatible with the of Tanuma Formation in both sections, while the upper bounder is conformable with the Mashura Formation within well (Ba-5) and is unconformable with the Hartha Formation in a well (TK-6). Petrographic study showed the presence of many microfacies at divided into five main microfacies and six submicrofacies Lime mudstone microfacies, Lime wackstone microfacies divided to (Calcispheres lime wackestone and Rotalid lime wackestone submicrofacies), Lime packestone microfacies divided to (keeled planktonic foraminiferal lime packstone, Hedbergella lime packstone, Calcispheres lime packstone and Rotalid lime packstone submicrofacies), lime grainstone microfacies and crystalline microfacies. Depending on microfacise the paleoenvironment of formation extended from slope, open marina, deep shelf and deep sea. The sequence stratigraphy defined of study divide to the sequences into sets, and each sets represents a sedimentary cycle that event a rise and fall in sea level during a certain period of time, the formation in well (Ba-5) compound one sequence and well (TK-6) consist three sequence, the sequence begins with the sequence boundary of (Type-2) and after the transgression system tract (TST) it deposit by Retrogadation and the upper surface of this tract represented by the Maximum Flood Surface (MFS), followed high stand system tract (HST) deposited in progradation pattern, which is characterized by a gradual decrease in sea level and a shallowing sedimentary environment. The presence of three sequence cycles through the Tk-6 well is due to the fact that the Tikrit field is shallower than the Balad field of sedimentation and is located at the edges of the deeper part of the sedimentary basin and the beginning of the shallowing, which is affected more The processes of marine Transgression, where the final report of the well (Tk-6) showed that the succession of shallow sedimentary facies with deep facies as shown, indicating the instability of the substratum and its significant impact on tectonic movements.

This research is based on (23) Samples selected from the Avanah Formation (Middle Eocene) in the Geli Bessri section in Dohuk to recognize the microfacies and depositional environments. The Avanah Formation consists of rocks of marly limestone and limestone containing Alveolina and thin layers of sandstone lithofacies found in the lower part of the Formation. The depositional environment was determined depending on skeletal and non- skeletal grains. The facies of the Avanah Formation were divided into four main microfacies and four submicrofacies based on skeletal and non- skeletal grains: The mudstone and wackestone, which is divided into benthic foraminifera wackestone and Rotaliids wackestone, the Formation also contains the packstone which is divided into the Rotaliid - Miliolid Lime packstone submicrofacies and benthic foraminifera lim packstone submicrofacies, in addition to the lime grainstone and also contains the Sandstone lithofacies located at the bottom of the Formation. The Avanah Formation in the middle and upper part is subjected to diagenesis process early dolomization and it is observed this through floating dolomite rohmb. According to the results of the facies analysis and the presence of foraminifera fossils, the Formation was deposited in open marine platform to restricted platform interior.