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The Callovian-Kimeridgian Naokelekan Formation is a heterogeneous sequence consisting principally of bituminous shales with bituminous limestone and dolomitic limestones. It is 48 m thick maximally in some parts of the area. One hundred forty four rock and cutting samples from six outcrops and eight boreholes in different parts of Iraqi Kurdistan have been studied using the Rock-Eval technique with the primary purpose of assessing their potentiality as promising source rocks for petroleum. The outcomes of the Rock-Eval study for examined samples shows that TOC ranges from 0.4 to 18.8 wt. % and types II and III kerogens are the main components of organic matter.Qualitative evaluations are also done by textural microscopy used in assessing amorphous organic matter for palynofacies. The organic matters are mature that have thermal alteration index of 2.6-3.2 by Pearson's scale with palynomorphs of dark orange and light brown colors and Tmax ranges between 434 to 493ºC. Thus the Naokelekan Formation can be considered as a source rock for generation and expulsion of oil and/or gas that has been charged largely oil fields in the area.Maturity increases toward the northeastern part of the studied area. Furthermore, the study revealed that Naokelekan Formation is within dry gas and/or late oil zone in the eastern part, early oil window in the central part and immature in the western part of the studied area.

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The Upper Cretaceous Shiranish Formation of Shkawtua Village, Mergasur area, Iraqi Kurdistan region consists of alternating mixed siliciclastic and carbonate strata interpreted as an outer shelf open marine (basinal) depositional environment. Fourteen thin sections were studied under polarized microscope to determine the petrographic component, fauna content, and microfacies analysis. The study tries to compare this formation with its equivalences throughout the region. Rock units are divided into: marly limestone, marlstone, and dolostone. The major petrographic constituents are: micrite, pseudospar, replacement dolomite, and fossils. Fossils are the main particles within mudstone, wackestone, and packstone microfacies types. The occurrence of some planktonic foraminifera such as globigerina cretacea, archaeoglobigerina cretacea, and rotalipora cushmani (rotalia sp.) suggests an Upper Cretaceous age.

The aim of this study is to assess the type, thermal maturity and the petroleum generation potential of the Upper Jurassic Naokelekan Formation, occurring across the Kurdistan Region of Iraq, by applying organic petrographical methods and Rock-Eval analysis. The Rock-Eval data would indicate the presence of kerogen types III, IV and II as the main constituents. However, the qualitative petrographical evaluation revealed that the main organic constituents are solid hydrocarbons, in the form of microgranular migrabitumens, with minor amounts of pyrobitumens. These secondary particles have affected the results of the Rock-Eval analysis and would have led to misinterpretation of organic matter typification based on pyrolysis results only. The combined results of petrography and pyrolysis indicate an active petroleum system within the Upper Jurassic sequence, where hydrocarbons are generated and reservoired within suitable lithologies.

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The studied samples were collected from the Palaeozoic outcrops, Khabour, Pirispiki, Kaista, Ora, Harur, and Chia Zairi formations in Nazdur Anticline, Amadia about 457 km due north of Baghdad, Iraq's capital city. Qualitative assessments of 29 samples were conducted by using textural microscopy in determining the percentage of amorphous organic matter for palynofacies type belonging to different types of kerogen. This organic matter contains acritarchs, spores, and algae deposited in the dysoxic-anoxic environment. The organic matters are from mature to post mature and have a thermal alteration index of-3 to +3 by Pearson's and Staplin's scales, respectively, with palynomorphs of orange to dark brown colors on the palynomorphs. These ranges of colors indicate mature organic matters.