Microfacies and Sequence Stratigraphy of the Saadi Formation within the sequences of the (Torunian - Santonian) cycle in Balad and Tikrit / Salah al-Din Governorate / Iraq

Abstract

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.