Article Details
Geology and critical review of the Upper Cretaceous Zagros chalky limestone (Kometan Formation) from Sulaimani Governorate, Northeastern Iraq
Indexed In
Volume 157 / 2018Authors:
Kamal Haji Karim KARİM, Sherzad Tofeeq AL-BARZINJY, Polla Azad KHANAQAKeywords:
chalky limestone, Late Cretaceous, Zagros geology, pseudo-bedding, depositional bedding, Kometan Formation, Thalassinoides,Abstract:
The chalky limestone (Kometan Formation) is aged Late Turonian–Middle Campanian and cropping out in the High, Imbricate and Thrust Zones of northeastern Iraq, Sulaimani area. It laterally changes to Bekhme and Mushurah formations toward northwest and west Iraq respectively and its reefal equivalents occurs too in subsurface of Central Iraq in the oil fields. Stratigraphically, it is located between Shiranish Formation (Middle-Late Campanian), at the top, and Gulneri Formation (Late Cenomanian-Early Turonian) at its base. It has the thickness of about 40-120 meter and deposited in pelagic realm. All previous studies have defined it as well bedded and fine grain limestone of deep marine facies with concentration of chert nodules and stylolites on or near bedding surfaces. The only recorded fossils are nannofossils, planktonic forms and rare benthonic forams. On the contrary, a most recent study has declined all the above features and changed lithology to massive, homogenous limestone with abundant Thalassinoides trace fossils. It additionally concluded that the bedding surfaces are not true bedding (pseudo-bedding) and formed by stylolization not by deposition. The present study is focusing on update the geology of the Cretaceous chalky limestone and critical review in addition to comparison of all the above ideas and introducing new ones. The features of the Thalassinoides, massiveness and pseudo-bedding of previous authors discussed and their absence confirmed and justified by field and laboratory works. Moreover, the massiveness is refused and well bedding (relatively has thin beds) is proved as an intrinsic characteristic of the formation in all section. The study also shows absence of relation of the chert nodules and chert bedding with traces fossils due to absence of bioturbation, detrital clasts, bioclasts, sorting, lamination and color change. Moreover, the idea of deposition of Kometan Formation in Zagros Foreland basin refused and assumed as deposition of continental margin of Neo-Tethys Sea (or ocean) before ophiolitic obduction and foreland generation.
DOI: 10.19111/bulletinofmre.428342
