The Use of Nannofossils in Determining the Age of the Sargelu Formation (Middle Jurassic) in the Hanjera section, Northern Iraq

Abstract

The Jurassic rocks are well exposed in Northern Iraq within the High Folded -Thrust Zone ( Western Zagros Fold Thrust Belt). The Sargelu Formation (Middle Jurassic) was studied from a well exposed section located NW of Suliamni city and about 2km NW of Ranya town , and close from Hanjera village. , at the southwestern side of Shawiri anticline. The Sargelu Formation consists of successive beds of sucrose dolomitic limestone, limestone and argillite limestone beds, interspersed with layers of shale rich in organic matter, as well as thin beds of flint. Some beds of the formation show the presence of large size ammonite fossils. It is bounded from the bottom by the Sehkanyan Formation, and the contact surface between them appears sharp, represented by the last appearance of the hard dolomite bed belonging to the Sehkanyan Formation, and it is bounded from the top by the Naokelekan Formation and the surface between them appears in the form of a sedimentary compatible surface. The current study relied on determining the age of the formation based on nannofossils, where many species and genus were diagnosed from the samples taken from the formation, and three biozones were identified, which are from the oldest to the most recent:1 - Watznaueria britannicaInterval biozone2 - Watznaueria manivitiae Interval biozone3 - Watznaueria barnesiaeInterval biozoneThese biozones were compared with global nannofossils biozones, and it was found that the age of the Sargelu formation is the middle Jurassic ( Bajocian - Bathonian).