Age determinations of Cretaceous sequences based on calcareous nannofossils in Zagros Thrust and Folded Zone in Kurdistan Region-Iraq.

The studied area is located in Northern Iraq in the Kurdistan Region, in the North- Western part of the Zagros Fold belt. This study concentrates on the biostratigraphic approach using nannofossil analysis to identify the age of the formations that have deposited during Cretaceous period in Kurdistan Region-Iraq. The sedimentary sequences in Kurdistan region exhibit many lateral and vertical environmental and facies changes. Previously most of the works to recognize the age of the formations were concentrated on the Foraminifera zonation. In the present study, attempts have been made to review the age of the formations and the contact between them by using nannofossil analysis technique. Nannofossils assemblage Chia Gara Formations show that conformable contact situation between Jurassic-Cretaceous. The contact is between Late Tithonian Chia Gara and Berriasian- Valanginian Balambo formations. In Kurdistan during Hauterivian-Barremian the outer shelf sediment of Sarmord Formation deposited that conformably overlay Balambo Formation. The Qamchuqa Formation is a heterogeneous group of limestone. The lower part is belongs to the Aptian to Albian periods, while The upper part of the Qamchuqa limestone is generally dolomitized, therefore, the existed nannofossils even within the locally thin marl layers are destroyed. The Dokan Formation, which appears along the Dokan dam, is a Cenomanian age. The Kometan Formation is represented an Early Turonian age. The top of the Kometan limestone is characterized by a hard ground most possibly indicating a hiatus. The sequence of marl-Limestone of Shiranish Formation we dated Early to Late Campanian. Toward north the Early to Late Campanian part of Shiranish Formation can be locally replaced by the reefal Bekmeh limestone Formation. Very rare nannofossils were found in the marly intercalations of the Bekmeh limestone indicating at least a Late Cretaceous age. The Shiranish/Tanjero formations boundary lies within the Upper Campanian. The age of Tanjero Formation ranges from Late Campanian to Late Maastrichtian.