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

Abstract

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.