Sequence stratigraphy of the Late Campanian – Early Maastrichtian Shiranish Formation, Jabal Sinjar, northwestern Iraq

Abstract

ABSTRACT The Late Campanian – Maastrichtian Shiranish Formation consists of deep-marine marls and limestones that were deposited in northern and central Iraq. In northwestern Iraq, in the core of EW-trending Jabal Sinjar, a 430-m-thick section of the Shiranish Formation crops out. The base of the Shiranish section is not exposed here. It is unconformably overlain by Paleocene – Lower Eocene formations: Sinjar Formation along the northern part of the Jabal, and Aaliji Formation along its eastern side. Eighty samples were collected from the section and used for facies analysis and biostratigraphic calibration. Previous studies of planktonic foraminifera recognized four biozones, which were confirmed in the present study: Globotruncanita calcarata Interval Zone, Globotruncanella havanensis-Rosita fornicata Partial Range Zone, Globotruncana aegyptiaca Interval Zone and Gansserina gansseri Interval Zone. These zones are here calibrated in several geological time scales. Six facies were distinguishable throughout the section, representing shallow-marine, middle-shelf, outer-shelf and upper-bathyal environments. These environments were used to interpret six depositional sequences. The older five Shiranish sequences are fourth order and grouped into one third-order sequence, while the sixth and youngest Shiranish Sequence was of third order. This suggests that the studied section was deposited in about 5 million years between ca. 76.0–74.4 and 69.5–69.8 Ma. The correlation between the Shiranish sequences and those of the Aruma Formation in Saudi Arabia implies that the northern Arabian Platform was regionally flooded starting in the Late Campanian and ending in the Maastrichtian. In the study area, an unconformity straddles the Cretaceous – Tertiary (K/T) boundary and represent a hiatus of ca. 10 or more million years.