Clay minerals of upper Cretaceous (Shiranish Formation) and lower Tertiary (Kolosh Formation) at selected sections from north Iraq

Abstract

Clay minerals investigation is conducted using X-ray diffraction and scanning electron microscopy from the upper Cretaceous Shiranish Formation and lower Tertiary Kolosh Formation at two sections in Dohuk and Shaqlawa, northern Iraq. The study revealed the presence of smectite, palygorskite, illite, smectite-chlorite mixed layers, chlorite, and kaolinite. Smectite and palygorskite found to be formed authigenically in the marl of the Shiranish Formation, whereas, other minerals are detrital in origin especially in the Kolosh Formation. The mineral variation reflects the environmental changes from Cretaceous to Tertiary times. Variation in source rocks and change in drainage conditions may lead to increase in the effectiveness of leaching processes and hence transformation of smectite to palygorskite. These changes also effects on the prevalence of inherited or detrital types of clay minerals in the Kolosh sediments.