HISTORY AND GEOLOGICAL SETTING OF INTERMONTANE BASINS IN THE ZAGROS FOLD – THRUST BELT, KURDISTAN REGION, NE IRAQ

Abstract

It is mentioned previously that the intermontane basins, in northeastern Iraq, are developed in the Early Paleocene. In present study, the timing, geographic location and geological setting of these intermontane basins are studiedfrom Iraqi Zagros Fold-Thrust Belt during Tertiary. The study achieved in view of literature and recent sedimentological studies. The terrigenous clastic cutoff and facies comparison with their distribution is used as evidence for spatial and temporal development of intermontane basin. The study concluded that the first intermontane basin is developed during the Middle Eocene.� ��� It is observed that the present position of Thrust and Imbricated Zones of Iraq was area of subsidence and generation of the intermontane basin during Middle Eocene. Concurrently with this subsidence and directly to the southwest of the latter zone a narrow paleohigh is developed which separated subsidence from the main basin. The present position of the paleohigh coincides with of the boundary High and Imbricated Zones. In these intermountain basin the flysch facies (sandstone and shale of Walash Nauperdan Group) are deposited at the beginning while later molasses facies (conglomerate of upper part of the Red Bed Series) are dominated. Concurrently, in the area of present Low Folded and Mesopotamian Zones (main water body of the main foreland basin) thick succession of pure carbonate (Pila Spi Formation) was deposited signalize the total cutoff of clastic sediments from the latter zones In contrary, during the Early Paleocene till Middle Eocene clastic (conglomerate and sandstone) influx was continued from source area into Early Zagros foreland basin and mixed (occasionally) with carbonate of Sinjar Formation in many places.�� During these latter ages, intermontane basin is not generated as cited in previous studies to trap transferred sediments from source area except some basin irregularities on which reefal limestones of Sinjar Formation are deposited. The separation of Early Zagros Foreland basin into twosmaller basins (Main foreland basin and intermontane basin) decreased the current circulation and wave activity therefore lagoonal dolomitic limestone of Pila Spi Formation was deposited.