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

M. Ameen, Bakhtiar; T. Al-Barzinjy, Sherzad; H. Karim, Kamal

	HISTORY AND GEOLOGICAL SETTING OF INTERMONTANE BASINS IN THE ZAGROS FOLD – THRUST BELT, KURDISTAN REGION, NE IRAQ
Iraqi Bulletin of Geology and Mining
Article 1, Volume 4, Issue 1, 2008, Pages 21-33
Authors
Bakhtiar M. Ameen; Sherzad T. Al-Barzinjy; Kamal H. Karim
Abstract
It is mentioned previously that the intermontane basins, in northeastern Iraq, are developed in Early Paleocene. In present study, the timing, geographic location and geological setting of these intermontane basins are studied from Iraqi Zagros Fold – Thrust Belt during Tertiary. This study is achieved in accordance to the previous literature and recent sedimentological studies. The terrigenous clastic cutoff and facies comparison with their distribution are used as evidences for spatial and temporal development of intermontane basins. The study concluded that the first intermontane basin is developed during Middle Eocene. It is observed that the present position of the Thrust and Imbricated Zones of Iraq was an 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 was developed, which separated the subsidence area from the main basin. The present position of the paleohigh coincides with the boundary of the High Folded and Imbricated Zones. In these intermontane basins the flysch facies (sandstones and shales of Walash and Naopurdan Groups) are deposited at the beginning while later molasse facies (conglomerate of upper part of the Red Bed Series) are deposited. Concurrently, in the area of the present Low Folded and Mesopotamian Zones (main water body of the main foreland basin) thick succession of pure carbonate (Pila Spi Formation) was deposited signalizing total cutoff of clastic sediments from the latter zones. In contrary, during Early Paleocene till Middle Eocene clastics (conglomerate and sandstone) influx was continued from source area into early Zagros Foreland Basin and mixed (occasionally) with carbonates of Sinjar Formation in many places. During Early Paleocene – Middle Eocene, intermontane basin was 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 two smaller basins (Main foreland basin and intermontane basin) decreased the current circulation and wave activity, therefore lagoonal dolomitic limestone of Pila Spi Formation was deposited.

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