LITHOSTRATIGRAPHIC STUDY OF THE CONTACT BETWEEN KOMETAN AND SHIRANISH FORMATIONS (CRETACEOUS),   IN SULAIMANIYAH GOVERNORATE, KURDISTAN REGION,  NE IRAQ

M. Ameen, Bakhtiar; M. Ismail, Khalid; H. Karim, Kamal

	LITHOSTRATIGRAPHIC STUDY OF THE CONTACT BETWEEN KOMETAN AND SHIRANISH FORMATIONS (CRETACEOUS), IN SULAIMANIYAH GOVERNORATE, KURDISTAN REGION, NE IRAQ
Iraqi Bulletin of Geology and Mining
Article 1, Volume 4, Issue 2, 2008, Pages 15-27
Authors
Bakhtiar M. Ameen; Khalid M. Ismail; Kamal H. Karim
Abstract
The contact between Kometan and Shiranish formations (Cretaceous) is re-studied in the field and laboratory. The study elucidates the nature of the contact and discusses the previous ideas of unconformable contact. On lithological basis, the contact is described and analyzed in eight different sections and grouped into three types: Obvious gradational, Burrowed-glauconitic and sharp contacts. Following recent studies, the basin in which the sediments of these types are deposited is considered as foreland basin and the location of each section is indicated within it. The sections are interpreted to be deposited in the beginning of clastic influx into the basin at threshold time and space between pure carbonate sedimentation and mixed sedimentation of clastic and carbonate, during and after drowning of the previous platform. The first type of the contact (Obvious gradational) is interpreted to be deposited in front of major submarine fans, which are supplied by regular but intermittent clay influx of highly diluted turbidity currents. The second type (Burrowed-glauconitic) is attributed to the areas between the fans, which are supplied by clear water and rich in nutrient, Fe, Mg and O2. This supply is most probably due to currents that are driven from the turbidity currents, when the basin was passing from deep water to shallower one. The pebbles and granules exist only in one section, out of eight and they are intraformational clasts (not terrigenous) and formed by submarine erosion. The third type (Sharp) represents sudden and unusual event of clay influx of the turbidity currents into the location of the sections, so that the marl is deposited instead of pure limestone of Kometan Formation. This rapid deposition may be due to a sudden switching of submarine channel, or an event such as large storm or tsunami. All evidences suggest that the contact is most probably conformable and shows no any signs of sub aerial erosion or long non-deposition, but does not exclude short submarine erosions and slow rate of sedimentation across the contact.

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