The Impact of Tectonic Setting on Distribution of Kolosh Formation during Paleocene –Lower Eocene in Northern Iraq

Abstract

This study covered most of Kolosh Formation exposure areas in northern Iraq. Description of the lithology and measuring the actual thickness of the Formation from exposures and well logs were performed. The isopach map of the Formation was constructed. The sedimentation of the Formation was affected by the tectonic activity of the northeastern edge of the Arabian plate during the closure of the Neo-Tethys Ocean. The tectonic setting outlined the depozone of foreland basin system and controlled the variation of the deposits of the Kolosh Formation along the orogenic front (It revealed that there are more than one basin of deposition). The deviations of the depocenters of the Kolosh deposit basins from the current folds are depicted. The counterclockwise rotation of Arabian plate and its oblique collision with Iranian plate as well as the rejuvenation of the basement faults during the peak of the orogeny might cause such deviation. Keyword: Kolosh formation-foredeep backbulgedepozone-depocenters. ريثأت نيسويلابلا للاخ شولوك نيوكت بساور عيزوت ىلع ينوتكتلا عضولا – يلامش لفسلأا نيسويلاا قا رعلا دانز فلخ عيبر يليمجلا دعس ميها ربإ ضرلأا مولع مسق مولعلا ةيلك لصوملا ةعماج شولوك نيوكت بساور عيزوت رثأت طاشنلاب يتاتفلا قبطلل ةيقرشلا ةيلامشلا ةفاحلل ينوتكتلا ءانثأ يبرعلا لحا رم سثيتلا طيحم قلاغنإ ءوشنو ديدجلا بساور راشتنا ريسفت مت .يقا رعلا هئزج يف سوركا ز دنلاروف ضوح قفو نيوكتلا ةينوتكتلا ميهافملا ضاوحا ةمظنلا ،دنلاروفلا للاخ نم جاتنتسلاا مت ثيح يرحتلا مسرو يلقحلا دجاوت ىلا يواستملا كمسلا ةطيرخ رثكأ يهو ةيلاحلا تايطلا رواحم نع فرحنت يبيسرت )روحم(زكرم نم ( قيمعلا ماملاا ضوحلا قاطن يف ةعزوم foredeep depozine ) قاطنو ( زوربلا فلخ backbulge depozone .) :ةلادلا تاملكلا .سوركاز ،زوربلا فلخ ،ماملاا ضوحلا ،دنلاروفلا ضوح ،شولوك نيوكت The Impact of Tectonic Setting on Distribution of Kolosh Formation...... 22 INTRODUCTION Kolosh Formation is one of the widely distributed clastic sediments throughout northern Iraq. Many researchers considered the Formation as flysch deposits due to its lithological characteristics. Thus, the distribution of these deposits reflects the dynamic tectonic setting of Arabian northeastern edge during its subduction under Iranian plate and initiation of foreland basin system during late Cretaceous. The control of this tectonic setting on the distribution of the foreland basin deposits continued throughout early Tertiary. Kolosh Formation represents the clastic unit of fore-deep depozone (Znad, 2013). The constructed isopach map of the Formation depends on detailed fieldwork notes and measure of true thickness on all accessible outcrops, besides well logs. The southwestern rim of Kolosh basin is outlined at its transitional zone with Aliji Formation. The study area comprises most of northern Iraq (Fig. 1). LITHOLOGY OF KOLOSH FORMATION Kolosh Formation type section is cited and described by Dunnington (1952 in Bellen et al., 1959) in Koya within high fold zone of northern Iraq. Its age extends from Paleocene to early Eocene, with 777 meter thickness. The formation consists of rhythmic alternation of thin sandstone, siltstone, marlstone, and less common conglomerate and limestone with calcareous silt shale inter-layers. They resemble flysch-like sediments (Dunnington, 1958). The Formation crops out on the most areas of northern Iraq without essential differences in lithological nature. Generally, the formation consists of dark grey easily drifted sandstone, shale and claystone (Fig. 2), making wet dark grey soil in the lowland. Sandstone beds range between (0.25m-3m) in thickness, of medium hardness and fine grained in general, occasionally pebbly (not more than 2-3 cm). Conglomerate beds have thicknesses of about (1-2 m) with pebbles (not more than 4cm in size). The SYRIA