Abnormal Ophiolite (Olivine/Pyroxene Rich) Sandstone NE Iraq: An Approach to the Origin and Tectonosedimentary Evolution of Zagros Foreland Basin

Abstract

Unusual Paleocene ophiolite sandstone rich in olivine/pyroxene identified in Zagros Thrust Belt (NZTB) in NE Iraq. NZTB is regionally extended from Iran to Alpen Belt. Kolosh sandstones are controlled by progressive thrusting during late Cretaceous-Paleocene. Zagros thrust sheets composed of ophiolites, oceanic crust, basaltic flows, and ash sequences. Kolosh sandstones reveal high percentages of fresh olivine-pyroxene grains accompanied by igneous intrusive and volcanic ultrabasic-basic fragments, which are reported for the first time in NE Iraq and along ZTB. Olivine, pyroxene, ultrabasic igneous altered, serpentine and chlorite fragments, heavy minerals (includes chrome spinal), anorthite, and labradorite all together composed about 70% of the mineralogical composition. Sanidine, anorthoclase, quartz and cristobalite, argillaceous, carbonate and chert fragments all together composed (12.25%), supported by argillaceous matrix (16.53%), which are derived from mantle and oceanic crust/ophiolite sequences from NE Iraq, emplaced during late Cretaceous with arc volcanism, which subjected to rapid submarine erosion and deposition. Intense wave action accelerated the erosion of beach rocks, and concentrate the heavy minerals insitue that slumped to deeper margins. Identified lithofacies types, grouped in four associations, slope/submarine channel, inner, outer fan, and hemipelagic/pelagic, respectively, represented progressive upward transgression from slope to basin plain systems controlled by progressive thrusting.