The provenance of Eocene sandstones (Gercus Formation), Northern Iraq


Gercus Formation is exposed in northern Iraq. When the passive Arabian continental margin collided with the active continental margin of the Turkish and Iranian plates, a part of the source rocks of Gercus red beds were carried out from Iran and Turkey territories and deposited in the molasses trough, parallel to the suture zone of the collision, and the others were driving from the longitudinal paleo-high lying parallel to the trough basin of Gercus Formation. The present study is based on three surface sections, Bekhme, Sarsank and Amadiya areas in Northern Iraq. Generally, the Gercus Formation consists of reddish brown to light grey, well bedded sandstones and mudstones in addition to thin beds of conglomerates. The most of sandstone particles are composed of polycrystalline and monocrystalline quartz (of metamorphic and plutonic origin), K and Na – feldspar (derived from igneous and metamorphic source rocks), and chert grains of sedimentary source. Carbonate and other rock fragments with low ratio of mica group and heavy minerals (magnetite and rutile) are present too. The sandstones of Gercus Formation, generally contain low-moderate quantities of clay as matrix in all sections, therefore, they are texturally immature. On the other hand, the low ratio of quatrz and chert to feldspar and other components indicates to mineralogically immature sandstones. According to McBride classification, it is sublith arenite - Lithic arenite sandstone. Petrographic analysis of sandstones in Bekhme section revealed that it consist of variable amount of detritus, represented by the abundance of quartz and chert rock fragments with low content of feldspar, and at Sarsank and Amadiya sections, the Gercus sandstones are characterized by the abundant chert rock fragments with high percentage of metamorphic rock fragments. So they lay in the recycled provenance source of collision orogen.