Biogenic-sedimentary structures of the Ordovician-Khabour formation from the Northern Thrust Zone, Kurdistan, Iraq

Abstract

The Ordivician-Khabour Formation from the Northern Thrust Zone of Iraqi-Kurdistan comprises between 500 and 800 m of alternating predominantly greenish-gray sandstones, siltstones, and shales. The succession has revealed an abundant ichnofossils characterized by 11 ichnogenus, namely: Helminthopsis, Gordia, Cruziana, Rusophycus, Monomorphichnus, Rhizocorallium, Thalassinoide, Planolite, Paleophycus, Deplocraterion, and Skolithose. Ethologically, the ichnofossils are distributed among domichnia and fodinichnia groups. This association of ichnofossils contains elements of the Skolithose and Cruziana ichnofacies. The presence of these ichnofacies indicates variations in energy of the sedimentary environment. High-energy condition with sandy-shifting substrate in foreshore zone is related to the Skolithos ichnofacies, while the Cruziana ichnofacies indicates unconsolidated-soft substrate developed under low-energy condition in the shoreface/offshore zone. These ichnogenera indicate shoreface-offshore zone of shallow-marine environment for the deposition of the rocks of the Khabour Formation.