ORIGINAL PAPER Biogenic-sedimentary structures of the Ordovician-Khabour formation from the Northern Thrust Zone, Kurdistan, Iraq Waleed S. Shingaly 1 Received: 3 April 2015 /Accepted: 10 September 2015 # Saudi Society for Geosciences 2015 Abstract The Ordivician-Khabour Formation from the Northern Thrust Zone of Iraqi-Kurdistan comprises be- tween 500 and 800 m of alternating predominantly greenish-gray sandstones, siltstones, and shales. The suc- cession has revealed an abundant ichnofossils character- ized 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 con- tains 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. Keywords Ichnofossils . Shoreface-offshore zone . Khabour formation . Iraq Introduction Strata belonging to the Khabour Formation crop out around Kaista and Nazdur villages, about 40 km northeast of Zakho city (Fig. 1). Several sedimentological studies have been made on the Khabour Formation in Iraqi-Kurdistan, and different sedimentary facies have been defined (e.g., Al-Bassam 2010). However, there is not yet a detailed study on the biogenic-sedimentary structures of these sediments. The study of biogenic-sedimentary structures in ancient sediments has provided important criteria that are commonly used to under- stand depositional environments recorded by sedimentary rocks. Published record of biogenic-sedimentary structures from the Ordovisian-Khabour Formation includes general de- scriptions and determinations of the stratigraphic age of for- mation (Seilacher 1963). Based on the sedimentary character- istics, the Khabour Formation is suggested to have deposited in a shallow to deeper marine environment, where a turbidite- affected deeper facies are recognized for the upper parts (Seilacher 1963; Buday 1980; Karim 2006; Al-Bassam 2010). The presence of evidence of organisms within the sed- iment is known as biogenic structures (ichnofossils) and is a very common feature in sedimentary rocks. Because they show minimal effects of compaction and of early diagenesis, ichnofossils may be the principal or only pre- served biogenic evidence of pleoenvironmental conditions in thick stratigraphic intervals (Pemberton et al. 1992). especially in those dominated by nearshore facies. Therefore, biogenic structures provide critical data for the interpretation of ancient depositional environment. The existence of different trace fossil associations in the Khabour Formation has been recognized since the 1960s (e.g., Seilacher 1963). However, the implications and sig- nificance of theses associations have not been clear. The recognition that the Khabour Formation encompasses a * Waleed S. Shingaly waleed_0076@yahoo.com 1 Geology Department, College of Science, Salahaddin University, Erbil, Iraq Arab J Geosci DOI 10.1007/s12517-015-2126-7