1 23 Arabian Journal of Geosciences ISSN 1866-7511 Volume 13 Number 13 Arab J Geosci (2020) 13:1-20 DOI 10.1007/s12517-020-05579-1 Biodegradation and the origin of surface bitumens in the Palaeocene Kolosh Formation, Northern Iraq Mohamed W. Alkhafaji, Mohamed A. Aljubouri, Falah A. Al-Miamary & Jacques Connan