Marine and Petroleum Geology xxx (xxxx) xxx Please cite this article as: Mohamed W. Alkhafaji, Marine and Petroleum Geology, https://doi.org/10.1016/j.marpetgeo.2020.104786 Available online 3 November 2020 0264-8172/© 2020 Elsevier Ltd. All rights reserved. Research paper Origin, biodegradation, and water washing of bitumen from the Mishraq Sulfur Mine, northern Iraq Mohamed W. Alkhafaji a, * , Jacques Connan b , Michael H. Engel c , Sami W. AL-Jubouri d a Applied Geology Department, College of Science, University of Tikrit, Iraq b University of Strasbourg, 23 rue Saint-Exup´ ery 64000-Pau, France c School of Geosciences, The University of Oklahoma, Norman, OK, 73019, USA d State Company for Mishraq Sulfate, Ministry of Industry and Minerals, Iraq A R T I C L E INFO Keywords: Mishraq Sulfur Fat’ha formation Biodegradation Water washing ABSTRACT Bitumens from Middle Miocene Fat’ha Formation at Mishraq Sulfur Mine were investigated to determine their sources and the extent to which they may have been diagenetically altered. For these purposes, fourteen bitumen samples were subjected to detailed biomarker analysis using gas chromatography-mass spectrometry (GC-MS). Stable carbon and deuterium isotopes were also measured on chromatographic fractions. These bitumens are present in cavities and fractures of limestone from the native sulfur productive series. Polar fractions accounts for about half of the bitumen composition. These bitumens are showing a partial removal of n-alkanes; whereas their terpanes and steranes are intact. In addition, dibenzothiophene (DBT) and phenanthrene (Phen.) concentrations and DBT/Phen. ratio are variable among the samples. Most deuterium isotope values of asphaltene and resin fractions are similar to those of non-biodegraded bitumen seeps from the Qaiyarah area. These criteria suggest that bitumens of Mishraq mine are slightly affected by biodegradation and they are water washed to different extents but are not affected by abiotic oxidation. The biodegradation of these bitumens is mainly due to sulfate- reducing (anaerobic) bacteria. Terpane and sterane ratios suggest that bitumens were generated from early-mid mature carbonate source rocks deposited under reducing conditions. They show high values of C29/C30 and C35S/C34S hopane (>1.0), low values of diasteranes/regular steranes, Ts/Tm, moretane/hopane, and low values of Pr/Ph for most samples. Regular sterane distributions show dominance of C29 over C27 steranes. Middle and Upper Jurassic Sargelu and Chia Gara formations are proposed as source rocks for these bitumens; but Chia Gara is most likely. 1. Introduction Mishraq Sulfur Mine (MSM), one of the most important mines in the Middle East, is located in North Iraq, about 45 Km southeast of Mosul (Fig. 1A). It contains about 100–250 million tons of bioepigenetic sulfur within the Middle Miocene Fat’ha Formation. It extends for about 10 km 2 within a doubly plunging anticline on the west bank of the Tigris River (Fig. 1B; Barker et al., 1979). Bitumen, widespread in MSM, is present in the Euphrates and Fat’ha formations. This bitumen causes problems in drilling and well log acquisition and interpretation. Northern part of the mine contain higher concentrations of bitumen than the southern part; therefore, the frst sulfur mining concentrated in the southern part. Previous studies of the Mishraq Mine focused on the origin and formation of native sulfur and the role of tectonic, sedimentological, and hydrological factors in native sulfur formation (Al-Sawaf, 1977; Barker et al., 1979; Jassim et al., 1999). There have been no published studies concerning the origin of bitumens in this area. The main goals of this study are to investigate the origin of bitumens and to document the extent to which alteration processes may have affected their original composition. 1.1. Distribution of bitumen in mishraq area Bitumen, widespread in the Mishraq Sulfur Mine, ranges between less than 0.1% and 8% of the rock sample of the sulfur productive series, but in individual horizons, the bitumen amount varies over a wider range. The average bitumen content rises from 0.2% in the non- * Corresponding author. E-mail address: mohamed_wagga@yahoo.com (M.W. Alkhafaji). Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo https://doi.org/10.1016/j.marpetgeo.2020.104786 Received 24 May 2020; Received in revised form 22 August 2020; Accepted 26 October 2020