New Ideas and Critical review of Middle Eocene Gercus Formation, Kurdistan Region, NE-Iraq

Abstract

In Iraq, Gercus Formation (Middle Eocene) crops out now near boundary between Low and High Folded Zone and generally consisted of red claystone and sandstone with occasionalbeds of conglomerate. Lithologically, it changes toward the southwest to carbonatesiliclastics of either Khurmala or Aliji Formations inside the Low Folded Zone. All previous studies have concluded that the environment of the formation was fluvial and deltaic of continental mollasse facies with possible some shallow marine sediments at its lower part. Conversely, the most recent two studies have assigned two different, opposite environments of the formation, which are deep marine (turbidite facies), and desert environments. The aim of the present study is critical and objective analysis of the previous studies in addition to introduction of new ideas that are opposite to deep marine and aeolian environments. The study gives many evidences and features for justification of the introduced new ideas, which are revealing the actual environment of the formation. This reveal is depended on the field and regional correlation in areas of boundary between High and Low Folded Zone (area of exposure of Gercus Formation) and area of Imbricated and Thrust Zone where its equivalent in age and facies (unit five of Red Bed Series) is exposed. The present study supports neither the deep marine turbidite nor the desert erg system of the previous studies. The present study proves that the Gercus Formation consists of the distal alluvial fan and its proximal part is unit five of Red Bed.

Petrography and geochemistry of siliciclastic rocks of the Middle Eocene Gercus Formation, northern Iraq: Implications for provenance and tectonic setting

“…The Gercus Formation was studied in Iran (e.g. James & Wynd, 1965;Yeganeh, Feiznia, & Van Loon, 2012), Turkey (Bolgi, 1961;Duran, Şemşir, Sezgin, & Perinçek, 1988;Maxon, 1936), and Iraq (Aghwan & Hussain, 2012;Al-Azzawi & Al-Hubiti, 2009;Al-Mashaikie, Al-Azzawi, & Kadhum, 2013Al-Qayim, Al-Mutwali, & Nissan, 2008;Al-Qayim & Al-Shaibani, 1994;Al-Rawi, 1980Ameen, 1998Ameen, , 2006Baziany, 2009;Hussain & Aghwan, 2015;Jassim & Buday, 2006;Jassim & Goff, 2006;Karim, Baziany, & Khanaq, 2018;Van Bellen et al, 1959). The original type section of the Gercus Formation was first described by Maxon (1936) near the Gercüş village in south-east Turkey.…”

Clay mineral diagenesis and red bed colouration: A SEM study of the Gercus Formation (Middle Eocene), northern Iraq

“…The lack of marine microfossils (Karim et al, 2018) would preclude a marine origin, while the predominance of fine-grained clastic sediments and rarer conglomerates would suggest an alluvial fan origin.…”

“…The Gercus Formation crops out near the boundary between the High Folded Zone and the Low Folded Zone (Karim, Baziany, & Khanaqa, 2018) and was deposited in a foreland basin which formed parallel to the orogenic belt (Buday, 1980). The evolution of this foreland basin – the Mesopotamian Basin – commenced with the collision of the Iranian block onto the Arabian margin and the subsequent emplacement of the Sanandaj‐Sirjan Zone (Le Garzic et al, 2019).…”

“…The Gercus Formation, which was initially defined in SE Turkey, crops out between the Palaeocene‐Early Eocene Sinjar (Khurmala) and Middle‐Upper Eocene‐age Pila Spi formations (Karim et al, 2018). Formation thickness is greatest in the NE part of the basin (ca.…”

“…Most of these studies have argued that deposition occurred in a fluvial or deltaic setting, with possible shallow marine sediments being present within the lower part of the succession (i.e., a progradational succession). However, a range of other environments have also been suggested, including tidal flats (Al‐Qayim et al, 1994), shelf and basin‐plain turbidites (Al‐Mashaikie, Al‐Azzawi, & Kadhum, 2014), and aeolian sediments (Hussain & Aghwan, 2015), delta and fan delta (Karim et al, 2018). The lack of marine microfossils (Karim et al, 2018) would preclude a marine origin, while the predominance of fine‐grained clastic sediments and rarer conglomerates would suggest an alluvial fan origin.…”