2-1-Stratigraphy
Stratigraphic columnar sections covering the entire Eastern Anatolian region are displayed in Fig 3. The sections summarize the data gathered mainly from our field work together with the TPAO reports, and the previous studies (Kurtman and Akkuş 1971; Özdemir 1981; Şenel et al 1984; Koçyiğit et al 1985; Şaroğlu and Yılmaz 1984;1986; 1987;1991; Uysal 1986; Gedik 1986; Yılmaz et al 1987 A and B; Yılmaz A. et al 1988; Tarhan 1997A; B; 1998 A, B; Akay et al 1989; Bozkuş 1990; Temiz et al 2002; MTA 2002; Konak and Hakyemez 2008; Yılmaz 2107; Bedi and Yusufoğlu 2017; 2018; Yılmaz A and Yılmaz 2019; Üner 20121) enabling correlations and comparisons along and across the east Anatolian Plateau possible.
The generalized stratigraphic columnar section of eastern Anatolia (GSS in Fig 3 A) shows the presence of an ophiolitic mélange below the Neogene cover in most outcrops (MTA 2002; Özdemir 1981; Şenel et al. 1984; Konak and Hakyemez 2008; Elitok and Dolmaz 2008; Yılmaz A and Yılmaz 2019; Üner 2021; TPAO field reports and drilling data, and our field observations). The overlying Neogene cover is represented commonly by terrestrial sedimentary rocks. However, the stratigraphy in the northeastern part of the East Anatolia (i.e., N of the Kars province; Fig 1) is entirely different (the Karst region in Fig 3A). It consists of two major components, an old metamorphic basement and an overlying thick Paleozoic, Mesozoic, and Cenozoic successions. This is shown in the stratigraphic column of the Kars region in Fig 3A, where the succession is identical to that of the eastern Pontide Region (see the accompanying paper by Yılmaz et al. in this volume). The western and northwestern parts of the Kars province are thus considered easterly continuation of the eastern Pontide.
There is no detailed study on the eastern Anatolian ophiolitic mélange-accretionary complex. The previous works generally outline its major constituents (Altınlı1966; Yılmaz A. et.al.1988; Tarhan1989;1997A and B;1998 A and B; Önal and Kaya 2009; Bedi and Yusufoğlu 2018; Yılmaz A and Yılmaz 2019). A pelagic sedimentary succession consisting of limestone (chalk), radiolarite, and siltstone of the Upper Cretaceous to Lower Eocene age range is observed in association with the mélange. They are either blocks incorporated into the mélange or deep-sea sedimentary sequences deposited above the mélange foundation. Altınlı (1966), Şenel, et al. 1984; Tarhan (1989; 1997A; B;1998 A; B; Kaya (2009), Bedi et al. (2017), and Bedi and Yusufoğlu (2018) documented Upper Cretaceous, Paleocene, and Eocene fossil lists from the pelagic sediments. In some exposures, Upper Cretaceous-Eocene shallow sea sediments are also observed lying stratigraphically over the ophiolitic mélange (Bedi and Yusufoğlu 2018; Yılmaz A and Yılmaz 2019).
The Neogene cover succession consists of four major rock groups separated by angular unconformities corresponding to: 1-Late Eocene-Oligocene (the lower unconformity), 2-Late Oligocene-Early Miocene (the middle unconformity), and 3-Late Pliocene (the upper unconformity). The lower unconformity separates the ophiolitic mélange-accretionary complex from the Upper Eocene-Oligocene terrestrial units consisting mainly of coarse clastic deposits (1 to 9 in Fig 3B and 3C). The middle unconformity separates the terrestrial sediments from the overlying Upper Oligocene-Lower Miocene transgressive sequence. The marine sediments begin with fine-grained sandstone-siltstones-marl alternations followed by reefal limestone and Lower-Middle Miocene neritic limestone (the Adilcevaz limestone; Şaroğlu and Yılmaz 1986). The limestone unit is observed in the entire eastern Anatolian region (Şaroğlu and Yılmaz 1986; 1987; Tarhan 1998; Kaya 2009; Gedik 2010., Yılmaz 2017; Bedi and Yusufoğlu 2018; Yılmaz A and Yılmaz 2019).
The shallow marine sediments grades upward into evaporites (Akkuş 1970; Yılmaz 2017; Bedi and Yusufoğlu 2018; Yılmaz A and Yılmaz 2019; Helvacı 2021) and lacustrine limestone, shale-sandstone alternations of Upper Miocene-Lower Pliocene age (Akkuş. 1970; 19071; Tarhan 1998., Nazik et al. 2008; Yılmaz 2017; Bedi and Yusufoğlu 2018; Yılmaz A and Yılmaz 2019). Thick Pleistocene-Holocene lacustrine-fluvial conglomerates and sandstones unconformably overlie them.
The upper unconformity marks a critical change in the region’s morphotectonics (Yılmaz 2017 and the references therein). The field data obtained from regional geological mapping in eastern Anatolia (unpublished maps of Turkish Petroleum Association) shows that the Miocene and Pliocene sediments are regionally distributed. However, the post‐Pliocene deposits are confined to the local depressions and display abrupt vertical-lateral facies changes within the basins (Şaroğlu and Yılmaz 1987; Tarhan 1989; 1997A, 1998A; Yılmaz 2017; Bedi and Yusufoğlu 2018).
The stratigraphic data outlined above reveal that the final stage of the uplift in eastern Anatolia began during the Late Miocene (Yılmaz 2017; Bedi and Yusufoğlu 2018). This event is also coeval with the elevation of the Central Anatolia, which leads to assume that the rise of eastern Anatolia also accelerated the uplift and magmatism in Central Anatolia (Schildgen et al. 2014; Bartol and Govers, 2014; Govers and Fichtner, 2016; McNab et al. 2018).
Stratigraphic and isotopic age data reveal that volcanic activity in the eastern Anatolian plateau began sporadically during the Late Miocene, possibly about 13-11 my ago (Şaroğlu and Yılmaz 1984; Yılmaz et al. 1987A; B; 1998; Yılmaz 2017). The volcanic edifices increased in the northern regions around 7-8 my ago and then migrated to the central areas around 5-4 m years ago (Pearce et al. 1990; Yılmaz et al. 1998; Keskin 2003; 2006; 2007; 2012). However, the volcanic activity intensified in the central and the southern regions about 3 my ago and has continued almost uninterruptedly to the present (Yılmaz et al. 1987 A; B.,1998; Yılmaz, 1990; Pearce et al., 1990; Keskin, 2003; 2007; Keskin et al., 2006; 2012). As a result, a thick volcanic blanket covered the entire eastern Anatolian plateau. Thick lava pile reaching up to 2 km in thickness was measured and drilled in the Kars plateau (unpublished TPAO data). The major volcanic centers, the Nemrut, Süphan, Tendürek, and Ağrı volcanoes, were built during the Quaternary (Yılmaz et al. 1988).