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).