Biostratigraphy of the Early Pleistocene (Palaeopleistocene) deposits of the Southern Fore-Urals, Russia

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Biostratigraphy of the Early Pleistocene (Palaeopleistocene) deposits of the Southern Fore-Urals, Russia Guzel Danukalovaa,b,∗, Eugenija Osipovaa, Anatoly Yakovleva, Ravil Kurmanova a b

Institute of Geology of the Ufimian Federal Research Centre (UFRC), Russian Academy of Sciences (RAS), Ufa, 16/2, K. Marx St., 450077, Russian Federation Kazan Federal University, 18, Kremlevskaya St., 420008, Kazan, Russian Federation

A R T I C LE I N FO

A B S T R A C T

Keywords: Early Pleistocene Gelasian Palaeopleistocene Biostratigraphy Southern Fore-Urals

A summary of published and unpublished data on the stratigraphy of the Early Pleistocene (Palaeopleistocene) of the Southern Urals region is presented in this paper. The summary follows previous reviews about the characteristics of the Pleistocene deposits of the easternmost part of Europe. The improvement and unification of the Regional Quaternary stratigraphical scheme was the main aim of these investigations. Deposits of different origin, which constitute the regional stratigraphical units (Zilim-Vasilyevo, Akkulaevo and Voevodskoe), are characterized. Malacological data form the base for the biostratigraphical subdivision. At the beginning of the Early Pleistocene, an ingression of the Akchagyl Sea (modern Caspian Sea area) began in the Zilim-Vasilyevo time, which developed as much as possible during Akkulaevo time, and then shortly re-emerged after regression into the territory of the Southern Fore-Urals during Voevodskoe time. During the Early Pleistocene (Palaeopleistocene), the Southern Fore-Urals region was characterized by continental climate conditions, which were influences by the wideapreaded brackish-water gulf of the Akchagyl Sea. Fossil molluscs, ostracods, mammals and pollen are used for the reconstruction of the palaeoenvironmental conditions and the biostratigraphical position of the main localities. The units have been correlated with the Gelasian stage of the Western European stratigraphical timescale.

1. Introduction The Southern Urals region includes the southeastern part of the Russian Platform, the Fore-Ural depression, the mountainous part of the Southern Urals and the Southern Trans-Urals area. The structural-geological subdivision of these zones, which have their own specific deposits and features, is shown in Fig. 1. A summary of published and unpublished data as well as authors' data dealing with the stratigraphy of Early Pleistocene (or Palaeopleistocene, a unit of the Russian stratigraphic scheme, equivalent to the early Early Pleistocene subseries; time interval 2.6–1.8 Ma) of the Southern Urals region is presented in this paper. It follows and complete previous reviews about the characteristics of the Quaternary deposits of the easternmost part of Europe (Danukalova et al., 2007, 2014, 2016; Yakovlev et al., 2013). At the beginning of the Early Pleistocene, the area was under the strong influence of the second (maximal) ingression of the Akchagyl Sea (modern Caspian Sea area) (the first ingression of the Akchagyl Sea was at the end of Pliocene during Piacenzian stage) which started in the

Zilim-Vasilyevo time, then developed as much as possible during Akkulaevo time, and then shortly re-emerged after regression into the territory of the Southern Fore-Urals during Voevodskoe time. The huge northern gulf of the Akchagyl Sea reached the footsteps of the western ridges of the Ural Mountains and Obzhyi Syrt Highland in the South. All hydrographic network existed before the Akchagylian time was overflooded and brackishwater liman (lagoon) was formed as a northern part of the Akchagyl Sea. During the Early Pleistocene (Palaeopleistocene), the Southern Fore-Urals region was characterized by semi-marine and continental climate conditions, which were influences by the wideapreaded brackish-water gulf of the Akchagyl Sea (Yakhemovich et al., 1970, 1988; Danukalova, 1996; Puchkov and Danukalova, 2006, 2009). Fluvial and marine deposits containing palaeontological remains form the base of the palaeogeographical reconstructions and the correlation of the different sedimentary units. The Early Pleistocene (Palaeopleistocene) marine sediments nowadays are distributed in limited areas largely occurring below the topographic surface (Zilim-Vasilyevo Horizon) as well as on the interfluves

∗

Corresponding author. Institute of Geology of the UFRC RAS, 16/2, K. Marx St., 450077, Ufa, Russian Federation. E-mail addresses: [email protected], [email protected] (G. Danukalova), [email protected] (E. Osipova), [email protected] (A. Yakovlev), [email protected] (R. Kurmanov). https://doi.org/10.1016/j.quaint.2018.11.026 Received 11 May 2018; Received in revised form 13 November 2018; Accepted 21 November 2018 1040-6182/ © 2018 Elsevier Ltd and INQUA. All rights reserved.

Please cite this article as: Danukalova, G., Quaternary International, https://doi.org/10.1016/j.quaint.2018.11.026

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Fig. 1. General overview Google Earth map (A) and location of the studied area showing the key Early Pleistocene (Palaeopleistocene) sites (B). Legend: I–IV are structural-facies zones: I-SouthEast of the Russian platform; II-Fore-Uralian; IIIUralian; IV-Trans–Uraltau. 1–11-regions: 1Bugulma–Belebei Highland, Obzhyi Syrt Highland (eastern part); 2-Ik and Dema Rivers Basin (upstreams); 3-High left bank of the Belaya River (Syun' and Baza Rivers); 4-Belaya River Basin between Ufa city and the river mouth; 5-High right bank of the Belaya River (Bui and Bystryi Tanyp Rivers); 6a-Ufa River Basin (between Krasnoufimsk city and the river mouth); 6b-western slope of the Ufimian Plateau; 7-Yuryuzan and Ai Rivers Basin (56°–55° N); 8-Belaya River Basin (including high right and left banks of the river) (55°–53° N); 9-Sakmara and Ural Rivers Basin (53°–52°30′ N); 10-Interfluves; 11-Belaya River Basin with tributaries (between the upstream of the Belaya River and the Nizhnebikkuzino village); 12Interfluves; 13-Ui, Sakmara, and Ural Rivers Basin (from the upstream of these rivers to Kuvandyk city); 14-Interfluves. Key Palaeopleistocene sites (small Arabic numbers): Palaeo-Sakmara basin: 1-borehole 4 Staro-Baryatino; 2-Shareevo; 3-borehole 9 Novokulevo; 4-borehole 375 Khabarovka; Palaeo–Belaya basin: 5-borehole 7 Krasny Zilim; 6-borehole 4 Kumurly; 7-borehole 5 Lipovka; 8-borehole 9 Karlaman; 9borehole 10 Karan-Kiishki; 10-borehole 6 Vasilyevka (Zilim-Vasilyevo Horizon stratotype); 11-borehole 22 Muravei; 12-borehole 1 Ishparsovo; 13-borehole 2 Aleksandrovka; 14-borehole 33 Sharypovsky; 15-Nickolo-Postupalovo quarry; 16-borehole 49 Bulan-Turgan; 17–21 Nur; 18-borehole 34, Karmaskaly; 19-borehole 117 Shugurovka; 20-Krezshenka; 21-borehole 4 Nagaevo; 22-Gulyukovo; 23-borehole 105 Bazilevka; 24-borehole 102 Bazilevka; 25-borehole 22 Sredny Izyak; 26borehole 448 Karaganka; 27-borehole 23 Uspenskaya; 28-borehole 30 Baltika; 29–30-borehole 82 Iglino; 31-borehole 35 Pyatiletka; 32-borehole 25 Sart-Lobovo; 33borehole 40 Chuvashkubovo; 34-borehole 53 Urman; 35-borehole 12 Novokulevo; 36-borehole 404 Rozhdestvensky; 37-borehole 8 Staroisaevo; 38-borehole 2 Nyzhny Chandar; 39-borehole 4 Novobedeevo; 40-Tukaevo; 41-borehole 52 Varyazh; 42-borehole 2 Nurlino; 43-borehole 1 Shelkanovo; 44-borehole 4 Sychevo; 45borehole 36 Starosultangulovo; 46-Symbugino; 47-Yulushevo; 48-Sultanaevo; 49-Voevodskoe; 50-Akkulaevo, section 4 (Akkulaevo horizon stratotype); 51Akkulaevo, sections 5u-5z, 6, 7, 8, 9, 11, 15, 16, 18, 21; 52-Karmaskaly, section in a ravine; 53-Karmaskaly, section in a quarry; 54-borehole 18 Karmaskaly; 55Uteimullino III; 56-Ilenka I, II, III; 57-borehole 36 Tyeply Klyuch; 58–61-Novosultanbekovo, sections I–V; 62-Chui-Atasevo I, 63-Karayar-Mustafino, 64-borehole 36 Starosultangulovo; 65-borehole 14 Sakharny.

“Palaeopleistocene” in the paper. The Palaeopleistocene corresponds to the lower part of the Lower Pleistocene in the International Stratigraphical Chart and to Gelasian stage of the Italian Marine Stages. From the palaeomagnetic point of view, the Palaeopleistocene as well as overlying deposits of the Eopleistocene were correlated with the epoch of the reverse polarity Matuyama. The unit “Palaeopleistocene” which is preferable to use corresponds to the lower part of the Mathuyama epoch (below Olduvai episode). In this paper, we will describe horizons, which are regional stratigraphical units with geographical names and which have a correlation function within their geographical distribution while comparing regional stratigraphical charts with the General Stratigraphical Scale. A horizon combine laterally various deposits formed in different facies zones of a single sedimentary palaeobasin and must have a stratotype (or a stratotypical section). The Superhorizon and subhorizon are additional stratigraphical units (Zhamoida et al., 2006). The Superhorizon can be used when there is need to group horizons in bigger regional units; the horizon can be subdivided into smaller subunits (subhorizons). Geochronological scale is a consistent series of geochronological equivalents of general stratigraphical units in their taxonomic sequence. A term “time” is a geochronological equivalent of the stratigraphical units “horizon”, “subhorizon” and “superhorizon”; usually it is used with the addition of the geographical name of the stratigraphical units to which it corresponds (Zhamoida et al., 2006).

(Akkulaevo and Voevodskoe Horizons). The unconformities within these units are related to tectonics, and Quaternary climatic changes. Improvement and unification of the Regional Quaternary stratigraphical scheme was the main aim of our investigations. In this paper, we give characteristic of the units (horizons) which now are formal units of the Fore-Uralian Quaternary stratigraphical scheme which was accepted by the All-Russian Stratigraphical Committee after our work in 2017. 2. Explanation of the terms used in this paper The authors used the formal Russian stratigraphical subdivision published by Zhamoida et al. (2006) in the Stratigraphical Code of Russia. About difference in structure between the Quaternary General Stratigraphical Chart of Russia (Zhamoida et al., 2006) and the International Stratigraphical Chart (Cohen and Gibbard, 2016). In the International Stratigraphic Chart, the Pleistocene consists of the Lower, Middle, and Upper Pleistocene. In the Stratigraphic Chart of Russia, the Pleistocene is subdivided into the lowermost unit Palaeopleistocene, and then there are the Eopleistocene and the Neopleistocene. The Gelasian stage, formerly belonging to the Neogene system, was referred to the lower part of the Quaternary system because of the official changing of the Quaternary lower boundary from 1.8 to 2.6 My in Russia, which followed the changes in the International Stratigraphical Chart (Table 1). In connection with the joining of the Gelasian stage with a duration of about 800 Ky, the question arose about the hierarchical sequence in the General Stratigraphical Scale of Russia. Name of the Quaternary unit in the age range from 1.8 to 2.6 Ma and its stratigraphical rank are now under discussion in Russia and there are two suggestions: to include this unit into the Eopleistocene division or to name it “Palaeopleistocene” (Tesakov et al., 2014; Zastrozhnov et al., 2015). Authors prefer second variant and use a term

3. Materials and methods 3.1. Study sections Zilim-Vasilyevo deposits were investigated in thirty-two borehole 2

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Table 1 Stratigraphical scheme of the Early Pleistocene (Palaeopleistocene) of the Southern Fore-Urals region and correlation with schemes of other regions (Zastrozhnov et al., 2018 with authors’ additions). Legend: 1-NW European Stratigraphical Divisions (the Netherlands) are given according to Zagwijn (1985), 1996; Turner (1998); 2-Central regions of the EastEuropean Plain stratigraphical divisions are given according to Shick et al. (2015)a,b; 3-Fore-Urals stratigraphical divisions are given according to Danukalova et al. in Provisions (2008); 4-Lower Volga stratigraphical divisions are given according to Zastrozhnov in Provisions, 1999. International Chart, Palaeomagnetic chart and Italian marine stages are given according to Cohen and Gibbard, 2016. Russian General Stratigraphical Scheme is given according to Zhamoida et al. (2006). Tyr.Tyrrenian; Seroglaz-Seroglazovka; Novokazan-Novokazanka.

and Monoszon (1971), Kupriyanova and Aleshina (1972, 1978), Bobrov et al. (1983), and the recent spore and pollen collection of the Institute of Geology UFRC RAS (Ufa) has been consulted. The traditional methods of dispersal of sediments in water, using sieves with a mesh size of 0.5, 1.0 mm were used to recover the molluscan and small-mammal remains (Zhadin, 1952; Kaplin, 1987). Mollusc species determination was done according to Zhadin (1952) and Danukalova (1996); small mammal species names are given according to Sukhov (1970), Tesakov (2004), and Agadjanian (2009). The shells of molluscs were photographed at the Institute of Geology UFRC RAS (Ufa) with camera Sony ILCE-6000 with lens Sony SEL35F18; rodent teeth were photographed on a stereomicroscope Motic SMZ-171 with a camera Moticam-10+. Local stratigraphical subdivisions for the Southern Fore-Urals region are given according to Danukalova (2007, 2010) as well as the stratigraphical scheme of the Palaeopleistocene of the Southern Fore-Urals and correlation with other regions (Table 1).

sections. Akkulaevo deposits were investigated in twelve key sections and three borehole sections. Voevodskoe deposits were investigated in thirteen key sections and one borehole section (Fig. 1, Table 2). Twenty-nine key sections have been studied palaeobotanically (more 450 samples in total). Three of these sections have yielded mammalian fossils. Fifty-four sections contain gastropods and fifty-one – bivalve mollusc shells. Fifty-one sections contain ostracod shells. The palaeontological collections are stored at the Institute of Geology of the UFRC RAS (Ufa) and Palaeontological institute RAS (Moscow). 3.2. Laboratory work The systematic study of Early Pleistocene (Palaeopleistocene) deposits in the Southern Fore-Urals region has been carried out for over 50 years (Yakhemovich et al., 1965a,b, 1970, 1977, 1980, 1983, 2000; Sukhov, 1970; Nemkova et al., 1972; Sydnev, 1985; Danukalova, 1996, 2014, 2015a, b; Danukalova et al., 2001, 2002, 2017; Danukalova and Shalaginov, 2002; Morozova and Danukalova, 2005; Osipova, 2009; Danukalova and Osipova, 2011, 2012, 2013). V.L. Yakhemovich, A.V. Sydnev, V.P. Sukhov, I.N. Semenov, and G.A. Danukalova did stratigraphical description of the Palaeopleistocene deposits. G.I. Popov, A.L. Chepalyga, A.V. Sydnev, G.A. Danukalova and E.M. Osipova studied Palaeopleistocene molluscs and indicated stages of their development. V.P. Sukhov, A.G. Yakovlev and A.S. Tesakov investigated small-mammal faunas. Spore and pollen remains were studied by V.K. Nemkova and L.I. Alimbekova. M.G. Popova-Lvova described ostracods. Palaeomagnetic investigations were obtained by F.I. Suleimanova. The processing for the palynological analyses was done following the standard methods described by Grichuk and Zaklinskaya (1948) and Pokrovskaya (1950) with some additions. For each sample, the quantity of pollen and spores is given in the pollen diagrams as: “Total sum of SP grains in sample”. The base of the calculation of the percentages for the various taxa is the sum of all the grains of pollen and spores (100%) found in the sample. Spore and pollen analysis was made for deposits of different genesis. Pollen and spore species determination was done according to Gladkova et al. (1950), Andreeva et al. (1966a,b), Grichuk

4. Stratigraphical subdivision of the Early Pleistocene (Palaeopleistocene) Three horizons are distinguished in the Early Pleistocene (Palaeopleistocene) – Zilim-Vasilyevo, Akkulaevo, and Voevodskoe that were investigated in the boreholes and outcrops (Fig. 1). Palaeopleistocene deposits are known in brackish water, alluvial, lacustrine and subaerial (eluvial, deluvial) facies which largely occurring below the surface level (Zilim-Vasilyevo Horizon) and on the high left and right banks of the Belaya River (Akkulaevo and Voevodskoe Horizons) at 130–160 m above the present-day sea level. Early Pleistocene (Palaeopleistocene) deposits are correlated with the lower part of the reverse polarity Matuyama palaeomagnetic epoch (Nemkova et al., 1972; Yakhemovich et al., 1977; Danukalova et al., 2002; Suleimanova and Yakhemovich, 2003) (Table 1). 4.1. Zilim-Vasilyevo Horizon Stratotype section: Borehole 6 Vasilyevka (25.3–52.7 m) (Yakhemovich et al., 1965 a) (Fig. 1; Table 2). V. Yakhemovich 3

4

Key sections Outcrops: Akkulaevo quarry: section 8, bed 2; 1.5 m; section 18, bed 8; 1.2 m; Karmaskaly quarry: beds 8–13; 5.35 m; Symbugino: beds 17–21; 5.5 m; Sultanaevo: beds 2–9; 4.85 m (vv2); beds 10–11; 0.6 м (vv1); Ilenka II section: beds 1–22; 18.6 m; Outcrops: Akkulaevo quarry: section 5s–5w: beds 3–6; 4.6 m (akk2), beds 7–8; 0.9 m (akk1); section 6, beds 7–10; 4.9 m (akk2), beds 11–13; 2.8 m (akk1); section 7, beds 14–16; 3.1 m (akk1); section 8, bed 3; 3.3 m (akk1); section 9, beds 4–6; 2.9 m (akk1); section 11, beds 3–6; 5.1 m (akk1); section 15, beds 1–3; 2 m (akk1); section 16, beds 3–5; 7.6 m (akk1); section 18, bed 9; 0.7 m (akk1); section 21, bed 5; 1.5 m (akk1); Karmaskaly quarry: beds 14–20; 21.35 m; Symbugino: beds 22а–25; 3.6 m; Boreholes: 375 Khabarovka (30.7–55 m); 4 Kumurly (6.8–27 m); 5 Lipovka (34–39.8 m); 10 Karan-Kiishki (26.1–54.1 m); 9 Karlaman (35.8–59.2 m); 22 Muravei (37–44.5 m); 1 Ishparsovo (30.65–39 m); 2 Alexandrovka (30.6–48 m); 8 Nagaevo (34–57.5 m); 33 Sharypovsky (16.4–49.5 m); 6 Zinino (40.2–50.2 m); 102 Bazilevka (18–26.5 m); 105 Bazilevka (27.2–58.1 m); 22 Sredny Izyak (20–61 m); 23 Uspenskaya (31.1–50 m); 82 Iglino (16–19.1 m); 30 Baltika (28.5–32.4 m); 448 Karaganka (27.8–50 m); 35 Pyatiletka (39–51.5 m); 40 Chuvashkubovo (19.6–49.7 m); 25 Sart-Lobovo (45.8–64.1 m); 53 Urman (32.8–37.8 m); 12 Novokulevo (40.5–44.9 m); 8 Staroisaevo (15–21 m); 2 Nizhny Chandar (16.5–27.5 m); 4 Novobedeevo (28.8–49.5 m); 2 Nurlino (25.7–41 m); 1 Shelkanovo (52.2–71 m); 4 Sychevo (15–33.6 m); 36 Starosultangulovo (37.2–50 m). 14 Sakharny (22.5–33 m); 7 Krasny Zilim (43–84.2 m); 4 Staro-Baryatino (23–48.5 m); 4 Nagaevo (38.3–74.1 m); 9 Novokulevo (35–40.5 m); 49 Bulan-Turgan (49.8–52.2 m); 21 Nur (12–24.5 m); 52 Varyazh (26–28.8 m); 34 Karmaskaly 117 Shugurovka Krezshenka Gulyukovo 404 Rozhdestvensky 36 Tyeply Klyuch Tukaevo

Sultanaevo: beds 24–12; 5.75 m (akk2); bed 25; 0.5 м (akk1); Yulushevo: beds 10–13 (akk2); 3.65 m; Ilenka II: beds 21–24; 5.2 m; Ilenka III: bed 9; 0.3 m; Chui-Atasevo I: bed 10; 10 m; Voevodskoe 1: bed 11; 2 m (akk2); bed 12; 2.4 m (akk1); Voevodskoe 2: beds 15–23; 5.4 m (akk2); bed 24; 1 m; Karayar-Mustafino: beds 16–22; 7.5 m; Shareevo: beds 18–19; 4.5 m; Uteimullino III: beds 10–22; 5 m. Boreholes: 18 Karmaskaly (4.8–0 m) (akk2); 36 Starosultangulovo (21.5–37.2 m); 1 Yulushevo: (3.4–6.1 m) (akk2).

Ilenka II section: beds 21–24; 5.2 m; Ilenka III section: beds 15–50; 4.75 m; Novosultanbekovo I, bed 3; 0.5 m; Novosultanbekovo II, bed 5; 0.8 m; Novosultanbekovo IV, bed 4; 0.7 m; Karayar-Mustafino quarry: beds 12–15; 3.9 m. Nickolo-Postupalovo Borehole 36 Starosultangulovo (3.7–21.9 m).

Legend: akk2-Akkulaevo Horizon, upper subhorizon; akk1-Akkulaevo Horizon, lower subhorizon; vv2-Voevodskoe Horizon, upper subhorizon; vv1-Voevodskoe Horizon, lower subhorizon; *-thickness of the horizon/ subhorizon in the section; 30.7–55 m-depth interval for the horizon’ deposits in the boreholes.

Stratotype: borehole 6 Vasilyevka (25.3–52.7 m) (Arkhangelsk region Bashkortostan Republic).

Stratotype: Akkulaevo quarry, section 4 (akk1): bed 3; 3.5 m (akk2); beds 4–5; 8.8 m (Davlekanovo region Bashkortostan Republic). Hypostratotypes: Karmaskaly: section in ravine; beds 7–12; 7 m. Ilenka I: beds 21–22; 8 m. Novosultanbekovo I: beds 4–10; 11.6 m.

Akkulaevo

Zilim-Vasilyevo

Stratotype/Hypostratotype sections Stratotype: Voevodskoe 2: beds 5–14; 5.3* m (Ufa city, Bashkortostan Republic). Hypostratotypes: Karmaskaly: section in ravine; beds 3–6; 6.3 m. Ilenka I: beds 1–20; 9.4 m.

Horizon Voevodskoe

Superhorizon South Uralian

Division Palaeopleistocene

System Quaternary

Superdivision Pleistocene

Southern Fore-Urals region (Danukalova et al., 2017)

General stratigraphical scale of Russia

Table 2 Main Early Pleistocene (Palaeopleistocene) key-sites for the Fore-Uralian area.

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nana and Lycopodium pungens. On ostracods the salinization of the reservoir was traced from the lower layers of the horizon up to the top with the appearance of euryhaline, and then typical Akchagylian brackish water and marine forms. Freshwater basins were inhabited by 48 ostracod species of 17 genera (Appendix: Table 5). Mollusc complex contain freshwater and brackish water species which indicate salinization of the basins. In total eighteen freshwater gastropod species (six genera), six freshwater bivalves species (three genera) and four brackish water gastropods species (four genera), one brackish water bivalve mollusc species (one genera) from twelve localities occur in the Zilim-Vasilyevo complex (Yakhemovich et al., 1965 a, 1970) (Appendix: Tables 6 and 7). The mollusc species composition of the Zilim-Vasilyevo time was transitional between the freshwater Late Pliocene (Karlaman and Kumurly) mollusc complex and the Akkulaevo brackish water complex and indicates relatively warm climatic conditions (Yakhemovich et al., 1970; Danukalova, 1996). According to palaeomagnetic data, the horizon corresponds to the lower part of the r-Matuyama orthozone; n-Reunion subzone base is often observed in its top (Suleimanova and Yakhemovich, 2003).

(Yakhemovich et al., 1965 a; Yakhemovich, 1982) named the horizon after the Vasilyevka village and Zilim River (Arkhangelsk region, Bashkortostan Republic, Russia). The key sections for this unit are given in Table 2 (Yakhemovich et al., 1965 a, 2000) (Fig. 1). The horizon is represented by lacustrine bluish-grey, greenish-grey and brown dense clay and silty clay with sandy interlayers. Black clay with pebble and gravel layer is at the base of the Zilim-Vasilyevo Horizon. The total thickness is minimum 4 m, maximum 41 m. Minimal thickness of the deposits is in the peripheral parts of the depressions or valleys, and maximal thickness is in their central parts. The deposits cover the eroded surface of the Permian rocks with the stratigraphical unconformity or conformably cover Neogene sediments (Piacenzian stage) and are, in turn, conformably overlain by Akkulaevo Horizon or unconformably overlain by late Early Pleistocene (Eopleistocene) or by Middle-Upper Pleistocene (Neopleistocene) sediments. During Zilim-Vasilyevo time the flooding of the hydrographic network began in connection with the approach of the second maximum phase of the Akchagylian Sea ingression. Flora and vegetation of the Zilim-Vasilyevo Horizon were investigated in the borehole sections: 375 Khabarovka; 4 Kumurly; 5 Lipovka; 10 Karan-Kiishki; 6 Vasylievka; 2 Aleksandrovka; 102 and 105 Bazilevka; 30 Baltika; 35 Pyatiletka; and 36 Starosultangulovo (Figs. 1–3, Appendix: Tables 3 and 4) (Yakhemovich et al., 1965 a, 1970, 2000). Pollen and spores of 152 taxa were identified in the samples. The most diverse composition are coniferous, broad-leaved tree species, aquatic plants, Polypodyophyta and Lycopodium. The earliest spectra of Zilim-Vasilyevo deposits characterize the spread of open spaces occupied by steppe vegetation and small birch and broadleaved forests. Light coniferous forests with an admixture of spruce, Tsuga and broad-leaved species occupied the hills in the southern part of the region. Later the dominant type of vegetation became coniferous forests of the Akchagyl taiga type. Spore and pollen spectra characterize the Picea-Abies taiga forests in the north of the studied area and Picea forests with Tsuga and Pinus in the south. At the end of the time a cooling occurred that resulted in a reduction in the species diversity of trees and a predominance of Artemisia and Chenopodiaceae among grasses, as well as in the development of mountain tundra with Betula

4.2. Akkulaevo Horizon Stratotype section: Akkulaevo quarry (section 4; bed 3 (upper subhorizon); beds 4–5 (lower subhorizon)) (Nemkova et al., 1972). The hypostratotype sections for this unit are Karmaskaly (section in ravine) (Yakhemovich et al., 2000), the Ilenka I site (Danukalova et al., 2001, 2002) and the Novosultanbekovo 1 site (Danukalova et al., 2002) (Fig. 1; Table 2). V.L. Yakhemovich (1982) named this horizon after the Akkulaevo village (Bashkortostan Republic, Russia). The key sections for this unit are listed in Table 2 (Nemkova et al., 1972; Yakhemovich et al., 1977, 1980, 1983, 2000; Danukalova et al., 2001, 2002, 2017; Danukalova and Osipova, 2013) (Fig. 1). The horizon is subdivided into lower and upper subhorizons. Lower subhorizon is represented by marine sands and clay (thickness is up to 25 m) with marine Akchagylian molluscs and ostracods. Upper subhorizon (thickness is up to 4.5 m) is represented by fluvial (deltaic) sands with clayish and pebble lenses containing marine Akchagylian

Fig. 2. The key section of the Zilim-Vasilyevo Horizon (Early Pleistocene). Borehole 4 Kumurly section (depth interval 6.8–27 m) and the spore and pollen diagrams for the main taxa (Yakhemovich et al., 1965 a; with authors' corrections). 5

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Fig. 3. The key section of the Zilim-Vasilyevo Horizon (Early Pleistocene). Borehole 5 Lipovka section (depth interval 34–39.8 m) and the spore and pollen diagrams for the main taxa (by Yakhemovich et al., 1965 a; with authors' corrections).

of this time reflects several phases of cooling and warming. At the beginning of Akkulaevo time, spruce forests with a small admixture of Abies, Pinus and Tsuga existed. Later, birch-broad-leaved forests and xerophytic steppes replaced them. Then dark-coniferous taiga forests with spruce and fir were common. During Late Akkulaevo time, the climate became noticeably warmer and herbaceous steppes with birchbroad-leaved forests became wide spread (Yakhemovich et al., 1970; Danukalova et al., 2002). The highest variety of brackish water and euryhaline ostracods (58 species of 20 genera) indicates the formation of the Akkulaevo deposits in brackish water reservoirs (Nemkova et al., 1972; Yakhemovich et al., 1977, 1980; Danukalova et al., 2001) (Appendix: Table 5).

molluscs and freshwater molluscs of the Levantine type (Yakhemovich et al., 1992; Danukalova, 1996). Flora and vegetation of the Akkulaevo Horizon were investigated in the Akkulaevo, Karmaskaly, Ilenka I–III, Sultanaevo, Yulushevo, ChuiAtasevo I, Voevodskoe, Symbugino localities and borehole 36 Starosultangulovo (Figs. 1, 4 and 5; Appendix: Tables 3 and 4) (Nemkova et al., 1972; Yakhemovich et al., 1977, 1980, 1983, 1987, 2000; Danukalova et al., 2001, 2002). The samples contain pollen and spores of 145 taxa. In the spectra, along with the high diversity of coniferous and deciduous trees, an increase in the role of various representatives of herbs and Cenopodiaceae including Halophytes, occupying low places, freed after Akchagylian regression. The vegetation

Fig. 4. The key section of the Akkulaevo Horizon (Early Pleistocene). Akkulaevo quarry summary section and the spore and pollen diagrams for the main taxa (Nemkova et al., 1972; with author's corrections). 6

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Fig. 5. The key section of the Akkulaevo Horizon (Early Pleistocene). Karmaskaly quarry summary section and the spore and pollen diagrams for the main taxa (Yakhemovich et al., 2000; Danukalova et al., 2002 with author's corrections).

4.3. Voevodskoe Horizon

Mollusc complex contain several terrestrial, numerous freshwater and some brackish water species. In total 10 terrestrial gastropod species (9 genera), 44 freshwater gastropod species (13 genera), 59 freshwater bivalve mollusc species (13 genera) and 11 brackish water gastropod species (6 genera), six brackish water bivalve mollusc species (2 genera) from 9 localities represented Akkulaevo complex (Nemkova et al., 1972; Yakhemovich et al., 1977; Danukalova et al., 2002) (Fig. 6; Appendix: Tables 6 and 7). For the Akkulaevo time, a mollusc complex is characterized by brackish water and marine molluscs (Mactridae, Cardiidae, Clessiniola). Some freshwater molluscs (Viviparus, Bithynia, Lithoglyphus) and a variety of smooth and sculpted Unionidea existed at that time (Yakhemovich et al., 1970, 1983; 1992; Danukalova, 1996). The bone remains representing fishes, amphibians, reptiles and small mammals are known from the Akkulaevo and Novosultanbekovo sites (Sukhov, 1970; Nemkova et al., 1972; Danukalova et al., 2002). (Fig. 7; Appendix: Table 8). Small-mammal remnants are most numerous among vertebrates. According to data of the different authors (Sukhov, 1970; Agadjanian and Danukalova, 2002; Tesakov, 2004), non-rooted Promimomys, Pitymimomys, Mimomys, Villania и Borzodia, were determined among voles. In general, the small-mammalian fauna reflects near-water biotops with steppe landscapes on the interfluves.

Stratotype site: Voevodskoe quarry (section 2) (Yakhemovich et al., 1980). The hypostratotype sites for this unit are Karmaskaly (section in ravine) (Yakhemovich et al., 2000) and the Ilenka I site (Danukalova et al., 2001, 2002) (Fig. 1; Table 2). V.L. Yakhemovich named the horizon after the Voevodskoe village (now it is part of the Ufa city) (Bashkortostan Republic, Russia) (Yakhemovich et al., 1980). The key sites for this unit are shown in Table 2 (Nemkova et al., 1972; Yakhemovich et al., 1977, 1983, 2000; Danukalova et al., 2001, 2002, 2017; Danukalova and Osipova, 2013) (Fig. 1). The deposits cover the eroded surface of the Akkulaevo Horizon and are subdivided into two subhorizons. The lower subhorizon (thickness is around 2.5 m) is represented by alluvial sand and pebble which are secondary strongly ferruginated. Brackish water lagoon sediments, which are constituted by pebble and silt with Akchagylian ostracods and molluscs, represent the upper subhorizon (Yakhemovich et al., 1980; Danukalova, 1996). Total thickness of Voevodskoe deposits is up to 10 m. Flora and vegetation of the Voevodskoe Horizon were investigated in the Voevodskoe, Karmaskaly, Ilenka I and II, Akkulaevo, Sultanaevo, 7

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Fig. 6. Key-species of molluscs found in the Akkulaevo deposits (Early Pleistocene), ForeUrals region, Russia. 1-Valvata pronaticina Lindholm, 1932, apertural view, Chepalyga and Sydnev, 1983: Tabl. II, Fig. 2, Sultanaevo site; 2-Lithoglyphus naticoides Ferussac, 1828, apertural view, Chepalyga and Sydnev, 1983: Tabl. V, Fig. 7, Sultanaevo site; 3Cerastoderma dombra dombra (Andrussow, 1902), IG 3/33, Yakhemovich et al. (2000), Tabl. III, Fig. 2, Karmaskaly (Chatra) site, layer 11, × 8; 4-Cerastoderma dombra vogdti (Andrussow, 1902), IG 3/37 (fragment), Yakhemovich et al. (2000), Tabl. III, Fig. 6, Karmaskaly (Chatra) site, layer 11, × 6; 5-Cerastoderma dombra pseudoedule (Andrussow, 1902), IG 3/34 (fragment), Yakhemovich et al. (2000), Tabl. III, Fig. 3, Karmaskaly (Chatra) site, layer 11, × 6; 6-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/27, Danukalova (1996): Tabl. XIX, Fig. 2, Akkulaevo site, × 3; 7Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/26, Danukalova (1996): Tabl. XIX, Fig. 1, Akkulaevo site, × 3; 8-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/28, Danukalova (1996): Tabl. XIX, Fig. 3, Akkulaevo site, × 3; 9Cerastoderma dombra dombra (Andrussow, 1902), PIN 4422/2, Danukalova (1996): Tabl. V, Fig. 3, Akkulaevo site, × 2; 10-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/30, Danukalova (1996): Tabl. XIX, Fig. 5, Akkulaevo site, × 3; 11-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/29, Yakhemovich et al. (2000): Tabl. XIX, Fig. 4, Akkulaevo site, × 3; 12-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/32, Danukalova (1996): Tabl. XIX, Fig. 7, Akkulaevo site, × 3; 13-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/31, Danukalova (1996): Tabl. XIX, Fig. 6, Akkulaevo site, × 3; 14-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/22, Danukalova (1996): Tabl. XVIII, Fig. 11, Karmaskaly site, × 3; 15-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/23, Danukalova (1996): Tabl. XVIII, Fig. 12, Karmaskaly site, × 3; 16-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/24, Danukalova (1996): Tabl. XVIII, Fig. 13, Karmaskaly site, × 3; 17-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/25, Danukalova (1996): Tabl. XVII, Fig. 14, Karmaskaly site, × 3; 18-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/15, Danukalova (1996): Tabl. XVIII, Fig. 4, Karmaskaly site, × 3; 19-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/16, Danukalova (1996): Tabl. XVIII, Fig. 5, Karmaskaly site, × 3; 20-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/18, Danukalova (1996): Tabl. XVIII, Fig. 7, Karmaskaly site, × 3; 21-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/17, Danukalova (1996): Tabl. XVIII, Fig. 6, Karmaskaly site, × 3; 22-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/75, Danukalova (1996): Tabl. XXII, Fig. 7, Novosultanbekovo site, × 3; 23-Aktschagylia ossoskovi (Andrussow, 1902), PIN 4422/77, Danukalova (1996): Tabl. XXII, Fig. 9, Novosultanbekovo site, × 3; 24-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/70, Danukalova (1996): Tabl. XXII, Fig. 2, Novosultanbekovo site, × 3; 25-Aktschagylia subcaspia (Andrussow, 1902), PIN 4422/72, Danukalova (1996): Tabl. XXII, Fig. 4, Novosultanbekovo, × 3.8, 12, 17, 21, 23-the right valve internal view; 5, 6, 7, 11, 14, 16, 22-the right valve external view; 9b, 13, 19, 25-the left valve internal view; 3, 4, 9a, 10, 15, 18, 20, 24-the left valve external view. PIN-Palaeontological institute, Russian Academy of sciences (Moscow).

coniferous forests which spreaded to the south. It should be noted that the latest finds of Tsuga pollen were found in these deposits; Tsuga do not occur in the younger sediments of the region. Ostracods were not numerous and were represented by 34 brackish water and euryhaline species of 13 genera (Nemkova et al., 1972; Yakhemovich et al., 2000; Danukalova et al., 2001, 2002) (Appendix: Table 5). Mollusc species complex is very close to Akkulaevo complex and contains few terrestrial, freshwater and brackish water species. In total 10 terrestrial gastropod species (9 genera), 17 freshwater gastropod species (11 genera), 6 freshwater bivalves species (3 genera) and 4

Symbugino localities and borehole 36 Starosultangulovo (Figs. 1 and 8; Appendix: Tables 3 and 4) (Nemkova et al., 1972; Yakhemovich et al., 1977, 1980, 1983, 1987, 2000; Danukalova et al., 2001, 2002). Pollen grains and spores of 150 taxa were encountered. The palynological composition found from the Voevodskoe deposits is close to Akkulaevo spore and pollen complex composition. Forest-steppe and steppe landscapes predominated during the first half of the Voevodskoe time. The role of the forest species gradually decreased, and broadleaved elements gradually fell out of the forest. In the second half of the Voevodskoe time, the area of open spaces was occupied by steppe vegetation. Only at the very end there is again a small increasing of the

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Fig. 7. Small mammals found in Early Pleistocene (Palaeopleistocene) deposits, Fore-Urals region, Russia. Legend: Akkulaevo Horizon: 1–12-m1; 1a–1a-occlusal surface, 1b–12b-labial view. 1–3-Mimomys polonicus Kowalski, 1960; 4–6-Mimomys hintoni hintoni Fejfar, 1961; 7–9-Pitymimomys baschkiricus (Suchov, 1970); 10, 11-Borsodia novoasovica (Topachevsky et Scoric, 1977); 12-Villanyia veterior Kretzoi, 1969.1–12-Akkulaevo site, section 16 in a quarry, layer 4. Species names are given according to Tesakov (2004).

corresponding to the upper half of the Middle Akchagylian (or Gelasian). Later, collections of the small mammals from the Akkulaevo section were reviewed by A.K. Agadjanian (Agadjanian and Danukalova, 2002) and A.S. Tesakov (2004) in accordance with the current state of the mammalian study and with their personal opinions. A.K. Agadjanian (Agadjanian and Danukalova, 2002) identified the following small-mammal species: Crocidurosorex sp., Sorex sp., Talpa sp., Ochotona sp., Pliolagus cf. brachygnatus Kormos, 1934, Trogontherium sp., Apodemus cf. sylvaticus L., 1758, Cricetus nanus Schaub, 1934, Cricetulus sp., Prosiphnaeus ex gr. praetingi Teilhard de Chardin, 1940, Villanyia ex gr. exilis Kretzoi, 1969, Borsodia sp., Promimomys gracilis akkulaewae Suchov, 1970, Promimomys baschkirica Suchov, 1970, Mimomys polonicus Kowalski, 1960. Agadjanian compared fauna from the Akkulaevo Horizon with the faunas of the second half of the Middle Akchagyl (Gelasian) and with the Uryv-2 section on the Don River. A.S. Tesakov identified the following voles’ species: Mimomys polonicus Kowalski, 1960, Mimomys hintoni hintoni Fejfar, 1961, Pitymimomys baschkiricus (Suchov, 1970), Borsodia novoasovica (Topachevsky et Scoric, 1977), Villanyia veterior Kretzoi, 1969. According to the species composition of voles and the evolutionary level of species, A.S. Tesakov compares the fauna from the upper Akkulaevo subhorizon with the Lower Villafrank and with the MN16 zone, thus suggesting the pre-Gelasian age of the fauna.

brackish water gastropod species (4 genera), six brackish water bivalves species (2 genera) from 6 localities represented Voevodskoe complex (Nemkova et al., 1972; Yakhemovich et al., 1977, 1983; Danukalova, 1996; Danukalova et al., 2002) (Fig. 9; Appendix: Tables 6 and 7). Last representatives of the endemic bivalves Cerastoderma, Aktschagylia and “Clessiniola”-like gastropods inhabited remnants of the Akchagyl lagoon of the Fore-Urals during Voevodskoe time. Single small-mammalian finds were discovered in the Voevodskoe Horizon deposits from the Symbugino and Novosultanbekovo sections. Voles are represented by rooted genera (Appendix: Table 8). 5. Discussion of faunal and floral assemblages In 1960-s V.P. Sukhov for the first time collected and determined remains of the small mammals from the fluvial (deltaic) deposits of the upper Akkulaevo subhorizon from the Akkulaevo quarry: ?Crocidosorex sp., Sorex sp., Talpa sp., Desmana sp., Ochotona sp., Hypolagus cf. brachygnatus Kormos, 1934, Trogontherium sp., Apodemus cf. sylvaticus L., 1758, Cricetus cricetus cf. nanus Schaub, 1934 Cricetulus sp., Mimomys (Cheria) gracilis akkulaewae Suchov, 1970, Mimomys (Cheria) baschkirica Suchov, Mimomys (Mimomys) cf. coelodus Kretzoi, 1954, Mimomys (Villanyia) praehungaricus Schevtschenko, 1965, Mimomys (Villanyia?) sp., Mimomys (Mimomys) pliocaenicus F. Major, 1902, Prosiphnaeus ex gr. praetingi Teilhard de Chardin, 1940. Sukhov (1970) compared this small-mammal fauna with the Khaprovian faunistic complex 9

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Fig. 8. The key section of the Voevodskoe Horizon (Early Pleistocene). Voevodskoe section and the spore and pollen diagrams for the main taxa (by Yakhemovich et al., 1980 with authors' additions).

in connection with the approach of the second maximum phase of the Akchagylian ingression. At this time flooding of small wetlands, the formation of a freshwater lake system, their merging with the formation of a vast lagoon (which was freshwater at the beginning and brackish water at the end of time) occurred. Flora of this time was different from the Pliocene and was actually the Akchagyl taiga type, close in composition to the modern one. Latitudinal zoning in the distribution of vegetation was noted for the Zilim-Vasilyevo time. In the north of the region and on the slopes of the mountains Picea-Abies-Pinus taiga forests dominated, in the south – Pinus taiga forests with Tsuga and pines grew. Pine forests with admixture of fir, Tsuga, broad-leaved trees and poor grass cover grew on the slopes of the Obzhyi Syrt Highland. At the beginning of this time, there was a warming with the appearance of pine and deciduous forests and a rich grass cover. At the end of the time there was a cooling that resulted in a reduction in the species diversity of trees and a predominance of Artemisia and Chenopodiaceae among grasses, as well as in the development of mountain tundra with Betula nana and Lycopodium pungens. On ostracods the salinization of the reservoir from the bottom up was traced with the appearance of euryhaline, and then typical Akchagylian brackish water and marine forms. Mollusc complex contain freshwater and brackish water species which indicate also a salinization of the basin. Akkulaevo time corresponds to the Akchagyl ingression maximum – there were two wide brackish water Akchagyl Sea gulfs in the Southern Fore-Urals (Fig. 10). One gulf existed at the place of the flooded hydrographic network of Palaeo-Belaya, the other – on the side of Palaeo-Sakmara. Between them there was the Sakmara-Belaya watershed, which is the eastern part of the Obzhyi Syrt Highland and the Nakas Upland. Within the Upland there were few freshwater lakes. The Urals was low mountains; in the southern part of Uralst there was a low Zilair Plateau. In the western part of the region there was a high plain (the eastern part of the Russian platform) with Ufa Plateau, Bugulma-

The brackish waters of the Akchagyl ingression entered to the ForeUrals only during the maximal extend of the Akchagyl Sea and the beginning of this event in the northern Fore-Caspian depression and Fore-Urals was dated at the Gauss-Matuyama boundary (Danukalova, 1996; Yakhemovich et al., 2000; Nevesskaya et al., 2005) (Gelasian, Early Pleistocene). The marine deposits of the lower Akkulaevo subhorizon contain Akchagyl mollusc key-species, alluvium of the upper Akkulaevo subhorizon which overlay marine sediments also contain together with brackish water molluscs Aktschagylia ossoskovi (Andrussow, 1902) vertebrate's bones. Thus, bone remnants if they are looking older according to Tesakov (2004) opinion, are redeposited probably. Flora of the Akchagyl type existed in the south of the Fore-Urals during the accumulation of the Zilim-Vasilyevo and Akkulaevo Horizons and, perhaps, during accumulation of some part of the Voevodskoe Horizon. This flora is characterized by the insignificant variety of the main forest-forming species and by the absolute predominance of the modern species with single relic and Pliocene species of the Kinel type flora (Yakhemovich et al., 1992). 6. Palaeogeography Based on the data presented above the palaeoecological and biostratigraphical changes observed at the studied area can be summarized as follows (Table 9, Fig. 10). At the end of Pliocene and beginning of the Early Pleistocene, the area was under the influence of the Akchagyl Sea (modern Caspian Sea area). The first ingression of the Akchagyl Sea was at the end of Pliocene during Piacenzian stage (Fig. 10 A), the second ingression started during Gelasian stage – in the Zilim-Vasilyevo time, then developed as much as possible during Akkulaevo time (Fig. 10 B), and then for the third time shortly re-emerged after regression into the territory of the Southern Fore-Urals during Voevodskoe time. In the Zilim-Vasilyevo time the flooding of the valley system began 10

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Fig. 9. Key-species of molluscs found in the Voevodskoe Horizon (Early Pleistocene), ForeUrals region, Russia: 1-“Clessiniola” julaevi G. Popov, 1970, IG 335/ 1123/21, × 15; 2-Valvata piscinalis (Müller, 1774), IG 335/307/20, × 5; 3-Cerastoderma dombra pseudoedule (Andrussow, 1902), Sydnev (1980): Tabl. IV, Figs. 1 and 2, × 8; 4-Cerastoderma dombra cf. pseudoedule (Andrussow, 1902), Sydnev (1980): Tabl. III, Fig. 3, × 10; 5Cerastoderma dombra dombra (Andrussow, 1902), Sydnev (1980): Tabl. V, Fig. 1, × 8; 6Cerastoderma dombra dombra (Andrussow, 1902), Sydnev (1980): Tabl. IV, Fig. 4, × 10; 7Cerastoderma dombra dombra (Andrussow, 1902), Sydnev (1980): Tabl. II, Fig. 8, × 8; 8Cerastoderma dombra dombra (Andrussow, 1902), Sydnev (1980): Tabl. III, Fig. 2, × 5; 9Aktschagylia ossoskovi (Andrussow, 1902), Sydnev (1980): Tabl. VI, Fig. 4, × 8; 10-Aktschagylia ossoskovi (Andrussow, 1902), Sydnev (1980): Tabl. VI, Fig. 8, × 8; 11-Aktschagylia subcaspia (Andrussow, 1902), Sydnev (1980): Tabl. V, Fig. 4, × 5; 12-Aktschagylia subcaspia (Andrussow, 1902), Sydnev (1980): Tabl. V, Fig. 3, × 5. a-apertural view; b-lateral view (top right); c-abapertural view (view from the opposite side of the aperture); d-top view; e-umbo view. 3f, 11-the right valve internal view; 3 h, 6, 8, 10-the right valve external view; 9-the left valve internal view; 4, 5, 7, 12-the left valve external view. 1-Ilenka I site, layer 17; 2-Ilenka I site, layer 18; 2–12-Voevodskoe site, excavation 2, layer 10.

The climate at that time was continental – dry and cool. In the open spaces after the regression, poor grassy vegetation represented mainly by Chenopodiaceae and Artemisia grew. At the end of the Gelasian stage, during Voevodskoe time, an ingressial short-term sea gulf was formed again in the territory of the Southern Fore-Urals (Yakhemovich et al., 1970, 1980; Sydnev, 1985; Danukalova, 1996). The marine deposits of the Voevodskoe time are separated from the Akkulaevo deposits by alluvial sediments. Flora of the Voevodskoe time was of the forest-steppe type, upwards passing into the taiga, there are some species phylogenetically close to modern one, and species that now have more southern areals (ash, loch). Vegetation varied from Poaceae-herbage-steppe, forest-steppe, xerophytic steppe with birch-pine island forests to the spruce taiga. Species composition of molluscs and ostracods of Voevodskoe time contains freshwater, brackish water and marine species, which do not differ from Akkulaevo species (Sydnev, 1985; Yakhemovich et al., 1970, 1980; 2000; Danukalova, 1996). The continental climate was warm; it became cooler at the end of the time. At the end of the Gelasian (Palaeopleistocene), the continental regime was established on the Fore-Urals territory.

Belebei Upland. The Ural Mountains and the high western plain of the studied territory were the main areas of denudation. The rivers flowed into the gulf and their existence is evidenced by deltas (Akkulaevo, Sultanaevo sections: Nemkova et al., 1972; Yakhemovich et al., 1983). Vegetation during Akkulaevo time at the initial stage was represented by taiga forests. Then xerophytic steppes and small deciduous forests replaced dark coniferous forests. Then again, the coniferous forests became the dominant type of vegetation, which were replaced again by forest-steppe landscapes at the end of this time. The vegetation of this time reflects several phases of cooling and warming. For the Akkulaevo time, a complex of various freshwater molluscs is characterized by Viviparus, Bithynia, Lithoglyphus, a variety of smooth and sculpted Unionidea, and brackish water and marine molluscs (Mactridae, Cardiidae, Clessiniola), and the highest variety of brackish water and marine ostracods (Yakhemovich et al., 1970, 1983; 1992; Danukalova, 1996). At the end of Akkulaevo time, as a result of tectonic uplifts, the gulf was reduced, and part of the territory formerly occupied by the sea was drained. Isolated residual reservoirs continued to exist. The hydrographic network began to form in the foothills of the western slope of the Urals. 11

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Table 9 Correlation of the Early Pleistocene (Palaeopleistocene) deposits from the different regions of the Southern Fore-Urals (by G. Danukalova).

(continued on next page)

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Table 9 (continued)

7. Conclusions

paleofaunistic, palynological, and paleomagnetic record, and are significant paleoarchives, which can be used for the reconstruction of the palaeoenvironmental conditions and the biostratigraphical position of the main localities. During Zilim-Vasilyevo time, forest vegetation dominated. The climate was cold and wet. Only at the very beginning of this time there was a warming associated with the appearance of pine and deciduous forests and a rich grass cover. Akkulaevo vegetation periodically changed from forest to foreststeppe and steppe. The climate at the very beginning of Akkulaevo time was quite cool and humid. Later climate became warmer and drier. At the end of Akkulaevo time, the climate was even warmer than the modern one. Voevodskoe vegetation is represented by steppe and forest-steppe. The climatic conditions were moderately cold and dry. Warming and moistening was noted only at the end of this time. 4. Small mammals from the Akkulaevo Horizon in the taxonomic composition were assigned to the Akchagyl. A different conclusion about the age of the fauna of small mammals from the Akkulaevo Horizon is probably connected with the alluvial type of sedimentation and significant redeposition of the material. 5. Mollusc fauna of the Early Pleistocene of the Southern Fore-Urals was mixed freshwater/brackish water fauna with Akchagylian

The biostratigraphical studies of the Lower Pleistocene (Palaeopleistocene) sediments of the Southern Fore-Urals indicate the following general conclusions: 1. During the Early Pleistocene (Palaeopleistocene), the Southern ForeUrals region was characterized by semi-marine and continental climate conditions, which were influences by the wideapreaded brackish water gulf of the Akchagyl Sea. 2. In the Early Pleistocene, the river valleys of the Fore-Urals were periodically flooded by brackish-waters of the Akchagylian ingression of the Caspian Sea as a consequence of the sea level uplifts. The Zilim-Vasilyevo Horizon was formed at the beginning of the ingression into the drainage system (before the ingression's maximum). The Akkulaevo horizon was accumulated during the maximum of the Akchagylian ingression and includes marine clay at the base and deltaic sand at the top of the unit. The Voevodskoye Horizon incorporates alluvial deposits and deposits of the new ingressial short-term sea gulf which was formed at the end of this time in the Southern Fore-Urals territory. 3. The Early Pleistocene (Palaeopleistocene) deposits contain 13

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Fig. 10. Schematic palaeogeographic maps of the northern gulf of the Akchagyl Sea during first (Late Pliocene, Piacenzian time) and second (Early Pleistocene, Gelasian time) ingressions of the sea to the territory of the Southern Fore-Urals region (Yakhemovich et al., 1970; Sydnev, 1985; Danukalova, 1996; with authors' additions). Legend: A-the northern gulf of the Akchagyl Sea during first (Late Pliocene, Piacenzian time) ingression; B-the northern gulf of the Akchagyl Sea during second maximal (Early Pleistocene, Gelasian time) ingression; C-a general map of the maximal extend of the Akchagyl ingression. 1-demolition direction; 2-borehole and Akchagyl deposits footmark; 3-coniferous forest, 4-broad-leaved and small-leaved elements, 5-xerophytic steppe.

INQUA-SACCOM: 1612F). The Authors also want to thank Guest Editor Prof. P. Pieruccini, Prof. Ph. L. Gibbard and the anonymous reviewer for their comments and suggestions, Editors and the editorial board of Quaternary International for the help and the improvement of the original text.

Cerastoderma and Aktschagylia key species which exactly indicate age of the deposits and give possibility to correlate them with Gelasian stage of the Early Pleistocene. Data availability The palaeontological collections are kept at the Institute of Geology UFRC RAS (Ufa) (mollusc shells and bones of small mammals, amphibians and reptiles) and Palaeontological Institute RAS (some Akchagylian Cardiidae and Mactridae) (Moscow).

Appendix A. Supplementary data

Acknowledgements

References

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.quaint.2018.11.026.

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We are thankful to Professor Varvara Yakhemovich (1913–1994) and her colleagues from the Institute of Geology Ufimian Federal Research Centre, Russian Academy of sciences (Ufa) and from the Geological Survey “Bashkirgeology” (Ufa), who created the basis for the stratigraphy of the Neogene and Quaternary deposits of the SouthernUralian region. Our paper is a summary of their materials and new data on the Early Pleistocene (Palaeopleistocene) part of the Quaternary. These data also form a base for the Quaternary and Neogene Stratigraphical Schemes of the Fore-Urals, which became the official documents in 2007 and 2017. Our schemes have been thoroughly reviewed and discussed by colleagues many times during meetings of the Regional Stratigraphical Commettee (Drs. V. Trubikhin, A. Tesakov, S. Popov, and S. Shick), Interregional Stratigraphical Commettee of Russia and its Commissions on Neogene and Quaternary systems (Drs. A. Gladenkov, B. Borisov, T. Tolmacheva, and G. Aleksandrova). Dr. Sergei Mikhailovich Shick who recently left the Earth was the Editor of our schemes. The authors would like to express their great thanks to these mentioned above persons. This work was partly achieved thanks to the State programs N-02522014-0006, N-0252-2016-0006 and Russian Government Program of Competitive Growth of Kazan Federal University. This paper is dealing with Quaternary key-sites of the Fore-Urals region in the frame of the DATESTRA (Database of Terrestrial European Stratigraphy) project (grant 14

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