Journal of the Geological Society, London, Vol. 152, 1995, pp. 903-906, 5 figs. Printed in Northern Ireland compression in the Early Devonian led to the inversion of the Timan and Varandey-Adz'va rifts to form ridges, which Tectonic evolution of the northern Ural acted as the source for the Middle Devonian clastic rocks Orogen found in the Timan-Pechora Basin. However, by the mid-Frasnian, shallow marine conditions were re- established, with carbonates deposited on highs and S. C. OTTO 1 & R. J. BAILEY 2 'Domanik' facies organic-rich shales laid down in the lPetroconsultants (UK) Ltd, 266 Upper Richmond intervening lows. Road, London SW15 6TQ, UK Closure of the ocean began in the Tournaisian, and 2Victoria Villa, 5 Station Road, Southwell, eastward subduction under the Siberian craton is made Nottinghamshire NG25 OET, UK evident by basement of volcanic island arc affinity found only to the east of the Urals (Churkin et al. 1981). In the Timan-Pechora Basin, the transpressional reactivation of faults resulted in the complete inversion of the earlier rifts. Local highs were formed, such as the Usa and Vozey highs, The closure of the Uralian Ocean occurred in Early Permian-Early which were a source of clastics during the Late Triassic time. In the northern Ural fold belt, overthrusting to the Tournaisian-Early Visean. Throughout the remainder of west produced a major foreland basin to the west of the mountain chain. In contrast, in the northern extension of the Ural Orogen, the Carboniferous and into the earliest Permian, the basin the Taymyr fold belt, thrusting was directed to the SE. It is formed part of the western passive margin of the Uralian proposed that Novaya Zemlya, at the interface of these two zones, Ocean, on which sequences of shallow marine carbonates acted as a thin-skinned allochthonous nappe emplaced by gravity and shales were deposited. Similar Carboniferous-Lower tectonics into a basin produced by rapid Permo-Triassic rifting in Permian carbonate passive margin sequences are found the eastern Barents Sea. throughout the region, in the South Barents Sea Basin (Johansen et al. 1993), the Urals and Novaya Zemlya (Churkin et al. 1981) and the West Siberia Basin (Peterson Keywords: Russia, Urals, Triassic, tectonics. & Clarke 1991; Ostisty & Cheredeev 1993). In mainland Russia, the Ural Mountains trend broadly N-S, Uralian Orogeny. Continental collision between East extending from the Arctic Ocean to the Aral Sea. The Europe and Siberia is first recorded in central and eastern northern part of the orogen is more complex and comprises West Siberia, where Late Carboniferous deformation three NE-SW-trending segments (Fig. 1): the Polar Urals, generated 'Early Hercynide' basement. In western West the island of Novaya Zemlya and the Taymyr fold belt. Siberia, the basement is younger (termed Late Hercynian) Novaya Zemlya is offset by some 600 km to the NW and is and contains Upper Palaeozoic granites (Clarke et al. 1978). linked to the remainder of the orogen by two NW-trending Initial effects of the collision are recorded in the highs: the Pay-Khoy fold belt in the SW, and the North Timan-Pechora Basin in the Early Permian (Sakmarian- Siberia Swell and Sverdrup Monocline that lie to the NE Artinskian) and suturing took place in the Kungurian. under the Kara Sea. Subsequent E-W compression led to the uplift and Previous studies, which have included reconstructions of deformation of the carbonate platform sequences, and the the northern Ural Orogen (Green et al. 1986; Ziegler 1989; obduction of ophiolitic suites onto the eastern edge of the Zonenshain 1990; Johansen et al. 1993), have shown the East European continent (Efimov et al. 1978). Ophiolites island of Novaya Zemlya as being 'fixed', retaining its offset are also found in the basement of the West Siberia Basin throughout time. Our study of the surrounding sedimentary (Clarke et al. 1978). basins and their interrelationships has led to the The Early Permian E-W convergence produced development of a new model for the tectonic evolution of overthrusting to the west, which, as the Ural mountain belt the northern Ural Orogen during the Permo-Triassic, which grew, in turn produced tectonic loading and flexing of the is discussed in detail and illustrated by a series of schematic crust, generating a foreland basin to the west of the Urals diagrams below. (Fig. 2) that filled with 2000m of Artinskian clastic sediments. The asymmetric foreland basin continued to develop, migrating to the west throughout the Late Permian Pre-Hercynian evolution. Evidence from the Timan- and Early Triassic, and was filled with over 4000 m of coarse Pechora Basin shows that a rifting event in the Early clastic sediments shed from the eroding mountains to the Riphean (Milanovsky 1981) produced a series of half- east. Farther to the west, the reactivation of the Timan grabens and grabens (including the Timan, Pechora-Kolva Ridge produced a further phase of uplift and inversion. and Varandey-Adz'va rifts) bounded by normal faults with Compression in the western parts of the Ural Orogen a NW-SE (Baikalian) trend (Fig. 1). This was the continued into the Late Triassic, but in the east at this time precursor to E-W extension in the Cambrian, which was post-orogenic collapse began, initiating a series of grabens followed by sea-floor spreading and the opening of the which filled with Triassic extrusive rocks (Figs 1 & 3). The Uralian Ocean in Ordovician-Silurian times. Passive graben, which reactivated pre-existing basement faults, have margin sequences developed on both sides of this ocean: an overall N-S trend (Rigassi 1986). thick Upper Ordovician to Lower Devonian carbonates are widespread throughout the Timan-Pechora Basin (Fig. 2), and deformed carbonate platform sequences are found in Taymyr fold belt. In the central part of the Taymyr fold belt the basement of the West Siberia Basin. Localized (Fig. 1), a sequence of Palaeozoic carbonates is identified 903 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/152/6/903/4893110/jgs_152_006_0903.pdf by guest on 29 September 2021 904 S. C. OTTO & R. J. BAILEY 80oN 75oN 70°N ural framework of northern Ural Orogen, :ion of Figs 2, 3 and 4. Note the alignment of 65°N lashed lines), parts of the orogen (Pay-Khoy Monocline) and some northerly rifts. Inset map 400E 50°E 60°E 70°E shows geographical location of the area. that is similar to that described above. Structurally, this belt, loading and flexing the Siberian plate to form the sector of the fold belt comprises complex, linear folds cut by Yenisey-Khatanga foreland basin. Collision continued in numerous thrusts that parallel the regional NE trend, and this area into the Jurassic (Ziegler 1989). intruded by small Upper Palaeozoic plutons (Churkin et al. 1981), confirming that this belt is also part of the Ural New model for Novaya Zemlya and the eastern Barents Orogen. The Yenisey-Khatanga foredeep, to the SE of the Sea. In the intervening portion of the fold belt between fold belt, developed (like the Uralian foredeep) in Late Taymyr and the Polar Urals, Novaya Zemlya shows similar Permian-Early Triassic time, as is shown by the large regional development of Late Palaeozoic carbonate passive thickness of Permo-Triassic sediments (up to 6200 m) which margin sequences, in this case grading eastwards into pass from Lower Permian marine shales through Upper fine-grained clastics (Churkin et al. 1981). These sediments Permian continental coal measures to Triassic clastic were compressively deformed in the Late Permian to Early molasse sediments. However, in the archipelagos of Triassic, the limits of deformation being significantly offset Severnaya Zemlya and Franz Josef Land to the N and NW, with respect to the Polar Urals (Fig. 1). the basement is of Caledonian origin and the overlying However, offshore the Permo-Triassic history of the sedimentary sequence is markedly different: for example, South Barents Sea Basin cannot be reconciled with its Devonian rocks are of continental facies and virtually no conventional depiction as a foreland basin to the west of Late Palaeozoic sediments are found (Churkin et al. 1981). Novaya Zemlya (e.g. Rider 1988; Ziegler 1989). Regional This suggests that this northern area was part of a separate seismic profiles (Johansen et al. 1993; Baturin et al. 1991) do terrain (Smith 1986) which was also involved in the Uralian not show the asymmetry expected of a Permo-Triassic collision, causing thrusting to the SE in the Taymyr fold foredeep, but instead show that significant extension and thinning of the continental crust occurred in Late Permian time. This extension led to the development of the South URALS Barents Sea Basin, which filled with up to 7000 m of Upper SW NE 2,ooo NW SE 4,000 i + 4 6,00O + s,ooo + +++ .% ** ++.~ L__ + 6,0(X)~ + + Jt + + 1o,ooo + i+ +++ Triassic 8,0oot ~ + + + Permian lo,ooo ~ Palaeozoic Carbonates [-~ Jurassic - Tertiary ~ PalaeozoicCarbonates Trtasstc [~ Basement Fig. 2. Cross-section of Timan-Pechora Basin (after Meyerhoff ~oo~ 1980). Note thickening of Permian section to form foreland basin of the Urals and evidence of repeated reactivation of basement faults. Fig. 3. Cross-section of Kara Sea, from a depth converted seismic (See Fig. 1 for location). interpretation. (See Fig. 1 for location). Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/152/6/903/4893110/jgs_152_006_0903.pdf by guest on 29 September 2021 TECTONIC EVOLUTION OF URAL OROGEN 905 PRINOVOZEMELSK NOVAYA HIGH ZEMLYA seen in Mid-Triassic time, when left-lateral transpressional NW SE reactivation of a pre-existing Baikalian fault trend uplifted the Ludlov High, dividing the depression into two major sinistrally offset depocentres (Fig. 5b). The development of the northwesterly-directed salient in the orogen is thought to date from this episode.