An isotopic appraisal of the Late Jurassic greenhouse phase in the Russian Platform Gregory D. Price a, ⁎, Mikhail A. Rogov b a School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK b Geological Institute of Russian Academy of Sciences, 7 Pyzhevskii Lane, Moscow,119017, Russia abstract article info Article history: Received 3 July 2008 Received in revised form 31 October 2008 Accepted 27 November 2008 Keywords: Belemnites Russian Platform Oxygen and carbon isotopes Late Jurassic Oxygen- and carbon-isotope ratios have been determined from Late Jurassic (Callovian–Volgian) belemnites from three locations on the Russian Platform (Gorodischi, Khanskaya Gora and Marievka). All samples were examined by means of trace element geochemistry and petrography in order screen for diagenetic alteration. Oxygen and carbon isotopes from well-preserved belemnites range from - 2.24 to - 0.09‰ and - 0.57 to 1.77‰ respectively. Oxygen isotopes, if interpreted in terms of temperature, reveal a rise of temperatures during the Oxfordian–Early Kimmeridgian and indicate a prolonged episode of warmth during the Kimmeridgian–Volgian. The isotope data only equivocally reflect a number of significant changes in Boreal– Tethyan ammonite assemblages. A positive carbon isotope excursion is observed within the Volgian, but not seen within composite carbon-isotope stratigraphies of the western Tethys. Hence the Jurassic may have been characterised by regional δ 13 C excursions related to non-simultaneous organic matter deposition resulting from localised ponding, semi restricted ocean circulation and a lack of tidal mixing. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Records of ocean temperatures in the Northern Hemisphere based upon the isotopic thermometry of fish and shark tooth enamel (Lécuyer et al., 2003; Dromart et al., 2003) indicate a severe cooling and subsequent rapid warming during the middle to Late Jurassic transition. For this reason Dromart et al. (2003) suggested that the middle to Late Jurassic transition may represent one of the major turning points of the climate history of the Earth. A number of compilations of Jurassic isotopic data (largely belemnite-derived) (e.g. Veizer et al., 1999; Barskov and Kiyashko, 2000; Jenkyns et al., 2002; Veizer, 2005) are supportive of this possible icehouse–greenhouse transition. Such isotopic databases frequently consist, however, of data from numerous dispersed locations where presumably potential differences exist with respect to temperature and the isotopic composition of seawater, hence making any global palaeotemperature reconstruction inherently complex. Certainly the Late Jurassic and in particular the Kimmeridgian has been identified as a period of time when temperatures reached a maximum (e.g. Frakes,1979; Valdes and Sellwood, 1992; Abbink et al., 2001). Detailed isotopic records through this potential greenhouse interval are, however, limited (c.f. Price and Grocke, 2002; Gröcke et al., 2003; Wierzbowski, 2004; Zakharov et al., 2005). This study presents new (belemnite-derived) isotopic data from the Kimmeridgian–Volgian of the Russian Platform (Gorodischi, Khanskaya Gora and Marievka) combined with data from previous studies (also from the Russian Platform). A comprehensive ammonite zonation permits these data to be placed within a recognized and detailed biostratigraphical scheme. 2. Geological setting During the Late Jurassic, the Russian Platform was located between palaeolatitudes ~35–50°N (Fig. 1; Smith et al., 1994; Thierry et al., 2000). Based on the palaeogeographic reconstructions of Sazonova and Sazanov (1967), land areas may have existed to the east and west of the study area, with marine connections to the Boreal and Tethyan seas. The width of the basin varied through time (Baraboshkin, 1997) but in the Late Jurassic was about 1200 km east to west and over 2000 km north to south. The succession of Gorodischi village (25 km north of Ulyanovsk, Fig. 1) represents the stratotype of the Volgian (Gerasimov and Mikhailov, 1966) and ranges from the Kimmeridgian Eudoxus Zone to the Nodiger Zone in the Upper Volgian (Hantzpergue et al., 1998; Rogov, 2002; 2004, Fig. 2). Notably the base of Volgian and Tithonian are considered by some authors to be coincident (but see discussion by Scherzinger and Mitta, 2006). The succession is exposed over a distance of 15 km along the right bank of the Volga River and was first described by Murchison et al. (1845). Sediments of the lowermost ammonite zone seen (Eudoxus Zone) are composed of grey calcareous clays that locally grade into marl and yields a number of ammonites including Aulacostephanus eudoxus, Sutneria aff. cyclodorsata, S. ex gr. Eumela, Aspidoceras quercynum, Discosphinctoides sp., Tolvericeras cf. sevogodense and Amoeboceras spp. (Hantzpergue et al., 1998; Rogov, 2002). The overlying succession of the Autissiosorensis Zone (Fig. 2) is composed of a series of calcareous bioturbated light-grey clays locally Palaeogeography, Palaeoclimatology, Palaeoecology 273 (2009) 41–49 ⁎ Corresponding author. E-mail address: g.price@plymouth.ac.uk (G.D. Price). 0031-0182/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2008.11.011 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo