Late Barremianeearly Aptian climate of the northern middle latitudes: Stable isotope evidence from bivalve and cephalopod molluscs of the Russian Platform Yuri D. Zakharov a, * , Eugenij Y. Baraboshkin b , Helmut Weissert c , Irina A. Michailova b , Olga P. Smyshlyaeva a , Peter P. Safronov a a Far Eastern Geological Institute, Russian Academy of Sciences (Far Eastern Branch), Stoletiya Prospect 159, Vladivostok 690022, Russia b Moscow State University, Leninskiye Gory MGU 1, Moscow 119991, Russia c Department of Earth Science, ETH-Z, CH-8092 Zurich, Switzerland article info Article history: Received 27 February 2013 Accepted in revised form 17 April 2013 Available online xxx Keywords: Cretaceous Oxygen isotopes Carbon isotopes Palaeotemperatures Molluscs Ulyanovsk area abstract Palaeotemperatures during the late Barremianeearly Aptian (Early Cretaceous) on the Russian Platform have been determined on the basis of oxygen isotope analysis of aragonitic bivalve molluscan and ammonoid shells and belemnite rostra with well-preserved microstructure from the Ulyanovsk area. Those obtained from the planispiral and heteromorph ammonoid shells from the lower Aptian VolgensiseSchilovkensis, DeshayesieTuberculatum, and DeshayesieRenauxianum zones range from 26.7 to 33.2  C, from 29.2 to 33.1  C, and from 27.0 to 29.5  C, respectively. A heteromorph Helicancylus? cf. philadelphius shell from the uppermost lower Aptian Bowerbanki Zone was secreted in highest temperature conditions (32.8e35.2  C). In contrast, upper Barremian molluscs (bivalve Cyprina sp. and belemnite Oxyteuthis sp.) of the Ulyanovsk area show significantly lower palaeotemperatures: 16.9e18.5  C and 7.9e17.8  C, respectively, which is in accordance with known palaeogeographic and palaeobotanical evidences, showing that a distinct climatic optimum seems to have occurred during the late early Aptian, when warm Tethyan water penetrated into the basin. Marked changes in calculated growth temperatures for investigated molluscs from the Russian Plat- form were most likely connected with both the general warming trend during the late Barremianeearly Aptian and local palaeonvironmental conditions. New data from the Bowerbanki Zone of the Russian Plat- form provide evidence on existence of the positive carbon isotope anomaly (2.4e6&) at the end of the lower Aptian. There were apparently the three positive C-isotope anomalies during the late Barremianeearly Aptian. The onset of mid early Aptian Oceanic Anoxic Event (OAE) 1a seems to coincide with both the beginning of significant warm conditions (followed by short-term cooling) and the abrupt decline in heavy carbon isotope concentrations in marine carbonates, which partly were the likely consequences of the intensive release of CO 2 (biased by volcanic activity) and/or dissociation of methane gas hydrate. Ó 2013 Published by Elsevier Ltd. 1. Introduction Available information on BarremianeAptian isotopic palae- otemperatures is very restricted. Bowen and Fontes (1963), and Teiss and Naidin (1973) were first, who have provided evidences of rather low (14.6e20.5  C) Barremian water temperatures for France and Crimea based upon isotopic data on belemnite rostra and ammonoid jaws Lamellaptychus, associated with belemnites. Higher palaeotemperature (23.7  C) was calculated from an Aptian belemnite rostrum of France (Bowen, 1961). Additional information on this topic during some years has been obtained from (1) lower upper Barremian belemnites of Yorkshire, England (McArthur et al., 2004), (2) lower-middle BarremianeAptian belemnites from Hungary (Price et al., 2011) and Southern Ocean (Jenkyns et al., 2011), (3) lower Barremian and upper Aptian fish teeth from France and Switzerland (Pucéat et al., 2003), (4) upper Barremiane lower Aptian apatite phosphate of reptile remains from China, Thailand and Japan (Amiot et al., 2011), (5) middle Barremian and lower Aptian bivalves from the high latitude area of the Koryak Upland (Zakharov et al., 2004), (6) Aptian belemnites of Australia, and New Zealand (Dorman and Gill, 1959; Clayton and Stevens, 1968; Stevens and Clayton, 1971), and Mosambic (Bowen, 1963), * Corresponding author. Tel.: þ7 423 2317 567; fax: þ7 423 2317 847. E-mail addresses: yurizakh@mail.ru (Y.D. Zakharov), barabosh@geol.msu.ru (E.Y. Baraboshkin), helmut.weissert@erdw.ethz.ch (H. Weissert), tamara_ soboleva@mail.ru (I.A. Michailova), olgasmysh@mail.ru (O.P. Smyshlyaeva), psafronov@mail.ru (P.P. Safronov). Contents lists available at SciVerse ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes 0195-6671/$ e see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.cretres.2013.04.007 Cretaceous Research xxx (2013) 1e19 Please cite this article in press as: Zakharov, Y.D., et al., Late Barremianeearly Aptian climate of the northern middle latitudes: Stable isotope evidence from bivalve and cephalopod molluscs of the Russian Platform, Cretaceous Research (2013), http://dx.doi.org/10.1016/ j.cretres.2013.04.007