Palaeogeography, Palaeoclimatology, Palaeoecology 202 (2004) 253^272 www.elsevier.com/locate/palaeo Belemnites of Valanginian, Hauterivian and Barremian age: Sr-isotope stratigraphy, composition (87Sr/86Sr, N13C, N18O, Na, Sr, Mg), and palaeo-oceanography J.M. McArthur a;Ã, J. Mutterlose b, G.D. Price c, P.F. Rawson a, A. Ru¡ell d, M.F. Thirlwall e a Department of Earth Science, University College London, Gower Street, London WC1E 6BT, UK b Institut fu«r Geologie, Ruhr-Universita«t Bochum, Universita«tsstr. 150, D-44801 Bochum, Germany c Department of Geological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK d School of Geography, Queen’s University of Belfast, Belfast BT7 1NN, UK e Department of Geology, Royal Holloway and Bedford New College, Egham Hill, Egham, Surrey TW20 0EX, UK Received 21August 2002; received in revised form 31July 2003; accepted 5 September 2003 Abstract We present new data on 87Sr/86Sr, N13C and N18O, and elemental compositions of belemnites from 85 m of Valanginian, Hauterivian and Barremian strata at Speeton, Yorkshire, eastern England. The 87Sr/86Sr data provide a global standard for 87Sr/86Sr isotopic dating, and correlation to the biostratigraphic schemes of NW Europe. Values of 87Sr/86Sr increase from 0.707380 þ 0.000003, at the base of the Hauterivian, to 0.707493 þ 0.000004 in the earliest Late Barremian Paracrioceras elegans ammonite Zone before decreasing thereafter towards an Aptian minimum. The downturn in the elegans Zone coincided with the onset of volcanism on the present Ontong Java Plateau. A linear interpretation of the 87Sr/86Sr profile shows that the relative durations of ammonite zones differ by a factor 9 18. The basal Hauterivian unconformably overlies Valanginian strata; the discontinuity in 87Sr/86Sr across this surface represents a gap in sedimentation of 2.0 myr. In our belemnites (mostly of the genera Hibolites, Acroteuthis, and Aulacoteuthis) the absence of a correlation between N18O and N13C suggests that strong non-equilibrium fractionation has not affected the isotopic composition of the calcite. Our N18O values therefore approximate to a valid record of marine palaeo-temperatures. Specimens of the genus Hibolites have N18O values that are 0.4x more positive than those of co-occurring specimens of the genus Acroteuthis. This offset may be explained as resulting from small (0.4x) departures from equilibrium during precipitation of calcite, different depth habitats, or changing temperature in the Speeton sea in the time that elapsed between deposition of our individual belemnites. The averaged belemnite record of N18O through the section shows that seawater warmed from around 11‡C at the base of the Hauterivian to a maximum around 15‡C in the middle of the Hauterivian regale Zone, and returned to a cooler temperature of around 11‡C by the middle of the overlying inversum Zone, a temperature that persisted to the basal Barremian. Through the Barremian, temperature increased to a peak of 20‡C in the early Late Barremian elegans Zone then, in the same zone, precipitately and temporarily decreased to around 14‡C at about the time of onset of volcanism on the Ontong Java Plateau, before they returned to around 16‡C in the uppermost part of the section. In specimens of Aulacoteuthis and Acroteuthis, a good correlation between N18O and the content of Na, Sr, and Mg suggests that incorporation of these * Corresponding author. E-mail address: [email protected] (J.M. McArthur). 0031-0182 / 03 / $ ^ see front matter ß 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0031-0182(03)00638-2 PALAEO 3220 12-12-03 254 J.M. McArthur et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 202 (2004) 253^272 trace elements in these genera is largely controlled by temperature. The dependency of concentration on temperature ranges from 7 to 20% per degree Celsius, if equilibrium fractionation of oxygen isotopic composition is assumed, so the Mg, Na and Sr content of these genera may be used as palaeo-temperature proxies. The trace element content of Hibolites shows no relation to stable oxygen isotopic composition and so does not record palaeo-temperature. ß 2003 Elsevier B.V. All rights reserved. Keywords: belemnites; 87Sr/86Sr; Sr isotope stratigraphy; N18O; N13C; Boreal; Tethyan; Cretaceous; Hauterivian; Barremian 1. Introduction 1997; Price and Sellwood, 1997; Podlaha et al., 1998; Price et al., 2000; van de Schootbrugge et Interpreting Earth history for Early Cretaceous al., 2000; Rosalesd et al., 2001;(Niebuhr and times has proven a challenging task, but one that Joachimski, 2002). In view of this, we follow Pod- is of interest because of the change to ‘green- laha et al. (1998) in asking whether belemnite cal- house’ conditions in the early-to-mid-Cretaceous cite forms in equilibrium, or in disequilibrium, (Lini et al., 1992), when the northern hemisphere with its ambient water, and so whether such in- was divided into Boreal and Tethyan biotic terpretations are valid. We do so by examining Realms. Of particular interest is the degree to the chemical and isotopic composition of Early which the emplacement in Barremian/Aptian Cretaceous belemnites of both Boreal and times of the World’s largest igneous province, Tethyan a⁄nities that are proven to be well-pre- the Ontong Java Plateau (OJP), contributed to served, not least because they retain their original environmental change. There is some evidence values of 87Sr/86Sr. We show that our belemnites that it did have an impact on climate, biotic di- precipitated calcite under conditions that closely versity and ocean-wide patterns of sedimentation approximated isotopic equilibrium for oxygen, (Larson and Erba, 1999; references therein). and that the Na, Sr, and Mg contents of belem- These authors acknowledge the di⁄culty of link- nites hold promise as palaeo-temperature proxies. ing OJP volcanism to world events, but amongst the evidence that does so is the onset of the de- cline of marine 87Sr/86Sr in the Late Barremian, at 2. Geological setting about the time of onset of OJP volcanism (ibid). We have determined a precise record of 87Sr/86Sr 2.1. Stratigraphy and faunas through much of Barremian time to test the link between emplacement of the OJP and the 87Sr/ The Speeton Clay Formation is exposed at Fil- 86Sr record. We extend the record back through ey Bay, Speeton, in Yorkshire, northeastern Eng- Hauterivian time, and a fragment of Valanginian land (Fig. 1). The formation (Fig. 2) comprises time, in order to provide a standard curve for about 100 m of interbedded marine claystones dating and correlation with 87Sr/86Sr in this inter- and calcareous mudrocks of which we sampled val. Such a record will assist the integration of 85 m. The sediments rest unconformably on the Boreal and Tethyan histories which have been Kimmeridge Clay Formation which is of Volgian hampered by marked £oral and faunal di¡erences age (Rawson et al., 1978). The stratigraphical suc- between the realms, particularly during latest Ju- cession and biozonations shown in Fig. 2 are ac- rassic and earliest Cretaceous times. companied by a plot of 87Sr/86Sr in belemnites Also of interest is the fact that palaeo-environ- against their stratigraphic level in order to show mental interpretations, for this and other periods, in outline the distribution of our samples through often invoke palaeo-temperatures determined the section. The sequence has a number of strati- from the oxygen isotopic composition of belem- graphic breaks and condensed intervals, the most nite calcite (Hudson and Anderson, 1989; Ander- notable of which is at the base of the Hauterivian son et al., 1994; Saelen et al., 1996; Ditch¢eld, part of the section where the Upper Valanginian PALAEO 3220 12-12-03 J.M. McArthur et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 202 (2004) 253^272 255 Fig. 1. Upper ¢gure shows the present location and geology of the Speeton area. Lower ¢gure shows the palaeo-geography of northwest Europe during Early Cretaceous times (adapted from Mutterlose, 1998). The locality at Speeton occupied a position proximal to both the Tethyan and Boreal Realms, with in£ux of Hibolites (Tethyan) belemnites from the south as sea level rose in early Hauterivian times. PALAEO 3220 12-12-03 256 J.M. McArthur et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 202 (2004) 253^272 Fig. 2. Ammonite and nannofossil biostratigraphy, lithostratigraphy and outline log, stratigraphic levels above Bed E as datum (see text for more explanation), and outline 87Sr/86Sr record of the sequence at Speeton, Yorkshire, UK. is absent (Fig. 2). Breaks and condensed intervals of their belemnite fauna. The A beds (Aptian^ are represented by phosphatic nodule beds, con- Albian) and the C beds (Hauterivian) are domi- centrations of belemnites, and intensely glauco- nated by characteristically Tethyan belemnites of nitic levels. The base of the Ryazanian (base of the genera Neohibolites (A beds) and Hibolites Bed E) is marked by a major transgression (Raw- (C beds). The B beds (Barremian; Rawson and son and Riley, 1982) which probably corresponds Mutterlose, 1983) and the D beds (upper Ryaza- to a maximum £ooding surface (Haq et al., 1987; nian ^ lowermost Hauterivian) are dominated by Ru¡ell, 1991). The early Hauterivian period was Boreal belemnites (e.g. Rawson, 1973; Mutter- marked by a series of minor regressive episodes lose, 1992) of the genera Acroteuthis (D beds), (Ru¡ell, 1991). Oxyteuthis, Praeoxyteuthis, and Aulacoteuthis The strata at Speeton were divided into four (B beds), with small Hibolites co-occurring in major units, beds A^D, labelled from the top the B beds. Overlap of forms is very limited: down by Lamplugh (1889) on the characteristics e.g. a few specimens of the Boreal genus Acroteu- PALAEO 3220 12-12-03 Table 1 Isotopic and chemical data for belemnites from the Berriasian-to-Barremian strata of the Yorkshire coast, UK Stage Sample No.