Climate and sea-level variations along the northwestern Tethyan margin during the Valanginian C-isotope excursion: Mineralogical evidence from the Vocontian Basin (SE France)

Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology

j ourna l homepage: www.e lsev ie r.com/ locate /pa laeo

Climate and sea-level variations along the northwestern Tethyan margin duringthe Valanginian C-isotope excursion: Mineralogical evidence from the VocontianBasin (SE France)

Stéphanie Duchamp-Alphonse a,⁎, Nicolas Fiet a,b, Thierry Adatte c, Maurice Pagel a

a UMR CNRS 8148, IDES, University of Paris Sud-XI, 91405 Orsay Cedex, Franceb AREVA, 75009 Paris, Francec Institut of Geology and Palaeontology, University of Lausanne, 1015 Lausanne, Switzerland

⁎ Corresponding author. Tel.: +33 1 69 15 67 57; faxE-mail address: [email protected] (S. D

0031-0182/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.palaeo.2011.01.015

a b s t r a c t

Article history:Received 1 April 2010Received in revised form 6 January 2011Accepted 21 January 2011Available online 26 January 2011

Keywords:Climate changesSea-level changesGreenhouse conditionsValanginianPositive C-isotope shiftTethys

A high resolution mineralogical study (bulk-rock and clay-fraction) was carried out upon the hemipelagicstrata of the Angles section (Vocontian Basin, SE France) in which the Valanginian positive C-isotopeexcursion occurs. To investigate sea-level fluctuations and climate change respectively, a Detrital Index (DI:(phyllosilicates and quartz)/calcite) and a Weathering Index (WI: kaolinite/(illite+chlorite)) wereestablished and compared to second-order sea-level fluctuations. In addition, the mineralogical data werecompared with the High Nutrient Index (HNI, based on calcareous nannofossil taxa) data obtained byDuchamp-Alphonse et al. (2007), in order to assess the link between the hydrolysis conditions recorded onthe surrounding continents and the trophic conditions inferred for the Vocontian Basin. It appears that themineralogical distribution along the northwestern Tethyan margin is mainly influenced by sea-level changesduring the Early Valanginian (Pertransiens to Stephanophorus ammonite Zones) and by climate variations fromthe late Early Valanginian to the base of the Hauterivian (top of the Stephanophorus to the Radiatus ammoniteZones). The sea-level fall observed in the Pertransiens ammonite Zone (Early Valanginian) is well expressed byan increase in detrital inputs (an increase in the DI) associated with a more proximal source and a shallowermarine environment, whereas the sea-level rise recorded in the Stephanophorus ammonite Zone correspondsto a decrease in detrital influx (a decrease in the DI) as the source becomes more distal and the environmentdeeper. Interpretation of both DI and WI, indicates that the positive C-isotope excursion (top of theStephanophorus to the Verrucosum ammonite Zones) is associated with an increase of detrital inputs under astable, warm and humid climate, probably related to greenhouse conditions, the strongest hydrolysisconditions being reached at the maximum of the positive C-isotope excursion. From the Verrucosumammonite Zone to the base of the Hauterivian (Radiatus ammonite Zone) climatic conditions evolved fromweak hydrolysis conditions and, most likely, a cooler climate (resulting in a decrease in detrital inputs) to aseasonal climate in which more humid seasons alternated with more arid ones. The comparison of the WI tothe HNI shows that the nutrification recorded at the Angles section from the top of the Stephanophorus to theRadiatus ammonite Zones (including the positive C-isotope shift), is associated with climatic changes in thesource areas. At that time, increased nutrient inputs were generally triggered by increased weatheringprocesses in the source areas due to acceleration in the hydrological cycle under greenhouse conditions. Thisscenario accords with the widely questioned palaeoenvironmental model proposed by Lini et al., (1992) andsuggests that increasing greenhouse conditions are the main factor that drove the palaeoenvironmentalchanges observed in the hemipelagic realm of the Vocontian Basin, during the Valanginian positive C-isotopeshift. This high-resolution mineralogical study highlights short-term climatic changes during the Valanginian,probably associated to rapid changes in the C-cycle. Coeval Massive Paraña–Etendeka flood basalt eruptionsmay explain such rapid perturbations.

: +33 1 69 15 48 82.uchamp-Alphonse).

l rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Marine sediments of Valanginian age bear witness to significantchanges in the ocean/atmosphere system associated with globalpalaeoceanographic and palaeobiological events. Valanginian sedi-ments have been the focus for numerous authors in recent years due

244 S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

to a globalpositive δ13Cexcursion (DouglasandSavin, 1973; Pattonet al.,1984; Weissert et al., 1985; Weissert and Channel, 1989; Weissert andLini, 1991; Lini et al., 1992; Hennig et al., 1999; Adatte et al., 2001; Erbaet al., 2004; Weissert and Erba, 2004; Gröcke et al., 2005; Duchamp-Alphonse et al., 2007; McArthur et al., 2007; Aguirre-Urreta et al., 2008;Bornemann andMutterlose, 2008; Fozy et al., 2010; Nunn et al., 2010) ata time of widespread carbonate platform drowning (Schlager, 1981;Föllmi et al., 1994; Graziano, 1999; Wortmann and Weissert, 2000;Duchamp-Alphonse et al., 2007), eutrophication, and crisis for marinecarbonate-producing biota (Lini et al., 1992; Bersezio et al., 2002; Erbaand Tremolada, 2004; Erba et al., 2004; Duchamp-Alphonse et al., 2007).The intensification of the Paranà–Etendeka subaerial volcanism, whichtriggered excess CO2 in the atmosphere, has subsequently been relatedto these global palaeoenvironmental changes. This event occurredbetween~138 and 130 Ma which, according to several geological timescales (Obradovich, 1993; Gradstein et al., 1994), places it within theValanginian. In such an eventuality, it is assumed that the Paranà–Etendeka volcanic activity would be responsible for an acceleration ofthe hydrological cycle under greenhouse conditions, an increase inweathering, and a subsequent higher terrigenous and nutrient transferfrom continents to oceans. This would lead to biocalcification crises incoastal marine ecosystems (Lini et al., 1992; Weissert et al., 1998; Erbaet al., 2004; Duchamp-Alphonse et al., 2007). It is thought that theassociated global increase of atmospheric CO2 would also generatechemical changes in the oceanic–sea-surface waters, acting either inneritic or open-sea pelagic environments to modify the biocalcificationof carbonate producers (Weissert and Erba, 2004).

However, in recent years this scenario has been questioned since:

i) The temporal calibration of the Early Cretaceous is not accurateand it is difficult to demonstrate synchronicity, relationships, orinteractions between major biological crises and magmaticemplacement. Large discrepancies in both absolute ages andrelative duration of stages are observed between proposed timescales (Fiet et al., 2006). The Berriasian–Valanginian boundary(chron CM15) ranges between 131 Ma (Odin, 1994) and140.2 Ma (Gradstein et al., 2004; Ogg et al., 2008), the durationof the Valanginian ranges between 3.8 and 8 Ma. According tothese recent time scales, the highest Paranà–Etendeka volcanicactivity either dated at 133–131 Ma (Courtillot et al., 1999), ormore recently at 134. 6±0.6 Ma with a rapid extrusion(b1.2 Ma; Thiede and Vasconcelos, 2010), would occur eitherduring the (Early) Berriasian (Odin, 1994) or the (Early)Hauterivian (Gradstein et al., 2004; Ogg et al., 2008), but inany case, not during the Valanginian.

ii) The Early Cretaceous global climate while assumed to have beendurably warm, may contain cooler episodes. For example, thediscovery in recent years of ice-rafted debris, coupled with newgeochemical data and models, challenge the Valanginian green-house hypothesis. Further, Valanginian tillites and dropstoneshave been described in the Eromanga basin of Australia (Frakes etal., 1995; Alley and Frakes, 2003). In addition, stable isotoperecords from Valanginian belemnite rostra suggest cooler condi-tions compared to data from earlier and later time periods(Gröcke, 2001 inGröckeet al., 2005;McArthur et al., 2004;Price etal., 2000). δ18Ocarb data obtained on high latitude belemnite rostra(Spitsbergenbasin, 70°N)give anaverage low temperatureof 8 °C(Ditchfield, 1997). δ18Ocarb data obtained from belemnite rostraand fish teeth located on the northwesternmargin of Tethys bothrecord a cooling of subtropical water-masses during the LateValanginian, with average temperatures of 15 °C and 13 °Crespectively (van de Schootbrugge et al., 2000; Pucéat et al.,2003). Based on δ13C data obtained from fossil plant material,Gröcke et al. (2005) documented a decrease in pCO2 during theLate Valanginian and suggests a cooler climate during the globalC-isotope anomaly. McArthur et al. (2004, 2007) analysed

belemnite rostra from SE France and Italy that recorded bothhigher δ18Ocarb values and a decrease in the Mg/Ca ratio duringthe Late Valanginian (Verrucosum ammonite Zone). According tothe authors, these results suggest a global cooling trend inresponse to the formation of substantial amounts of polar ice.Also, recently, Brassell (2009) interpreted the occurrence of sterylethers in Early Valanginian sediments (NK3a calcareous nanno-fossil Zone) from the central Pacific as being a biological responseto cooler temperatures thatmight suggest a global cooling duringthat time interval.

Climate is the fundamental parameter of the model proposed byLini et al. (1992) as it is linked to both geodynamic (Paranà–Etendekavolcanism) and stratigraphic events (eutrophication and biocalcifica-tion crises in marine ecosystems). In order to test the validity of thismodel and in the absence of a robust temporal calibration for the EarlyCretaceous, it is crucial to define precisely the climatic conditionsassociated with the Valanginian C-isotope excursion. However, despitethe ongoing importance of the debate onValanginian climate variations,there are relatively few high-resolution studies that detail long-termclimatic changes during the positive C-isotope shift. Moreover, climaticreconstructions are typically based on geochemical data while alterna-tive climate proxies such as clay-mineral assemblages are less used tosupport interpretations. Geochemical data are usually obtained frombelemnite rostra, however the precise stratigraphic position of thesemay be uncertain and diagenetic alteration may inhibit their use astemperature indicators. Thus, a high-resolutionmineralogical approachmay be useful for Valanginian climate reconstructions. Additionally,global climatic changes are usually associated with major sea-levelfluctuations that may have a significant impact on both terrigenous/nutrient transfer rates from continent to ocean andmarine biocalcifica-tion. However, very few studies deal with sea-level fluctuations andassociated palaeoenvironmental changes during the Valanginian,despite the occurrence of significant global second-order sea-levelvariations (Haq et al, 1987; Hardenbol et al., 1998).

The objectives of this study are: i) to provide new insight into theweathering conditions of the north-western Tethyan realm during theValanginian positive C-isotope shift, ii) to determine the factors thatdrove these palaeoenvironmental changes and iii) to test the modelproposed by Lini et al. (1992) through a comparison of the palaeocli-matic record discussed herein and the palaeoceanographic data alreadyobtained on the same samples (Duchamp-Alphonse et al. 2007). Thisstudy is based on bulk-rock and clay mineral data from the Anglessection,which is located in thehemipelagic realmof theVocontianBasin(SE France). Its palaeolocation close to the continent is ideal for such astudy, because it provides intermediate sedimentological recordsbetween neritic carbonate platforms and pelagic realms characterizedby a nearly continuous sedimentation. The essentially continuousnatureof the succession offers a good opportunity to establish a high-resolutionmineralogical recordwithout any unconformity-induced artefacts. Sincemineralogical data are sensitive to diagenetic processes, particularattention has been paid to the mineralogical assemblages in order toevaluate their potential diagenetic overprint.

2. Palaeogeographic setting of the Vocontian Basin (SE France)

The Vocontian Basin is situated in the region of the “Alpes de HauteProvence” in south-eastern France (Fig. 1). During the Valanginian, itwas a 150 km wide epicontinental sea situated in the north-westernpart of the Tethyan realm, located at a palaeolatitude of 25 to 30° N(Dercourt et al., 1993), and characterized by a palaeodepth of a fewhundredmetres (Donze, 1979;Wilpshaar et al., 1997). It was boundedby the Jura carbonate platform to the north and west and by theProvencal platform to the south. TheVocontianBasinwas connected tothe Ligurian Tethys to the east (Masse, 1993).

Fig. 1. Late Jurassic to early Cretaceous paleogeographical map of the Subalpine Basin. The investigated site is the Angles section located in the hemipelagic realm of the VocontianBasin.

245S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

3. Material and methods

3.1. Material

The Angles section is defined as the Valanginian stage stratotype byBusnardo et al. (1979), the advantages of its continuous nature anddiverse fossil assemblage are also highlighted; 96 samples have beencollected from this section. The studied section is composedof alternatedhemipelagic marl–limestones, well dated by ammonoids (Cotillon,1971; Busnardo et al., 1979; Bulot and Thieuloy, 1994; Reboulet, 1995;Reboulet and Atrops, 1999), calcareous nannofossils (Manivit, 1979;Bergen, 1994; Gardin et al., 2000; Duchamp-Alphonse et al., 2007), andcalpionellids (Allemann and Remane, 1979).Micropalaeontological datahave recently been complemented by a high resolution C-isotopestratigraphy (Duchamp-Alphonse et al., 2007) (Fig. 2).

The Vocontian marl–limestone alternations are interpreted asrepresenting variations in carbonate productivity vs clay content and itis now accepted that rhythmic bedding (calcareous beds and marlyinterbeds) is linked to cyclic variations in Earth's orbit (Boulila et al.,2008). At Angles, a high-resolution spectral analysis study of thevariations in carbonate contents and colour intensity carried out overthe Valanginian interval revealed the presence of orbital frequencies inprecession and obliquity (Giraud et al., 1995). The precession signal(~21 ka) is the dominant forcing factor during the limestone-dominantalternations of the LowerValanginian, andobliquity (~40 ka) is themostclearly defined signal during the marly-dominant alternations of theUpper Valanginian. As the aim of this work is to reconstruct long-termclimatic variations superimposed on the astronomical signal, and ascalcareous beds are absent at Angles during the Late Valanginian,samples were only taken from the bulk marly-interbeds (the darkestpart of the interbeds), with a constant temporal step of around 100 kaover the whole section (see Duchamp-Alphonse et al., 2007 for moredetails). 2 samples were collected in certain 100 ka intervals in order to

better constrain mineralogical data, leading to a resolution of approx-imately 50 ka. This strategy allows analysis of a quasi-homogeneouslithology and therefore minimizes the lithological artefacts associatedwith astronomical climatic changes, mainly expressed by the 21 kyr and40 kyr cyclicity in this study.

3.2. Methods

For mineralogical analyses, approximately 20 g of each rock samplewere coarsely crushed in a “jaw” crusher, dried at a temperature of 110 °C,and crushed again in an agate mortar to obtain a fine, homogeneous andrandom powder of the bulk rock with particles b40 μm.

3.2.1. Bulk mineralogyBulk rock mineralogy samples were prepared and analysed at the

Geological Institute of the University of Neuchâtel, following theprocedure described by Adatte et al. (1996) after Ferrero (1965, 1966),Klug and Alexander (1974) and Kübler (1983). About 800 μg of bulk rockpowder were pressed into a powder holder covered with blotting paperat a pressure of 20 bar, then analysed by XRD (SCINTAG XRD 2000Diffractometer). The bulk mineralogy of sediments was determined bysemi-quantitativemeasurements, usingX-raydiffractionpeak intensitiesof the main minerals present (Ferrero, 1966; Kübler, 1983) comparedwith external standards. Analytical uncertainties vary between5 and10%for phyllosilicates and 5% for grain minerals.

3.2.2. Clay mineralogyClay mineralogy samples were prepared following the procedure

described in detail by Colin et al. (1999) at the IDES Laboratory(Interaction et Dynamique des Environnements de Surface) of theUniversity of Paris Sud. Samples were treatedwith diluted hydrochloricacid (HCl) and hydrogen peroxide (H202) to remove carbonate andorganic matter. Clay deflocculation was done by successive washing in

Fig. 2. Bulk rock mineralogy of the Angles section (%) plotted against: the lithological column of the Angles section from the Upper Berriasian to the Lower Hauterivian; Ammonite biostratigraphy from Bulot and Thieuloy (1994) in whichBerrias p.p. = Berriasian p.p., H. p.p. = Hauterivian p.p., Bois. p.p. = Boissieri p.p., Pertrans. = Pertransiens, Ino = Inostranzewi, Cal. = Callidiscus, Rad = Radiatus, alp. = alpillensis, oto. = otopeta, th. = thieuloyi, hir. = Hirsutus, subcam. =Subcampylotoxus, campylo. = Campylotoxus, verruco. = Verrucosum, prone. = Pronecostratum, peregri. = Peregrinus, cal. = Callidiscus; and C-isotope stratigraphy (‰) from Duchamp-Alphonse et al. (2007). Note that bulk rock mineralogy isobtained from the marl interbeds and is composed, in decreasing quantities of: calcite, phyllosilicates quartz, plagioclase and feldspar. Plagioclase and feldspar contents are not represented in this figure since they are absent or very rare(respective averages of 1 and 0.5%). Periods 1, 2 and 3 (and related subperiods) are based on the vertical distribution of the bulk-rock minerals and the C-isotope stratigraphy (see text for details). Shaded bands highlight the periods describedin the results (Section 4).

246S.D

uchamp-A

lphonseet

al./Palaeogeography,Palaeoclim

atology,Palaeoecology302

(2011)243

–254

247S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

distilled water. The b2 μm clay fraction was then separated from thebulk samples by settling according to the Stoke's law (Galehouse, 1971).Oriented slides were prepared from the concentrated clay suspensionsby pipetting onto glass slides and allowing them to dry at ambienttemperature. Three X-ray diagrams were measured using a PANalyticalDiffractometer: one after air-drying, one after ethylene–glycol solvationfor 24 h and one after heating at 490 °C for 2 h. Clay minerals wereidentifiedbasedon theposition of the (001) series of basal reflections onthe 3 X-ray diagrams. Semi-quantitative measurements were per-formed on the glycolated curve with the MacDiff software (Petschick,2000) using the main X-ray diffraction peaks of eachmineral [smectite,including mixed-layers (15–17 Å); illite (10 Å); and kaolinite/chlorite(7 Å)]. Relative proportions of kaolinite and chlorite were determinedbased on the ratio of the 3,5/3,54 Å peak areas. Analytical uncertaintiesare estimated to be 2%.

4. Results

4.1. Bulk mineralogy

Minerals identified include calcite, phyllosilicates and quartz, withaccessoryminerals such as plagioclase and feldspar (Fig. 2). Carbonateand phyllosilicates are the dominant minerals with proportionsranging from 36 to 74% (average of 58%) and from 17 to 44% (averageof 27%) respectively. Quartz is generally less abundant, ranging from1.5 to 15%, with an average of 9%. Plagioclase and feldspar are rare orabsent, with averages of 1 and 0.5% respectively. These two mineralswill not be discussed further.

Bulk rock mineral type shows a distinctive evolution during theValanginian time interval. Three major successive periods (periods 1,2 and 3) have been identified. Periods 1 and 3 have been furthersubdivided into 2 subperiods (Fig. 2):

1) Period 1 ranges from the top of the Boissieri ammonite Zone to theStephanophorus ammonite Zone. It is characterized by variableproportions of calcite, phyllosilicates and quartz. Calcite contenttends to decrease in the Pertransiens ammonite Zone (from 74 to50%, subperiod 1a) then values significantly increase in theStephanophorus Zone (to 68%, subperiod 1b). The phyllosilicatescontent curve shows an inverse trend with increased values in thePertransiens Zone (from 19 to 35%; subperiod 1a) followed by adecrease in the Stephanophorus Zone (to 18%, subperiod 1b).Quartz content mimics the phyllosilicates trend with slightvariations in amplitude (from 2 to 11%).

2) Period 2 corresponding to the Stephanophorus–Verrucosum ammo-nite Zones that includes the positive C-isotope shift shows the moststriking feature in the bulk mineralogy evolution, with a long-termdecreasing trend of the calcite content (Fig. 2). In particular, calciteproportion decreases pronouncedly from 68 to 46% at the top of theStephanophorus Zone (Campylotoxus ammonite Subzone), increasesin the Inostransewi ammonite Zone (to 69%) and finally drops offagain at the base of the Verrucosum Zone (to 48%). Phyllosilicatesproportion againmirrors carbonate content and increases from18 to30%. Quartz slightly increases from 6 to 10%.

3) Period 3 corresponds to the Verrucosum to Radiatus ammonite Zones(Fig. 2). It has a comparatively large sedimentary thickness markedby fairly abundant calcite, the proportion of which tends to increaseup-section (from 49 to 68%), with the exception of the Furcillata–Callidiscus ammonite Zones in which it is less abundant (average of47%, subperiod 3b). These calcite trends are accompanied by variableamounts of phyllosilicates, decreasing from 30 to 20% in theVerrucosum to Trinodosum ammonite Zones (subperiod 3a). Phyllo-silicate content is significantly higher in the Furcillata–CallidiscusZones to the detriment of calcite (average of 35%, subperiod 3b).Quartz proportion slightly but gradually increases from 9 to 15%,then decreases in the Callidiscus–Radiatus Zones (to 8%).

4.2. Clay mineralogy

Clay mineral assemblages are mainly composed of illite, kaolinite,smectite, chlorite and illite-smectite mixed layers (Fig. 3). As for bulkrock mineralogy, the vertical distribution of clay-mineral assemblagesis not random and the same 3 successive mineral assemblage timeintervals (and associated sub-intervals) can be identified within thesuccession (Fig. 3):

1) Period 1 ranges from the top of the Boissieri to the StephanophorusZones. It is characterized by variable clay assemblages with largeamounts of illite, as well as by the presence of significant amounts ofkaolinite. Smectite, illite–smectite mixed layers and chlorite are lessabundant. Illite gradually increases from 33% at the base of thePertransiensZone to67% in the StephanophorusZone(SubcampylotoxusSubzone; subperiod 1a), it thendecreases slightly (reaching 45% at thetop of the Stephanophorus Zone (subperiod 1b)). Kaolinite mirrorsillite's trend and increases from 20 to 45% in the Pertransiens Zone,achieves maximum values during the Subcampylotoxus Zone (subpe-riod 1a), and then decreases again to 20% in the Stephanophorus Zone(subperiod 1b). Smectite sporadically occurs with fairly high propor-tions in the Stephanophorus Zone, reaching 26% of the assemblages(Campylotoxus Zone; subperiod 1b). The illite–smectite mixed layerproportion drastically decreases from 44 to 3% (subperiod 1a), thenstays relatively low (subperiod 1b). Chlorite is occasionally presentwith higher proportions (average of 5%) at the top of the Stephano-phorus Zone.

2) Period 2 ranges from the top of the Stephanophorus Zone to theVerrucosum Zone and corresponds to the positive C-isotope shift(Fig. 3). It is marked by a significant increase in kaolinite content,ranging from 11 to 42%, with an average of 39%. Illite is generallyless abundant compared to period 1, with a sharp decrease from 73to 37%. Illite–smectite mixed layers slightly increase from 4 to 15%.Chlorite remains relatively low, never exceeding 12%. Smectite isabsent.

3) Period 3 correlates with the Verrucosum to Radiatus Zones (Fig. 3).As for period 1, clay assemblages are variable but are generallyrelatively illite rich (highest value of 77% observed in the RadiatusZone, subperiod 3b), containmoderate amounts of kaolinite (long-term decreasing trend from 42 to 6% in the Verrucosum–

Trinodosum Zones, subperiod 3a), and low but constant proportionof illite–smectite mixed layers (that never exceed 10% except inthe Furcillata Subzone (15%)). This time interval is marked by thepresence of smectite, which significantly increases at the base ofthe Trinodosum Zone, and reachs 45% of the clay assemblages in theFurcillata and Radiatus Subzones (subperiod 3b).

5. Discussion

5.1. Diagenetic overprint

In marine sediments, relative changes in clay mineral assemblagesmay record palaeoenvironmental (mainly climatic and eustatic) and/ordiagenetic changes. Thus, before any palaeoenvironmental interpreta-tion of clay mineral assemblages is made, it is necessary to distinguishthe detrital and authigenic clays and estimate their potential diageneticoverprint. Authigenesis of clayminerals can be either a synsedimentary(e.g. glauconite formation) or post-sedimentary process (e.g. smectiteinto illite transformation), through fluid flow and burial diagenesis. Theoccurrence of authigenic clay minerals is more often observed in highlyporous lithologies promoting fluid circulations, such as sandstones.Argillaceous sediments such as the Angles marls are less prone toauthigenic mineral development. Previously published studies on theclaymineral distribution of theMesozoic series of the Vocontian Troughdocument an increasing diagenetic impact eastward as a result of theAlpine orogeny (Deconinck and Chamley, 1983; Ferry et al., 1983).

Fig. 3. Clay mineralogy of the Angles section (relative %) plotted against: the lithological column of the Angles section (marl–limestone alternations, SE France) from the Upper Berriasian to the Lower Hauterivian; Ammonite biostratigraphyfrom Bulot and Thieuloy (1994), see Fig. 2 for abbreviations; and C-isotope stratigraphy (‰) from Duchamp-Alphonse et al. (2007). Note that clay mineralogy is obtained from the marl layers which show the following composition, indecreasing order of: illite, kaolinite, smectite, illite–smectite mixed layers and chlorite. Periods 1, 2 and 3 (and related subperiods) are based on the vertical distribution of the clay-minerals and the C-isotope stratigraphy (see text for details).Shaded bands highlight the periods described in the results (Section 4).

248S.D

uchamp-A

lphonseet

al./Palaeogeography,Palaeoclim

atology,Palaeoecology302

(2011)243

–254

249S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

Burial diagenesis would be responsible for the usual replacement ofsmectite by chlorite in the calcareous beds and illite in the marlyinterbeds (Chamley, 1989; Deconinck, 1993; Lanson and Meunier,1995). However, at the Angles section, the diversity of the claymineralsand the lack of any continuous vertical trend in clay mineral compositionwithin the 240 m-thick succession (Fig. 3) suggests that the clay mineraldiagenesis driven by burial effects is weak (Kisch, 1983; Chamley et al.,1997) and that relative variations in the mineralogical assemblage mostlikely reflect a primary signal driven by palaeoenvironmental changes.The two sporadic appearances of smectite, reaching highs of 26% and 45%of the assemblages in the Stephanoporus and the Furcillata and RadiatusZones respectively, support this interpretation (Fig. 3). Recently, Fesneauet al. (2009) recognized a bentonite horizon in the Vocontian Basin in theSubcampylotoxusSubzone;CampylotoxusZoneaccording toHoedemaeker(1995). This bentonite is detected in both La Charce and Vergol sectionsand consists of a centimetre-thick ochre-layer, characterized by anenrichment of both well-crystallized smectite and trace elements thatexhibit a magmatic affinity (Zr, Th, Y…). At the Angles section, theSubcampylotoxus Zone is associated with the appearance of smectite. Avolcanic origin for this smectite is unlikely since: i) the coeval ochre-coloured horizon has not been sampled; ii) at Angles, during the EarlyValanginian, the smectite is present from the base of the SubcampylotoxusZone to the top of the Campylotoxus Zone, corresponding to a 33-m-thicksedimentological unit, lasting up to 1.5 Ma (according to a cyclostrati-graphic study of the Angles section (Duchamp-Alphonse, unpublisheddata)); and iii) contrary to Fesneau et al. (2009), this smectite enrichmentcorrelates with a decrease in the abundance of elements having amagmatic affinity, such as Zr, Th andTi (Duchamp-Alphonse, unpublisheddata).

Several other datasets obtained at the Angles section support aweakdiagenetic overprint at the Angles section. For the Valanginian,Duchamp-Alphonse et al. (2007) present well-preserved geochemicaldata (C- and O- isotopes as well as major and trace elements) andcalcareous nannofossil assemblages that are not significantly affectedbyetching or secondary calcite overgrowth. From the Late Hauterivian tothe Early Aptian, Godet et al. (2008) demonstrate that clay-mineralassemblages from Angles did not suffer from a significant diageneticoverprint. From theHauterivian to Aptian, Godet (2006) and Bodin et al.(2009) interpret bulk-rock δ18O signal variations as a palaeoenviron-mental andpalaeoclimatic signal, arguing that the long term δ18O trendsare comparable to the ones recorded inother regions. Bodin et al. (2009)also document belemnites with well-preserved isotopic and elementalcompositions. These results, combined with those presented in thepresent paper suggest that the clay mineral assemblages of the Anglessection, and, notably, the kaolinite, did not undergo strong diageneticalteration; therefore, their trends can be used as palaeoenvironmentalproxies.

5.2. Palaeoenvironmental changes

The distinct trends occurring in the bulk and claymineralogies of theAngles section are interpreted as reflecting variations in theweatheringthatprevailed in theperivocontian source areas.During theValanginian,the nature and intensity of weathering are mainly the products ofinteractions between climate (rainfall and temperature in particular),topography, tectonic activity linked to the structural evolution ofmargins and associated sea-level changes (Chamley, 1989; Weaver,1989).

5.2.1. Sea-level changesSea-level changes are commonly recognized in the field using a

sequence stratigraphic approach combined with bulk rock and claymineral analysis. A detailed sequence stratigraphic study of the Anglessection has previously been published by Arnaud-Vanneau et al. (1982).It is herein compared to the global sea-level curve proposed byHardenbol et al. (1998), and the mineralogical results obtained in this

study. A Detrital Index (DI: detritus (phyllosilicates and quartz)/calciteratio) and the relative proportions of illite and kaolinite compared tosmectite have beenused (Figs. 3 and 4). Both represent useful indicatorsof sea-level variations (Chamley et al., 1983; Deconinck et al., 1985;Adatte et al., 2002):

1) A decrease of the DI generally reflects amore distant detrital sourceand decreased erosion. Thus, it reflects a higher sea-level or deeperwater conditions (Adatte et al., 2002). An increasing DI indicates amore proximal detrital source, increased erosion associated toincreased accumulation of detrital matter, and, consequently, alower sea-level or shallower water environment.

2) Differential flocculation and settling play an important role indetermining the distribution of clay minerals in sediments. As illiteand kaolinite are denseminerals, they settle more rapidly than otherclay minerals and tend to be deposited nearest the shore in shallowwater settings. Conversely, smectite tends to be particularly fine-grained and settles much more slowly. It remains dispersed forlonger and tends to settle in deeperwaters inmore offshore settings.As a consequence, the relative proportions of illite and kaolinitecompared to smectite have been used to infer shallowing/regressiveand deepening/transgressive episodes (Hallam, 1975; Chamley et al.1983; Deconinck et al., 1985).

In their sequence stratigraphic study of the Angles section, Arnaud-Vanneau et al. (1982) recognizedmajor second order sea-level variationsduring the Early Valanginian (Pertransiens to Stephanophorus Zones,period 1, see Section 4), and a durable and stable highstand sea-levelcharacterizing the late Early Valanginian up to the base of the Hauterivian(top of the Stephanophorus to the Radiatus Zones, periods 2 and 3, seeSection 4 and Fig. 3). The Pertransiens Zone ismarked by amajor sea-levelfall (subperiod 1a) followed by a major rise during the StephanophorusZone, the onset ofwhich occurs at theHirsutus–Subcampylotoxus Subzonetransition (subperiod1b). This interpretation is corroboratedby theglobalsea-level curve obtained by Hardenbol et al. (1998) and is also supportedby themineralogical data obtained in this study. Themost significant sea-level fluctuations recorded during the Early Valanginian are in agreementwith theDI and the illite andkaolinite vs. smectite proportions (Figs. 4 and5). During the Pertransiens–Stephanophorus Zones (subperiod 1a), theobserved sea-level fall is associated with a sharp increase of the DI (from0.33 to 0.83), an absence of smectite, and a progressive rise of illite andkaolinite contents (from 33% to 67% and from 20% to 45% respectively;Fig. 3). The sharp reduction of the calcite proportion relative to theterrigenous inputs, and the augmentation of the dense clay mineralsrelative to the fine-grained clay-minerals suggest shallower conditionsand a more proximal terrigenous source (Adatte et al., 2002). This trendreflects an increase of continental erosion during a sea-level lowstand.Similarly, in the Stephanophorus Zone (subperiod 1b), mineralogical datafit the sedimentological and lithological observations. During this timeinterval, the major sea-level rise identified by Arnaud-Vanneau et al.(1982) and Hardenbol et al. (1998), corresponds to a relative decrease ofthe DI (from 0.83 to 0.36), the appearance of smectite (up to 26%) and asignificant decrease in illite and kaolinite contents (to 45% and 20%respectively, Figs. 3 and 4). This distribution reflects a deeper depositionalenvironment, and a more distal detrital source due to high sea-level.

In conclusion, during the Pertransiens to Stephanophorus Zones(Lower Valanginian, Period 1), the distribution of the detrital materialfrom the Angles section (bulk and clayminerals of themarl interbeds)is mainly influenced by second order sea-level changes, while climateinfluence is only of minor importance. In contrast, from the top of theStephanophorus Zone to the Radiatus Zone, since second-order sea-level changes are not significant, themineralogical record is inferred tomostly reflect climate changes in the source areas.

5.2.2. Climate changesIn contrast to the Pertransiens–Stephanophorus Zones, during the

Stephanophorus–Radiatus Zones interval (uppermost Lower Valanginian

Fig. 4. Sea-level, climate and terrigenous input variations during the Valanginian at the Angles section inferred from mineralogical ratios (this study) and sequence stratigraphy study (local sea-level curve from Arnaud-Vanneau et al., 1982)(A) compared to the global sea-level curve from Chart 1 of Hardenbol et al. (1998) (B)). The ratio of quartz and phyllosilicates (main terrigenous components) to calcite corresponds to the Detrital Index (DI). Palaeoclimatic reconstructions arebased on the Weathering Index (WI: kaolinite/(illite+chlorite) ratio). During the Early Valanginian, both the second-order sea-level changes inferred from sequence stratigraphy and mineralogical data support high amplitude sea-levelchanges. During this time interval, a decrease in the DI reflects decreased detritus vs carbonate, a more distant detrital source and a higher sea-level; whereas an increase in the DI indicates an increase in detritus, a more proximal terrigenoussource and a lower sea-level. As the sequence stratigraphic studies (sea-level curves from Arnaud-Vanneau et al., 1982 (A) and Hardenbol et al. (1998) (B)) document a durable and stable sea-level highstand for the Late Valanginian, it isassumed thatmineralogical ratio variations are linked to palaeoclimatic changes during this time interval. The decreased detritus ratio testifies of lower terrigenous inputs whereas increasing trend indicates a higher terrigenous supply. At thistime, increasedWI indicates a wetter and probably warmer climate (higher hydrolysis), whereas a decreasing trend indicates a drier and probably cooler climate (lower hydrolysis). Shaded bands highlight the periods described in the results(Section 4).

250S.D

uchamp-A

lphonseet

al./Palaeogeography,Palaeoclim

atology,Palaeoecology302

(2011)243

–254

Fig. 5. Sea-level, climate and nutrient input variations during the Valanginian at the Angles section inferred from Weathering Index (WI, this study), Nutrient Index (HNI based onthe calcareous nannofossil fertility indicators ratio from Duchamp-Alphonse et al., 2007), and sequence stratigraphy study (local sea-level curve from Arnaud-Vanneau et al., 1982)(A) compared to the global sea-level curve of Hardenbol et al. 1998) (B)). Increased WI indicates a wetter and probably warmer climate (higher hydrolysis conditions), whereas adecreasing trend documents a drier and probably cooler climate (lower hydrolysis conditions). Higher HNI values testify of higher water fertility and vice versa. Shaded bandshighlight the periods of fairly good correlation between the WI and the HNI for the Late Valanginian.

251S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

to Lower Hauterivian, Periods 2 and 3) the Vocontian Basin ischaracterized by a steady and long-term sea-level highstand (Arnaud-Vanneau et al., 1982; Hardenbol et al., 1998; Fig. 4). Detrital inputchanges linked to sea-level fluctuations are therefore not significant, andmineralogical variations are mainly driven by palaeoclimatic variationswhich influence the type of weathering and the intensity of pedogenesis(Chamley, 1989). Thus, the DI is reflecting fluctuations in terrigenoussupply linked with changes in hydrolysis conditions. In addition, theWeathering Index (WI: kaolinite/(illite+chlorite) ratio) and theoccurrence vs absence of smectite (Figs. 3 and 4) are used. Kaolinitemainly forms during highly hydrolytic weathering reactions in warmhumid climates (Chamley, 1989) whereas mica and chlorite are thecommon by-products under cool to temperate, dry conditions with lowhydrolysis (Singer, 1984; Chamley, 1989). Abundant illite reflectsminimum hydrolyzing conditions i.e. physical weathering (Chamley,1989; Robert and Chamley, 1990) under either cold or dry conditions.WIwill therefore show fluctuations between warm humid and cool totemperate, dry climate conditions. The relationship between smectiteformation and climate is more uncertain. Smectite originates either fromtropical soil under semi-arid and seasonal climatic conditions or as aweathering by-product of basalt (Singer 1984; Chamley, 1989). Thepresence or absence of smectite will therefore give detailed insights onclimate seasonality.

Based on the changes in vertical distribution of δ13C and bulk andclaymineralogies described above, twomajor climatic episodes can bedistinguished in the Stephanophorus–Radiatus Zones (Fig. 4):

1) The first major climatic episode corresponds to the period 2, whichshows the most striking feature of the C-isotope and mineralogicalevolutions (Fig. 4). The bulk rock positive C-isotope excursion

(amplitude of+1.5‰) coincideswith a significant increase in bothDI (from 0.42 to 0.83) andWI indices (from 0.18 to 0.95). Smectiteis absent (Fig. 4). These results suggest a significant increase ofterrigenous input under a warm and humid climate. Since both DI,and WI indices reach their highest values (0.83, and 0.95respectively) during the δ13C shift, it is assumed that the peak ofthe C-isotope excursion coincides, at a regional scale, with themost humid and warmest conditions of the (Late) Valanginian.This result is not inconsistent with the discovery of ice-rafteddebris in Australia, during the Valanginian (Frakes et al., 1995;Alley and Frakes, 2003) implying the presence of polar ice. Further,as shown by the palaeobiogeographical distributions of bothforaminifera and calcareous nannofossils, more pronouncedlatitudinal temperature gradients might have characterized theValanginian (Mutterlose and Kessels, 2000; Mutterlose et al.,2003), which is consistent with glaciation (Gröcke et al., 2005). Itis thus assumed, as has already been proposed by Price (1999) forthe Mesozoic, that the Earth's climate regime during theValanginian, and especially during the Valanginian positive C-isotope excursion, could have been characterised by a relativelysteep pole-to-equator temperature gradient, where low-latituderegions (the Angles section for example) were warmer than today,and high-latitudes regions experienced cold or sub-freezingconditions.

2) The second major climatic episode corresponds to period 3,representing a greater amount of time and marked by relativelyhigh C-isotope values, with a gradual upward decreasing trend.Detrital inputs and weathering are variable, reflecting an overallunstable climate (Fig. 4). However, long-term general trendsobserved in subperiods 3a and 3b present some differences.

252 S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

In subperiod 3a, the mineral assemblages are characterized by: i) adecrease in the DI from 0.83 to 0.43 in the Pronecostratum Subzone(Verrucosum Zone) and fairly steady low DI values (average of 0.6) inthe Peregrinus–Nicklesi Subzone; ii) a significant decrease of the WI,from 0.95 to 0.11 in the Trinodosum Zone; and iii) a near absence ofsmectite (Fig. 4). These trends reflect a gradual change from a warmhumid climate to a more temperate climate with lower hydrolysisconditions in the source areas and, consequently, lower terrigenousinputs into the Vocontian Basin. This interpretation implies a decreaseinmoisture/rainfall, and, most likely, a drop in temperature; this latteris supported by previous geochemical and paleontological data fromthe Vocontian Basin that point to decreasing temperatures during theVerrucosum Zone (van de Schootbrugge et al., 2000; Pucéat et al.,2003; McArthur et al., 2004, 2007) and highlight the presence ofBoreal ammonites and calcareous nannofossils respectively (Rebouletand Atrops, 1999; Reboulet, 1995; Melinte and Mutterlose, 2001).

In subperiod 3b, the mineral assemblages are characterized by: i) anincreaseof theDI to1.66 in theCallidiscusZone; ii) an increase inWIvalues(to 0.83, Nicklesi Zone); and iii) the presence of fairly abundant smectite,reaching 45% of the clay assemblages in the Trinodosum and RadiatusZones (Fig. 4), implying that a seasonally contrasted climate (more humidvs more arid periods) prevailed during the Trinodosum to Radiatus Zones.At the smaller scale, DI and WI show similar trends which can beexplained by alternations of humid seasons triggering higher detritalinputs with more arid periods characterized by lower terrigenous inputs.

Therefore, themineralogical patterns described for period 3 probablyreflect a period of unstable climate, linked to an overall chain of feedbackmechanisms induced by the strong greenhouse conditions whichprevailed during the positive δ13C excursion. Given that the durationof such climatic changes does not exceed a fewmillions of years, they areassumed to be closely linked to “short-term”perturbations in theC-cyclethat could be induced by the Paranà–Etendeka volcanism and theassociated CO2 degassing in the atmosphere as proposed by Lini et al.(1992). Moreover, this assumption is not inconsistentwith the record ofa cooler episode during the Verrucosum Zone. Indeed, rapid coolingevents have already been documented in the aftermath of greenhousewarming associated with the formation of subsequent Large IgneousProvinces. In particular, the Early Aptian and Cenomanian–Turoniangreenhouse episodes that exhibit positive C-isotope excursions areusually interpreted as the consequence of a pCO2 rise in the atmospheretriggered by the emplacement of the Ontong-Java/ Manihiki andCaribbean Plateaus respectively. Such events could be followed bycooler episodes (Arthur et al., 1988;Menegatti et al., 1998). Such coolingevents are recorded during Oceanic Anoxic Events (OAEs) and are thusassociated with the accumulation and burial of large amounts of organiccarbon (OC) in the sediments; a process that can lead to a significantdrop in atmospheric pCO2 and a subsequent climate cooling (Arthuret al., 1988; Menegatti et al., 1998; Kuypers et al., 1999). During theValanginian organic matter (OM) rich layers are only described fromrestricted basins within the North Atlantic and Weddell Sea, and aregenerally rare in the Tethyan Realm (Westermann et al., 2010).However, the coeval formation of individual black shale layers, and theincreased storage of OM on continents, as proposed by Westermannet al. (2010), couldhave triggered climatic cooling in the aftermathof theValanginianpositive C-isotope shift. It is thus assumed that these general“forced” feedbacks have the potential to enable the atmosphere–oceansystem toweaken greenhouse conditions and thus return tomore stableconditions (Föllmi et al., 1994).

5.2.3. Palaeoenvironmental modelUsing a high-resolution calcareous nannofossil analysis in association

with geochemical data, Duchamp-Alphonse et al. (2007) documented acalcareous nannofossil biocalcification crisis at the Angles section,associated with the eutrophication of the photic zone during theStephanophorus–Verrucosum Zones. Trophic conditions were in partinferred using a High Nutrient Index (HNI) to distinguish oligo- meso-

and eutrophic conditions (Duchamp-Alphonse et al., 2007). This HNIindex has been compared with the WI index measured on the samesamples, to better understand the link between climatic variationsrecorded in the surrounding continents and the trophic conditionsinferred in the Vocontian photic zone (Fig. 5). Furthermore, it is also avaluable and independent test of the palaeoclimatic and palaeoceano-graphic “greenhouse model” proposed by Lini et al. (1992) for environ-ments quite similar to the hemipelagic realm of the Vocontian Basin.

From the Boissieri to the Stephanophorus Zones, e.g., during most ofthe Early Valanginian (Period 1), the WI and the HNI indices do notshow any correlation (Fig. 5). This result is not surprising, since theWIis based on clay mineral associations which are mainly influenced bysecond order sea-level changes during the earliest Valanginian.Therefore, theWI cannot beused as a climate proxy and its relationshipswith nutrient inputs (e.g., HNI) are difficult to decipher.

In contrast, periods 2 and 3 (Stephanophorus to Radiatus Zones) arecharacterized by clay-mineralogical variations that mainly reflectcontinental weathering associated to climate changes, as this intervalcorresponds to a steady and durable second-order highstand sea-level. Here, the WI and the HNI long-term trends show a remarkablesimilarity in shape (Fig. 5); generally an increase or decrease in theHNI coincides with an increase or decrease in the WI long-termtrends. This data highlights the significant relationship that existsbetween climate and the nutrient supply in a hemipelagic environ-ment such as the Vocontian Basin. The most significant correlationbetween WI and HNI indices occurs in the Inostransewi–VerrucosumZones, which include the positive C-isotope shift, and in the FurcillataSubzone to the Radiatus Zone (both intervals corresponding to stronghydrolysis conditions and high terrigenous inputs).

Consequently, it is proposed that at times of significantly highhydrolysis, nutrients are rapidly transferred from continent to ocean. Adirect hydrolysis/element leaching relationship is then established ashydrolysis conditions are the more powerful forcing factor in climaticand pedogenetic processes. Thus, this study clearly demonstrates thatduring the late Valanginian, nutrification in the Vocontian Basin isdirectly caused by increased weathering linked to acceleration in thehydrological cycle and thus greenhouse conditions. These nutrificationevents probably represent a local response to the global increase of pCO2

in the atmosphere. Furthermore, these results support the hypothesis ofFöllmi et al. (1994), Lini et al. (1992), andWeissert et al. (1998), whichsuggests an intensification of the greenhouse conditions as the maincause of the palaeoenvironmental changes during the Valanginianpositive C-isotope shift, in that part of the Tethys realm.

TheWI is out of phasewith (even inversely proportional to) the HNIonly once, during the Nicklesi Subzone, indicating that, at a time ofweaker hydrolysis, a pulse of nutrient supplies is nevertheless recordedin the Vocontian Basin. This result highlights a more complex systemincluding a larger number of interacting factors within the weatheringprocesses, and/or the occurrence of thresholds and delays in theinteraction processes, which is expected in the aftermath of an extremeepisode such as the Weissert event. A better understanding of thesefactors and processes will assist future interpretations.

6. Conclusions

This high resolution multiproxy study of the Valanginian intervalof the Angles section (SE France) shows that:

1) Weathering processes along the northwestern Tethyan margin aremainly influenced by sea-level changes during the Early Valanginian(Pertransiens to Stephanophorus Zones), and by climate variationsfrom the late Early Valanginian to the base of theHauterivian (top ofthe Stephanophorus Zone to the Radiatus Zone).

2) The positive C-isotope excursion is associated with a warm andhumid climate and greenhouse conditions which lead to increasedterrigenous supplies to the Vocontian Basin. The highest hydrolysis

253S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

activity, and thus the most pronounced greenhouse conditionscoincide with the positive C-isotope excursion peak.

3) An overall unstable climate is recorded in the aftermath of thisgreenhouse climate followed by a rapid cooling event; this latteroccurred,most likely, during theVerrucosum–TrinodosumZones. Theoverlying Trinodosum–Radiatus interval is marked by a seasonallycontrasted climate in which more humid periods alternate withmore arid ones.

4) During the Late Valanginian, (e.g. during and in the aftermath of thegreenhouse conditions) the increased nutrient transfer to theVocontian Basin and the associated nutrification responsible for thecalcareous nannofossil biocalcification crisis (Duchamp-Alphonseet al., 2007) are generally triggered by periods of acceleration in thehydrological cycle.

This high resolution mineralogical study demonstrates moreprecisely that greenhouse conditions during the Valanginian C-isotopeexcursion (as proposed Lini et al., 1992) are coupled with a drierepisode during the Verrucosum Zone. It provides a mineralogicalrecord consistent with previous geochemical studies, which depict acooling event during this drier episode (van de Schootbrugge et al.,2000; Pucéat et al., 2003;McArthur et al. 2007). Thiswork furthermorehighlights rapid changes in the C-cycle during the Valanginian. Sincesuch processes are mostly linked with the formation of Large IgneousProvince in the Lower Cretaceous world, the intensification of theParanà–Etendeka volcanism may be considered as the main driver ofsuch rapid climatic changes.

Acknowledgements

The authors acknowledge Professor Jean-François Deconinck forstimulating discussions and Domenico Lodola and Dr. Alice Thomasfor their helpful assistance with the English version. We thank theEditor F. Surlyk and the two anonymous reviewers for theirconstructive comments that improved the manuscript.

References

Adatte, T., Stinnesbeck, W., Keller, G., 1996. Lithostratigraphic and mineralogiccorrelations of near K/T boundary sediments in northeastern Mexico: implicationsfor origin and nature of deposition. In: Ryder, G., Fastovsky, D., Gartner, S. (Eds.),The Cretaceous–Tertiary Event and Other Catastrophes in Earth History: GeologicalSociety of America Special Paper, 307, pp. 211–226.

Adatte, T., Stinnesbeck,W., Hubberten, H., Remane, J., Guadalupe, L.O., 2001. Correlationof a Valanginian stable isotopic excursion in Northeastern Mexico with theEuropean Tethys. In: Bartolini, C., Buffler, R.T., Cantu-Chapa, A. (Eds.), The WesternGulf of Mexico Basin: Tectonics, Sedimentary Basins, and Petroleum Systems:American Association of Petroleum Geologists Memoir, 75, pp. 371–388.

Adatte, T., Keller, G., Stinnesbeck, W., 2002. Late Cretaceous to Early Palaeocene climateand sea-level fluctuations: the Tunisian record. Palaeogeography, Palaeoclimatol-ogy, Palaeoecology 178, 165–196.

Aguirre-Urreta, M.B., Price, G.D., Ruffell, A.H., Lazo, D.G., Kalin, R.M., Ogle, N., Rawson, P.F.,2008. Southern Hemisphere Early Cretaceous (Valanginian-Early Barremian) carbonand oxygen isotope curves from the Neuquen Basin, Argentina. Cretaceous Research29, 87–99.

Allemann, F., Remane, J., 1979. Les faunes de calpionelles du Berriasien supérieur/Valanginien. In: Busnardo, R., Thieuloy, J.P., Moullade, M. (Eds.), HypostratotypeMésogeen de l'Etage Valanginian (Sud-Est de la France): Les Stratotypes Français.C.N.R.S., 6, pp. 99–109. Paris.

Alley, N.F., Frakes, L.A., 2003. First know Cretaceous glaciation: Livingston tillitemember of the Cadna-owie Formation, South Australia. Australian Journal of EarthSciences 50, 139–144.

Arnaud-Vanneau, A., Arnaud, H., Boisseau, T., Darsac, C., Thieuloy, J.P., Vieban, F., 1982.Synchronisme des crises biologiques et paléogéographiques dans le Crétacéinférieur du S.E. de la France: un outil pour les corrélations plate-forme–bassin.Géologie Méditerranéenne IX (3), 153–165.

Arthur, M.A., Dean,W.E., Pratt, L.M., 1988. Geochemical and climatic effects of increasedmarine organic carbon burial at the Cenomanian/Turonian boundary. Nature 335,714–717.

Bergen, J.A., 1994. Berriasian to Early Aptian calcareous nannofossils from theVocontian trough (SE France) and deep-sea drilling site 534: new nannofossiltaxa and summary of low-latitude biostratigraphic events. Journal of NannoplantonResearch 16 (2), 59–69.

Bersezio, R., Erba, E., Gorza, M., Riva, A., 2002. Berriasian–Aptian black shales of theMaiolica formation (Lombardian Basin, Southern Alps, Northern Italy): local toglobal events. Palaeogeography, Palaeoclimatology, Palaeoecology 180, 253–275.

Bodin, S., Fiet, N., Godet, A., Matera, V., Westermann, S., Clément, A., Janssen, N.M.M.,Stille, P., Föllmi, K.B., 2009. Early Cretaceous (Late Berriasian to Early Aptian)palaeoceanographic change along the northwestern Tethyan margin (VocontianTrough, southeastern France): δ13C, δ18O and Sr-isotope belemnite and whole-rockrecords. Cretaceous Research 30, 1247–1262.

Bornemann, A., Mutterlose, J., 2008. Calcareous nannofossil and δ13C records from theEarly Cretaceous of the western Atlantic ocean: evidence for enhanced fertilizationacross the Berriasian–Valanginian transition. Palaios 23, 821–832.

Boulila, Slah, Hinnov, L.A., Huret, E., Collin, P.-Y., Galbrun, B., Fortwengler, D., Marchand,D., Thierry, J., 2008. Astronomical calibration of the Early Oxfordian (Vocontian andParis basins, France): consequences of revising the Late Jurassic time scale. Earthand Planetary Science Letters 276, 40–51.

Brassell, S.C., 2009. Steryl ethers in a Valanginian claystone: molecular evidence forcooler waters in the central Pacific during the Early Cretaceous? Palaeogeography,Palaeoclimatology, Palaeoecology 282, 45–57.

Bulot, L.G., Thieuloy, J.P., 1994. Les biohorizons du Valanginien du Sud-Est de la France:un outil fondamental pour les corrélations au sein de la Téthys occidentale.Géologie Alpine, Mémoire H. S. 20, 15–41.

Busnardo, R., Thieuloy, J.P., Moullade, M., 1979. Hypostratotype mésogéen de l'étageValanginien (SE de la France). Les Stratotypes Français. C.N.R.S, 6. Paris.

Chamley, H., 1989. Clay Sedimentology. Springer- Verlag, Berlin. 623 pp.Chamley, H., Debradant, P., Candillier, A.-M., Foulon, J., 1983. Clay mineralogy and

inorganic geochemical stratigraphy of Blake-Bahama Basin since the Callovian, site534. Deep Sea Drilling Project leg 76: Initial Reports of the Deep-Sea DrillingProject, 76, pp. 437–451.

Chamley, H., Proust, J.N., Mansy, J.L., Boulvain, F., 1997. Diagenetic and palaeogeo-graphic significance of clay, carbonate and other sedimentary components in themiddle Devonian limestones of western Ardenne, France. Palaeogeography,Palaeoclimatology, Palaeoecology 129, 369–385.

Colin, C., Bertaux, J., Desprairies, A., Turpin, L., Kissel, C., 1999. Erosional history of theHimalayan and Burman ranges during the last two glacial–interglacial cycles. Earthand Planetary Science Letters 171, 647–660.

Cotillon, P., 1971. Le Crétacé inférieur de l'arc subalpin de Castellane entre l'Asse et leVar, Stratigraphie et Sédimentologie. Mémoire du B.R.G.M. Bureau de RecherchesGéologiques et Minières 68, 1–243.

Courtillot, V., Jaupart, C., Manighetti, I., Tapponnier, P., Besse, J., 1999. On causal linksbetween flood basalts and continental breakup. Earth and Planetary Science Letters166, 177–195.

Deconinck, J.F., 1993. Clay mineralogy of the Late Tithonian–Berriasian deep-seacarbonates of the Vocontian Trough (SE France): relationships with sequencestratigraphy. Bulletin des Centres de Recherche Exploration-Production ElfAquitaine 17 (1), 223–234.

Deconinck, J.F., Chamley, H., 1983. Héritage et diagenèse des minéraux argileux dans lesalternances marno-calcaires du Crétacé inférieur du domaine subalpin. CompteRendu de l'Académie des Sciences (Paris) 297 (2), 589–594.

Deconinck, J.F., Beaudoin, B., Chamley, H., Joseph, P., Raoult, J.F., 1985. Contrôlestectonique, eustatique et climatique de la sedimentation argileuse du domainesubalpin français au Malm-Crétacé. Revue de Géologie Dynamique et deGéographie Physique 26 (5), 311–320.

Dercourt, J., Ricou, L.E., Vrielynck, B., 1993. Atlas Tethys Paleoenvironmental Maps.Gauthier-Villars, Paris.

Ditchfield, P.W., 1997. High northern palaeolatitude Jurassic–Cretaceous palaeotem-perature variation: new data from Kong Karls land, Svalbard. Palaeogeography,Palaeoclimatology, Palaeoecology 130, 163–175.

Donze, P., 1979. Les ostracodes. In: Busnardo, R., Thieuloy, J.P., Moullade, M. (Eds.),Hypostratotype Mesogeen de l'Etage Valanginian ( Sud-Est de la France): LesStratotypes Français. C.N.R.S., 6, pp. 77–86. Paris.

Douglas, R.G., Savin, S.M., 1973. Oxygen and carbon isotope analysis of Cretaceous andTertiary foraminifera from the central North Pacific. Initial Report of the Deep-SeaDrilling Project, 17. U.S. Government Printing Office, Washington, D.C., pp. 591–605.

Duchamp-Alphonse, S., Gardin, S., Fiet, N., Bartolini, A.C., Blamart, D., Pagel, M., 2007.Fertilization of the northwestern Tethys (Vocontian basin, SE France) during theValanginian carbon isotope perturbation: evidence from calcareous nannofossils andtrace element data. Palaeogeography, Palaeoclimatology, Palaeoecology 243, 132–151.

Erba, E., Tremolada, F., 2004. Nannofossil carbonate fluxes during the Early Cretaceous:Phytoplancton response to nutrification episodes, atmospheric CO2, and anoxia.Paleoceanography 19, 1–18.

Erba, E., Bartolini, A.C., Larson, R.L., 2004. Valanginian Weissert oceanic anoxic event.Geology 149–152.

Ferrero J., 1965. Dosage des principaux minéraux des roches par diffraction de Rayon X.Rapport C.F.P. (Bordeaux), inédit.

Ferrero J., 1966. Nouvelle méthode empirique pour le dosage des minéraux pardiffraction R.X. Unpublished report C.F.P. (Bordeaux).

Ferry, S., Cotillon, P., Rio, M., 1983. Diagenèse croissante des argiles dans les niveauxisochrones de l'alternance calcaire-marne valanginienne du bassin vocontien.Zonation géographique. Comptes Rendus de l'Académie des Sciences (Paris) 297(2), 51–56.

Fesneau, C., Deconinck, J.F., Pellenard, P., Reboulet, S., 2009. Evidence of aerial volcanicactivity during the Valanginian along the northern Tethys margin. CretaceousResearch 30, 533–539.

Fiet, N., Quidelleur, X., Parize, O., Bulot, L.G., Gillot, P.Y., 2006. Lower Cretaceous stagedurations combining radiometric data and orbital chronology: Towards a morestable relative time scale? Earth and Planetary Science Letters 246, 407–417.

254 S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 302 (2011) 243–254

Föllmi, K.B., Weissert, H., Bisping, M., Funk, H., 1994. Phosphogenesis, carbon-isotopestratigraphy, and carbonate-platform evolution along the Lower Cretaceousnorthern Tethyan margin. Geological Society of American Bulletin 106, 729–746.

Fozy, I., Janssen, N.M.M., Price, G.D., Knauer, J., Palfy, J., 2010. Integrated isotope andbiostratigraphy of a Lower Cretaceous section from the Bakony Mountains(Transdanubian Range, Hungary): a new Tethyan record of the Weissert event.Cretaceous Research 31, 525–545.

Frakes, L.A., Alley, N.F., Deynoux, M., 1995. Early Cretaceous ice rafting and climatezonation in Australia. International Geology Review 37, 567–583.

Galehouse, J.S., 1971. Sedimentation Analysis. In: Carver, R.E. (Ed.), Procedures inSedimentary Petrology. Wiley-Interscience, New York, pp. 69–94.

Gardin, S., Bulot, L.G., Coccioni, R., De Wever, P., Hishida, K., Lambert, E., 2000. TheValanginian to Hauterivian hemipelagic successions of the Vocontian basin (SEFrance): New high resolution integrated biostratigraphical data. 6th InternationalCretaceous symposium, Geozentrum, University of Vienna, Austria, p. 34.

Giraud, F., Beaufort, L., Cotillon, P., 1995. Periodicities of carbonates cycles in theValanginian of the Vocontian Trough: a strong obliquity control. In: House, M.R.,Gale, A.S. (Eds.), Orbital forcing timescales and cyclostratigraphy: GeologicalSociety Special Publication, 85, pp. 143–164.

Godet, A., 2006. The evolution of the Urgonian platform in theWestern Swiss Jura realmand its interactons with palaeoclimatic and palaeoceanographic change along theNorthern Tethyan Margin (Hauterivian - earliest Aptian). Unpublished PhD thesis,University of Neuchâtel, Switzerland, 412 pp. Downloadable from the Internet (14September 09): http://doc.rero.ch/record/6348?ln=fr.

Godet, A., Bodin, S., Adatte, T., Föllmi, K., 2008. Platform-induced clay-mineralfractionation along northern Tethyan basin-platform transect: implications forthe interpretation of Early Cretaceous climate change (Late Hauterivian-EarlyAptian). Cretaceous Research 29, 830–847.

Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, J., Van Veen, P., Thierry, J., Huang,Z., 1994. A Mesozoic time scale. Journal of Geophysical Research 99, 24051–24074.

Gradstein, F., Ogg, J., Smith, A., 2004. A Geological Time Scale. Cambridge University Press.Graziano, R., 1999. The Early Cretaceous drowning unconformities of the Apulia

carbonate platform (Gargano Promontory, southern Italy): local fingerprints ofglobal palaeoceanographic events. Terra Nova 11, 245–250.

Gröcke, D.R., Price, G.D., Robinson, S.A., Baraboshkin, E.Y., Mutterlose, J., Ruffell, A.H.,2005. The Upper Valanginian (Early Cretaceous) positive carbon-isotope eventrecorded in terrestrial plants. Earth and Planetary Science Letters 240, 495–509.

Hallam, 1975. Jurassic Environments. Cambridge University Press, Cambridge.Haq, B.U., Hardenbol, J., Vail, P.R., 1987. The new chronostratigraphic basis of Cenozoic

and Mesozoic sea-level cycles. In: Ross, C.A., Haman, D. (Eds.), Timing anddepositional history of eustatic sequences constraints on seismic stratigraphy:Cushman Foundation for Foraminiferal Research, Special Publications, 24, pp. 7–13.

Hardenbol, J., Thierry, J., Farley, M.B., de Graciansky, P.C., Vail, P.R., 1998. Mesozoic andCenozoic sequence chronostratigraphic framework of European Basins. In: deGraciansky, P.C., Hardenbol, J., Jacquin, T., Vail, P.R. (Eds.), Mesozoic and CenozoicSequence Stratigraphy of European Basins: Special Publication Society forSedimentary Geology, 60, pp. 3–13.

Hennig, S., Weissert, H., Bulot, L., 1999. C-isotope stratigraphy, a calibration toolbetween ammonite- and magnetostratigraphy: the Valanginian- Hauterivientransition. Geologica Carpathica 50, 91–96.

Hoedemaeker, P.J., 1995.Ammoniteevidence for long-termsea-levelfluctuations betweenthe2nd and the3 rdorder in the lowest Cretaceous. CretaceousResearch 16, 231–241.

Kisch, H.J., 1983. Mineralogy and petrology of burial diagenesis (burial metamorphism)and incipient metamorphism in clastic rocks. In: Larsen, G., Chilingar, G.V. (Eds.),Diagenesis in Sediments and Sedimentary Rocks, 2. : Developments in Sedimen-tology, 25B. Elsevier, Amsterdam, pp. 289–493.

Klug, H.P., Alexander, L., 1974. X-ray Diffraction Procedures for Polycrystalline andAmorphous Materials. John Wiley and Sons, Inc., New York. 992 pp.

Kübler, B., 1983. Dosage quantitative des minéraux majeurs des roches sédimentairespar diffraction X. Cahiers de l'Institut de Géologie, Université de Neuchâtel, SuisseSérie AX n°1.1 and 1.2, 13 pp.

Kuypers, M.M.M., Pancost, R.D., Sinninghe Damsté, J.S., 1999. A large and abrupt fall inatmospheric CO2 concentration during Cretaceous times. Nature 399, 342–345.

Lanson, B., Meunier, A., 1995. La transformation des interstratifiés ordonnés (S≥1)illite-smectite en illite dans les séries diagénétiques. Bulletin des Centres deRecherche Exploration-Production Elf Aquitaine 19, 149–165.

Lini, A., Weissert, H., Erba, E., 1992. The Valanginian carbon isotope event: a firstepisode of greenhouse climate conditions during the Cretaceous. Global ChangeSpecial Issue, Terra Nova 4, 374–384.

Manivit, H., 1979. Les nannofossiles. In: Busnardo, R., Thieuloy, J.P., Moullade, M. (Eds.),Hypostratotype Mesogeen de l'Etage Valanginian (Sud-Est de la France): LesStratotypes Français. C.N.R.S., 6, pp. 87–98. Paris.

Masse, J.P., 1993. Valanginian-Early Aptian carbonate platforms from Provence,Southeastern France. In: Simo, J.A.T., Scott, R.W., Masse, J.-P. (Eds.), CretaceousCarbonates Platforms: American Association of Petroleum Geologists Memoir,Tulsa, OK, United States, pp. 363–374.

McArthur, J.M., Mutterlose, J., Price, G.D., Rawson, P.F., Ruffell, A., Thirwall, M.F., 2004.Belemnites of Valanginian, Hauterivian and Barremian age: Sr-isotope stratigraphy,composition (87Sr/86Sr, δ13C, δ18O, Na, Sr, Mg) and palaeo-oceanography.Palaeogeography, Palaeoclimatology, Palaeoecology 202, 253–272.

McArthur, J.M., Janssen, N.M.M., Reboulet, S., Leng, M.J., Thirlwall, M.F., van deSchootbrugge, B., 2007. Palaeotemperatures, polar ice-volume, and isotopestratigraphy (Mg/Ca, δ18O, δ 13C, 87Sr/86Sr): The Early Cretaceous (Berriasian,

Valanginian, Hauterivian). Palaeogeography, Palaeoclimatology, Palaeoecology248, 391–430.

Melinte, M., Mutterlose, J., 2001. A Valanginian (Early Cretaceous) boreal nannoplank-ton excursion in sections from Romania. Marine Micropaleontology 43, 1–25.

Menegatti, A.P., Weissert, H., Brown, R.S., Tyzon, R.V., Farrimond, F., Strasser, A., Caron, M.,1998. High-resolution δ13C stratigraphy through the Early Aptian “Livello Selli” of theAlpine Tethys. Paleoceanography 13, 530–545.

Mutterlose, J., Kessel, K., 2000. Early Cretaceous calcareous nannofossils from Highlatitudes: implications for palaeobiogeography and palaeoclimate. Palaeogeography,Palaeoclimatology, Palaeoecology 160, 347–372.

Mutterlose, J., Brumsack, H., Flögel, S., Hay, W., Klein, C., Langrock, U., Lipinski, M.,Ricken, W., Söding, E., Stein, R., Swientek, O., 2003. The Greenland-NorwegianSeaway : a key area for understanding Late Jurassic to Early Cretaceouspaleoenvironments. Paleoceanography 18 2001PA000625.

Nunn, E.V., Price, G.D., Gröcke, D.R., Baraboshkin, E.Y., Leng, M.J., Hart, M.B., 2010. TheValanginian positive carbon isotope event in Arctic Russia : Evidence fromterrestrial and marine isotope records and implications for global carbon cyling.Cretaceous Research 31, 577–592.

Obradovich, J.D., 1993. A Cretaceous time scale. In: Caldwell, W.G.E., Kauffman, E.G.(Eds.), Evolution of the Western Interior Basin: Geological Association of Canada,Special Paper, 39, pp. 379–396.

Odin, G.S., 1994. Geological time scale. Compte Rendu de l'Académie des Sciences, Paris,t. Série II 318, 59–71.

Ogg, J.G., Ogg, G., Gradstein, F.M., 2008. The Concise Geologic Time-Scale. CambridgeUniversity Press, p. 184.

Patton, J.W., Choquette, P.W., Guennel, G.K., Kaltenback, A.J., Moore, A., 1984. Organicgeochemistry and sedimentology of Lower tomid-Cretaceous deep-sea carbonates,Site 535 and 540, Leg 77. Initial Reports of the Deep-Sea Drilling Project, 77. U.S.Government Printing Office, Washington, D.C, pp. 417–443.

Petschick, R., 2000. MacDiff 4.2.5manualAvailable at http://www.geologie.unifrankfurt.de/Staff/Homepages/Petschick/PDFs/MacDiff_Manual_E.pdf 2000.

Price, G.D., 1999. The evidence and implications of polar ice DURING the Mesozoic.Earth-Science Reviews 48, 183–210.

Price, G.D., Ruffell, A.H., Jones, C.E., Kalin, R.M., Mutterlose, J., 2000. Isotopic evidence fortemperature variation during the Early Cretaceous. Journal of Geological Society ofLondon 157, 335–343.

Pucéat, E., Lécuyer, C., Sheppard, S.M.F., Dromart, G., Reboulet, S., Grandjean, P., 2003.Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygenisotope composition of fish tooth enamels. Paleoceanography 18 (2), 1029–1041.

Reboulet, S., 1995. L'évolution des ammonites du Valanginien-Hautérivien inférieur dubassin Vocontien et de la plate-forme provençale (Sud-Est de la France): Relationsavec la stratigraphie séquentielle et implications biostratigraphiques. Documentdes Laboratoires de Géologie, 137, p. 371. Lyon, France.

Reboulet, S., Atrops, F., 1999. Comments andproposals about Valanginian–LowerHauterivianammonite zonation of south-eastern France. Eclogae Geologicae Helvetiae 92, 183–197.

Robert, C., Chamley, H., 1990. Paleoenvironmental significance of clay mineralassociations at theCretaceous–Tertiarypassage. Palaeogeography, Palaeoclimatology,Palaeoecology 79, 205–219.

Schlager, W., 1981. Mesozoic calciturbidites in DSDP hole 416A- petrographic recognitionof a drowned carbonate platform. Initial Report of DSDP Project, 50, pp. 733–749.

Singer, A., 1984. The palaeoclimatic interpretation of clay minerals in sediments – areview. Earth Science Review 21, 251–293.

Thiede, D.S., Vasconcelos, P.M., 2010. Paraná flood basalts: rapid extrusion hypothesisconfirmed by new 40Ar/39Ar results. Geology 38, 747–750.

van de Schootbrugge, B., Föllmi, K., Bulot, L.G., Burns, S.J., 2000. Paleoceanographicchanges during the Early Cretaceous (Valanginian-Hauterivian): evidence fromoxygen and carbon stable isotopes. Earth and Planetary Science Letters 181, 15–31.

Weaver, C.E., 1989. Clays, Muds and Shales. Developments in Sedimentology, 44.Elsevier, Amsterdam. 819 pp.

Weissert, H., Channel, J.E.T., 1989. Tethyan carbonate carbon isotope stratigraphy acrossthe Jurassic–Cretaceous boundary: an indicator of decelerated global carboncycling? Palaeoceanography 4 (4), 483–494.

Weissert, H., Erba, E., 2004. Volcanism, CO2 and paleoclimate: a Late Jurassic–EarlyCretaceous carbon and oxygen isotope record. Journal of the Geological Society,London 161, 695–702.

Weissert, H., Lini, A., 1991. Ice age interludes during the time of greenhouse climate? In:Müller, D.W., McKenzie, J.A., Weissert, H. (Eds.), Controversies in Modern Geology.Academic Press, London, pp. 173–191.

Weissert, H., McKenzie, J., Judith, A., Channel, J.E.T., 1985. Natural variations in thecarbon cycle during the Early Cretaceous. In: Sundquist, E.T., Broecker, W.S. (Eds.),The Carbon Cycle and Atmospheric CO2: Natural variations Archean to the Present:Geophysical Monograph, 32, pp. 531–545.

Weissert, H., Lini, A., Föllmi, K.B., Kuhn, O., 1998. Correlation of Early Cretaceous carbonisotope stratigraphy and platform drowning events: a possible link? Palaeogeo-graphy, Palaeoclimatology, Palaeoecology 137, 189–203.

Westermann, S., Föllmi, K., Adatte, T., Matera, V., Schnyder, J., Fleitmann, D., Fiet, N., Ploch, I.,Duchamp-Alphonse, S., 2010. The Valanginian δ13C excursion may not be an expressionof a global oceanic anoxic event. Earth and Planetary Science Letters 290, 118–131.

Wilpshaar,M., Leereveld, H., Visscher, H., 1997. Early Cretaceous sedimentary and tectonicdevelopment of the Dauphinois Basin (SE France). Cretaceous Research 18, 457–468.

Wortmann, U.G., Weissert, H., 2000. Tying platform drowning to perturbations of theglobal carbon cycle with a δ13Corg-curve from the Valanginian of DSDP Site 416.Terra Nova 12, 289–294.