Paleoenvironmental changes during the Valanginian: New insights fromvariations in phosphorus contents and bulk- and claymineralogies in thewestern Tethys

Stéphane Westermann a,b,⁎, Stéphanie Duchamp-Alphonse c, Nicolas Fiet d, Dominik Fleitmann e,f,Virginie Matera g, Thierry Adatte b, Karl B. Föllmi b

a Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, CH, Switzerlandb Institute of Earth Sciences, University of Lausanne, Géopolis, 1015 Lausanne, Switzerlandc UMR 8148-I.D.E.S., Bât. 504, University of Paris Sud, 91405 Orsay Cedex, Franced AREVA, 33 Rue La Fayette, 75009 Paris, Francee Institute of Geological Sciences, University of Bern, Baltzerstrasse 1-3, 3012 Bern, Switzerlandf Department of Archaeology, School of Human and Environmental Sciences, University of Reading, RG6 6AB Reading, UKg IRSN, Avenue de Bourgogne, 54500 Vandoeuvre-Les-Nancy, France

a b s t r a c ta r t i c l e i n f o

Article history:

Received 20 September 2012

Received in revised form 16 August 2013

Accepted 19 September 2013

Available online 25 September 2013

Keywords:

Clay mineralogy

Detrital index

Phosphorus

Valanginian

Climatic changes

Carbon cycle perturbation

Tethys

Paleoenvironmental and paleoclimatic changes during theValanginian carbon isotopic excursion (CIE) have been

investigated in the western Tethys. For this purpose, bulk-rock and clay mineralogies, as well as phosphorus

(P) contents were evaluated in a selection of five sections located in the Vocontian Basin (Angles, SE France;

Alvier, E Switzerland; Malleval, E France), and the Lombardian Basin (Capriolo, N Italy; Breggia, S Switzerland).

Within the CIE interval, bulk-rock and clay mineralogies are inferred to reflect mostly climate change. The onset

of the CIE (Busnardoites campylotoxus ammonite Zone) is characterized by higher detrital index (DI: sum of

the detritalminerals dividedby calcite contents) values and thepresence of kaolinite in their clay-mineral assem-

blages. In the late Valanginian (from the Saynoceras verrucosum Zone up to the end of the Valanginian), the sam-

ples show relatively variable DI and lower values or the absence of kaolinite. The variation in the mineralogical

composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions

associated with an increase in terrigenous input on the southern European margin during the CIE towards an

overall unstable climate associated with drier conditions in the late Valanginian. This is contrasted by a dissym-

metry (proximal vs distal) along the studied transect, the northern Tethyan margin being more sensitive to

changes in continental input compared to the distal environments.

P accumulation rates (PAR) present similar features. In the Vocontian basin, P content variations are associated

with changes in terrigenous influx, whereas in the Lombardian basin (i.e. Capriolo and Breggia), PAR values

are less well correlated. This is mainly because the deeper part of the Tethys was less sensitive to changes in

continental inputs. The onset of the CIE (top of the B. campylotoxus Zone) records a general increase in PAR

suggesting an increase in marine nutrient levels. This is linked to higher continental weathering rates and the

enhanced influx of nutrients into the ocean. In the period corresponding to the shift itself, P contents show a

dissymmetry between the Vocontian and Lombardian basins (proximal vs distal). For the sections of Malleval,

Alvier and Angles, a decrease in P concentrations associated to a decrease in detrital input is observed. In Capriolo

and Breggia, PAR show maximum values during the plateau, indicating a more complex interaction between

different P sources. The time interval including the top of S. verrucosum Zone up to the end of the Valanginian

is characterized by variable PAR values, suggesting variable nutrient influxes. These changes are in agreement

with an evolution towards seasonally contrasted conditions in the late Valanginian.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The Valanginian includes the first major perturbation in the Creta-ceous carbon cycle, the so-called “Weissert event” (Erba et al., 2004),which is defined by a positive excursion in marine carbonate- andmarine and terrestrial organic-carbon isotope records (Lini et al., 1992;Föllmi et al., 1994; Weissert et al., 1998; Hennig, 2003; Erba et al.,

Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

⁎ Corresponding author at: Institute of Geochemistry and Petrology, ETH Zürich,

Clausiusstrasse 25, 8092 Zürich, CH, Switzerland. Tel.: +41 44 632 37 45; fax: +41

44 632 11 12.

E-mail address: stephane.westermann@erdw.ethz.ch (S. Westermann).

0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved.

http://dx.doi.org/10.1016/j.palaeo.2013.09.017

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology

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

2004; Gröcke et al., 2005; Föllmi, 2012). In contrast to younger pertur-bations (e.g. Aptian, Cenomanian–Turonian: Schlanger and Jenkyns,1976; Jenkyns, 1980; Jenkyns et al., 1994; Leckie et al., 2002; Erba,2004; Kuypers et al., 2004; Mort et al., 2007), organic-rich deposits cor-responding in time to the Valanginian carbon-isotope excursion (CIE)are limited to a few localities (Herbin et al., 1983; O'Connell, 1990; Erbaet al., 2004; Westermann et al., 2010; Kujau et al., 2012). Nevertheless,the Valanginian δ13C shift is coeval with paleoenvironmental changes(Fig. 1) indicated by a crisis in carbonate-producing biota in both neritic(shallow-water ecosystems) and (hemi-) pelagic environments (calcare-ous nannofossils and especially nannoconids) (Lini et al., 1992; Erba andTremolada, 2004;Duchamp-Alphonse et al., 2007). In the northern Tethy-an Helvetic realm, the onset of the Valanginian CIE marks a long-lastingdrowning episode (“D1”, Föllmi et al., 1994, 2006), which is documentedby the presence of condensed glauconite and phosphate-rich sediments(Gemsmättli member, Fig. 1; Föllmi et al., 2007). Fundamental changesin the carbonate factory have, however, already been observed in the ear-liest Valanginian with the switch from photozoan to heterozoan assem-blages and a first platform drowning phase, which predates theValanginian carbon-isotope excursion (Fig. 1; Föllmi et al., 2006, 2007).

A weathering-productivity feedback model has been proposed to ex-plain the Valanginian CIE. In this model, greenhouse conditions, due tovolcanism, induced higher nutrient input into the oceans,which triggeredmarine productivity (Lini et al., 1992; Weissert et al., 1998; Erba et al.,2004; Weissert and Erba, 2004). However, many aspects of this modelstill remain unclear. For example, the formation of the Paraña–Etendekabasaltic plateau has been proposed as a potential trigger (Lini et al.,1992; Weissert et al., 1998; Peate, 2009; Duchamp-Alphonse et al.,2011). A recent revision and precision of its age (134.7 Ma; Thiede andVasconcelos, 2010) preclude, however, its correlation with the positiveCIE according to the latest calibration of the Early Cretaceous time scale(Gradstein et al., 2012).

Furthermore, the evolution of the Valanginian climate is not wellconstrained. The Early Cretaceous has generally been thought as agreenhouse period with high atmospheric CO2 content (Royer et al.,2007),which is in agreementwith recent TEX86 data suggesting a ratherstable and relatively warm climate throughout the Valanginian stage(Littler et al., 2011). This is, however, in contrast with evidence for a

cooling event during the late Valanginian (Saynoceras verrucosum

ammonite zone), which is provided by several geochemical proxies(i.e., δ18O values from belemnite and fish teeth, Mg/Ca ratios frombelemnite calcite and δ13C data from terrestrial fossil plant material;van de Schootbrugge et al., 2000; Price et al., 2000; Mutterlose andKessels, 2000; Pucéat et al., 2003; Gröcke et al., 2005; McArthur et al.,2007), and by biomarkers (Brassel, 2009). More recently, the study ofclay-mineral assemblages from the Angles section (SE France) providedfor the first time high-resolution evidence of rapid climate changesduring the Valanginian with a warm and humid climate during theδ13C shift and drier, probably cooler conditions directly following theexcursion (S. verrucosum Zone; Duchamp-Alphonse et al., 2011).

Despite the ongoing debate on the Valanginian climate, only a fewhigh-resolution studies offer a long-term climatic reconstruction duringthe positive CIE. The temporal evolution in clay and bulk-rock mineral-ogies has been used to study climate changes through other periods ofthe Early Cretaceous (Ruffell and Blattern, 1990; Adatte et al., 2002;Ruffell et al., 2002; Godet et al., 2008). Clayminerals are valid indicatorsof the intensity ofweathering processes in the source areas sinceminer-alogical variations are mainly influenced by average changes in humid-ity, temperature and seasonality (Ruffell et al., 2002). Climate variationshave also a direct influence on the export rates of continental nutrients,such as P, into the oceans. P is an important and often limiting elementin primary productivity (Ingall and Jahnke, 1994; Tyrrell, 1999).Also, the P cycle is closely linked to the carbon cycle by two processes:(1) continental weathering during which atmospheric CO2 is trans-formed into HCO3

− and P is mobilized; and (2) photosynthesis, whichis often limited by P as a nutrient (Föllmi, 1996; Bodin et al., 2006).

In this study, bulk-rock and claymineralogies have been analyzed ina selection of deeper-shelf, hemipelagic and pelagic sections from thewestern Tethys, in order to reconstruct the changes in hydrolysis andthe related weathering conditions on the continents surrounding thisarea during the Valanginian. This has been complemented by the mea-surements of P contents and calculation of P accumulation rates (PAR)to see if temporal and spatial variations in nutrient supply can be traced.Thismay help to improve our understanding of themechanisms leadingto the positive δ13C excursion and the associated paleoenvironmentalchanges during the Valanginian.

2 2.51 1.5 3 +

Lower Kieselkalk

Upper Betliskalk

Upper Oehrlikalk

Büls

Platform drowning

phase D1,

Gemsmättli

Lower Betliskalk

Na

nn

oco

nid

crisis

11 129 10 13

cold warm

0 -0.40.4

VA

LA

NG

INIA

NB

ER

.H

AU

T.

pertransiens

boissieri

campylotoxus

verrucosum

peregrinus

furcillata

radiatus

loryi

ST

AG

E

AMMONITE

BIOZONES

13C

(‰ VPBD) SEA-LEVEL

(long/short term)

HELVETIC

RECORD

Mg/Ca

(mM/M)

18Obel

(‰ VPBD)

B

Aea

rly

late

Fig. 1. Trends in environmental and climate-sensitive parameters through the Valanginian calibrated in time against ammonite biostratigraphy (Gradstein et al., 2012). Bulk-rock δ13C

record after Föllmi et al. (2006), Mg/ca ratios and δ18O from belemnites after McArthur et al. (2007), long- (A) and short-term (B) sea-level change after Haq et al. (1988) and Hardenbol

et al. (1998), and the evolution of the Helvetic platform after Föllmi et al. (2006).

197S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

2. Geological setting

Five sections from the western Tethys have been selected along ashelf/basin transect in order to characterize spatial and temporalchanges in weathering conditions, terrigenous inputs and nutrientlevels during the Valanginian. Tracing these changes along a shelf/basin transect will help to i) distinguish regional paleoenvironmentalvariations frommore global trends, ii) assess the influence of the differ-ential settling on clayminerals and iii) estimate the impact of diagenesison the primary environmental signal.

The five sections have been selected according to the followingcriteria: the presence of the Valanginian CIE interval, a good temporalframework provided by previous studies, and their paleogeographicalposition in the western Tethys (Fig. 2).

2.1. The central Tethyan realm

In order to characterize the distal, pelagic environment, the sectionsof Capriolo and Breggia have been selected. The Capriolo section is situ-ated in an abandoned quarry near the village of Capriolo (northern Italy,Lini et al., 1992; Fig. 2). The Breggia section outcrops in the MonteGeneroso half-graben close to the Breggia River (southern Switzerland;Bersezio et al., 2002; Fig. 2). Both sections belong to the LombardianBasin, one of the major rift-related basins of the Mesozoic Tethys pre-served in the southern Alps (Weissert and Bernoulli, 1985). The UpperJurassic to Lower Cretaceous sediments (Maiolica Formation, upperTithonian to lower Aptian; Lini et al., 1992) consist of a monotonoussuccession of white to gray limestones with chert nodules and bands.The temporal framework is provided in both sections by magneto-stratigraphy, nannofossil biostratigraphy and carbon-isotope stratigra-phy (Channel et al., 1987, 1993; Channel and Erba, 1992; Lini et al.,1992; Bersezio et al., 2002).

2.2. The northern Tethyan margin

Three localities have been studied to characterize the northernTethyan margin, with the sections of Alvier (eastern Switzerland) and

Malleval (Vercors, eastern France) characterizing the deeper shelf envi-ronment, and the section of Angles, representing the hemipelagic realmof the Vocontian basin (Fig. 2). The Alvier section, located along a cliffnear Sargans and Buchs (eastern Switzerland), corresponds to theouter part of the shelf. This section is composed by amonotonous lime-stone and marly-limestone succession. The base of the section belongsto theDiphyoides Formation (Valanginian) and the top to the KieselkalkFormation (Hauterivian; Briegel, 1972). The stratigraphic framework isgiven by the δ13C record (Föllmi et al., 1994). The section of Malleval islocated along a road between Malleval and the inn of Lombardière(Vercors, eastern France). It consists of a limestone succession coveringthe Busnardoites campylotoxus and S. verrucosum Zones (Blanc, 1996).The section of Angles outcrops along the road to St André-les-Alpesand represents the deeper part of the Vocontian basin (SE France;Busnardo, 1965; Fig. 2). It consists of a hemipelagic marl-limestonealternation well dated by ammonoids (Cotillon, 1971; Bulot andThieuloy, 1994; Reboulet and Atrops, 1999), calcareous nannofossils(Manivit, 1979; Duchamp-Alphonse et al., 2007), calpionellids(Allemann and Remane, 1979), and carbon-isotope chemostratigraphy(Duchamp-Alphonse et al., 2007).

3. Methods

3.1. X-ray diffraction

X-ray diffraction analyses were performed to identify and quantifythe bulk-rock and clay-mineral assemblages. The mineralogical compo-sition is determined by using a semi-quantifying method described byKübler (1987) and Adatte et al. (1996) on a SCINTAG XRD 2000 diffrac-tometer. This method allows the semi-quantification of the whole-rockmineralogy (obtained by XRD patterns of random powder samples) byusing external standards with an error varying between 5 and 10% forthe phyllosilicates and 5% for grain minerals.

For the bulk-rock analyses, about 800 mg of powdered sample waspressed in a powder holder. The different minerals recognized andquantified are calcite, phyllosilicates, quartz, Na plagioclase (albite)and K feldspar (microcline). Poorly crystallized minerals (goethite for

30°N

10°N

20°N

HELVETICS

VOCONTIAN

TROUGH

LOMBARDIAN

BASIN

B

1

2

4

3

5

FRANCE

ITALY

GERMANY

MERDITERRANEAN

SEA

SWITZERLAND

A

12

4

3

5

1

2

3

Capriolo

Breggia

Angles

4

5

Alvier

Malleval

Volcanism

Fault

Oceanic subduction

Thrust

Active spreading ridge

Transform fault

Legend

Emerged land

Shallower water

Intermediate water

Deep-sea water

Fig. 2. A. Localization of the studied sections. B. Paleogeographic map of the western Tethys in the Early Cretaceous.

Redrawn after Hennig et al. (1999) and references therein.

198 S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

example), and ankerite and dolomite were not quantified due to thelow intensity of their respective peaks and were included in the non-quantified component of the sample.

With regard to the clay-mineral assemblages, we identified mica,kaolinite, smectite, chlorite, illite–smectite mixed layers for this study.Samples were decarbonated by 10% HCl during 20 min. After beingwashed, the insoluble residue was centrifuged in order to separatetwo granulometric fractions (b2 μm and 2–16 μm) (see Adatte et al.,1996 and references therein for more information). The selected frac-tion is then pipetted and deposited on a glass plate. A first analysis isperformed after air-drying at temperature room, a second one after sat-uration of the sample with ethylene-glycol, in order to identify swellingminerals, and a third one after heating at 350 °C for selected samples.

3.2. Phosphorus contents

Total P analyses were performed on bulk-rock samples. 1 mL of 1 MMg(NO3)2was added to 100 mg of powder and left in an oven at 130 °Cduring 2 h to oxidize the organicmatter. Then, the samples were heatedat 550 °C during 2 h. After cooling, 10 mL of HCL (1 N) was added inorder to liberate the P from the sediment matrix and the solutionswere placed in a shaker during 16 h. The solutions were filtered(0.45 μm) and analyzed using the ascorbic acid method (Eaton et al.,1995). For this process, the solutions were diluted ten times andmixedwith 100 μLmolybdatemixing reagent to formphosphomolybdicacid. 100 μL of ascorbic acidwas added to the solution to reduce the acidand produce a blue color to the solution, which intensity is dependenton the P concentration. Total P analyses were performed on bulk rockusing a UV/Vis spectrophotometer (Perkin Elmer UV/Vis Spectropho-tometer Lambda 10, λ = 865 nm). Individual samples were measuredthree times and precisionwas better than 5%. Replicate analyses of sam-ples have a precision better than 10% in the case of low P concentrations(such as in samples of the Capriolo and Malleval sections) and betterthan 5% in the other sections.

3.3. Carbon isotopes

Carbon-isotope analyses were performed on powdered bulk-rocksamples at the University of Paris XI (IDES laboratory, France) using aVG Optima triple collector instrument mass spectrometer, and at theUniversity of Bern, Switzerland, using a Finnigan Delta V Advantagemass spectrometer equippedwith an automated carbonate preparation(Gas-Bench II) (Thermo Fisher Scientific AG, Reinach, Switzerland). Theresults were calibrated to the Vienna Pee Dee Belemnite (V-PDB) scalewith the standard deviation of 0.06%. The δ13C measurements havebeen used to calibrate the stratigraphic position of the studied sampleswith the previously published δ13C curves of the sections.

4. Results

Mineralogical analyses (bulk rock and clay fraction) and P contentshave been performed on the samples from the sections of Capriolo,Breggia, Alvier and Malleval. The P distribution has been investigatedat the Angles section (SE France; Fig. 2) in complement to the high-resolution mineralogical study (bulk-rock and clay-fraction) recentlypublished by Duchamp-Alphonse et al. (2011).

4.1. The Capriolo section

The bulk-rock mineralogy of the Capriolo section is dominated bycalcite, with an average proportion of 86% (Fig. 3). Phyllosilicateand quartz contents show rather low values never exceeding 7%.Phyllosilicates decrease slightly in the first part of the section from 6%at the base of the section (CM 14; Fig. 3) to 3% at the onset of the δ13Cexcursion (CM 12; Fig. 3). The positive C-isotopic shift is marked by an

increase in phyllosilicates (up to 7%), and followed by a decreasingtrend in the second part of the section (to 2% in the CM 10 N).

Clay-mineral assemblages (fraction b 2 μm) of the Capriolo sectionare composed of smectite, mica, I/S mixed layers, kaolinite and chlorite(Fig. 3). Smectite andmica dominate the clay-mineral spectrawith an av-erage abundance of approximately 50% and 30%, respectively. The onsetof the CIE interval is characterized by low smectite values (between 0and 6%) and amaximum inmica content (up to 75%). Kaolinite contentsshow rather low values (with an average of 2%) along themeasured sec-tion. In the sediment belonging to CM12 (i.e. just before the δ13C shift;Fig. 3), higher kaolinite values are observed, with a maximum of 16%.

Total P values vary between 66 and 203 ppm (Fig. 3). A slightly de-creasing trend is observed close to the Berriasian–Valanginian boundary(from 147 to 66 ppm), followed by an increase in the lower part of theValanginian sediments (up to 215 ppm in the CM 12). At the onset ofthe positive CIE, P contents remain rather constant, fluctuating around120 ppm. In the interval corresponding to the positive excursion inδ13C, a peak reaching 154 ppm is observed (Fig. 3).

4.2. The Breggia section

As for Capriolo, the bulk-rock mineralogy in the Breggia section isdominated by calcite contentswith valuesfluctuating aroundan averagevalue of 89% (Fig. 4). Quartz and phyllosilicate contents never exceed 15and 10%, with average values of 4% and 5% of the bulk-rock mineralogy,respectively. If present, plagioclase and feldspar contents are very lowand represent less than 1% of the bulk-rock mineralogy (Fig. 4).

In the insoluble residue of the b2 μm fraction, smectite and micadominate the assemblages and show opposite trends (Fig. 4). In thelower part of the section (0–2 m), smectite contents show relativelyhigh values (up to 80%), which decrease to 4% in the interval justbelow the onset of the positive δ13C shift. This is coeval with an increaseof the mica content from 7% to 39%. Then, smectite increases again (upto 78%) in the interval corresponding to the CIE. Kaolinite and chloritecontents show relatively low values (average of 3% and 5%, respective-ly). The interval corresponding to the onset of the δ13C shift is, however,marked by significantly high kaolinite and chlorite contents (up to 12%and 11%, respectively; Fig. 4).

P contents display rather stable values at the base of the section,fluc-tuating around an average value of 98 ppm (Fig. 4). A slightly increasingtrend is observed in the interval just below the CIE and followed by amarked peak of 187 ppm at the onset of the positive δ13C excursion. Asecond increase in P values is observed during the magnetochronCM11 with values fluctuating around 110 ppm (Fig. 4).

4.3. The Angles section

P contents display a rather scattered evolution along almost thewholesection with short-term variations (Fig. 5). However, a long-term trendcan be distinguished. In the first part of the section (from the top of theSubthurmannia boissieri Zone to the top of the B. campylotoxus Zone), Pcontents show decreasing values from 600 to about 200 ppm (Fig. 5).The following interval, encompassing the top of the B. campylotoxus

Zone and the S. verrucosum Zone (i.e., the CIE interval), is characterizedby rather low and stable values (fluctuating around 200 ppm)interrupted by a sharp peak of 623 ppm at the B. campylotoxus–

S. verrucosum transition. In the second half of the section (from theNeocomites peregrinus to the Acanthodiscus radiatus Zones), P valuesshow a long-term increasing trend to 640 ppm in A. radiatus Zonecontrasted by short-term decreases at approx. 180, 200 and 230 mreaching 107, 113 and 287 ppm, respectively (Fig. 5).

4.4. The Alvier section

Calcite is the dominantmineral throughout themeasured Alvier sec-tion. The section displays, however, the highest quartz contents of all

199S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

Capriolo, Italy

Lithology

limestone marlchert slumped interval

VA

LA

NG

INIA

NB

ER

RIS

IAN

CM

10 N

CM

11

CM

12

CM

13

CM

15

CM

14

3.01.5 2.0 2.5

Sta

ge

Magneto

chr.

0

10

(‰ to PDB)

Ptot

0 100 200

Calcite Quartz Mica Smectite Kaolinite Chlorite I/SPhyllo-

silicates

25 2 6 2 6 25 7575 25 75 5 15 10 30 10 40

(ppm)

(relative %)

Bulk-rock

Mineralogy

<2 µm fraction

Mineralogy

Fig. 3.Mineralogy (bulk-rock and clay-mineral assemblage, expressed in relative % and P content (in ppm) variations along the section of Capriolo. The temporal framework is given by the

δ13C curve (Lini et al., 1992) and magnetostratigraphy (Channel and Erba, 1992). The gray band indicates the position of the Valanginian shift in δ13C.

CM

10n

CM

11

CM

11n

?

VA

LA

NG

INIA

NS

tage

Magneto

chr.

2.51.5 2.01.0

Breggia, Switzerland

10

0

100 200015 4 8525 75 25 7510 40 5 15 20 604 12

Lithology

limestone chert slumped interval

Calcite QuartzPhyllo-

silicatesMica Smectite Kaolinite Chlorite I/S Ptot

(ppm)(‰ to PDB) (relative %)

Bulk-rock

Mineralogy

<2 µm fraction

Mineralogy

Slump interval

Slump interval

Fig. 4. Bulk-rock mineralogy (%), clay-mineral distribution (%), and P contents (in ppm) along the Breggia section. Chemo- and magnetostratigraphy is after Channel et al. (1993). The

stratigraphic position of the positive shift in C-isotopes is indicated by the gray band.

200 S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

sections studied here, with values fluctuating around the average valueof 13% (Fig. 6). A slight decrease in quartz is observed in the intervalcorresponding to the CIE (average value of 7%). Phyllosilicate contentsremain rather constant with an average value of 5% (Fig. 6). Feldsparand plagioclase contents show relatively low values, close to the quan-tification limit.

P contents show rather low values (with an average value of200 ppm) from the base of the section to 30 m upward. The sedi-mentary interval corresponding to the onset of the CIE is markedby higher values (790 ppm) followed by a slight decrease (to an averagevalue of 300 ppm) in the S. verrucosum Zone. The top of the section ischaracterized by a second increase in P contents up to 798 ppm in theN. peregrinus Zone (Fig. 6).

4.5. The Malleval section

Calcite contents show rather high values along most of the Mallevalsection, fluctuating around 92%, except at approximately 20 and 75 mabove the base of the sectionwhereminima (69% and 81%, respectively)are observed. The quartz content shows an inverse trend, with twointervals of higher values between 15–25 m, and 60–80 m, reaching 6and 8%, respectively. Phyllosilicate contents tend to mirror quartz con-tents, but remain relatively low along the section fluctuating between2 and 5%.

In the insoluble residue of the b2 μm fraction, kaolinite and smectitedominate the assemblages, with average values of 39 and 20%, respec-tively (Fig. 7). Given the distribution of these two minerals, the sectioncan be divided into three intervals: a first interval (from the base to15 m) dominated by kaolinite (with an average of 75%); a second inter-val (from 20 to approximately 45 m) showing a transition betweenkaolinite and smectite-dominated clay minerals; and a third interval

Angles, France

0

10 30 1 2

cam

pylo

toxus

pert

rans.

pert

r.in

o.

call.

bois

. p. p.

bois

. p. p.

pere

grinus

furc

illata

radia

t.

radia

t.

verr

ucosum

verr

ucosum

trin

odosum

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phanophoru

s

earl

y V

ala

ng

inia

nla

te V

ala

ng

inia

nB

err

ias

ian

Hau

t.S

tage

Bio

zon

es

Bio

zon

es

400 6000 200

(ppm)(‰ to PDB)

Ptot

Lithology Limestone Marl

(b) (a)

Fig. 5. Total P contents (in ppm) at the Angles section. The temporal framework is given by

the δ13C curve (Duchamp-Alphonse et al., 2007) and the ammonite biostratigraphy(a; Bulot

and Thieuloy, 1994), both calibrated on the concise geologic time scale (b, Gradstein et al.,

2012). The gray band indicates the position of the positive excursion in δ13C.

cam

pylo

toxus

pert

ransie

ns

pere

grinus

verr

ucosum

2.00.5 1.0 1.5

0

10

earl

y V

ala

ng

inia

nla

te V

ala

ng

inia

nB

err

iasia

nS

tage

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zones

400 600 8000 200

Limestone Marly limestone

Lithology

Alvier, Switzerland

(‰ to PDB)

PtotCalcite QuartzPhyllo-

silicates

25 75 5 20 2 6 10

(ppm)

(relative %)

Fig. 6. Bulk-rockmineralogy (%) and P contents (in ppm) along the section of Alvier. The temporal framework is given by the δ13C curve (Föllmi et al., 1994). The stratigraphic position of

the positive shift in C-isotopes is indicated by the gray band.

201S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

(45 m to the top of the section) dominated by smectite (with an aver-age of 60%).

In the B. campylotoxus Zone, P contents display a maximum value of285 ppm (at 12 m approx. from the base of the section) followed bya decreasing trend to 45 ppm (from 23 to 30 m from the base of thesection). Around the B. campylotoxus–S. verrucosum Zone boundary(onset of the CIE), P contents remain low with a minimum of 26 ppm.Then, at 60 m, an increase to 175 ppm is observed, corresponding tothe S. verrucosum Zone (top of the δ13C shift).

5. Discussion

5.1. Mineralogy as paleoenvironmental index

i) Diagenetic overprint

In marine settings, changes in bulk-rock mineralogy and clayfraction may record paleoenvironmental changes and/or a diageneticoverprint. Thus, before any paleoenvironmental interpretation, it isimportant to estimate the diagenetic impact on the mineralogical com-position of each section, especially in the clay-fraction assemblages.Most authigenic clay-mineral formations (recrystallization and theformation of new minerals) occur during burial diagenesis. It has beendemonstrated that burial diagenesis may result in the replacement ofsmectite by chlorite and illite in the calcareous beds andmarly interbeds,respectively, and an increase of the proportion of regularly mixed inter-stratified illite–smectite (I/S) with the burial depth (Chamley, 1989;Deconinck, 1993; Kübler and Jaboyedoff, 2000; Godet et al., 2008). Inthe studied sections, the relatively high smectite and kaolinite contentscompared to regular mixed I/S indicate a significantly lower diageneticoverprint (Godet et al., 2008). Furthermore, the diversity of the clay

minerals and the presence of significant variations (N5%) in themineral-ogical composition and the lack of any continuous vertical trend withinthe selected sections (b100 m-thick except for the Angles section that is240 m-thick) suggest a relatively low impact on the primary environ-mental signal by burial diagenesis (Duchamp-Alphonse et al., 2011,and references therein). Therefore, the trends in both bulk-rock andclay-mineral assemblages can be used as paleoenvironmental proxies.

Illite crystallinity (Kübler index) and isograds for kaolinite/pyrophyllite and glauconite/stilpnomelane have evidenced a strongtectonic overprint, showing a general increase in the diagenetic gradefrom north to south in the Helvetic Alps of eastern Switzerland (Wanget al., 1996). For this reason, clayminerals in the samples from theAlviersection have not been investigated.

ii) Climate versus sea-level signal

The distinct trends in the bulk and clay mineralogies observedalong the studied transect are interpreted as reflecting variationsin weathering processes in the source areas. The formation of clayminerals in terrestrial soils depends on the type of rocks and climaticconditions. Kaolinite (K) preferentially forms under tropical or subtrop-ical conditions (i.e., under warm and humid climate conditions), where-as mica (M) and chlorite (Chl) form under cool to temperate, dryconditions with low hydrolysis conditions (Chamley, 1989). Smectiteoriginates either from tropical soil under semi-arid and seasonallycontrasted climatic conditions or as a weathering by-product of basaltwith a strong contrast between dry and wet seasons (Chamley, 1989).The presence or absence of smectite will therefore give detailed insightson climate seasonality. Apart from climate change on the adjacent con-tinent, the mineralogical composition of the detrital fraction in marinesediments is influenced by sea-level variations (Chamley, 1989; Adatteet al., 2002) and the differential settling of clay minerals (Thiry, 2000;

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Fig. 7. Bulk-rock mineralogy (%), clay-mineral distribution (%), and P contents (in ppm) along the section of Malleval. The gray bands indicate the position of slumped intervals. The gray

band indicates the position of the Valanginian shift in δ13C.

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Godet et al., 2008). The differential settling of clay minerals is mainlycaused by the physical segregation of clay particles, related to theirdifferent sizes (Chamley, 1989). Thus, dense and coarser minerals (kao-linite, mica and chlorite) settle preferentially closer to the coast, in plat-form environments, whereas fine grained-minerals such as smectite arepreferentially carried into offshore basins. This may explain the relative-ly low values of kaolinite contents in the sections of Capriolo and Breggiacompared to the sections of Angles (Duchamp-Alphonse et al., 2011)and Malleval. Sea-level variations over longer time periods may alsoinfluence the clay assemblages due to the differential settling of clayparticles. Second-order sea-level change has been postulated to haveoccurred during the Valanginian (Haq et al., 1987; Hardenbol et al.,1998). A period of long-term sea-level fall has been proposed duringthe Tirnovella pertransiens Zone, followed by a major sea-level riseduring the B. campylotoxus Zone (Hardenbol et al., 1998). The intervalincluding the latest B. campylotoxus Zone to the base of the Hauterivianis characterized by a relatively steady and more stable long-term sea-level trend (Haq et al., 1987; Hardenbol et al., 1998). This has beencorroborated by the data obtained from the sequence stratigraphicstudy of the Angles section (Arnaud-Vanneau et al., 1982) and morerecently from the peri-Vocontian zone (Gréselle and Pittet, 2010). Sea-level variation may have influenced the clay mineral distributionsalong the studied sections during the early Valanginian, whereas thevariations observed during the latest early Valanginian up to theHauterivian are rather related to climatic change. Thus, the relativelyhigher kaolinite content observed at Capriolo may be linked to themajor sea-level drop at the top of the T. pertransiens Zone might as ithas been proposed for the Angles section (Duchamp-Alphonse et al.,2011).

iii) Change in weathering regime during the Valanginian CIE

As explained above, the period between the CIE interval (top of theB. campylotoxus–S. verrucosum zone) and the base of the Hauterivianis characterized by a steady sea-level highstand (Fig. 8; Haq et al.,1987; Hardenbol et al., 1998). The variations in themineralogical recordobserved during this time interval are, therefore, driven by paleoclimatechange and related fluctuations in hydrolytic conditions (Chamley,1989). In order to better distinguish the general trends, a detritalindex (DI) was calculated by dividing the sum of quartz, phyllosilicates,Na plagioclase, and K feldspar intensities by calcite (Fig. 8A). For thesections of Capriolo and Breggia, the presence of abundant radiolariansin thin sections has been observed. Therefore, for these sections, SiO2

contents have not been associated to quartz contents only, and havenot been taken into account when calculating the DI.

Just before the onset of the shift in δ13C (within the B. campylotoxus

Zone), a decreasing trend in DI values is observed along the studiedtransect (top of interval 1, Fig. 8A), with a higher magnitude in themore proximal sections (i.e. Malleval, Alvier and Angles) and a lowermagnitude in the pelagic sections (i.e. Capriolo and Breggia). Thesetrends are coeval with a significant decrease in kaolinite at MallevalandAngles, and slightly lower kaolinite contents at Breggia and Capriolo(Fig. 8B). These trends are interpreted to represent the consequence of adrier climate. The differences in the DI values observed between thesections from the northern Tethyan margin (i.e. Malleval, Alvier andAngles) and the “Lombardian” sections (i.e. Capriolo and Breggia) mayreflect a proximal–distal dissymmetry along the transect. The kaolinitedistribution is in agreement with this interpretation (significant de-crease in the proximal settings and lower but variable contents in distalsettings; Fig. 8B).

During the CIE (interval 2, Fig. 8A), from the top of the B. campylotoxus

Zone to the base of the S. verrucosum Zone, the more proximal sections(e.g. Alvier, Malleval and Angles) show a significant increase in DI valuesassociated with generally higher kaolinite contents (up to 80% for theMalleval section, Fig. 7) and K/(M + Chl) ratios (Fig. 8B). This generaltrend is contrasted by the slightly increasing trend in DI values of themore distal sections (i.e. Capriolo and Breggia) and their low kaolinite

content (average of 2%) associated to rather constant K/(M + Chl)values (Fig. 8 B). As for the latest early Valanginian, this divergence isprobably due to the proximal vs distal position of the sections. These re-sults indicate a renewed change towardsmore humid conditions duringthe Valanginian CIE, near the boundary between the early and the lateValanginian, which induced higher hydrolyzing conditions and a signif-icant increase in terrigenous inputs.

From the late Valanginian (S. verrucosum Zone) up to the earlyHauterivian (A. radiatus Zone), the bulk-rock and clay mineralogiesare characterized relatively by the variable DI and K/(M + Chl) values(Fig. 8B). However, based on the change in vertical variations of bulkand claymineralogies, two successive periods are distinguished. Duringthe second half of the S. verrucosum Zone (corresponding to the plateauin δ13C values, Interval 3a; Fig. 8A), a general decrease in DI is observed.These decreasing DI values are associated either with low values (in thesections of Malleval and Capriolo) or a slightly decreasing trend in thekaolinite abundances (in the Breggia section, this study, and Angles sec-tion, Duchamp-Alphonse et al. (2011); Fig. 8B). These changes in bulkand clay mineralogies are interpreted as being related to a decrease interrigenous input into the western Tethys, which was probably linkedto an evolution towards a drier climate on the surrounding continents(interval 3a, Fig. 8A). From the N. peregrinus Zone up to the base of theHauterivian, the general increase in DI recorded in the sections of Alvierand Angles is associated with an increase in smectite content at Angles(Duchamp-Alphonse et al., 2011) and might be the expression of aseasonally more contrasted climate during the late Valanginian (inter-val 3b, Fig. 8A). This is coherent with the report of a transition towardssediments where smectite represents up to 50% of the clay fraction inthe Jura Mountains from the late Valanginian to the Hauterivian(Adatte and Rumley, 1989).

5.2. Phosphorus as a proxy for global changes?

i) Phosphorus accumulation

The flux of dissolved P into the ocean is mainly controlled by conti-nental runoff (Föllmi, 1996; Delaney, 1998; Compton et al., 2000). Thetransfer of P into the sediments occurs by sedimentation of organic P,P adsorbed on surface-reactive particles, P in fish debris, or by directprecipitation (Ruttenberg and Berner, 1993; Filippelli and Delaney,1996; Föllmi, 1996). During early diagenesis, a part of the P trappedwithin the sediments may be removed and transferred back into thebottom waters. Early diagenetic P regeneration is redox dependentand becomes more efficient in oxygen-depleted bottom waters (Ingalland Jahnke, 1994; Van Cappellen and Ingall, 1996; Colman andHolland, 2000; Emeis et al., 2000; Tamburini et al., 2002; Bodin et al.,2006; Mort et al., 2007). Global P accumulation over large time scales(i.e. exceeding 10 kyr, the actual residence time of P; Ruttenberg, 1993;Filippelli and Delaney, 1996; Colman and Holland, 2000) is thereforedriven by twomain processes: (1) riverine input, which is linked to con-tinental weathering, and (2) oxygenation state of the ocean. A temporaldecrease in P accumulation may, therefore, indicate a decrease in conti-nental runoff and/or an expansion of anoxic bottom-water conditions.On the other way, an increase in P accumulation rates may be relatedto an increase in nutrient inputs and/or more oxygenated conditions.

ii) Comparison of the P accumulation rates along the studied transect

To avoid the masking effect of sediment condensation and to bettercompare the different sections, Phosphorus accumulation rates (PAR)expressed in mg/cm2/kyr have been calculated as followed:

PAR (mg/cm2/kyr) = [P](mg/g) × Sedimentation rate (cm/kyr) ×Rock density

Rock density is depending on the lithology. We used a rock densityequal to 2.5, 2.4 and 2.3 g/cm3 for limestone, shale andmarl, respective-ly (Attewell and Farmer, 1976). The sedimentation rates have beenconstrained using the δ13C record and the duration of ammonite zones

203S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

(Duchamp-Alphonse

et al., 2011)

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Terrigenous inputs and kaolinite variations

(Duchamp-Alphonse

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B) Distribution of kaolinite during the Valanginian CIE in the W-Tethys

0.40.20

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840

Fig. 8.Variations in detrital index (DI) and kaolinite (K) content though theValanginian in theWestern Tethys compared to the Angles section (Duchamp-Alphonse et al., 2011) and to the

global sea-level variation (Haq et al., 1988; Hardenbol et al., 1998). The distribution of kaolinite is compared to mica (M) and chlorite (Chl) for the sections of Capriolo, Breggia and

Malleval. The dark-gray band shows the stratigraphic position of the δ13C positive excursion in the five studied sections. The variations observed in the interval 1 are mainly reflecting

relative sea-level variations. The CIE interval (interval 2) records a general increase in terrigenous inputs (increasing DI) linked to higher hydrolysis conditions (higher kaolinite content).

The interval 3 is characterized by variable DI values and lower kaolinite contents reflecting a more contrasted climate.

204 S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

and magnetochrons calibrated with the time scale of Gradstein et al.(2012).

The average PAR obtained for the more proximal settings (Anglesand Alvier) shows 8–10 times higher values compared to the PAR ofthe more distal sections (Capriolo and Breggia, Fig. 9). This differencein absolute PAR values is likely related to the different paleogeographicpositions of the sections. Indeed, the paleogeographical location ofCapriolo andBreggia is remote fromany continental source, as indicatedby their low DI values (Fig. 8A). The low PAR values observed for thesesections are comparable to the values from theDeep Sea Drilling Project(DSDP) and Ocean Drilling Program (ODP) compilation from Föllmi(1995), and are probably related to the lower detrital influx rates tothis remote area.

For the early Valanginian, the general trends in the PAR correlatewith the PAR trend established from the DSDP and ODP data (Föllmi,1995). On a higher resolution scale, however, more scattered trendsare superimposed on this general pattern along the studied transect.The Breggia section shows a long-term increase in PAR in sedimentsbelow the δ13C excursion, which culminates in a maximum at theonset of the positive shift in δ13C. The Capriolo PAR curve correlatesonly moderately with that of the Breggia in that the maximum belowthe δ13C excursion is not evidenced (Fig. 9). At Angles and Alvier, apeak in PAR values occurred within the first half of the B. campylotoxus

Zone, followed by a decreasing trend leading lower P enrichmentstowards the onset of the Valanginian CIE (top of interval 1, Fig. 9). Alsothe Malleval section, for which the age model does not allow the calcu-lation of PAR, shows a similar trend in P contents in the segment, whichcorresponds in time to the period just below the δ13C excursion. Thesedifferent shorter-term trends seem to be influenced by the paleogeo-graphical location of the different sections and probably reflect changesin the P delivery rate from the continent and fractionation along thetransect studied (Froelich et al., 1982; Föllmi, 1995; Filippelli, 2008) asno evidence formajor change in the oceanoxygenation state is observed

in thewestern Tethys during the Valanginian (Westermann et al., 2010;Kujau et al., 2012). In proximal settings, the higher PAR values withinthe early B. campylotoxus Zone are more likely the consequence of thehigh-amplitude transgression and the related disappearance of thereef barrier platform on the northern margin of the Tethys (Föllmiet al., 2006, 2007) leading to changes in the sediment flux towards theopen ocean. During the late B. campylotoxus Zone, the decreasing trendin PAR is mirrored in the Helvetic domain by the development of anew platform (Föllmi et al., 2006, 2007). The deeper parts of the Tethys,being less sensitive to these local input variations, may have recorded amore averaged signal of the seawater P content. The progressiveincrease in PAR values observed along the sections of Capriolo andBreggia is therefore interpreted as a general increase in P burial fluxinto the sediments during the early Valanginian (B. campylotoxus

Zone; Fig. 9, interval 1), and indicates higher nutrient levels present inocean waters.

The period corresponding to the CIE itself displays unsteady but gen-erally high PAR values in the pelagic basin, and rather low PAR values onthe shelf. During this time interval, the trends are less well correlatedbetween the measured sections, which seem to be related to the paleo-geographical location of the sections. At Capriolo and Breggia, PARincrease at the end of the shift and show maxima during the plateauin δ13C (S. verrucosumZone),whereas at Angles andAlvier, theCIE inter-val is characterized by relatively low PAR values and a sharp peak nearthe B. campylotoxus–S. verrucosum boundary (interval 2, Fig. 9). Thegood agreement of the trend observed in the basinal sections withthe compiled data set of the NW Tethys (van de Schootbruggeet al., 2003) suggests that the higher PAR values at Capriolo andBreggia are related to a general increase in P content of seawater ata larger scale (at least the western Tethys). Two mechanismsexerting control on large-scale P accumulation have been proposedfor the Valanginian (van de Schootbrugge et al., 2003): (1) eustaticsea-level rise, and (2) change in weathering conditions. One of the

Ptot

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Fig. 9. Comparison of the evolution in P accumulation rates (PAR) along the studied sections with the global PAR curve (Föllmi, 1995). The sedimentation rates (SR) have been estimated

from magnetochron durations for the sections of Capriolo and Breggia (Channel and Erba, 1992; Channel et al., 1993) whereas for the sections of Angles and Alvier, they have been

calculated using the duration of ammonite zones. For the Malleval section, the stratigraphy did not allow to calculate accumulation rates. PAR and SR are expressed in mg/cm2/kyr and

cm/kyr, respectively. Before the CIE, an increasing trend or relatively higher values are observed (interval 1), indicating a higher nutrient level. During the shift (interval 2), PAR are

lesswell correlated, and probably related to the paleogeographical location of the different sections. Interval 3 (from the S. verrucosum to theN. peregrinus zone) shows variable PAR values.

205S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

effects of the Valanginian transgression was the establishment of agateway between the Tethys and Boreal realms through the PolishFurrow (Price et al., 2000; van de Schootbrugge et al., 2000). Withthis, cooler and possibly nutrient-enriched waters may have enteredthe Tethys in association with strong westerlies (Poulsen et al.,1998) and offshore currents, putting the western Tethys in a favor-able position for P accumulation (van de Schootbrugge et al., 2003).At Angles and Alvier, the lower PAR values are reflecting a local trendprobably related to the presence of a heterozoan platform in the north-ern margin of the W-Tethys (Föllmi et al., 2006, 2007), preventing Paccumulation in the deeper part of the northern Tethyan margin(Vocontian basin). The rapid increase in PAR near the B. campylotoxus–

S. verrucosum boundary at Angles andAlviermay reflect a shorter periodof intense weathering at the beginning of the positive shift in δ13C.

The period following the δ13C excursion (from the top of S. verrucosumZone up to the base of the Hauterivian) is characterized by variable PARvalues, suggesting variable nutrient influx (Fig. 9). In the proximal set-ting, a good correlation between DI and PAR is observed, suggestingthat a strong control has existed on P delivery to the ocean by the conti-nental weathering regime and associated terrigenous output.

5.3. Towards a paleoenvironmental model for the Valanginian?

During theValanginian, the variations in bulk-rock and claymineral-ogies, as well as in P contents, recorded in the western Tethys, along abasin–shelf transect appear to be related to both regional and globalenvironmental changes. These variations seem to bemost especially re-lated to changes in the weathering pattern on the surrounding conti-nents, and to the paleogeography (Vocontian vs Lombardian Basin),but also the specific position of the sections within each basin. Duringthe CIE (from the top of the B. campylotoxus Zone to the base of theS. verrucosum Zone), warmer and more humid conditions prevailed,which led to higher terrigenous inputs from the continents to theocean. This is suggested by higher DI and K/(M + Chl) values alongthe northern Tethyan margin (i.e., in more proximal settings). Thisobservation finds its confirmation in reports on increases in overall de-trital, iron and Mn flux rates during the Valanginian CIE (Weissert andBréhéret, 1991; Kuhn et al., 2005; Westermann et al., 2010) and higherhydrolyzing conditions across the early/late Valanginian boundary(Duchamp-Alphonse et al., 2011). Higher terrigenous inputs may haveincreased the general nutrient level in the ocean as shown by the globalPAR curve (Föllmi, 1995). Enhanced supply of P during the earlyValanginian may have led to higher trophic levels in the ocean andtriggered the intensification of primary productivity and eutrophisationof the ecosystems. This is consistent with the report of two phases ofplatform drowning in the Helvetic realm (top of the T. pertransiens tothe base of the B. campylotoxus Zones, and S. verrucosum to Crioceratites

loryi Zones; Föllmi et al., 1994, 2006). The decrease in PAR recordedwithin the Vocontian basin is coeval with the development of aheterozoan platform in the Helvetic realm (Föllmi et al., 2006). Thissuggests that, despite lower PAR values, the nutrient level must haveremained high enough to sustain a green water mode carbonate pro-duction. This is also in agreement with the report of high-fertility incoccolithophorids during the CIE interval (Erba and Tremolada, 2004;Erba et al., 2004; Duchamp-Alphonse et al., 2007; Bornemann andMutterlose, 2008).

The early/late Valanginian boundary corresponds to an overturn inthe evolution of the Valanginian climate. In the S. verrucosum Zone, adrop in terrigenous input associated with a decrease or disappearanceof kaolinite, is recorded in the proximal settings (interval 3a; Fig. 8Aand B), suggesting a change towards a drier and probably morecontrasted climate, as already proposed by Duchamp-Alphonse et al.(2011). This change in terrigenous influx is coeval with lower PARvalues in themore proximal sections. The Lombardian basin (character-izing the deeper environment) records an increase in PAR, probablyrelated to the arrival of cooler and nutrient rich water into the Tethys

(van de Schootbrugge et al., 2003). Also it corroborates previous geo-chemical studies (Mg/Ca and δ18O data), which depict a cooling eventduring the S. verrucosum Zone (van de Schootbrugge et al., 2000;Pucéat et al., 2003; McArthur et al., 2007; Brassel, 2009).

The environmental variations observed within the western Tethysare in agreementwith enhanced greenhouse conditions, probably relat-ed to increased pCO2. However, triggering mechanisms remain unclear(e.g. Föllmi, 2012). A link between the Paraña–Etendeka volcanic activ-ity and the Weissert event has been proposed (Erba et al., 2004). How-ever, recent radiogenic ages of the Paraña–Etendeka basalts (Thiedeand Vasconcelos, 2010) have dated its formation in the Hauterivianaccording the latest calibration of the Early Cretaceous (Gradsteinet al., 2012). The environmental changes leading to the ValanginianCIE seem to be related to the climatic changes that started during thelate Berriasian and the earliest Valanginian, where for the first time dur-ing the Cretaceous, the Earth was exposed to humid climate conditionson a larger scale (e.g. Föllmi, 2012; Morales et al., 2013). The enhancedgreenhouse conditions triggered a progressive increase in continentalweathering rates and nutrient transfer to the ocean, and enhanced up-welling in the ocean (Föllmi, 1995; van de Schootbrugge et al., 2003).This led to the installation of a dense vegetation cover on the continentand major evolutionary change both on the continent and in the ocean(cf Föllmi, 2012 and references therein). Surprisingly enough, evidencesforwidespread anoxia are lacking (Westermann et al., 2010). Thismightsuggest that the ocean circulation was strong enough to replenishdeeper waters with oxygen (Westermann et al., 2010). Vigorous oceansurface and subsurface circulation are indicated by the widespreadoccurrence of phosphorites (e.g. Föllmi, 2012).

Our data are contradictory to the TEX86 record obtained from proto-Atlantic DSDP sites, which shows relatively invariant tropical sea-surface temperatures (SSTs) for the Early Cretaceous (Littler et al.,2011), and suggest rapid changes in hydrologic and climatic conditionsduring the Valanginian CIE. This contrast may be linked to the paleoge-ography of the studied areas and regional differences in climate sensi-tivity between the tropics and the mid-latitudes (Littler et al., 2011).Recently, in the Middle Eocene, high-latitude cool temperatures havebeen evidenced during intervals showing high tropical SSTs comparableto those obtained for the Early Cretaceous (Stickley et al., 2009). Thus,the rapid changes observed in the continental inputs around the Tethysmight be the expression of an increased sensitivity at the northernmid-latitudes. The climatic variations observed in themid-latitudes dur-ing the Valanginian CIE may be controlled by an increase in organic-matter storage on continents (Westermann et al., 2010), as marineorganic-rich deposits of Valanginian age are restricted to marginal partthe global ocean (Herbin et al., 1983; O'Connell, 1990; Erba et al.,2004; Westermann et al., 2010). Increasing preservation of OM is as-sumed to act as a negative feedback on the pCO2, with the potential toenable the atmosphere–ocean system toweaken greenhouse conditionsand thus return to more stable conditions (Föllmi et al., 1994).

6. Conclusions

The analysis of the mineralogical composition (bulk-rock and clayfraction) combined with P content measurements performed along ashelf–basin transect in the western Tethys during the Valanginian CIEshows that:

1) A lack of symmetry (proximal vs distal) exists in the mineralogicaldistribution and P contents along the studied transect. This is relatedto regional differences in the paleogeography andpaleoceanographicconditions of each section. In the Vocontian basin (more proximalsettings), the mineralogical and geochemical variations show a rela-tion to change in weathering processes due to changes betweenmore arid and humid climate conditions. The Lombardian basin(more distal sections), being less affected by changes in continentalinfluxes, records less-well correlated trends.

206 S. Westermann et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013) 196–208

2) The Valanginian CIE is characterized by the prevalence of warmerand more humid climatic conditions, leading to higher terrigenousinputs in the western Tethys. This is coeval with higher P contentsindicating increased nutrient levels in the Vocontian Basin. In theLombardian Basin, this increase in P is less marked. This is inferredto the establishment of a gateway between the Tethys and Borealrealms, which may have added other sources of P to the deep basinsection (i.e. Capriolo and Breggia), depending on the regional cur-rents. After the positive δ13C excursion (in the S. verrucosum Zone),a drier episode followed by a seasonally more contrasted climate(from the top of S. verrucosum Zone to the end of C. furcillata Zone)is recorded and characterized by variable terrigenous and nutrientinputs.

Acknowledgments

We thank Stéphane Bodin, Alexis Godet and Melody Stein for theirassistance in the field and Tiffany Monnier and André Villard for theirtechnical support. We acknowledge the constructive reviews of F.Surlyk and of two anonymous reviewers, which all helped to improvethis publication. Funding for this research was provided by the SwissNational Science Foundation (Grant 200021-109514, 200020-121600to K. F., and PP002–110554/1 to D. F.).

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