Fertilization of the northwestern Tethys (Vocontian basin, SE France) during the Valanginian carbon isotope perturbation: Evidence from calcareous nannofossils and trace element data

Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132 – 151 www.elsevier.com/locate/palaeo

Fertilization of the northwestern Tethys (Vocontian basin, SE France) during the Valanginian carbon isotope perturbation: Evidence from calcareous nannofossils and trace element data Stéphanie Duchamp-Alphonse a,⁎, Silvia Gardin b , Nicolas Fiet a , Annachiara Bartolini b , Dominique Blamart c , Maurice Pagel a a

c

UMR CNRS 8148, IDES, Bât 504, Université Paris Sud-XI, 15 rue Georges Clémenceau, 91405 Orsay Cedex, France b UMR CNRS 5143, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris 05, France UMR CEA/CNRS 1572, LSCE, Campus du CNRS, Bât 12, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France Received 18 November 2005; received in revised form 11 July 2006; accepted 14 July 2006

Abstract A high resolution calcareous nannofossil study associated with a geochemical analysis (major, trace elements, and carbon and oxygen isotope stratigraphies) was carried out in the Angles section (hemipelagic setting of the Vocontian basin, SE France) during the Valanginian positive carbon isotope excursion. The behaviour of calcareous nannofossil taxa in relation to fertility conditions was studied to elaborate new nutrient indices in this environment: a high nutrient index based on Biscutum spp., Discorhabdus rotatorius, Zeugrhabdotus fissus, (high fertility indicators) and Watznaueria barnesae (low fertility indicator); and a medium nutrient index based on Lithraphidites carniolensis (medium fertility indicator) and W. barnesae (low fertility indicator). These two indices show a major fertilization from the Stephanophorus ammonite Zone to the Trinodosum ammonite Zone, with a maximum during the positive carbon isotope excursion. Since high values of the nutrient indices are in phase with high values of chemical elements related to terrigenous material and low values of the coccolith total abundance, it is proposed that pulses of detrital inputs into the basin triggered the nutrification which, in turn, caused a biocalcification crisis of the calcareous nannofossils. Nutrification is also responsible for the reef demise in the surrounded platforms, as indicated by the increased Sr/Ca seawater ratio at that time. The intensification of the Paranà–Etendeka volcanic activity, triggering CO2 excess in the atmosphere, is probably responsible for an acceleration of the hydrological cycle, the increased weathering, and the subsequent higher terrigenous and nutrient transfer from continents to the Vocontian basin. In such a scenario, nutrification is a dominant factor controlling neritic and hemipelagic biocalcification. However, one cannot exclude that the global increase of atmospheric CO2 could generate chemical changes of the sea-surface waters, acting with the nutrification, to modify the biocalcification of the carbonate producers. © 2006 Elsevier B.V. All rights reserved. Keywords: Valanginian positive carbon isotope excursion; Tethys; Calcareous nannofossils; Major and trace elements; Fertilization

1. Introduction ⁎ Corresponding author. Tel.: +33 1 69 15 67 47; fax: +33 1 69 15 48 82. E-mail address: [email protected] (S. Duchamp-Alphonse). 0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.07.010

A global positive carbon isotope excursion was recognized in sediments of late Valanginian–early Hauterivian time interval, with an amplitude of +1.5‰ and a duration

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

of up to 5 Ma (Douglas and Savin, 1973; Patton et al., 1984; Weissert et al., 1985; Weissert and Channel, 1989; Weissert and Lini, 1991; Lini et al., 1992; Hennig et al., 1999; Adatte et al., 2001; Erba et al., 2004; Weissert and Erba, 2004). This isotopic shift coincides with a widespread eutrophication of marine ecosystems associated with an important platform drowning event (Schlager, 1981; Föllmi et al., 1994; Graziano, 1999), associated with a crisis of carbonate producing biota (Lini et al., 1992; Bersezio et al., 2002; Erba and Tremolada, 2004; Erba et al., 2004). This widespread nutrification event is probably triggered by the intensification of the Paranà– Etendeka volcanism and the increasing spreading rates between South America and Africa, and India and Western Australia (Lini et al., 1992; Weissert et al., 1998; Erba et al., 2004). The fertilization was presumably significant in coastal environments, where higher nutrient transfers were triggered by an acceleration of the hydrological cycle via the increase of CO2 in the ocean–atmosphere system and by subsequent increase runoff and erosion (Lini et al., 1992; Weissert et al., 1998). The excess of CO2 released in the atmosphere would lead major perturbations in ocean communities, and particularly in phytoplankton primary producers such as calcareous nannofossils. In modern settings, coccolithophores inhabit the photic zone and flourish in warm, stratified, oligotrophic, mid-ocean environments (McIntyre and Bé, 1967). They play a major role in the earth's carbon cycle, converting dissolved carbon dioxide into organic matter during photosynthesis processes and producing calcite during the calcification of their coccospheres. The distribution of calcareous nannofossils in past and modern oceans depends essentially on the temperature and the trophic resources (McIntyre and Bé, 1967; Molfino and McIntyre, 1990; Ziveri et al., 1995) but other factors like salinity, available light, nutrients and major elements such as iron (Martin et al., 1989; Chester, 2000) may play an important role in their distribution. Thus, calcareous nannofossils represent an ideal proxy to record the palaeoceanographic conditions of surface waters. A variation in the composition of the assemblages and the abundance of some specific taxa may reflect changes in palaeoclimate, nutrient supply, detritus input and/or surface water salinity. Particular attention has already been devoted to the biotic variations of open-sea calcareous nannofossils during the late Valanginian δ13C excursion. This event is associated with a crisis of oligotrophic-related nannoconides (Channell et al., 1993; Erba, 1994; Bersezio et al., 2002; Erba, 2004; Erba and Tremolada, 2004), the acme of Diazomatolithus lehmanii and an increase in abundance of higher fertility indicators such as Zeugrhabdotus erectus (Erba et al., 2004).

133

Records of past marl/limestone chemistry also infer changes in past environmental and/or oceanographic conditions. SiO2 and Al2O3 are generally assumed to represent detrital inputs into sedimentary basins (Hild and Brumsack, 1998; Bréhéret and Brumsack, 2000). FeO is usually correlated with terrigenous flux but it can also be related to productivity (Martin et al., 1989) and/or hydrothermalism (Larson and Erba, 1999). The CaO content of coccolith-dominated marly-limestone sediments is usually related to the carbonate fraction (Bréhéret and Brumsack, 2000). Sr/Ca is generally used as a proxy for sea-level changes, reef crisis and/or changes in Sr partitioning due to variations in calcareous nannoplankton productivity (Graham et al., 1982; Stoll and Schrag, 2001). A detailed record of calcareous nannofossils and elemental geochemistry, throughout the Valanginian positive carbon isotope perturbation is still lacking in hemipelagic basins. Due to their proximal position to the continent, these environments are sensitive to the weathering changes and related nutrient flux. Our study focuses on the Angles section, located in the hemipelagic realm of the Vocontian basin. This site offers the possibility for a high-resolution micropalaeontological and geochemical investigation due to an apparent continuous sedimentation, with a good biostratigraphical control. It provides midway sedimentological records between calcareous platforms (Föllmi et al., 1994) and pelagic settings (Weissert, 1989; Lini et al., 1992; Erba and Tremolada, 2004; Erba et al., 2004). The objectives of this study are: (i) to provide new insight on the trophic conditions of the North-Western Tethys basin during the Valanginian positive carbon isotope perturbation; (ii) to define factors that exerted main controls on these palaeoceanographic changes. Calcareous nannofossil palaeofertility indicators are studied to elaborate new nutrient indices. These data are compared with major and trace element data to unravel the influence of terrigenous inputs and weathering changes on continents, during the global carbon perturbation. 2. Palaeogeographic setting of the Vocontian basin (SE France) and location of the studied section (Angles) The Vocontian basin is located in the South-East of France (Fig. 1). From the late Jurassic and throughout the early Cretaceous, it was surrounded by an isolated carbonate platform system, opened to the Western Ligurian Tethys ocean to the east (Masse, 1993). During the Valanginian time interval, the basin was approximately about 150 km wide and estimated to be of few hundred meters in depth (Donze, 1979; Wilpshaar et al., 1997). The estimated palaeolatitude was 30–35°N (Smith et al.,

134

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 1. Geographical and early Cretaceous palaeogeographic map of southeastern France and adjacent regions (Hennig et al., 1999). The site investigated is the Angles section located in the hemipelagic realm of the Vocontian basin.

1994). Its location between the Boreal and the Tethyan realms allowed floral and faunal exchanges, and mixing of water masses via the Polish Trough (Mutterlose, 1991; Williams and Bralower, 1995). 3. Lithology and biostratigraphy of the Angles section The lithology and the compiled biostratigraphy of the Angles section are provided in Fig. 2. This section was defined as the Valanginian stage stratotype (Busnardo et al., 1979). Due to its abundance of macro and microfossils, several authors have previously studied this section. It is 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; this work, see Section 5.1), and calpionellids (Allemann and Remane, 1979). The biostratigraphic scheme used in this study is the one proposed by Bulot and Thieuloy (1994) improving the resolution of the standard zonation (Hoedemaeker and Rawson, 2000; Hoedemaeker et al., 2003) by establishing more subdivisions of the classically admitted zones within the early Valanginian (Fig. 2). The studied section belongs to the Boissieri to Radiatus ammonite Zones (Bulot and Thieuloy, 1994; Hoede-

maeker et al., 2003), to the Calpionellopsis to Calpionellites calpionellids Zones and to the Cretarhabdus crenulatus to Calcicalathina oblongata nannofossil Zones (Thierstein, 1973). The NK-2 to NC-4 and CC3 to CC4 nannofossil Zones are from Bralower et al. (1995) and Applegate and Bergen (1986), respectively. The lithology of the Angles section consists of hemipelagic marl–limestone alternations. A few syn-sedimentary faults and small slumps affect the lower part of the section but the interval studied in this work is continuous. The early Valanginian is marked by dominantly calcareous beds during the Boissieri and Pertransiens ammonite Zones whereas marly-interbeds become more pronounced in the Stephanophorus ammonite Zone (Fig. 2). The section is most argillaceous from the Inostransewi to the Furcillata ammonite Zones and regular marl–limestone alternations reappear in the Radiatus ammonite Zone, during the early Hauterivian. According to the work of Busnardo et al. (1979), this study focuses on interval between beds 198 (Boissieri ammonite Zone, Otopeta ammonite Subzone) and 386 (Radiatus ammonite Zone) (Fig. 2). 4. Material and methods This work focuses on the bulk marly-interbeds. As a consequence, the studied interval corresponds to an

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

135

Fig. 2. Lithological column of the upper Berriasian to the lower Hauterivian of the Angles section (SE France) with marl–limestone alternations plotted with biostratigraphy and carbon and oxygen records; (1) ammonite biostratigraphy from Bulot and Thieuloy (1994); (2) calpionellid biostratigraphy from Allemann and Remane (1979); (3) calcareous nannofossil biozonation (a) from Bralower et al. (1995); (b) from Applegate and Bergen (1986); (c) calcareous nannofossil biohorizons, this work; (4) lithology after Bulot and Thieuloy (1994); (5) isotope stratigraphy (circles, triangles and squares correspond to the samples located in the carbon isotopic period 1, 2 and 3, respectively). HA. P.P. = Hauterivian p.p; Ino. = Inotranzewi; Rad. = Radiatus.

136

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

almost homogeneous lithology, easily correlated to the calcareous nannofossil biostratigraphy. A cyclostratigraphic study of the rhythmic lithological alternations has been made. Two approaches have been used. The first approach is based on the analysis of the fluctuations of the carbonate content of the lithology by spectral analysis (Huang et al., 1993; Giraud et al., 1995). The second approach is based on the analysis of the lithological stacking pattern, from the thickness/hardness of the strata and from the colour variations. It uses the recognition of different orders of cyclicity and their logic of fitment, in a similar fashion to Russian dolls (e.g. Fiet and Gorin, 2000; Fiet et al., 2001). The combination of the two approaches allowed sampling with a constant temporal step of about 100 kyr of the whole succession. Some 100-kyr intervals are composed of two samples in order to better constrain micropalaeontological and geochemical data. 104 samples were analyzed for calcareous nannofossils, carbon and oxygen stable isotopes whereas 35 samples were selected for major and trace element analyses. 4.1. Sample preparation and nannofossil counts Calcareous nannofossils were analyzed in smear slide using a technique modified from de Kaenel and Villa (1996). A weight of 200 mg of sediment was heated at 40 °C (in a steamroom) during 48 h, then powdered and finally diluted in 35 ml of distilled water. 5 ml of the homogeneous solution was shaken several times on a test tube and held still for 95 s to insure that the larger particles of the sediment settling. 250 μl of the floating portion was spread on a cover slide to disperse the specimens uniformly. Counting was carried out using a light polarizing microscope at 1600× magnification. For each slide, 100 visual fields were observed and all calcareous nannofossils with more than half of the specimens preserved were counted. Between 900 and 4360 individuals were counted on each slide. The frequency of the coccolith total abundance was converted to the number of specimens per mm2 (Backman and Shackleton, 1893; de Kaenel and Villa, 1996; Erba et al., 1999). These values were corrected according to the sedimentation rates of each studied cycle as follow: Coccolith total abundance=mm2 corrected of these dimentation rates ¼ Coccolith total abundancemm2 *Fc with Fc (correction factor) = sedimentation rate of each 100-kyr cycle/Valanginian average sedimentation rate of the Angles section.

Some samples were counted twice to test the reproducibility of this approach. Values show a reproducibility of about +/− 1%. 4.2. Carbon and oxygen stable isotope stratigraphy Approximately 400 μg of powder bulk samples was reacted with 100% H3PO4 at 90 °C. The CO2 produced was analyzed at the Laboratoire des Sciences du Climat et de l'Environnement (Gif sur Yvette) with a VG Optima mass spectrometer. The results are reported relative to PDB (Pee Dee Belemnite) standard. The uncertainties of the measures are estimated at better than 0.05% for the carbon isotope analyses and 0.07% for the oxygen isotope analyses, respectively. Duplicate measurements on a given sample are in the range of 0.1–0.2‰ for C and O. 4.3. Major and trace elements Elemental concentrations were determined at the “Centre de Recherche Pétrographiques et Géochimiques” of Nancy (CRPG-CNRS). Samples were fused with LiBO2, dissolved with HNO3 and analyzed using a JobinYvon JY 70 ICP-AES (major elements) and a PerkinElmer ELAN 5000 ICP-MS (minor elements). Precision was checked by repeated measurements of reference materials. Precision was 2% for CaO, 3% for Al2O3, 5% for FeO, 6% for Sr and 10% for Th. 5. Results 5.1. Calcareous nannofossil biostratigraphy The complete succession of the nannofossil bioevents identified in this study is represented Fig. 2. The Boissieri ammonite Zone is characterized by the first occurrences (FO) of the high latitude taxa Nodosella silvaradion (Alpillensis ammonite Subzone), and Sollasites horticus (Thieuloyi ammonite Subzone). The Otopeta ammonite Subzone is marked by the last occurrences (LO) of Rhagodiscus nebulosus and Cyclagelosphaera sp. The Pertransiens and Stephanophorus ammonite Zones contain the first occurrences of several species: C. oblongata, Rhagodiscus dekaenelii, Pickelhaube umbellata, Eiffellithus windii, Zeugrhabdotus trivectis, Z. diplogrammus and Markalius vetulus. The boreal marker species Micrantholithus speetonensis sporadically occurs. The top of the Stephanophorus ammonite Zone (Campylotoxus Subzone) and the Inostransewi ammonite Zone are characterized by a succession of nannofossil LO's: Cyclagelosphaera deflandrei, Eiffellithus primus, P. umbellata, M. vetulus and Rucinolithus wisei. Eiffellithus striatus

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

first occurs in the Trinodosum ammonite Zone (Nicklesi Subzone) as well as the last regular occurrence of T. verenae. The top of the Trinodosum ammonite Zone (Furcillata Subzone) and the Callidiscus ammonite Zone are marked by the first occurrences of two “wide canal nannoconids”: Nannoconus bucheri and N. wassallii, respectively. Zeughrabdotus fissus last occurs in the Furcillata ammonite Subzone. 5.2. Carbon and oxygen stable isotope stratigraphy Carbon isotope values range from 0.3 to 2.5‰ (PDB) (Fig. 2). The Valanginian positive carbon isotope excursion is well defined and three “isotopic periods” can be distinguished: 1) At the base of the section, the Boissieri–Stephanophorus ammonite Zones are characterized by the lowest δ13C values (0.3 to 1.0‰ (PDB)). 2) The major carbon isotope excursion starts in the upper part of the Stephanophorus ammonite Zone (Campylotoxus Subzone) and reaches maximum values at about 2.5‰ (PDB) within the Verrucosum ammonite Zone (Verrucosum Subzone). 3) This perturbation is followed by a period of relatively high isotope values slightly decreasing to 1.5‰ in the Hauterivian stage. Oxygen isotope data range from − 4.1 to −2.5‰ vs. PDB, showing regular fluctuations of about 1‰ from Boissieri to Verrucosum ammonite Zones (Fig. 2). The oxygen values remain around − 3‰ in the Boissieri– Pertransiens ammonite Zones. After a shift toward − 4‰ in the upper part of the Pertransiens ammonite Zone, the values increase gradually to − 3‰ in the Stephanophorus ammonite Zone (Subcampylotoxus Subzone) and mark a pronounced decreasing trend to − 3.8‰ until the Verrucosum ammonite Zone (Verrucosum Subzone). Upward, the values tend to become more positive, with pronounced negative fluctuations of 0.5‰ of amplitude. 5.3. Trace and major element data and comparison with the δ13C signal The fluctuations of Al2O3, FeO, CaO, FeO/ Al2O3, and Sr/Ca, plotted against the lithology, the ammonite biostratigraphy and the carbon isotope signal are shown Fig. 3. From the upper part of the Stephanophorus ammonite Zone to the Verrucosum ammonite Zone, including the positive carbon isotope excursion (isotopic period 2), the increase of Al2O3 (6.5 to 12.0%) is followed by the increase of FeO (1.5 to 3.0%). The good correlation

137

between Al2O3 and FeO during this time interval (r2 = 0.7) is also well evidenced by the FeO/ Al2O3 curve, that shows relatively constant values (Fig. 3). Such a correlation is weaker during the isotopic period 1 (r2 = 0.2) and in the Trinodosum–Callidiscus ammonite Zones (r2 = 0.4) (Fig. 3). CaO percentages are clearly inverse correlated with those of Al2O3 (r2 = − 0.9; Fig. 8b). Decreasing values (37.0 to 25.5%) are recorded from the upper part of the Stephanophorus to the Verrucosum ammonite Zones, including the positive carbon isotope shift. The Sr/Ca ratio gradually increases (0.7 to 1.5) during the carbon isotopic period 1 (Fig. 3). It shows maximum values in the uppermost Stephanophorus–Verrucosum ammonite Zones, including the major positive carbon isotope excursion (carbon isotopic period 2). After a slight decrease at the top of the Verrucosum ammonite Zone (Pronecostratum Subzone) the ratio remains quite steady until the Callidiscus ammonite Zone. In synthesis, from the top of the Stephanophorus ammonite Zone to the Verrucosum ammonite Zone, period including the major carbon isotope perturbation (carbon isotopic period 2), all the analyzed elements strongly react and show clear trends: increase of Al2O3, and FeO; decrease of CaO; and maximum values of Sr/Ca. Elsewhere, the correlations between δ13C and the analyzed major and trace elements are less obvious. 5.4. Distribution of calcareous nannofossil taxa and comparison with the δ13C signal The correlation of the δ13C signal, the coccolith total abundance and the abundance of the calcareous nannofossil fertility indicators are shown Fig. 4. Nine taxa, corresponding to the most abundant species/genus, were selected for their palaeoecological and palaeoceanographical significance: Watznaueria barnesae, D. lehmanii, Biscutum spp., Discorhabdus rotatorius, Zeugrhabdotus fissus, Rhagodiscus asper, Micrantholithus spp., Nannoconus spp. and Lithraphidites carniolensis. To avoid possible distortion of the calcareous nannofossil absolute abundance due to dilution factors, results are turned into relative abundance (Fig. 4). Total abundance ranges from 644 to 6683 specimens/ mm2 with the minimum during the positive δ13C excursion (carbon isotopic period 2) (Fig. 4). In the Verrucosum ammonite Zone (Pronecostatum and Peregrinus Subzones), a gradual increase of the coccolith total abundance is associated with constant high values of the δ13C. High coccolith total abundance is also reached during the Trinodosum ammonite Zone (Nicklesi–Furcillata Subzones), correlated with a slight decreasing values of δ13C.

138 S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 3. Ammonite zonations and lithology plotted against carbon isotope stratigraphy and periods, and variations of some major and trace element contents and ratios. FeO/Al2O3 ratio point out the good correlation between FeO and Al2O3 during the Stephanophorus–Verrucosum ammonite Zones time interval, including the carbon isotopic period 2.

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 4. Ammonite zonations and lithology plotted against carbon isotope stratigraphy and periods and distribution of selected calcareous nannofossils.

139

140

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

W. barnesae's abundance decreases of 12.5% during the carbon isotopic period 1. The lowest percentages (16 to 20%) are reached during the carbon isotopic period 2 (major carbon isotope positive excursion). Increasing percentages (16 to 50%) are recorded in the carbon isotopic period 3 and maximum values are reached at the base of the Hauterivian (Radiatus ammonite Zone) (Fig. 4). Nannoconid's abundance fluctuates between 2 and 11% in the carbon isotopic period 1. The lowest percentages (2 to 6%) are recorded during the carbon isotopic period 2. After an interval of increasing values (4 to 9%) during the upper Verrucosum ammonite Zone (Pronecostatum–Peregrinus Subzones), nannoconid's abundance decreases again from 9 to about 3%. The abundance pattern of Biscutum spp. differs from the previous ones. Three distinct intervals characterized by highest values (10 to 12%) are recognized: a) in the Stephanophorus ammonite Zone (isotopic period 1), b) during the positive carbon isotope excursion (Verrucosum ammonite Subzone: isotopic period 2), and c) in the uppermost part of the section (Furcillata–Callidiscus ammonite Subzones, and Radiatus ammonite Zone, isotopic period 3). The abundance of D. rotatorius sharply increases in the Stephanophorus ammonite Zone (Subcampylotoxus Subzone, isotopic period 1), as observed for Biscutum spp. Highest values (2–3%) are maintained throughout the positive δ13C excursion (isotopic period 2) and till the top of Verrucosum-base of Trinodosum ammonite Zones (isotopic period 3). At the Peregrinus–Nicklesi ammonite Subzone transition, the abundance decreases (0.4%) and remains relatively low throughout the late Valanginian. Zeugrhabdotus spp. are always very rare: Z. erectus is too scarce to be taken into account (a maximum of 5 specimens/ 100 visual fields had been observed) and the abundance of Z. fissus is generally very low (between 0 and 1%).The latter species shows highest abundance (1%) in the Trinodosum ammonite Zone (Furcillata Subzone). D. lehmanii reaches highest abundance (17%) at the base of the section, in the Boissieri–Stephanophorus ammonite Zones (Thieuloyi–Subcampylotoxus Subzones). The abundance gradually decreases along the Stephanophorus ammonite Zone to reach lowest values (3 to 4%) during the carbon isotope excursion (carbon isotopic period 2). Then, the abundance keeps relatively stable until the early Hauterivian. The trends of L. carniolensis show relatively high abundance from the Stephanophorus ammonite Zone (Subcampylotoxus Subzone) to the Trinodosum ammonite Zone (Furcillata Subzone). Steady values are recorded during the positive δ13C excursion. R. asper and Micrantholihus spp. abundances never reach 3%. Their trends do not show any marked feature.

6. Discussion 6.1. Diagenesis 6.1.1. Preservation of calcareous nannofossils We investigated the possible effect of diagenesis on the calcareous nannofossil assemblages by visual observations and statistical analysis. SEM observations of nannofossil preservation were performed following the scale given by Roth and Thierstein (1972). Ten samples with different amount of total calcareous nannofossils were observed throughout the section. The nannofossils of the Angles section are affected by etching; delicate structures are however still preserved and not significantly affected by secondary calcite overgrowth. Some coccolith central structures tend sometimes to be lightly overgrowth but are never obliterated. Moreover, it was assumed that a strong differential preservation of calcareous nannofossils would significantly alter the composition of the assemblages, keeping more resistant specimens and losing delicate species. From this assumption, many authors use the percentages of the robust form W. barnesae, less susceptible to dissolution, to assess the impact of the diagenesis. According to Roth and Bowdler (1981) and Roth and Krumbach (1986), the assemblages containing less than 40% of W. barnesae are thought to be only slightly altered by diagenesis and can be used as primary signal. Williams and Bralower (1995) further propose that the composition of nannofossil assemblages is resistant to alteration by preservational changes when assemblages contain less than 70% of W. barnesae. In this study, the abundance of W. barnesae varies in most cases from 14 to 36% but never exceeds 50% (Fig. 4). No significant correlation with the total nannofossil abundance could be find (r2 = 0.008; Fig. 5). Delicate specimens (Biscutum spp., D. rotatorius and Diadorhombus rectus) are still commonly present and the calcareous nannofossil species richness fluctuates between 45 and 80. In conclusion, it is reasonable to think that the calcareous nannofossil assemblages of the Angles section reflect a primary signal and can be therefore used as palaeoenvironmental proxies to reconstruct the surface water conditions of the Vocontian basin. 6.1.2. Preservation of the δ13C and δ18O signals The similar shape of δ13C variations to those found on similar age sections around the world (Fig. 6), and the absence of co-variations trends of δ18O vs. δ13C (r2 = 0.09; Fig. 7), indicates that carbon-isotopes probably reflect a primary signal, and can be used as a proxy for the global carbon cycle during the Valanginian.

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 5. Relationships between W. barnesae (%) and the total nannofossil abundance.

The carbon as well as the oxygen isotope values of Angles measured on marlstones are often more negative than those recorded from most calcareous sections of southern Tethyan margin (Lini et al., 1992; Weissert et al., 1998; Weissert and Erba, 2004). Lighter values of δ13C maybe related to a local carbon isotope composition of the Vocontian basin sea-waters, due to salinity and/or primary productivity variations. The more negative δ18O values (−4.1 to −2.5‰ vs. PDB) recorded at the Angles section compared to the La Charce, located a few kilometers away (1‰ +/− 0.2, according to Hennig et al., 1999), could suggest a slight overprint of the section at low temperature due to the important temperature-dependent isotopic fractionation during diagenetic processes (e.g. Friedman

141

Fig. 7. Relationships between δ13C (‰ vs. PDB) and δ18O (‰ vs. PDB) of the bulk marl samples. Circles, triangles and squares correspond to the samples located in the carbon isotopic period 1, 2 and 3, respectively.

and O'Neil, 1977). However, clearly discernible general stratigraphic trends are recorded for the δ18O at Angles. We suggest that the δ18O composition of the marl may have not experienced high impact of diagenetic processes and that the shape of the δ18O variations may reflects palaeotemperature trends. 6.1.3. Preservation of the major and trace element signals: carbonates versus terrigenous detrital material According to the triangular SiO2–Al2O3–CaO plot (Fig. 8a), all samples fall on a mixing line between the average shale data point (Wedepohl, 1991) and the

Fig. 6. Compilation of carbon-isotope data by localities (Lini et al., 1992; Hennig et al., 1999; Adatte et al., 2001; this work).

142

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 8. (a) Major element composition of the bulk marl samples represented in a triangular diagram SiO2–Al2O3–CaO; (b) correlations of CaO vs. Al2O3 for the bulk marl samples; (c) correlations of FeO versus Al2O3. 1) Correlation of all of the samples analyzed for their major element contents; 2) correlation of the samples showing in Fig. 3, a good correlation between Al2O3 and FeO, from the top of the Stephanophorus ammonite Zone to the Verrucosum ammonite Zone.

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

carbonate pole. This implies that bulk samples correspond to an homogeneous mixture of terrigenous-detrital material and different proportions of biogenic carbonate end-members (Hild and Brumsack, 1998; Bréhéret and Brumsack, 2000). Moreover, the terrigenous-detrital material is often considered as being chemically inert (Brumsack, 2005). In Particular, Al2O3, commonly found in terrigenous aluminosilicate minerals shows a low abundance in seawater (Orians and Bruland, 1986), and is not usually affected by diagenetic processes (Brumsack, 2005). This indicates that the variations of this element and most probably those of SiO2 and CaO represent a primary signal. The fact that CaO is negatively correlated to Al2O3 (r2 = − 0.9; Fig. 8b), excludes a detrital origin of this element. It indicates that CaO resides in carbonates linked to the “in situ” primary productivity and/or represents some carbonate muds exportation from the platform oozes basinward. Iron is present as a structural component of detrital material but can precipitates as oxide/hydroxide coating on mineral grains (Canfield et al., 1992) and/or may be incorporated into sediments as iron sulfide under reductive leaching (Brumsack, 2005). Plots of FeO versus Al2O3 of the data set do not show a clear correlation (r2 = 0.4; Fig. 8c). However, a certain positive correlation is observed between FeO and Al2O3, on selected intervals as the correlation (r2 = 0.6; Fig. 8c) observed from the upper part of the Stephanophorus to the Verrucosum ammonite Zones (Campylotoxus–Peregrinus subzones), including the major positive carbon excursion (carbon isotopic period 2). This local good correlation of FeO and Al2O3 is likely linked to terrigenous inputs and the transfer of nutrients such as the iron from continent to oceans. The Sr/Ca ratio is used as a proxy for temporal variations in seawater Sr/Ca (Stoll and Schrag, 2001). Because of the good homogeneity of the sedimentation and the lack of condensed or erosional surfaces, the diagenetic recrystrallisation behaviour of the whole sedimentation can reasonably be considered as homogeneous. Thus the Sr loss by porewaters that can occur during diagenetic processes, would simply shifts the Sr/Ca towards lighter values and the variations of the ratio along the sedimentary succession may be regarded as a primary signal. 6.2. Ecological significance of Neocomian calcareous nannofossils from the Vocontian basin 6.2.1. Fertility indicators The calcareous nannofossils used in this study were chosen for their palaeoecological significance, mainly established in pelagic, open-sea environments such as the

143

North Atlantic, Pacific, Indian Oceans and the Umbria– Marche and Lombardian basin (Italy) (Roth and Bowdler, 1981; Bersezio et al., 2002; Erba et al., 2004). Their behaviour in more proximal hemipelagic settings needs to be studied before using them as adequate proxies for surface trophic conditions in the Vocontian basin. To do this, the trends of each species/genus were checked throughout the section and particularly during the Stephanophorus–Verrucosum ammonite Zones which include the positive carbon isotope excursion, to unravel the palaeoecological affinities of each specimen. The abundance of Biscutum spp. and D. rotatorius, related to high surface water fertility conditions (Roth and Bowdler, 1981; Premoli Silva et al., 1989; Coccioni et al., 1992; Erba et al., 1992), sharply increases during this time interval and peaks during the highest values of the carbonisotopes (δ13C peak). L. carniolensis, associated with neritic environments in the near-shore area (Thierstein, 1973; Janin, 1998) shows a similar trend but does not show this peak. This nannolith appears to be also controlled by fertility conditions in hemipelagic settings, though it does not seem to tolerate the conditions triggered by the major carbon isotope excursion (tolerance threshold). In contrast to these high fertility indicators, the relative abundance of the cosmopolitan eurytopic W. barnesae, related to low fertility conditions (Roth, 1989; Premoli Silva et al., 1989; Erba et al., 1992; Williams and Bralower, 1995) decreases during the Stephanophorus–Verrucosum ammonite Zones and reaches its lowest values during the major δ13C shift. Thus, W. barnesae, Biscutum spp., D. rotatorius and L. carniolensis seem to draw a coherent pattern of changes in sea-surface fertility conditions, with more meso-eutrophic conditions during the carbon isotope perturbation. These taxa seem to be suitable low/high fertility indicators, even in an epicontinental environment. 6.2.2. Vocontian basin features According to the literature Z. erectus is considered as a high fertility indicator in fully pelagic settings, probably linked to vigorous upwellings (Roth, 1989; Erba et al., 1992; Erba et al., 2004). Because this taxon shows very low abundance (a maximum of 5 specimens/100 visual fields were observed) at Angles, these specific conditions were not present in the Vocontian basin. D. lehmanii, generally related to mesotrophic conditions can also have possible relationships with warm waters (Premoli Silva et al., 1989; Coccioni et al., 1992; Williams and Bralower, 1995; Erba et al., 2004). Its abundance pattern differs significantly from the fertility indicator pattern, (decreasing trends from the carbon

144

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

isotopic period 1 to the carbon isotopic period 2, and low percentages in the carbon isotopic period 3) and this species does not seem to be mainly influenced by trophic conditions. Because the bulk O-isotope curve used as palaeotemperature proxy reveals no apparent correlation with the distribution of this taxon, it does not seem to be mainly influenced by sea-surface temperature changes either. In this epicontinental sea, D. lehmanii does not depend on the same factors as those of pelagic settings. Its distribution could reflect other factors than nutrient inputs such as salinity and turbidity. A better control on these parameters will help future interpretations. Nannoconids are commonly related to warm water taxa (Mutterlose, 1991; Mutterlose and Kessels, 2000) while their trophic preferences are discussed: (1) According to numerous authors they are interpreted as oligotrophic, deep-dwelling forms compared to Florisphaera profunda (Erba, 1994; Bersezio et al., 2002; Herrle, 2003; Bornemann et al., 2003; Reboulet et al., 2003); (2) Scarparo Cunha and Koutsoukos (1998) challenge this interpretation arguing that F. profunda's blooms, and thus nannoconids abundance, would be intensified under mesotrophic conditions (Molfino and McIntyre, 1990; Young, 1994, Street and Brown, 2000); (3) Kruse and Mutterlose (2000), interpret Nannoconus spp. as nearshore taxa, possibly correlated with eutrophic conditions. In the Angles section, the abundance of nannoconids shows different trends (Fig. 4): (a) it is always opposite to that of Biscutum spp. and in a lesser degree to the coccolith total abundance, except during the major δ13C excursion (carbon isotopic period 2), where it tends slightly to increase; (b) it reaches its highest values just before and after the major carbon isotope excursion, when D. rotatorius and L. carniolensis abundances are still relatively high; (c) no significant correlation is observed between nannoconids and W. barnesae. These results show that, in the hemipelagic realm of the Vocontian basin, the nannoconid proliferation is probably hampered by eutrophic conditions related to the proliferation of Biscutum spp., and do not tolerate the high fertility conditions reached during the major carbon isotope perturbation. The slight increase of the Nannoconus spp. abundance during this perturbation until the top of the Verrucosum ammonite Zone (Pronecostratum–Peregrinus Subzones), is likely due to a higher proportion of “wide canal” forms after a period dominated by the “narrow canal” forms (Duchamp-Alphonse, personal observations) as similarly observed by Erba (1994), during the early Aptian positive δ13C excursion (acme of the “wide canal” form Nannoconus truittii). The oligotrophic conditions required by W. barnesae are not optimal. The nannoconids (both wide and narrow canals) seem to prefer intermediate

mesotrophic conditions still tolerated by species such as D. rotatorius and L. carniolensis. The inverse correlation of the Nannoconus spp. with the coccolith total abundance may suggest that these nannoliths lived in the lower euphotic zone, as already proposed by numerous authors (Erba, 1994; Bersezio et al., 2002; Herrle, 2003; Bornemann et al., 2003; Reboulet et al., 2003). 6.3. Calcareous nannofossil nutrient indices, sea-surface nutrification, terrigenous/nutrient inputs and greenhouse climate The analysis of species ratios provides a clearer record of surface water fertility conditions than the evaluation based on single species abundance (Gale et al., 2000). New nutrient indices based on the distribution and the ecological significance of the index species selected in this study (Section 6.2), were created in order to establish trophic conditions at Angles (Herrle, 2003) (Fig. 9). Biscutum spp., Z. fissus (despite its low percentages), D. rotatorius and W. barnesae were used to establish the High Nutrient Index corresponding to eutrophic conditions. L. carniolensis and W. barnesae were used for the Medium Nutrient Index (MNI), related to mesotrophic conditions (Fig. 9). HNI ¼ R %ðZf ; Bs; DrÞ=R %ðZf ; Bs; Dr; WzÞ*100 MNI ¼ % Li=R %ðLi; WzÞ*100 (with Zf = Z. fissus, Bs = Biscutum spp., Dr = D. rotatorius; Li = L. carniolensis and Ws = W. barnesae). The resulting MNI and HNI (Fig. 9) show that mesotrophic to eutrophic conditions prevail from the Stephanophorus to the Callidiscus ammonite Zones (Hirsutus–Callidiscus Subzones), roughly corresponding to more argillaceous lithologies. This general trend is punctuated by very short episodes of oligotrophic intervals (Fig. 9). The correlation of the nutrient index with coccolith's abundance and the geochemical proxies allows to outline 4 major phases: 1) From the Boissieri to the Pertransiens ammonite Zones (base of the isotopic period 1), low nutrient indices values attest of relatively stable and oligotrophic conditions. These conditions are favourable to a nannofossil speciation (FOs of S. horticus, C. oblongata, Z. trivectis, R. dekaenelii, P. umbellata, Z. diplogrammus, and E. windi). In the Stephanophorus ammonite Zone (isotopic period 1) the coccolith total abundance sensibly decreases and the nutrient indices

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Fig. 9. Lithological column plotted against ammonite zonations, carbon and oxygen isotope stratigraphies, carbon isotopic periods, coccolith total abundance, nutrient indices (High Nutrient Index (HNI) and Medium Nutrient Index (MNI)), Al2O3 and Sr/Ca variations and short-term eustatic curves from (A) Arnaud-Vanneau et al. (1982) and (B) Haq et al. (1987). Higher nutrient indices values testify of higher water fertility and vice versa. Shaded bands depict more oligotrophic interludes.

145

146

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

values increase. Al2O3 percentages are relatively high though FeO values remain low. During this time interval, more meso- to eutrophic conditions probably hamper the biocalcification of coccoliths. Since Al2O3 is related to the terrigenous material, nutrification is probably associated with pulses of terrigenous/nutrient inputs in the basin. This suggests a possible increase of run-off in the hinterland, due to an acceleration of the hydrological cycling. Therefore, the decoupling recorded at that time between Al2O3 and FeO is probably associated with the chemical weathering pattern. The hydrolysis conditions likely favour the mobilisation of Fe-poor terrigenous material. 2) After a short oligotrophic interlude in the Campylotoxus ammonite Subzone, testified by a slight decrease of the nutrient indices values and slight increase of the coccolith total abundance, the environment abruptly shifts to a maximum of eutrophication in the carbon isotopic period 2 (major carbon isotope shift). The intensity of these trophic condition changes is reflected by the highest HNI values coinciding with the lowest coccolith abundance and the δ13C peak. Calcareous nannofossil biocalcification is hampered and the initial conditions favourable to their diversification are disrupted (successive extinctions of C. deflandrei, E. primus, P. umbellata, M. vetulus and R. wisei) (Weissert and Erba, 2004). At that time, highest nutrient values correlate well with high values of Al2O3 and FeO. Nutrification is associated with pulses of terrigenous/nutrient inputs in the basin. This confirms the hypothesis of increased weathering probably due to an acceleration of the hydrological cycle and suggests the intensification of greenhouse conditions as proposed by Lini et al. (1992), Föllmi et al. (1994) and Weissert et al. (1998). This hypothesis is furthermore supported by the correlation between the Al2O3 percentage peaks and the δ18O lightest values, probably indicative of increased temperature and/or lowered salinity related to increased run-off. In such a scenario, the coupling trend recorded at that time between Al2O3 and FeO is probably ascribed to changes in the chemical weathering pattern, compared to the carbon isotopic period 1. The amplification of the hydrolysis conditions likely supports the mobilization of FeO-rich aluminosilicates. 3) From the top of the Verrucosum to the Trinodosum ammonite Zones (Pronecostatum to Nicklesi Subzones), corresponding to the carbon isotopic period 3, mesotrophic conditions interrupted by short oligotrophic episodes prevail. These conditions allow the biocalcification to start again, as attested by the increase of the total coccolith abundance. Decreasing values of

Al2O3, and FeO, testify of a decrease of terrigenous inputs and implies weaker hydrolysis conditions on continents and a return to more stable conditions. 4) The HNI (High Nutrient Index) indicates a return to eutrophic conditions on top of the section in the Trinodosum ammonite Zone (Furcillata Subzone). However, contrary to the Verrucosum ammonite Zone, it is associated with high values of coccolith total abundance and a decrease of δ13C and MNI values. A second eustatic sea-level rise is contemporary in this time interval (Arnaud-Vanneau et al., 1982; Haq et al., 1987) (Fig. 9). Thus, the apparent discrepancy of nannofossil data can be explained considering that the nannofossil taxa used in this index (Biscutum spp. and Z. fissus despite its low percentages) are rather abundant in the boreal realm, and could likely reflect cooler surface water temperatures due to more pronounced connections with the boreal realm and/or changes in the water mass circulation. This hypothesis is further supported by more positive δ18O values, likely indicative of cooler temperatures at Angles as already proposed by Van de Schootbrugge et al. (2000) and Pucéat et al. (2002). 6.4. Sr/Ca and carbonate crisis The Stephanophorus ammonite Zone (Hirsutus to Campylotoxus Subzones) is characterized by a pronounced rise of the Sr/Ca ratio values (Fig. 9). High availability of Sr related to Ca in seawaters can be ascribed to a crisis of aragonitic biomineralisation and increasing carbonate Sr/Ca ratio values can reflect changes in the proportion of carbonate removed in aragonitic vs. calcitic sediments. Generally, such a scenario testifies of a decrease in reef carbonate accumulation (Graham et al., 1982; Stoll and Schrag, 2001). Since the Stephanophorus ammonite Zone is marked by the drowning of helvetic carbonate ramps and platforms (Föllmi et al., 1994), it is proposed that the increased Sr/Ca ratio recorded at the Angles section, reflect the degeneracy of the surrounded carbonate platform system. Therefore, in the Stephanophorus ammonite Zone, the “aragonitic” calcification crisis of the neritic realm (as inferred by Föllmi et al., 1994), correlates with the calcification crisis in the hemipelagic setting, as attested by a decrease of coccolith total production at that time (Figs. 3 and 9). In the Inostransewi–Verrucosum ammonite Zones, corresponding to the major carbon isotope perturbation (carbon isotopic period 2), maximum values of Sr/Ca coincide with minimum values of coccolith total abundance, related with conditions of maximum eutrophy

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

(Fig. 9). The Sr/Ca and HNI curves show an outstanding similarity in shape (double spike). Through this interval, the Sr/Ca signal is in agreement with palaeoenvironmental changes recorded in the hemipelagic realm. It probably reflects the acme of the carbonate platform demise (Föllmi et al., 1994) and mirrors the signature of high fertility hemipelagic calcareous nannofossils. As noticed by previous authors (Weissert and Erba, 2004), the onset of the biocalcification crises, recorded in the Vocontian basin and in the surrounded platforms during the Stephanophorus ammonite Zone, predates the beginning of the positive carbon isotope excursion (isotopic period 2). Our results suggest that the reduced calcification of calcareous nannofossils is clearly associated with elevated nutrient levels. It is proposed therefore, in agreement with Föllmi et al. (1994), that the neritic biocalcification crisis is also associated with the nutrification of the Vocontian basin. The intensification of the Paranà–Etendeka volcanism, dated at 132 +/− 1 Ma (Renne et al., 2001), was possibly responsible for an increase of CO2 in the atmosphere triggering greenhouse conditions and accelerated hydrological cycling, possibly causing an indirect fertilization (Weissert, 1989; Lini et al., 1992; Föllmi et al., 1994; Weissert et al., 1998; Erba et al., 2004). Due to its hemipelagic setting, the Vocontian basin is particularly sensitive to the terrigenous/nutrient transfer as outlined by the increase of calcareous nannofossil nutrient indices at the base of the Stephanophorus ammonite Zone (isotopic period 1) (Fig. 9). This nutrification event is probably a local response to the global increase of pCO2 in the atmosphere, with probably no incidence in the openocean settings. In fully oceanic environments the biocalcification crisis, that also predates the onset of the positive δ13C excursion, is likely triggered by other factors rather than nutrification. According to Weissert and Erba (2004), pCO2 affecting ocean chemistry is the most important factor controlling carbonate production. These authors suggest therefore that decreasing pH and carbonate ion concentration of surface waters through excess amount of CO2 in the ocean–atmosphere system could have weakened the calcification potential of the carbonate producers. Chemistry changes probably occurred in the Vocontian basin as well and affected the biocalcification of the carbonate producers together with nutrification. A better control of the Vocontian basin seasurface chemistry will help future interpretations. The maximum of eutrophy, recorded in the Vocontian basin during the major positive carbon isotope excursion coincides with the nutrification event at a global scale (Erba et al., 2004). According to Weissert and Erba (2004), nutrient flow by weathering is not the only

147

mechanism to have induced enhanced primary productivity in the global ocean. In the remote parts of the oceans, the increasing flux of hydrothermal biolimiting elements related to the break-up of the Gondwana could have induced global nutrification. In this scenario, the major positive carbon isotope excursion would attest of an increased primary productivity and a shift from carbonate carbon burial to organic carbon burial in response to the global nutrification. 7. Conclusions The high resolution multiproxy study of the Angles section reveals major palaeoenvironmental changes in the hemipelagic Vocontian basin during the Valanginian. The studied sediments record the global positive C-isotope excursion from the top of the Stephanophorus to the base of the Verrucosum ammonite Zone. This time interval is regarded as a time of accelerated global carbon cycling. Three isotopic periods are recorded: isotopic period 1, at the base of the section (Boissieri–Stephanophorus ammonite Zones), characterized by the lowest δ13C values; isotopic period 2, from the upper part of the Stephanophorus to the Verrucosum ammonite Zone, characterized by the major carbon isotope excursion; isotopic period 3, characterized by relatively high isotope values slightly decreasing to the Hauterivian stage. Calcareous nannofossil assemblages depict significant changes. Coccolith total abundance indicates a lowered biocalcification potential of calcareous nannofossils with a minimum during the major carbon isotope excursion. Fertility indicators show mesotrophic to eutrophic conditions in the euphotic zone from the Stephanophorus to the Callidiscus ammonite Zones. Highest nutrient index values correlate well with lowest coccolith total abundance, highest Sr/Ca values and highest percentages of Al2O3, related to the terrigenous material. This suggests that detrital inputs were the trigger of the nutrification event that caused a biocalcification crisis of neritic carbonate producers and hemipelagic calcareous nannofossils. In the Stephanophorus ammonite Zone, the increased fertility conditions is possibly a local response to the global increase of CO2 in the atmosphere through the intensification of the Paranà–Etendeka volcanism. The global CO2 excess in the atmosphere likely increased weathering and run-off from continents in response to the increase weathering. The maximum of eutrophy, recorded in the Vocontian basin during the major positive carbon isotope excursion (Inostransewi–Verrucosum ammonite Zones) coincides with a global-scale nutrification event. Our results indicate that fertilization is the principal factor for biocalcification crises in the Vocontian

148

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

basin, particularly sensitive to weathering changes and consequent flux of nutrients due to its hemipelagic setting. Otherwise, this scenario does not exclude that the global increase of CO2 in the atmosphere could have triggered sea-surface chemical changes that could have affected the biocalcification of the carbonate producers, as probably occurred in fully pelagic environments. Acknowledgments The authors acknowledge Luc Bulot and Stéphane Reboulet for stimulating discussions. We thank the team of the “Reserve Géologique de Haute-Provence” to make the fieldwork possible. We also thank Gregory D. Price and Helmut Weissert for their helpful reviews. Appendix A List of calcareous nannofossils with author attributions and dates: Biscutum Black in Black and Barnes, 1959 Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971 Cyclagelosphaera Noël, 1965 Cyclagelosphaera deflandrei (Manivit, 1966) Roth, 1973 Diazomatolithus lehmanii Noël, 1965 Discorhabdus rotatorius (Bukry, 1969) Thierstein, 1973 Eiffellithus striatus Applegate and Bergen, 1988 Eiffellithus primus Applegate and Bergen, 1988 Eiffellithus windii Applegate and Bergen, 1988 Florisphaera profunda Okada and Honjo, 1973 Lithraphidites Deflandre, 1963 Markalius vetulus Bergen, 1994 Micrantholithus Deflandre in Deflandre and Fert, 1954 Micrantholithus speetonensis Perch-Nielsen, 1979 Nannoconus Kamptner, 1931 Nannoconus bucheri Brönnimann, 1955 Nannoconus wassallii Brönnimann, 1955 Pickelhaube umbellata Bergen, 1994 Rhagodiscus asper (Stradner, 1966) Reinhardt, 1967 Rhagodiscus dekaenelii Bergen, 1994 Rhagodiscus nebulosus Bralower et al. 1989 Rucinolithus wisei Thierstein, 1971 Sollasites horticus (Stradner et al in Stradner and Adamiker, 1966) Tubodiscus verenae Thierstein, 1973 emend. Grün in Grün and Allemann, 1975 Watznaueria barnesae (Black in Black and Barnes, 1959) Perch-Nielsen, 1968

Zeugrhabdotus diplogrammus (Deflandre in Deflandre and Fert, 1954) Burnett in Gale et al. 1996 Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965 Zeugrhabdotus fissus Grün et Zweili, 1980 Zeugrhabdotus trivectis Bergen, 1994 References Adatte, T., Stinnesbeck, W., Hubberten, H., Remane, J., Guadalupe, L.O., 2001. Correlation of a Valanginian stable isotopic excursion in Northeastern Mexico with the European Tethys. In: Bartolini, C., Buffler, R.T., Cantu-Chapa, A. (Eds.), The Western Gulf of Mexico Basin: Tectonics, Sedimentary Basins, and Petroleum SystemsAAPG Memoir, vol. 75, pp. 371–388. Allemann, F., Remane, J., 1979. Les faunes de calpionelles du Berriasien supérieur/Valanginien. In: Busnardo, R., Thieuloy, J.P., Moullade, M. (Eds.), Hypostratotype Mésogeen de l'Etage Valanginian (Sud-Est de la France). Les Stratotypes Français, vol. 6. C.N.R.S., Paris, pp. 99–109. Applegate, J.L., Bergen, J.A., 1986. Cretaceous calcareous nannofossil biostratigraphy of sediments recovered from the Galicia Margin of Leg 103. In: Boillot, G., Winterer, E.L., et al. (Eds.), Proc. ODP, Sci. Results, vol. 103. Ocean Drilling Project, College Station, TX. Arnaud-Vanneau, A., Arnaud, H., Boisseau, T., Darsac, C., Thieuloy, J.P., Vieban, F., 1982. Synchronisme des crises biologiques et paléogéographiques dans le Crétacé inférieur du S.E. de la France: un outil pour les corrélations plate-forme bassin. Géologie Méditerranéenne IX (3), 153–165. Backman, J., Shackleton, N.J., 1893. Quantitative biochronology of Pliocene and early Pleistocene calcareous nannofossils for the Atlantic, Indian and Pacific oceans. Marine Micropaleontology 8, 141–170. Bergen, J.A., 1994. Berriasian to early Aptian calcareous nannofossils from the Vocontian trough (SE France) and deep-sea drilling site 534: new nannofossil taxa and summary of low-latitude biostratigraphic events. Journal of Nannoplankton Research 16 (2), 59–69. Bersezio, R., Erba, E., Gorza, M., Riva, A., 2002. Berriasian–Aptian black shales of the Maiolica Formation (Lombardian Basin, southern Alps, northern Italy): local to global events. Palaeogeography, Palaeoclimatology, Palaeoecology 180, 253–275. Bornemann, A., Aschwer, U., Mutterlose, J., 2003. The impact of calcareous nannofossils on the pelagic carbonate accumulation across the Jurassic–Cretaceous boundary. Palaeogeography, Palaeoclimatology, Palaeoecology 3180, 1–42. Bralower, T.J., Leckie, R.M., Sliter, W.V., Thierstien, H.R., 1995. An integrated Cretaceous microfossil biostratigraphy; geochronology time scales and global stratigraphic correlation. SEPM Special Publication 54, 65–79. Bréhéret, J.G., Brumsack, H.J., 2000. Barite concretions as evidence of pauses in sedimentation in the Marnes Bleues Formation of the Vocontian basin (SE France). Sedimentary Geology 130, 205–228. Brumsack, H.J., 2005. The trace metal content of recent organic carbon-rich sediments: implications for Cretaceous black shale formation. Palaeogeography, Palaeoclimatology, Palaeoecology 232, 344–361. Bulot, L.G., Thieuloy, J.P., 1994. Les biohorizons du Valanginien du SudEst de la France: un outil fondamental pour les corrélations au sein de la Téthys occidentale. Géologie Alpine. Mémoire HS 20, 15–41.

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151 Busnardo, R., Thieuloy, J.P., Moullade, M., 1979. Hypostratotype mésogéen de l'étage Valanginien (SE de la France). Les Stratotypes Français, vol. 6. C.N.R.S., Paris. Canfield, D.E., Raiswell, R., Bottrell, S., 1992. The reactivity of sedimentary irons minerals toward sulfide. American Journal of Science 292, 659–683. Channell, J.E.T., Erba, E., Lini, A., 1993. Magnetostratigraphic calibration of the late Valanginian carbon isotope event in pelagic limestones from northern Italy and Switzerland. Earth and Planetary Science Letters 118, 145–166. Chester, R., 2000. Marine Geochemistry, 2nd edn. Blackwell, London. 520 pp. Coccioni, R., Erba, E., Premoli Silva, I., 1992. Barremian–Aptian calcareous plankton biostratigraphy from the Gorgo Cerbara section (Marche, central Italy) and implications for plankton evolution. Cretaceous Research 13, 517–537. Cotillon, P., 1971. Le Crétacé inférieur de l'arc subalpin de Castellane entre l'Asse et le Var, Stratigraphie et Sédimentologie. Mémoire du B. R.G.M, Bureau de Recherches Géologiques et Minières 68, 1–243. de Kaenel, E., Villa, G., 1996. Oligocene–Miocene calcareous nannofossil biostratigraphy and paleoecology from the Iberia abyssal plain of Leg 149. In: Whitmarsh, R.B., Sawyer, D.S., Klaus, A., Masson, D.G. (Eds.), Proc. ODP, Sci. Results, vol. 149. Ocean Drilling Project, College Station, TX. 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). Les Stratotypes Français, vol. 6. C.N.R.S., Paris, pp. 77–86. Douglas, R.G., Savin, S.M., 1973. Oxygen and carbon isotope analysis of Cretaceous and Tertiary foraminifera from the central North Pacific. Initial Report of the Deep-Sea Drilling Project, vol. 17. U.S. Government Printing Office, Washington, D.C., pp. 591–605. Erba, E., 1994. Nannofossils and superplumes: the early Aptian “nannoconid crisis”. Paleoceanography 9 (3), 483–501. Erba, E., 2004. Calcareous nannofossils and Mesozoic oceanic anoxic events. Marine Micropaleontology 52, 85–106. Erba, E., Tremolada, F., 2004. Nannofossil carbonate fluxes during the early Cretaceous: phytoplankton response to nutrification episodes, atmospheric CO2, and anoxia. Paleoceanography 19, 1–18. Erba, E., Castradori, D., Guasti, G., Ripepe, M., 1992. Calcareous nannofossils and Milankovitch cycles: the example of the Albian Gault Clay Formation (southern England). Palaeogeography, Palaeoclimatology, Palaeoecology 93, 47–69. Erba, E., Channell, J.E.T., Claps, M., Jones, C., Larson, R., Opdyke, B., Premoli Silva, I., Riva, A., Salvini, G., Torricelli, S., 1999. Integrated stratigraphy of the Cismon apticore (southern Alps, Italy): a “reference section” for Barremian–Aptian interval at low latitudes. Journal of Foraminiferal Research 29 (4), 371–391. Erba, E., Bartolini, A.C., Larson, R.L., 2004. Valanginian Weissert oceanic anoxic event. Geology 149–152. Fiet, N., Gorin, G., 2000. Lithological expression of Milankovitch cyclicity in carbonate-dominated, pelagic, Barremian deposits in central Italy. Cretaceous Research 21, 457–467. Fiet, N., Beaudoin, B., Parize, O., 2001. Lithostratigraphic analysis of Milankovitch cyclicity in pelagic Albian deposits of central Italy: implications for the duration of the stage and substages. Cretaceous Research 22, 265–275. Föllmi, K.B., Weissert, H., Bisping, M., Funk, H., 1994. Phosphogenesis, carbon-isotope stratigraphy, and carbonate-platform evolution along the lower Cretaceous northern Tethyan margin. Geological Society of America Bulletin 106, 729–746.

149

Friedman, I., O'Neil, J.R., 1977. Compilation of stable isotope fractionation factors of geochemical interest, In: Fleischer, M. (Ed.), Data of Geochemistry, 6th edition. United States Geological Survey Professional Paper 440-KK. 12 pp. Gale, A.S., Smith, A.B., Monks, N.E.A., Young, J.A., Howard, A., Wray, D.S., Huggett, J.M., 2000. Marine biodiversity through the late Cenomanian–early Turonian: palaeoceanographic controls and sequence stratigraphic biases. Journal of the Geological Society (London) 157, 745–757. Gardin, S., Bulot, L.G., Coccioni, R., De Wever, P., Hishida, K., Lambert, E., 2000. The Valanginian to Hauterivian hemipelagic successions of the Vocontian basin (SE France): new high resolution integrated biostratigraphical data. 6th International Cretaceous Symposium, Geozentrum. University of Vienna, Austria, p. 34. Giraud, F., Beaufort, L., Cotillon, P., 1995. Periodicity of carbonate cycles in the Valanginian of the Vocontian Trough: a strong obliquity control. Geological Society Special Publication 85, 143–164. Graham, D.W., Bender, M.L., Williams, D.F., Keigwin Jr., L.D., 1982. Strontium–calcium ratios in Cenozoic planktonic foraminifera. Geochimica et Cosmochimica Acta 46, 1281–1292. Graziano, R., 1999. The early Cretaceous drowning unconformities of the Apulia carbonate platform (Gargano Promontory, southern Italy): local fingerprints of global palaeoceanographic events. Terra Nova 11, 245–250. 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 and Depositional History of Eustatic Sequences Constraints on Seismic Stratigraphy Cushman Foundation for Foraminiferal Research, Special Publications, vol. 24, pp. 7–13. Hennig, S., Weissert, H., Bulot, L., 1999. C-isotope stratigraphy, a calibration tool between ammonite- and magnetostratigraphy: the Valanginian–Hauterivien transition. Geologica Carpathica 50, 91–96. Herrle, J.O., 2003. Reconstructing nutricline dynamics of mid-Cretaceous oceans: evidence from calcareous nannofossils from the Paquier black shale (SE France). Marine Micropaleontology 47, 307–321. Hild, E., Brumsack, H.J., 1998. Major and minor element geochemistry of lower Aptian sediments from the NW German Basin (core Hoheneggelsen KB 40). Cretaceous Research 19, 615–633. Hoedemaeker, P.J., Rawson, P.F., 2000. Report on the 5th International Workshop of the Lower Cretaceous Cephalopod Team (Vienna, 5 September 2000). Cretaceous Research 21, 857–860. Hoedemaeker, P.J., Reboulet, S., Aguirre-Urreta, M.B., Alsen, P., Aoutem, M., Atrops, F., Barragán, R., Company, M., GonzálezArreola, C., Klein, J., Lukeneder, A., Ploch, I., Raisossadat, N., Rawson, P.F., Ropolo, P., Vašíèek, Z., Vermeulen, J., Wippich, M.G.E., 2003. Report on the 1st International Workshop of the IUGS Lower Cretaceous Ammonite Working Group, the ‘Kilian Group’ (Lyon, 11 July 2002). Cretaceous Research 24, 89–94. Huang, Z., Ogg, J.G., Gradstein, F.M., 1993. A quantitative study of lower Cretaceous cyclic sequences from the Atlantic Ocean and the Vocontian basin (SE France). Paleoceanography 8, 275–291. Janin, M.C., 1998. Remarques sur l'ultrastructure et les affinités biologiques des Lithraphidites, nannofossile calcaire du Crétacé. Revue de Micropaléontologie 41 (4), 281–296. Kruse, S., Mutterlose, J., 2000. Coccoliths under stress? Lower Cretaceous calcareous nannofossil assemblages of nearshore and pelagic settings (NW Africa). Journal of Nannoplankton Research 22 (2), 171. Larson, R.L., Erba, E., 1999. Onset the mid-Cretaceous greenhouse in the Barremian–Aptian: igneous events and the biological, sedimentary, and geochemical responses. Paleoceanography 14, 663–678.

150

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151

Lini, A., Weissert, H., Erba, E., 1992. The Valanginian carbon isotope event: a first episode of greenhouse climate conditions during the Cretaceous. Global Change Special 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). Les Stratotypes Français, vol. 6. C.N.R.S., Paris, pp. 87–98. Martin, J.H., Gordon, R.M., Fitzwater, S., Broenkow, W.W., 1989. Phytoplankton/iron studies in the Gulf of Alaska. Deep-Sea Research 36, 649–680. Masse, J.P., 1993. Valanginian–earlyAptian carbonate platforms from Provence, southeastern France. In: Simo, J.A.T., Scott, R.W., Masse, J.P. (Eds.), Cretaceous Carbonate Platform. AAPG Mem., vol. 56, pp. 363–374. McIntyre, A., Bé, A.W.H., 1967. Modern Coccolithophoridae of the Atlantic Ocean — placoliths and cyrtoliths. Deep-Sea Research 14, 561–597. Molfino, B., McIntyre, A., 1990. Precessional forcing of nutricline dynamics in the equatorial Atlantic. Science 249, 766–769. Mutterlose, J., 1991. Biostratigraphy and palaeobiogeography of early Cretaceous calcareous nannofossils. Cretaceous Research 13, 167–189. Mutterlose, J., Kessels, K., 2000. Early Cretaceous nannofossils from high latitudes: implications for palaeobiogeography and palaeoclimate. Palaeogeography, Palaeoclimatology, Palaeoecology 160, 347–372. Orians, K.J., Bruland, K.W., 1986. The biogeochemistry of aluminum in the Pacific Ocean. Earth and Planetary Science Letters 78, 397–410. Patton, J.W., Choquette, P.W., Guennel, G.K., Kaltenback, A.J., Moore, A., 1984. Organic geochemistry and sedimentology of lower to midCretaceous deep-sea carbonates, site 535 and 540, Leg 77. Initial Reports of the Deep-sea Drilling Project, vol. 77. U.S. Government Printing Office, Washington, D.C., pp. 417–443. Premoli Silva, I., Erba, E., Tornaghi, M.E., 1989. Palaeoenvironmental signals and changes in surface water fertility in mid Cretaceous Corg-rich pelagic facies of the Fucoid Marls (Central Italy). Geobios. Memoire Special 11, 225–236. Pucéat, E., Lécuyer, C., Sheppard, S.M.F., Dromart, G., Reboulet, S., Grandjean, P., 2002. Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels. Paleoceanography 18 (2), 1029–1041. Reboulet, S., 1995. L'évolution des ammonites du ValanginienHautérivien inférieur du bassin Vocontien et de la plate-forme provençale (Sud-Est de la France): Relations avec la stratigraphie séquentielle et implications biostratigraphiques. Document des Laboratoires de Géologie, vol. 137. Lyon, France. Reboulet, S., Atrops, F., 1999. Comments and proposals about Valanginian–lower Hauterivian ammonite zonation of southeastern France. Eclogae Geologicae Helveticae 92, 183–197. Reboulet, S., Mattioli, E., Pittet, B., Baudin, F., Olivero, D., Proux, O., 2003. Ammonoid and nannoplankton abundance in Valanginian (early Cretaceous) limestone–marl successions from the southeast France Basin: carbonate dilution or productivity? Palaeogeography, Palaeoclimatology, Palaeoecology 3189, 1–27. Renne, P.R., Glen, J.M., Milner, S.C., Duncan, R.A., 2001. Age of Etendeka flood volcanism and associated intrusions in southwestern Africa. Geology 24, 659–662. Roth, P.H., 1989. Ocean circulation and calcareous nannoplankton evolution during the Jurassic and Cretaceous. Palaeogeography, Palaeoclimatology, Palaeoecology 74, 111–126.

Roth, P.H., Bowdler, J.L., 1981. Middle Cretaceous calcareous nannoplankton biogeography and oceanography of the Atlantic Ocean. The Society of Economic Paleontologists and Mineralogists, SEPM Special Publication 32, 517–546. Roth, P.H., Krumbach, K.R., 1986. Middle Cretaceous calcareous nannofossil biogeography and preservation in the Atlantic and Indian oceans: implications for paleoceanography. Marine Micropaleontology 10, 235–266. Roth, P.H., Thierstein, H.R., 1972. Calcareous nannoplankton, Leg 14 of the Deep-sea Drilling Project. In: Hayes, D.E. (Ed.), Init. Reports of Deep-sea Drilling Project, vol. 14. U.S. Government Printing Office, Washington, D.C., pp. 421–485. Scarparo Cunha, A.A., Koutsoukos, E.A.M., 1998. Calcareous nannofossils and planktic foraminifers in the upper Aptian of the Sergipe Basin, northeastern Brazil: palaeoecological inferences. Palaeogeography, Palaeoclimatology, Palaeoecology 142, 175–184. Schlager, W., 1981. The paradox of drowned reefs. GSA Bulletin 92, 197–211. Smith, A.G., Smith, D.G., Funnell, B.M., 1994. Atlas of Mesozoic and Cenozoic Coastlines. Cambridge University Press, Cambridge. Stoll, H.M., Schrag, D.P., 2001. Sr/Ca variations in Cretaceous carbonates: relation to productivity and sea-level changes. Palaeogeography, Palaeoclimatology, Palaeoecology 168, 311–336. Street, C., Bown, P.R., 2000. Palaeobiogeography of early Cretaceous (Berriasien–Barremien) calcareous nannoplankton. Marine Micropaleontology 39, 265–291. Thierstein, H., 1973. Lower cretaceous calcareous nannoplankton biostratigraphy. Abhandlungen der Geologischen Bundesanstalt (Austria) 29, 1–52. Van de Schootbrugge, B., Föllmi, K., Bulot, L.G., Burns, S.J., 2000. Paleoceanographic changes during the early Cretaceous (Valanginian–Hauterivian): evidence from oxygen and carbon stable isotopes. Earth and Planetary Science Letters 181, 15–31. Wedepohl, K.H., 1991. The composition of the upper Earth's crust and the natural cycles of selected metals. Metals in natural raw materials. Natural resources. In: Merian, E. (Ed.), Metals and their Compounds in the Environment. VCH, Weinheim, pp. 3–17. Weissert, H., 1989. C-isotope stratigraphy, a monitor of palaeoenvironmental change: a case study from the early Cretaceous. Surveys in Geophysics 10, 1–61. Weissert, H., Channel, J.E.T., 1989. Tethyan carbonate carbon isotope stratigraphy across the Jurassic–Cretaceous boundary: an indicator of decelerated global carbon cycling? Palaeoceanography 4 (4), 483–494. Weissert, H., Erba, E., 2004. Volcanism, CO2 and paleoclimate: a late Jurassic–early Cretaceous carbon and oxygen isotope record. Journal of the Geological Society 161, 695–702 (London). 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 the carbon cycle during the early Cretaceous. In: Sundquist, E.T., Broecker, W.S. (Eds.), The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to the PresentGeoGeophys. Monogr., vol. 32, pp. 531–545. Weissert, H., Lini, A., Föllmi, K.B., Kuhn, O., 1998. Correlation of early Cretaceous carbon isotope stratigraphy and platform drowning events: a possible link? Palaeogeography, Palaeoclimatology, Palaeoecology 137, 189–203.

S. Duchamp-Alphonse et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007) 132–151 Williams, J.R., Bralower, T.J., 1995. Nannofossil assemblages, fine fraction stable isotopes, and the paleoceanography of the Valanginian–Barremian (early Cretaceous) North-Sea Basin. Paleoceanography 10, 815–839. Wilpshaar, M., Leereveld, H., Visscher, H., 1997. Early Cretaceous sedimentary and tectonic development of the Dauphinois Basin (SE France). Cretaceous Research 18, 457–468.

151

Young, J.R., 1994. Functions of coccoliths. In: Winter, A., Siesser, W. (Eds.), Coccolithophores. Cambridge University Press, Cambridge, pp. 63–82. Ziveri, P., Thunnell, R.C., Rio, D., 1995. Export production of coccolithophores in an upwelling region: results from San Pedro Basin, southern California borderlands. Marine Micropaleontology 24, 335–358.