Niveau Breistroffer - GeoScienceWorld

Journal of the Geological Society, London, Vol. 162, 2005, pp. 623–639. Printed in Great Britain.

Reconstruction of short-term palaeoceanographic changes during the formation of the Late Albian ‘Niveau Breistroffer’ black shales (Oceanic Anoxic Event 1d, SE France) ¨ R G P RO S S 2,3 , K E R S T I N R E I C H E LT 4, J E N S O. H E R R L E 4,5 , A N D R E´ B O R N E M A N N 1,6, J O ¨ RG MUTTERLOSE 1 C H R I S TO P H H E M L E B E N 4 & J O 1 Institut fu¨r Geologie, Mineralogie und Geophysik, Ruhr-Universita¨t Bochum, Universita¨tsstr. 150, D-44780 Bochum, Germany (e-mail: [email protected]) 2 Laboratory of Palaeobotany and Palynology, Department of Geobiology, Universiteit Utrecht, Budapestlaan 4, NL-3584 CD Utrecht, The Netherlands 3 Institut fu¨r Geologie und Pala¨ontologie, Johann Wolfgang Goethe-Universita¨t Frankfurt, Senckenberganlage 32–34, D-60054 Frankfurt, Germany 4 Institut fu¨r Geowissenschaften, Eberhard-Karls-Universita¨t Tu¨bingen, Sigwartstr. 10, D-72076 Tu¨bingen, Germany 5 Southampton Oceanography Centre, School of Ocean and Earth Science, European Way, Southampton SO14 3ZH, UK 6 Present address: Scripps Institution of Oceanography - UCSD, La Jolla, CA 92093-0244, USA (e-mail: [email protected]) Abstract: The Niveau Breistroffer black shale succession in the Vocontian Basin (SE France) is the regional equivalent of the widely distributed Late Albian Oceanic Anoxic Event 1d. The studied black shale-rich interval at the Col de Palluel section is 6.28 m thick and comprises four black shale units with up to 2.5 wt% total organic carbon (TOC) intercalated with marlstones. Calcareous nannofossil, palynomorph, planktic Foraminifera and stable isotopic data from the Niveau Breistroffer succession suggest that short-term climate changes influenced its deposition, with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition. An increase in the terrigenous/marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation. A nutrient index based on calcareous nannofossils and the abundance pattern of small (63– 125 ìm) hedbergellid Foraminifera show short-term changes in the productivity of the surface water. Surfacewater productivity was reduced during black shale formation and increased during marlstone deposition. A calcareous nannofossil temperature index and bulk-rock oxygen isotope data indicate relative temperature changes, with warmer surface waters for black shale samples. At these times, warm–humid climate and reduced surface-water productivity were accompanied by greater abundances of ‘subsurface’-dwelling calcareous nannofossils (nannoconids) and planktic Foraminifera (rotaliporids). These taxa presumably indicate more stratified surface-water conditions. We suggest that the formation of the Niveau Breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation. This, in turn, caused a decrease in low-latitude deep-water formation and probably an increase in surface-water stratification. The combination of these two mechanisms caused depleted O2 concentrations in the bottom water that increased the preservation potential of organic matter. Keywords: SE France, Albian, black shale, palaeoceanography, palaeoclimatology.

termed Oceanic Anoxic Events (OAEs; Schlanger & Jenkyns 1976). The storage of large amounts of organic carbon during OAE formation caused major perturbations of the global carbon cycle as they are recorded, for instance, in the carbon isotopic signature of marine carbonates (e.g. Jenkyns et al. 1994; Weissert et al. 1998). The OAE intervals correspond to positive carbon isotope excursions with amplitudes larger than 1.5‰ observed in hemipelagic to pelagic carbonates, platform sediments and terrestrial records (e.g. Gro¨tsch et al. 1998; Weissert et al. 1998; Wilson et al. 1998; Gro¨cke et al. 1999; Jenkyns & Wilson 1999). Most studies on mid-Cretaceous OAEs have focused either on the Early Aptian OAE 1a (e.g. Erba 1994; Menegatti et al. 1998; Beerling et al. 2002) or the Cenomanian–Turonian OAE 2 (e.g. Arthur et al. 1988; Kuhnt 1992; Gale et al. 1993; Huber et al. 1999). Less research has been undertaken on the sub-OAEs

The mid-Cretaceous has been commonly characterized as a time of prevailing greenhouse conditions caused by elevated atmospheric pCO2 levels (e.g. Barron & Washington 1985; Bice & Norris 2002) triggered by high rates of ocean crust production and submarine volcanism (Larson 1991a, b). These warm conditions were accompanied by a long-term sea-level rise (Haq et al. 1987), low latitudinal temperature gradients (e.g. Huber et al. 1995) and an accelerated hydrological cycle (e.g. Weissert et al. 1998; Wortmann et al. 2004). Earlier studies on the oxygen isotopic composition of benthic and planktic foraminiferal tests suggest that both surface- and bottom-water temperatures were higher than in modern oceans (e.g. Savin 1977; Huber et al. 2002; Wilson et al. 2002). The sedimentological record of the mid-Cretaceous is punctuated by repeated occurrence of globally distributed black shales, 623

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(OAE 1b–1d). In this study, we focus on the Late Albian OAE 1d. Black shales or equivalent strata of this age have been described in detail from SE France (‘Niveau Breistroffer’, Bre´he´ret 1988, 1994, 1997; Giraud et al. 2003) and the Atlantic Ocean (Mazagan Plateau, Nederbragt et al. 2001; Leckie et al. 2002; Blake Nose Plateau, Wilson & Norris 2001). An overview of the supraregional occurrence of the OAE 1d black shales has been provided by Wilson & Norris (2001). To understand better the mechanisms that led to the formation of mid-Cretaceous black shales, various approaches have been followed. Sedimentological studies supplied information on sealevel fluctuations and the depositional environment (e.g. Bre´he´ret 1994; Wignall 1994). Geochemical investigations focused on elemental analyses (e.g. Wortmann et al. 1999), stable isotopes (e.g. Menegatti et al. 1998; Erbacher et al. 2001; Wilson & Norris 2001) and organic geochemistry (e.g. Bre´he´ret 1994; Erbacher et al. 1996; Baudin et al. 1998). These studies provided information on weathering conditions, the chemical composition of seawater and the source of organic matter, as well as data on surface-water productivity, oceanic carbon cycling and temperatures. Microfossils have been used to reconstruct biological, ecological and palaeoceanographic changes in the oceans during black shale formation. (See Leckie et al. (2002) for an overview; for calcareous nannofossils, e.g. Bralower et al. (1993), Erba (1994), Mutterlose (1996) and Herrle et al. (2003a, b); for planktic Foraminifera, e.g. Galeotti (1998), Huber et al. (1999), Premoli-Silva et al. (1999) and Nederbragt et al. (2001); for benthic Foraminifera, e.g. Erbacher et al. (1999), Luciani et al. (2001) and Friedrich et al. (2003); for Radiolaria, Erbacher & Thurow (1997); for palynomorphs, Tribovillard & Gorin (1991), Hochuli et al. (1999) and Herrle et al. (2003a, b).) The formation of mid-Cretaceous black shales has commonly been linked to productivity changes caused by variations in nutrient supply (e.g. Pedersen & Calvert 1990; Hochuli et al. 1999; Wilson & Norris 2001) and/or increased organic matter preservation in a stratified water column with low bottom-water oxygenation (e.g. Bralower & Thierstein 1984; Pedersen & Calvert 1990; Erbacher et al. 2001). Stable isotope data from excellently preserved foraminiferal tests suggest that the origin of mid-Cretaceous black shales in the western Atlantic Ocean may be either similar to the formation of Mediterranean sapropels (Ryan & Cita 1977; Erbacher et al. 2001) or related to a collapse of water column stratification (Wilson & Norris 2001). Recently, Herrle et al. (2003a, b) proposed a model suggesting that the formation of the OAE 1b in the western Tethys was triggered by changes in deep-water formation rates resulting from changes in monsoonal activity. This may have influenced bottom-water oxygenation and thus the preservation of organic matter. Similarities between the processes that led to the formation of mid-Cretaceous black shales and that of Pliocene to Quaternary sapropels in the Mediterranean Sea have been stressed by various workers (e.g. Ryan & Cita 1977; Erbacher et al. 2001; Herrle et al. 2003b; Friedrich et al. 2005). Multi-proxy studies dealing with the formation of Quaternary black shales, however, indicate that many processes that are responsible for the accumulation of organic matter operate on either Milankovitch or even subMilankovitch time scales (e.g. van Os et al. 1994). This contrasts with our present understanding of the controls on mid-Cretaceous black shale formation, which is mainly based on studies that have a relatively low stratigraphic resolution and/or utilize few proxies. Hence, fundamental differences in the available datasets hinder an in-depth comparison of mid-Cretaceous with Pliocene to Quaternary black shale successions.

This paper presents high-resolution data from calcareous nannofossils, planktic Foraminifera, palynomorphs and stable isotopes for the Late Albian OAE 1d. The aim of our study is (1) to reconstruct short-term palaeoceanographic changes, (2) to calibrate and compare signals between different microfossil groups and geochemical data, (3) to develop a model for the formation of this black shale event on a regional and supraregional scale, and (4) to compare the results with other Cretaceous black shales and Mediterranean sapropels. We have chosen the Vocontian Basin (SE France; Fig. 1) as a study area because this marginal basin was very sensitive to climatic and oceanographic changes during the mid-Cretaceous.

Location, lithology, stratigraphy and palaeogeography Location of the study section The OAE 1d black shales, which are named Niveau Breistroffer in SE France (Bre´he´ret 1988), have been studied at the Col de Palluel section (Fig. 1) south of the road D994 c. 5 km east of Rosans, De´partement Droˆme (TK 25 Rosans, Nr. 3239 Ouest, Se´rie Bleues, Lambert III coordinates: x, 853 750; y, 3238 425). There is some inconsistency in the definition of the Niveau Breistroffer interval in the Vocontian Basin. Bre´he´ret (1997) described seven black shale bundles (BR1–BR7) over a 40 m sequence as the Niveau Breistroffer. In contrast, Gale et al. (1996) used this term for a bundle of five black shale units covering a total of 10 m at the Col de Palluel section. Here we have followed an intermediate approach and named the black shale interval of Gale et al. (1996) the ‘main Niveau Breistroffer’ (Fig. 2), which includes the black shale bundles BR2 and BR3 after Bre´he´ret (1997).

Fig. 1. Palaeogeographical reconstruction of SE France for the Albian (modified after Arnaud & Lemoine 1993).

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Fig. 2. Lithological and stratigraphic framework for the Marnes Bleues Formation and the Niveau Breistroffer (Col de Palluel section, SE France) based on ammonites (Bre´he´ret 1997), planktic Foraminifera (Moullade 1966; Reichelt 2005), calcareous nannofossils (Gale et al. 1996; Herrle & Mutterlose 2003), lithostratigraphy (Bre´he´ret 1997) and carbon isotope data (Reichelt 2005; this study). Isotope data have been smoothed using the weighted harmonic mean method. Samples marked by a * or § have not been studied with respect to palynomorphs (*) or planktic Foraminifera (§).

Lithology The investigated main Niveau Breistroffer interval is 6.28 m thick and consists of weakly lithified, fine-grained marlstones and four laminated black shale units. These sediments consist of variable proportions of mainly biogenic carbonate (calcareous nannofossils, planktic and benthic Foraminifera, calcispheres) and siliciclastic material (clay minerals, fine-grained quartz); to a lesser extant, organic matter and diagenetic carbonate occur (for details see Bre´he´ret 1997). Pale–dark bedding rhythms are indicated by slight colour differences that reflect variations of the carbonate and organic carbon content. Marlstones are bioturbated and show a blocky fabric. A 0.4 m thick dark marlstone layer occurs between 50 and 50.4 m. This unit is homogeneous and has a blocky to platy appearance. The intercalated black shales

are 0.2–0.7 m thick. They are platy to fissile and exhibit varying degrees of sub- to millimetre-scale lamination. Ammonites and aucelline bivalves are common in the black shales. A sporadic occurrence of calcareous nodules has been observed at 49.8 m. These nodules are less than 10 cm in size and seem to trace fossil burrows.

Stratigraphy and chronostratigraphic framework According to Gale et al. (1996), the main Niveau Breistroffer can be assigned to the Upper Albian Stoliczkaia dispar ammonite zone and Eiffellithus turriseiffelii nannofossil zone (¼ NC10A after Bralower et al. 1993; Fig. 2). The last appearance datum of the planktic Foraminifera Planomalina buxtorfi has been ob-

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served 17 m above the top of the study interval, supporting the assignment to the P. buxtorfi/Rotalipora appenninica planktic foraminiferal subzone (Reichelt 2005). Bulk-rock carbon isotope data from the P. buxtorfi/R. appeninnica foraminiferal subzone show a negative shift in the lower interval of the main Niveau Breistroffer. This shift is followed by a positive excursion with an amplitude of 1.5‰ (Fig. 2) and is herein correlated with the planktic Foraminifera carbon isotope record from Ocean Drilling Program (ODP) Hole 1052E on Blake Nose Plateau (Wilson & Norris 2001; Fig. 3). Time control for the investigated succession was achieved through the correlation of the carbon isotope record from the Col de Palluel section to the carbon isotope record of Wilson & Norris (2001) from the Blake Nose Plateau (Fig. 3). The age model of ODP Hole 1052E is based on orbitally tuned neutron log data (see Wilson & Norris (2001) for details). According to this correlation, the mean sedimentation rate for the studied section was calculated at c. 44 mm ka
1 , and therefore the entire section comprises c. 159 ka. Sedimentation rates after compaction increased from c. 27 mm ka
1 at the base of the section to c. 52 mm ka
1 in the upper part. This change in sedimentation rate is also reflected by increasing thickness of the marlstones

between the black shale units. The applied method gives an estimate of the sedimentation rates. However, short-term variations in sedimentation rates cannot be ruled out, as possibly indicated by the occurrence of calcareous nodules. Depending on the proxies studied, sample resolution varied between c. 3.2 and c. 3.7 ka (see the Methods section).

Palaeogeography and palaeobathymetry During the mid-Cretaceous, the Vocontian Basin was located at a palaeo-latitude of 25–308N (Savostin et al. 1986; Hay et al. 1999) and was part of the European continental margin of the Ligurian Tethys (Lemoine et al. 1986). The basin was surrounded by the Massif Central landmass to the NW and by carbonate platforms to the north and south (‘Urgonian’ platform carbonates, Arnaud-Vanneau & Arnaud 1990). To the east, it was open toward the Tethyan Ocean (Fig. 1). From the Early Aptian to the latest Albian, a c. 750 m thick succession of cyclically bedded marlstones and limestones was deposited in the centre of the basin (Marnes Bleues Formation, Flandrin 1963). Black shales, limestones and glauconite-bearing turbidites are intercalated in this succession and serve as

Fig. 3. Age control on the formation of the Niveau Breistroffer black shales is based on a correlation of the carbon isotope record from the Blake Nose Plateau (planktic Foraminifera (a, b), ODP Hole 1052E; Wilson & Norris 2001) with that from the Col de Palluel (bulk-rock (c); Reichelt 2005; this study). The age model of ODP Hole 1052E is based on orbitally tuned neutron log data (for details see Wilson & Norris 2001). Based on our correlation, the studied succession of the main Niveau Breistroffer at the Col de Palluel section covers c. 159 ka, with the calculated sedimentation rate increasing from the bottom (27 mm ka
1 ) to the top (52 mm ka
1 ). The calculated average sedimentation rate for the entire section is 44 mm ka
1 . Shaded area indicates assumed correlation of the studied succession at the Col de Palluel section to the Blake Nose Plateau section. Isotope data have been smoothed based on the weighted harmonic mean method. (For explanations of lithological symbols see Fig. 2.)

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lithostratigraphic marker beds (Bre´he´ret 1997; Fig. 2). The studied succession at the Col de Palluel section is situated close to the depocentre of the basin (Fig. 1). Palaeobathymetric estimates for the Vocontian Basin are under debate. They vary from several hundred metres (Wilpshaar & Leereveld 1994) to 2 km (Cotillon & Rio 1984). The latter estimate, however, seems unlikely, based on the faunal and floral composition (Wilpshaar & Leereveld 1994). Holbourn et al. (2001) undertook a statistical analysis of late Albian benthic Foraminifera from the Col de Palluel section, which suggests a water depth of about 1 km.

Methods Geochemistry (CaCO3, TOC, ä13 Cbulk , ä18 Obulk ) A total of 50 samples (Fig. 2) was measured for CaCO3, total organic carbon (TOC) and stable isotopes of bulk-rock carbonate (ä13 Cbulk , ä18 Obulk ). CaCO3 content was determined from atomic absorption spectrometry (Varian SpectrAA 300) measurements assuming that the total Ca is bound to CaCO3. TOC was calculated from the difference between the total carbon content, measured with a Deltronik coulometer at the Ruhr-University Bochum, and the total inorganic carbon derived from the CaCO3 values. Stable isotope preparation was performed using an off-line preparation technique (see Shackleton et al. 1984; Bruckschen & Veizer 1997). Measurements were carried out using a Finnigan MAT Delta S mass spectrometer at the Ruhr-University Bochum. The measurements yielded a precision of 0.10 and 0.12‰ for carbon and oxygen isotope values, respectively.

abundance of calcareous nannofossils accompanied by high abundances of W. barnesae. Calcareous nannofossil nutrient and temperature indices. Temporal and spatial changes in the distribution and abundance of calcareous nannofossils are controlled by climatic and oceanographic parameters. Thus, they allow the reconstruction of palaeoenvironmental conditions in the geological record (e.g. Erba et al. 1992; Mutterlose 1996; Street & Bown 2000). Surface-water temperature and nutrient availability are thought to be the most important parameters controlling the distribution and composition of recent calcareous nannoplankton assemblages (e.g. Brand 1994; Winter et al. 1994). In this study, short-term changes in surface-water nutrient content and temperature were assessed through nannofossil-based nutrient and temperature indices. Based on literature data and a Varimax-rotated R-mode principal component analysis, Herrle et al. (2003b) developed such indices from a dataset of Aptian–Albian nannofossils from the Vocontian Basin. Those workers used ratios of index species instead of single taxon abundances to assess changes in surface-water nutrient availability and temperature. Results from the literature suggest that Biscutum constans, Discorhabdus ignotus (¼ D. rotatorius) and Zeugrhabdotus erectus have an affinity to elevated nutrient levels in the surface waters (e.g. Roth & Krumbach 1986; Premoli-Silva et al. 1989; Erba 1992; Erba et al. 1992). According to Erba (1992), a differentiation in the abundance pattern between these taxa occurs with respect to different nutrient concentrations, with D. ignotus and Z. erectus being adapted to higher nutrient levels than B. constans. Watznaueria barnesae is often interpreted as an oligotrophic taxon (e.g. Roth & Krumbach 1986; Erba et al. 1992; Williams & Bralower 1995). Based on the principal component analysis calculated by Herrle et al. (2003b), D. ignotus and Z. erectus were used as indicators for high and W. barnesae (including W. fossacincta) for low nutrient levels:

Calcareous nannofossils The same samples as used for geochemistry were investigated for their content of calcareous nannofossils. The random settling technique (Williams & Bralower 1995; Geisen et al. 1999) was applied for slide preparation. The obtained absolute abundances were corrected to the total water column within the settling box (see Bollmann et al. 1999; Geisen et al. 1999). To detect preservation changes induced by preparation, simple smear slides were prepared and the state of nannofossil preservation was compared with the settling slides. Abundances were determined by counting at least 300 specimens. In addition, one random traverse of the slide was scanned for rare species. Counts were performed using an Olympus BH-2 light microscope with cross-polarized light at a magnification of 31500. The diversity of the nannoflora was characterized by the parameters of species richness (S) and heterogeneity (HS ). The latter was calculated by using an information function after Shannon & Weaver (1949). Nannofossil preservation is a critical factor in the palaeoecological interpretation of nannofossil data. Carbonate dissolution can take place in the water column, at the sediment–water interface and in the sediment (e.g. Honjo 1976; Steinmetz 1994). To characterize the preservation of calcareous nannofossils, visual criteria for etching (E) and overgrowth (O) were applied during the light microscope study (see Roth & Thierstein 1972; Roth 1973). Moreover, investigations with a scanning electron microscope (SEM) on selected samples were performed using a LEO Gemini 1530 at the Ruhr-University Bochum (technical details: beam voltage 10 kV, spot size 4 nm, working distance 9 mm, gold sputtered). Another approach to evaluate nannofossil preservation in Cretaceous sediments is based on the relative abundance of Watznaueria barnesae. This taxon is believed to be relatively resistant to dissolution (e.g. Roth & Krumbach 1986). According to Roth & Krumbach (1986), assemblages consisting of more than 40% of W. barnesae may have been significantly altered. Williams & Bralower (1995) pointed out that high abundances of Watznaueria can also result from specific palaeoenvironmental conditions. Therefore they suggested that the abundance pattern of dissolution-resistant species such as W. barnesae should be compared with changes of species richness and absolute abundance. Diagenetically altered assemblages should show low numbers of species and absolute

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NI ¼

D: ignotus þ Z: erectus 3 100: D: ignotus þ Z: erectus þ W : barnesae

As a result of evolutionary changes of the calcareous nannofossil assemblages from the Early to the Late Albian the temperature index of Herrle et al. (2003b) was modified based on literature data. Crucibiscutum salebrosum (incl. C. hayii), Repagulum parvidentatum and Tranolithus orionatus were considered as cold-water species (e.g. Roth 1983; Mutterlose & Wise 1990; Crux 1991; Mutterlose & Kessels 2000; Street & Bown 2000; Herrle et al. 2003b), and Rhagodiscus spp. (R. asper and R. achlyostaurion) as indicators for warmer surface waters (e.g. Roth & Krumbach 1986; Mutterlose 1989; Crux 1991; Erba et al. 1992;Herrle et al. 2003b): TI ¼ C: salebrosum þ T : orionatus þ R: parvidentatum C: salebrosum þ T : orionatus þ R: parvidentatum þ Rhagodiscus spp: 3100:

Palynomorphs Palynomorphs were studied from 43 samples (Fig. 2). Sample preparation followed standard palynological preparation techniques (e.g. Wood et al. 1996; Pross & Schmiedl 2002). Known weights of sample material (between 12 and 19 g) were treated with HCl and HF. To facilitate the calculation of absolute palynomorph abundances, samples were spiked with Lycopodium marker spores prior to chemical processing. Because of the high amount of amorphous organic matter in the residues, a short oxidation with HNO3 was performed. For each sample at least 300 palynomorphs were counted from strew mounts. To quantify terrestrial input, the terrigenous/marine ratio of palynomorphs was calculated (e.g. Pross 2001). Absolute spore abundances and the ratio between absolute spore and non-saccate pollen abundances were used as proxies for humidity in the hinterland. To minimize taphonomic effects, saccate pollen, which are especially prone to long-distance aeolian transport, were not considered in the evaluation.

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Planktic Foraminifera Forty-seven samples were studied with respect to planktic Foraminifera (Fig. 2). Sample preparation followed standard techniques (H2 O2, Wick 1947; tenside, Wissig & Herrig 1999). Samples were washed over a 63 ìm sieve and dried for c. 24 h. The sample was then soaked in 5–10 ml of an ethanol–tenside (Rewoquad) mixture for 24–72 h. In a second washing over a 63 ìm sieve the remaining sediment was removed. Residues were split into three fractions (63–125, 125–250 and 250–500 ìm). A total of 200–300 specimens per fraction were counted from each sample. The preservation of planktic Foraminifera has been studied using a LEO 1450VP SEM at the University of Tu¨bingen (technical details: beam voltage 10 kV, spot size 4 nm, working distance 15 mm, gold sputtered). As small globular forms are thought to have been better adapted to high surface-water nutrient levels and an unstable environment (Caron & Homewood 1982; Leckie 1989; Premoli-Silva & Sliter 1999), we studied abundance changes of Hedbergella spp. within the size fraction 63– 125 ìm as a representative of this group. In contrast, flattened, keeled forms are thought to have preferred a deeper environment close to the thermocline (Wilson & Norris 2001; water depth .100 m, Leckie 1987) and more stable, stratified conditions (Caron & Homewood 1982; Hart

1999; Premoli-Silva & Sliter 1999). From this group Rotalipora spp. (.125 ìm) were counted. The full dataset is available from the PANGAEA database (http:// www.pangaea.de).

Results Geochemistry (CaCO3, TOC, ä13 Cbulk , ä18 Obulk ) CaCO3 contents vary between 47 and 67 wt% (mean 56 wt%), and are up to 20 wt% higher in the marlstones than in the black shales (Fig. 4). Distinctive minima occur in the black shale sample at 49.26 m and in the dark marlstone at 50.19 m. TOC contents show a mean of 1.3 wt%, but the values differ significantly between marlstones and black shales. Whereas marlstones exhibit TOC contents around 1 wt%, black shales have up to 2.5 wt% TOC (Fig. 4). The bulk-rock carbon isotope record shows fluctuations between 1 and 2.6‰ (mean 1.6‰; Fig. 4), with generally heavier

Fig. 4. Results from geochemical (CaCO3 , TOC, ä13 Cbulk , ä18 Obulk ) and calcareous nannofossil (species richness, heterogeneity, absolute abundance, relative abundances of selected taxa) analyses from the Col de Palluel section. (For explanations of lithological symbols see Fig. 2.)

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values in the black shales. Higher oxygen isotope values (from
4.9 to
3‰; mean
4.1‰; Figs 4 and 5) have been observed in the marlstones. Three of the four black shale units are characterized by decreasing values with minima as low as
4.8‰. The oxygen isotope record shows a general trend from lighter values in the lower part to heavier ones in the upper part of the succession.

Calcareous nannofossils In all samples the investigated nannofossils are well to moderately preserved and show only slight indications of etching (E1) and/or overgrowth (O1). Diagenetic micrite and cements have been rarely observed during the light microscopic and SEM studies (see, for instance, Fig. 6a, b and e). The studied material yielded highly diverse nannofloras with a species richness between 44 and 66 (mean 58; Fig. 4). High species numbers occur generally in the black shale samples, but values are equally high in the marlstones between 49.5 and 52.5 m. Similar to the species richness, the assemblage heterogeneity peaks in the lowermost three black shale units (2.71– 3.28, mean 3.0) and shows high values in the upper part of the studied succession. Absolute calcareous nannofossil abundances range from 1.2E þ 9 to 3.2E þ 9 nannofossils per gram of sediment (mean 2.1E þ 9; Fig. 4). Highest absolute abundances occur in the marlstone samples. Between 60.6 and 76.6% of the total nannofossil assemblage is made up by the eight nannofossil groups mentioned below. Biscutum constans shows relative abundances between 26.9 and 43.4% (mean 35.6%; Fig. 4). D. ignotus and Z. erectus make up 3.6–13.2% (mean 8.0%) and 0.6–5.6% (mean 3.2%) of the

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assemblage, respectively. These three taxa show generally higher values in the marlstones. Relative abundances of W. barnesae vary between 3.3 and 13.3% (mean 7.2%), with slightly higher percentages in the black shales (mean for black shales is 7.5%; for marlstones 7.1%). The percentages of Nannoconus spp. (N. elongatus, N. fragilis, N. truitti regularis, N. truitti rectangularis, N. truitti truitti, Nannoconus sp.) fluctuate between 0 and 4.7% (mean 1.4%), with maxima occurring in or close to the black shale units. Nannoconids are not present at the base and the top of the studied succession (Figs 4 and 5). Rhagodiscus spp. exhibit relative abundances between 6.3 and 15.5% (mean 11.0%). Maximum values have been observed in the black shales or close to them. Both C. salebrosum and T. orionatus show generally high percentages in the marlstones. Their relative abundances are in the range of 0–2.2% (mean 0.7%) and 1.3–5.6% (mean 3.7%), respectively (Fig. 4). In contrast to the abundance changes of single nannofossil taxa, the nutrient index and temperature index records suggest a more uniform picture with lower surface-water productivity and slightly higher temperatures during black shale formation as compared with marlstones (Fig. 5). The nutrient index fluctuates between 39 and 82 (mean 60), with minima occurring in the two lowermost and the topmost black shale units. Nutrient index maxima are observed in the marlstones. The temperature index indicates a long-term trend from higher surface-water temperatures in the lower part of the succession to cooler conditions in the upper part. Highest values occur during the formation of the second black shale (48.79 m; temperature index 13; mean 29). This temperature maximum is followed by a cooling trend (minimum at 51.84 m; temperature index 49).

Fig. 5. Comparison of nutrient and temperature indices based on calcareous nannofossils with palynomorph data (relative abundances, terrigenous/marine ratio) and abundance patterns of nannoconids and planktic Foraminifera (small hedbergellids, rotaliporids). Error bars indicate the binomial standard error (Fatela & Taborda 2002). Bold lines represent smoothed records based on the weighted harmonic mean method. (For explanations of lithological symbols see Fig. 2.)

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Fig. 6. Scanning electron micrographs to document the preservation of calcareous nannofossils and planktic Foraminifera. (a, b) Calcareous nannofossils; scale bar represents 2 ìm. (a) Well-preserved specimen of Biscutum constans (distal view) enclosed with a clayey matrix; calcitic cements are nearly absent (black shale sample, 48.79 m). (b) Specimens of Nannoconus truitti and other nannofossils; again no significant amount of secondary calcite can be recognized. Nannofossils show a pristine preservation (black shale sample, 52.56 m). (c, d) Planktic Foraminifera; scale bar represents 50 ìm. (c) Dorsal view of Planomalina buxtorfi (marlstone sample, 47.43 m). Primary tests are altered and recrystallized, but pores are still visible. (d) Dorsal view of Rotalipora appenninica (marlstone sample, 50.29 m). This specimen shows the same preservational characteristics as that shown in (c). (e) Coccolithdominated marlstone sample (52.86 m); scale bar represents 1 ìm. The marlstone consists mainly of coccolith calcite and clay minerals. Coccoliths are well preserved, but show sometimes slight indications of overgrowth and a low degree of secondary cementation. Bc, Biscutum constans; cm, clay minerals; dc, diagenetic carbonate; N, Nannoconus; nf, nannofossil fragments; Z, Zeugrhabdotus.

Palynomorphs All studied samples contain abundant marine and terrigenous palynomorphs as well as foraminiferal linings in good preservation. Palynomorph assemblages from the marlstone samples are dominated by marine palynomorphs (mainly dinoflagellate cysts, up to 75%; Fig. 5), whereas there is a high percentage of terrestrial palynomorphs (mainly pollen and spores; up to 50% of the total assemblage) in the black shale samples. Accordingly, terrigenous/marine ratio values differ strongly between ,0.5 in the marlstone samples and 1–2.5 in the black shale samples (Fig. 5). Furthermore, terrigenous palynomorphs show also an increase in their absolute abundances (.19 000 individuals g
1 sediment) during black shale formation (Fig. 7a). Absolute spore abundances are ,6500 individuals g
1 sediment in the marlstone samples and reach .20 000 individuals g
1 sediment in the black shale samples. Non-saccate pollen show a similar distribution pattern, with ,9000 individuals g
1 sediment in the marlstones to a maximum of 32 000 individuals g
1 sediment in the black shales (Fig. 7b and c).

Planktic Foraminifera Planktic foraminiferal tests are moderately preserved and usually filled with secondary calcite or pyrite. SEM studies reveal that the test walls show different forms of diagenetic alteration such as recrystallization and encrustation. The walls of hedbergellids are often replaced and no pores can be recognized. In contrast, the keeled taxa Rotalipora and Planomalina are generally better

preserved. Here, primary pores are still visible, but the originally calcitic walls are also replaced (Fig. 6c and d). The relative abundance of small hedbergellids (63–125 ìm) varies between 61 and 91% (mean 83.3%; Fig. 5). Thus, hedbergellids are the most common planktic foraminiferal group in the size fraction studied. Highest relative abundances have been observed in marlstones. Rotaliporids are much less abundant and show percentages between 0 and 2.2% (mean 0.3%). Relative abundances of rotaliporids peak in the upper three black shale units. Despite the low percentages these maxima can be considered to be statistically significant, as indicated by the error bars in Figure 5.

Discussion Diagenesis Carbonate preservation and stable isotopes. As revealed by light microscope and SEM studies, nannofossils are moderately to well preserved (Fig. 6a and b) with slight indications of overgrowths in the marlstones (Fig. 6e). In contrast, planktic Foraminifera tests are less well preserved (Fig. 6c and d). The slightly better preservation of coccoliths is probably linked to the transport via faecal pellets through the water column (Honjo 1976), where organic coatings minimize coccolith dissolution in the water column and at the sea floor. The good nannofossil preservation as inferred from the abovementioned visual criteria is also supported by other observations. The abundances of the most dissolution-resistant nannofossil W. barnesae are significantly below 40% (maximum 13.3%; Fig.

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Fig. 7. x–y plots of absolute palynomorph abundances. (a) Niveau Breistroffer, Col de Palluel section. Marine v. terrestrial palynomorphs. Black shale samples show higher absolute abundances of terrestrial palynomorphs as compared with the marlstones, indicating a higher terrestrial input during black shale deposition. (b) Niveau Breistroffer, Col de Palluel section. Non-saccate pollen v. spores. Absolute spore and pollen abundances are generally higher in black shale samples than in marlstone samples, suggesting enhanced humidity during black shale formation. (c) Non-saccate pollen v. spores for various black shales from the mid-Cretaceous of the Vocontian Basin. Absolute spore and pollen abundances from two mid-Cretaceous black shale events (Niveau Paquier, Niveau Breistroffer) in the Vocontian Basin. Absolute abundances of the two palynomorph groups are very low during the formation of the late Albian main Niveau Breistroffer black shales. This is possibly due to a larger distance to the source area during a sea-level highstand as compared with times of Niveau Paquier formation. Palynomorph data for the Niveau Paquier are from Herrle et al. (2003b). (For stratigraphic position of the Niveau Paquier see Fig. 2.)

absent in sediments from the Marnes Bleues Formation (Weissert & Bre´he´ret 1991; Bre´he´ret 1997). This points to a minor influence of diagenetic carbonate on the isotopic signal. Carbon isotope data are considered to represent a primary environmental signal. A significant diagenetic alteration can probably be excluded based on the following three observations. (1) There is a low positive correlation coefficient between carbon and oxygen isotopes (Fig. 8c) as has been attributed to an early diagenetic overprint (Jenkyns 1974) or deep burial (Jenkyns & Clayton 1986; Jenkyns 1995) by the precipitation of secondary isotopically lighter calcite cements. This is in accordance with the findings of Levert & Ferry (1988) and Weissert & Bre´he´ret (1991), who noted that the Marnes Bleues Formation of SE France had not been subject to deep burial (i.e. it had been buried to less than c. 700 m). (2) The observed carbon isotope excursions can be traced throughout different localities with

4), which suggests an original preserved nannofossil assemblage (Roth & Krumbach 1986). Moreover, there is no linear relationship between W. barnesae percentages and species richness or nannofossil absolute abundances (Fig. 8a and b) as suggested by Williams & Bralower (1995) for diagenetically altered assemblages. In addition, highly dissolution-susceptible taxa (holococcoliths, Scapholithus fossilis, small zeugrhabdotids, Biscutaceae) occur throughout the interval studied. As the biogenic carbonate fraction of the sediments is dominated by calcitic skeletons of organisms dwelling in the uppermost water column (calcareous nannofossils, planktic Foraminifera and calcispheres, in descending order of abundance), the geochemical composition of the carbonates predominantly reflects a surface-water signal. Light microscope and SEM investigations indicate that diagenetic carbonate is rare (see Fig. 6). Dolomite as a possible product of bacterial methanogenesis is

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alteration during burial diagenesis lead us to conclude that the stable isotope data used in this study represent a reliable signal. Based on the good correlation between bulk-rock oxygen isotope values and the temperature changes given by calcareous nannofossils (Figs 5 and 10) we believe that the oxygen isotope data reflect primary temperature trends despite their sensitivity to diagenesis.

different depositional environments and histories (Fig. 3). (3) There is a lack of inverse relationship between TOC and carbon isotope data (Fig. 9a; Jenkyns & Clayton 1986). Oxygen isotope values are more prone to diagenetic alteration than carbon isotope data during burial diagenesis (e.g. Anderson & Arthur 1983; Marshall 1992) because carbon isotopes show no significant temperature-controlled fractionation. Therefore the influence of isotopically lighter cements precipitated during burial diagenesis on the oxygen isotope values is more important. Previous studies emphasized enhanced diagenetic alteration of pelagic carbonates with burial depth as the most important factor in comparing diagenetic model results with oxygen isotope measurements of Cenozoic bulk-carbonates (Schrag et al. 1995). According to Schrag et al. (1995), the effect of rapid recrystallization is small for mid-latitudinal biogenic carbonates such as those of the Vocontian Basin, where primary oxygen isotope values are close to isotopic equilibrium with cold pore fluids. The influence of different vital effects of calcareous nannofossils is also expected to be minor because no major changes in the nannofossil assemblages occurred during the interval studied and bulk-rock oxygen isotope data are less sensitive to compositional variations (Schrag et al. 1995). Furthermore, our data show no obvious relationship between the studied oxygen and carbon isotopes and lithological parameters such as CaCO3 and TOC (Fig. 9a–d). This supports our assumptions that the values are not primarily controlled by changes in the amount of organic carbon or CaCO3 and linked diagenetic processes such as sulphate reduction or recrystallization. Small amounts of diagenetic carbonate in combination with a generally well-preserved nannofossil flora and a minor degree of

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Palynomorph preservation. The preservation of palynomorphs strongly depends on the oxygenation of the depositional environment, with reduced oxygenation improving preservation and vice versa (e.g. Traverse 1988). To detect a possible differential degradation of palynomorphs that may have obscured the original signal, the occurrence of foraminiferal test linings in the samples was examined. Such linings are the most oxidation-sensitive elements of palynomorph assemblages (G. Versteegh, pers. comm.). As well-preserved foraminiferal test linings were found during the quantitative evaluation or during the examination of additional slides from each sample horizon, the palynological assemblages can be considered to represent a primary signal.

Reconstructing palaeoenvironmental and palaeoceanographic changes Surface-water productivity. Variations of surface-water productivity are recorded by the nannofossil-based nutrient index and relative abundances of small hedbergellids. The applicability of the nutrient index in reconstructing surface-water productivity and its relation to palynological and foraminiferal signals has been discussed in detail by Herrle et al. (2003b). Increased abundances of hedbergellids during the Cretaceous have often

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been considered to indicate a rise in surface-water productivity (see Premoli-Silva & Sliter 1999, for a detailed discussion). Both the nutrient index and the abundances of Hedbergella spp. show similar trends in the studied succession (Fig. 5). Higher surfacewater productivity can be recognized during the deposition of marlstones, whereas lower productivity prevailed during black shale formation. According to the estimated mean sedimentation rate for the section (c. 44 mm ka
1 ; see the section ‘Location, chronostratigraphy and palaeogeography’; Fig. 3) a black shale– marlstone couplet (c. 0.85 m thick in the lower part) has probably been deposited within c. 19.4 ka or slightly more as a result of a somewhat lower sedimentation rate in this interval. This indicates that productivity changes are possibly controlled by precessional cycles. This is well in accordance with other data from sedimentary bedding rhythms in the Aptian–Albian Marnes Bleues Formation, which are generally considered to follow orbitally tuned Milankovitch cycles (Bre´he´ret 1994, 1997; Ko¨ßler et al. 2001). Further support for this assumption comes from time series analyses performed by Herrle et al. (2003b) on a more extended record of a high-resolution nannofossil-based nutrient and temperature index from the Marnes Bleues Formation. This study also revealed a precessional control of surfacewater productivity. A further attempt to reconstruct changes of surface-water productivity has been performed by Giraud et al. (2003). Those workers studied the macrofauna (ammonites, bivalves, echinoderms, etc.), ichnofossils and calcareous nannofossils over the entire Niveau Breistroffer interval at the Blieux section, which is located in a marginal setting of the Vocontian Basin, on a coarser temporal resolution (80 m sequence, 60 samples). Based on their benthic and planktic record they recognized only minor productivity changes. Surface-water temperature. Both the nannofossil temperature index and oxygen isotope data indicate rising surface-water

20

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Fig. 10. Temperature trends during the formation of the Niveau Breistroffer black shales at the Blake Nose Plateau (ODP Hole 1052E; oxygen isotope data from Wilson & Norris 2001) and in the Vocontian Basin (Col de Palluel section; bulk-rock oxygen isotope data and nannofossil-based temperature index). In both areas, similar trends in surface-water temperature (black arrows) occur. They probably follow eccentricity-controlled cycles (see text for details). Shaded area indicates assumed correlation between Blake Nose and SE France (see Fig. 3). Bold lines represent smoothed records based on the weighted harmonic mean method.

temperature with the onset of black shale formation in the lower part of the studied succession. In contrast, the marlstonedominated succession in the upper part is characterized by a cooling trend. According to our age estimates, these long-term changes must have lasted between c. 99 and c. 115 ka. As can be inferred from Herrle et al. (2003b) and our estimates, an eccentricity control of temperature is feasible. Eccentricitycontrolled cycles have also been suggested by Bre´he´ret (1994) for the same strata in the Vocontian Basin. Moreover, subordinate short-term temperature fluctuations indicate warming during the formation of single black shale units (Figs 5 and 10). Humidity. Enhanced humidity and terrigenous input into the Vocontian Basin during black shale formation are indicated by high values of the terrigenous/marine ratio and maxima in the absolute abundance of spores and pollen (Figs 5 and 7a). This interpretation is supported by findings of Bre´he´ret (1997), who observed increasing amounts of kaolinite in the Niveau Breistroffer black shales from the Col de Palluel section. Surface-water stratification. To assess surface-water stratification during black shale formation, two plankton groups that probably inhabited subsurface water masses (Nannoconus and Rotalipora) have been studied. Recently, the ecology of Nannoconus spp. has been studied extensively and will be briefly summarized below. Busson & Noe¨l (1991) interpreted this group as calcareous dinoflagellate cysts that preferred shallow-water environments and oligotrophic conditions with low terrigenous supply. Other workers (e.g. Erba 1987; Coccioni et al. 1992; Mutterlose 1996) proposed that the group flourished in warm surface waters impoverished in nutrients. Erba (1994) suggested that Nannoconus spp. inhabited the lower photic zone similar to the recent Florisphaera profunda (Okada & Honjo 1973; Molfino & McIntyre 1990; Ahagon et al. 1993). According to Molfino & McIntyre (1990), abundance

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variations of F. profunda are related to changes in nutricline depth and stability. A shallow nutricline causes a greater nutrient transfer into the upper photic zone, leading to blooms of coccoliths and low percentages of F. profunda. During periods of a deep nutricline mesotrophic conditions in the lower photic zone prevailed and led to high percentages of F. profunda. Herrle (2003) presented evidence for similar ecological preferences of Nannoconus and F. profunda with respect to the water depth. This author observed high abundances of nannoconids and low numbers of coccoliths during periods of enhanced stratification. During times of increased wind stress, in contrast, a rise of the nutricline caused an entrainment of nutrients into the surface waters. This scenario was reflected by low abundances of nannoconids, higher abundances of coccoliths and an increase of the nutrient index. During the OAE 1d nannoconids occur in higher abundances only in or close to the black shale units (Fig. 5). Based on our present understanding of Nannoconus palaeoecology, this may indicate phases of a deep nutricline. Higher abundances of Nannoconus correspond to lower nutrient index values and decreasing percentages of Hedbergella, both indicating lower surface-water productivity. There is also a trend to higher relative abundances of subsurface-dwelling rotaliporids in the black shales. They are believed to have preferred a stratified upper water column (e.g. Caron & Homewood 1982; Leckie 1987; Hart 1999). The scenario of stratified surface waters during black shale formation is also supported by increasing values for the heterogeneity of calcareous nannofossils (McIntyre & Be´ 1967; Brand 1994). The co-occurrence of the two subsurface-dwelling groups may indicate that both groups proliferated within the lower photic zone and/or under similar oceanographic conditions. This supports the interpretation of Erba (1994) and Herrle (2003) that the abundance pattern of the nannoconids follows changes between phases of more stratified surface waters and those of enhanced mixing.

Driving mechanisms for OAE 1d formation in SE France As inferred from our age model, temperature changes during OAE 1d deposition (as evidenced by the nannofossil temperature index and oxygen isotopes) occur on a time interval of c. 100 ka, which suggests an eccentricity-controlled orbital forcing (Figs 5 and 10). Variations of productivity went along with lithological changes from black shales and marlstones (Fig. 5). These have also been interpreted to follow precessional cycles. An orbital control of both temperature and productivity has been confirmed by a time series analysis of the Early Albian Niveau Paquier in the Vocontian Basin (Herrle et al. 2003b). A modern analogue for the observed climatic and oceanographic variations is found in the Asian–African monsoon system. Palaeoproductivity records from Quaternary sediments in the Arabian Sea are driven by precessionally controlled changes of monsoonal intensity and fluctuations in summer surface-water productivity (e.g. Reichart et al. 1997). These changes are associated with strong fluctuations in wind velocities and precipitation rates (e.g. Clemens & Prell 1990). By analogy to the modern monsoon system, higher precipitation rates during warmer periods may have caused a decrease in evaporation rates during formation of OAE 1d black shales. This led, in combination with lower surface-water densities, to a drastic reduction of deep-water formation in low-latitudinal epicontinental areas when a threshold value was reached (Bice et al. 1997). The shelf areas of the western and eastern Tethys were subject to a strong monsoonal circulation during the latest Albian

(100 Ma; Oglesby & Park 1989). Moreover, a part of midCretaceous deep-water formation is considered to have taken place in the shelf and epicontinental areas of the western and eastern Tethys driven by the sinking of warm, saline waters as a result of high evaporation rates (Brass et al. 1982; Barron & Peterson 1990; Herrle et al. 2003b). This mechanism may have affected the bottom-water circulation on a regional scale, but it only partly accounts for the global deep-water formation, which is located in the high latitudes (North Pacific) as suggested by numerical models (e.g. Poulsen et al. 2001; Bice & Norris 2002). Changes in the rates of deep-water formation have also been postulated for the deposition of the Early Albian Niveau Paquier black shale (OAE 1b) in the Vocontian Basin (Herrle et al. 2003a, b). For this black shale, high terrigenous/marine ratio values and spore/pollen ratios indicate that the formation occurred under extremely humid conditions. The extreme humidity probably reduced evaporation in the low latitudes (i.e. the western Tethys) and thus slowed down deep-water formation. This had a widespread impact on the bottom-water ventilation and the preservation potential of organic matter (Herrle et al. 2003b). Similar scenarios for the preservation of organic matter have been proposed for the formation of the OAE 1b in the Atlantic Ocean (Erbacher et al. 2001) and the Vocontian Basin (Tribovillard & Gorin 1991). The above interpretation of our data is also compatible with a model for the formation of Mediterranean sapropels. There, higher rates of monsoonal fluvial discharge led to sapropel formation (Rossignol-Strick 1985; Rossignol-Strick et al. 1998). Elevated runoff was responsible for lower surface-water salinities and stratification (Rohling & Gieskes 1989), allowing the transport of nutrient-rich thermocline or intermediate waters into the lower photic zone. This led to high abundances of the subsurface-dwelling coccolithophorid F. profunda in the sapropels (Castradori 1993). By analogy, lower abundances of subsurfacedwelling plankton (nannoconids, rotaliporids) in the Late Albian black shales may indicate a lower influence of fluvial discharge compared with the sapropel formation in the Mediterranean Sea. Numerous workers (e.g. Fo¨llmi et al. 1994; Weissert et al. 1998; Hochuli et al. 1999) have linked the formation of Cretaceous black shales to intensified weathering and elevated runoff. This is believed to have caused enhanced surface-water productivity. However, during the formation of Quaternary sapropels increasing fluvial supply did not necessarily lead to elevated productivity, as pointed out by Rossignol-Strick & Paterne (1999). They argued that a runoff increase led to elevated productivity, which was restricted to the river mouths, where nutrient fixation mainly takes place. Further offshore only a water lens with lower salinity and low nutrient content would develop. Such conditions are supported by findings of Sachs & Repeta (1999), who observed high abundances of algae in the sapropels, which prefer oligotrophic, stratified environments with reduced salinities in the surface water. A similar scenario may have occurred during the formation of the main Niveau Breistroffer black shales. For the Niveau Breistroffer black shales, our data suggest a deep nutricline and a low primary production in the upper photic zone. Based on the above discussion, we consider the Niveau Breistroffer black shale periods to have been characterized by a strong monsoon and warm–humid climate presumably accompanied by elevated runoff. This should have increased the density contrast within the water column. Consequently, a more stable stratification prevented the mixing of nutrient-rich thermocline or intermediate waters with oligotrophic surface-water masses. Increasing humidity and runoff additionally diminished the rates of

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deep-water formation in the eastern and western Tethys, leading to poor benthic oxygenation. We conclude that increased preservation of organic matter at the sea floor was more important for the formation of the Niveau Breistroffer black shales in the Vocontian Basin than enhanced production of organic matter in the upper water column. Drier and cooler conditions during marlstone deposition were probably characterized by increased mixing and well-oxygenated bottom waters caused by enhanced deep-water formation. This interpretation is supported by obvious bioturbation in the marlstones.

Supraregional palaeoenvironmental signals for OAE 1d formation The OAE 1d black shale event has mainly been reported from the North Atlantic and the western Tethys, but sporadic occurrences are also known from the South Atlantic, Pacific Ocean, southern high-latitude sites and Western Interior Seaway (Wilson & Norris 2001). To date, only few localities have been studied in detail. These include the Mazagan Plateau (Deep Sea Drilling Project (DSDP) Site 547, Nederbragt et al. 2001), the Blake Nose Plateau (ODP Hole 1052E, Wilson & Norris 2001) and the Vocontian Basin (Bre´he´ret 1988, 1994, 1997; Giraud et al. 2003). At all three localities the late Albian is characterized by a positive carbon isotope excursion with an amplitude between 0.5 (Mazagan Plateau, Nederbragt et al. 2001) and 1.5‰ (Blake Nose, Wilson & Norris 2001; Vocontian Basin, this study). At the Mazagan Plateau (eastern Atlantic, DSDP Site 547) the micropalaeontological study of calcareous nannofossils, and planktic and benthic Foraminifera by Nederbragt et al. (2001) did not yield major productivity changes. Only high turnover rates within the planktic Foraminifera mark the OAE 1d interval. According to Nederbragt et al. (2001), these changes are linked to an oxygenation decrease of the subsurface waters coupled with the expansion of the oxygen minimum zone, which affected the habitat of some of the disappearing planktic foraminiferal species. By contrast, Leckie et al. (2002) found high amounts of fish debris and glauconite during the OAE 1d interval in a lowresolution study of DSDP Site 545. Both may indicate either an increase of productivity or condensation. For the OAE 1d formation on the Blake Nose Plateau (western Atlantic, ODP Hole 1052E) Wilson & Norris (2001) proposed a collapse of the thermocline. Based on oxygen isotope data for subsurface-dwelling planktic Foraminifera and surface-dwelling species they observed a decrease in the temperature gradient (Fig. 10), suggesting enhanced mixing and thereby elevated surface-water productivity. Based on the observations presented herein we propose a tentative model that could explain the supraregional distribution of the OAE 1d black shales. As shown in Figure 10, a careful correlation between the Blake Nose Plateau and the Vocontian Basin reveals similar trends in surface-water temperature. According to these data, the onset of black shale formation is accompanied by a temperature rise at both sites. This suggests that the widespread OAE 1d formation can be linked to the same driving mechanisms. We assume that eccentricity-controlled monsoonal climate, as suggested by Herrle et al. (2003b) and to a lesser extent by our data, characterized by rising temperature, humidity and wind stress, is well coupled with the collapse of the thermocline in the NW Atlantic Ocean. The models for OAE 1d formation in the North Atlantic and Vocontian Basin can be brought into line when considering the different palaeogeographical and palaeoceanographic settings.

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Because of the epicontinental position of the Vocontian Basin water temperatures may have been higher than in the western Atlantic Ocean. In addition, changes of humidity and evaporation must have had a greater influence, because of the proximal situation. As shown in Figure 11, phases of black shale formation are characterized by warmer climate accompanied by monsoonal activity, enhanced seasonality and a strengthening of the Westerlies. We believe that stronger wind stress presumably forced a cooling of the surface-water masses and led to increasing mixing rates in the open-oceanic Atlantic Ocean. Enhanced wind stress may also account for the observed long-term surface-water cooling, which predates the OAE 1d formation on the Blake Nose (see data of Wilson & Norris 2001) and may have contributed to the collapse of stratification.

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Fig. 11. Model for deep-water formation during periods of black shale or marlstone deposition of the main Niveau Breistroffer with schematic mean annual atmospheric circulation pattern for the low latitudes at insolation maximum (adopted from Herrle et al. 2003b). Principal elements of the mid-Cretaceous climate in the low-latitude region are as depicted by climate models (e.g. Oglesby & Park 1989; Barron & Peterson 1990; Price et al. 1995; Poulsen et al. 1998). Palaeogeography is adopted from Hay et al. (1999) for the late Albian (100 Ma). During warm and humid climate conditions and a strong monsoonal circulation (as proposed for the formation of the Niveau Breistroffer black shales), deep-water formation was restricted in the northern and eastern Tethyan area. During marlstone deposition, no restriction of deep-water formation occurred, leading to better oxygenation of the bottom water in the Vocontian Basin. H, high-pressure system; L, low-pressure system; BN, Blake Nose; VB, Vocontian Basin.

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Comparison between OAE 1d and OAE 1b formation in SE France In comparison with black shales formed during the earliest Albian (Niveau Paquier ¼ OAE 1b; Herrle et al. 2003a, b), the boundary conditions for the formation of the late Albian main Niveau Breistroffer black shales were significantly different. The sea level was much higher (Haq et al. 1987) than in the earliest Albian, causing a more distal position of the studied succession and smaller continent masses in the west and the north (see palaeogeography of Hay et al. 1999; Fig. 11). We assume that the density of vegetation in the hinterland did not significantly change from the earliest to the latest Albian. Thus, the small difference in the mean sedimentation rate (c. 37 mm ka
1 for the Niveau Paquier, Herrle et al. (2003a, b); c. 44 mm ka
1 for the Niveau Breistroffer, this study) and the fact that absolute numbers of spores and pollen are up to six times lower than in the Niveau Paquier (Herrle et al. 2003b; Fig. 7c) support our assumption that the Niveau Breistroffer was deposited at a greater distance from the hinterland. A more distal position would also explain the oligotrophic surface waters during the formation of the Niveau Breistroffer black shales. In contrast, the onset of the Niveau Paquier formation as observed by Herrle et al. (2003a, b) was accompanied by increasing humidity and elevated surface-water productivity.

Conclusions The high-resolution quantitative analysis of various microfossil groups and bulk-rock stable isotope data provide the following insights into palaeoclimatic and palaeoceanographic conditions prevailing during the formation of the main Niveau Breistroffer black shales in the Vocontian Basin. (1) The main Niveau Breistroffer formed under short-term cool–dry to warm–humid cycles probably controlled by intensity changes of monsoonal activity, with black shales forming under relatively warm and humid conditions. By contrast, a cooler and more arid climate may have prevailed during the deposition of the marlstones. Results from calcareous nannofossils and planktic Foraminifera suggest more oligotrophic conditions for the black shales compared with the marlstones. (2) The nannofossil indices used to to record changes in surface-water nutrient conditions and temperature correspond well to abundance changes of higher nutrient levels indicating planktic Foraminifera (small hedbergellids) and variations of oxygen isotope data. (3) As inferred from the terrigenous/marine ratio of palynomorphs and absolute abundances of terrigenous palynomorphs, periods of black shale formation were characterized by high terrigenous input and thus increased runoff. (4) The more warm–humid phases were accompanied by higher abundances of subsurface-dwelling plankton (nannoconids, rotaliporids). The co-occurrence of higher abundances of nannoconids and rotaliporids supports the hypothesis that nannoconids flourished within the lower photic zone and proliferated under stratified, stable conditions with low nutrient levels in the surface water. (5) Similar to some depositional models of Mediterranean sapropels, we assume that increasing humidity during black shale formation led to a decrease in deep-water formation and probably an increase in surface-water stratification. Both mechanisms led to oxygen consumption in the bottom water, which in turn increased the preservation potential of organic matter. The accumulation of organic matter in the main Niveau Breistroffer

black shales was controlled by preservation rather than by increased productivity in the photic zone. (6) Based on carbon isotope data, the Niveau Breistroffer can be correlated with the OAE 1d observed at the Blake Nose Plateau (ODP Hole 1052E). The supraregional distribution of the OAE 1d within the Atlantic Ocean is explained by increased mixing during periods of enhanced monsoonal activity. This study was funded by the German Research Foundation (DFG) within the Collaborative Research Centre SFB 275 (project A5/Hemleben) of the University of Tu¨bingen and through additional grants of the DFG to C.H. (He 697/34 and He 697/41) and J.M. (Mu 667/20). Thoughtful reviews by P. Wilson, M. Leckie and J. Macquaker are gratefully acknowledged. J. Lehmann (Bremen) is thanked for field assistance, R. Neuser (Bochum) assisted with the SEM. P. Wilson (Southampton) kindly provided the isotope data from ODP Hole 1052E.

References Ahagon, N., Tanaka, Y. & Ujiie, H. 1993. Florisphaera profunda: a possible nannoplankton indicator of late Quaternary changes in sea-water turbidity at the northwestern margin of the Pacific. Marine Micropaleontology, 22, 255–273. Anderson, T.F. & Arthur, M.A. 1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. In: Arthur, M.A., Anderson, T.F., Kaplan, I.R, Veizer, J. & Land, L.S. (eds) Stable Isotopes in Sedimentary Geology. Society of Economic Paleontologists and Mineralogists, Short Courses, 10, 1–151. Arnaud, H. & Lemoine, M. 1993. Structure and Mesozoic–Cenozoic evolution of the South-East France Basin (SFB). Ge´ologie Alpine, 3, 3–58. Arnaud-Vanneau, A. & Arnaud, H. 1990. Hauterivian to Lower Aptian carbonate shelf sedimentation and sequence stratigraphy in the Jura and northern subalpine chains (southeastern France and Swiss Jura). In: Tucker, M.E., Wilson, J.L., Crevello, P.D., Sarg, J.R. & Read, J.F. (eds) Carbonate Platforms. International Association of Sedimentologists, Special Publications, 9, 203–233. Arthur, M.A., Dean, W.E. & Pratt, L.M. 1988. Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary. Nature, 335, 714–717. Barron, E.J. & Peterson, W.H. 1990. Mid-Cretaceous ocean circulation: results from model sensitivity studies. Paleoceanography, 5, 319–337. Barron, E.J. & Washington, W.M. 1985. Warm Cretaceous climates: high atmospheric CO2 as a plausible mechanism. In: Sunquist, E.T. & Broecker, W.S. (eds) The Carbon Cycle and Atmospheric CO2 : Natural variations from Archean to Present. Geophysical Monograph, American Geophysical Union, 32, 546–553. Baudin, F., Fiet, N., Coccioni, R. & Galeotti, S. 1998. Organic matter characterisation of the Selli Level (Umbria–Marche Basin, central Italy). Cretaceous Research, 19, 701–714. Beerling, D.J., Lomas, M.R. & Gro¨cke, D.R. 2002. On the nature of methane gas–hydrate dissociation during the Toarcian and Aptian oceanic anoxic events. American Journal of Science, 302, 28–49. Bice, K.L. & Norris, R.D. 2002. Possible atmospheric CO2 extremes of the middle Cretaceous (late Albian–Turonian). Paleoceanography, 17, 10.1029/ 2002PA000778. Bice, K.L., Barron, E.J. & Peterson, W.H. 1997. Continental runoff and early Cenozoic bottom-water sources. Geology, 25, 951–954. Bollmann, J., Brabec, B., Corte´s, M.Y. & Geisen, M. 1999. Determination of absolute coccolith abundances in deep-sea sediments by spiking with microbeads and spraying (SMS-method). Marine Micropaleontology, 38, 29–38. Bralower, T.J. & Thierstein, H.R. 1984. Low productivity and slow deep-water circulation in mid-Cretaceous oceans. Geology, 12, 614–618. Bralower, T.J., Sliter, W.V., Arthur, M.A., Leckie, R.M., Allard, D. & Schlanger, S.O. 1993. Dysoxic/anoxic episodes in the Aptian–Albian (Early Cretaceous). In: Pringle, M.S., Sager, W.W., Sliter, W.V. & Stein, S. (eds) The Mesozoic Pacific: Geology, Tectonics, and Volcanism. Geophysical Monograph, American Geophysical Union, 77, 5–37. Brand, L.E. 1994. Physiological ecology of marine coccolithophores. In: Winter, A. & Slesser, W.G. (eds) Coccolithophores. Cambridge University Press, Cambridge, 39–50. Brass, G.W., Southam, J.R. & Peterson, W.H. 1982. Warm saline bottom water in the ancient ocean. Nature, 296, 620–623. Bre´he´ret, J.-G. 1988. E´pisodes de se´dimentation riche en matie`re organique dans les marnes bleues d’aˆge aptien.bien de la partie pe´lagique du bassin

N I V E AU B R E I S TO F F E R PA L A E O C E A N O G R A P H Y vocontien. Bulletin de la Socie´te´ Ge´ologique de France, 8, 349–356. Bre´he´ret, J.-G. 1994. The Mid-Cretaceous organic-rich sediments from the Vocontian Zone of the French Southeast Basin. In: Mascle, A. (ed.) Hydrocarbon and Petroleum Geology of France. Special Publication of the European Association of Petroleum Geoscientists, 4, 295–320. Bre´he´ret, J.-G. 1997. L’Aptien et l’Albien de la Fosse vocontienne (des bordures au bassin)—e´volution de la se´dimentation et enseignements sur les e´ve´nements anoxiques. Socie´te´ Ge´ologique du Nord, 25. Bruckschen, P. & Veizer, J. 1997. Oxygen and carbon isotopic composition of Dinantian brachiopods: paleoenvironmental implications for the Lower Carboniferous of Western Europe. Palaeogeography, Palaeoclimatology, Palaeoecology, 132, 243–264. Busson, G. & Noe¨l, D. 1991. Les nannoconide´s indicateurs environnementaux des oce´ans et mers e´picontinentales du Jurassique terminal et du Cre´tace´ infe´rieur. Oceanologica Acta, 14, 333–356. Caron, M. & Homewood, P. 1982. Evolution of early planktonic Foraminifera. Marine Micropaleontology, 7, 453–462. Castradori, D. 1993. Calcareous nannofossils and the origin of eastern Mediterranean sapropels. Paleoceanography, 8, 459–471. Clemens, S.C. & Prell, W.L. 1990. Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity: eolian records from the lithogenic component of deep-sea sediments. Paleoceanography, 5, 109–145. 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. & Rio, M. 1984. Cyclic sedimentation in the Cretaceous of Deep Sea Drilling Project sites 535 and 540 (Gulf of Mexico), 534 (central Atlantic) and in the Vocontian Basin (France). In: Buffler, R.T., Schlager, W. et al. (eds) Initial Reports of the Deep Sea Drilling Project, 77. US Government Printing Office, Washington, DC, 339–376. Crux, J. 1991. Albian calcareous nannofossils from the Gault Clay of Munday’s Hill (Bedfordshire, England). Journal of Micropalaeontology, 10, 203–222. Erba, E. 1987. Mid Cretaceous cyclic pelagic facies from the Umbrian–Marchean Basin: what do calcareous nannofosssils suggest? INA Newsletters, 9, 52–53. Erba, E. 1992. Middle Cretaceous calcareous nannofossils from the western Pacific (Leg 129): evidence for paleoequatorial crossings. In: Larson, R.L. & Lancelot, Y. (eds) Proceedings of the Ocean Drilling Program, Scientific Results, 129. Ocean Drilling Program, College Station, TX, 189–201. Erba, E. 1994. Nannofossils and superplumes: the early Aptian ’nannoconid crisis‘. Paleoceanography, 9, 483–501. 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. Erbacher, J. & Thurow, J. 1997. Influence of oceanic anoxic events on the evolution of mid-Cretaceous radiolaria in the North Atlantic and western Tethys. Marine Micropaleontology, 30, 139–158. Erbacher, J., Thurow, J. & Littke, R. 1996. Evolution patterns of radiolaria and organic matter variations: a new approach to identify sea-level changes in mid-Cretaceous pelagic environments. Geology, 24, 499–502. Erbacher, J., Hemleben, C., Huber, B.T. & Markey, M. 1999. Correlating environmental changes during early Albian oceanic anoxic event 1b using benthic foraminiferal palaeoecology. Marine Micropaleontology, 38, 7–28. Erbacher, J., Huber, B.T., Norris, R.D. & Markey, M. 2001. Increased thermohaline stratification as a possible cause for an oceanic anoxic event in the Cretaceous period. Nature, 409, 325–327. Fatela, F. & Taborda, R. 2002. Confidence limits of species proportions in microfossil assemblages. Marine Micropaleontology, 45, 169–174. Flandrin, J. 1963. Remarques stratigraphiques, pale´ontologiques et structurales sur la re´gion de Se´deron. Bulletin du Service de la Carte Ge´ologique de la France, 272, 815–845. Fo¨llmi, 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. Friedrich, O., Reichelt, K., Herrle, J.O., Lehmann, J., Pross, J. & Hemleben, C. 2003. Formation of the Late Aptian Niveau Fallot black shales in the Vocontian Basin (SE France): evidence from Foraminifera, palynomorphs, and stable isotopes. Marine Micropaleontology, 49, 65–85. Friedrich, O., Nishi, H., Pross, J., Schmiedl, G. & Hemleben, C. 2005. Millenial- to centennial-scale interruptions of the Oceanic Anoxic Event 1b (Early Albian, Mid-Cretaceous) inferred from benthic foraminiferal repopulation events. Palaios, 20, 64–77. Gale, A.S., Jenkyns, H.C., Kennedy, W.J. & Corfield, R.M. 1993. Chemostratigraphy versus biostratigraphy—data from around the Cenomanian–Turonian boundary. Journal of the Geological Society, London, 150, 29–32. Gale, A.S., Kennedy, W.J., Burnett, J.A., Caron, M. & Marshall, J.D. 1996.

637

The Late Albian to Early Cenomanian succession near Rosans (Droˆme, SE France), an integrated study (ammonites, inoceramids, planktonic Foraminifera, nannofossils, oxygen and carbon isotopes). Cretaceous Research, 17, 515–606. Galeotti, S. 1998. Planktic and benthic foraminiferal distribution patterns as a response to changes in surface fertility and ocean circulation: a case study from the Late Albian ‘Amadeus Segment‘ (Central Italy). Journal of Micropalaeontology, 17, 87–96. Geisen, M., Bollmann, J., Herrle, J.O., Mutterlose, J. & Young, J.R. 1999. Calibration of the random settling technique for calculation of absolute abundances of calcareous nannoplankton. Micropaleontology, 45, 123–138. Giraud, F., Olivero, D., Baudin, F., Reboulet, S., Pittet, B. & Proux, O. 2003. Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian, SE France) evidenced by calcareous nannofossils. International Journal of Earth Sciences, 92, 267–284. Gro¨cke, D.R., Hesselbo, S.P. & Jenkyns, H.C. 1999. Carbon-isotope composition of Lower Cretaceous fossil wood: ocean–atmosphere chemistry and relation to sea-level change. Geology, 27, 155–158. Gro¨tsch, J., Billing, I. & Vahrenkamp, V. 1998. Carbon-isotope stratigraphy in shallow-water carbonates: implications for Cretaceous black-shale deposition. Sedimentology, 45, 623–634. Haq, B.U., Hardenbol, J. & Vail, P.R. 1987. Chronology of fluctuating sea levels since the Triassic. Science, 235, 1156–1167. Hart, M.B. 1999. The evolution and biodiversity of Cretaceous planktonic foraminiferida. Ge´obios, 32, 247–255. Hay, W.W., DeConto, R. & Wold, C.N. et al. 1999. An alternative global Cretaceous paleogeography. In: Barrera, E. & Johnson, C.C. (eds) The Evolution of Cretaceous Ocean/Climate Systems. Geological Society of America, Special Papers, 332, 1–47. Herrle, J.O. 2003. Reconstructing nutricline dynamics of mid-Cretaceous oceans: evidence from calcareous nannofossils from the Niveau Paquier black shale (SE France). Marine Micropaleontology, 47, 307–321. Herrle, J.O. & Mutterlose, J. 2003. Calcareous nannofossils from the Aptian– early Albian of SE France: palaeoecological and biostratigraphic implications. Cretaceous Research, 24, 1–22. Herrle, J.O., Pross, J., Friedrich, O. & Hemleben, C. 2003a. Short-term environmental changes in the Cretaceous Tethys ocean: micropaleontological evidence from the Early Albian Oceanic Anoxic Event 1b. Terra Nova, 15, 14–19. Herrle, J.O., Pross, J., Friedrich, O., Ko¨ßler, P. & Hemleben, C. 2003b. Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France). Palaeogeography, Palaeoclimatology, Palaeoecology, 190, 399–426. Hochuli, P.A., Menegatti, A.P., Weissert, H., Riva, A., Erba, E. & PremoliSilva, I. 1999. Episodes of high productivity and cooling in the early Aptian Alpine Tethys. Geology, 27, 657–660. Holbourn, A., Kuhnt, W. & Soeding, E. 2001. Atlantic paleobathymetry, paleoproductivity and paleocirculation in the late Albian: the benthic foraminiferal record. Palaeogeography, Palaeoclimatology, Palaeoecology, 170, 171–196. Honjo, S. 1976. Coccoliths: production, transportation and sedimentation. Marine Micropaleontology, 1, 65–79. Huber, B.T., Hodell, D.A. & Hamilton, C.P. 1995. Middle–Late Cretaceous climate of the southern high latitudes: stable isotopic evidence for minimal equator-to-pole thermal gradients. Geological Society of America Bulletin, 107, 1164–1191. Huber, B.T., Leckie, R.M., Norris, R.D., Bralower, T.J. & CoBabe, E. 1999. Foraminiferal assemblage and stable isotopic change across the Cenomanian– Turonian boundary in the subtropical North Atlantic. Journal of Foraminiferal Research, 29, 392–417. Huber, B.T., Norris, R.D. & MacLeod, K.G. 2002. Deep-sea paleotemperature record of extreme warmth during the Cretaceous. Geology, 30, 123–126. Jenkyns, H.C. 1974. Origin of red nodular limestones (Ammonitico Rosso, Knollenkalke) in the Mediterranean Jurassic: a diagenetic model. In: Hsu, K.J. & Jenkyns, H.C. (eds) Pelagic Sediments: on Land and under the Sea. International Association of Sedimentologists, Special Publications, 1, 249–271. Jenkyns, H.C. 1995. Carbon-isotope stratigraphy and palaeoceanographic significance of the Lower Cretaceous shallow-water carbonates of Resolution Guyot, Mid-Pacific Mountains. In: Winterer, E.L., Sager, W.W., Firth, J.V. & Sinton, J.M. (eds) Proceedings of the Ocean Drilling Program, Scientific Results, 143. Ocean Drilling Program, College Station, TX, 99–104. Jenkyns, H.C. & Clayton, C.J. 1986. Black shales and carbon isotopes in pelagic sediments from the Tethyan Lower Jurassic. Sedimentology, 33, 57–106. Jenkyns, H.C. & Wilson, P.A. 1999. Stratigraphy, paleoceanography, and evolution of Cretaceous Pacific guyots: relics from a greenhouse Earth. American Journal of Science, 299, 341–392. Jenkyns, H.C., Gale, A.S. & Corfield, R.M. 1994. Carbon- and oxygen-isotope

638

A. BORNEMANN ET AL.

stratigraphy of the English Chalk and Italian Scaglia and its palaeoclimatic significance. Geological Magazine, 131, 1–34. Ko¨ßler, P., Herrle, J.O., Appel, E., Erbacher, J. & Hemleben, C. 2001. Magnetic records of climatic cycles from mid-Cretaceous hemipelagic sediments of the Vocontian Basin. Cretaceous Research, 22, 321–331. Kuhnt, W. 1992. Abyssal recolonization by benthic Foraminifera after the Cenomanian/Turonian boundary anoxic event in the North Atlantic. Marine Micropaleontology, 19, 257–274. Larson, R.L. 1991a. Latest pulse of the Earth: evidence for a mid-Cretaceous superplume. Geology, 19, 547–550. Larson, R.L. 1991b. Geological consequences of superplumes. Geology, 19, 963–966. Leckie, R.M. 1987. Paleoecology of mid-Cretaceous planktonic Foraminifera: a comparison of open ocean and epicontinental sea assemblages. Micropaleontology, 33, 164–176. Leckie, R.M. 1989. A palaeoceanographic model for the early evolutionary history of planktonic Foraminifera. Palaeogeography, Palaeoclimatology, Palaeoecology, 73, 107–138. Leckie, R.M., Bralower, T.J. & Cashman, R. 2002. Oceanic anoxic events and plankton evolution: biotic response to tectonic forcing during the midCretaceous. Paleoceanography, 17, 10.1029/2001PA000623. Lemoine, M., Bas, T. & Arnaud-Vanneau, A. et al. 1986. The continental margin of the Mesozoic Tethys in the Western Alps. Marine and Petroleum Geology, 3, 179–199. Levert, J. & Ferry, S. 1988. Diagene`se argileuse complexe dans le Me´sozoı¨que subalpin re´ve´le´e par cartographie des proportions relatives d’argiles selon des niveaux isochrones. Bulletin de Socie´te´ Ge´ologique de France, 8, 1029–1038. Luciani, V., Cobianchi, M. & Jenkyns, H.C. 2001. Biotic and geochemical response to anoxic events: the Aptian pelagic succession of the Gargano Promontory (southern Italy). Geological Magazine, 138, 277–298. Marshall, J.D. 1992. Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation. Geological Magazine, 129, 149–160. McIntyre, A. & Be´, A.W.H. 1967. Modern Coccolithophoridae of the Atlantic Ocean—I. Placoliths and cyrtoliths. Deep-Sea Research, 14, 561–597. Menegatti, A.P., Weissert, H., Brown, R.S., Tyson, R.V., Farrimond, P., Strasser, A. & Caron, M. 1998. High-resolution ä13 C stratigraphy through the early Aptian ‘Livello Selli‘ of the Alpine Tethys. Paleoceanography, 13, 530–545. Molfino, B. & McIntyre, A. 1990. Precessional forcing of nutricline dynamics in the Equatorial Atlantic. Science, 249, 766–769. Moullade, M. 1966. E´tude stratigraphique et micropale´ontologique du Cre´tace´ infe´rieur de la ‘Fosse Vocontienne’. Documents des Laboratoires de Geologie de la Faculte des Sciences de Lyon, 15, 181–217. Mutterlose, J. 1989. Temperature controlled migration of calcareous nannofloras in the north-west European Aptian. In: Crux, J.A. & Van Heck, S.E. (eds) Proceedings of the INA Conference. Ellis Horwood, Chichester, 122–142. Mutterlose, J. 1996. Calcareous nannofossil palaeoceanography of the Early Cretaceous of NW Europe. Mitteilungen aus dem Geologischen Staatsinstitut in Hamburg, 77, 291–313. Mutterlose, J. & Wise, S.W. 1990. Lower Cretaceous nannofossil biostratigraphy of ODP Leg 113 Holes 692B and 693A, continental slope off east Antarctica, Weddell Sea. In: Barker, P.F., Kennett, J.P. et al. (eds) Proceedings of the Ocean Drilling Program, Scientific Results, 113. Ocean Drilling Program, College Station, TX, 325–351. Mutterlose, J. & Kessels, K. 2000. Early Cretaceous calcareous nannofossils from the high latitudes: implications for palaeobiogeography and palaeoclimate. Palaeogeography, Palaeoclimatology, Palaeoecology, 160, 347–372. Nederbragt, A.J., Fiorentino, A. & Klosowska, B. 2001. Quantitative analysis of calcareous microfossils across the Albian–Cenomanian boundary oceanic anoxic event at DSDP Site 547 (North Atlantic). Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 401–421. Oglesby, R. & Park, J. 1989. The effect of precessional insolation changes on Cretaceous climate and cyclic sedimentation. Journal of Geophysical Research, 94(D12), 14793–14816. Okada, H. & Honjo, S. 1973. The distribution of oceanic coccolithophorids in the Pacific. Deep-Sea Research, 20, 355–374. Pedersen, T.F. & Calvert, S.E. 1990. . Anoxia vs. productivity: what controls the formation of organic-carbon-rich sediments and sedimentary rocks? AAPG Bulletin, 74, 454–466. Poulsen, C.J., Seidov, D., Barron, E.J. & Peterson, W.H. 1998. The impact of paleogeographic evolution on the surface oceanic circulation and the marine environment within the mid-Cretaceous Tethys. Paleoceanography, 13, 546–559. Poulsen, C.J., Barron, E.J., Arthur, M.A. & Peterson, W.H. 2001. Response of the mid-Cretaceous global oceanic circulation to tectonic and CO2 forcings. Paleoceanography, 16, 576–592. Premoli-Silva, I. & Sliter, W.V. 1999. Cretaceous paleoceanography: evidence

from planktonic foraminiferal evolution. In: Barrera, E. & Johnson, C.C. (eds) The Evolution of Cretaceous Ocean/Climate Systems. Geological Society of America, Special Papers, 332, 301–328. 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). Ge´obios, Memoire spe´cial, 11, 225–236. Premoli-Silva, I., Erba, E., Salvini, G., Locatelli, C. & Verga, D. 1999. Biotic changes in Cretaceous Oceanic Anoxic Events of the Tethys. Journal of Foraminiferal Research, 29, 352–370. Price, G.D., Sellwood, B.W. & Valdes, P.J. 1995. Sedimentological evaluation of general circulation model simulations for the ‘greenhouse’ Earth: Cretaceous and Jurassic case studies. Sedimentary Geology, 100, 159–180. Pross, J. 2001. Palaeo-oxygenation in Tertiary epeiric seas: evidence from dinoflagellate cysts. Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 369–381. Pross, J. & Schmiedl, G. 2002. Early Oligocene dinoflagellate cysts from the northern Rhine Graben (SW Germany): paleoenvironmental and paleoclimatic implications. Marine Micropaleontology, 45, 1–24. Reichart, G.J., den Dulk, M., Visser, H.J., van der Weijden, C.H. & Zachariasse, W.J. 1997. A 25 kyr record of dust supply, palaeoproductivity and oxygen minimum zone from the Murray Ridge (northern Arabian Sea). Palaeogeography, Palaeoclimatology, Palaeoecology, 134, 149–169. Reichelt, K. 2005. Late Aptian–Albian of the Vocontian Basin (SE France) and Albian of NE Texas: biostratigraphic and paleoceanographic implications by planktic Foraminifera fauna. PhD thesis, Eberhard Karls Universita¨t Tu¨bingen. Rohling, E.J. & Gieskes, W.W.C. 1989. Late Quaternary changes in Mediterranean and intermediate water density and formation rate. Paleoceanography, 4, 531–545. Rossignol-Strick, M. 1985. Mediterranean Quaternary sapropels, an immediate response of the African monsoon to variations of insolation. Palaeogeography, Palaeoclimatology, Palaeoecology, 49, 237–263. Rossignol-Strick, M. & Paterne, M. 1999. A synthetic pollen record of the eastern Mediterranean sapropels of the last 1 Ma: implications for the timescale and formation of sapropels. Marine Geology, 153, 221–237. Rossignol-Strick, M., Paterne, M., Bassinot, F.C., Emeis, K.-C. & Delange, G.J. 1998. An unusual mid-Pleistocene monsoon period over Africa and Asia. Nature, 392, 269–272. Roth, P.H. 1973. Calcareous nannofossils—Leg 17, Deep Sea Drilling Project. In: Winterer, E.L, Ewing, J.I. et al. (eds) Initial Reports of the Deep Sea Drilling Project, 17. US Government Printing Office, Washington, DC, 695–795. Roth, P.H. 1983. Jurassic and Lower Cretaceous calcareous nannofossils in the western North Atlantic (Site 534): biostratigraphy, preservation, and some observations on biogeography and paleoceanography. In: Sheridan, R.E., Gradstein, F. M. et al. (eds) Initial Reports of the Deep Sea Drilling Project, 76. US Government Printing Office, Washington, DC, 587–621. 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. 1972. Calcareous nannoplankton: Leg 14 of the Deep Sea Drilling Project. In: Hayes, D.E., Pimm, A.C. et al. (eds) Initial Reports of the Deep Sea Drilling Project, 14. US Government Printing Office, Washington, DC, 421–485. Ryan, W.B.F. & Cita, M.B. 1977. Ignorance concerning episodes of ocean-wide stagnation. Marine Geology, 23, 197–215. Sachs, J.P. & Repeta, D.J. 1999. Oligotrophy and nitrogen fixation during Eastern Mediterranean sapropel events. Science, 286, 2485–2488. Savin, S.M. 1977. The history of the Earth’s surface temperature during the past 100 million years. Annual Review of Earth and Planetary Sciences, 5, 319–355. Savostin, L.A., Sibuet, J.C., Zonenshain, L.P., Le Pichon, X. & Roulet, M. 1986. Kinematic evolution of the Tethys belt from the Atlantic Ocean to the Pamirs since the Triassic. Tectonophysics, 123, 1–35. Schlanger, S.O. & Jenkyns, H.C. 1976. Cretaceous anoxic events: causes and consequences. Geologie en Mijnbouw, 55, 179–184. Schrag, D.P., DePaolo, D.J. & Richter, F.M. 1995. Reconstruction of past sea surface temperatures. Correcting for diagenesis of bulk marine carbonate. Geochimica et Cosmochimica Acta, 59, 2265–2278. Shackleton, N.J., Hall, M.A. & Boersma, A. 1984. Oxygen and carbon isotope data from Leg 74 Foraminifers. In: Moore, T.C. jr, Rabinowitz, P.D., et al. US Government Printing Office, Washington, DC, 599–612. Shannon, C.E. & Weaver, W. 1949. The Mathematical Theory of Communication. University of Illinois Press, Urbana, IL. Steinmetz, J.C. 1994. Sedimentation of coccolithophores. In: Winter, A. & Slesser, W.G. (eds) Coccolithophores. Cambridge University Press, Cambridge, 179–198. Street, C. & Bown, P.R. 2000. Palaeobiogeography of Early Cretaceous (Berriasian–Barremian) calcareous nannoplankton. Marine Micropaleontol-

N I V E AU B R E I S TO F F E R PA L A E O C E A N O G R A P H Y ogy, 39, 265–291. Traverse, A. 1988. Paleopalynology. Unwin Hyman, Boston, MA. Tribovillard, N.P. & Gorin, G.E. 1991. Organic facies of the Early Albian Niveau Paquier, a key black shales horizon of the Marnes Bleues Formation in the Vocontian Trough (Subalpine Ranges, SE France). Palaeogeography, Palaeoclimatology, Palaeoecology, 85, 227–237. van Os, B.J.H., Lourens, L.J., Hilgen, F.J., Delange, G.J. & Beaufort, L. 1994. The formation of Pliocene sapropels and carbonate cycles in the Mediterranean—diagenesis, dilution, and productivity. Paleoceanography, 9, 601–617. Weissert, H. & Bre´he´ret, J.-G. 1991. A carbonate carbon-isotope record from Aptian–Albian sediments of the Vocontian trough (SE France). Bulletin de la Societe´ Ge´ologique de France, 162, 1133–1140. Weissert, H., Lini, A., Fo¨llmi, 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. Wick, W. 1947. Aufbereitungsmethoden in der Mikropala¨ontologie. Jahresbericht der Naturhistorischen Gesellschaft Hannover, 98, 35–41. Wignall, P. 1994. Black Shales. Clarendon Press, Oxford. Williams, J.R. & Bralower, T.J. 1995. Nannofossil assemblages, fine fraction stable isotopes, and the palaeoceanography of the Valanginian–Barremian (Early Cretaceous) North Sea Basin. Paleoceanography, 10, 815–839. Wilpshaar, M. & Leereveld, H. 1994. Palaeoenvironmental change in the early Cretaceous Vocontian Basin (SE France) reflected by dinoflagellate cysts.

639

Reviews of Palaeobotany and Palynology, 84, 121–128. Wilson, P.A. & Norris, R.D. 2001. Warm tropical ocean surface and global anoxia during the mid-Cretaceous period. Nature, 412, 425–429. Wilson, P.A., Jenkyns, H.C., Elderfield, H. & Larson, R.L. 1998. The paradox of drowned carbonate platforms and the origin of Cretaceous Pacific guyots. Nature, 392, 889–894. Wilson, P.A., Norris, R.D. & Cooper, M.J. 2002. Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise. Geology, 30, 607–610. Winter, A., Jordan, R.W. & Roth, P.H. 1994. Biogeography of living coccolithophores in ocean waters. In: Winter, A. & Slesser, W.G. (eds) Coccolithophores. Cambridge University Press, Cambridge, 161–177. Wissig, F.-N. & Herrig, E. 1999. Arbeitstechniken der Mikropala¨ontologie. Enke, Stuttgart. Wood, G.D., Gabriel, A.M. & Lawson, J.C. 1996. Palynological techniques— processing and microscopy. In: Jansonius, J. & McGregor, D.C. (eds) Palynology: Principles and applications, vol. 1, American Association of the Stratigraphical Palynological Foundation, 29–50. Wortmann, U., Hesse, R. & Zacher, W. 1999. Major-element analysis of cyclic black shales: palaeoceanographic implications for the Early Cretaceous deep western Tethys. Paleoceanography, 14, 525–541. Wortmann, U.G., Herrle, J.O. & Weissert, H. 2004. Altered carbon cycling and coupled changes in Early Cretaceous weathering pattern: evidence from integrated Tethyan isotope and sandstone records. Earth and Planetary Science Letters, 220, 69–82.

Received 2 December 2003; revised typescript accepted 8 December 2004. Scientific editing by Joe Macquaker