Interactive comment on “ Bridging the Faraoni and Selli oceanic anoxic events : short and repetitive dys-and anaerobic episodes during the late Hauterivian to early Aptian in the central Tethys ”

The manuscript by Föllmi et al. presents new data for the Hauterivian to Aptian from the central Tethys. In contrast to many earlier contributions, the authors focus on the time interval between the well-known OAEs, which makes this contribution an important and welcome study. The text is well written but a bit wordy at some points (see comments below) and the figures have to be done in a more illustrative way to support the reader in understanding the author’s point. What is definitely missing is a discussion about possible trigger mechanisms for the formation of the observed organic-rich layers. A scenario of paleoenvironmental changes is promised in the last chapter of the


Introduction
The Early and early Late Cretaceous represents a time interval of considerable paleoenvironmental change, which found its expression in the repeated installation of widespread dysaerobic to anaerobic conditions in outer-shelf and basinal settings (Schlanger and Jenkyns, 1976;Jenkyns, 1980;Weissert and Erba, 2004). One of the 15 oldest "oceanic anoxic episodes" (OAE) of the Cretaceous dates from the latest Hauterivian and is known as the "Faraoni event" (Cecca et al., 1994). This episode was originally identified in the central Italian Apennines, where it is preserved in the form of a well-distinguishable interval of thin and closely spaced organic-rich mudstone layers in pelagic carbonate (Cecca et al., 1994;Coccioni et al., 1998Coccioni et al., , 2006Baudin et al., 20 2002; Baudin, 2005). A coeval equivalent of the Faraoni Level was subsequently found in northeast Italy (eastern part of the Trento Plateau and Lessini Mountains; Cecca et al., 1996;Faraoni et al., 1997;Baudin et al., 1997;Cismon, Venetian Alps;Erba et al., 1999;Tremolada et al., 2009) and in the southern Swiss Alps (Breggia;Bersezio et al., 2002). In the following, other Faraoni equivalents were identified outside the central 25 Tethyan realm, such as in the Vocontian Basin (Vergons; Baudin et al., 1999), Ultrahelvetic Basin (Veveyse de Châtel St. Denis; Busnardo et al., 2003), and in the Rio Argos section of the Subbetic unit in Spain (Company et al., 2005). 2024 OAE 1a have been documented from different marine basins, such as the Vocontian Basin (Bréhéret, 1988), the northwest German Basin (Kemper and Zimmerle, 1978;Mutterlose et al., 2009), the southern Tethyan realm (Heldt et al., 2008), the central and southern Atlantic (Bralower et al., 1994) and the middle and northwestern Pacific (Sliter, 1989;Bralower et al., 2002). Together with the Late Cenomanian "Bonarelli event", the Selli episode represents a model OAE for a wide range of investigations (e.g., Menegatti et al., 1998;Erba et al., 2010;Tejada et al., 2010;Stein et al., 2011a).
In the central Tethys and northern Atlantic, the pelagic sediments between the Faraoni and Selli OAEs are characterized by the presence of a series of thin, organicrich mudstone layers, which have been interpreted as the result of short-lasting and 15 cyclically reappearing anoxic episodes (Weissert et al., , 1985Weissert, 1981a;cf. also Herbert, 1992;Bralower et al., 1994;Bersezio et al., 2002). Intermittent anoxic conditions spanning the latest Hauterivian to the early Aptian time interval have also been documented from the northern German Lower Saxony Basin (Mutterlose et al., 2009(Mutterlose et al., , 2010. Brief anoxic episodes predating the Selli event have equally been estab- 20 lished from the southern Atlantic and Mid-Pacific (e.g., Bralower et al., 1994). These short-lived anoxic episodes bridging the Faraoni and Selli OAEs are generally less well characterized in terms of their geochemistry, and their implications for the general paleoceanographic and paleoenvironmental conditions during this time interval are less well established. It is for example not known, if these short episodes have their expres- 25 sion in shallow-water sediments, and if they had a larger-scale, inter-basinal impact or if they were only of regional importance.
In this contribution we present new insights on the time interval spanning the late Hauterivian and earliest Aptian based on data from the Breggia and Capriolo sections in southern Switzerland and northern Italy, respectively (Fig. 1). These two sections are complementary with regards to their age ranges and offer the possibility to cover the time interval between the late Hauterivian and earliest Aptian. Based on our data and their interpretation, we suggest that (1) these brief anoxic events are widespread within the Tethys, (2) can be correlated with their counterparts in the boreal northwest Ger-5 man Basin, and (3) are correlated with changes in the ecology of carbonate-producing benthos on adjacent shallow-water carbonate platforms.

The Breggia and Capriolo sections
The Breggia section is located in southern Switzerland, in an abandoned quarry near the Breggia Gorge, close to Balerna (canton Ticino; Fig. 1). The Capriolo section has been measured in the upper part of an abandoned quarry northeast of Capriolo, southwest of the Lago d'Iseo, in northern Italy (Fig. 1). In both sections, the upper part of the Maiolica Formation has been sampled, which consists of a light-coloured pelagic, micritic carbonate including siliceous levels and nodules, and thin and dark-coloured mudstone interlayers. 15 For both sections, the magnetostraphies by Channel et al. (1987Channel et al. ( , 1993Channel et al. ( , 1995Channel et al. ( , 2000 and Channel and Erba (1992) were projected onto the measured sections. In addition, a crosscheck was performed by the analysis of calcareous nannofossils on selected mudstone samples. We used the last appearance of Lithraphidites bollii as a fix point to correct for apparent differences in measured thicknesses between the published 20 and our sections. The resulting stratigraphies indicate that for the Breggia section, the upper Hauterivian and lower Barremian intervals are quite complete and that the top of the Maiolica Formation is marked by a major hiatus, which starts in the early late Barremian. The overlying Scaglia variegata is already of Aptian age.
The Maiolica Formation in the Capriolo section extends well into the lower Aptian. Introduction Based on the first appearance of Rucinolithus irregularis (Channell and Erba, 1992) we assume that the normal magnetochron underneath CMO represents at least in part CM1. As such most of the upper Barremian interval may have been preserved, whereas the lower Barremian interval appears largely reduced. Also the uppermost Hauterivian succession shows slumped intervals. The lowermost Aptian interval appears, on the contrary, well preserved. Besides for its magnetostratigraphy and nannofossil biostratigraphy, the Hauterivian to Barremian interval in the Breggia section was also investigated for its facies and sedimentology by Weissert (1979Weissert ( , 1981b and Weissert et al. (1979); stable carbonisotope composition by Weissert et al. (1985); clay-mineral composition by Deconinck and Bernoulli (1991); organic matter by Arthur and Premoli-Silva (1982) and Bersezio et al. (2002); ammonites by Rieber (1977); and aptychi by Renz and Habicht (1985). The Hauterivian to lowermost Aptian interval in the Capriolo section was furthermore described by Weissert (1981b).

Conclusions References
Here we provide detailed stratigraphic logs and records of stable carbon and oxygen 15 isotopes, organic-matter and phosphorus contents, and redox-sensitive trace element distributions for both sections. These data were acquired in the framework of three bachelor theses, which were completed at the University of Neuchâtel (Jammet and Froidevaux, 2008;Bôle, 2009).

Organic-carbon analysis
The total organic carbon (TOC) content of preserved organic matter was analyzed on a Rock Eval™6 (Espitalié et al., 1985), with an instrumental precision of <2 %. Approximately 70 mg of powdered sample was first pyrolyzed and subsequently completely oxidized. The amount of hydrocarbon released during pyrolysis was measured by a 25 FID detector, whereas the amount of CO 2 and CO during both steps was measured by infrared absorbance. A standard cycle was applied, in which pyrolysis started isothermally at 300 • C for three minutes (S1: hydrocarbons released during the isothermal phase). The sample was then heated to 650 • C (S2: hydrocarbons released between 300 and 650 • C). The oxidation step started isothermally at 400 • C for three minutes (S3: CO 2 released) and subsequently, the sample was heated up to 850 • C. Obtained 5 TOC contents are expressed in weight % (wt %). The hydrogen and oxygen indices (HI = S2/TOC × 100 in mg hydrocarbons per g TOC; OI = S3/TOC × 100 in mg CO 2 per g TOC) were plotted in a Van Krevelen-type diagram and used to characterize preserved organic matter (Espitalié et al., 1985). Two standards (IFP 160000 and VP143h) were applied to calibrate the measurements. The error relative to standard IFP 160000 10 is 0.77, 0.25 and 1.5 % for TOC, HI and OI, respectively.

Total phosphorus analysis
Total phosphorus (P) contents were measured on powdered bulk-rock samples. 1 ml of 1 M MgNO 3 was added to 100 mg powder and the resulting solution was dried in an oven at 130 • C during 30 min. The sample was then heated at 550 • C during two 15 hours to oxidize the organic matter. After cooling, 10 ml of 1N HCl was added to the sample to liberate P and the solution was placed in a shaker during 16 h. The solution was then filtered, diluted 10 times and mixed with 100 µl molybdate mixing reagent to form phosphomolybdic acid (Eaton et al., 1995). In the following, 100 µl of ascorbic acid was added to reduce the acid and colour the solution blue. The intensity of the 20 blue colour is a function of the P concentration. The total P content was measured by a UV/Vis spectrophotometer (Perking Elmer UV/Vis Spectrophotometer Lambda 10; λ = 865 nm). Selected samples were measured three times and the obtained precision is better than 5 %.

Stable carbon-and oxygen isotope analysis
Stable carbon-and oxygen-isotope ratios were measured on powdered bulk-rock samples using a Thermo Fisher Delta V Advantage at the University of Berne, and a Thermo Fisher Delta Plus XL at the University of Lausanne, both equipped with an automated carbonate preparation line. The results were calibrated to the Vienna Pee 5 Dee Belemnite (V-PDB) scale with a standard deviation better than 0.05 ‰ for δ 13 C and 1 ‰ for δ 18 O.

Redox-sensitive trace-element analysis
Carbonate samples were analyzed for molybdenum (Mo), uranium (U), cobalt (Co), vanadium (V), and arsenic (As) contents. These elements are considered as redox-10 sensitive trace elements (RSTE), which are used as indicator of the presence and intensity of oxygen depletion at the site of sediment deposition (Algeo and Maynard, 2004;Tribovillard et al., 2006;Bodin et al., 2007). 10 ml suprapur nitric acid (HNO 3 ) was added to 250 mg of rock sample reduced to powder in a PFA vessel and subsequently digested in a microwave oven (MSL- 15 Ethos plus, Milestone; heating program EPA 3051). The solution was cooled, filtered (0.45 µm) and diluted to 100 ml with ultrapure water (Bodin et al., 2007). Dissolution percentages determined after filtration were between 89 and 94 wt % for all carbonate samples. Westermann et al. (2010) showed for comparable pelagic carbonates of Valanginian age from the same Breggia and Capriolo sections that RSTE contents and 20 dissolution percentages are not positively correlated. This suggests that the RSTE are present in the soluble carbonate phase and not derived from partial leaching of the detrital fraction (cf. also Bodin et al., 2007). The RSTE data were, therefore, not normalized by aluminum contents.
RSTE contents (in ppm) were determined by a quadrupole ICP-MS (ELAN 6100, Introduction calibration was based on two certified reference materials (LKSD-1 lake sediment and NIST-1640 natural water).

Total organic carbon
Samples of the dark, laminated and organic-rich layers in the Breggia section show range between approximately 90-370 mg HC g −1 TOC and 20-120 mg CO 2 g −1 TOC (Breggia), and 30-300 mg HC g −1 TOC and 30-120 mg CO 2 g −1 TOC (Capriolo). In a Van Krevelen-type diagram, the preserved organic matter plots mostly within or nearby the type III field (Fig. 4). 20 Total P contents were measured on a series of carbonate and mudstone samples. In samples of the Breggia section, total P contents for carbonates and mudstones vary between approximately 100 and 250 ppm, and 250 and 1000 ppm, respectively, whereas in the Capriolo section, total P contents range between approximately 70 and The stratigraphic evolution in total P contents in carbonates of the Breggia section is marked by two maxima around 250 ppm within the upper Hauterivian and a further maximum around 250 ppm in the middle lower Barremian interval. In the Capriolo 5 section, carbonate P contents are generally higher in the Barremian and lower Aptian interval, in comparison to the upper Hauterivian interval. In both sections, the mudstone samples display rather disparate spreads of values, and trends are difficult to be discerned.

Total phosphorus
In the Breggia section, the C org :P tot molar ratios show departures above 300 in mudstone levels with higher TOC values (>4 wt %; Fig. 2) dating from the latest Hauterivian and middle early Barremian. Similar departures are observed in two layers above the Hauterivian-Barremian boundary and one layer within the lower Aptian interval of the Capriolo section. There, the Barremian levels are not necessarily those with the highest TOC levels, whereas the lower Aptian level is the one which possesses the highest 15 TOC value of the entire measured section (14.7 wt %).

Stable-carbon and oxygen isotopes
The δ 13 C record of the Breggia section shows comparable values and a consistent trend for both the carbonate and mudstone samples (Fig. 2). It is characterized by rather stable values for the upper Hauterivian interval at around 1.5 ‰. The δ 13 C record 20 rises to maximal values around 1.8 ‰ in the Hauterivian-Barremian boundary interval. In the following, the δ 13 C values slowly decrease to near 1.5 ‰ and increase again to fluctuate around 1.8 ‰ for the remainder of the lower Barremian interval. Just above the boundary between the lower and upper Barremian, the δ 13 C record increases by approximately 1 ‰ to values of 2.5 ‰. 25 The δ 13 C record of the Capriolo section is only shown for the carbonate samples ( Fig. 3 carbonate samples of the upper Hauterivian interval are characterized by a gentle trend towards more negative values from near 2 ‰ to 1.8 ‰, followed by a short-lasting positive trend to around 1.9 ‰ and a renewed negative trend towards a minimum of 1.5 ‰ near the Hauterivian-Barremian boundary. δ 13 C values in the lower part of the Barremian interval are rather stable and fluctuate between 1.5 and 1.8 ‰, whereas in the 5 upper part, they move to a maximum of near 2.2 ‰. The Barremian-Aptian boundary interval shows a negative excursion to a minimal value of near 1.8 ‰, which is followed by an irregular positive trend towards values of 2.2 ‰ near the top of the section (Fig. 3).
In the Breggia section, the δ 18 O values for the marlstone samples are approximately shows in the following an irregular negative trend towards the lowest value (−2.6 ‰) measured in the entire section, near the Hauterivian-Barremian boundary (Fig. 3). This is followed by a rapid positive trend towards values near −1.8 ‰ and the remainder of the Barremian interval shows rather stable δ Barremian-Aptian boundary interval shows decreasing values towards −2.2 ‰ and the 25 lower Aptian interval is again characterized by an increase to −1.8 ‰, a slight decrease to 2 ‰ and a renewed increase to −1.4 ‰ (Fig. 3 for levels underneath the Hauterivian-Barremian boundary (for all measured RSTE) and in the upper Barremian interval (for U and Co).
In carbonate samples of the Capriolo section, Mo, U, Co, V and As contents range between 0-545ppb, 43-3557 ppb, 964-8127 ppb, 1219-13941 ppb, and 0-2883 ppb, respectively (Fig. 3). The mean values for Mo, U, Co, V and As are 71 ppb, 451 ppb, 10 2051 ppb, 2618 ppb, and 442 ppb (n = 42). Excursions in RSTE contents are observed for carbonates underneath the Hauterivian-Barremian boundary and within the lower Aptian interval. 15 TOC contents reach values above 10 wt % in two mudstone layers below the Hauterivian-Barremian boundary in the Breggia section and in one layer within the lower Aptian interval in the Capriolo section (Figs. 2 and 3). All other measured intervals possess TOC contents below 10 wt %. These values are generally lower than the values measured for the Faraoni interval in central Italy (e.g., Baudin, 2005), whereas 20 they are higher than the ones measured in organic-rich layers immediately underneath the Selli Level in central Italy (Stein et al., 2011a). In comparison to the Breggia section, the TOC values in Capriolo are generally lower, probably due to a higher degree of tectonic overprint. This is also indicated by the somewhat higher T max values in Capriolo (average value = 430

Organic-carbon contents and preservation
• C) relative to Breggia ( The HI and OI values plot within or nearby the type-III field (Fig. 4), and no real trends are discernable between TOC contents and HI/OI values, except for very low values underneath 0.5 wt %, which tend to have very low HI and higher OI values. These values suggest that preserved organic matter in both sections is partly altered by its tectonic history and aerial exposure, but may also include a terrestrial component.

5
The levels close to the Hauterivian-Barremian boundary in the Breggia and Capriolo sections show systematically lower HI values than the Faraoni level in central Italy (with values up to 600; Baudin, 2005).

Phosphorus contents and C org :P tot molar ratios
Trends in P burial rates are used as a proxy for temporal changes in the amount of P 10 transferred into the basin (Föllmi, 1995(Föllmi, , 1996Bodin et al., 2006a), assuming steadystate conditions over time periods covering several residence times of reactive P in the ocean (approximately 10 000-20 000 yr in modern oceans; e.g., Filippelli, 2008). Lacking a major detrital fraction, total P in pelagic carbonate sections may be used as a proxy for reactive P, which was transferred into an authigenic phase, became 15 adsorbed onto reactive mineral surfaces, or remained associated with organic matter (e.g., Ruttenberg, 2004). Under dysaerobic conditions, buried P may be preferentially released and returned to bottom waters, and P burial rates may tend to lower, thereby masking the initial P flux rates into the basin (e.g., Slomp et al., 2004;Mort et al., 2007). Evidence for this is provided by the C org :P tot molar ratios in organic-rich layers, 20 which tend to be significantly higher than the Redfield ratio (106:1) under dysaerobic conditions (e.g., Algeo and Ingall, 2007;Mort et al., 2007).
In both sections, P contents in carbonates and mudstone layers are generally higher in those intervals, where mudstone layers are more frequent and characterized by higher TOC contents (Figs. 2 and 3). The overall P contents are relatively low and 25 comparable to those of other sections in the Maiolica Formation (e.g., Gorgo a Cerbara, Stein et al., 2011a) or in older intervals of the Maiolica Formation in the same sections (Westermann et al., 2011 show a maximum in the upper Hauterivian interval and tend to become lower in the Hauterivian-Barremian boundary interval. The P values are higher again in the lower Barremian interval. The Capriolo P values tend to decrease in the upper Barremian interval and remain low in the lower Aptian interval, except for a small maximum. These trends are comparable to those compiled by Bodin et al. (2006a) andFöllmi (1995).

5
In the Breggia section, the C org :P tot molar ratios are larger than 300 for mudstone interlayers with the highest TOC values (underneath the Hauterivian-Barremian boundary and in the higher part of the lower Barremian interval; exception is a mudstone layer just above the boundary between the lower and upper Barremian intervals: Fig. 2). In the Capriolo section, this relationship holds only for one mudstone interlayer within the 10 lower Aptian interval.

Stable-carbon isotope records
For the purpose of this contribution, only the carbon-isotope records will be discussed, since they serve as correlation tools. In the Breggia section, the general trend is similar to trends in other sections of the central and northern Tethys (  The long-term trends in the δ 13 C record in the Capriolo section appear also correlatable, with minimal values near the Hauterivian-Barremian boundary, followed by a trend towards more positive values, which are typical for the late Barremian. The δ 13 C record seems to confirm that most of the lower Barremian interval is missing (Fig. 5).
The trend towards more negative values during the upper part of the Barremian inter- 25 val and the minimum in the δ 13 C record near the Barremian-Aptian boundary is also known from the Cismon Apticore in northeastern Italy (Erba et al., 1999), the Gorgo a Cerbara section in central Italy (Godet et al., 2006;Sprovieri et al., 2006), and the Angles section in southeastern France (Wissler et al., 2002;Godet et al., 2006). It is clear from the correlations shown in Fig. 5 that the accumulation rates of the Breggia and Capriolo sections are much lower compared to those of other sections from the central and northern Tethyan realms.

Redox-sensitive trace-element records
Stratigraphic distributions of RSTE (here: Mo, U, Co, V and As) and enrichments therein are widely used as a tracer of the presence and intensity of oxygen-depletion within the water column during sediment deposition. The here-investigated suite of RSTE appears preferentially in dissolved form under oxidizing conditions, and tends to form 10 organo-metal complexes or precipitate as oxides, hydroxides and sulfides under anoxic conditions (Algeo and Maynard, 2004;Tribovillard et al., 2006;Brumsack, 2006;Bodin et al., 2007;Westermann et al., 2010).
The RSTE contents discussed here have been measured on carbonate samples, and the absolute values are generally depleted relative to those for post-Archean aver-15 age shale (PAAS; Mo = 1 ppm, U = 2.8 ppm, Co = 17 ppm, V = 107 ppm, As = 1.5 ppm; Taylor andMcLennan, 1985, 1995). This implies that enrichments in RSTE relative to the background values in the carbonates of both sections are not of a magnitude, which would allow for the definite identification of dysaerobic or anaerobic conditions. It is only in combination with the other parameters used here (TOC, C org :P tot ratios) that 20 certain observations can be made.
The RSTE enrichments in carbonates associated with mudstone layers underneath the Hauterivian-Barremian boundary in the Breggia section go along with high TOC values and elevated C org :P tot ratios (Fig. 2). To a lesser extent, the same coincidence is observed for the middle part of the lower Barremian interval in the Breggia section. 25 For the Capriolo section, similar RSTE enrichments are observed for the carbonates near the mudstone layers underneath the Hauterivian-Barremian boundary; TOC and C org :P tot ratios of the same layers, are, however, not exceptionally high. around a mudstone layer with high TOC and C org :P tot ratio within the lower Aptian interval are not enriched in RSTE (Fig. 3). Carbonate samples above this level are more enriched in RSTE, but the associated mudstone layers are not exceptionally enriched in TOC and their C org :P tot ratio is not increased relative to the Redfield ratio of 106:1. For the Breggia section, these observations imply that anaerobic conditions may 5 have prevailed during mudstone deposition in the latest Hauterivian and in the middle part of the early Barremian. For the Capriolo section, the data are less conclusive, and only hints can be made for a certain degree of oxygen depletion during the latest Hauterivian and eventually also for the early Aptian. For the remainder of the laminated organic-rich mudstone layers, depositional conditions were dysaerobic, rather 10 than anaerobic. Given the paleogeographic proximity of both sections, the aforementioned discrepancy in terms of bottom-water oxygenation may reflect the development of local anaerobic pockets within larger dysaerobic bottom-water masses.

The Faraoni oceanic anoxic episode
In the Breggia section, the two organic-rich mudstone layers with TOC contents over 15 12 wt %, RSTE enrichment and C org :P tot ratios over 300 near the base of magnetochron CM4 are identified as an equivalent of the Faraoni level of central Italy. The correlation is confirmed by the nannofossil assemblages identified in the organic-rich mudstone interlayers, which consist of abundant large-sized Assipetra terebrodentarius, Assipetra infracretacea, and Zeugrhabdotus embergeri, and the last occurrence of Lithraphidites 20 bollii.
In the Capriolo section, the identification of the Faraoni level is less conclusive with regards to the geochemical tracers. There are no levels within the upper Hauterivian interval, which are particularly enriched in TOC or P (relative to C org ). A level enriched in RSTE right underneath the last occurrence of Lithraphidites bollii is taken as the equivalent of the Faraoni level. This is confirmed by the presence of the same largesize nannofossil species as in the Faraoni level of the Breggia section. Introduction In both sections, the Faraoni level is preceded by organic-rich layers, which appear approximately 5 and 3 m below the Faraoni level in the Breggia and Capriolo sections, respectively. The Faraoni level is also succeeded by a series of organic-rich mudstone interlayers, which extend well into the Barremian. These interlayers are thinner than the layers associated with the Faraoni event and their TOC contents are not higher than 2 wt %. Furthermore, they lack major departures in RSTE contents and C org :P tot ratios, which suggests that they are the product of dysaerobic rather than anaerobic conditions.
Overall, it appears that the Faraoni event is not a singular event, but rather a culminating episode of anaerobic conditions within a longer time interval of periodically resur-10 facing dysaerobic conditions leading to enhanced organic-matter preservation and/or diminishing carbonate deposition (cf. Bodin et al., 2006a).

Temporal pattern in organic-matter preservation during the latest Hauterivian to earliest Aptian time interval
In order to quantify the relative importance of organic-matter deposition and preserva-15 tion per time unit, we established a density profile of the organic-rich mudstone layers. The profile was calculated as where OML stands for organic-rich mudstone layer, t for time unit (corresponding to entire or parts of magnetochrons in the case of the Breggia and Capriolo sections; in 20 my) and q OML as parametrization for the thickness (h) of each layer, where q OML = 1 (h < 2 cm), q OML = 2 (2 cm < h < 4 cm), q OML = 3 (4 cm< h < 6 cm), q OML = 4 (6 cm< h < 8 cm), q OML = 5 (8 cm< h < 10 cm), etc. Thicknesses greater than 20 cm have not been observed. Σq OML corresponds to the sum of q OML . For example, if an interval corresponding to 2my has five organic-rich interlayers with thicknesses of 1, 5, 11, 2 and Introduction The results of this quantification are shown in Fig. 6 and suggest that periods of increased OML density occurred during the late Hauterivian, latest early Barremian and earliest Aptian. Periods of low OML density are identified for the late Barremian and the time interval just preceding the Selli episode.  , 2007). Evidence for the presence of a Faraoni equivalent was also not excluded for the Argentinean Neuquén Basin (Tyson et al., 2005).

Comparison with other regions
For the Tethyan localities of the Faraoni level and its equivalents, the prevalence of anaerobic conditions has been shown based on paleontological (lack of benthos; 15 Baudin, 2005), sedimentological (presence of laminated, organic-rich sediments with TOC values of up to 27 wt %; Baudin, 2005) and geochemical criteria (C org -P tot ratios; excursions in RSTE contents; Bodin et al., 2006aBodin et al., , 2007. The Faraoni anoxic episode coincides also with important evolutionary change in rudists (Masse and Fenerci-Masse, 2008 With respect to the deposition of the younger, Barremian to lower Aptian organic-rich interlayers, we estimated the OML density for the Gorgo a Cerbara section in central 25 Italy, using the stratigraphic plots of Fiet and Gorin (2000) and Stein et al. (2011a) (Fig. 6) distinctly richer in organic-rich interlayers relative to the Capriolo section. Interestingly, a good correspondence is also given between the OML density curves for the central Tethys and the presence of laminated mudstone layers in the northwest German Basin (Mutterlose et al., 2009(Mutterlose et al., , 2010. We searched for further basinal records of this time interval; and indeed, the presence of organic-rich mudstone interlayers is known from 5 different DSDP and ODP Sites from the central and northern Atlantic (e.g., Weissert, 1981a;Stein et al., 1988). The current age models for those deposits do, however, not allow for high-resolution correlations.
Besides basin-to-basin correlations, we also observe interdependencies between the periods of enhanced organic-matter preservation and the evolution of the northern Tethyan platform presently outcropping in the Helvetic Alps (Fig. 6). A prolonged phase of platform drowning along the northern Tethyan margin has been documented from the Jura Mountains and Helvetic Alps, which started in the latest Hauterivian and lasted until the late early Barremian (Bodin et al., 2006b;Godet et al., 2010). The onset of this drowning episode slightly predates the onset of the Faraoni anoxic episode 15 (Föllmi et al., 200615 (Föllmi et al., , 2007. The early late Barremian is characterized by the deposition of marly carbonate and carbonate-marl succession, which is interrupted by a short phase of condensation and phosphogenesis during the middle late Barremian. Thereafter, Urgonian-type shallow-water carbonates prograde and show the installation of a photozoan carbonate platform. The deposition of Urgonian carbonate is interrupted 20 around the Barremian-Aptian boundary by a phase of heterozoan carbonate, marl and sand deposition ("Lower Orbitolina Beds": LOB). On top of the younger Urgonian unit overlying the LOB, a phase of platform drowning is observed, which is followed by heterozoan carbonate deposition ("Upper Orbitolina Beds": UOB), a second drowning phase (corresponding partly in time to the Selli oceanic anoxic event), and further het- One of the environmental parameters, which may have changed conditions on the platform and in the basin, are variations in the nutrient flux, which interfere both with the composition and efficiency of shallow-water carbonate-producing ecosystems and the pelagic organic-matter export flux. P accumulation rates established for this time interval go rather well along with the contents measured in the Breggia and Capriolo 5 sections and show an increase across the Hauterivian-Barremian boundary interval and higher values during the early Barremian, followed by lower values during the late Barremian (Bodin et al., 2006a) and higher values again for the early Aptian (Föllmi, 1995).

Hauterivian to the early Aptian
During the latest Hauterivian, the central and northern Tethyan basin witnessed short and repetitive phases of dysaerobic conditions and increased organic-matter preservation, whereas on its northern margin, the carbonate platform attached to the southern European margin started to drown. This phase of paleoceanographic change culmi-15 nated in the Faraoni anoxic episode, which was probably not limited to the Tethyan realm, but may also have left its traces in other basins, probably as far as the Pacific. The late Hauterivian is characterized by a minimum in the Italian δ 18 O whole-rock record ( Fig. 6; Weissert and Erba, 2004;Godet et al., 2006;Bodin et al., 2009) and the onset in kaolinite deposition (in southeast France, Godet et al., 2008;Fig. 6;cf. De-20 coninck and Bernoulli, 1991), which may indicate humid and eventually warmer climate conditions. The early Barremian is a period of generally increased organic-matter preservation, both in the Tethys as well as in the Boreal German Basin, and likely also in the central and northern Atlantic. The Helvetic and Jurassic segment of the northern Tethyan 25 platform remained largely subjected to a halt in carbonate production, condensation and phosphogenesis, with a culmination in drowning pattern in the later part of the early Barremian (Bodin et al., 2006b). This time period is characterized by increasing 2041 Introduction

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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | P burial rates and generally high kaolinite depositional rates (Fig. 6), which may indicate continuing humid climate conditions, with an increasing tendency towards the end of the early Barremian (Deconinck and Bernoulli, 1991;Godet et al., 2008 lighter values for most of the early Barremian (Fig. 6). The late Barremian is characterized by lower rates of organic-matter preservation in the Tethyan basin and the progressive installation of the Urgonian carbonate platform on the northern Tethyan margin. P burial rates diminished during this time period and the same is true for kaolinite deposition, with the exception of a maximum in the mid-10 dle late Barremian. The French δ 18 O records are characterized by relatively positive values for a larger part of the late Barremian, which, in generally, is explained by a tendency towards cooler temperatures (cf. also Ruffell and Batten, 1990).
The renewed increase in organic-matter burial around the Barremian-Aptian boundary goes along with decreasing values in the δ 18 O records and a change towards 15 heterozoan carbonate production on the northern Tethyan platform. Even if the kaolinite record does not show a change in the Vocontian basin record, increases have been established on the adjacent carbonate platform (Godet et al., 2008;Stein et al., 2011b). This phase is followed by a decrease in organic-carbon burial and a second episode in Urgonian platform build up. The Selli OAE is finally preceded by a platform 20 drowning phase and a change to heterozoan carbonate production, and goes along with a further platform drowning phase.
Our reconstruction of paleoenvironmental change during the period from the late Hauterivian to the early Aptian suggests that the Faraoni and Selli OAEs are culminations of longer periods of paleoenvironmental change with a widespread impact, and 25 that the intervening periods of dys-to anaerobic conditions in the Tethys were related to those of other basins and had tele-connections with the evolution of the adjacent northern Tethyan carbonate platform. The higher frequency of dys-to anaerobic intervals in the pelagic realm and the vulnerability of the northern Tethyan carbonate platform to drowning during the late Hauterivian, Barremian and early Aptian can be seen as the expression of a regularly perturbed world.

Conclusions
We performed a detailed stratigraphic and geochemical analysis of two pelagic sections in southern Switzerland (Breggia) and northern Italy (Capriolo) and suggest that 5 the latest Hauterivian, early Barremian and the Barremian-Aptian boundary interval were times of preferential organic-matter preservation under episodic dys-to anaerobic conditions, whereas the late Barremian and the period following the Barremian-Aptian boundary interval are characterized by a lower density in periods of organicmatter preservation. We compare this evolution to the section of Gorgo a Cerbara (central Italy), to the temporal pattern of organic-matter preservation in the northwest German Basin, and the evolution of the northern Tethyan shallow-water carbonate platform presently preserved in the Helvetic Alps, and observe synchroneity between the dysaerobic to anaerobic episodes in the Tethyan and Boreal Basins and a correspondence to the evolution of the northern Tethyan carbonate platform and its drowning 15 phases. The paleoceanographic changes during the late Hauterivian and early Aptian are likely driven by changes towards more humid climate conditions. This implies that the Faraoni and Selli anoxic episodes do not represent singular events in an otherwise unperturbed world, but are embedded in longer-lasting phases of environmental change preceding and following the anoxic episodes. They are 20 bridged by a series of shorter-lasting dysaerobic and anaerobic episodes during the Barremian and early Aptian, which did not impact the world oceans in the same way as the Selli and probably also the Faraoni episodes. They are, however, more important than hitherto assumed, since a similar record is identified in the Boreal northwest German Basin and since relationships are seen between the frequency and intensity Introduction

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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Acknowledgements. We gratefully acknowledge the advice and assistance in the field of Melody Stein and Stéphane Westermann, the assistance of Tiffany Monnier in the preparation of samples for the ICP-MS analyses, and the expertise of Silvia Gardin for the determination of calcareous nannofossils. We thank the Swiss National Science Foundation for its support during various stages of this research. Poppe de Boer, Caroline Slomp and Henk Brinkhuis 5 are thanked for the organization of the meeting on "Climate and Ocean Dynamics of the Cretaceous Greenhouse World", 26-28 January 2011, Utrecht, and their invitation to contribute this paper. Introduction

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