Closing the Mid-Palaeocene gap: Toward a complete astronomically tuned Palaeocene Epoch and Selandian and Thanetian GSSPs at Zumaia (Basque Basin, W Pyrenees)

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Earth and Planetary Science Letters 262 (2007) 450 – 467 www.elsevier.com/locate/epsl

Closing the Mid-Palaeocene gap: Toward a complete astronomically tuned Palaeocene Epoch and Selandian and Thanetian GSSPs at Zumaia (Basque Basin, W Pyrenees) Jaume Dinarès-Turell a,⁎, Juan Ignacio Baceta b , Gilen Bernaola b , Xabier Orue-Etxebarria b , Victoriano Pujalte b a

b

Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 Rome, Italy Departamento de Estratigrafía y Paleontología, Facultad de Ciencia y Tecnologia, Basque Country University, Ap. 644, E-48080 Bilbao, Spain Received 24 April 2007; received in revised form 30 July 2007; accepted 3 August 2007 Available online 23 August 2007 Editor: M.L. Delaney

Abstract An integrated magneto-, bio- and cyclostratigraphic framework is presented for the Mid-Palaeocene interval from the (hemi) pelagic sea-cliff section of Zumaia in the Basque basin. The new ∼ 55 m long studied section expands about 3.5 Myr and closes the gap between previously published integrated studies in the section. The occurrence of magnetochron C26n is now documented, and its duration (complemented also by data from the Ibaeta section), and that for chrons C26r and C25r is estimated by counting precession related lithologic couplets assigned to have 21-kyr duration (C25r = ∼ 1449 kyr, C26n = ∼ 231 kyr, C26r = ∼ 2877 kyr). Consequently, the Zumaia section now provides the first complete Palaeocene astronomically derived chronology, rendering this section a master reference section. Due to limitations in the orbital calculations and uncertainties in the radiometric dating method no robust tuning and absolute ages can be given for the moment. However, the FOs (First Occurrences) of key calcareous plankton species and the Mid Palaeocene Biotic Event (MPBE) are placed within the magnetostratigraphic and cyclostratigraphic template along the studied Mid-Palaeocene interval. In addition, the dataset provides the key elements for a proper settling of the Thanetian and Selandian Global Stratotype Section and Point (GSSPs), which is one of the primary objectives of the ICS (International Commission of Stratigraphy). We consider the base of chron C26n and the criteria associated to the lithostratigraphic change between the Danian Limestone Fm and the Itzurun marl Fm at Zumaia, as the respective delimiting points for the Thanetian and Selandian bases as recently agreed by the Paleocene Working Group of the International Subcommission of the Paleogene Stratigraphy of the ICS. Consequently, the duration of the Thanetian, Selandian and Danian component stages can be estimated at Zumaia to be about ∼ 3129 kyr, ∼ 2163 kyr and ∼ 4324 kyr respectively (see text for error considerations). However, the MPBE located 8 precession cycles below the base of C26n in correspondence to a short eccentricity maxima at Zumaia, could also serve as a guiding criteria to approximate or redefine the Thanetian base if this level demonstrated synchronous. © 2007 Elsevier B.V. All rights reserved. Keywords: Astronomical Polarity Time Scale; cyclostratigraphy; chronostratigraphy; stratotype

⁎ Corresponding author. Tel.: +39 06 51860387; fax: +39 06 51860397. E-mail address: [email protected] (J. Dinarès-Turell). 0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2007.08.008

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1. Introduction

2. Geological setting and studied sections

A robust Astronomical Polarity Time Scale (APTS) is being built during the last two decades starting at the young end of the time scale and then moving progressively deeper in time. A recent achievement on this effort has been the completion of an astronomical time scale for the Neogene, cumulating in the “Astronomically Tuned Neogene Time Scale” (ATNTS2004) (Lourens et al., 2004). Tuning the Palaeogene becomes more challenging despite new full numerical solutions for the Solar System (Varadi et al., 2003; Laskar et al., 2004) due to uncertainties and limitations inherent to the chaotic behaviour of the Solar System and poor radiometric age control in the Palaeocene (see below). The aim of this paper is twofold. In the first place, to complete (and expand) the APTS for the Palaeocene, by completing previous studies carried out at the Zumaia section (Basque basin, northern Spain). Here, we present integrated magnetostratigraphy and calcareous plankton biostratigraphy (planktonic foraminifera and calcareous nannofossils) for the ∼ 4.8 Myr midPalaeocene interval at Zumaia (from chron C27n to chron C25n) and evaluate the lithologic cyclicity in terms of cycle counting. The Zumaia section is one of the most expanded land-based deep-water marine section so far reported for the latest Cretaceous–early Eocene interval, and had earlier been the subject of detailed integrated cyclo- and biomagnetostratigraphic studies in its lower and upper parts (Ten Kate and Sprenger, 1993; Baceta et al., 2000; Dinarès-Turell et al., 2002, 2003). Thus, by closing the intervening gap a complete astronomically calibrated Palaeocene scale is been made available. On the other hand, Zumaia has been the leading candidate to place the Selandian and Thanetian Global Standard Stratotype-section and Points (GSSPs) (http:// www.stratigraphy.org/), both of which have been recently agreed by unanimity in a meeting of the Paleocene Working Group of the International Subcommission of the Paleogene Stratigraphy of the ICS (Zumaia, June 2007) to be selected within the gap here considered (see below). Consequently, the second objective of this paper is to substantiate and provide a sound biomagneto- and cyclostratigraphy of the interval. In addition, constraints and uncertainties to the age of the Palaeocene/Eocene (P/E) and Cretaceous/Palaeogene (K/Pg) boundaries and timing of Palaeocene magnetic chrons and intervening biostratigraphic and climatic events in the light of current astronomical solutions are assessed.

Two sections have been examined for this study, Zumaia and Ibaeta. The sediments from these sections accumulated in an offshore basin called the Basque Basin at an estimated water-depth of about 1000 m (Pujalte et al., 1995, 1998). The Zumaia section (latitude/ longitude 43°17.98′N/2°15.63′W) is a sea-cliff section outcropping at the Itzurun beach, in the Gipuzkoa province of northern Spain (Fig. 1). The bulk of the Palaeocene is represented by rhythmic alternations of hemipelagic limestones and marlstones, plus numerous intercalations of thin-bedded turbidites (Baceta et al., 2000). The mid-Palaeocene studied succession at the Itzurun beach above the top of the Danian Limestone Fm is about 55 m thick and occurs dipping 40–60° to the NNE. The outcrops have a similar orientation and thus offer a continuous dip section, only interrupted by the presence of three fault systems (F1 to F3 on Fig. 1). These are normal faults with associated joints and small synthetic and antithetic faults. Faults F1 and F2 have duplicated significant intervals of the succession. A careful correlation of distinctive beds in the hangingwalls and footwalls of the fault systems has allowed a detailed reconstruction of the stratigraphy of the midPalaeocene succession and its more representative intervals (Fig. 1). Fault F3 is sub-parallel to bedding and is apparently not additive. Stratigraphically, the midPalaeocene comprises the upper part of the Danian Limestone (Apellaniz et al., 1983) and the lower-middle parts of the Itzurun Fm (Baceta et al., 2004). The two units are mainly made up of regular alternations of (hemi)pelagic indurated limestones, marlstones and marls. In the Danian Limestone the indurated limestones are dominant, whereas in the Itzurun Fm the proportions of the three lithologies vary considerably. Additionally, they also include minor but significant amounts of thinbedded turbidites, of siliciclastic, calcareous and mixed nature. The lower part of the Itzurun Fm has been divided in two informal members (members A and B) (Figs. 1 and 5). The member A is largely dominated by marly lithologies, whereas the member B includes significant proportions of indurated limestones. However, the base of the formation is defined by a 5.5 m thick interval of marls and marlstones of a characteristic red colour (the red marl) (Figs. 1 and 5). In contrast to the Danian Limestone, largely of pink-reddish colours, dark to light grey colours dominate across the Itzurun Fm. The transition between the Danian Limestone and Itzurun formations is marked by an abrupt lithologic change from limestone- to marl-dominated that creates a distinct retreat of the cliff face (Fig. 1). This lithologic change is

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Fig. 1. (A) Generalised early Palaeogene palaeogeography of Western Europe; (B) Syntetic sketch of the Mid-Palaeocene outcrops in the Itzurun beach, showing the distribution of the main lithological units/members and the three fault systems that disrupt the succession; (C) Synthetic lithologic section of the uppermost Cretaceous–Lower Palaeogene interval of the Zumaia section showing four main stratigraphic units: unit I, Upper member of the Zumaia–Algorri Fm; unit II, Danian Limestone Fm (Apellaniz et al., 1983); unit III, Itzurun Fm (Baceta et al., 2004); unit IV, unnamed unit above the Carbon Isotopic Excursion (CIE) that marks the Palaeocene/Eocene boundary . Published magnetostratigraphies from the Zumaia section and the Mid-Palaeocene interval reported herein are indicated; (D) Panoramic view of the documented Itzurun section in this work above the Danian limestone formation (note the red marl unit and the circled person for scale). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

interpreted as the expression of the prominent episode of sea level fall that characterised the end of the Danian across the whole Pyrenean Domain (Baceta et al., 2004, 2005). The Ibaeta section (latitude/longitude 43°18.23′N/ 2°00.72′W), is devoid of turbidites and therefore the hemi(pelagic) cyclicity is more obvious (supplementary online Fig. S1). This section is partially outcropped, and only about 18 m thick succession is accessible. Fortunately, the outcropped interval contained chron C26n, and thus has been very useful to check the

reliability of the magnetostratigraphic results obtained at Zumaia (see below). 3. Palaeomagnetic results and cycle counting In order to locate chron C26n a total of 101 samples from different stratigraphic levels were collected using a gasoline-powered drill or as oriented hand-samples along the mid-Palaeocene interval above the top of the Danian Limestone Fm from Zumaia. This study extends upwards the integrated magnetostratigraphy presented

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by Dinarès-Turell et al. (2003) and jointly with the uppermost Palaeocene magnetostratigraphy from Dinarès-Turell et al. (2002) represents the completion of the entire Palaeocene Epoch interval (see Fig. 1), for which now all magnetic reversals are documented at a marl-limestone couplet level. In order to increase the reliability of chron C26n position and its cycle duration along the magnetically weak (see below) mid-Palaeocene interval at Zumaia, 23 levels were sampled at Ibaeta. Natural remanent magnetisation (NRM) and remanence through all demagnetisation stages were measured using a 2G-Enterprises high-resolution (45 mm diameter) pass-through cryogenic magnetometer equipped with DC-squids and operating in a shielded room at the Istituto Nazionale di Geofisica e Vulcanologia in Rome, Italy. Alternating field (AF) demagnetisation was performed with three orthogonal coils installed inline with the cryogenic magnetometer. Orthogonal vector demagnetisation plots (Zijderveld, 1967) were used to represent demagnetisation data and a

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least-squares line-fitting procedure (Kirschvink, 1980) was used to determine the magnetisation components. One or two specimens per stratigraphic level (165 and 35 specimens from Zumaia and Ibaeta, respectively) were routinely subjected to stepwise alternating field (AF) demagnetisation, up to 100 mT, including 14 steps with intervals of 5, 10 and 20 mT. Thermal demagnetisation up to 150 °C was sometimes applied prior to AF demagnetisation. In general, the intensity of the NRM was relatively low, around 4 × 10− 4 A/m although it was lower for some of the carbonate-rich beds. Two magnetisation components can be recognised in most samples upon demagnetisation, in addition to a viscous magnetisation removed below 5 mT or 100°–150 °C (Fig. 2). Component L is unblocked usually below 25 mT and conforms to the present magnetic field (Fig. 2). Component H is unblocked above 25 mT, conforms the characteristic remanent magnetisation (ChRM) and has either normal or reverse polarity in bedding-corrected

Fig. 2. Bedding-corrected orthogonal plots of alternating field demagnetisation data from representative specimens from the Zumaia–Itzurun (IZ) and Ibaeta (IB) sections. Solid (open) symbols represent projections onto the horizontal (vertical) plane. The fitted characteristic remanent magnetisation (ChRM) direction, the natural remanent magnetisation (NRM) intensity, the stratigraphic level in meters, and some step treatments are indicated for each example. Sample IZ51-1b includes a thermal step before AF demagnetisation.

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coordinates (Fig. 2). Magnetic behaviour upon demagnetisation was similar to the one documented for the uppermost Palaeocene samples (Dinarès-Turell et al., 2002). Before bedding-correction, component H has a steep inclination not compatible with a Palaeocene to recent geomagnetic field direction, whereas the mean ChRM inclination after bedding correction is near the expected Palaeocene inclination for the site palaeolatitude (Fig. 3) indicating a primary origin. Some isolated samples displayed a more complex behaviour where a third unresolved component seems to exist above about

80 mT in addition to a reverse H component (Fig. 2B). It is difficult to asses the reliability and significance of this component that could represent a spurious behaviour due to the low intensity of the samples, a diagenetic overprint or even the signature of tinny-wiggles within chron C26r. We have preferred to take the reverse H component unblocked above 25 mT as the primary ChRM component. The declination and inclination of the ChRM components have been used to derive the relative latitude of the virtual geomagnetic pole (VGP) for each sample by equating the pole position derived from the mean

Fig. 3. (A) Equal area projections of the ChRM directions before and after bedding correction for the Zumaia–Itzurun section. The 95% confidence ellipse for the normal and reverse mean directions is indicated. Statistical information is given (N, number of samples; Dec., declination; Inc., inclination; k, Fisher's precision parameter; α95, radius of the 95% confidence cone). (B) Same as (A) for the Ibaeta section.

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direction of each section with the Earth's rotation axis (calculating the angles between the individual VGPs and the mean palaeomagnetic pole of the section) (e.g., Lowrie et al., 1980). The VGP latitude as indicative of magnetic polarity together with the lithologic log for both the Zumaia and Ibaeta sections is shown in Fig. 4 (see supplementary online Fig. S2 for original declination/inclination data). Considering the possibility that a delayed magnetic acquisition process may occur (see Dinarès-Turell et al., 2002), we have taken the youngest evidence for a reverse or normal polarity to delineate respectively the base and the top of the normal chron

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comprising eccentricity bundles E67 and E68 (Fig. 4). It is interesting to note that the mean post-tilt inclination for the reverse samples (Inc = − 44.0°) (Fig. 4), is about 10 degrees shallower than the mean inclination calculated for the underlying Danian limestone Fm reported in Dinarès-Turell et al. (2003) (Inc = − 54.9°). This may be accounted by the relative marly nature of the MidPalaeocene interval, which is probably more affected by a remanence compacting effect. The same observation is precluded for the normal mean inclination due to an overlapped intermediate (I) component for the Danian Limestone Fm dataset as discussed in Dinarès-Turell

Fig. 4. Computed virtual geomagnetic pole (VGP) latitudes and lithologic logs for the Zumaia–Itzurun and Ibaeta sections. Open circles denote unreliable data and crosses mark the position of samples that have provided no data. The position of chron C26n and correlation between both sections is shown. MPBE denotes the Mid Palaeocene Biotic Event (Bernaola et al., 2006, 2007) and dashed lines correlate some distinct relatively thick and carbonatic beds. Numbering of the eccentricity (∼ 110 kyr) related E-cycles follows numbering for underlying strata that starts above the K/P boundary as reported by Dinarès-Turell et al. (2003). Numbering of the carbonate layers from the basic couplets or precession P-cycles arbitrarily starts at the MPBE event (see text for discussion).

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et al. (2003). Following the underlying magnetostratigraphy from Zumaia (Dinarès-Turell et al., 2003) and all biostratigraphic constraints (see below) this chron is unambiguously correlated to C26n. The bed-to-bed correlation between Zumaia and Ibaeta is consistent in terms of lithologic features (apparent carbonate content and couplet thickness) and the position of chron boundaries despite C26n contains two reverse samples of uncertain significance at Ibaeta. Note for instance the thick and apparent carbonate-rich cycles P6–P7, P11–P12 and P19–P20 or the thinner and less pronounced marly interval between cycles P14–P15 in both sections, which are distinct of the centre of eccentricity E-cycles (eccentricity minima) (Fig. 4 and supplementary online Fig. S1). The cycle identification at Ibaeta is more straightforward and facilitated by the lack of turbidite levels with respect to Zumaia where, for instance, identification of cycles P14 and P15 straddled by thin turbidites could be less obvious. These conspicuous lithologic features together with the magnetostratigraphic data make the correlation between both sections very robust. The identification of the (∼ 110 kyr) short eccentricity related bundles (E-cycles) for the mid-Palaeocene interval from Zumaia is shown in Fig. 5 (see also supplementary online Fig. S3 for an extended version). The astronomical origin of these lithological cycles has previously been demonstrated (Ten Kate and Sprenger, 1993; Dinarès-Turell et al., 2002, 2003). Note that the E-cycles contain about 4–6 basic couplets (precession cycles) and that the carbonate beds of the central couplets of the E-cycles are comparatively thick and carbonaterich (Figs. 4 and 5). Numbering of the E-cycles follows that of the underlying strata as reported in Dinarès-Turell et al. (2003). The carbonate layer of P-cycle − 130 in E-cycle 36 (supplementary online Fig. S3), corresponds to bed-layer 161 from Dinarès-Turell et al. (2003). The cycle duration of chron C26r and C26n and relative positioning of the Mid-Palaeocene Biotic Event (MPBE) and biostratigraphic events (see below) can be established (Fig. 4 and supplementary online Fig. S3). Cycle counting for chron C26r provides about 30 ∼110 kyr eccentricity E-cycles or 137 precession (∼21 kyr) P-cycles. At the Zumaia–Itzurun section, chron C26n contains 10 precession cycles (cycles P9 to P18 both inclusive). However, at the Ibaeta section (Fig. 4 and supplementary online Fig. S1), precession cycle P19 provides normal polarity, suggesting that the reverse data from the same cycle at Zumaia may represent a delayed magnetisation (Fig. 4). Cycle P20 at Ibaeta does not provide reliable data but we take the reverse data from the same cycle at Zumaia as primary. Therefore, considering both sections we estimate

C26n to contain 11 precession cycles. Cycle definition for the interval above E-cycle 74 up to the base of chron C25n is difficult due to the presence of numerous turbidite levels that mask the (hemi)pelagic cyclicity. Nevertheless, a tentative cycle counting for chron C25r determines 69 precession cycles or about 13 E-cycles for this chron (supplementary online Fig. S2). The MPBE is located ∼8 precession cycles below the base of chron C26n in correspondence to an eccentricity maxima if the phasing between the lithologic cycles and the orbital parameters hypothesized in Dinarès-Turell et al. (2003) for the lower Palaeocene is correct (i.e. eccentricity minima corresponds to relative high carbonate content). We do not elaborate on a precise tuning in this paper and restrict our analysis to duration estimates by cycle counting and assess the chronostratigraphic implications in the light of published astronomically tuned chronologies and available orbital solutions (see below). Table 1 provides duration estimates for Palaeocene magnetic chrons as established by cycle counting at Zumaia and elsewhere compared to the CK95 (Cande and Kent, 1995) and GTS2004 (Gradstein et al., 2004) time scales. Other cycle counting estimates for some Ocean Drilling Program (ODP) Hole sediments (Cramer, 2001; Cramer et al., 2003) are not considered because they only cover the upper Palaeocene (chrons C25n and C24r) and where already discussed and superseded by data in Westerhold et al. (2007). Likewise, cycle counting estimates from the Bjala section from Bulgaria (Preissinger et al., 2002) are omitted because data was not adequately reported and most likely need some revision (Dinarès-Turell et al., 2006). We emphasize that our cycle counting provides minimum estimates for the duration of intervening intervals as the identification of the more stable 404-kyr eccentricity cycle is not obvious at present suggesting perhaps that some “missing” beats could be present at Zumaia. As an alternative, we argued (Dinarès-Turell et al., 2003) that a sea-level signal (tectonically driven?) could be superimposed on the climatic forcing at the Milankovitch band masking the full expression of the low-frequency astronomical periods. 4. Calcareous plankton biostratigraphy 4.1. Calcareous nannofossils Ninety-three samples were processed for calcareous nannofossil determinations from the new studied interval (Fig. 5). From each sample a smear slide was prepared following the standard method of sample preparations and then analyzed using a light microscope at 1500X magnification. The calcareous nannofossil assemblages recorded in the mid-Palaeocene of Zumaia section are

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Fig. 5. Integrated lithostratigraphy, biostratigraphy and magnetostratigraphy of the Mid-Palaeocene of the Zumaia section. (A) main calcareous plankton bioevents, (B) magnetic polarity stratigraphy (Dinarès-Turell et al. (2003) and this study), (C) planktonic foraminifera biozonation (OrueEtxebarria et al. (2006) and this study), (D) biozonation of Berggren et al. (1995), (E) calcareous nannofossil biozonation of Bernaola (2002) according to Martini (1971). Biostratigraphic events represent first occurrences (FOs), otherwise they are indicated as first common occurrences (FCOs), first rare occurrence (FROs) or last common occurrences (LCOs).

well preserved, quantitatively rich and very diverse (Bernaola, in press). Following the standard biostratigraphic zonation of Martini (1971) the interval studied spans from the upper part of Zone NP4 to Zone NP8 (Fig. 5). Throughout the last 15 m of the Danian

Limestone Fm the assemblage is dominated by Coccolithus pelagicus, Prinsius martinii and Braarudosphaera bigelowii that together with Sphenolithus primus, Ericsonia spp., Prinsius bisulcus and Toweius pertusus constitute the major components. In the uppermost

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Table 1 Estimates for the duration of Palaeocene magnetic chrons based on cycle counting Chron

CK95

GTS04

ODP Holes 1001A, 1050C

ODP Hole 1051

(Röhl et al., 2001)

C24r_Pal C25n C25r C25 C26n C26r C26 C27n C27r C27 C28n C28r C28 C29n C29r_Pal

Zumaia

(Röhl et al., 2003)

This study

Duration Duration Cycles (kyr) (kyr)

Duration (kyr)

Cycles

Duration (kyr)

Cycles

Durationa (kyr)

ΔCK95 ΔGTS04 (kyr) (kyr)

904 467 1163 1630 357 3009 3366 356 1223 1579 1135 342 1477 769 245

924–966 481–523 – – – – – 444–525 929–1010 ~ 1450 – – 1280b 670 300

45 (53)d 25 (23)d 51 – – – 88 obliq. – – – – – – – –

945 (1113)d 525 (483)d 1066 – – – 3608 – – – – – – – –

47 21–23 69 91 11 137 148 11 50 61 49 12–13 61–62 38–39 12

987 462–483 1449 1911 231 2877 3108 231 1050 1281 1029 252–273 1281–1302 796–819 252

83 5 266 281 − 126 − 132 − 258 − 125 − 173 − 298 − 106 − 79 –185 38 7

865 515 1199 1960 359 2913 3272 333 1121 1480 1024 304 1280 685 300

44–46 23–25 – – – – – 11–13 obliq. 23–25 obliq. 36 obliq.c – – – ∼ 32 ∼ 14

a

a

122 − 42 250 − 49 − 128 − 36 − 164 − 102 − 71 − 199 5 − 41 11 122 − 48

Cycles refer to precession otherwise is specified. Applying a modern mean precession and obliquity periods of 21 kyr and 40.4 kyr respectively. b) Estimated assuming an intermediate spreading rate (16.7 km Ma− 1) for C28 (interpolated from the South Atlantic magnetic anomaly profile. c) Cycle counting in Hole 1001A indicates 47 precession cycles + 11 obliquity (obliq.) cycles for C27. d) Number of cycles and duration in parenthesis are from multiple holes (1051, 1262 and 1267) as estimated by Westerhold et al. (2007). a)

Danian, upper part of Zone NP4, the calcareous nannofossil diversity is relatively high (S-H 2,1 and 26-31 species per sample), especially if we compare it with that registered in the lower Danian (Bernaola, 2002). The calcareous nannofossil assemblage does not show significant changes throughout most of the upper Danian Limestone Fm. However, a few metres below the top of the unit a decrease in the relative abundance of B. bigelowii and S. primus and a relative abundance increase of T. pertusus are registered. In the upper 15 m of the Danian Limestone Fm several calcareous nannofossil bioevents have been recorded, the following four deserving special mention: FRO (first rare occurrence) of S. primus, first radiation of the genus Fasciculithus, FCO (first common occurrence) of S. primus and FRO of Neochiastozygus perfectus (Fig. 5). The most important calcareous nannofossil assemblage turnover across the entire mid-Palaeocene at Zumaia occurs in connection with the lithologic change from the Danian Limestone Fm to the overlying Itzurun Fm. Such turnover is recorded by a significant increase in the total abundance of calcareous nannofossils and, by a concomitant abrupt decrease in the relative and total abundance of B. bigelowii, which is abundant in the uppermost Danian Limestone (up to 22%) and becomes very rare in the Itzurun Fm (Fig. 5). The onset of a second diversification of the genera Fascicu-

lithus occurs at the same levels, represented by FOs of Fasciculithus janni and Fasciculithus ulii (Bernaola, in press). In the red marl interval of the lowermost part of the Itzurun Fm (Fig. 5), the calcareous nannofossil assemblage is dominated by the same species that prevail in the Danian Limestone, with the exception of B. bigelowii. In this interval, besides the FOs of the above-mentioned fasciculithus, we also observe the FOs of Chiasmolithus consuetus, Fasciculithus billii and Fasciculithus tympaniformis. Close to the boundary between the red marl and the overlying grey marly beds, we observe a slight total abundance decrease in calcareous nannofossil but no other significant change, with the exception of the FOs of Fasciculithus pileatus and Toweius tovae. The calcareous nannofossil assemblage across the grey marlstones (member A) of the Itzurun Fm is similar to that found in the underlying red marl and is mainly dominated by C. pelagicus, P. martinii, P. bisulcus and T. pertusus. The most important change in calcareous nannofossil assemblages across the A and B members of the Itzurun Fm is the occurrence and diversification of the genus Heliolithus and the first occurrence of the specimens of the genus Discoaster, one of the most important calcareous nannofossil group throughout the whole Palaeogene. Across the upper A and the B members of the Itzurun Fm the FOs of Coronocyclus nitescens, Zygodiscus

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bramlettei, Toweius eminens, Heliolithus cantabriae, Sphenolithus anarrhopus, Heliolithus kleinpellii, Bomolithus conicus and Discoaster bramlettei, among others are also recorded (Bernaola et al., 2006). 4.2. Planktic foraminifera All the samples analysed for calcareous nannofossils were processed also for planktic foraminifers. They were washed and screened to obtain residues of a 100–500 μm size range. All these residues contained planktic foraminifer in sufficient quantity and degree of preservation to permit a detailed biostratigraphic study. The high abundance and species richness of planktic foraminifera found in all the mid-Palaeocene samples together with the expanded character of the Zumaia section, have allowed fixing the position of FOs of selected biohorizons with a higher resolution that was hitherto possible. This has led to the establishment of a refined planktic foraminiferal biozonation of the interval (Orue-Etxebarria et al., 2006, Fig. 5 and Appendix A) with respect to other zonation schemes elsewhere (Berggren et al., 1995, 2000; Berggren and Pearson, 2005). Five biozones based on the FOs of selected species have been differentiated in the studied succession (Fig. 5). In general, the planktic foraminifera total abundance and species richness, particularly those of morozovellids and igorinids, increase progressively from the upper part of the Danian Limestone to the top of the studied succession, in agreement with the ideas of Norris (1997) and Olsson et al. (1999). The first species of the velascoensis group (Morozovella velascoensis, M. occlusa, etc.) are recorded about 7 m below the top of the Danian Limestone Fm (Fig. 5) towards the base of chron C26r. The rest of the assemblage species is similar to that found in the I. pusilla biozone (=P3a of Berggren et al., 1995). No significant change in the planktic foraminifera composition is observed at the beginning of the red marl interval above the Danian Limestone Fm. However, it is interesting to note the change of coiling in the M. occlusa and M. velascoensis forms at ∼10 m from the base of the marly unit towards the middle part of C26r, that passes from random to a predominant dextral coiling (80% of the tests). Further up, the FOs of Igorina albeari and Globanomalina pseudomenardii are located about 10 m and 16 m above the top of the Danian limestones respectively. At the beginning of the G. pseudomenardii biozone there is a new increase in the planktic foraminifer diversity, especially in acarininids and globanomalinids. On the other hand, the ratio of planktic foraminifera to the total foraminifera content increases from 0.8 in the lower part of the succession to 0.9 in the G. pseudomenardii biozone.

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5. The Mid-Palaeocene biotic event (MPBE) Recent studies at Shatsky Rise (ODP Leg 198, Central Pacific) and Walvis Ridge (ODP Leg 208, SE Atlantic) have confirmed the existence of several dissolution levels in deep-sea carbonates of the late Palaeocene-early Eocene (ELMO; X-event layer; MidPalaeocene Biotic Event layer, MPBE) (Bralower et al., 2002; Zachos et al., 2004; Lourens et al., 2005). Similarly to the Palaeocene–Eocene Thermal Maximum (PETM) interval, these levels are characterized by the presence of a clay-rich layer, associated with an abrupt drop in carbonate content, and a pronounced peak in magnetic susceptibility (MS) that reflects an increase in clay content. All these dissolution intervals have been interpreted as the sedimentary response to abrupt warming climatic changes (hyperthermal events). The MPBE, the oldest of these events, has been identified in the studied interval at the Zumaia and the Ibaeta sections. The MPBE is recorded in both cases by a 1 m thick clay-rich interval characterized by a drop in carbonate content, a peak in MS and important calcareous nannofossil and foraminifer assemblage changes (Bernaola et al., 2006, 2007) (Figs. 4 and 5). It is located ∼ 4.5 m above the FO of H. kleinpellii, the marker of the base of Zone NP6, ∼ 2 m below the C26r/C26n reversal and within the lower part of Zone P4 of planktic foraminifera. These data indicate that the event is coeval to that identified in boreholes at Shatsky Rise and Walvis Ridge (Bralower et al., 2002; Zachos et al., 2004; Petrizzo, 2005) and points to the global character of the MPBE. The Zumaia section is the first land-based locality in which the MPBE has been recognized and described in detail. The MPBE is characterized by several important changes in the micropalaeontological record. Changes in calcareous nanoplankton assemblages mainly consist of a replacement of R-mode specialists by warmer more oligotrophic taxa, suggesting a shift from relatively cooler mesotrophic to warmer oligotrophic conditions during the event. Planktic foraminiferal assemblages were more severely affected during the MPBE, as is evidenced by a sharp drop in their total abundance and species richness. In addition, test-size minima would indicate a clear disruption of the photic zone, with most planktic foraminiferal species living outside their ecological optima. Benthic foraminifers were also significantly affected during the MPBE, as recorded by the drop in relative abundance of laevidentalinids and buliminids, and the increase of deep-water and opportunistic species. These changes suggest oligotrophic and unstable conditions at the sea floor during the MPBE.

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The reorganization of planktic ecosystems may have affected both surface productivity and the transfer of organic matter from the surface to the seafloor, thus triggering changes in the benthic communities. The core of the biotic event coincides with a negative excursion of δ13C that, as in the PETM of this section and elsewhere, may be interpreted as an input of a large mass of isotopically depleted carbon into the ocean and atmosphere. The CO2 input lowered deep-sea pH, triggering a rapid shoaling of the lysocline and contributing to a greenhouse warming. Further details about the changes that took place in the calcareous plankton and benthos at the time of the MPBE and their palaeoceanographic significance are given in Bernaola et al. (2006, 2007). 6. Discussion 6.1. Palaeocene chronostratigraphy and astronomical solutions The ∼10 Myr long Palaeocene Epoch is bracketed by two of the most dramatic and best studied chronostratigraphic limits, the K/Pg boundary at its base and the P/E boundary at the top. During the last two decades, the Palaeocene time scale has relied on an age model for magnetic polarity chrons derived from a cubic-spline fit of marine magnetic anomaly pattern in the South Atlantic to two radiometrically dated calibration points (Cande and Kent, 1992, 1995). These include an age of 65 Ma for the K/Pg boundary (66 Ma in the CK92 time scale) and a derived age of 55 Ma for the P/E boundary (this age constrained from 40Ar/39Ar dated volcanic ash layers within a clay sequence in Denmark occurring halfway in chron C24r in the Eocene). This magnetic time scale was then extrapolated to several biostratigraphic zonation schemes (Berggren et al., 1995; Berggren and Pearson, 2005). An age of 65.5 ± 0.3 Ma for the K/Pg and 55.8 ± 0.2 Ma for the P/E are retained in the most recent geological time scale GTS2004 (Gradstein et al., 2004) which paradoxically combines both isotopically (using a 28.02 Ma age for the Fish Canyon Sanidine FCT monitor standard) and astronomically derived ages in the Neogene. However, it is known the lack of synchronicity between both dating methods (e.g. Kuiper et al., 2005), as intercalibration of single crystal sanidine dates of primary ash layers in astronomically dated sections arrives at an astronomically calibrated age of 28.24 ± 0.1 Ma for the FCT standard (Hilgen et al., 2006a). This will suggest an ∼1% underestimate in current Palaeogene ages. Therefore, the astronomically tuned chronology for the (hemi)-pelagic basal Palaeocene succession at Zumaia (Dinarès-Turell et al., 2003)

that arrives at an estimated age of ∼ 65.8 Ma for the K/Pg would appear consistent. In that study we presented an ∼ 4 Myr long tuned chronology based on the R7 full numerical solution for the Solar System of Varadi et al. (2003). However, more recently, a second full numerical solution has been also put forward (La04, Laskar et al., 2004), which differs notably in the Palaeocene with respect to R7 (offsets between the ∼ 2.25 Myr long-term cycles) (Fig. 6). The differences arise from the uncertainty due to the chaotic behaviour of the inner planets to some resonant argument that limits an accurate age determination of successive minima in this very long eccentricity cycle. It is interesting to note, however, that in the Palaeocene both solutions share one of such nodes of reduced eccentricity amplitude at about 62.2 Ma (Fig. 6), which was the feature used as starting point in our tuning at Zumaia (Dinarès-Turell et al., 2003). Recent tuning efforts of hyperthermal events within the lower Cenozoic greenhouse climate record documented in ODP Leg 208 core sediments (Lourens et al., 2005) have provided tuned ages for the P/E thermal maximum (PETM) using both the La04 and R7 astronomical target solutions (∼ 55.270 Ma and ∼55.675 Ma respectively) and Elmo event (Fig. 6). It was shown that hyperthermal events correspond to maxima in the ∼ 405kyr and ∼ 100-kyr eccentricity cycles that postdate prolonged minima in the 2.25-Myr eccentricity cycle. However, this tuning has recently been revised in the light of high-resolution X-ray fluorescence (XRF) measurements on the same ODP Leg 208 sediments by Westerhold et al. (2007), who also reassessed previous data from ODP Site 1051 (Röhl et al., 2003; Cramer et al., 2003). Different cycle recognition with respect to previous estimates from Leg 208 (Lourens et al., 2005), indicates a shorter duration between the PETM and the Eocene thermal maximum (ETM2) or Elmo event (∼1.827 Myr rather than ∼ 2 Myr). Two possible tuning options are provided in Westerhold et al. (2007), which bring the age of the PETM to 55.53 ± 0.2 Ma and 55.93 ± 0.2 Ma respectively. These two alternative tuning options are independent of the used astronomical target but derive after tuning to successive 405-kyr eccentricity cycles. 6.2. Astronomically calibrated magnetostratigraphy at Zumaia Two alternative magnetic polarity chronologies derived from astronomical tuning for ODP Leg 208 (Westerhold et al., 2007) and the astronomically calibrated magnetostratigraphy from Zumaia illustrate the actual inconsistencies and difficulties to achieve an

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Fig. 6. (A) Filter outputs for the Laskar et al. (2004) (La04) eccentricity orbital solution. The ∼ 100 kyr, the 404-kyr and the ∼ 2.3-Myr cycles of eccentricity were extracted using a gaussian filter with a frequency of 0.0095 ± 0.002 (kyr− 1), 0.00247 ± 0.0001 (kyr− 1) and of 0.00043 ± 0.0001 (kyr− 1), respectively. The lower panel is the eccentricity local wavelet power spectrum using a Morlet wavelet and the eccentricity period bands are indicated to the right. The spectrum was computed for the interval 50–70 Ma so no substantial edge effects occur for the plotted data (see Torrence and Compo, 1998). (B) Same as (a) for the R7 orbital solution of Varadi et al. (2003). Black and shaded boxes mark the nodes of low eccentricity amplitude (∼ 2.3 Myr modulation) for each orbital solution (note the common node at about 62.2 Ma). The position of the Elmo and PETM climatic events indicated on each orbital solution follows the astronomical tuning of Lourens et al. (2005).

unambiguous and consistent astronomical tuning. The latter builds up from the tuning for the Danian part (chron C29r to C27n) (Dinarès-Turell et al., 2003) and the cycle duration estimates for chrons C26r, C26n and C25r in this paper, together with estimates for C25n and the Palaeocene part of C24r (Dinarès-Turell et al., 2002) (see Table 1). Note that the construction of the absolute chronology from Zumaia is intended provisional and used just for comparison. It has been build by assigning and age of 62.26 Ma to the top of chron C27n, which is about 1.5 precession cycles above cycle P-131 (see

supplementary online Fig. S2) that was tuned to the eccentricity minima at 62.29 Ma in either of the R7 or the La04 orbital solutions (Dinarès-Turell et al., 2003), and then adding the average duration estimate for every chron (Table 1) (note that no error estimates are provided for the sake of simplicity although these can be generalized to be about 1–2 precession cycles). It is obvious that the entire Palaeocene chronology from Zumaia is shifted to older ages with respect to the CK95 standard GPTS and that it clashes with either of the tunings proposed from ODP Leg 208 sediments which

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virtually imply younger ages. For instance, the PETM onset at Zumaia can be estimated at ∼ 56.26 Ma, about 330 kyr or 930 kyr older with respect to the alternative tunings from Leg 208 (Fig. 7). However, if we take the robust estimate (53 precession cycles or 1113 kyr) for the duration of the Palaeocene part of chron C24 (Westerhold et al., 2007) instead of the estimate from Zumaia (see Table 1), then the age of the PETM onset at Zumaia will be ∼ 56.14 Ma (Fig. 7). This latter estimate is only about two short 110-kyr eccentricity cycles apart from the oldest estimate from Westerhold et al. (2007) (55.93 ± 0.02 Ma). Given that the cycle identification in the upper part of C26r is somewhat ambiguous at Zumaia, it could be possible that the duration of this chron is underestimated and, therefore, compatibility between tuning at Zumaia and ODP Leg 208 could be envisaged. However, as a general observation, there can be three main explanations for discrepancies in the attained tuned chronologies (or a combination of them): a) mistakes in the criteria and assumptions in the tuning procedures, b) inadequacy of the actual orbital solutions, c) incompleteness of the sedimentary records or uncertain identification of cycles. It is known the lack of precision of the La04 and R7 computations beyond

45 Ma despite they represent full numerical orbital solutions (Laskar et al., 2004). However, the very stable 400-kyr component in eccentricity can be used as prime target (Laskar, 1999; Kent, 1999; Hilgen et al., 2006a; Westerhold et al., 2007). For the Palaeocene, in addition to the intrinsic limitations of the orbital computations the absolute chronology is hampered by sparse age calibrated points and remaining discrepancies of astronomical and radio-isotopic ages (see above). Clearly, data from different basins and oceans, outcropping on land and/or from the deep-sea, and supported directly or indirectly by precise radiometric dating are urgently needed to expand the present APTS and consolidate a Palaeocene astronomical chronology. This should lead to a new generation of geological time scales at unprecedented resolution beyond the Neogene (Hilgen et al., 2006b), eventually providing constraints for the astronomical computations and, in turn, granting new insight to some crucial information to the Earth system. The data presented herein are but a step towards that goal. Finally, it is interesting to observe the sediment accumulation rates (SAR) computed at Zumaia, which is independent of the absolute chronology (Fig. 8). Both the CK95 and the Zumaia astronomically derived

Fig. 7. Laskar et al. (2004) (La04) and Varadi et al. (2003) (R7) eccentricity solutions for the interval 53–66 Ma compared to the standard GPTS (Geomagnetic Polarity Time Scale) of Cande and Kent (1995) (CK95), shifted 0.5 Myr to older ages to account for a K/Pg boundary at 65.5 Ma, and orbitally tuned magnetostratigraphies. The two alternative tunings for the ODP Leg 208 data (a and b) are those from Westerhold et al. (2007), which differ and supersede those proposed by Lourens et al. (2005) (see text for discussion). The corresponding position of the Elmo and PETM events is indicated. (c) The orbital tuning for the C29r–C28r interval from the Zumaia section is from Dinarès-Turell et al. (2003) who tuned a relative highcarbonate interval in the upper part of chron C27n to a node of low eccentricity amplitude in the R7 orbital solution at about 62.2 Ma. The rest of the Palaeocene magnetic chronology follows this constraint and the established chron duration by orbital cycle counting provided herein and in DinarèsTurell et al. (2002) for the uppermost Palaeocene interval (Table 1). An alternative derived age at 56.138 Ma (dashed) for the PETM from Zumaia considers a duration of 53 precession cycles for the Palaeocene part of C24r as proposed in Westerhold et al. (2007).

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Fig. 8. Sediment accumulation rates (SAR) as derived by correlation of the Zumaia magnetostratigraphy (vertical panel) to the CK95 and to the Zumaia astronomical polarity time scales (horizontal panel). Two options for the P/E age at Zumaia are considered (see text for explanations).

age models yield similar SARs and trends along the entire Palaeocene. There is first a decreasing trend above the K/Pg boundary up to the base of C28n (from around 1.6 cm/kyr to 0.9 cm/kyr). SARs then follow more or less constant or slightly increasing (around 1–1.2 cm/kyr) up to about C26n where SAR substantially increases and attains values between 2–3 cm/kyr along the uppermost Palaeocene. This increase denotes the input of terrigenous material to the basin as reflected by the conspicuous increase of the number of turbidite layers at the base of the Itzurun Fm member B upward (Figs. 1 and 5). 6.3. Selandian and Thanetian global standard stratotype-section and point (GSSP) The Palaeogene Subcommission of the International Commission on Stratigraphy (ICS) has already agreed on the criteria for the base and top of the Palaeocene and the respective GSSPs have been established. The base of the negative Carbon Isotopic Excursion (CIE) was chosen as criterion for the P/E boundary (i.e. the base of the Ypresian stage of the Eocene series) (Luterbacher et al., 2000) and

the GSSP was placed at the Dababiya Quarry Section near Luxor, Egypt (http://www.stratigraphy.org/ypresian.htm, Dupuis et al., 2003). The GSSP for the base of the Danian Stage of the Palaeogene System (i.e., the K/Pg boundary) is defined at the base of the boundary clay at a section near El Kef, Tunisia (Molina et al., 2006), and is marked by an Iridium geochemical anomaly associated with a major extinction horizon, (http://www.stratigraphy.org/danian. htm). However, the internal Palaeocene GSSPs (i.e., Selandian and Thanetian lower limits) have only been agreed in a recent meeting of the Paleocene Working Group of the International Subcommission of the Paleogene Stratigraphy of the ICS and still await formal ratification by the International Union of Geological Sciences (IUGS). The base of chron C26n has been indicated for the Thanetian base, while the lithostratigraphic change (and associated criteria) between the Danian Limestone Fm and the overlaying Itzurun marl Fm in Zumaia has been chosen to delimit the Selandian base, although several possibilities have been previously proposed for the Selandian base including the top or bottom of foraminifera zone P3a, or the δ13C excursion

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near base of calcareous nannofossil Zone NP5 (Schmitz et al., 1998, http://www.stratigraphy.org). Presently then, Zumaia has become the hosting section for both GSSPs. Other alternative Tunisian sections for the Danian/Selandian boundary appear unsuitable due to significant hiatus (Van Itterbeeck et al., 2007). When selecting GSSPs it is important to consider the potential utility of the new global stage concepts, however, historical tradition should be respected. The respective time-rock extents of the new Selandian and Thanetian GSP-delimited stages should, ideally, reflect global change, but also roughly coincide with the stratigraphic extents of the respective historical, regional stages (Knox, 1994). In the type region, Denmark, the base of the Selandian is marked by an unconformity between the limestones of the Danskekalk Fm and the greensands and marls of the Lellinge Fm signalling the cessation of 40 million years of carbonate deposition in the North Sea Basin and a shift to siliciclastic deposition (Clemmensen and Thomsen, 2005). The basal Selandian in Denmark falls in the upper part of Zone NP4 or to the lower part of Zone NP5 (Clemmensen and Thomsen, 2005). Prestwich (1850a,b, 1854) introduced the term “Thanet Sands” to describe the succession of fine, locally glauconitic and argillaceous sandstones and sandy clays that overlie the Upper Cretaceous chalk in the Isle of Thanet and adjacent districts in southern England. In its original type area, the unconformity related base of the Thanetian has been dated with the upper part of the nannofossil zone NP6 (Aubry, 1994; Knox, 1994). All the events traditionally used to place the Danian/ Selandian (i.e., the top of chron C27n, FO of M. angulata and I. albeari planktic foraminifera, The FO of F. tympaniformis) and Selandian/Thanetian (i.e., the base of chron C26n) boundaries can be identified in the Zumaia section. The integrated biomagneto- and cyclostratigraphic framework presented in this paper undoubtedly facilitates the settling of criteria already agreed and strengthen the potential of the Zumaia section for chronostratigraphic purposes. It should be stressed that the Zumaia section does not only contain excellent P/E and K/Pg boundary outcrops, but also after the present study the entire Palaeocene is documented on an integrated cyclo-, magneto- and biostratigraphic basis. Given the available high-resolution chronostratigraphic framework and potentiality of the Zumaia section we decisively propose to link the established criteria for the Thanetian and Selandian GSSPs to the cycle pattern, independently of the final tuning eventually reached for the Palaeocene. For instance, a reasonable alternative criterion for the Thanetian base could be the MPBE event. Indeed this event can be referred to the

magnetostratigraphy and climatic cycle pattern (∼ 8 precession cycles below the base of C26n in correspondence to an eccentricity maxima) and thus offers enormous potential for long-range correlation. The Zumaia section certainly fulfils now most if not all the infrastructural, biostratigraphic and geological requirements demanded according to the International Commission on Stratigraphy (ICS) guidelines, summarized by Remane et al. (1996), to be erected the Selandian and Thanetian GSSPs. Furthermore, the Zumaia section, as a continuous, deep marine and cyclic sequence, offers the possibility to establish a potential Selandian unit stratotype in the sense amply discussed by Hilgen et al. (2006b). Therefore, the Selandian stage would be defined by its content (and not only by its boundaries), and the importance of time-rock units would be strengthened by the introduction of astronomically defined chronozones as formal chronostratigraphic units. 7. Conclusions The presented mid-Palaeocene integrated magneto-, bio- and cyclostratigraphy for the (hemi)pelagic sea-cliff section of Zumaia closes the gap of our previous integrated studies in the section (Dinarès-Turell et al., 2002, 2003), and allows a complete astronomically calibrated chronology for the entire Palaeocene succession to be proposed. Short eccentricity cycles (bundles) in addition to precession cycles (couplets) are identified, and duration of magnetochrons are established by assigning a mean duration of 21-kyr to precession cycles (Table 1). Calcareous plankton bioevents and the Mid Palaeocene biotic event (MPBE) are placed within the magnetostratigraphic and cyclostratigraphic template. Following a recent agreement by the Paleocene Working Group of the International Subcommission of the Paleogene Stratigraphy of the ICS, we consider the base of chron C26n and the criteria associated to the lithostratigraphic change between the Danian Limestone Fm and the Itzurun marl Fm at Zumaia, as the respective delimiting points for the Thanetian and Selandian bases. Consequently, the duration of the Thanetian, Selandian and Danian component stages can be estimated at Zumaia to be about ∼ 3129 kyr, ∼ 2163 kyr and ∼ 4324 kyr respectively. These figures may be read with caution since they only represent minimum estimates based on precession cycle counting in our section, where the full hierarchy of astronomical cycles has not yet been substantiated (i.e. the more stable 404-kyr eccentricity cycle). Therefore the possibility exists that at Zumaia there could be some misidentified cycles or missing cycles especially along the marly Itzurun Fm, in

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addition that the presence of turbiditic layers in its upper part also hampers proper identification of cycles along chron C25r. Collectively, the reported dataset represents the first complete astronomically calibrated Palaeocene succession. This renders Zumaia a very exceptional and unique section, where it will be possible in the future to refine and consolidate a complete tuned Palaeocene record after thorough analysis of proxy records. The new integrated chronologic framework presented herein provides the basis for a proper definition of the Selandian and Thanetian GSSPs. We suggest adopting the MPBE, located 8 precession cycles below the base of chron C26n in correspondence to an eccentricity maximum, as alternative criteria to define the Thanetian base. Given the uncertainties in astronomical calculations and errors associated in radioisotopic dating, our derived absolute chronology is only provisory. Therefore, robust ages for the PETM and K/Pg boundary (and all Palaeocene magnetochron and biostratigraphic datums) cannot be provided for the moment. We anticipate that a definitive Palaeocene chronology can only be achieved by astronomical tuning based on the stable 404-kyr eccentricity cycle sustained by high-quality radiometric dating. Possibly, long cyclic deep marine successions on land like that of Zumaia, together with suitable records from (I)ODP multiple hole core sediments will make possible to attain a robust Palaeogene astronomically derived chronology and ultimately extend this approach into the Mesozoic. Acknowledgments JIB acknowledges support from a “Ramón y Cajal” research grant from the Spanish Ministry of Science and Technology. GB acknowledges support from a postdoctoral grant from the Basque Country Government. James Ogg and other four unnamed referees provided useful comments. Isaías P. M. is thanked for his enlightening enthusiasm. This research is a contribution to projects UPV 00121-1455/2002, CGL2005-01721/BTE and CGL2005-02770/BTE. Appendix A Morozovella angulata Interval Zone (= lower part of P3a of Berggren et al. (1995) and of Berggren and Pearson (2005)). Definition: Biostratigraphic interval between the LO of M. angulata and the LO of Igorina pusilla. Remarks: In the studied section only the final part of this biozone is represented, and includes the lower 3 m of the succession. The most characteristic species of the assemblage are M. angulata, M. conicotruncata,

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Subbotina triloculinoides, Parasubbotina varianta and Globanomalina ehrenbergi among others. Igorina pusilla Interval Zone (emended herein; = middle part of P3a of Berggren et al. (1995) and of Berggren and Pearson (2005)). Definition: Biostratigraphic interval between the LO of I. pusilla and the LO of M. occlusa. Remarks: This biozone is 10 m thick and has a planktic foraminifera assemblage similar to the previous biozone, also including S. linaperta, S. velascoensis, different igorinids and the first specimens of the genus Acarinina. Morozovella occlusa Interval Zone (herein defined; = upper part of P3a of Berggren et al. (1995) and of Berggren and Pearson (2005)). Definition: Biostratigraphic interval between the LO of M. occlusa (= M. crosswicksensis) and the LO of Igorina albeari. Remarks: We use the FO of M. occlusa to mark the base of this 11 m thick biozone because this taxon is the most abundant of the velascoensis group in all the samples of the Middle and Upper Palaeocene. M. velascoensis first occurs together with M. occlusa. M. occlusa extents throughout the Thanetian up to the P/E boundary. Igorina albeari Interval Zone (= P3b of Berggren et al. (1995) and P3b and P4a of Berggren and Pearson (2005)). Definition: Biostratigraphic interval between the LO of I. albeari and the LO of G. pseudomenardii. Remarks: The first specimen of I. albeari, which mark the base of this biozone, appear 10 m above the lithological change from the Danian Limestone to the overlying red marls of the Itzurun Fm. I. albeari includes those forms with a biconvex trochospiral growth, more than 7 chambers in the last whorl with a peripheral margin with muricocarina in the last chambers and a high spiral side in the central part. This biozone is 7 m thick. Globanomalina pseudomenardii Interval Zone (= lower part of P4a of Berggren et al. (1995) and of P4b of Berggren and Pearson (2005)). Definition: Biostratigraphic interval between the LO of G. pseudomenardii and the LO of Acarinina soldadoensis. Remarks: The upper part of the studied section belongs to the G. pseudomenardii biozone, whose base has been defined by the first occurrence of this taxon. G. pseudomenardii is very rare in the first samples of the biozone and the first specimens are relatively small and have a smooth keel. Appendix B. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j. epsl.2007.08.008.

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References Apellaniz, E., Lamolda, M.A., Orue-Etxebarria, X., 1983. Posición estratigráfica de las “Calizas del Danés”, País Vasco. Rev. Esp. Micropaleontol. 15, 447–455. Aubry, M.P., 1994. The Thanetian Stage in NW Europe and its significance in terms of global events. GFF 116, 43–44. Baceta, J.I., Pujalte, V., Dinarès-Turell, J., Payros, A., Orue-Etxebarria, X., Bernaola, G., 2000. The Palaeocene/Eocene boundary interval in the Zumaia section (Gipuzkoa, Basque basin): Magnetostratigraphy and high-resolution lithostratigraphy. Rev. Soc. Geol. Esp. 13, 375–391. Baceta, J.I., Pujalte, V., Serra-Kiel, J., Robador, A., Orue-Etxebarria, X., 2004. El Maastrichtiense final, Paleoceno e Ilerdiense inferior de la Cordillera Pirenaica. In: Vera, J.A. (Ed.), Geología de España. Sociedad Geológica de España — Instituto Geológico y Minero de España, Madrid, pp. 308–313. Baceta, J.I., Pujalte, V., Bernaola, G., 2005. Paleocene coralgal reefs of the western Pyrenean Basin, N Spain: Evidence concerning the post-Cretaceous recovery of reefal ecosystems. Palaeogeogr. Palaeoclimatol. Palaeoecol. 224, 117–143. Berggren, W.A., Pearson, P.N., 2005. A Revised Tropical To Subtropical Paleogene Planktonic Foraminiferal Zonation. J. Foraminiferal Res. 35, 279–298. Berggren, W.A., Kent, D.V., Swisher, C.C., Aubry, M.-P., 1995. A revised Cenozoic geochronology and chronostratigraphy. In: Berggren, W.A., Kent, D.V., Aubry, M.-P., Hardenbol, J. (Eds.), Geochronology Time Scales and Global Stratigraphic Correlation Spec. Publ., vol. 54. SEPM, Tulsa, OK, pp. 129–212. Berggren, W.A., Aubry, M.-P., van Fossen, M., Kent, D.V., Noris, R.D., Quillevere, F., 2000. Integrated Paleocene calcareous plankton magnetobiochronology and stable isotope stratigraphy: DSDP Site 384 (NW Atlantic Ocean). Palaeogeogr. Palaeoclimatol. Palaeoecol. 159, 1–51. Bernaola, G., 2002. Los nannofósiles calcáreos del Paleoceno en el dominio Pirenaico. Bioestratigrafía, cronoestratigrafía y paleoecología, PhD thesis, University of the Basque Country, Bilbao, 445 pp. Bernaola, G., in press. New high-resolution calcareous nannofossil analysis across the Danian/Selandian transition at the Zumaia section: comparison with south Tethys and Danish sections. Geol. Acta. Bernaola, G., Baceta, J.I., Orue-Etxebarria, X., Alegret, L., MartínRubio, M., Arostegui, J., Dinarès-Turell, J., 2006. The Mid Paleocene Biotic Event. In: Bernaola, G., Baceta, J.I., Payros, A., Orue-Etxebarria, X., Apellaniz, E. (Eds.), The Paleocene and lower Eocene of the Zumaia section (Basque Basin). Climate and Biota of the Early Paleogene 2006. Post conference Field Trip Guidebook, Bilbao, pp. 49–51. Bernaola, G., Baceta, J.I., Orue-Etxebarria, X., Alegret, L., MartinRubio, M., Arostegui, J., Dinarès-Turell, J., 2007. Evidences of an abrupt environmental disruption during the Mid Paleocene Biotic Event (Zumaia section, W Pyrenees). Bull. Soc. Geol. Am. 119, 785–795. Bralower, T.J., Premoli Silva, I., Malone, M.J., et al., . Proceedings of the Ocean Drilling Program, Initial Reports, Leg 198 [Online] Available from World Wide Web: http://www.odp.tamu.edu/ publications/198_IR/198ir.htm. Cande, S.C., Kent, D.V., 1992. A New Geomagnetic Polarity Time Scale for the Late Cretaceous and Cenozoic. J. Geophys. Res. 97, 13917–13951. Cande, S.C., Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. J. Geophys. Res. 100, 6093–6095.

Clemmensen, A., Thomsen, E., 2005. Palaeoenvironmental changes across the Danian–Selandian boundary in the North Sea Basin. Palaeogeogr. Palaeoclimatol. Palaeoecol. 219, 351–394. Cramer, B.S., 2001. Latest Palaeocene–earliest Eocene cyclostratigraphy: using core photographs for reconnaissance geophysical logging. Earth Planet. Sci. Lett. 186, 231–244. Cramer, B.S., Wright, J.D., Kent, D.V., Aubry, M.-P., 2003. Orbital climate forcing of δ13C excursions in the late Paleocene – Eocene (chrons C24n–C25n). Paleoceanography 18, 1097. doi:10.1029/ 2003PA000909. Dinarès-Turell, J., Baceta, J.I., Pujalte, V., Orue-Etxebarria, X., Bernaola, G., 2002. Magnetostratigraphic and ciclostratigraphic calibration of a prospective Paleocene/Eocene stratotypes at Zumaia (Basque Basin, northern Spain). Terra Nova 14, 371–378. Dinarès-Turell, J., Baceta, J.I., Pujalte, V., Orue-Etxebarria, X., Bernaola, G., Lorito, S., 2003. Untangling the Palaeocene climatic rhythm: an astronomically calibrated Early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain). Earth Planet. Sci. Lett. 216, 483–500. Dinarès-Turell, J., Stoykova, K., Ianov, M., 2006. Paleocene integrated cyclo-, magneto- and calcareous nannofossils stratigraphy in the Bjala section (Black Sea coast, Bulgaria). CBEP2006, Climate and Biota of the Early Paleogene International Meeting, Bilbao, Spain. Dupuis, C., Aubry, M., Steurbaut, E., Berggren, W.A., Ouda, K., Magioncalda, R., Cramer, B.S., Kent, D.V., Speijer, R.P., Heilmann-Clausen, C., 2003. The Dababiya Quarry Section: Lithostratigraphy, clay mineralogy, geochemistry and paleontology. Micropaleontology 49, 41–59. Gradstein, F., Ogg, J., Smith, A., 2004. A Geological Timescale 2004. Cambridge University Press. Hilgen, F.J., Krijgsman, W., Kuiper, K.F., Lourens, L.J., Wijbrans, J.R., 2006a. Astronomical calibration of geological time. Geophys. Res. Abstr. 8, 07782. Hilgen, F.J., Brinkhuis, H., Zachariasse, W.-J., 2006b. Unit stratotypes for global stratotypes: The Neogene perspective. Earth Sci. Rev. 74, 113–125. Kent, D.V., 1999. Orbital tuning of geomagnetic polarity time-scales. Philos. Trans. R. Soc. Lond., A 357, 1995–2007. Kirschvink, J.L., 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc. 62, 699–718. Knox, R., 1994. From regional stage to standard stage: implications for the historical Paleogene stratotypes of NW Europe. GFF 116, 56–57. Kuiper, K.F., Wijbrans, J.R., Hilgen, F.J., 2005. Radioisotopic dating of the Tortonian Global Stratotype Section and Point: implications for intercalibration of 40Ar/39Ar and astronomical dating methods. Terra Nova 17, 385–398. Laskar, J., 1999. The limits of Earth orbital calculations for geological time-scale use. Philos. Trans. R. Soc. Lond., A 357, 1735–1759. Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A., Levrard, B., 2004. A long-term numerical solution for the insolation quantities of the Earth. Astron. Astrophys. 428, 261–285. Lourens, J.L., Hilgen, F.J., Laskar, J., Shackleton, N.J., Wilson, D., 2004. The Neogene Period. In: Gradstein, F., Ogg, J., Smith, A. (Eds.), Geological Time Scale. Cambridge University Press, pp. 409–440. Lourens, J.L., Sluijs, A., Kroon, D., Zachos, J.C., Thomas, E., Röhl, U., Bowles, J., Raffi, I., 2005. Astronomical pacing of late Paleocene to early Eocene global warming events. Nature 435, 1083–1087. Lowrie, W., Alvarez, W., Premoli Silva, I., Monechi, S., 1980. Lower Cretaceous magnetic stratigraphy in Umbrian pelagic carbonate rocks. Geophys. J. R. Astron. Soc. 60, 263–281.

J. Dinarès-Turell et al. / Earth and Planetary Science Letters 262 (2007) 450–467 Luterbacher, H.P., Hardenbol, J., Schmitz, B., 2000. Decision of the Voting Members of the International Subcommission on Paleogene Stratigraphy on the Criterion for the Recognition of the Paleocene/ Eocene boundary. ISPS Working Group Newsletter, vol. 9, p. 13. Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: Farinacci, A. (Ed.), Proceedings of the Second Planktonic Conference, Tecnoscienza, Roma, pp. 739–761. Molina, E., Alegret, L., Arenillas, I., Arz, J.A., Gallala, N., Hardenbol, J., von Salis, K., Steurbaut, E., Vandenberghe, N., Zaghbib-Turki, D., 2006. The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, “Tertiary”, Cenozoic) at El Kef, Tunisia: Original definition and revision. Episodes 29, 263–273. Norris, R.D., 1997. Symbiosis as an evolutionary innovation in the radiation of Paleocene planktic foraminifera. Paleobiology 22, 461–480. Olsson, R.K., Hemleben, C., Berggren, W.A., Huber, B.T., 1999. Atlas of Paleocene planktonic foraminifera. Smithson. Contrib. Paleobiol. 85, 252. Orue-Etxebarria, X., Caballero, F., Apellaniz, E., 2006. New planktic foraminifera biozonation from the Mid-Paleocene. In: Bernaola, G., Baceta, J.I., Payros, A., Orue-Etxebarria, X., Apellaniz, E. (Eds.), The Paleocene and lower Eocene of the Zumaia section (Basque Basin). Climate and Biota of the Early Paleogene 2006. Post conference Field Trip Guidebook, Bilbao, pp. 46–47. Petrizzo, M.R., 2005. An early late Paleocene event on Shatsky Rise, northwest Pacific Ocean (ODP Leg 198): evidence from planktonic foraminiferal assemblages. In: Bralower, T.J., Premoli Silva, I., Malone, M.J. (Eds.), Proc. ODP, Scientific Results, 198 [Online]. Available from World Wide Web: bhttp://www.odp. tamu.edu/publications/198_SR/102/102.htmN. Preissinger, A., Aslanian, S., Brandstatter, F., Grass, F., Stradner, H., Summesberger, H., 2002. Cretaceous–Tertiary profile, rhythmic deposition, and geomagnetic polarity reversals of marine sediments near Bjala, Bulgaria. In: Koeberl, C., MacLeod, K.G. (Eds.), Catastrophic Events and Mass Extinctions: Impacts and Beyond, Boulder, Colorado. Geol. Soc.Am. Special Paper, vol. 356, pp. 213–229. Prestwich, J., 1850a. On the structure of the strata between the London Clay and the Chalk in the London and Hampshire Tertiary systems. Part I. Q. J. Geol. Soc. Lond. 6, 252–281. Prestwich, J., 1850b. On the structure of the strata between the London Clay and the Chalk in the London and Hampshire Tertiary systems. Part I. Q. J. Geol. Soc. Lond. 8, 235–264. Prestwich, J., 1854. On the structure of the strata between the London Clay and the Chalk in the London and Hampshire Tertiary systems. Part III. Q. J. Geol. Soc. Lond. 10, 75–154. Pujalte, V., Baceta, J.I., Dinarès-Turell, J., Orue-Etxebarrie, X., Parès, J.M., Payros, A., 1995. Biostratigraphic and magnetostratigraphic intercalibration of late Maastrichtian and Paleocene depositional

467

sequences from the deep-water Basque basin, W Pyrenees, Spain. Earth Planet. Sci. Lett. 136, 17–30. Pujalte, V., Baceta, J.I., Orue-Etxebarrie, X., Payros, A., 1998. Paleocene strata of the Basque Country, western Pyrenees, northern Spain: facies and sequence development in a deep-water starved basin. In: de Graciansky, P.-Ch., Hardenbol, J., Jacquin, T., Vail, P. (Eds.), Mesozoic and Cenozoic Sequence Stratigraphy of European Basins. S.E.P.M. Spec. Publ., vol. 60, pp. 311–325. Remane, J., Basset, M.G., Cowie, J.W., Gohrbandt, K.H., Lane, R., Michelsen, O., Naiwen, W., 1996. Revised guidelines for the establishment of global chronostratigraphic standards by the International Commission on Stratigraphy. Episodes 19, 77–81. Röhl, U., Ogg, J.G., Geib, T.L., Wefer, G., 2001. Astronomical calibration of the Danian time scale. In: Kroon, D., Norris, R.D., Klaos, A. (Eds.), Western North Atlantic: Palaeogene and Cretaceous Palaeoceanography. Geol. Soc. Lond., Spec. Pub., vol. 183, pp. 163–183. Röhl, U., Norris, R.D., Ogg, J.G., 2003. Cyclostratigraphy of upper Paleocene and lower Eocene sediments at Blake Nose Site 1051 (western North Atlantic). In: Wing, S.L., Gingerich, P.D., Schmitz, B., Thomas, E. (Eds.), Causes and Consequences of Globally Warm Climates in the Early Paleogene. Geological Society of America Special Paper, Boulder, Colorado, pp. 576–589. Schmitz, B., Molina, E., Von Salis, K., 1998. The Zumaya section in Spain: a possible global stratotype section for the Selandian and Thanetian stages. Newsl. Stratigr. 36, 35–42. Ten Kate, W.G., Sprenger, A., 1993. Orbital cyclicities above and below the Cretaceous/Paleogene boundary at Zumaya (N Spain), Agost and Relleu (SE Spain). Sediment. Geol. 87, 69–101. Torrence, C., Compo, G.P., 1998. A practical guide to wavelet analysis. Bull. Am. Meteorol. Soc. 79, 61–78. Van Itterbeeck, J., Sprong, J., Dupuis, C., Speijer, R.P., Sterbaut, E., 2007. Danian/Selandian boundary stratigraphy, paleoenvironment and Ostracoda from Sidi Nasseur, Tunisia. Mar. Micropaleontol. 62, 211–234. Varadi, F., Runnegar, B., Ghil, M., 2003. Successive refinements in long-term integrations of planetary orbits. Astrophys. J. 592, 620–630. Westerhold, T., Röhl, U., Laskar, J., Raffi, I., Bowles, J., Lourens, L.J., Zachos, J.C., 2007. On the duration of magnetochrons C24r and C25n and the timing of early Eocene global warming events: Implications from the Ocean Drilling Program Leg 208 Walvis Ridge depth transect. Paleoceanography 22, PA2201. doi:10.1029/ 2006PA001322. Zachos, J.C., Kroon, D., et al., . Early Cenozoic extrem climates: the Walvis Ridge transect: Proceedings, Ocean Drilling Program, Leg 208http://www.odp.tamu.edu/publications/208-IR/208ir.htm. Zijderveld, J.D.A., 1967. AC demagnetisation of rock: Analysis of results. In: Collinson, D.W., et al. (Ed.), Methods in palaeomagnetism. Elsevier, Amsterdam, pp. 254–286.