High-resolution intra- and interbasinal correlation of the Danian–Selandian transition (Early Paleocene): The Bjala section (Bulgaria) and the Selandian GSSP at Zumaia (Spain)

Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p a l a e o

High-resolution intra- and interbasinal correlation of the Danian–Selandian transition (Early Paleocene): The Bjala section (Bulgaria) and the Selandian GSSP at Zumaia (Spain) J. Dinarès-Turell a,⁎, K. Stoykova b, J.I. Baceta c, M. Ivanov d, V. Pujalte c a

Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 Rome, Italy Department of Paleontology and Stratigraphy, Geological Institute, Bulgarian Academy of Science, BG-1113 Sofia, Bulgaria c Department of Stratigraphy, Univ. Basque Country, PO Box 644, E-48080 Bilbao, Spain d Department of Geology and Paleontology, University of Sofia, BG-1000 Sofia, Bulgaria b

a r t i c l e

i n f o

Article history: Received 23 June 2010 Received in revised form 1 September 2010 Accepted 6 September 2010 Available online 16 September 2010 Keywords: Paleocene Magnetostratigraphy Orbital tuning Calcareous nannofossils Selandian GSSP

a b s t r a c t The Danian–Selandian (D–S) boundary has been identified for the first time in the Black Sea coast at Bjala (Bulgaria) based on a new integrated bio-, magneto- and cyclostratigraphic study. Several correlation criteria as established for the basal Selandian GSSP from Zumaia (Basque Basin) are evaluated. Noteworthy, is the almost complete lack of calcareous nannoplankton species Braarudosphaera bigelowi in the Bulgarian sections, a sharp decrease of which was indicated as suitable criteria for defining the D–S boundary as it occurred both at Zumaia and in the classical locations of the North Sea basin. Conversely, the second evolutionary radiation of the calcareous nannofossil genus Fasciculithus together with the occurrence of Fasciculithus tympaniformis that define the NP4/NP5 zonal boundary seem to be reliable criteria to approximate the D–S boundary. In detail, however, the best approach is to integrate biostratigraphic data within a magnetostratigraphic and/or cyclostratigraphic framework. Refinements on the placement of chron C27n at Zumaia and robust bed-by-bed correlation between several Basque sections and Bjala indicates that the D–S boundary is located 30 precession cycles (~ 630 ky) above C27n. In addition to the precession-related marl–limestone couplets and 100-ky eccentricity bundles recognized in the studied sections, expression of the stable 405-ky long eccentricity allows direct tuning to the astronomical solutions. A correlation of the land-based sections with previously tuned data from ODP Site1262 from the Southern Atlantic is challenged. Our choice is consistent with original tuning at Zumaia but shifts one 100-ky cycle older previous tuning from Site 1262 along the interval above C27n. Under the preferred tuning scheme the D–S boundary can be given an age of 61.641 ± 0.040 Ma on the La04 orbital solution. © 2010 Elsevier B.V. All rights reserved.

1. Introduction The Global Stratotype Section and Point (GSSP) for the base of the Selandian Stage (Middle Paleocene) has recently been established (ratified by the International Union of Geological Sciences in September 2008) on the sea-cliff Zumaia section in the Basque Country (Schmitz et al., submitted for publication; http://stratigraphy.science.purdue. edu/gssp/index.php?parentid=2) which constitutes one of the most complete and expanded sections in open-marine facies across this interval. It has been defined (Schmitz et al., 2008) in coincidence with a prominent lithological change between the limestone-dominated Aitzgorri Formation and the marl-dominated lower member of the Itzurun Formation. The GSSP coincides with the second evolutionary radiation of the calcareous nannofossil genus Fasciculithus, a sharp

⁎ Corresponding author. Tel.: + 39 06 51860 387; fax: + 39 06 51860 397. E-mail address: [email protected] (J. Dinarès-Turell). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.09.004

decrease in the abundance of Braarudosphaera and is close to the NP4/NP5 zonal boundary (Bernaola et al., 2009). Magneto- and cyclostratigraphic studies at Zumaia placed the Danian–Selandian boundary (D–S hereafter) about 34 precession cycles above the top of magnetochron C27n (i.e. ~714 ky from C27n top) (Dinarès-Turell et al., 2003, 2007). One of the requisites imposed by the International Commission of Stratigraphy (ICS) when choosing a suitable criterion and boundary level for a given GSSP is its potentiality for reliable correlation elsewhere. The guidelines by Remane et al. (1996) indicate that a succession of events, enabling better correlation in the absence of the primary marker, is preferable. The usefulness of the main biostratigraphic criterion and the array of additional criteria established at the Zumaia section GSSP to pinpoint the Danian–Selandian boundary have only been partially explored. The study of Steurbaut and Sztrákos (2008), on sections from the Aquitaine area some 100–150 km NE from Zumaia, has only considered calcareous nannofossils, planktic foraminifers and some lithological aspects. Studies from Tethyan sections in Egypt and Tunisia have dealt basically on biostratigraphic issues and

512

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

environmental implications, as these locations lack magnetostratigraphy or well-preserved cyclical bedding arrangements (e. g. Speijer and Schmitz, 1998; Speijer, 2003; Guasti et al., 2006; Sprong et al., 2009). Furthermore, the late Danian is getting much attention as it could record one of the earliest Cenozoic hyperthermals (e.g. Arenillas et al., 2008; Bornemann et al., 2009) that seems to be linked to perturbations of the global carbon cycle with strong effects on sea-level and Earth climatic history. In addition, the astronomical time scale for the Paleocene is still a putative issue and alternative tunings have been proposed (DinarèsTurell et al., 2003, 2007; Westerhold et al., 2008; Kuiper et al., 2008). Consequently, substantiating the chronostratigraphic framework along this interval in different basins and testing the correlation criteria from the Zumaia GSSP becomes essential. Here we present an integrated magneto-, bio-, and cyclostratigraphic study of the Tethyan–Boreal Bjala succession on the Black Sea coast from Bulgaria (Fig. 1) spanning chron C27n and the D–S boundary which is identified for the first time at this location. The data together with new insights from Zumaia and other sections allows refining and confirming the quality of the Selandian GSSP. Comparison of the land-based sections with published results from ODP Site 1262 from the Southern Atlantic sheds light to the Paleocene astronomical tuning on which we will elaborate elsewhere. 2. Studied sections and previous work 2.1. The Bjala Bulgarian sections The Danian–Selandian boundary succession from the Bjala locality (Black sea coast of Bulgaria, latitude/longitude, 42° 52′ N/27° 54′ E) is studied in two sections from different faulted blocks separated about 1 km from each other along the beach cliffs: the Bjala E and the Bjala 1 sections, located respectively at the northern and southern ends of the Bjala beach (Fig. 2). The studied succession consists of alternating marl and marly limestones of the Maastrichtian–Paleocene (hemi)-pelagic Bjala Formation which was deposited, as indicated by macrofossils (echinoderms and ammonites), at a paleowater depth of about

300–600 m (Preisinger et al., 1993). It is located at the boundary of two major tectonic units — the Alpine orogen with its East Balkan Unit and the Moesian platform with its Lower Kamchia Unit (Dabovski and Zagorchev, 2009). Since the discovery of a complete and well-preserved Cretaceous–Paleogene (K–Pg) boundary section in 1991, the Bjala succession has been the focus of different biostratigraphic, geochemical, sequence stratigraphy and paleoenvironmental studies (e. g. Stoykova and Ivanov, 1992; Preisinger et al., 1993; Ivanov and Stoykova, 1994; Adatte et al., 2002; Preisinger et al., 2002; Stoykova and Ivanov, 2002; Peybernes et al., 2004; Stoykova and Ivanov, 2004). Most studies were centered on the K–Pg boundary that outcrops in different faulted blocks along the coast giving rise to various Bjala subsections and nomenclatures. Schematically, the succession along the coast that is gently dipping south–southwesterly follow a succession of faulted blocks limited by transpressive (?) faults that generally displace the succession to higher stratigraphic levels towards the southern blocks (individual vertical throws between few to dozens of meters). Only the works by Preisinger et al. (1993, 2002) included magnetostratigraphy and a crude lithological cycle counting along the Paleocene from the so-called 70 m long Bjala 2b profile. The difficulties to fully and unambiguously anchor the available magneto- and biostratigraphic data to a detailed bed-bybed litholog prompted us to undertake an integrated high-resolution magnetostratigraphic, geochemical and calcareous nannofossil biostratigraphic study throughout the Paleocene Bjala succession along the different faulted blocks with the aim to build a composite Lower Paleocene sequence amenable for cyclostratigraphic studies and astronomical tuning. The Bjala E section was initially logged and sampled in May 2004 with a later additional sampling in 2005–06. The Bjala E section is located in a faulted block south of the original Bjala 2b section of Preisinger et al. (1993). Results and field observations indicated that the Bjala E succession does not contain the complete Upper Danian stratigraphy and that the lithological apparent D–S boundary there, approximated by the calcareous nannofossil biozone boundary NP4/NP5, represents a tectonic contact at the southern edge of the block. Observations and detailed lithological correlation of the succession between the different tectonic blocks along the beach suggested that the Bjala 1 section had a more complete and undisturbed stratigraphy of the upper part of the Danian with respect to the Bjala E section, and was extensively sampled in 2008 (Fig. 2). The section extents and overlaps the interval studied at Bjala E, permitting an unambiguous bed-by-bed correlation of both sections (see below) despite the block containing the Bjala1 section having a reduced Lowest Paleocene and Maastrichtian succession (Ivanov and Stoykova, 1994). In this block, the uppermost Maastrichtian is missing and the Paleocene succession starts just above the NP2/NP3 calcareous nannofossil biozone boundary. This has been interpreted as evidences of tectonic truncation and/or no deposition (Ivanov and Stoykova, 1994; Peybernes et al., 2004). 2.2. The Zumaia Basque sections

Fig. 1. A 60 Ma (Thanetian–Selandian) paleogeographic reconstruction using the Webbased software at http://www.odsn.de/odsn/services/paleomap/paleomap.html with location of the studied sections.

The Zumaia sea-cliff section that contains the Selandian GSSP (latitude/longitude 43o 17′ 56.98″ N/2o 15′ 39.38″ W) is located in the Itzurun beach (Schmitz et al., 2008). The Danian part of the Paleocene succession extents toward the west–northwest from the San Telmo chapel along the Aitzgorri headland with some faults disturbing the succession (see Fig. 1 in Dinarès-Turell et al., 2007). Outcrops are partly reachable at sea-level (during low-tides) but given the subvertical bedding attitude the published integrated cyclo- and magnetobiostratigraphic study was conducted mostly along the top part of the headland (Dinarès-Turell et al., 2003). Now, additional magnetostratigraphic samples have been taken from that succession on the headland top along the C27n/C26r chron boundary in order to better refine its position (see below). In addition, an Upper Danian section located about 1 km northeast from the Itzurun beach on the other side of the Urola

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

513

Fig. 2. Field photographs of the Upper Danian Bjala E (image tilted) and Bjala1 sections with first order lithological correlation. Note the unambiguous correlation of prominent carbonate-rich cycles numbered 22–28 and 11 on the lithological log of Bjala E (see text for explanation of the cycle counting nomenclature adopted herein). The correlation indicates that Bjala 1 has and additional stratigraphic cyclic succession before a sharp lithological boundary to a more marly succession. At Bjala E this cyclic interval is missing and therefore must be truncated by a tectonic contact at the base of the homogeneous marls (containing fauna from the Selandian NP5 biozone) above cycles 8/9.

River mouth has been studied. This section that we call Zumaia–Artadi was sampled at a very high-resolution in an attempt to reproduce the magnetostratigraphic results from the reference section at the sea cliffs (Zumaia–Aitzgorri section). Bedding along the uppermost Danian interval at the Zumaia–Artadi section is overturned and constitutes the less deformed limb of a relatively complex faulted fold. The 17 m long studied succession encompasses chron C27n and contains the D–S boundary and the lowermost Selandian at its top. 2.3. The Loubieng Basque–Aquitaine section The Loubieng section (latitude/longitude 43o 25′ 37.32″ N/0o 44′ 40.27″ W) is located in an abandoned quarry near this town in SW France (Basque–Aquitaine Basin). It has been previously analyzed in an integrated calcareous nannofossil and foraminifera study (Steurbaut and Sztrákos, 2008). The finding of the acme of the nannofossil family Braarudosphaeraceae at the lithological change from limestone-dominated (Lasseube Formation) to marly sedimentation (Latapy Member of the Pont–Labau Formation) was indicative of correlation to the D–S boundary as established at the Zumaia GSSP at the base of the red marls of the Itzurun Formation. This bioevent coincides with the original D–S boundary as originally defined in Denmark at the start of clastic sedimentation at the base of the Lellinge Greensand Formation suggesting a common link to this lithological change across Europe. In addition, the study of Steurbaut and Sztrákos (2008) provides a detailed succession of calcareous planktic bioevents spanning the upper Danian and lower Selandian interval allowing high-resolution correlations to be made. Here, we have sampled the lower part of the Loubieng section for paleomagnetic purposes to try to locate chron C27n and logged the succession to be able to perform a bed-to-bed correlation with Zumaia. The upper Danian–lower Selandian deposits dip 5–15° to the south and can be followed continuously

along the 300 m long and 20 m high carved front of the quarry with some minor disrupting normal faults with throws between 1 and 3 m. The studied section is located at the central part of the quarry front and starts above a slumped limestone interval denoted “D” in Steurbaut and Sztrákos (2008). The succession consists of an alternation of whitish limestone beds and thin pale grey marly intercalations that belong to the upper 14 m of the Lasseube Limestone or Lasseube Formation (Steurbaut and Sztrákos, 2008 and references therein). These rhythmic limestones are overlain by grayish and locally pinkish marls from the Latapy Member representing the lowermost unit of the Pont–Labau Formation. Several centimeters thick turbiditic levels are found throughout the succession than can be traced along the quarry front in the different faulted blocks as an aid for correlation. A conspicuous 60–80 cm thick calciturbidite (locally as a massive pebbly sandstone), noted as level “E”, is present at about 5 m from the section base and 8 m below the D–S boundary. 3. Magnetostratigraphy Samples for paleomagnetic analysis were taken with a portable gasoline-powered drill and/or as hand-samples. Samples were oriented in situ with an orienting device and magnetic compass and subsequently standard cylindrical or cubic specimens were cut in the laboratory for analysis. Natural remanent magnetization (NRM) and remanence through demagnetization were measured on a 2G Enterprises DC SQUID high-resolution pass-through cryogenic magnetometer (manufacturer noise level of 10− 12 Am2) operated in a shielded room at the Istituto Nazionale di Geofisica e Vulcanologia in Rome, Italy. A Pyrox oven in the shielded room was used for thermal demagnetizations and alternating field (AF) demagnetization was performed with three orthogonal coils installed inline with the cryogenic magnetometer. Progressive stepwise AF demagnetization was routinely used and applied

514

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

after a single heating step to 150 °C. AF demagnetization included 14 steps (4, 8, 13, 17, 21, 25, 30, 35, 40, 45, 50, 60, 80, 100 mT). Samples that did not fully demagnetize after this protocol were further demagnetized thermically and a number of samples from Zumaia were demagnetized using only thermal treatment. Characteristic remanent magnetizations (ChRM) were computed by least-squares fitting (Kirschvink, 1980) on the orthogonal demagnetization plots (Zijderveld, 1967). The ChRM declination and inclination were used to derive the latitude of the virtual geomagnetic pole (VGP) of each sample. This parameter was taken as an indicator of the original magnetic polarity, normal polarity being indicated by positive VGP latitudes and reverse polarity by negative VGP latitudes. 3.1. The Bjala Bulgarian sections A total of 38 and 32 samples were collected from the Bjala E and Bjala 1 section respectively. Section Bjala E completely overlaps Bjala1 so sampling on the later was devised to the location of chron C27n and to cover the additional stratigraphic succession at the top. The entire covered stratigraphic interval includes about 21 m of succession and a total of 58 lithological basic couplets that have been numbered from top to bottom (Fig. 3). The intensity of the NRM in the studied rocks usually ranges between 0.1 mA/m and 0.6 mA/m with a few marly samples showing higher intensities up to 4 mA/m. Upon stepwise demagnetization two components can normally be distinguished in addition to a small viscous component removed at the first demagnetization step likely related to a drilling/handling overprint. A low-field components conforming to the present geomagnetic field is removed up to fields of 13–21 mT. Then, a characteristic remanent magnetization (ChRM) is removed up to the maximum field applied (100 mT) that trends toward the origin of the diagram and presents dual polarity (Fig. 4). The relative low coercivity of this component suggests that magnetite is most likely the magnetic carrier. A similar gentle dip toward the W–SW in both sections prevents a significant fold test to be performed but the primary nature of the ChRM component is guaranteed by: 1) the dual polarity and the consistent results among the two sections; 2) the removal of the ChRM after a present-day field and viscous component; and 3) the lack of lithological correlation with polarity. The mean directions from the normal and reverse directions are not antipodal (Fig. 4D) and this may denote partial overlap of the present geomagnetic component to the ChRM component. The normal mean direction appears more westerly and steeper that the reverse component. Although no demagnetization data and mean directions were published in the study of Preisinger et al. (1993), observation of their Fig. 5 with plotted declinations and inclinations along their 70 m long section seemingly shows the same effect among normal and reverse directions which may arise from partial overlap of the present field. Our results clearly depict a consistent normal polarity zone comprising cycles 31 to 43 (Fig. 3) that can be inferred from biostratigraphic results (see below) to be chron C27n. The D–S boundary as defined by the secondary evolutionary radiation of the calcareous nannofossil genus Fasciculithus is placed at the top of cycle 1 at the passage to a marly unit (see below). Therefore, the D–S boundary is located about 30 precession-related cycles above C27n top at Bjala. 3.2. The Basque–Aquitaine sections 3.2.1. Zumaia–Aitzgorri The magnetostratigraphy from the Zumaia–Aitzgorri section was presented in Dinarès-Turell et al. (2003). Three magnetization components (L, I and H) were recognized upon thermal demagnetization, in addition to a viscous component removed below 100–150 °C. A low-temperature component (L) is unblocked between 100 and 150 °C and 250 and 300 °C and conforms to the present-day geomagnetic field. At intermediate temperatures between 250 and 300 °C and 450 and 500 °C a second component (I) is removed. Above

500 °C a third component (H) trending toward the origin of the diagram is usually fully removed up to temperatures of 600 °C (occasionally at higher temperatures). The H component displays dual polarity and represents the primary direction on which the magnetostratigraphy was based. Usually component H is a very small percentage of the total NRM. Component I always had a reverse polarity and represents a pre-tilting overprint of uncertain origin and nature and can be a dominant contributor to the NRM or be almost absent along different intervals of the Danian succession. There was no clear pattern for the I component that would support and early diagenetic overprint similar to other marine cyclic succession in which a delayed magnetic acquisition mechanism (up to few precession cycles) has been demonstrated along detailed study along the reversal boundaries (e. g., Dinarès-Turell and Dekkers, 1999 and references therein). The main difference at Zumaia is that this reverse component I is not ubiquitous to the normal-to-reverse transitions but, rather, variably occurs at any position along the successive normal or reverse magnetozones defined within the 50 m long Danian succession (Dinarès-Turell et al., 2003). However, the issue here is that the magnetostratigraphy published in Dinarès-Turell et al. (2003) places the top of C27n about 34 precession cycles below the D–S boundary. This result is in contrast to the results from the Bjala sections presented herein which show ~30 precession cycles for the same interval. Moreover (see below), the cyclostratigraphic pattern identification of eccentricity related bundles definitely indicates that the C27n/C26r chron boundary occurs 4 precession cycles higher (i.e., younger) at Bjala with respect to Zumaia. Hence, we have resampled the Zumaia– Aitzgorri section to better ascertain the position of this chron boundary given the outcome from Bjala and the relatively complex NRM structure envisaged earlier at Zumaia. Fifteen new samples have been taken from cycles 162 to 167 just above the C27n/C26r chron boundary as originally established between cycles 161–162 (Fig. 5). One conspicuous feature is the observation of the color banding in the limestone beds of some of the considered cycles. It is obvious that for cycles 162, 163 and 166 reddish to pinkish color occurs both at the base and at the top of these limestone beds whereas the central part remains whitish (Fig. 5). Samples have been taken both from the whitish and reddish–pinkish parts. Isothermal remanent magnetization (IRM) acquisition experiments up to 2.5 T (Fig. 6) on representative samples indicate that the whitish limestones saturate at relatively low fields of less than 1 T (80% of the IRM attained already at 0.1 T) typical for magnetite-like minerals. Instead, reddish samples do not completely saturate at the maximum applied field suggesting a high-coercivity mineral to be also present (most likely hematite, see below). Note also that reddish samples have an IRM intensity of about one order of magnitude higher with respect to the whitish limestones (Fig. 6). The combined initial single 150 °C heating step followed by AF and final thermal demagnetization protocol has been used to demagnetize the NRM (Fig. 7). It can be seen that similar to the previous thermal demagnetization only data (Dinarès-Turell et al., 2003), three magnetic components can be distinguished. The initial viscous and L components are removed at about 13 mT. The reverse I component unblocks during AF demagnetization up to 100 mT. Component H is unblocked at the end up to temperatures of 550–600 °C. Collectively, the different NRM demagnetization strategies and IRM data permit to assign to hematite the magnetic carrier of component H whereas component I must be blocked in the “magnetite” fraction. Component H is indeed absent in the whitish lithologies whereas reddish lithologies from the same limestone beds contain that component. The relatively lowtemperature unblocking of the H component is consistent with authigenic fine-grained pigmentary hematite (most likely early diagenetic) and therefore the ChRM is interpreted as an early postdepositional remanence (CRM) rather that a detrital remanence (DRM) which is commonly carried by relatively coarse-grained hematite (specularite) (e. g., Turner and Ixer, 1977; Channell et al., 1982; Dekkers and Linssen, 1989). The early origin and ability for an

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

515

Fig. 3. Lithologic logs for the Bjala 1 and Bjala E sections with paleomagnetic results (crosses: no data; open circles: unreliable directions; closed circles: reliable directions) and magnetostratigraphic interpretation. Numbering of the precession-related couplets starts at the D–S boundary and proceeds downward. Note that the Bjala E section has the Upper Danian truncated by a tectonic contact at cycle 8/9. Position of paleomagnetic and biostratigraphic samples is indicated.

516

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

A)

B)

B27-1 13 mT

B40-1

up/W

30 mT

17 mT 13 mT

up/W

30 mT 150oC

C)

up/W

B52-1

100 mT

N N

100 mT 13 mT N

150oC

150oC

NRM 3.768 mA/m

NRM 0.739 mA/m

NRM 0.469 mA/m

D)

Sample N Dec. Inc. k α 95 Group R 54 189.3 -13.1 7.8 7.4 Group N 30 1.0 38.7 8.1 9.8

Sample Dec. Inc. k Reverse 179.5 -29.9 8.8 Normal 332.9 45.9 7.8

α 95 6.9 10.1

Fig. 4. (A–C) Examples of orthogonal demagnetization diagrams representative of normal (B) and reverse (A, C) samples in bedding-corrected coordinates from the Bjala sections (open and closed symbols denote projections onto the vertical and horizontal planes, respectively). The stratigraphic position in meters and NRM intensity and some demagnetization steps are indicated. (D) Stereographic projections of the ChRM components before (in situ) and after bedding correction (tilt corrected) are shown (open and closed symbols indicate projections onto the upper and lower hemisphere, respectively), together with the mean direction and statistics of normal and reverse polarity directions.

authigenic/microcrystalline hematite population to acquire an almost primary direction (slightly delayed with respect to a DRM also from hematite) has been observed in some red-bed sequences (e.g., DinarèsTurell et al., 2005) whereas in others, a complex situation of several generations of authigenic pigmentary hematite carrying both early and late CRMs coexisting with a primary DRM has been observed (e.g., Roy and Park, 1972; Roy and Lapointe, 1978). The crucial point here is that the reddish samples from limestone beds from cycles 162–164 (and possibly 165) unblock an H component with northerly declination after tilt correction and variable shallow inclination (Fig. 7 and Supplementary Fig. 1). It is not clear if this is a result of partial overlap of components or if they represent normal to intermediate/transitional directions as we are close to the normal-to-reverse C27n/C26r chron boundary. We retain those samples with northerly H component as representing normal primary directions from C27n. As the first limestone bed with a fully reverse H component is cycle 166 (see Fig. 7F) we update the position of C27n/C26r at cycle 165 (Fig. 5 and Supplementary Fig. 2). Note that the whitish parts from cycles 162–163 only contain the reverse I component blocked in “magnetite” that we regard as a secondary component. Component I directions appear somewhat scattered probably due to partial overlap with the presentday field L component and/or H component (see Supplementary Fig. 1). Coloring along the hemipelagic Danian limestones is chiefly controlled by climatic forcing at the astronomical band where whitish color beds are related to relatively higher carbonate content and

eccentricity minima whereas reddish–pinkish colors are related to relatively higher detrital input and/or oxidizing conditions as in the marl beds from the basic precession couplets (precession minima or insolation maxima) which in turn are modulated by eccentricity (Dinarès-Turell et al., 2003). Reddish coloring of the limestone beds of cycles 162, 163 and 166 can be regarded as original (primary) transitions to the marl beds above and below but secondary early or late diagenetic and/or biologic remobilization and diffusion from these marl beds cannot be ruled out. Indeed, burrowing has been observed throughout the Danian succession but preferentially remobilizes material from the reddish marl beds into the limestone beds above. This could explain the reddish tanning at the lower part of the limestone beds but not at the top part of these limestone beds. An instructive observation can be made where faults and joints, that occur all along the Aitzgorri headland, cross-cut bedding. In some of those, decoloration that progresses sideway from them is obvious suggesting a relatively late origin for such decolorations. In one of these joints cutting cycle 163 a few meters away from the location shown in Fig. 5B it can be observed that fluids that have probably circulated away of the joint (at least 20 cm) have turned completely whitish at cycle 163. Henceforth, the possibility that some of the bedding-parallel partitions, as the ones depicted for cycles 162 and 162 in Fig. 5C, could act in a similar way producing bedding-parallel decoloration in the center, of an otherwise more reddish limestone bed, cannot be ruled out. Most likely, combinations of the outlined processes above have been acting with

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

517

A) B)

C)

Fig. 5. (A) Lithologic log from the Zumaia–Aitzgorri section that contains chron C27n. Samples and original results (Dinarès-Turell et al., 2003) and new samples studied herein are shown along magnetostratigraphic interpretations. (B–C) Filed photographs showing precession-related couplets 160–163 and location of samples studied herein. Note the coloring of the limestone beds (see text for explanations).

different proportions and intensity in time and space contributing to the actual complexity. In this scenario, component H is mostly consistent with an early authigenic fine-grained hematite although a small contribution of detrital hematite may also be present when occasionally component H unblocks at higher temperatures than 600 °C. Component I blocked in “magnetite” is best explained as a widespread secondary pre-tilting overprint. The coexistence in the same limestone bed of whitish intervals carrying component I only (locally related to crosscutting joints, faults and bedding partitions) and reddish intervals carrying both the I and H components is interpreted by diagenetic/ chemical bleaching that locally has erased away component H. 3.2.2. Zumaia–Artadi In an effort to duplicate the magnetostratigraphic results from the Zumaia–Aitzgorri section the nearby Zumaia–Artadi section was sampled in detail. A total of 121 samples were drilled in the interval comprising cycles 144 to 188 with higher resolution (almost with adjacent cores) in the interval from cycles 159 to 171 to pinpoint the C27n/C26r chron boundary (Fig. 8). Detailed bed-by-bed correlation between both sections is straightforward and only subtle differences in color and/or bed thicknesses are observed. Overall the Zumaia– Artadi section appears somewhat lighter in color especially in its lower part but is otherwise analogous to the Zumaia–Aitzgorri section. Strikingly, the combined demagnetization strategy outlined above does not clearly identify normal ChRM directions throughout the expected position of C27n (cycles 151 to 165). In this interval, only a few samples present northerly and downward directions of poor quality (Fig. 9C and E) or southerly shallow directions (Fig. 9B and D) which appear to be mostly blocked in “magnetite” as limestone color along this interval is predominantly whitish (see also Supplemental Fig. 3). Reddish lithologies located above and below the interval from cycles 151 to 165 display unambiguous reverse hematite H directions

(Fig. 9A and F). Directions from within that interval and outside of it reveal some differences (Supplemental Fig. 4) with directions being more scattered and shallower in the interval comprising cycles 151 to 165 which could be indication of overlap of components. There is not a fully satisfactory explanation for the presence of this blurred C27n at Artadi (Supplemental Fig. 3), but it appears that a combination of factors may have lead to this situation. These include lack of hematite along this interval, differential overprinting and overlap of components. 3.2.3. Loubieng The Loubieng section, located about 125 km from Zumaia, contains the D–S boundary and has previously been studied biostratigraphically in detail (Steurbaut and Sztrákos, 2008). Here, it has been explored for magnetostratigraphic purposes and a bed-by-bed correlation to the Zumaia–Aitzgorri section can easily be achieved (Fig. 10). Twenty-seven limestone beds have been sampled from the lower part in order to locate chron C27n. Unfortunately, all samples display a reverse direction unblocked by 100 mT (Fig. 9G, H, I) and therefore blocked in a magnetite-like mineral (only whitish or light grey color is present for the entire Danian succession here). Bedding is subhorizontal and it is difficult to ascertain the age of this component but considering that C27n is not recorded it seems an overprint consistent with the intermediate I component from Zumaia (see also Supplemental Fig. 5). The unsuccessful determination of chron C27n at Zumaia–Artadi and Loubieng sections could appear to cast some doubt to the results from the original Zumaia–Aitzgorri section where C27n was first identified in Dinarès-Turell et al. (2003) and refined herein. However, the unambiguous and consistent results from the Bjala sections fully support the outcome from Zumaia–Aitzgorri (Fig. 10) (see also biostratigraphic and cyclostratigraphic inferences below).

518

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

A)

taken from the marly interval between carbonate cycles (Fig. 3). All samples were processed using the standard methods of preparation for quantitative analysis (Bown, 1998). The smear slides were fixed using Canada balsam as adhesive medium. Samples were analyzed under a Zeiss Axioscop 40 Pol polarizing microscope at 1000× or 1250× magnification. Microphotographs of important calcareous nannofossil taxa were produced using ProgRes® CapturePro 2.5 digital camera. They are illustrated on the paleontological plates (Plates I–V). For quantitative estimates the evaluation of the relative abundance of 20 selected nannofossil taxa (shown on Supplemental Figs. 6 and 7) was carried out. The rest of the nannofossil association, comprising 23–25 less abundant species, was considered separately. The quantitative study is based on counting the specimens of different taxa per field of view (FOV). Three to five traverses in the central part of each smear slide (2 × 2 cm) are considered, comprising a minimum of 300 FOV. The following categories were estimated: abundant (A), N10 specimens/FOV; common (C), 1−10 specimens/FOV; few (F), 1 specimen/b20 FOV; rare (R), 1 specimen/N20 FOV. The standard zonal scheme of Martini (1971) was applied here, although the high-resolution low latitude scheme of Varol (1989) (reference section Kokaksu, Zonguldak, N Turkey, south Black sea coast) can also be applied to some extent. The taxonomy is mainly according to Perch-Nielsen (1985), with modification of Van-Heck et al. (1987). The calcareous nannofossil material (smear slides and microphotos) is stored at the moment in the collection of the Geological Institute BAS, Sofia (Bulgaria), but will be permanently stored in the collections of the Paleontological Museum of Sofia University (PM-SU), Sofia.

B)

4.2. Results Fig. 6. Raw (A) and normalized (B) isothermal remanent magnetization (IRM) acquisition curves for representative whitish and reddish colored limestone from Zumaia–Aitzgorri.

4. Calcareous nannofossil biostratigraphy 4.1. Material and methods A total of 30 samples (BB1–BB30) have been studied from Bjala E section, corresponding with samples taken for magnetostratigraphy (Fig. 3). Thirty-two samples were examined from Bjala 1 section, usually

A)

DZ1-1

B)

The calcareous nannofossil assemblages recovered from all Bjala samples exhibit excellent preservation, with no sign of dissolution and/or overgrowth. The species diversity is high, varying between 30 and 45 species at different levels. One important and relevant difference between Bulgarian and Basque (and also SW Aquitaine and North Sea) basins should be emphasized: the complete absence of Braarudosphaera bigelowii in the Bulgarian D–S succession. In the Basque and North Sea area its influx (abundance) is used for biostratigraphic purposes in the Uppermost Danian (e.g., Clemmensen and Thomsen, 2005; Steurbaut and Sztrákos,

DZ4-1

DZ3-1

up/W

up/W

up/W

C)

N N

N

D)

DZ6-1

E) up/W

DZ7-1

F)

up/W DZ20A

up/W N N N

Fig. 7. (A–F) Bedding-corrected orthogonal demagnetization diagrams from the Zumaia–Aitzgorri section (open and closed symbols denote projections onto the vertical and horizontal planes, respectively). The corresponding cycle, lithology color, NRM intensity and some demagnetization steps are indicated.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

519

reddish pinkish whitish Fig. 8. Lithologic logs and correlation between the Zumaia–Aitzgorri and Zumaia–Artadi sections. The precession-related couplets and eccentricity related bundles or E-cycles are indicated following numbering as in Dinarès-Turell et al. (2003) that proceeds from the K–T boundary upwards. Note that position of C27n at Zumaia–Artadi is inferred from correlation to the Zumaia–Aitzgorri section.

2008; Bernaola et al., 2009) as a key to pinpoint the D–S boundary. The abundance of B. bigelowii is considered to indicate environmental changes to more near-shore, marginal conditions (Clemmensen and

Thomsen, 2005). At Bjala B. bigelowii is sporadically observed as single specimens in 2–3 samples, one of them being illustrated on Plate IV (14), but does not occur consistently in the section and therefore no sharp

520

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

A)

up/W

ZA-2B B)

ZA-8A

C)

ZA-10B up/W

up/W

N N

N

D)

up/W ZA-11C

E)

up/W

ZA-88A

F)

ZA-83A

N

N N

G)

up/W LB1

H)

up/W

LB7

I)

LB11

up/W

N N

N

Fig. 9. Bedding-corrected representative orthogonal demagnetization diagrams from the Zumaia–Artadi section (A–F) and Loubieng (G–I) sections (open and closed symbols denote projections onto the vertical and horizontal planes, respectively). The corresponding cycle, NRM intensity and some demagnetization steps are indicated.

decrease is observed at the D–S boundary which can be established both by other biostratigraphic constraints and precession-related cycle counting (see below). To facilitate correlation between Bulgarian and Basque D–S successions, we adopt the approach and definitions of major nannofossil events given by Bernaola et al. (2009) for Zumaia — first rare occurrence (FRO), first common occurrence = first occurrence (FCO, = FO), first radiation of small Fasciculithus species (first radiation of fasciculiths), second radiation of Fasciculithus (FO of Fasciculithus billii, Fasciculithus janii, etc.). 4.2.1. Biostratigraphy and major bioevents The studied sections Bjala 1 and Bjala E fall within the upper part of Martini's zone NP4 and lower part of NP5 (subzone NTp 7A to zone NTp 9 of Varol, 1989). The Bjala 1 section is more complete, including the Upper Danian, the D–S boundary and the Lower Selandian, whereas Bjala E has a restricted Upper Danian (NP4 truncated at its top) with samples containing Fasciculithus tympaniformis (NP5) on the marls immediately above a sharp lithological contact interpreted as a tectonic disruption as outlined above. The following major bioevents are recorded and their reliability for correlation (interbasinal) is evaluated (see Supplemental Figs. 6 and 7 for a complete account): 1. FRO and FCO of Neochiastozygus perfectus. The taxonomical identification of this species is rather difficult in Bjala because the presence of a gradual evolutionary lineage between Neochiastozygus modestus and N. perfectus, recorded in most of samples (see Plate I, figs. 3–4).

Moreover, its size varies greatly — from small (4–5 μm) to large (N7 μm) forms. Therefore, it is an inappropriate marker for correlation. It is recorded in different positions in Bjala 1 and Bjala E section (Fig. 10). 2. FRO of Chiasmolithus edentulus. The usefulness of this event, especially for the Bulgarian succession, is evident. FRO of the species is represented by 3–4 specimens only. It is recorded both in Bjala 1 (sample CL45, Plate I, figs. 9–10) and Bjala E sections (sample BB1). This datum is pinpointed in Loubieng (sample L4, Steurbaut and Sztrákos, 2008), as well as in Zumaia (Bernaola et al., 2009) (Fig. 10). 3. FCO of Chiasmolithus edentulus. The event is clearly recognizable in Bjala. It occurs shortly after FRO of the species, respectively in sample CL47 and BB3 (Plate I, figs. 11–12). Its documentation in many locations implies it has a high interbasinal correlation potential, especially between the North Sea and Tethys. It is evidenced in the North Sea (Van-Heck et al., 1987; Varol, 1989), Zumaia (Bernaola et al., 2009) and Loubieng (Steurbaut and Sztrákos, 2008). However, in Bulgarian successions it is pinpointed almost at the middle of Chron C27n, whereas at Zumaia appears to occur a few precession cycles higher in the section. Agnini et al. (2007) and Westerhold et al. (2008) reported the lowest occurrence of “Chiasmolithus bidens group (including C. edentulus, Chiasmolithus solitus, Chiasmolithus bidens)” in the middle of the Chron C27n, which is consistent with our results from Bjala. 4. FRO of Sphenolithus primus. Our observations about this datum confirm these of Bernaola et al. (2009). The first rare occurrence of primus is difficult to detect due to its very scarce distribution. In

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

521

Fig. 10. Lithologic logs, biostratigraphic results and cyclostratigraphic correlation between Loubieng, Zumaia–Aitzgorri and the Bjala sections. The precession-related couplets and eccentricity related bundles or E-cycles for the Zumaia section follow numbering as in Dinarès-Turell et al. (2003) that proceeds from the K–T boundary upwards. Individual couplets from Loubieng and Bjala start at the D–S boundary and proceed downward. A straightforward bed-by-bed correlation is established following the identification of eccentricity related bundles following the same numbering in all three sections (see text for discussion). Data from Bernaola (2002), Dinarès-Turell et al. (2003), Bernaola et al. (2009) and Steurbaut and Sztrákos (2008).

522

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate I. Bjala 1 D–S. Abbreviations: B1 = section Bjala 1; BE = section Bjala E; c.p. = cross-polarized light; t.l. = transmitted light. All microphotos × 3000. 1. 2. 3–4. 5. 6. 7. 8. 9–10. 11–12. 13. 14. 15. 16. 17. 18. 19. 20.

Neochiastozygus perfectus Perch-Nielsen, 1971. B1, sample CL1, c.p. Neochiastozygus perfectus Perch-Nielsen, 1971. B1, sample 2, c.p. Transitional forms between Neochiastozygus modestus Perch-Nielsen, 1971 and N. perfectus Perch-Nielsen, 1971. B1, sample CL6, c.p. Neochiastozygus saepes Perch-Nielsen, 1971. B1, sample CL4, c.p. Neochiastozygus saepes Perch-Nielsen, 1971. B1, sample CL1, t.l. Neochiastozygus primitivus Perch-Nielsen, 1981. B1, sample CL4, t.l. Neochiastozygus modestus Perch-Nielsen, 1971. B1, sample CL6, t.l. Chiasmolithus edentulus van Heck and Prins, 1987. B1, sample CL45, c.p. Chiasmolithus edentulus van Heck and Prins, 1987. B1, sample CL47, c.p. Toweius pertusus (Sullivan, 1965) Romein, 1979. B1, sample CL1, c.p. Coccolithus subpertusus (Hay and Mohler, 1967) Wei and Pospichal, 1991. B1, sample CL4, c.p. Placozygus sigmoides (Bramlette and Sullivan, 1961) Romein, 1979. B1, sample CL4, c.p. Prinsius bisulcus (Stradner, 1963) Hay and Mohler, 1967. B1, sample 3, c.p. Prinsius martini (Perch-Nielsen, 1969) Haq, 1971. B1, sample CL16, c.p. Ellipsolithus macellus (Bramlette and Sullivan, 1961) Sullivan, 1964. B1, sample CL45, c.p. Cruciplacolithus tenuis (Stradner, 1961) Hay and Mohler, 1967. B1, sample CL1, c.p. Cruciplacolithus tenuis (Stradner, 1961) Hay and Mohler, 1967. B1, sample CL4, c.p.

Plate II. Bjala 1 D–S. (see on page 524) 1–2. 3–4. 5. 6–7. 8. 9–10. 11. 12. 13. 14–15. 16. 17. 18. 19–20.

Chiasmolithus edentulus van Heck and Prins, 1987. B1, sample CL45, 1 — t.l., 2 — c.p. Chiasmolithus edentulus van Heck and Prins, 1987. B1, sample CL47, c.p. Bomolithus elegans Roth, 1973. B1, sample CL59, c.p. Sphenolithus primus Perch-Nielsen, 1971. B1, sample CL49, c.p. Coccolithus subpertusus (Hay and Mohler, 1967) Wei and Pospichal, 1991. B1, sample CL49, c.p. Fasciculithus vertebratoides Steurbaut and Sztrákos, 2008. B1, first radiation of fasciculiths, sample CL63, c.p. Fasciculithus aff. Fasciculithus sp.3 Bernaola 2009. B1, sample CL63, c.p. Fasciculithus ulii Perch-Nielsen, 1971. B1, sample CL63, c.p. Fasciculithus vertebratoides Steurbaut and Sztrákos, 2008. B1, sample CL63, c.p. Fasciculithus transitional form between F. vertebratoides Steurbaut and Sztrákos, 2008 and F. billii Perch-Nielsen, 1971. B1, sample CL63, c.p. Fasciculithus sp. 1 Bernaola's. B1, sample CL63, c.p. Fasciculithus sp. 2 Bernaola's. B1, sample CL63, c.p. Fasciculithus sp. nov. 1, (short column). B1, sample CL63, c.p. Fasciculithus sp. aff. Fasciculithus sp. 5 Bernaola's. B1, sample CL63, c.p.

Plate III. Bjala 1 D–S. (see on page 525) 1. 2–5. 6. 7–8. 9–10. 11–12. 13–14. 15. 16–18. 19–20.

Fasciculithus ulii Perch-Nielsen, 1971. B1, sample CL63, c.p. Fasciculithus ulii subsp. Nov. minor. B1, sample CL63, c.p. Sphenolithus primus Perch-Nielsen, 1971. B1, sample 1, c.p. Fasciculithus sp. nov.2 (long column). B1, sample 6 (Second radiation of fasciculiths); 7— c.p., 8 — t.l. Fasciculithus billii Perch-Nielsen, 1971. B1, sample 6; 9 — c.p., 10 — t.l. Fasciculithus vertebratoides Steurbaut and Sztrákos, 2008. B1, sample 8; 11 — c.p., 12 — t.l. Fasciculithus billii Perch-Nielsen, 1971. B1, sample 8; 13 — c.p., 14 — t.l. Fasciculithus involutus Bramlette and Sullivan, 1961. B1, sample 9, c.p. Fasciculithus janii Perch-Nielsen, 1971. B1; 17 — sample 10; 16, 18 — sample 11, c.p. Fasciculithus tympaniformis Hay and Mohler, 1967. B1, First occurrence (FO) in sample 10; 19 — sample 10; 20 — sample 11, c.p.

Plate IV. Bjala E D–S. (see on page 526) 1–4. 5. 6. 7–8. 9. 10. 11. 12. 13. 14. 15.

Chiasmolithus edentulus van Heck and Prins, 1987. First rare occurrence (FRO) in BE, sample BB1; 1, 3 — c.p., 2, 4 — t.l. Chiasmolithus edentulus van Heck and Prins, 1987. BE, First occurrence (FO) in sample BB3, c.p. Toweius spp. BE, sample BB1, c.p. Coccolithus subpertusus (Hay and Mohler, 1967) Wei and Pospichal, 1991. BE; 7 — sample BB3, 8 — sample BB10, c.p. Ellipsolithus macellus (Bramlette and Sullivan, 1961) Sullivan, 1964. BE, sample BB5, c.p. Cruciplacolithus tenuis (Stradner, 1961) Hay and Mohler, 1967. BE, sample BB10, c.p. Sphenolithus primus Perch-Nielsen, 1971. BE, sample BB8, c.p. Chiasmolithus edentulus van Heck and Prins, 1987. BE, sample BB8, c.p. Chiasmolithus sp. aff. Ch. consuetus (Bramlette and Sullivan) Hay and Mohler, 1967. BE, sample BB3, c.p. Braarudosphaera bigelowii (Gran and Braarud, 1935) Deflandre, 1947. BE, single rare specimen in sample BB1, c.p. Markalius apertus Perch-Nielsen, 1979. BE, coccosphere in sample BB3, c.p.

Plate V. Bjala E D–S. (see on page 527) 1–2. 3–4. 5. 6. 7. 8. 9–10. 11–12. 13–14. 15–16. 17–18. 19. 20.

Neochiastozygus transitional form between Neochiastozygus modestus Perch-Nielsen, 1971 and Neochiastozygus perfectus Perch-Nielsen, 1971. BE, sample BB6; 1 — c.p., 2 — t.l. Neochiastozygus perfectus Perch-Nielsen, 1971. First rare occurrence (FRO) in BE, sample BB12; 3 — c.p., 4 — t.l. Fasciculithus sp. aff. Fasciculithus sp.4 Bernaola's. BE, sample BB5, c.p. Bomolithus elegans Roth, 1973. BE, sample BB11, c.p. Fasciculithus sp. aff. Fasciculithus sp.4 Bernaola's. BE, sample BB8, c.p. Fasciculithus cf. billii Perch-Nielsen, 1971. BE, sample BB7, c.p. Fasciculithus sp. 2 or sp.3 of Bernaola. BE, first radiation of fasciculiths, sample BB6; 9 — c.p., 10 — t.l. Fasciculithus sp. 2 or sp.3 of Bernaola. BE, first radiation of fasciculiths, sample BB6; 11 — c.p., 12 — t.l. Fasciculithus sp. 4 of Bernaola. BE, first radiation of fasciculiths, sample BB6; 13 — c.p., 14 — t.l. Fasciculithus sp. aff. Fasciculithus sp.5 of Bernaola. BE, first radiation of fasciculiths, sample BB6; 15 — c.p., 16 — t.l. Fasciculithus sp. 2 or sp.3 of Bernaola. BE, sample BB7, 17 — c.p., 18 — t.l. Fasciculithus sp. 2 of Bernaola. BE, sample BB7, c.p. Heliolithus cantabriae Perch-Nielsen, 1971. BE, sample BB7, c.p.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate I.

523

524

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate II (caption on page 522).

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate III (caption on page 522).

525

526

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate IV (caption on page 522).

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Plate V (caption on page 522).

527

528

5.

6.

7.

8.

9.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

Bulgaria it occurs in sample CL49 (within C27n) and possibly in sample BB8. In all locations, it appears that the lower portion of the range of S. primus is poorly documented. First radiation of Fasciculithus. This event is absolutely distinct and clearly recognizable in the Bulgarian successions. It is evidenced in samples CL57–CL63 (Bjala 1) and BB6–BB13 (Bjala E). It spans only 2.00–2.40 m of the sedimentary succession, similarly to Zumaia. The first, usually small-sized representatives of the genus Fasciculithus occur, marking the first radiation: Fasciculithus sp.2′ Bernaola, Fasciculithus sp.3′ Bernaola, and Fasciculithus aff.sp.5′ Bernaola. At the end of this first radiation, Fasciculithus vertebratoides Steurbaut and Sztrákos, 2008, Fasciculithus sp.1′ Bernaola, Fasciculithus ulii PerchNielsen, 1971, F. ulii subsp. nov minor and Fasciculithus sp.nov1 appeared (Plate II, figs. 9–20; Plate III, figs. 1–5). Elsewhere — Bjala, Zumaia, the event is fixed close to C27n/C26r chron boundary. FRO and subsequent FCO of Bomolithus elegans. In Bulgarian succession this bioevent is recorded simultaneously or shortly after the first radiation of Fasciculithus (Plate II, fig. 5). So far it is not evidenced in Zumaia, but mentioned in Loubieng (Steurbaut and Sztrákos, 2008, sample L28) in the basal Selandian. Bomolithus elegans has a distinct morphology and is easily recognizable in the samples, therefore could be potentially appropriate datum, although looks diachronic. FCO or FO of Sphenolithus primus. This bioevent is well documented in Bjala E section, occurring at sample BB19. In Bjala and Zumaia it is recorded well above the first radiation of fasciculiths, whereas in Loubieng it is just above it. Eventually, diachroneity of this event should be considered, as indicated by Fuqua et al. (2008) on their Fig. 11. Second radiation of Fasciculithus. The bioevent is recorded in Bjala 1 section only (sample 8), because the succession here is complete. The simultaneous FO and relative abundance of Fasciculithus billii, F. janii, Fasciculithus sp.nov. 2 (Plate III, figs. 7–8; 9–10, 16–18) and previously appeared F. ulii and F. vertebratoides manifested the event. Shortly after, F. involutus (Plate III, fig. 15) occurs. FRO and FCO of Fasciculithus tympaniformis. Evidenced in Bjala 1 section only (samples 10–11, Plate III, figs. 19–20). This is a widely recognizable bioevent, recorded in Zumaia and Loubieng. The FCO of F. tympaniformis marks the NP4/NP5 zonal boundary. Having in hand all available data, the position of this datum should be

precised in detail with respect to the D–S stage boundary as it appears to occur close to it but in a somewhat different cyclostratigraphic position among sections. In summary, considering the data from the Basque–Aquitaine sections (Zumaia, Loubieng), the Bjala Tethyan–Boreal section and the South Atlantic ODP Site 1262 it can be concluded that the most reliable biostratigraphic datums useful for interbasinal correlation are as follows: (1) the FO of Chiasmolithus edentulus; (2) the first radiation of Fasciculithus; (3) the second radiation of Fasciculithus; (4) the FO of Fasciculithus tympaniformis. The last two bioevents bracket the D–S boundary. 5. Cyclostratigraphy 5.1. Cycle pattern recognition and correlation between sections The calcareous nannofossil data reported above combined with the magnetostratigraphy from the Bjala sections (Fig. 3) allows identifying the D–S boundary at the topmost limestone bed numbered 1 (Fig. 10). This places the D–S boundary 30 precession cycles above the top of chron C27n which is consistent with the new data from Zumaia, implying that limestone beds from couplets 1 to 31 from Bjala correlate to beds 195–166 at Zumaia (Fig. 10). At Zumaia, the marl–limestone couplets along the Paleocene are organized in bundles of 4–6 basic couplets of different characteristics described in Dinarès-Turell et al. (2003). These bundles are related to the 100-ky eccentricity cycles and were termed E-cycles and numbered from the K–Pg boundary upwards. The boundaries between these 100-ky cycles were chosen approximately at the mid-points of the more marly intervals representing eccentricity maxima whereas the more carbonate part at the center of the E-cycle correlate with eccentricity minima. At Zumaia these prominent carbonate beds are usually thicker, with less distinct marly partitions and lighter in color (Fig. 10). The Bjala section is overall less carbonatic than Zumaia but a similar arrangement into bundles of 4–6 basic couplets is obvious (Fig. 11). The identified eccentricity related bundles match perfectly among all studied sections (Fig. 10). The correlation is very robust from the D–S boundary down to E-cycle 36 with the top of C27n occurring at the same position in Bjala and Zumaia– Aitzgorri. The identification of the E-cycles in the lower part of Bjala is

Fig. 11. Field photograph of part of the Bjala E section with identification of precession-related couplets and eccentricity bundles. Numbering of couplets starts at the D–S boundary. Eccentricity bundles follow the scheme from Zumaia that start numbering at the K–T (Dinarès-Turell et al. 2003). Note the relative thin limestone beds 12, 15, 20–21, 25 and 30–31 which are bounded by relative thick marl layers corresponding to bundle boundaries that correlate to eccentricity maxima. An interval of relative low amplitude of the basic couplets in bundles 39 and 40 indicates a minimum of the long eccentricity 405-ky cycle.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

529

A)

B)

C)

Fig. 12. Field photographs of part of the Artadi (A) and Loubieng (B, C) sections with identification of precession-related couplets and 100-ky eccentricity bundles. Note intervals with low-amplitude of the marl–limestone couplets marking minima of the 405-ky eccentricity cycle and large-scale clusters of well developed marls between 100-ky limestone bundles denoting 405-ky eccentricity maxima.

somewhat less obvious due to outcrop constraints but couplet identification is unambiguous. Chron C27n contains 15 precession cycles at Zumaia whereas 13–14 cycles are counted at Bjala. As the top of C27n occurs at the same precession cycle at both sections the lower boundary of C27n may require further attention in the future. As no magnetostratigraphic data could be retrieved from Loubieng the correlation of cycles below the thick turbidite bed E (Fig. 10) to Zumaia is less certain but looks robust and no couplet appears to be missing. Field pictures from the Loubieng quarry and from the Artadi section (Fig. 12) clearly illustrate the basic couplet arrangement in eccentricity related bundles which have been numbered following the scheme outlined in Dinarès-Turell et al. (2003). Visual inspection of the stacking pattern of the precession-related couplets and eccentricity bundles

clearly makes evident intervals where amplitude of the basic marl– limestone couplets is relatively minor for about two consecutive bundles. This is observed for bundles 39–40, 35–36 and 32–31 (Fig. 12). Seemingly, the same features can be observed in Bjala at the same relative positions (Figs. 10 and 11). These extended zones or clusters of relative low amplitude of the precession-related couplets are separated by about four short eccentricity (110-ky) bundles and reflect eccentricity minima of the 405-ky long eccentricity cycle. A similar criteria but focusing on the well developed (large amplitude) precession-related couplet clusters marking successive 405-ky eccentricity maxima was used in Kuiper et al. (2008) for Zumaia. Both strategies are compatible and allow to successfully identifying the expression of the 405-ky eccentricity cycle. The bed-by-bed correlation

530

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

proposed herein (Fig. 10) between the Basque–Aquitaine sections (Zumaia, Loubieng) and the Bjala Bulgarian sections is consistent in terms of both the lithologic stacking pattern and arrangement of the 100-ky eccentricity related bundles and 405-ky eccentricity cycle. The correlation is supported by identification of magnetic chron C27n and calcareous nannofossil biostratigraphy as outlined above. 5.2. Correlation to ODP Site 1262 and orbital tuning ODP Site 1262 from the southern Atlantic is one of the records used by Westerhold et al. (2008) (W08 hereafter) to construct an astronomically tuned Paleocene time scale. For the late Danian timespan in consideration here constitutes the highest sedimentation record. The X-ray fluorescence (XRF) measurements of iron (Fe) at a resolution of 2 cm from the interval 188–202 m composite depth (mcd) from W08 that contains chron C27n, is taken here and evaluated in terms of cycle identification and astronomical tuning. A correlation to

the Zumaia–Aitzgorri section (as representative of all the studied landbased sections) is then attempted and evaluated. W08 performed wavelet spectral analysis of the Fe record to identify distinct periods of the spectral power along Site 1262 record. Significant power along two bands was inferred by bio- and magnetostratigraphic data to represent the long and short eccentricity cycles respectively. Subsequently, Gaussian band-pass filters centered at those significant periods on the spectrogram were used to extract the eccentricity related cycles. The filters were varied along different intervals of the record attending shifts of the spectral bands interpreted to arise from changes in sedimentation rate. For the interval 176–205 (mcd) of Site 1262 filters centered at frequencies of 1.26 cycles/m (c/m) and 0.29 c/m were used to extract the ~ 100-ky and 405-ky eccentricity cycles respectively (Fig. 13). The relatively high sedimentation rate (1 to 3 cm/ky) for the Walvis Ridge Site 1262 should entail also to extract precession-related cycles in the Fe record. Indeed those cycles are visually obvious in the record particularly

Fig. 13. XRF Fe intensity data for ODP Site1062 (Westerhold et al., 2008, W08), filter outputs and correlation to the Laskar et al. (2004) (La04) eccentricity solution and alternative correlations to the eccentricity bundles from Zumaia. The Varadi et al. (2003) (Va03_R7) solution is also shown. Duration in ky between eccentricity minima is shown for both astronomical solutions. The Gaussian band-pass filters to extract the short and long (PC405) eccentricity cycles are the same as in W08 (1.26 ± 0.38 cycles/m and 0.29 ± 0.09 cycles/m respectively) which are based on identification of spectral peaks. An additional filter (6.082 ± 1.5 cycles/m) based on a weak peak reflecting precession on the spectrogram for the interval under consideration is here used to infer amplitude modulation of the precession signal. Numbering of the identified eccentricity cycles is the same as in W08 but tuning to La04 is different (see text for further information). Note that W08 numbers eccentricity maxima whereas numbering at Zumaia follows eccentricity minima.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

along some intervals (e.g. ~ 190.9–192.8 mcd, ~ 194.–195.6 mcd, ~ 197.5–198.4 mcd and ~ 200.7–201.5 mcd) (Fig. 13) which corresponds to maxima of the 405-ky filter output or the numbered PC405 cycles of W08. Since eccentricity modulates the precession signal amplitude an additional filter centered at the 6.082 c/m frequency (inferred by spectral analysis of the Fe data for the interval under consideration) has been used to extract precession and to better visualize eccentricity modulation (Fig. 13). Conspicuous low-amplitude intervals of that filter output that correlate to minima of the 405ky cycle have been noted in Fig. 13. W08 presented two alternative complete Paleocene tuning schemes to the Laskar et al. (2004) (La04) eccentricity solution shifted one 405-ky cycle. Their option 2 match prominent eccentricity cycles 38 and 39 from Site 1262 to 405-ky maxima around 62.15 Ma which brings eccentricity cycles within C27n to a 405-ky minima. The W08 tuning option 2 is close to our original Zumaia tuning to the Varadi et al. (2003) orbital solution that used the prominent carbonate-rich eccentricity cycles E35–E36 within C27n to correlate to conspicuous eccentricity minima related to a node of reduced eccentricity amplitude related to the long-term 2.5 Myr cycles (Dinarès-Turell et al., 2003, 2007). During the Paleocene the La04 and the Va03 solutions only share this node at around 62.15 Ma but otherwise the solutions differ (see Fig. 6 in Dinarès-Turell et al., 2007). This is probably coincidental as neither solution is accurate in the Paleocene due to the chaotic behavior of the Solar System (Laskar et al., 2004) and only the stable 405-ky eccentricity cycle is reliable for tuning purposes. In the interval above C27n, eccentricity cycles 45 and 41 from Site 1262 present the lowest amplitude in the precession filter output and are tuned to correspondent 405-ky eccentricity minima in the La04 solution (Fig. 13). This is consistent with the observed low amplitude of the marl–limestone couplets within E-cycles 39–40 at Zumaia (Fig. 13) and our published tuning to the Va03-R7 solution. However, this implies shifting tuning for Site 1262 one 100-ky eccentricity cycle older with respect to the W08 tuning. Following the new tuning, lowamplitude cycles 37 and 32/31 from Site 1262 match respective lowamplitude 100-ky cycles centered at 405-ky eccentricity minima in the La04 solution. W08 interpreted the single cycle filter output at 200 mcd as a double cycle (32/31) as inferred from data from Site 1001 but there is no need for that. Thus, following our tuning, cycles 30 and 29 from Site 1262 consistently match eccentricity cycles involving high amplitude modulation in the La04 solution (Fig. 13). Below C27n at Zumaia relative low-amplitude cycles denoting 405-ky minima are observed within cycles 31–32. This interval would therefore correlate with cycle 32/31 at Site 1262 and the eccentricity low in the La04 solution. However, this interpretation does not match our original tuning for Zumaia (Dinarès-Turell et al., 2003) which was consistent with the Va03-R7 solution. This situation arises by the fact that the La04 and Va03-R7 astronomical solutions depart by one eccentricity cycle at this level (Fig. 13). The La04 solution includes 5 short eccentricity cycles between minima of the 405-ky cycle around 62.5 Ma whereas Va03-R7 only involves 4 short eccentricity cycles (of relative longer duration) (Fig. 13). If one intends to make consistent the tuning of Site 1262 to the La04 solution and to Zumaia, then an additional short eccentricity cycle not been identified previously at Zumaia has to be invoked. This additional cycle should be located between cycles 36 and 37. Although the presence of this cycle is not evident (see Figs. 8, 12 and 13), it is noted that about 8 precession couplets are counted between the carbonate-rich prominent parts at the center of cycles 36 and 37 when normally only 4–6 cycles are observed. Although this abnormality could be an indication of the existence of this additional eccentricity cycle, it is also noted that this would involve the presence of 3 consecutive relative short duration eccentricity cycles (containing about 4 precession cycles each) which is not observed in the astronomical solutions (Fig. 13).We depict in Fig. 13 the alternative tuning considering this additional cycle that is named 36b which is more consistent with the Site 1262 data and the

531

La04 solution. Under our tuning scheme, the D–S boundary for Site 1262 would occur in eccentricity cycle 44 of W08 (Fig. 13). This is consistent with the presence of the LO of Fasciculithus sp. close to the eccentricity minima between cycles 43 and 44 in Site 1262 (Agnini et al., 2007; Westerhold et al., 2008). Note also that for Site 1209 from the Pacific this bioevent is constrained between the two eccentricity minima around cycle 44 (Westerhold et al., 2008). 5.3. Integrated chronostratigraphy for the Upper Danian and absolute age for the D–S boundary The integrated calcareous nannofossil biostratigraphy, magnetostratigraphy and cyclostratigraphy from Bjala have permitted a robust correlation with sections from the Basque–Aquitaine basin along the Upper Danian interval up to the D–S boundary. The intra- and interbasin chronostratigraphic framework allows some consideration to be made regarding suitability of correlation criteria as established in the Selandian base GSSP from Zumaia. One of the pivotal criteria, the end of the acme of Braarudosphaera bigelowi is not a suitable criterion in Bjala since this species does not occur consistently in the Danian in this and in other warm-water Tethyan sections. These forms appear only to be suitable in the north Atlantic and adjacent areas (e. g. Zumaia and the D–S type area in the North Sea Basin). The abrupt decrease in the presence of Braarudosphaera is related to the interruption of freshwater influx, probably related to a sudden decrease in precipitation (Steurbaut and Sztrákos, 2008). On the other hand, the second evolutionary radiation of the calcareous nannofossil genus Fasciculithus together with the occurrence of Fasciculithus tympaniformis that define the NP4/NP5 zonal boundary seem to be reliable criteria to approximate the D–S boundary in most Tethyan and Atlantic sections. Also the first radiation of Fasciculithus appears to be a meaningful chronostratigraphic datum, and together the FO of Chiasmolithus edentulus, are key bioevents around the top of chron C27n. Other nannofossil events in the Upper Danian have less value for high-resolution chronostratigraphic purposes (i.e. FO of Neochiastozygus perfectus, FO of Sphenolithus primus, FO of Bomolithus elegans). Nevertheless, the best approach is to integrate biostratigraphic data within a magnetostratigraphic and/or cyclostratigraphic framework. Refinements on the placement of chron C27n at Zumaia and robust bed-by-bed correlation between several Basque sections and Bjala indicates that the D–S boundary is located 30 precession cycles (~630 ky) above C27n. To derive an absolute age for the D–S boundary the preferred tuning option that uses the expression of the 405-ky cycle and makes consistent the land-based sections with data from ODP sites can be used (Fig. 13). Using the La04 orbital solution, the D–S age is computed adding the time (average of 21 ky) of the precession-related cycles to the age of the last tuned eccentricity minima (E-cycle 42 from Zumaia). Three precession cycles are counted and therefore the age for the D–S arrives at 61.641 Ma. An error of 40 ky (Laskar et al., 2004; Kuiper et al., 2008) in the orbital solution for the mid Paleocene should be added to that figure. As outlined by Steurbaut and Sztrákos (2008) and Bernaola et al. (2009) a major discontinuity recorded in the Late Danian of several North African basins (e. g. Tunisia, Egypt) and traditionally used to delineate the D–S boundary there represents and older event as detailed calcareous nannofossil biostratigraphy has evidenced. The FO of Chiasmolithus edentulus and the first radiation of Fasciculithus, the calcareous nannofossil bioevents recorded in connection with the organic-rich layer associated to that discontinuity in the southern Tethys area are events that are close to the top of chron C27n and therefore much older than the D–S as established in the Zumaia GSSP and the original sections in Denmark and confirmed herein at Bjala (Bulgaria). The break in sedimentation in the Tethys area, additionally pinpointed by the planktic foraminifera P3a/P3b zonal boundary (Steurbaut and Sztrákos (2008)), has been associated to a major sealevel fall. Recently, Bornemann et al. (2009) have presented benthic

532

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533

foraminiferal δ13C records from four upper Danian–lower Selandian sections in the Nile Basin (eastern Egypt). All records show a negative δ13C shift with amplitude of up to 2‰ at the base of planktonic foraminiferal subzone P3b, suggesting that the event may represent a “hyperthermal”. It is interesting to note that in the Basque–Aquitaine area some sedimentation changes can be noticed along the equivalent interval to generally more developed marly interbeds (e. g. above Ecycle 36, Fig. 12) in coincidence with the boundary of the “crowded” and “stratified” defined members of the Aitzgorri limestone Formation (Bernaola et al., 2009). Following our tuning to ODP Site 1262, this interval coincides with a pronounced eccentricity cycle characterized by a prominent peak in Fe content and magnetic susceptibility (cycle 38 from W08) referred as “Top Chron C27n Event” also observed in Site 1001 in the Caribbean Sea (Westerhold et al., 2008), though isotope data is not yet available for these records. However, Schulte et al. (2010) have reported new stable isotope data from ODP Leg 165 Site 1001 that shows a clay layer as well as a negative carbon isotope excursion associated with the Top Chron C27n Event as identified from Fe-content by Westerhold et al. (2008). Whole-rock δ13C data from Zumaia (Schmitz et al., 1997, 1998; Arenillas et al., 2008) show a negative excursion of up to 1‰ at a stratigraphic level about 10 m below the D–S boundary that could represent the same event. However, that information from Zumaia cannot be confidentially pinpointed to our high-resolution lithological log hampering a direct correlation with other datasets to be made which remains a possibility to be tested. 6. Conclusions The high-resolution intra and inter basin framework presented herein provides a solid chronostratigraphic and astronomical time scale for the Danian–Selandian boundary interval and outlines the suitability and accuracy of the several criteria defining the boundary. By using the stable 405-ky eccentricity cycle and its expression in the lithologic stacking pattern in the land-based studied section a consistent correlation with published data from ODP Sites from the Southern Atlantic is achieved. The preferred tuning option shifts one 100-ky eccentricity cycle previous tuning for Site 1262 and arrives to an age of 61.641 ± 0.040 Ma for the D–S boundary on the La04 orbital solution. Our detailed framework also allows to speculating about some sedimentary and climatic events recorded prior to the D–S boundary in sections located in the southern Mediterranean Tethys Realm (Tunisia, Egypt) and elsewhere although a detailed isotope stratigraphy still remains to be substantiated both in the cyclic landbased sections and the marine ODP records. Supplementary materials related to this article can be found online at doi: 10.1016/j.palaeo.2010.09.004.

Acknowledgements Field work in Bulgaria for JDT, KS and MI was supported by the Bulgarian National Science Fund grant NZ-1311 and the INGV. Funds for fieldwork for JIB and VP provided by projects CGL2008-01780/BTE and CGL2008-00009/BTE, of the Spanish Ministerio de Ciencia e Innovación. Peter Schulte and an anonymous reviewer provided thoughtful comments. References Adatte, T., Keller, G., Burns, S., Stoykova, K.H., Ivanov, M.I., Vangelov, D., Kramar, U., Stueben, D., 2002. Paleoenvironment across the Cretaceous–Tertiary transition in eastern Bulgaria. Special Paper — Geological Society of America 356, 231–251. Agnini, C., Fornaciari, E., Raffi, I., Rio, D., Roehl, U., Westerhold, T., 2007. High-resolution nannofossil biochronology of middle Paleocene to early Eocene at ODP Site 1262; implications for calcareous nannoplankton evolution. Marine Micropaleontology 64, 215–248.

Arenillas, I., Molina, E., Ortiz, S., Schmitz, B., 2008. Foraminiferal and delta (super 13) C isotopic event-stratigraphy across the Danian–Selandian transition at Zumaya (northern Spain); chronostratigraphic implications. Terra Nova 20, 38–44. Bernaola, G., 2002. Los nannofósiles calcáreos del Paleoceno en el dominio Pirenaico. Bioestratigrafía, cronoestratigrafía y paleoecología: Leioa. Doctoral thesis. University of the Basque Country, 445 pp. Bernaola, G., Martín-Rubio, M., Baceta, J.I., 2009. New high resolution calcareous nannofossil analysis across the Danian/Selandian transition at the Zumaia section: comparison with South Tethys and Danish sections. Geologica Acta 7, 79–92. Bornemann, A., Schulte, P., Sprong, J., Steurbaut, E., Youssef, M., Speijer, R.P., 2009. Latest Danian carbon isotope anomaly and associated environmental change in the southern Tethys (Nile Basin, Egypt). Journal of the Geological Society of London 166, 1135–1142. Bown, P.R. (Ed.), 1998. Calcareous Nannofossil Biostratigraphy. Kluwer Academic, London, p. 315. Channell, J.E.T., Freeman, R., Heller, F., Lowrie, W., 1982. Timing of diagenetic haematite growth in red pelagic limestones from Gubbio (Italy). Earth and Planetary Science Letters 58, 189–201. Clemmensen, A., Thomsen, E., 2005. Palaeoenvironmental changes across the Danian– Selandian boundary in the North Sea Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 219, 351–394. Dabovski, Ch., Zagorchev, I., 2009. Introduction: Mesozoic evolution and Alpine Structure. In: Zagorchev, I., Dabovski, Ch., Nikolov, T. (Eds.), Geology of Bulgaria. : Mesozoic geology, vol. 2. Academic Press, Sofia, pp. 13–37. Dekkers, M.J., Linssen, J.H., 1989. Rockmagnetic properties of fine-grained natural lowtemperature haematite with reference to remanence acquisition mechanisms in red beds. Geophysical Journal of the Royal Astronomical Society 99, 1–18. Dinarès-Turell, J., Dekkers, M., 1999. Inferred multistage diagenetic pathway for the Early Pliocene Trubi marls at Punta di Maiata (southern Sicily): paleomagnetic and rock-magnetic observations. In: Tarling, D.H., Turner, P. (Eds.), Palaeomagnetism and Diagenesis in Sediments: Geol. Soc. London Spec. Publ., 15, pp. 53–69. 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 and Planetary Science Letters 216, 483–500. Dinarès-Turell, J., Diez, J.B., Rey, D., Arnal, I., 2005. “Buntsandstein” magnetostratigraphy and biostratigraphic reappraisal from eastern Iberia; Early and Middle Triassic stage boundary definitions through correlation to Tethyan sections. Palaeogeography, Palaeoclimatology, Palaeoecology 229, 158–177. Dinarès-Turell, J., Baceta, J.I., Bernaola, G., Orue-Etxebarria, X., Pujalte, V., 2007. Closing the Mid-Palaeocene gap: toward a complete astronomically tuned Palaeocene Epoch and Selandian and Thanetian GSSPs at Zumaia (Basque Basin, W Pyrenees). Earth and Planetary Science Letters 262, 450–467. Fuqua, L., Bralower, T., Arthur, M., Patzkowsky, M., 2008. Evolution of calcareous nannoplankton and recovery of marine food webs after the Cretaceous–Paleocene mass extinction. Palaios 23, 185–194. Guasti, E., Speijer, R.P., Brinkhuis, H., Smit, J., Steurbaut, E., 2006. Paleoenvironmental change at the Danian–Selandian transition in Tunisia; Foraminifera, organic-walled dinoflagellate cyst and calcareous nannofossil records. Marine Micropaleontology 59, 210–229. Ivanov, M., Stoykova, K., 1994. Cretaceous/Tertiary boundary in the area of Bjala, Eastern Bulgaria — biostratigraphical results. Geologica Balcanica 24, 3–23. Kirschvink, J.L., 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophysical Journal of the Royal Astronomical Society 62, 699–718. Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R., Wijbrans, J.R., 2008. Synchronizing rock clocks of Earth history. Science 320, 500–504. Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A.C.M., Levrard, B., 2004. A longterm numerical solution for the insolation quantities of the Earth. Astronomy Astrophysics 428, 261–285. Martini, E., 1971. In: Farinacci, A. (Ed.), Standard Tertiary and Quaternary Calcareous Nannoplankton Zonation: Proc. II Plankt. Conference Roma, 1970, 2, Tecnoscienza, pp. 739–785. Perch-Nielsen, K., 1985. In: Bolli, H.M., Saunders, J.B., Perch-Nielsen, K. (Eds.), Mesozoic Calcareous Nannofossils. Cenozoic Calcareous Nannofossils. : Plankton Stratigraphy. Cambridge University Press, Cambridge. 329–426, 427–554. Peybernes, B., Fondecave-Wallez, M.J., Stoykova, K., Ciszak, R., Ivanov, M., Nikolov, T., 2004. Location of the Cretaceous–Tertiary boundary in Bulgaria by means of the planktonic foraminifera. Geobios 37, 755–769. Preisinger, A., Aslanian, S., Stoykova, K., Grass, F., Mauritsch, H.J., Scholger, R., 1993. Cretaceous/Tertiary boundary sections on the coast of the Black Sea near Bjala (Bulgaria). Palaeogeography, Palaeoclimatology, Palaeoecology 104, 219–228. Preisinger, A., Aslanian, S., Brandstaetter, F., Grass, F., Stradner, H., Summesberger, H., 2002. Cretaceous–Tertiary profile, rhythmic deposition, and geomagnetic polarity reversals of marine sediments near Bjala, Bulgaria. Special Paper — Geological Society of America 356, 213–229. Remane, J., Bassett, M.G., Cowie, J.W., Gohrbandt, K.H., Lane, H.R., Michelsen, O., Wang, N., 1996. Revised guidelines for the establishment of global chronostratigraphic standards by the International Commission on Stratigraphy (ICS). Episodes 19, 77–81. Roy, J.L., Lapointe, P.L., 1978. Multiphase magnetizations: problems and implications. Physics of the Earth and Planetary Interiors 16, 20–37. Roy, J.L., Park, J.K., 1972. Red beds: DRM or CRM? Earth and Planetary Science Letters 17, 211–216. Schmitz, B., Asaro, F., Molina, E., Monechi, S., von Salis, K., Speijer, R.P., 1997. Highresolution iridium, delta (super 13) C, delta (super 18) O, foraminifera and nannofossil profiles across the latest Paleocene benthic extinction event at Zumaya, Spain. Palaeogeography, Palaeoclimatology, Palaeoecology 133, 49–68.

J. Dinarès-Turell et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 511–533 Schmitz, B., Molina, E., von Salis, K., 1998. The Zumaya section in Spain; a possible global stratotype section for the Selandian and Thanetian stages. Newsletters on Stratigraphy 36, 35–42. Schmitz, B., Alegret, L., Apellaniz, E., et al., 2008. Proposed Global Stratotype Sections and Points for the bases of the Selandian and Thanetian stages (Paleocene Series). http://www.earth-prints.org/bitstream/2122/3795/1/pwg20.pdf. Schmitz, B., Pujalte, V., Molina, E. et al. (submitted for publication). The global stratotype sections and points for the bases of the Selandian (Middle Paleocene) and Thanetian (Upper Paleocene) stages at Zumaia, Spain. Episodes. Schulte, P., Bornemann, A., Speijer, R.P., 2010. The Top Chron C27n Event on the Western Atlantic: Evidence for a Transient Perturbation of the Carbon Cycle in the Late Danian: Geophysical Research Abstracts, Vol. 12. EGU2010-13049, EGU General Assembly 2010. Speijer, R.P., 2003. Danian–Selandian sea-level change and biotic excursion on the southern Tethyan margin (Egypt). Special Paper—Geological Society of America 369, 275–290. Speijer, R.P., Schmitz, B., 1998. A benthic foraminiferal record of Paleocene sea level and trophic/redox conditions at Gebel Aweina, Egypt. Palaeogeography, Palaeoclimatology, Palaeoecology 137, 79–101. Sprong, J., Speijer, R.P., Steurbaut, E., 2009. Biostratigraphy of the Danian/Selandian transition in the southern Tethys. Special reference to the lowest occurrence of planktic foraminifera Igorina albeari. Geologica Acta 7, 63–77. Steurbaut, E., Sztrákos, K., 2008. Danian/Selandian boundary criteria and North Sea basin–Tethys correlation based on calcareous nannofossil and foraminiferal trends in SW France. Marine Micropaleontology 67, 1–29.

533

Stoykova, K., Ivanov, M., 1992. An uninterrupted section across the Cretaceous/Tertiary boundary at the town of Bjala, Black Sea coast (Bulgaria). Comptes rendus de l'Académie bulgare des Sciences 45 (7), 61–64. Stoykova, K., Ivanov, M., 2002. The Cretaceous/Tertiary transition in Bulgaria; palaeoenvironmental interpretation from calcareous nannofossils, macrofauna and lithology. Journal of Nannoplankton Research 24, 164–165. Stoykova, K., Ivanov, M., 2004. Calcareous nannofossils and sequence stratigraphy of the Cretaceous/Tertiary transition in Bulgaria. Journal of Nannoplankton Research 26, 47–71. Turner, P., Ixer, R.A., 1977. Diagenetic development of unstable and stable magnetization in the St. Bees Sandstone (Triassic) of northern England. Earth and Planetary Science Letters 34, 113–124. Van-Heck, S.E., Prins, B., Stradner, H., Perch-Nielsen, K., 1987. A refined nannoplankton zonation for the Danian of the central North Sea. Abhandlungen der Geologischen Bundesanstalt 39, 285–303. Varadi, F., Runnegar, B., Ghil, M., 2003. Successive refinements in long-term integrations of planetary orbits. Astrophysical Journal 592, 620–630. Varol, O., 1989. Paleocene calcareous nannofossil biostratigraphy. In: Crux, J., van Heck, S. (Eds.), Nannofossils and their Applications. : British Micropal. Soc. Ser. Ellis Horwood Ltd, Chichester, pp. 267–310. Westerhold, T., Roehl, U., Raffi, I., Forniaciari, E., Monechi, S., Reale, V., Bowles, J., Evans, H.F., 2008. Astronomical calibration of the Paleocene time. Palaeogeography, Palaeoclimatology, Palaeoecology 257, 377–403. Zijderveld, J.D.A., 1967. In: Collinson, D.W., et al. (Ed.), AC Demagnetisation of Rock: Analysis of Results. : Methods in palaeomagnetism. Elsevier, Amsterdam, pp. 254–286.