Jaume Dinarès-Turell

The magnetostratigraphic study of the evaporitic Rı́o Chicamo section (240 m) in the Neogene Fortuna Basin (Murcia, southeast Spain) has identified the record of five magnetozones. The most probable correlations with the standard geomagnetic polarity time scale (GPTS) imply that the marine evaporitic sedimentation of this basin was not coeval with the Messinian evaporites of the Sorbas Basin (Almeria, southeast Spain) and the Caltanissetta Basin (central Sicily) (assigned to the reverse Chron C3r, late Messinian by Gautier et al., 1994). The marine evaporites and diatomites from the Fortuna Basin are older (late Tortonian to early Messinian) than the evaporites of those basins. The chronological framework for the sedimentation in the Fortuna Basin together with the isotopic data from the sulphates in these evaporitic units indicate the following. (1) Restriction and confinement in the basin initiated as early as uppermost Tortonian, leading to deposition of evaporites under mixed (marine–continental) conditions. (2) The subsequent sedimentation of marine evaporites and diatomites in this basin occurred in a period between the Tortonian and Messinian transition and the early Messinian: the onset of this sedimentation pre-dates similar sediments of restricted marine environments in the eastern Betics basins, and possibly of the western Mediterranean region also. (3) Episodes of restriction and reflooding in the basin would have occurred in response to periodic fluctuations of the oceanic level under local tectonic controls. In the Fortuna Basin, the global base level drop associated with the `late Messinian Salinity Crisis' was recorded by the progradation of alluvial fans leading to thick clastic deposits overlying the youngest evaporites. These observations hint to: (a) the peculiar characteristics and sensitiveness of some of the marginal intramontane basins in the eastern Betics to reflect structural controls framed in the late Neogene global climatic changes; and (b) the diachronism of the beginning of the marine evaporitic deposition in the Mediterranean region linked to the salinity crisis during the Messinian.

Neogene intermontane basins in Almería Province, SE Spain, display excellent exposures of Messinian (Late Miocene) sequences. The Sorbas, Almería-Níjar and Vera basins maintained connection with the Mediterranean throughout the Messinian, except during the major desiccation phase leading to the formation of salt in the deep centre of the Western Mediterranean. These basins were part of the Western Mediterranean with no separate link to the Atlantic Ocean. The presence of normal marine sediments in these basins reflects the Western Mediterranean watermass. Messinian pre-evaporitic sediments in the basins of southeastern Almería do not show gradual change towards evaporite deposits. Instead they contain stenohaline invertebrates right up to a major erosion surface that separates them from overlying gypsum deposits. This contradicts suggestion of progressive salinity increase in this part of the Western Mediterranean prior to the Messinian Salinity Crisis (MSC); it also indicates that initiation of evaporite precipitation was not synchronous throughout the Mediterranean Basin. There is no major erosion surface within or at the top of the evaporites in these Almería basins, and the gypsum beds exhibit upward transition to siliciclastic and carbonate deposits. This is inconsistent with a model of Messinian Mediterranean evaporite formation whereby deposition of marginal evaporites was followed by their erosion during drawdown that resulted in formation of evaporites in the centre of the Western Mediterranean. The presence of stenohaline biotas in siliciclastic deposits interbedded with the gypsum and in the Messinian post-evaporitic sediments, challenges the view that a long-standing large body of brackish water (the Lago Mare) filled the Western Mediterranean following the MSC and prior to Early Pliocene flooding. It also contradicts the concept of many relatively small brackish basins spread across an otherwise desiccated Western Mediterranean basin. The basins of southeastern Almería record normal marine Early Messinian sedimentation that was abruptly interrupted by sealevel fall. This drawdown most likely resulted in precipitation of evaporites in the central deep Western Mediterranean basin. Following this episode, final marine reflooding of the Western Mediterranean took place during the Late Messinian, and the Mediterranean Sea rose to a level similar to, or higher than, that preceding the Salinity Crisis.

The analysis of the Messinian and Pliocene stratigraphy of the southern Bajo Segura Basin (Betic Cordillera, Spain) has revealed three highstand sedimentary phases (Messinian I, Messinian II, and Pliocene) bounded by two lowstand erosional surfaces (intra-Messinian and end-Messinian unconformities). The Messinian I highstand phase is characterized by the progradation of coastal and shallow marine sandstones (La Virgen Fm) over slope and pelagic-basin marls (Torremendo Fm). After this first phase, a fall in sea level brought about the intra-Messinian unconformity, a subaerial erosional surface with local accumulations of karstic breccias and caliche-like carbonate crusts. The Messinian II highstand phase is represented by sandy beaches and muddy lagoons (Garruchal Fm) correlative with shallow marine evaporites (San Miguel Fm); this second phase records the intra-Messinian reflooding of the basin, which characterizes the salinity crisis in the marginal basins of the Mediterranean. A new sea-level fall resulted in the end-Messinian unconformity, of which the most significant feature is the presence of a broad palaeovalley, c. 200 m deep, which, along its course, completely eroded the deposits of the Messinian II phase and part of the deposits of the Messinian I phase. The Pliocene highstand phase begins with coastal and shallow marine conglomerates and sandstones (La Pedrera Fm) which fill the deep part of the above-mentioned palaeovalley. These bottom deposits evolved gradually upwards towards pelagic marls (Hurchillo Fm), over which shallow marine and coastal sandstones prograded (Rojales Fm). This third phase records the flooding of the basin at the beginning of the Pliocene, when the salinity crisis ended in the marginal basins of the Mediterranean.The combination of calcareous nannoplankton biostratigraphy and magnetostratigraphy has confirmed that both the end of the sedimentation of the Messinian I phase, as well as the two lowstand erosional surfaces (intra- and end-Messinian unconformities) and also the onset of the Pliocene phase occurred in the chron C3r (c. 5.9–5.2 Ma). Under the assumption of the classical model of a desiccated deep basin, either of the two aforementioned erosional surfaces, or even both, could be correlative with the evaporites deposited in the abyssal parts of the Mediterranean.

Thirteen Lower–Middle Eocene (Ypresian–Lutetian) successions, including the Gorrondatxe section in the western Pyrenees, show biomagnetostratigraphic correlation schemes that do not agree with the current standard framework. The main discrepancy concerns the position of the boundary between planktonic foraminiferal Zones P9 (=E7, approximately) and P10 (=E8, approximately), which was thought to occur within calcareous nannofossil Subzone CP12a and at the boundary between magnetic polarity Chrons C22n and C21r. However, in the differing correlation scheme the boundary between Zones P9 (=E7) and P10 (=E8) occurs close to the base of Subzone CP13a and to the boundary between Chrons C21n and C20r. An attempt at a new Ypresian–Lutetian boundary biomagnetochronology is made based on data from the Gorrondatxe section, which shows that the boundary between Zones P9 (=E7) and P10 (=E8) is 3.1 Myr younger than hitherto considered. Therefore, the duration of the Early Eocene, most commonly defined according to this planktonic foraminiferal zonal boundary, has generally been underestimated over the last four decades.

The Gorrondatxe section, a prospective Lutetian Global Stratotype Section and Point (GSSP), has recently been used as the master reference section to reassess the correlation between Eocene magnetostratigraphic and calcareous planktonic biostratigraphic scales. However, the exact calibration of some events remained ill defined, as they were thought to be missing in Gorrondatxe due to a fault. The most important missing events were the first occurrence of the planktonic foraminifera Turborotalia frontosa and the C22n/C21r chron boundary. Either might be a reliable correlation criterion for the Ypresian/Lutetian boundary, as both approach the age of the original Lutetian Stratotype. New studies allowed the identification of the former event 9 m above the Gorrondatxe fault, within magnetic polarity Chron C21r and calcareous nannofossil Zone CP12a. Distinctive test features that characterize the most primitive morphotype of T. frontosa are described. Despite the high turbidite content, recurrent pelagic limestone–marl couplets and bundles occur, whose formation was driven by precession and eccentricity astronomical cycles. The first occurrence of T. frontosa was found 27 couplets and 5.5 bundles (60 m) below the first occurrence of the calcareous nannofossil Blackites inflatus, which is dated at 48 Ma. Hence, the age of the first occurrence of T. frontosa is estimated at 48.55 Ma, confirming that it is the most suitable planktonic foraminiferal correlation criterion for the Ypresian/Lutetian boundary. These results show that the stratigraphic interval missing due to the Gorrondatxe fault cannot be greater than a few metres and reinforce the value of this section as a prospective Lutetian GSSP.

An integrated pilot paleomagnetic and sedimentological study has been conducted in the Neogene-Quaternary infilling materials of the Bajo Segura Basin (Eastern Betics, SE Spain). The studied sediments belong to the youngest (late Pliocene-Quaternary) lithostratigraphic unit of the basin (P-Q unit). The statistical analysis of tectonic striations and stylolitic dissolutions on the conglomerate limestone clasts indicates a NNW-SSE maximum compression direction. This is in accordance with the principal susceptibility axes, determined from the anisotropy of magnetic susceptibility measurements (AMS) of the interbedded siltstones where the Kmax axis group in a subhorizontal N 080° E direction. A total of 45 core samples have been collected from 16 stratigraphic siltstone levels encompassing the described section at Crevillente with the aim to establish a magnetochronology. Upwards in the section the NRM intensity and bulk susceptibility vary from 10−2 to 10−3 A/m and from 1550 to 100 × 10−6 SI, respectively. The mean characteristic remanent magnetization (ChRM) after bedding correction (Dec/Inc = 10°/60°, α95 = 8.7°, k = 15.9) is deviated slightly towards the E from the reference N direction, and could reflect a deflection related to the observed magnetic fabric although no clear correlation exists with AMS parameters. The derived magnetostratigraphy reveals only one reversal boundary within the upper third of the section, delimiting an upper reversal magnetozone which has been tentatively correlated with the Olduwai subchron close to the Plio-Pleistocene boundary. Pilot and preliminary rock-magnetic experiments and standard X-ray difraction (XRD) analysis have been performed on typical samples in order to establish the carriers of magnetization and characterize the sedimentological and magnetic-acquisition processes in these sediments. Magnetic carriers seem to be dominated by magnetite with a relative grain size within the PSD state (pseudo single-domain) threshold, but closer to the MD (multi domain) threshold, which favours the detrital origin for the magnetite.

A new magnetic polarity stratigraphy is reported from 214 sampling sites representing 265 m of fluviatile red beds of the Buntsandstein facies succession from the Catalan Coastal Ranges (Riera de Sant Jaume, RSJ section). The Buntsandstein constitutes the lowermost of the six lithostratigraphic units in which the Triassic from the CCR is subdivided (also grouped into the typical three-fold subdivision of the Germanic Facies from the Tethys Realm: Buntsandstein, Muschelkalk and Keuper). Magnetostratigraphic data from four sections though the uppermost Buntsandstein facies located in the Molina de Aragón area in the Iberian Ranges (Rey, D., Turner, P., Ramos, A., 1996. Palaeomagnetism and Magnetostratigraphy of the Middle Triassic in the Iberian Ranges (Central Spain). In: Morris, A., Tarling, D.R. (Eds.), Palaeomagnetism and Tectonics of the Mediterranean Region, Geol. Soc. Sp. Pub. 105, 59–82) are also discussed in the light of a new biostratigraphic reappraisal of the palynoflora content presented herein. Characteristic magnetizations are carried mostly by hematite with minor contributions by magnetite for the Buntsandstein red beds. The magnetic polarity sequence at the RSJ section consists of 9 magnetozones (and one additional less reliable magnetozone) that are represented by more than two samples. A detailed study along a magnetic reversal indicates that the nature of the remanence in the studied red beds is partially controlled by a chemical magnetization process (delayed remanence acquisition), in addition to a detrital signature (the characteristic primary direction). Chronostratigraphic constraints are provided by conodont fauna from the overlying Muschelkalk facies that indicates a middle–late Pelsonian to late Illyrian age (middle–late Anisian) (Marquez-Aliaga, A., Valenzuela-Rios, J.I., Calvet, F., Budurov, K., 2000. Middle Triassic conodonts from northeastern Spain; biostratigraphic implications. Terra Nova 12, 77–83) and a few palynostratigraphic determinations in the Buntsandstein red beds. These biostratigraphic constraints and the magnetic polarity pattern allow an unambiguous correlation of the RSJ magnetostratigraphy to the conodont-ammonoid-calibrated magnetostratigraphy from the Tethys realm (Muttoni, G., Kent, D.V., Meco, S., Balini, M., Nicora, A., Rettori, R. Gaetani, M., Krystine, L., 1998. Towards a better definition of the Middle Triassic magnetostratigraphy and biostratigraphy of the Tethyan realm. Earth Planet. Sci. Lett. 164, 285–302; Muttoni, G., Gaetani, M., Budurov, K., Zagorchev, I., Trifonova, E., Ivanova, D., Petrounova, L., Lowrie, W., 2000. Middle Triassic paleomagnetic data from northern Bulgaria; constraints on Tethyan magnetostratigraphy and paleogeography. Palaeogeogr. Palaeoclimatol. Palaeoecol. 160, 223–237; Muttoni, G., Nicora, A., Brack, P., Kent, D.V., 2004a. Integrated Anisian–Ladinian boundary chronology. Palaeogeogr. Palaeoclimatol. Palaeoecol. 208, 85–102; Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S., Hernandez, F.M., 2004b. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale. Geol. Soc. Amer. Bull. 116, 1043–1058). The proposed correlation identifies for the first time in the Triassic from Iberia the Olenekian (Scythian)–Anisian stage boundary (245 Ma) within magnetozone N3 in the Riera de Sant Jaume units. Likewise, the new palynostratigraphic reconsideration allows the identification of the Anisian–Ladian stage (Illyrian–Fassanian substage) boundary (taken the option at the base of the Curionii ammonoid Zone favored by Muttoni et al. (2004a) [Muttoni, G., Nicora, A., Brack, P., Kent, D.V., 2004. Integrated Anisian–Ladinian boundary chronology. Palaeogeogr. Palaeoclimatol. Palaeoecol. 208, 85–102] for this boundary within the upper part of the Rillo Mudstone and Sandstones Formation (RMS Formation) and the Fassanian–Longobardian substage boundary (Ladinian) within the Torete Multicoloured Mudstone and Sandstone Formation (TMMS Formation). Our data are consistent with the notion that the lower Muschelkalk transgression progressed from east to west (i.e., the Buntsandstein/Muschelkalk boundary is younger in the Iberian Ranges with respect to the Catalan Coastal Ranges).The Early/Middle Triassic paleopole for the Catalan Coastal Ranges is located at 55.1°N 172.4E (Dp = 1.4, Dm = 2.7).and the Middle/Late Triassic paleopole for the Iberian Ranges is 55°N 201E (Dp = 1.7, Dm = 3.1). These paleopoles are compatible with the general trend of the Iberian apparent polar wander path which indicates a northward motion during the Triassic related to the general northward translation of Pangea.

An integrated sedimentological, magnetostratigraphic, and paleontological study of the Vallcebre section (south eastern Pyrenees, Spain) is carried out in order to define and portray the transition from the Cretaceous to the Tertiary in a continental setting. A robust magnetostratigraphy is correlated to the standard polarity scale in light of known biochronological constraints (charophyte, marine invertebrates, eggshells and other dinosaur remains). Our results show that this section is among the thickest stratigraphic records for the continental Maastrichtian in the Old World. Sedimentology indicates a progressive regression from marine through lagoonal to entirely continental environments. The section is dominated by mudstones deposited under low energy conditions. Exceptionally, a basin-wide regression maximum is recorded some time before the Cretaceous–Tertiary boundary (K/T). This regression maximum is marked by the input of coarse-grained (alluvial) sediments that record a dramatic change in the landscape (quiet mud plains changed to sandy floodplains deposited by high-energy currents). After a period of renewed quiescence following the regression maximum, a Cenozoic flooding took place. Such terminal Cretaceous sequence of events has been recorded in shorter sections in several other basins from southwestern Europe. This energetic sediment input suggests that some time before the K/T event, a sudden paleoenvironmental reorganization took place in the continental basins of south western Europe.

The Lorca Basin (southeastern Spain) is part of a chain of small marginal Neogene basins located in the structurally active Betic area. The Upper Miocene (Messinian) sequence is composed of a thick diatomite-bearing series (Tripoli Unit) overlain by the Main Evaporites, analogous to the classical succession that records the main events during the Salinity Crisis in the Mediterranean region. The shallow restricted conditions of this region amplified the sedimentary responses to local and global forcings. An integrated approach using sedimentology, micropalaeontology, stable isotope geochemistry and organic geochemistry has been applied to the Tortonian/Messinian succession of the Lorca Basin, in order to obtain a continuous record of the environmental changes. The sediments record two major events which affected the whole Mediterranean: (1) high levels of productivity that led to the formation of the diatomite-bearing deposits in the early Messinian (Tripoli); and (2) the Messinian Salinity Crisis with its two major stages, represented by the Halite and Gypsum Units, both mainly precipitated from marine-derived brines. The rapid reflooding of the Mediterranean by normal marine waters at the base of the Pliocene did not reach the Lorca Basin, nor other basins of this part of the Betic area. Instead, continental sediments were deposited as a consequence of the regional uplift of SE Iberia, which started close to the Messinian/Pliocene boundary. The most prominent feature of this basin concerns the record of its restriction by the time of the deposition of the Tripoli Unit, which led to intercalations of precursor evaporitic layers, consisting of Ca-sulphate deposited in sub-aqueous and sabkha conditions, interbedded with diatomites. This alternation of evaporites and diatomites proves that the Lorca Basin was periodically restricted and reflooded by marine waters, a possible cause for this being relative sea-level fluctuations in the Mediterranean. This strengthens evidence of diachronism that suggests that the onset of the first Messinian evaporitic deposition was not synchronous, but was dependent on bathymetry and local tectonics. High productivity during the early Messinian in this basin is demonstrated by the thick deposits of diatomites. However, stagnation episodes may have occurred during this interval, as suggested by the preservation of high amounts of organic matter (organic-rich shales) and the extent of bacterial sulphate reduction which apparently occurred during early diagenesis. The formation of organo-sulphur compounds, replacement of sulphates by carbonates and the high levels of elemental sulphur are by-products of diagenetic processes occurring in a restricted hypersaline environment.

We report high-resolution magnetic measurements from two Mediterranean piston cores: LC07 (Sicily Strait) and LC10 (Ionian Sea). Magnetostratigraphic results and δ18O data provide age constraints for core LC07, where we investigate magnetic property variations for two age intervals (0–600 kyr and 660–1020 kyr). For core LC10, rock magnetic parameters appear to be climatically controlled and are used to derive an astronomically tuned age model for the interval between 780 and 1200 kyr. In core LC07, the dominant control on the magnetic properties appears to be glacial–interglacial variations in the concentration of biogenic magnetite. In addition, an increased contribution from high coercivity minerals (e.g. hematite and/or goethite) probably reflects an enhanced eolian input during glacial periods. Climatic control of magnetotactic bacterial populations has been previously suggested in other environments, but this is the first such report from the Mediterranean. In contrast, the rock magnetic response to Quaternary climatic variability in core LC10 seems to be better expressed by variations in the concentration of high coercivity magnetic minerals. The contrast between a dominantly detrital/eolian flux and a dominantly biogenic flux at the same time for the two Mediterranean settings might relate to the presence of an active current regime in the Sicily Strait, which might decrease delivery of an eolian component to the seafloor compared to the deep Ionian Sea.

Piston core LC07, located west of the Sicily Strait in the Mediterranean Sea, unambiguously records the Matuyama/Brunhes (M/B) and the upper Jaramillo polarity reversals, with similar average sediment accumulation rates (SARs) for the Brunhes Chron (2.29 cm/kyr) and late Matuyama Chron C1r.1r (2.19 cm/kyr). We report a relative paleointensity record for the interval spanning the M/B boundary down into the Jaramillo Subchron, which is unique in the Mediterranean because existing records from this basin cover only the last 80 kyr. The average SAR in core LC07 is used to translate the depth-related paleointensity record to the time domain; the ratio of anhysteretic remanent magnetization to low-field magnetic susceptibility is climatically sensitive and is used to tune the age model. This correlation produces a good fit to the global ice volume model derived for summer insolation at 65°N. With this age model, a paleointensity minimum in association with the M/B boundary has a duration of about 4–5 kyr, while the directional change has a duration of <3 kyr. A second paleointensity minimum of similar duration is found about 16 kyr below the M/B boundary. This feature (precursor or ‘dip’ in the literature) has previously been recognized at the same time interval in many marine records, which reinforces the validity of our age model. Other relative paleointensity minima are found within chron C1r.1r, and, within the uncertainties of the respective age models, these minima coincide with those observed from the few published coeval paleointensity records. In particular, there is good correspondence between the ages of minima at about 0.92 and 0.89 Ma, which probably correlate with two geomagnetic excursions (Santa Rosa and Kamikatsura, respectively) that have been recorded in lava flows and dated using the 40Ar/39Ar technique. In contrast, a recently dated excursion at 0.83 Ma from La Palma seems to correspond to a paleointensity maximum. This observation is opposite to that expected and this excursion needs to be confirmed. In contrast to some recently published paleointensity records, spectral analysis of the LC07 record does not reveal identification of significant power at the orbital obliquity frequency.

We report a biomonitoring study of air pollution in Rome based on the magnetic properties of tree leaves.In a first step, magnetic properties of leaves from different tree species from the same location were compared. It was observed that leaves of evergreen species, like Quercus ilex, present much higher magnetic intensities than those of deciduous species, like Platanus sp., suggesting that leaves accumulate magnetic pollutants during their whole lifespan.In a second step, leaves from Q. ilex and Platanus sp. trees, both very common in Rome, have been used to monitor traffic emission pollution in two different periods. A Platanus sp. sampling campaign was undertaken in October 2001, at the end of the seasonal vegetational cycle, and 5 Q. ilex monthly sampling campaigns from April to August 2002.The strong difference observed in the magnetic susceptibility from leaves collected in green areas and roads allowed the realization of detailed pollution distribution maps from the south of Rome. Magnetic properties indicate that high concentrations and relatively larger grain-sizes of magnetic particles are observed in trees located along roads with high vehicle traffic and in the vicinity of railways. The decrease in concentration and grain size of magnetic particles with distance from the roadside confirms that magnetic properties of leaves are related to air pollution from vehicle emissions.The results indicate that a magnetic survey of tree leaves, which is relatively rapid and inexpensive, may be used in addition to the classical air quality monitoring systems to identify and delineate high-polluted areas in urban environments.

Tectonic deformation can take place in unlithified sediments shortly after deposition. Similarly, laboratory induced stresses can produce a magnetic fabric in wet and unlithified sediments. This is the case of the Holocene sediments from proglacial Lake Barrancs (Central Southern Pyrenees) which we studied for both geomagnetic and paleoclimatic purposes. The sediments are constituted by glaciolacustrine rhythmites with a high phyllosilicate content. The Anisotropy of Magnetic Susceptibility (AMS) of the sediments was measured with a KLY-2 apparatus. Directional data of different cores from the same borehole provide a striking distribution of the principal maximum axes of the susceptibility ellipsoid, suggesting that a laboratory induced AMS was introduced during the acquisition of samples.

The magnetostratigraphy of a 54-m-long section above the Cretaceous–Tertiary boundary at the sea-cliff section of Zumaia in the Basque basin (northern Spain) has been established. The section encompasses the entire Danian and the lower part of the Selandian stages as indicated by calcareous plankton biostratigraphy. The studied interval consists of (hemi)pelagic limestone–marl alternations in the form of couplets and bundles, which range from centimetre/decimetre to metre scale respectively and a few thin-bedded calcareous turbidites. The magnetostratigraphy, based on samples from about 200 stratigraphic levels, allows the identification of six reversal boundaries from chron C29r to C26r at a bed level. The spatial (or temporal) evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique. A preliminary age model based on the standard CK95 GPTS indicates that the basic lithologic carbonate–marl couplet corresponds to the 19–23-kyr precession cycle (21–31-cm cycle in the depth domain) and that a bundle cycle (usually groups of four to six basic couplets) with global periodicity centred at 1.22 m corresponds to the ∼110-kyr eccentricity cycle. We have tuned the bundle cycles to the Va03_R7 eccentricity orbital solution [Astrophys. J. 592 (2003) 620–630] following an initial match of a node of the ∼2.4-Ma eccentricity modulatory cycle in the target time series to particularly carbonate-rich bundles from the upper part of the Zumaia section that displays significant power of a 4.4-m-period cycle corresponding to the ∼404-kyr eccentricity cycle. Consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the ∼404-kyr eccentricity cycle is not persistent throughout. The tuning, however, appears robust as it brings the age of the K/T boundary at ∼65.8 Ma. It is argued that a sea-level signal (tectonically driven?) is superimposed on the climatic forcing at the Milankovitch band masking the full expression of the low-frequency astronomical periods. We provide a cycle-tuned duration for all intervening Early Palaeocene polarity chrons and estimate relative ages for bioevents. The cycle-tuned chronology indicates that the CK95 GPTS overestimates the duration of chrons C28 and C27 by 20 and 26% respectively. Our data may prove useful to better constrain Early Palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the Danian and Selandian stages.

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.