Jaume Dinarès-Turell

Evolution of magnetic fabrics during incipient deformation of mudrocks (Pyrenees, northern Spain)

Abstract The anisotropy of magnetic susceptibility (AMS) of Eocene mudrocks from the Southern Pyrenean Foreland Basin documents the progressive development of tectonic fabrics in sediments that mesoscopically show no evidence for deformation. Two end members are observed: (1) a strong oblate fabric, with strong clustering of the minimum axes of susceptibility that is characteristic of depositional and compaction processes; and (2) a prolate magnetic ellipsoid with moderate to strong minimum axes girdle that reflects weak cleavage in the mudrocks. Low-temperature experiments and anhysteretic remanent magnetization reveal that the paramagnetic fraction dominates the AMS signal and thus, represent the preferred orientation of phyllosilicates. Characteristic stages of magnetic fabrics in mudrocks can be established and thus the AMS can be used as an indicator of cleavage development and intensity in mudrocks. The three stages of fabric development (early deformation, pencil structure and weak cleavage) reflect a process of increasingly preferred crystallographic orientation of the phyllosilicates that is evidenced by the change of distribution of the minimum susceptibility axes. This is particularly evident in the eigenvalues, which we plot on a Woodcock diagram that describes both shape and fabric strength, and allows different stages of deformation to be distinguished. Because appreciable depth during deformation (elevated temperatures and high confining pressures) can be ruled out, we propose that the sediments were wet and only partly lithified when the phyllosilicates became progressively reoriented. Thus, the observed fabric is explained as a result of the close interaction of deformation and diagenetic processes. Tectonically induced deformational fabrics formed while diagenesis progressed. Although the study area is a foreland basin, it offers a valuable analogue to active accretionary wedges. The application of AMS in these settings, where sediments are progressively dewatered through the development of fabrics, permits a similar quantification of fabric development and, eventually, of deformation.

Biomonitoring of traffic air pollution in Rome using magnetic properties of tree leaves

Abstract 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.

The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late middle Eocene and consequent global CO 2 -driven climate change.

Untangling the Palaeocene climatic rhythm: an astronomically calibrated Early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain) ☆

Abstract 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.

Sedimentary and diagenetic markers of the restriction in a marine basin: the Lorca Basin (SE Spain) during the Messinian

Apparatus for automatically measuring and plotting the force-deflection curve of springs, especially small springs on which forces are to be applied in order of 0.1 to 100 grams.

Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements

Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial “pozzolanico” cement containing oxidized magnetite with grain size of less than 0.1 μm according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2–13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 μm. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a “King plot” of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material.

Evidence of an abrupt environmental disruption during the mid-Paleocene biotic event (Zumaia section, western Pyrenees)

An abrupt environmental disruption occurred in the photic zone and at the seafloor during the mid-Paleocene biotic event (MPBE). Calcareous nannoplankton, planktic foraminifer, and benthic foraminifer assemblages at Zumaia section (western Pyrenees) underwent a rapid and remarkable transformation. The major calcareous plankton assemblage changes suggest a shift from relatively cooler mesotrophic to warmer, more oligotrophic conditions, indicating a disturbed environment due to the warming of the ocean. Benthic foraminifer assemblages were also significantly affected by the MPBE; diversity of the assemblages and buliminids show net decline and the low food and opportunistic taxa increase in abundance. The reorganization of the planktic ecosystem possibly involved changes in the food flux (type and quantity) to the seafloor, thus triggering changes in the benthic communities. A 1‰ negative δ 13 C shift and a 30% carbonate content decrease are recorded in connection with the biotic event. This suggests that during the MPBE, as in the Paleocene-Eocene Thermal Maximum (PETM), an input of a large mass of isotopically depleted carbon into the ocean and atmosphere could have lowered the deep-sea pH, triggering a rapid shoaling of the lysocline and contributing to greenhouse warming. The MPBE was short lived: according to the counting of limestonemarl couplets, the stratigraphic expression of precession cycles throughout the Zumaia section, the MPBE lasted for ∼52–53 k.y., with the core of the event representing ∼10–11 k.y. The Zumaia section is the first land-based locality in which the MPBE is recognized and described in detail. Due to its expanded character and excellent paleontological record, this section may prove to be a global reference section for the study of this short-lived event.

Evidence for a variable paleomagnetic lock‐in depth in the Holocene sequence from the Salerno Gulf (Italy): Implications for “high‐resolution” paleomagnetic dating

We report on a paleomagnetic and rock magnetic study of two adjacent marine gravity cores from the Salerno Gulf (Italy), with measurements carried out on u-channel samples at 1-cm spacing. The cores recover a sedimentary sequence spanning, in the overlapping part, the last ∼6000 years and include a thick (∼1 m) pumice layer produced during the Somma-Vesuvius eruption of 79 A.D. Rock magnetic and lithostratigraphic data provide several tie-points for a detailed correlation between the two cores. Paleomagnetic data allow the determination of a well-defined characteristic remanent magnetization, with very similar stratigraphic trends and distinct features that can also be unambiguously correlated between the cores. However, the comparison of the various data sets points out that the paleomagnetic lock-in depth in the two adjacent cores varies through the stratigraphic succession. We discuss the implication of such results for assessing the potential of high-resolution paleomagnetic studies in dating sedimentary sequences on the basis of paleosecular variation of the geomagnetic field. In the studied case, the relative difference in the lock-in depth in the two cores causes “spreading” of the assigned paleomagnetic ages at a century scale.

Remagnetization of Lower Cretaceous limestones from the southern Pyrenees and relation to the Iberian plate geodynamic evolution

Paleomagnetic study (34 sites) of thick Cretaceous ~5000 m marine carbonate strata from the Organya Basin (OB) in the southern Pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination ( D) (Berriasian-Barremian, D = 295 o ; Aptian- Albian, D = 348 o , upper Cretaceous, D = 354 o ) that resides in magnetite and predates Late Cretaceous/Tertiary folding. The lack of reverse polarity magnetizations in the Berriasian- Barremian series, together with their distinct hysteresis properties that are typical of remagnetized carbonates elsewhere, are taken as evidence for a secondary overprint in the lower part of the succession. A hypothesized age of remagnetization near the Barremian/Aptian boundary fits with a major tectosedimentary event in the basin that changed deposition from platform to basinal conditions and increased subsidence during the Aptian. The angular difference (~53 o ) between declination from the remagnetized strata and the mean for Aptian- Albian strata indicates that a counterclockwise rotation occurred between the two acquisition times. Part of this rotation is interpreted to be local and due to slip variation along strike of a normal fault that bounded the basin and tilted the pre Aptian series. This Cretaceous extensive phase is framed in the rift evolution of the northern margin of the Iberian plate. The inferred remagnetization age within the OB falls within the range of previously inferred widespread Cretaceous remagnetization events affecting the Iberian plate. In the OB, remagnetization is speculated to have taken place through chemical (burial diagenetic) origin rather than simple thermoviscous resetting.

Basin infill architecture and evolution from magnetostratigraphic cross-basin correlations in the southeastern Pyrenean foreland basin

Magnetostratigraphy, numerical dating, and facies mapping have been combined to provide the first cross-basin correlation of the Eocene southeastern Pyrenean foreland basin in northeastern Spain. This has enabled (1) depositional systems on the northern and southern margins of the basin to be dated and correlated across the basin and (2) changes in the rates of sediment accumulation in time and space to be evaluated. By sampling correlative intervals at several locations in a transect across the basin, magnetozones were detected that otherwise may have been misinterpreted due to recent magnetic overprinting, or missed by wide sampling intervals in previous magnetostratigraphic surveys. Results of this study indicate that marginal marine strata of the southeastern part of the foreland near the Vic area of Spain are 5 m.y. older than previously thought, the base of the interval (46 Ma) being middle Lutetian in age. By proposing an age of at least 35.68 Ma for the overlying Cardona evaporite unit, the age span of the marine interval in the studied part of the foreland is ~10 m.y. Contrary to earlier interpretations, no major southward migration of the southeastern Pyrenean foreland basin depocenter is recorded by the basin stratigraphy during the initial stages of middle Eocene marine sedimentation in the southern margin of the basin. However, marked basin asymmetry is observed later in its evolution as the top of the marine deposits records northward increase in the thickness of chron C17n.1n (37.47‐36.61 Ma). This asymmetry is also proved by the presence of a larger number of magnetozones within marine strata at the top of the marine interval in the northern sector. These results imply that previous age calibrations and the estimated rates of tectonic processes and sedimentation within the foreland need to be reassessed. The implications for basin infill architecture evolution through time and space, subsidence analysis, and depocenter evolution through time are addressed.