Sagnotti, Leonardo

Biomonitoring of magnetic properties of tree leaves has been postulated to be a good approach to measure particulate matter (PM) pollution levels. We studied the variation of magnetic hysteresis parameters on leaves of Quercus ilex, an evergreen oak previously used for magnetic biomonitoring of air pollution in Rome (Italy). The hysteresis parameters (MRS, MS, BCR and BC) measured on specimens collected at a close spacing on the surface of two single leaves show variances that are smaller than those observed on a collection of Q. ilex leaves sampled from several trees distributed along high-traffic roads. The variability is higher for magnetizations than for coercivities. This suggests a uniform source for the magnetic particles, such that variations are due mainly to changes in concentration. The normalized hysteresis cycles are remarkably similar for all the specimens. Normalization of magnetic moments by mass appears however more efficient than normalization by volume.

In this study, we report an extensive paleomagnetic study (76 sites) carried out in the Alborz Mts. (northern Iran), with the aim of reconstructing the rotation history and the origin of curvature of this orogenic chain. The analyzed deposits are the sedimentary successions of the Upper Red Formation (Miocene), Lower Red Formation (Oligocene) and Eocene clastic units. Paleomagnetic results indicate that the Alborz Mts. can be considered a secondary arc that originated as a linearmountain belt that progressively acquired its present day curvature through opposite vertical axis rotations along its strike. The curvature of the arc was entirely acquired after the middlelate Miocene,which is the age of the youngest investigated sediments (Upper Red Formation). Overall, our paleomagnetic data indicate that the Alborz Mts. can be considered an orocline. Our results define, for the first time, the rotational history of the entire Alborz curved mountain belt, and enable us to reconstruct the paleogeographic and tectonic evolution of northern Iran in the framework of Arabia-Eurasia continental deformation. The kinematics inferred by the pattern of paleomagnetic rotations is at odds with the present day kinematics of northern Iran, characterized by the westward extrusion of the South Caspian block, and by a left lateral shear between Central Iran and the central and western sectors of the Alborz Mts. By integrating paleomagnetic datawith stratigraphic, thermochronological, structural and GPS information,we propose that the initiation of South Caspian subduction and the activation of westward extrusion of South Caspian block occurred diachronously and that the initiation of the present-day kinematics of northern Iran was quite recent (Lower Pleistocene, b2 Ma).

The climatic transitions during the Miocene-Pliocene epochs had significant impacts on the worldwide biological diversity and were associated with large turnovers of continental vegetation and fauna. Previous studies have shown that late Miocene cooling and continental aridification which was initiated 7 Ma reversed to warm conditions across the Miocene-Pliocene Boundary ∼5.3 Ma. Here, we present detailed orbital pacing of Asian monsoon deposits to constrain further the global climate change during this period. We produce high-resolution magnetic susceptibility records which reveal that the 1.2 Myr obliquity modulation would have been the main driving factor of the cooling and warming that occurred ∼7 and 5.3 Ma, respectively. The Tibetan rise and closures of the Panama and Indonesian seaways enhanced the impact of the 405 Kyr eccentricity cycles to an oscillatory climatic state while the Northern Hemisphere glaciations were increasing from 4 to 2.5 Ma.

The age of spreading of the Liguro–Provençal Basin is still poorly constrained due to the lack of boreholes penetrating the whole sedimentary sequence above the oceanic crust and the lack of a clear magnetic anomaly pattern. In the past, a consensus developed over a fast (20.5–19 Ma) spreading event, relying on old paleomagnetic data from Oligo–Miocene Sardinian volcanics showing a drift-related 30° counterclockwise (CCW) rotation. Here we report new paleomagnetic data from a 10-mthick lower–middle Miocene marine sedimentary sequence from southwestern Sardinia. Ar/Ar dating of two volcanoclastic levels in the lower part of the sequence yields ages of 18.94±0.13 and 19.20±0.12 Ma (lower–mid Burdigalian). Sedimentary strata below the upper volcanic level document a 23.3±4.6° CCW rotation with respect to Europe, while younger strata rapidly evolve to null rotation values. A recent magnetic overprint can be excluded by several lines of evidence, particularly by the significant difference between the in situ paleomagnetic and geocentric axial dipole (GAD) field directions. In both the rotated and unrotated part of the section, only normal polarity directions were obtained. As the global magnetic polarity time scale (MPTS) documents several geomagnetic reversals in the Burdigalian, a continuous sedimentary record would imply that (unrealistically) the whole documented rotation occurred in few thousands years only. We conclude that the section contains one (or more) hiatus(es), and that the minimum age of the unrotated sediments above the volcanic levels is unconstrained. Typical back-arc basin spreading rates translate to a duration ≥3 Ma for the opening of the Liguro–Provençal Basin. Thus, spreading and rotation of Corsica–Sardinia ended no earlier than 16 Ma (early Langhian). A 16–19 Ma, spreading is corroborated by other evidences, such as the age of the breakup unconformity in Sardinia, the age of igneous rocks dredged west of Corsica, the heat flow in the Liguro–Provençal Basin, and recent paleomagnetic data from Sardinian sediments and volcanics. Since Corsica was still rotating/drifting eastward at 16 Ma, it presumably induced significant shortening to the east, in the Apennine belt. Therefore, the lower Miocene extensional basins in the northern Tyrrhenian Sea and margins can be interpreted as synorogenic "intra-wedge" basins due to the thickening and collapse of the northern Apennine wedge.

Small lakes in low relief areas are atypical candidates for studies on paleoseismicity, but their sediments can contain seismically induced event layers (seismites) generated through strong ground shaking, sediment transport, hydrological reorganization and/or changes in groundwater chemistry and flow. Lakes Lungo and Ripasottile are shallow lakes (<10 m deep) located in the tectonically active Rieti Basin in the central Apennines, Italy, where strong normal faulting earthquakes (Mw 6.5 to 7.0) regularly occur. Sediment cores from these lakes provide paleoseismic indicators for the past similar to 1000 years. Sedimento-logical and geochemical analysis reveals four event layers identified in both lakes that correspond with documented large-scale earthquakes in 1298, 1349, 1639, and 1703 AD. Chronological correlation between earthquakes and paleoseismic features is reliable because of the resolution of sediment dating available for the studied cores. The common physical structure is a physically homogenous bed (homogenite) of re-suspended sediment consisting of a denser, high magnetic susceptibility (kappa) clastic base, with organic matter concentrated above. Co-seismic to post-seismic chemical signatures are associated with some event layers and may represent abrupt or transient shifts to a groundwater-dominated system, or permanent changes in groundwater flow and/or spring discharge. Excursions in delta C-13(org) may represent disruptions or changes in carbon source. Not all event layers show the same features, a result attributed to differences in seismic processes as well as the lake attributes, and anthropogenic modification. The observations made here may provide a new means of detecting paleoseismicity and may be applied to other low relief lakes in seismically active areas. (C) 2019 Elsevier Ltd. All rights reserved.

Reconstruction of Paleomagnetic Secular Variation (PSV) of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks, sediments and archaeological material. We present refined age-calibrated Holocene PSV and relative paleointensity (RPI) stack curves derived from Arctic marine sediments (Northwestern Barents Sea). The Holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models, and stacked. The resultant composite PSV and RPI Holocene records (NBS stack) and the reconstructed Holocene Virtual Geomag- netic Pole (VGP) path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models. The data indicate that during the Holocene time, the VGPs moved within the superficial projection of the inner core tangent cylinder, with the exception of short time intervals around 5600 and 3200 cal yr BP when VGPs extended to lower latitudes. These deviations might reflect regional geomagnetic features, such as persistent geomagnetic flux lobes at core-mantle boundary. Our data confirm that the large VGP shift observed around 5600 cal yr BP is the result of an increased radial magnetic field at the core-mantle boundary over North America, whilst the VGP shift around 3200 cal yr BP represents a major swing to middle latitudes toward the Middle East and might be associated to a regional high paleointensity peak, known as Levantine Iron Age Anomaly (LIAA).

A recent study of the Matuyama–Brunhes (M-B) geomagnetic field reversal recorded in exposed lacustrine sediments from the Sulmona Basin (Italy) provided a continuous, highresolution record indicating that the reversal of the field direction at the terminus of the M-B boundary (MBB) occurred in less than a century, about 786 ka ago. In the sediment, thin (4–6 cm) remagnetized horizons were recognized above two distinct tephra layers—SUL2- 19 and SUL2-20—that occur ∼25 and ∼35 cm below the MBB, respectively. Also, a faint, millimetre-thick tephra (SUL2-18) occurs 2–3 cm above the MBB.With the aim of improving the temporal resolution of the previous Sulmona MBB record and understanding the possible influence of cryptotephra on the M-B record in the Sulmona Basin,we performed more detailed sampling and analyses of overlapping standard and smaller samples from a 50 cm-long block that spans the MBB. The new data indicate that (i) the MBB is even sharper than previously reported and occurs ∼2.5 cm below tephra SUL2-18, in agreement with the previous study; (ii) the MBB coincides with the rise of an intensity peak of the natural remanent magnetization (NRM) intensity, which extends across SUL2-18; (iii) except for a 2-cm-thick interval just above tephra SUL2-18, the rock magnetic parameters (k, ARM, Mr, Ms, Bc, Bcr) indicate exactly the same magnetic mineralogy throughout the sampled sequence. We conclude that either SUL2-18 resulted in the remagnetization of an interval of about 6 cm (i.e. during the NRM intensity peak spanning ∼260 ± 110 yr, according to the estimated local sedimentation rate), and thus the detailed MBB record is lost because it is overprinted, or the MBB is well recorded, occurred abruptly about 2.5 cm below SUL2-18 and lasted less than 13 ± 6 yr. Both hypotheses challenge our understanding of the geomagnetic field behaviour during a polarity transition and/or of the NRM acquisition process in the Sulmona lacustrine sediment.

The 91.15 m thick St. Thomas section belongs to the Middle Globigerina Limestone, which is the intermediate member of the Globigerina Limestone Formation, and crops out along the eastern cliff of the Delimara Peninsula (the south-eastern part ofMalta Island). The sedimentary record is composed of alternating calcareous marls and marly limestones with subordinated prominent bioturbated indurated limestones that are deposited in a pelagic environment. For the first time paleomagnetic analyses of a Burdigalian succession have provided reliable data that allow the identification of five magnetozones that have been correlated to the Astronomically Tuned Neogene Time Scale, spanning the Early Miocene C6n–C5Dn interval. Calcareous plankton quantitative analyses integrated with paleomagnetic analyses, allowed us to identify and date several bioevents that have great potential for Mediterranean and extra-Mediterranean correlations in the interval between ~19.7 and ~17.2 Ma. In particular, the complete distributional range of the calcareous nannofossil Sphenolithus belemnos has been recorded as follows: the First Occurrence (FO) at 19.12 Ma, the First Common Occurrence (FCO) at 19.05 Ma, the Last Common Occurrence (LCO) at 18.44 Ma, and the Last Occurrence (LO) at 18.02 Ma. In addition, the FO and the FCO of Sphenolithus heteromorphus have been documented at 18.29 Ma and at 17.99 Ma, respectively. A new paracme interval in the lower part of the range of this species is described between 17.56 and 17.31 Ma. Concerning the planktonic Foraminifera, the main bioevents are the Common Interval top of Paragloborotalia siakensis at 19.55 Ma, a Common Interval of Globoquadrina dehiscens between 19.34 and 18.48 Ma, the Globigerinoides subquadratus FO at 18.43 Ma, and the onset of an acme interval of Paragloborotalia acrostoma that changes its coiling from random to prevalently sinistral at the same time, at 18.40 Ma. These new biostratigraphic data allowed us to place the succession in the standard Mediterranean calcareous plankton zonal schemes and to make some amendments to these schemes. The FCO of S. belemnos was revealed a more reliable marker than its FO for the base of the MNN3a Zone.With regard to the planktonic Foraminifera, the P. acrostoma AB-r/s has been used as a subzonal marker of the G. dehiscens/Catapsydrax dissimilis Zone, which now comprises three subzones instead of two. The deep marine paleoenvironmental setting, the excellent outcrops and the recognition of a continuous succession of bio-magnetostratigraphic events suggest that the St. Thomas section should be considered as a reference section for the lower Burdigalian of theMediterranean area and for future studies in the definition of the Burdigalian GSSP.

We report on new paleomagnetic results obtained from 27 sites sampled in the Plio-Pleistocene sequences at the external front of the central-northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the 'Acquasanta' domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. A local significant CCW rotation (23° ± 10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma.

The sedimentary sequence deposited during the deglaciation phase following the last glacial maximum in the Storfjorden trough, on the northwestern Barents Sea south of Svalbard, was sampled with 10 piston and gravity cores during the SVAIS and EGLACOM cruises. Three cores (SV-02, SV-03 and SV-05) collected on the upper continental slope are characterized by a thin (20–40 cm) Holocene interval and a thick (up to 4.5 m in core SV-03) late Pleistocene sequence of finely laminated fine-grained sediments that have been interpreted as plumites deposited during the Melt Water Pulse 1a (MWP-1a). Radiocarbon ages obtained at the top and bottom of this stratigraphic interval revealed that deposition occurred during less than two centuries at around 15 ka ago, with a very high sedimentary rate exceeding 3 cm a−1. We studied the palaeomagnetic and rock magnetic properties of this interval, by taking magnetic measurements at 1 cm spacing on u-channel samples collected from the three cores. The data show that this sequence is characterized by good palaeomagnetic properties and the palaeomagnetic and rock magnetic trends may be correlated at high resolution from core to core. The obtained palaeomagnetic data therefore offer the unique opportunity to investigate in detail the rate of geomagnetic palaeosecular variation (PSV) in the high northern latitudes at a decadal scale. Notwithstanding the palaeomagnetic trends of the three cores may be closely matched, the amplitude of directional PSV and the consequent virtual geomagnetic pole (VGP) scatter (S) is distinctly higher in one core (SV-05) than in the other two cores (SV-02 andSV-03). This might result from a variable proportion of two distinct populations of magnetic minerals in core SV-05, as suggested by the variable tendency to acquire a gyromagnetic remanent magnetization at high fields during the AF demagnetization treatment. For the plumite interval of cores SV-02 and SV-03, where the magnetic mineralogy is uniform and magnetite is the main magnetic carrier, a S value of about 9◦ is obtained. We consider this value as a reliable approximation of palaeomagnetic secular variation at a latitude of 75◦N over a time interval spanning a couple of centuries around 15 ka ago.