Roberto Lanza’s research while affiliated with University of Turin and other places

The temperature of the deposits (Tdep) emplaced by the pyroclastic density current (PDC) generated by the seven major explosive eruptions from Somma–Vesuvius during the last 22 kyr were investigated using the thermal remanent magnetization of lithic clasts embedded within the deposits. New data are presented for the Pomici di Base, Greenish Pumice, Mercato and 1631 AD deposits and compared to the literature data from the Avellino, 79 AD-Pompeii and 472 AD-Pollena eruptions. The Tdep mainly fall in the range 270–370 8C and no significant correlation is evidenced between sedimentological features, eruptive and depositional processes and the final Tdep. The admixture of ambient air during the run-out appears the most effective process to cool the temperature of the ash and gases of the PDC, and is therefore the main factor affecting the deposit temperature.

The main objective of this work is to compare directional (declination and inclination) volcanic and archaeomagnetic data for the last four centuries (1600–1990) with the historical geomagnetic predictions given by the GUFM1 model which spans from 1590 to 1990. The results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model. However, when comparing the volcanic data with the model predictions, marked inclination shallowing is observed. This systematically lower inclination has already been observed in local palaeomagnetic studies (Italy, Mexico and Hawaii) for the 20th century, by comparing recent lava flows with the International Reference Geomagnetic Field (IGRF) model. Here, we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3º lower than the historical geomagnetic field model predictions.

The potential of magnetic grain-size variations as an obsidian source characteristic is investigated using geological and archaeological obsidians from five islands of the Mediterranean Sea: Lipari, Sardinia, Palmarola, Pantelleria, Melos. Four parameters are used: magnetic (χ) and anhysteretic (χa) susceptibilities, saturation isothermal remanent magnetizations at room (SIRM293) and liquid nitrogen (SIRM77) temperature. The ratio ST = SIRM77/SIRM293, which depends on the superparamagnetic grains relative abundance, varies little in each individual site, with the exception of Lipari which is characterized by large variations and the highest content of superparamagnetic grains. The χa vs. χ plot (King et al., 1982) shows some within-site dispersion of the samples; but the ratio Qa = χa/χ, which is strongly influenced by the single domain grains content, is characteristic for each site. The combined use of the King and Qa vs. ST plots discriminates the samples from most of the sites and suggests that the grain-size analysis is a promising approach in sourcing obsidian archaeological artefacts. Moreover, the measurements of the four parameters used are simple, quick and feasible with no or little damage to archaeological finds.

This paper reports on the complex relation between rock emplacement and remanence acquisition in tuffs deposited by pyroclastic density currents, disclosed by systematic measurements of the anisotropy of magnetic susceptibility and natural remanent magnetization (NRM). Thermal demagnetization shows that the NRM consists of two components with different blocking-temperature spectra. The direction of the low-temperature component is consistent with the geocentric axial dipole value, whereas the high-temperature component has dispersed directions. The magnetic fabric is oblate, the magnetic foliation is close to the bedding and the lineations are generally dispersed along a girdle within the foliation plane. The directions of the magnetic lineation and the high-temperature remanence component of individual specimens are close to each other. This correspondence suggests that the high blocking-temperature grains acquired a remanence aligned to their long dimension before deposition, while cooling within the explosive cloud and the moving pyroclastic current. Thereafter, during deposition, the traction processes at the base of the current oriented the grains along the flow direction and affected both fabric and high-temperature remanence. This NRM component results from mechanical orientation of previously magnetized grains and is thus detrital in origin. A second, thermal component was then acquired during the cooling of the low blocking-temperature grains after deposition. These results show that NRM in fine-grained pyroclastic rocks is affected by the Earth’s magnetic field as well as the emplacement processes and that magnetic fabric data are essential to unravel its complex nature. KeywordsMagnetic fabric–Remanent magnetization–Pyroclastic rocks

The PM10 particulate collected on filters from four air-quality monitoring stations in the city of Torino (Italy) has been investigated by means of detailed magnetic measurements, transmission electron microscopy and energy-dispersive X-ray analysis. The magnetic fraction mainly consists of magnetite-like ferrimagnetic phase and a minor contribution from a high-coercivity phase, which probably results from oxidation of the smallest magnetite grains. The magnetic particles have a grainsize mostly comprised in the single-domain/superparamagnetic range with a large prevalence of the latter. A large fraction of superparamagnetic particles of nanometric dimension were identified in the particulate matter by magnetic techniques and directly observed by electron microscopy. Energy dispersive X-ray elemental analysis showed that ultrafine Fe-rich particles have a spherical shape and are often associated with other metals. The analysis of daily-average variations of magnetic particle concentration found a close correlation of magnetic moment with total nitrogen oxides suggesting that the largest part of magnetic minerals in particulate matter originates from anthropogenic combustion processes. A simple model linking total nitrogen oxides with magnetic particles, for the city of Torino, is proposed. The correlation of magnetic moments and PM10 mass is generally poor because of the different sources of the latter, therefore in the studied contest PM10 is not a good proxy for ultrafine magnetic particles.

We report on a series of experiments designed to test the ability of hematite-bearing colors to record the direction of the ambient magnetic field. Plasterboards accurately oriented with respect to the Earth's magnetic field were painted with red tempera colors prepared with hematite pigments. Magnetic measurements indicate that the color film retains a remanent magnetization and acquires a well developed magnetic fabric. The remanence direction is close to, yet slightly deviated from the Earth's magnetic field. The deviation is interpreted to result from preferential alignment of the pigment grains parallel to the plasterboard surface and depends on both its orientation with respect to magnetic north and the degree of magnetic anisotropy of the color film, which in turn varies according to the pigment used. Investigation of the magnetic remanence of murals may complement archaeomagnetic information derived from traditional materials such as baked and fired structures.

The Bathonian GSSP is defined at the base of limestone bed RB071 in the Ravin du Bès Section, Bas-Auran area, southern Subalpine Chains (France). This section satisfies most of the erquirements recommended by the International Commission on Stratigraphy. The exposure extends over 13 m in thickness. No vertical biofacies, ichnofacies or taphofacies changes, stratigraphic gaps or hiatuses have been recorded at the Bajocian-Bathonian transition. Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints. There is a well-preserved, abundant and diverse fossil record, with key markers (ammonites and nannofossils). The base of Bathonian Stage and Zigzag Zone corresponds to the first occurrence level of Gonolkites convergens Buckman that coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils are present in all beds. The GSSP is below the Tethyan calcareous nannofossil NJT10b/11 zonal boundary (lowest Watznaueria barnesiae) and above the Bo real nannofossil NJ10/11 boundary (lowest Pseudoconus enigma). Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate interpretation of an Early Bathonian deepening half-cycle of second order. The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”. The Cabo Mondego Section (Portugal) is the Bathonian auxiliary section and point (ASSP) .The proposal was voted by the Bathonian Working Group in December, 2007, and by the International Subcommission on Jurassic Stratigraphy in March, 2008, approved by the ICS in June 2008, and ratified by the IUGS in July 2008.