Giulio Bigazzi

Magnetostratigraphy and Pliocene-Pleistocene boundary in Italy

Abstract Analysis of some sedimentary series near Rome and comparison with other series in northern and southern Italy give evidence that Arctica islandica, considered a marker species for the beginning of the Pleistocene, appears during the Re´union paleomagnetic event (about 2 my ago). A period of erosion, called the Aullan erosional phase, is evident in the lower part of the late Villafranchian (= early Pleistocene, Olivola faunal unit).

Obsidian-bearing lava flows and pre-Columbian artifacts from the Ecuadorian Andes: First new multidisciplinary data

Abstract All known outcrops of obsidian flows in the Cordillera Real (Ecuador) have been mapped and sampled to reconstruct their eruptive history using geological observations, age determinations, and trace element data. Our results bear also on the recognition of the sources of obsidian artifacts, used in pre-Columbian tools, and on the reconstruction of ancient trading patterns in Ecuador. Three obsidian flow groups were identified on the basis of flow structures and state of preservation. The groups are further defined by differences in radiometric age, fission-track measurements made at two laboratories (Pisa, Italy, and Campinas, Brazil), and different trace element patterns, determined by neutron activation analysis (Pavia, Italy). The oldest obsidian flows form the upper part of the Basal Volcanic Complex (BVC), the basement of Quaternary Ecuadorian stratovolcanoes. Their ages fix the upper limit of the BVC at 1.5 Ma, in the central Cordillera Real. The two more recent episodes of obsidian rhyolitic volcanism are date at ∼0.85 Ma and slightly less than 0.2 Ma, corresponding in age to the present volcanic arc.

A PC compatible Brazilian software for obtaining thermal histories using apatite fission track analysis

Abstract In this work a software developed in the Instituto de Fisica Gleb Wataghin, IFGW, UNICAMP, Campinas, SP, Brazil for obtaining thermal histories using apatite fission track analysis is presented. This software works in Microsoft-Windows environment. It will be freely disposable in the web site of the Departamento de Raios Cosmicos, IFGW, UNICAMP. Thermal histories obtained through this software are compared with those deduced using Monte Trax the software compatible with Apple Macintosh developed by Gallagher.

New radiometric dating of volcanic ash layers in Periadriatic foredeep basin system, Italy

Abstract New geochronological data are reported for two key ash beds interbedded in Upper Miocene (Messinian)–Early Pleistocene rocks at Maccarone, Bellante, and Mosciano S. Angelo on the Adriatic side of the Italian peninsula. Major element chemistry of glass shards was determined with electron microprobe analysis on the younger key bed. The older, Messinian-age ash bed, sampled at Maccarone, yields a corrected glass fission-track age of 5.38±0.42 Ma. The younger ash bed, sampled at Mosciano S. Angelo and at two localities at Bellante, yields corrected glass ages of ∼2.1 Ma, similar to ages previously determined on Pliocene–Pleistocene ash collected along the Ionic coast and on the Tyrrhenian side of Italy. Apatite fission-track dating of one of the Bellante samples confirms the glass age, whereas apatite from the Mosciano S. Angelo sample yields an excessively old age due to the presence in the sample of a significant component of detrital grains. An unusual bimodal spontaneous track-diameter distribution is found in the Maccarone glass, similar to the distributions previously obtained on other Messinian-age tephra samples from the same region. This anomalous track-diameter distribution is interpreted as a thermal disturbance coeval with the volcanic activity that produced the Pliocene–Pleistocene key volcanic ash bed sampled at Bellante and Mosciano S. Angelo. The contemporaneity of this ash with the event detected by the Maccarone glass suggests that it was related to the tectonic phase which marked, with numerous erosive levels distributed along the whole Apennine region, the end of the Pliocene sedimentary cycle and the onset of the Pleistocene cycle.

Early pleistocene palynostratigraphy of fornace tini, Valle Ricca (Central Italy)

Abstract Pollen assemblages of a well-dated marine section, Fornace Tini in Central Italy, were studied. The section covers a time-span of about 300,000 years between 2.1 m.y. (Reunion event) and 1.8 m.y. ago (Olduvai event). Assuming a constant sedimentation rate, intervals of 3000 to 6000 years were sampled. Around the Reunion event a cool mountain forest vegetation prevailed in Valle Ricca. The climate improved afterwards. A shift of the coast line caused by a sea level rise can be deduced from the expansion of coastal forests in a warmer period following the Reunion event. Another climatic deterioration followed, as is shown by high amounts of pollen from a mountain conifer forest. At the base of Olduvai the coastal forest with thermophilous plants starts to expand again, marking the onset of another mild period.

A reactor intercalibration for fission track-dating and uranium micromapping

Abstract Selected positions of three reactors in France, Italy and Brazil were studied for Fission-Track dating and Uranium distribution micromapping. Spatial gradients of neutron fluxes within the chosen irradiation facilities resulted negligible. Comparison of FT ages calculated by different neutron dosimetries (SRM 962a and SRM 963a standard glass; Fish Canyon Tuff apatite used as age standard) shows that equivalent results are obtained, despite widely differing irradiation conditions in three different reactors. Some observed systematics trends are very probably due to the individual fluence determination.

FISSION-TRACK DATING OF A TEPHRA LAYER IN THE ALAT FORMATION OF THE DANDIERO GROUP (DANAKIL DEPRESSION, ERITREA)

Attempts to date a biotite separate from a tephra layer recognized near Buia (Danakil Depression, Eritrea) in the liwer part of the Homo remains – bearing Dandiero group (formerly attributed to the Danakil Formation) using the 39Ar/40Ar method failed because of xenocrystic contamination. For this reason it was applied the fission-track method on glass, since no other phases datable with this technique were present. The quality of glass was very poor for fission-track dating, because of the small size of grains. In addition, after polishing only few glass shards showed useful surfaces for track counting and only 25 spontaneous tracks were counted. The determined fission-track age - 0.75 +/- 0.16 Ma - is a rejuvenated age due to the presence of a certain amount of annealing of spontaneous tracks. An attempt to apply the plateau method for correcting this apparent age failed. A corrected age of 1.3 +/- 0.3 Ma was computed using the size-correction method. In spite of its low precision, this fission-track age represents a significant result, since it corroborates the attribution to Jaramillo Subchron of the normal magnetozone near the base of which the tephra is located.

Characterisation of Armenian Obsidians: Implications for Raw Material Supply for Prehistoric Artifacts

Obsidians from occurrences located in Armenia have been analysed using neutron activation analysis, both instrumental and epithermal, in order to enhance the knowledge of characteristics of potential sources of raw material exploited during prehistory. An alternative characterization technique, the fission-track dating method, was also applied. Results contribute to increase the data-set for provenance studies of prehistoric obsidian artifacts in the Mediterranean and adjacent regions.

Fission-track dating of Macusanite glasses with plateau and size correction methods

Abstract Two Macusanite pebbles (MB1 and MB2) were dated with the fission-track method. Six irradiations were carried out in different nuclear reactors: Pavia (Italy), IPEN-CNEN (Brazil) and IPEN-Lima (Peru). Measurements of the thorium and uranium induced-fission per target nucleus using natural thorium thin films and natural U-doped glasses calibrated against natural uranium thin films, together with a λ F of 8.46×10 −17 a −1 were used to determine the ages. The apparent ages were corrected using the plateau and size correction methods. Track measurements were performed by different analysts, using different counting criteria. In addition, tracks were measured on samples which had been submitted to thermal treatment as well as on samples which had not been heated. Thermal treatments were carried out to erase the fossil tracks before neutron irradiation. No significant differences have been found in individual results, using the two Macusanite pebbles and the different nuclear reactors, age correction techniques, analysts, track-counting criteria, and thermal treatments before neutron irradiation. The great majority of the results (14/17) is compatible with the Ar–Ar ages of 5.12±0.11 and 5.10±0.11 Ma , Macusanite MB1 and MB2, respectively. However, the fission-track ages are systematically less (∼8%) than the Ar–Ar ages of the two Macusanite samples studied.

Spontaneous 238U fission half-life measurements based on fission-track techniques

In the last recommendation of the International Union of Pure and Applied Chemistry (I.U.P.A.C.) on spontaneous fission half-lives for ground-state nuclides, a number of measurements of 238U based on fission-track techniques were discarded. The arguments given by the authors are not clear. In this work a more detailed discussion of these determinations is given, considering the possible systematical errors inherent in fission-track approaches.