Andrea Albianelli

A one-million-year-old Homo cranium from the Danakil (Afar) Depression of Eritrea

One of the most contentious topics in the study of human evolution is that of the time, place and mode of origin of Homo sapiens. The discovery in the Northern Danakil (Afar) Depression, Eritrea, of a well-preserved Homo cranium with a mixture of characters typical of H. erectus and H. sapiens contributes significantly to this debate. The cranium was found in a succession of fluvio-deltaic and lacustrine deposits and is associated with a rich mammalian fauna of early to early-middle Pleistocene age. A magnetostratigraphic survey indicates two reversed and two normal magnetozones. The layer in which the cranium was found is near the top of the lower normal magnetozone, which is identified as the Jaramillo subchron. Consequently, the human remains can be dated at ∼1 million years before present.

Cesi, an early Middle Pleistocene site in the Colfiorito Basin (Umbro-Marchean Apennine), central Italy

Near the village of Cesi, at the head of the Chienti River, in the Colfiorito Basin (Umbro-Marchean Apennines, central Italy), fluvio-lacustrine deposits have yielded mammal fossil remains. The results of a multidisciplinary investigation indicate that the vertebrate-bearing sediments date about 700 ka and accordingly provide a fossil assemblage for the Middle–Late Galerian. Palynological investigations carried out from sediments underlying the fossiliferous level suggest predominantly cold and dry conditions, whereas the fauna suggests a slight climatic amelioration towards cool and moist conditions in the uppermost part of the sequence.

MAGNETOSTRATIGRAPHY OF THE HOMO -BEARING PLEISTOCENE DANDIERO BASIN (DANAKIL DEPRESSION, ERITREA)

Four magnetozones have been found in the 530 m thick profile of the Dandiero Group. The lower unit, the Bukra Sand and Gravel, extends in the R1 reversed magnetozone from 150 m below the tephra level which was used as the reference marker between the sampled sections. The normal magnetozone N1 is almost completely covered by the lacustrine and deltaic sediments of the Alat Formation, while the following reversed magnetozone contains both the Wara Sand and Gravel and the lacustrine Goreya Fm. The N2 polarity zone is completely occupied by the Aro Sand. This polarity sequence has been calibrated to the geomagnetic time scale using the Early to Middle Pleistocene age of the associated vertebrate fauna and fission-track dating. The four magnetozones were thus regarded as representing the chrons by which the Pleistocene is correlated with magnetochronology. Their three reversal boundaries provided the dates of 1.07, 0.99 and 0.78 Ma, allowing to determine average sedimentation rates close to 1 m/ky. Cyclostratigraphy of the magnetic signal, analysed by the spectral analysis of the time series across the Jaramillo and late Matuyama chrons, confirmed that value. The evidenced cyclicities were directly related to the alternating lithofacies, and both to the astronomical parameters driving the climate changes during the deposition of the Dandiero group (some five hundred thousand years). The section with the Homo site covers the Jaramillo/Matuyama boundary, and the Homo bed located 2 m below this limit is dated 0.992 Ma.

PALEOMAGNETIC AND PALYNOLOGIC INVESTIGATIONS IN THE UPPER VALDARNO BASIN (CENTRAL ITALY): CALIBRATION OF AN EARLY VILLAFRANCHIAN FAUNA

The silty clays embedding an early Villafranchian mammal fauna of the Triversa faunal unit (f.u.) have been paleomagnetically and palynologically studied in a continuous sequence exposed in the Santa Barbara quarry.The study has allowed to date the earliest occurrence in Italy of a faunal assemblage of this unit and to define the corresponding climatic conditions. The sampled section has provided a magnetic polarity sequence of the late Gauss,where the fossiliferous layer fits the Kaena reversed interval.Its age of ca. 3.1 Ma,during subtropical climate conditions correlatable to the Reuverian of Netherlands, suggests an older age for the beginning of the Villafranchian, possibly associated to a more dramatic scenario able to trigger the faunal turnover.

THE POGGIO ROSSO LOCALITY CALIBRATED TO THE END-PLIOCENE AND ITS SIGNIFICANCE FOR DATING THE LATE VILLAFRANCHIAN MAMMAL FAUNAS OF THE UPPER VALDARNO, CENTRAL ITALY

A rich deposit of mammals was discovered in September 1995 at Poggio Rosso, the hill-top of the Matassino clay pit, in the Upper Valdarno Basin, 30 m above another deposit whose local fauna was assembled 30 years earlier. This latter provided the Matassino Locality, assigned to the beginning of the late Villafranchian Mammal Neogene age on the basis of its affinity with the Olivola faunal unit, which was also taken to represent the earliest assemblage in the Pleistocene. The paleomagnetic record in the short section across the Matassino Locality revealed the Olduvai chron, which was imprinted also in the fossil-bearing stratum of Poggio Rosso, so constraining both their ages to the latest Pliocene. The Poggio Rosso fauna, yet to be paleontologically determined, and the other late Villafranchian faunas collected in the Upper Valdarno from the Montevarchi complex fit a similar time span. Therefore, their magnetostratigraphically calibrated ages provide the time constraints for the biochronological relationships between faunas which can be tuned to several tie points for numerically evaluating their diversification steps during the whole Olduvai chron and shortly out of it.