Jackie Despriée

ESR Dating of Sedimentary Quartz from Two Pleistocene Deposits Using Al and Ti-Centers

ESR Dating of Sedimentary Quartz from Two Pleistocene Deposits Using Al and Ti-Centers One sample from a fluvial terrace of Loir river (France) deposited during isotopic stages 7-8 and two samples from isotopic stage 5 marine sediments of Echizen Coast (Japan) were dated by ESR of quartz grains. Both additive and regenerative techniques were used on Ti-Li and Ti-H centers of quartz. No change of sensitivity of the centers was observed during regeneration which significantly reduced the errors on the equivalent doses. Bleaching experiments indicated that the Ti-Li center is less sensitive to UV(ultra-violet)-A (365-412 nm) than to the full sun spectrum whereas UVA alone is sufficient to reset the bleachable component of the Al-center. This effect could be the origin of the strong overestimation of the ages determined using the Ti-Li center in this study. The comparison of the equivalent doses determined by the two Ti-centers indicated that bleaching before deposition of the fluvial sediment was apparently better than for the marine sample.

The very high alluvial formation of early Pleistocene age in the Creuse River Valley at Eguzon (Indre) : cryoturbation patterns, prehistoric occupation sites and absolute dating

Around twenty prehistoric sites of the very early Palaeolithic were discovered on the northern edge of the Massif Central, in the Creuse Valley between Crozant and the Paris Basin, and on the Aigurande crystalline plateau that borders it. Concentrated more particularly around Eguzon, the sites are all closely linked to fluviatile formations, whose study, despite difficult exploration conditions, revealed many remnants of alluvial deposits. Those of the very high formation, some up to 15 m thick, were the best preserved. The most significant site, at “Pont-de-Lavaud”, is in a thin bed of gravel made up mainly of quartz pebbles and debris with small, interbedded sand lenses. Tilted 6 to 7° in a small depression in the weathered foliated crystalline basement, the bed is at mid-slope of an interfluve between the Creuse River and one of its small tributaries. Excavation done between 1983 and 1995 uncovered many prehistoric artefacts carved out of quartz in the upper part of the sediment and, below this, various cryoturbation patterns (sorted circles, polygons, inclusions in the alluvium of alterite from the bedrock) and scattered, less abundant artefacts of the same type. Due to the outstanding state of conservation of these findings, they could be studied in a particularly detailed manner and, when coupled with the study of the alluvial formations, enabled us to : – place them at the base of the very high terrace, located 90–110 m above the river’s present-day low water level – attribute the unusual position of the outcrop to the tilting of a block of bedrock by new displacement of an old fault, thus confirming the role of recent tectonics in the regional morphology ; Absolute age dating by Electron Spin Resonance (ESR) of the best conserved outcrops of the very high alluvial formation gave an age of 1 to 1.2 million years, thus placing them at the end of the early Pleistocene. However, dating of alluvial remains near the site and of the site itself, gave ages between 0,9 and 1 million years. Differences are attributed to the role that greater erosion and pedogenic weathering might have played. Therefore, the “Pont-de-Lavaud” occupation sites are among the oldest presently known in Europe.

High handaxe symmetry at the beginning of the European Acheulian: The data from la Noira (France) in context

In the last few decades, new discoveries have pushed the beginning of the biface-rich European Acheulian from 500 thousand years (ka) ago back to at least 700 ka, and possibly to 1 million years (Ma) ago. It remains, however, unclear to date if handaxes arrived in Europe as a fully developed technology or if they evolved locally from core-and-flake industries. This issue is also linked with another long-standing debate on the existence and behavioral, cognitive, and social meaning of a possibly chronological trend for increased handaxe symmetry throughout the Lower Paleolithic. The newly discovered sites can provide a link between the much older Acheulian in Africa and the Levant and the well-known assemblages from the later European Acheulian, enabling a rigorous testing of these hypotheses using modern morphometric methods. Here we use the Continuous Symmetry Measure (CSM) method to quantify handaxe symmetry at la Noira, a newly excavated site in central France, which features two archaeological levels, respectively ca. 700 ka and 500 ka old. In order to provide a context for the new data, we use a large aggregate from the well-known 500 ka old site of Boxgrove, England. We show that handaxes from the oldest layer at la Noira, although on average less symmetric than both those from the younger layers at the same site and than those from Boxgrove, are nevertheless much more symmetric than other early Acheulian specimens evaluated using the CSM method. We also correlate trends in symmetry to degree of reduction, demonstrating that raw material availability and discard patterns may affect observed symmetry values. We conclude that it is likely that, by the time the Acheulian arrived in Europe, its makers were, from a cognitive and motor-control point of view, already capable of producing the symmetric variant of this technology.