Pleistocene fluvial systems of the Creuse river (Middle Loire Basin - Centre Region, France) Les systèmes fluviatiles pléistocènes de la Creuse (Bassin moyen de la Loire, Région Centre, France).

摘要

The Creuse River is a tributary of the Vienne River which joins the Loire Valley on its left bank downstream Tours (Centre Region, France). Recent field works has significantly increased the number of fossil fluvial formations identified in the Middle Creuse River Valley, has confirmed their penglacial character and shown the impact of recent tectonics and the magnitude of uplift which affect the geometry of the deposits on the northern edge of the Massif Central and the southern and western parts of the Pans Basin. Three sectors have been distinguished : - a "Massif Central" sector, with an endogenous bed-rock, where some five stepped higher alluvial formations are studied. - an "Intermediate" sector characterized by the opening of the valley when the river joins the Pans Basin. Eleven sandy formations, which constituted advancing fans in this actively tectonic zone, have been identified. - a "Pans Basin" sector in which the Creuse flows westwards along a major fault. Eight stepped terraces have been recognized here. Several geochronological data were obtained by electronic spin resonance (ESR) method applied to bleached alluvial quartz. The results show a good reproducibihty and generally a good coherence with the altimetry. They indicate, in close correlation with sedimentological and tectonic studies, that the response of the river is variable and depends of local geology and tectonic characteristics. From the results obtained on each sector, a first synthetic but schematic history of the fluvial system can be proposed for the Middle Creuse River valley between 1,7 Ma BP and today Some major tectonic movements are dated between 1,7 and 1,2 Ma, around 600 ka and between 450 and the present. On the other hand, the "Pont-de-Lavaud" Early Palaeolithic site with archaic pebble quartz industry was dated to the end of the Lower Pleistocene, around 1,1 Ma BP.