Sedimentation processes and facies on a semi-vegetated Talus, Lousteau, southwestern France

A two-year survey of clast displacements on a small rockfall talus at Loust eau, southwestern France, shows that creep reaches up to 19 cm/month near t he talus apex, whereas the distal segment remains stable. Movements are not distributed homogeneously but concentrate in distinct areas because of the deflection of clasts by Vegetation patches. Sections across the talus reve al stratified deposits, thought to result from the lateral shifting of the tongues of very mobile debris. Poorly sorted gravel layers alternate with c oarser debris corresponding to former pavements developed where sedimentati on is reduced due to the protective effect of vegetation. Similar deposits have been found in larger, semi-vegetated taluses from the forest belt of t he French Alps. Interactions between vegetation development and sedimentati on, possibly controlled by the climatic changes during postglacial times, m ay be responsible for their stratification. Copyright (C) 1999 John Wiley & Sons, Ltd.