BIOSTRATIGRAPHY PROBLEMS IN THE CONTINENT AL UPPER PALEOZOIC (STEPHANIAN - AUTUNIAN) IN THE FRENCH MASSIF-CENTRAL

Coexistence of Autunian floras and Stephanian floras within the same f ormation and within several limnic Upper Palaeozoic basins of the fren ch Massif central, is associated with palaeoenvironmental variations: ''Autunian'' floras are meso- to xerophile and have grown on the topog raphic highs bordering basins, whereas ''Stephanian'' floras are hygro phile, grown in lower marshy zones within basins. The climatic change recorded at the Carboniferous - Permian limit, from wet to dryer condi tions, led to the extension of the xerophile floras at the expenses of the hygrophile ones that nearly completely disappeared. This indicate s the importance of palaeoecological conditions on both the repartitio n and evolution of Permo-Carboniferous floras. Consequently, biostrati graphy of the continental Upper Palaeozoic (based on floras) can not p rovide a fine tuned chronology for the structural events of that time.