Abstract

Despite numerous researches concerning the Massif Central southern border, there are no certainties about the number and the chronology of the erosion surfaces, the uplift stages of the Massif Central and the incision stages of the rivers. Located on the Massif Central basement and on the Languedocian piedmont, the Orb, Libron and Hérault tributaries basins show a good pattern of shapes and formations, from the Caroux to the littoral plain. Geomorphological and sedimentological study brings some new insights to these questions.

Heavy minerals analysis allows us to separate different formations among the deposits located on the erosion surfaces and in the valleys. It is used to reconstruct the main sedimentary pathways. North-south fluxes crossed the Avant-Monts up to the Upper Pliocene, despite of the Miocene uplift. Upper Pliocene uplift of the Avant-Monts caused the bifurcation of the Orb towards the west, the antecedent incision between the Jaur confluence and Cessenon and the stepped pediments and glacis on the Avant-Monts southern border. The longitudinal paleoprofiles argue for a progressive uplift of the Massif Central since the Messinian unconformity. Incision of the valleys began before the Messinian in the Massif Central, but only during the Lower Pleistocene in the Languedocian piedmont.

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