科研之友
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摘要
This study aims to reconstruct the Cenozoic and Pleistocene morphodynamic evolution of the Orb, a Mediterranean river which crosses all the structural units of the south Massif Central border. A geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations and reconstructing the palaeodrainage. Heavy minerals were used to reconstruct the main sedimentary palaeochannels since the Messinian. The successive Orb longitudinal profiles show anomalies which can be caused by structure and by interactions between fluvial dynamics and tectonics. Evidence of volcanic heavy minerals on the Faugeres Mountains and in the Upper Pliocene deposits of the Languedocian piedmont demonstrates that a north-south flow took place during the Upper Pliocene. Nevertheless, a palaeo-Orb existed at the place of the present Course when the basaltic lava flows were spreading, but headward erosion did not reach them until the Upper Pleistocene, because the Orb middle and high terraces do not contain volcanic minerals sourced from the Escandorgue. The Successive Orb longitudinal profiles show that headward erosion clue to Pleistocene low sea levels does not reach beyond Beziers and that a tectonic hinge has functioned near the shoreline. The non-lithologic knickpoints are explained by the Montagne Noire and Avant-Monts uplift up until the Pleistocene. A progressive continental uplift is necessary to explain the Orb terraces staircase in the Beziers district, and the fluctuations of incision from upstream to downstream are due to laterally differential movements, which are isostatic effects of thick regressive deposits on the Gulf of Lion shelf during the cold periods.
- 出版日期2009-3
