Morphology of scarps and piedmonts on the equatorial passive margin of northeast Brazil: Neogene to present evolution and its factors - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2006

Morphology of scarps and piedmonts on the equatorial passive margin of northeast Brazil: Neogene to present evolution and its factors

Résumé

Steep slopes form the marginal scarp of the semi-arid northern Brazilian “Nordeste” and bound inner residual plateaus and ridges rising up to 800-1,200 m. They overlook a low pediplain merging seaward with a well developed coastal erosional-gradational piedmont. Only a few of them coincide with geological contacts and/or fault zones. Their location, their straight or sinuous outlines, and the presence or lack of residual landforms in front of them give indications on their origin and evolution. Dissected pediments and sparse debris fans visible at the base of some escarpments suggest recent erosive activity and possible slope retreat, although most of these forms are decoupled from major valleys. In order to understand scarp morphology and evolution in a context where various factors (lithology, neotectonics, climatic and eustatic changes) can be considered, we describe the morphostructural patterns of chosen escarpments, as well as the morphodynamic conditions of their evolution since the Neogene. Only a few scarps retained in our study show strong structural control. It could not be determined in all cases whether they are residual or active fault scarps, or fault-line scarps. Most of them, straight or sinuous, controlled or not by local structures, are mainly inherited landforms, initiated during the Cretaceous rifting (south of the Potiguar basin) or later. The Neogene clastic sedimentation on the piedmonts and on coastal areas probably reflect the occurrence of dry periods inducing widespread stripping of deep soil horizons and erosion of bare rock slopes and surfaces, even without tectonic forcing. Dissection stages occurred in periods of more humid climate and/or low sea level. Only slight or local backwearing of slopes occurred, associated with downwearing on pediments, probably in diachronic ways. The moderate volumes of Neogene clastic sediments imply overall low uplift and erosion rates until the Present, still to be more precisely quantified, and favourable to morphological and lithological resistance effects in the landscapes.

Domaines

Géomorphologie
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Dates et versions

hal-01082533 , version 1 (13-11-2014)

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  • HAL Id : hal-01082533 , version 1

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Jean-Pierre Peulvast, Francois Betard, Vanda Claudino Sales. Morphology of scarps and piedmonts on the equatorial passive margin of northeast Brazil: Neogene to present evolution and its factors. I.A.G. Regional Conference on Geomorphology and IVth Brazilian Symposium on Geomorphology, Sep 2006, Goiânia, Brazil. ⟨hal-01082533⟩
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