Basin inversion, scarp retreat and soil distribution in the Araripe basin (northeast Brazil): implications for denudation history
Résumé
At the border between the Ceará, Piauí, and Pernambuco states (northeast Brazil), the high sandstone table called Chapada do Araripe overlooks lower and drier plateaus and depressions shaped into underlying post-rift and rift layers, in the east, or in the basement, to the west and south. The modes and rates of relief inversion that lead the upper layers of the Araripe basin to their culminating position are examined in relation with geological structure and regional uplift, through the presentation and discussion of morphostructural patterns and types of escarpments, differential erosion landforms, soil sequences, modalities of scarp retreat, and possible differential vertical movements (tectonic inversion). The geomorphic and pedological contrast between the plateau (a near-structural surface covered by Ferralsols) and its lower surroundings (either an exhumed Pre-Cenomanian paleosurface covered by Plinthosols, or lower surfaces with relatively immature soils of Luvisol type, often associated with Leptosols) is explained through a study of the evolution of the cuesta-like scarps or glints and outliers that fringe the chapada above sedimentary depressions and basement surfaces. A reconstruction of the conditions and chronology of relief inversion and corresponding area reduction is proposed, according to principles and methods of morphostratigraphy and morphopedology. It brings elements for discussing recently published models of episodic burial and exhumation history, based upon interpretations of thermochronological data obtained in nearby regions. This discussion also bears strong implications about long-term landform evolution in northeast Brazil and other passive margin areas. From a more general point of view, the present work is considered as a case study for analysing processes and rates of vertical erosion and scarp retreat in tropical tabular structures and sandstone plateaus.