Drainage network evolution and divide retreat along a passive margin: the permanence of disequilibrium under unfavourable natural conditions in eastern South America

Abstract

Passive margins typically present escarpments that separate high relief coastal draining catchments from lower-relief inland ones. Widespread drainage reorganization processes in these areas commonly lead to drainage divide retreat inland. This study examines how unfavorable natural factors-long distance from the regional base level, dry climate, and resistant basement lithology-interfere in the processes of inland advance of coastal catchments. Therefore, morphological evidence of drainage reorganization was identified within the northern Serra do Espinhaço Mountain range, and Gilbert's metrics and χ values were calculated. Thisrange forms a significant drainage divide along South America's passive margin, located hundreds of kilometers inland. It is also characterized by erosion-resistant quartzites substratum and currently experiences a semiarid climate. Our results demonstrate that while the northern Serra do Espinhaço is not a typical passive margin escarpment, it behaves like one since this mountain range acts as a divider between rivers that drain directly into the Atlantic and rivers draining westwards towards the continent's interior. This significant drainage divide retreats inland, driven by ocean draining rivers headward erosion through captures despite adverse geographical location and geological conditions. Divide retreat is ongoing along South America's passive margin, and this process has not yet reached equilibrium.