A Geomorfologia do Brasil Oriental

Abstract

The region studied herein lies between the valley of the Rio São Francisco and the Atlantic seaboard, continued southwestwards as far as São Paulo. It includes portions of six states and covers approximately one million square kilometers. The author states that the various types of landscapes were analyzed by referring the multitudinous forms of Eastern Brazil to a relatively small number of denudational cycles, following each other successively in geologic time, and so operative that each, in its development from the coast towards the interior encroaches upon the land forms of its predecessor and is itself in turn encroached upon by the freshly developing features of its successor. According to the author it is in this conception of orderly development by sequential landscape cycles that lies the secret to the understanding of Brazilian geomorphology. Though, in few words, the fundamental element of modern Brazilian scenery was a vast plain produced by denudation between the late Cretaceous and mid-Tertiary, when it was uplifted, later polycyclic stream incision has almost everywhere carved vaneys into the surface reducing it to a dissected upland or, locally, even to a set of mere even crested skylines upon the ridges This vast planation is termed the Sul-Americana planation. The post Gondwana surface, late Cretaceous in age, is never very smoothly planed and is often a relatively rough topography. The desert landscape, Sud Botucatu, of late Triassic age, and a fossil surface which emerges locally and of Carboniferous age, are reviewed by the author, together with the evidence for their ages. Erosional cycles succeeding the Sul Americana and current during the late Tertiary and Quaternary, after mid-Tertiary and later epeirogenic uplifts, are evidences by river incisions and valley excavations that have destroyed most of the Sul Americana upland and now occupy most of the landscape. The Velhas cycle of erosion, immediately succeeding the Sul Americana and graded to a late Tertiary base-level, for instance, is typically present as valley incisions dissecting the Sul Americana upland. Quaternary cyclic erosion is represented in the coastal hinterlands of the East, Paraguaçú cycle, where it is sometimes destructive of all former topographies. After describing the cycles which actuated on the Brazilian landscape, the author studies the mode of development of the same, discussing in detail the. relief units, the series involved and the evidence pertaining to each denudational cycle. A comparison with data from Africa will be made in a second, and later, report.