Estudos geomorfológicos no Nordeste brasileiro

Resumo

In the Post-Cretaceous era occurred an exhumation in Nozoitheast, Brazil, regionally diffe1ent from the paleography peneplain: The remnants of the Mesozoic sedimentary layer (table hills) show that this exhumation it is not yet completed The new evolutive cycle began with a positive epeirogenic movement probably in the end of Cretaceous period.. The tectonic movement from which resulted the faults began to be shown more and more in the relief. We can see through the displacements that the influence of the fault formations on the relief features is more evident in north than in south.

            The rise movements didn't occur only in transitory phases but their intensity during these phases was modified from a region to another. It is p1obable that in Borborema Plateau displacements had existed since the beginning. Later this region remained stationa1y regarding the other zones that nowadays show the highest levels (800/1000 m).

            In the relief features we can see three remarkable zones whose directions are NNE and E and probably correspond to greater rise axis during the main phase of tectonic movement:

1. a) Arcoverde Zone, which later, in direction to Garanhuns by width pe1haps adopted a cupola form, breaking to East;
2. b) Teixeira Zone, which goes to the Borborema North Plateau;
3. c) Maritns-Santana Zone, formed by a series of "horts" (onrth edge mountain)

            Among the th!ee rise a xis there are two valleys: between a and b, the Floresta Campina Grande Depression which rims in the east with the lowest plain of Borborema Plateau from 400/500; between b and c an inter mountain depression situated in the region of Rio Piranha System in which by a side, the paleographic peneplain (arquipeneplain) continues its development on the other side it was ca1ved by erosion laterally (functional part of the planeplain)

            The low and intermountain areas of denudation are connected to a north coastal platform by the 1arge Jaguarire and Piranhas valleys. In contrary, the east coastal region shows stepped erosion levels divided in valleys that present the rhythm of the rise movements. The platform conditions in the north cost and its connection with in ‘ermountain’ denunciation areas which formation continued recently, show that the expression "peneplain in situ" has only one parographic sense to the Northeast of Brazil Actually the coastal platform and the intermountain plains belongs to the functional part of a peneplain whose formation recently had a differential continuation. The argui-peneplain exhumed on them continued its formation to the botton ant to the sides. The flat surfaces of the highest levels, in contrary, have the cha1acteristics of a fossil peneplain on which the arqui-peneplain was put down vertically.

            The Borborema plateau, also originated from the arqui-peneplain, was situated between the recent functional part of the peneplain and the higher levels of fossil plains Although this plateau is higher than the inte1mountain denudation area of Patos begun its graduate union to the intermountain denudation plains of Piranhas System by regressive erosion over Picui area.

             The closing of the rise zone and of the valleys directed to the East with the watershed who e direction probably is N/S, constitute a geographic feature of intermountain plains and o· the Borrmema Plateau Watching attentively we find that the direction must be NNE the one which appears in other 1anges between Alagoas cost and Ceará west mountains.

            The transportation and special formations of erosion to which belong the "inselberge" prove that the surface denudation continue in lowest inter mountains plains as in Borborema Plateau and S Francisco Depression. Important testimonies are the 'inselberge" regions of Quixadá and Patos. There the 'inselberge" are situated in front of closed mountainous regions. In Quixadá area the "inselberge" formation is due to the wideness of the valley system and in Pato Zone by the erosion of small "horts". The "in elberge" are placed over rocky surfaces which surround them and are laterally increased by erosion. The two "inselberge" regions are as the others testimonies (ruined rocks, flat bottom valleys) a prove that the denudation process is continuing. In the Northeast geomorphologica1 genesis the tectonic forces cooperated and the erosion process were due to the meteorological action. A variate and hot climate give the condition to the erosion process and NE is an excellent objective to the study for the knowledge of these process.