Notas sobre a geologia e formação da costa do extremo norte do Brasil


  • Fritz Louis Ackermann


Amapá, Marajó, Ilha de - PA, Costa, Geologia


In this work the author describes the geology and the geography of the northern coast of the Amazon River, the present mouth of this river, his previous course and the formation of an actual delta.

            As the junction of the Amazon river with the sea was previously more next to the north, the river formed in the southern part an area of "annexed lands" to the continent, that the big river in his recoil to the south had clip off forming the present archipelago at the mouth o f the Amazon.

            The northern coast had suffered a strong marine abrasion, latter recovered by the Amazon slime when the rivers Uaçá, Urucaná, and part of the Cassiporé river had cut his bed.

            That marine transgression had produced a complete penetration at the seaboard strip of Amapá letting the island-mound and the fossil cliff in the region of the Uaçá river and below the Oiapoque river.

            An isostatic reflex due to the raising of the Andes Mountains had provoked a slight rise of the northern coast which produced the formation of a string of coastal lakes in that region.

            There was also a small alteration in the course of sedimentation of the Amazon slime which in great part was deposited on the northern Brazilian coast which produced a gradual rise of the continental shelf law by itself, that forbade and forbid the free departed of the waters of the rivers of that coast. The smaller courses of water, which volume of water does not allow the keeping of a free way out, due to this circumstances became rivers without outlet to the sea and former the new bottom lands the new lakes in formation.

            The effect of the flats existent in the coast and in the continental shelf makes itself to feel violently at the times of the equinoxes occurs, when the sea waters encounters barriers in the masses of liquid mud which cause the delay of the tide, thus exciting the POROROCA phenomenon.

The author also study the influence of the northern direction of the water volume of the Amazon river, which forces the rivers Cassiporé and Uaçá to follow it in its march to the North. Thence the curious formation of this rivers, parallels to the marine coast, since they enter in the full of flats part made by the Amazon slime.