Evolução paleogeográfica, durante o cenozóico, da região de Bragança, NE do estado do Pará

Abstract

The main morphologic features of northeastemn Para State are strongiy related to middle Cenozoic extensional tectonics which is responsible by the Gondwana break up resulting in the formation of the Equatorial Atlantic Ocean and of the passive margin. The area is included in the Bragança-Viseu Basin, which evolved from the extensional tectonics incidence on the northeastem of the Para State since the Upper Jurassic. During the Miocene this area underwent transtensional tectonics that generated NW-SE normal faults and E-W and NE-SW dextral strike-slip faults. This tectonic event formed large subsided areas and corridors that facilitated transgression towards the continent since 150 km from the present coastline. This transgression originated the carbonatic sequence included in the Pirabas Formation, deposited in areas with drainage systems typical of subsided regions. Some areas remained emerged during the transgression. In the Bragança-Viseu Basin the sediments of Pirabas Formation are scarce, which suggest presence of a structural high blocking the transgression of the “Pirabas Sea”. The occurrence of limestone towards the south of Bragança suggest a cost line characterized by bay heads and promontories facing northwest. On the basis of geophysics interpretation, it was demonstrated in the Bragantina region the absence limestone towards the main depocenter of the Bragança-Viseu Basin. Therefore in this area, there are only occurrence of Precambrian rocks overlaid by Quaternary sediments (debris flows) included in the Post-Barreiras sequence.. The landscape has not change since Miocene - Pliocene, as can be demonstrated by the colinas relief. The geologic data suggest that the landscape evolution is controlled by structures related to the transtensional event.