Classification of Onshore Sedimentary Basins in Brazil: ABSTRACT

Abstract

The major sedimentary basins of Brazil range in age from late Proterozoic to Cenozoic. They overlie a stable Precambrian craton consolidated by several orogenic events. Two major regions can be distinguished in this basement: the relatively calm Amazonic Province and the strongly tectonized Atlantic Province, welded together 900 to 1,200 m.y. ago. The oldest of the major superimposed basins is the Bambui (Sao Francisco) basin, whose sedimentary sequence was, especially along the margins, slightly folded and metamorphosed during End_Page 618------------------------------ the Braziliano-Panafrican orogenic-thermotectonic event 450 to 750 m.y. ago. Large Paleozoic basins are superposed both over the Amazonic craton (Amazon basin) and over the Atlantic craton (Maranhao and Parana basins). They were subjected to regional cratonic subsidence and broad regional arches separate several subbasins. The architectural framework and shape of the basins (saucer or elongated trough) allow them to be classified either as remote interior basins (Middle and Lower Amazon, Maranhao, and Parana) or as near interior basins (Upper Amazon), the latter being affected by the Hercynian orogeny. In westernmost Brazil, the Acre basin forms part of the mobile subandean belt and displays intense deep-focus (500 to 700 km) seismic activity. Its architecture and tectonic behavior are that of a typical intracontinental cratonic composite basin. In Early Cretaceous time, intense faulting marked the breakup of the Gondwana supercontinent. A series of rifts opened along the present Atlantic coast, with characteristic horst-and-graben system. Some rifts remained aborted aulacogens (Takutu, Marajo, Reconcavo-Tucano) whereas others developed into the pull-apart basins of the widening South Atlantic Ocean. The Cenozoic basins can be divided into two groups: (1) those of southeastern Brazil along the Serra do Mar and the Serra da Mantiqueira where half-grabens formed through vertical reactivation of faults following Precambrian lines of weakness, and (2) those of central Brazil (Pantanal and Bananal) where large interior basins are being formed through slow cratonic subsidence. End_of_Article - Last_Page 619------------