Evolution of the Pernambuco-Paraiba-Rio Grande do Norte Basin and the problem of the South Atlantic connection

Abstract

The easternmost sedimentary basin of the NE Brazilian Atlantic margin shows special tectonic and sedimentary features due to the fact that it was the last link between South America and Africa. The basin is strongly influenced by the rotational separation of both continents and by the reactivation of Precambrian faultlines. The basin may be subdivided into seven subbasins which all have a homoclinal structure. The differential downwarp of the crystalline basement resulted in deeper and shallower parts that are bounded by faults. A crystalline basement high disrupts continuity between the three southern subbasins in Pernambuco and Paraíba States, and the four northern ones in Rio Grande do Norte State. Sedimentation in the basin started in about Santonian time with meandering, sometimes braiding fluvial sandstone systems passing seaward into calcareous littoral sandstones. In the Maastrichtian the sea advanced over the area. As a consequence, sedimentation in the southern subbasins began then with the accumulation of transgressive phosphorites and calciclastics from a South Atlantic source. Later, somewhat deeper-water limestones were deposited. A Paleocene regression is represented by detrital limestones and calcareous clays. Marine sediments of Maastrichtian age in the northern subbasins, which belong to the Equatorial Atlantic, are restricted to shallow-water shelf limestones which became strongly recrystallized and partly dolomitized. From the structural, geophysical, sedimentological and paleontological analyses of the basin we conclude that (1) the last link between South America and Africa was broken only at the end of the Cretaceous, (2) the sill tilted southward before its rupture, (3) the sedimentary fills north and south of the sill came from different sources, and (4) upwelling in the South Atlantic against the sill caused phosphorite deposition.