Tertiary tectonism in the Tapajós River area, Amazon Basin

Abstract

A zone of sediments deformed during the Tertiary occurs in the southern part of the Amazonas Basm and encompasses an area roughly 540 km long by 50 to 100 km wide m the region of the Abacaxis, Tapajós, and Curuá do Sul rivers. The eastern end of this zone is found inside the Tapajós Block, which is located principally on the eastern side of the Tapajós River. Within this block, the boundaries of the deformed zone are defined by strike-slip faults which may correspond to old basement weak zones that were intermittently reactivated during the geological evolution of the basin. In structural terms, the area is characterized by a set of folds and faults, arranged en echelon with a general NE trend. The origin of these strained features is attributed to the convergent E-W stresses that acted on pre-existent NE-trending discontinuity surfaces. The identification of this prominent shearing event was made possible by geophysical evidence, especially seismic reflection corroborated by gravity and aeromagnetometric data.