Tectonics and paleogeography along the Amazon river

The main structural and geomorphological features along the Amazon River ar e closely associated with Mesozoic and Cenozoic tectonic events. The Mesozoic tectonic setting is characterised by the Amazonas and Marajo B asins, two distinct extensional segments. The Amazonas Basin is formed by N NE-SSW normal faults, which control the emplacement of dolerite dykes and d eposition of the sedimentary pile. In the more intense tectonic phase (mid- Late Cretaceous), the depocentres were filled with fluvial sequences associ ated with axial drainage systems, which diverge from the Lower Tapajos Arch . During the next subsidence phase, probably in the Early Tertiary, and und er low rate extension, much of the drainage systems reversed, directing the paleo-Amazon River to flow eastwards. The Marajo Basin encompasses NW-SE n ormal faults and NE-SW strike-slip faults, with the latter running almost p arallel to the extensional axes. The normal faults controlled the depositio n of thick rift and post-rift sequences and the emplacement of dolerite dyk es. During the evolution of the basin, the shoulder (Gurupa Arch) became di stinct, having been modelled by drainage systems strongly controlled by the trend of the strike-slip faults. The Arari Lineament, which marks the nort hwest boundary of the Marajo Basin, has been working as a linkage corridor between the paleo and modern Amazon River with the Atlantic Ocean. The neot ectonic evolution since the Miocene comprises two sets of structural and ge omorphological features. The older set (Miocene-Pliocene) encompasses two N E-trending transpressive domains and one NW-trending transtensive domain, w hich are linked to E-W and NE-SW right-lateral strike-slip systems. The tra nspressive domains display aligned hills controlled by reverse faults and f olds. and are separated by large plains associated with pull-apart basins a long clockwise strike-slip systems (e.g. Tupinambarana Lineament). Many cha nges were introduced in the landscape by the transpressive and transtensive structures, such as the blockage of major rivers, which evolved to river-l akes, transgression of the sea over a large area in the Marajo region, and uplift of long and narrow blocks that are oblique to the trend of the main channel. The younger set (Pliocene-Holocene) refers to two triple-arm syste ms of rift/rift/strike-slip and strike-slip/strike-slip/rift types, and two large transtensive segments, which have controlled the orientation of the modern drainage patterns. (C) 2001 Elsevier Science Ltd. All rights reserve d.