A belt of deformation in the Solimões basin of northwestern Brazil extends east-northeast from near the Peruvian border for about 1300 km. The belt is characterized by the en echelon arrangement of folds and faults interpreted as the result of right-slip displacements in a transpressive regime. The structures were formed during Late Jurassic time, probably due to collision of South America with allochthonous terranes as the opening of the South Atlantic Ocean began. The Iquitos arch near the western end of the megashear separates the Solimões basin from Subandean basins. The development of the Iquitos arch is interpreted to be related to orogenic loading along western South America by the Andean mountain belt. In Brazil,folds and faults associated with the Solimões megashear hold hydrocarbons within Paleozoic strata, and 15 gas and oil fields have so far been discovered.