Triassic aeolian megadune field reveals paleo-monsoon wind directions for low-latitude Gondwana

Linear dunes are rarely recognized in the geological record. By integrating sedimentological observations with aeromagnetic, magnetic susceptibility and magnetization datasets, we reconstruct the morphology of an Upper Triassic aeolian dune field from the sedimentary architecture of deposits preserved in the Sambaíba Formation, Parnaíba Basin, from northeast Brazil. This dune field was buried by lavas from the central Atlantic magmatic province. Aeolian architecture records the migration of superimposed crescentic dunes along the flanks of parent linear megadunes. These bedforms were part of a large aeolian dune field (>55,000 km2), comprising megadunes with east-northeast to west-southwest oriented crestlines, up to 167 m in height, and ~2.7 km in crest-to-crest spacing. Mantled by lava, it is the largest and best-preserved instance of a linear megadune field yet documented in the rock record. The dune field developed in response to the coalescence of north-easterly and south-easterly paleowinds driven by a monsoon system operating at low latitudes (~10°S) of Gondwana during the Late Triassic: this validates atmospheric circulation models which had lacked direct geological support.