Eolian dunes of the Botucatu Formation (Cretaceous) in southernmost Brazil: morphology and origin

Abstract

Abstract The Botucatu Formation consists of eolian sandstones that cover a large area of the central portion of South America, being one of the most impressive occurrences of continental deposits globally. A detailed facies analysis was performed in several exposures of the Botucatu Formation in the Rio Grande do Sul State (southernmost Brazil). Two basic morphological types of eolian dunes were identified: (1) simple, locally compound crescentic dunes; (2) complex linear dunes. Superimposed dunes migrating obliquely to the lee slope of the main bedforms characterize the crescentic draas. Superimposed crescentic dunes migrating parallel to the draa brink compose the linear draas. The linear draas experienced important lateral migration. Both types of composed dunes are morphodynamically interpreted as oblique dunes. The eolian dunes succession of the Botucatu Formation may be defined as a dry eolian system. As super surfaces are absent within the eolian strata, the Botucatu Formation represents a single eolian accumulation. The end of the eolian sedimentation and the development of a super bounding surface were the result of the rapid extrusion of the Serra Geral basaltic lava floods, which preserved the bedforms morphology. This fact, associated with the flexural subsidence caused by the thick lava floods, allowed the preservation of the entire eolian accumulation into the geological record.