Sedimentology of the proximal portion of a large-scale, Upper Jurassic fluvial-aeolian system in Paraná Basin, southwestern Gondwana

Abstract

Upper Jurassic sedimentary rocks of Guará Formation record the environmental and geotectonic changes of the early break-up stages in the southwestern portion of Gondwana. Newly-described occurrences of this formation allow the expansion of its areal distribution to the central part of the Paraná Basin, Brazil. Four vertical sections are presently described in Paraná State, Brazil. Nineteen lithofacies were grouped in five facies associations, through the classical method of facies analysis. The facies analysis included Guará Formation and the adjacent portions of the underlying Pirambóia Formation and the overlying Botucatu Formation. The depositional system of Pirambóia Formation was wet aeolian fluvial-influenced and is composed by aeolian dunes, aeolian sandsheets/interdunes and ephemeral fluvial deposits facies associations. The Guará Formation is composed of multistorey fluvial facies association constituting a highly amalgamated perennial fluvial system. It is overlaid by the Botucatu Formation, characterized as a dry aeolian system formed by aeolian dune deposits. The stratigraphic units are separated by regional unconformities marked by a shift in facies and depositional systems that reflect climatic changes. The Guará Formation depositional model, established in correlation with southern sections, represents a broad fluvial system with aeolian interaction deposited in a wide basin with more than 800 km in extension. This large depositional paleoenvironment, together with other Upper Jurassic records in southwestern Gondwana, represents the early rift stage of Gondwana break-up.