Pulses of life: Wet events in Botucatu Paleodesert evidenced by trace fossils analysis (earliest Cretaceous, Paraná Basin, Brazil)

Abstract

The earliest Cretaceous Botucatu Formation (Paraná Basin, Brazil) comprises an erg deposit developed in the central part of Gondwana and is dominated by eolian dune facies. In this paper, we improve understanding of the ichnology of eolian deposits by describing trace fossil assemblages in São Bento Quarry in Araraquara County. The trace fossils occur on paleodune slipface surfaces, and include trackways (Paleohelcura tridactyla and P. araraquarensis) and burrows (Arenicolites isp., Skolithos isp., Taenidium serpentinum, Vagorichnus anyao, and Planolites beverleyensis). The Skolithos isp. and Vagorichnus anyao specimens also occur in clusters in more intensely bioturbated beds. We interpret these assemblages as evidence of episodic wet events, which were unable to generate subaqueous facies, but triggered plant growth and invertebrate proliferation. Based on studies of modern hot deserts, we infer that the overall longstanding water input promoted some primary productivity sustaining striving invertebrates, recorded as low bioturbation levels. Episodic wet events controlled the bioturbation bursts by increasing the primary productivity and inducing consequent invertebrate proliferation. We propose that these bursts of invertebrate bioturbation observed along the stratigraphic section of dry facies can be taken as the main ichnological characteristic of a dry eolian system. We also propose refinements to the Octopodichnus–Entradichnus ichnofacies model, addressing unsolved issues to enhance the interpretation of ancient eolian environments.