A Zoophycos carnival in Devonian beds: Paleoecological, paleobiological, sedimentological, and paleobiogeographic insights

Devonian occurrences of Zoophycos are often observed in successions representing shelfal deposits and have been interpreted as the first expansion of this trace fossil during the Paleozoic. Dense Zoophycos occurrences in storm-generated Paleozoic beds have been interpreted as the result of ecological opportunist strategy when the tracemaker exploited quiet, nutrient garden substrates after storms. In the Devonian Ponta Grossa Formation (Pragian to Frasnian) of the Paraná Basin (Brazil), Zoophycos is both preserved in storm-generated strata indicating oxyc substrates, and in association with Chondrites and Phycosiphon suggesting dysoxic offshore deposition. This study focuses on the analysis of Zoophycos observed in the Devonian strata to understand the depositional context reflected by paleoecologic strategies and taphonomic signatures. We analyzed the ichnofabrics and sedimentary facies of Devonian sections from the Paraná Basin, focusing on the occurrences of Zoophycos. The tiering structure involving dense Zoophycos ichnofabrics demonstrated that shallower burrows (e.g., Asterosoma, Palaeophycus, Cylindrichnus, Schaubcylindrichnus, Skolithos) reworked deep-tier burrows (Chondrites, Phycosiphon, and Zoophycos), indicating erosion of surficial levels. The dense Zoophycos ichnofabric representing the fair-weather suite obliterated primary sedimentary structures of storm deposits, which favored the visibility of deep-tier structures in a lam-scram pattern. In this sense, dense Zoophycos ichnofabric from Paraná Basin cannot be linked to an opportunistic behavior, but to an over-represented occurrence in space and time, being a taphonomic artifact related to low accommodation space in prograding context. The association with other trace fossils allowed the attribution of Zoophycos as a component of distal and archetypal expressions of Cruziana Ichnofacies rather than Zoophycos Ichnofacies. Concerning the vertical distribution of Zoophycos in the Paraná Basin, this trace appears in strata related to the first occurrence of land plants, being common in the Pragian-Eifelian interval, and declining in upper strata. This decline might be related to a potential structural change of the Paraná Basin during Middle Devonian.