Tafonomy of macroinvertebrates and Albian marine ingression as recorded by the Romualdo Formation (Cretaceous, Araripe Basin, Brazil)

The Romualdo Formation, Araripe Basin, crops out in the municipality of Exu, Pernambuco State, exposing coquinas. Fauna survey, taphonomic analysis of the macrobenthos, and identification of sedimentary facies of the outcrop were carried out to contribute to paleoenvironmental understanding of the Romualdo Formation. The association of molluscs (Cerithium sp., Tylostoma ranchariensis, Aguileria dissita, Brachidontes araripensis and unidentified cassiopids) and echinoids of the species Bothryopneustes araripensis suggests sedimentation in the marine environment. The taphonomic similarities made possible the grouping of coquinas into two types. Coquinas type 1 exhibit characteristics of transport and reworking of bioclast generated by storms in proximal setting. Coquinas type 2 demonstrates echinoids in situ and articulated with spines connected to shells, suggesting a fast sedimentation by distal tempestite. Regarding sedimentary facies, the concentrations of invertebrates would have been formed in the transitional offshore zone of siliclastic platform. The results presented here evidence a broader distribution of echinoids and expand the geographic limits of the shallow marine environment in the Romualdo Formation.