On the ex situ Ophiomorpha and other burrow fragments from the Rio Grande do Sul Coastal Plain, Brazil: paleobiological and taphonomic remarks

The Rio Grande do Sul Coastal Plain (southern Brazil) is composed of extended marine and continental deposits related to at least four barrier-lagoon systems of Pleistocene-Holocene age. Part of these deposits is currently submerged and passing through erosion processes by waves. Vertebrate and invertebrate body and trace fossils are constantly exhumed from these deposits and redeposited on the modern beach face. Among them, a total of 253 fragments of crustacean burrows were collected for this study. Two ichnospecies of Ophiomorpha were recognized (O. nodosa and O. puerilis), but most of the materials can only be assigned to the SOT group (Spongeliomorpha, Ophiomorpha and Thalassinoides), mainly because of the lack of a pelleted lining. The absence of pellets and, by consequence the ichnotaxonomy of these specimens, is related to taphonomical processes (exhumation, reworking and transportation) that acted in the formation of the ex situ assemblage. The paleoenvironmental dynamics and a...