Pleistocene Ophiomorpha nodosa from Buenos Aires, Argentina: Paleoenvironmental implications for ghost shrimp trace fossils along South America

摘要

Ophiomorpha nodosa Lundgren1891 is described from Puente de Pascua Formation Late Pleistocene of northeastern Buenos Aires province. The pelletal morphology and the base of ramifications of O. nodosa burrows are compared with mid-Holocene, Late Pleistocene Pehuen-C ' o locality and southern Brazil records. The preservation between sites differs in the degree of erosion and weathering, in situ or ex situ provenance, fragmentary shafts with or without branching and degree of cementation. These comparisons between sites suggest that different environmental conditions have generated the accumulation of trace fossils in transgressive and highstand depositional environments from foreshore through offshore. Neoichnological observations ascribe the burrowing of Ophiomorpha to ghost shrimps. For South American records Audacallichirus (formerly Sergio) mirim Rodrigues and Ho center dot dl, 1990 has been suggested as the producer, due to the similarity in morphology between modern and fossil burrows, and geographic distribution of ghost-shrimps. Finding of a widespread ichnotaxon possibly produced by the same taxon in different environmental conditions in the southwestern Atlantic suggests behavioral plasticity. The paleoenvironment of Puente de Pascua Formation in the level with Ophiomorpha burrows is interpreted a tidal flat in intertidal to subtidal depositional environments and relatively calm waters.