Ichnology of Cenozoic marine deposits from Patagonia (southern Argentina): the role of the modern evolutionary fauna in Neogene infaunal ecosystems

CARMONA, N.B.; BUATOIS, L.A.; MÁNGANO, M.G.; BROMLEY, R.G.; PONCE, J.J.; BELLOSI, E.

Ichnology of Latin America

Monografias da Sociedade Brasileira de Paleontologia

Año: 2012; p. 83 - 97

Neogene deposits from Patagonia are characterized by extremely diverse ichnofaunas, including a great variety of feeding (e.g., Asterosoma, Helicodromites, Phycosiphon, Rosselia, Teichichnus), grazing (e.g., Nereites, Scolicia, Taenidium) and dwelling (e.g., Balanoglossites, Gastrochaenolites, Gyrolithes, Ophiomorpha, Siphonichnus, Spongeliomorpha, Schaubcylindrichnus, Thalassinoides) structures. Subordinately, locomotion (e.g., Protovirgularia) and equilibrium/ escape structures (e.g., Scalichnus) occur. Trace fossils in open-marine deposits are abundant and diverse, with extremely complex tiering structures, and most commonly characterized by the presence of the archetypal Cruziana Ichnofacies. On the contrary, restricted, commonly tide-infl uenced, brackish-water environments show low to moderate ichnodiversity, monospecifi c associations, trace fossils generally of small sizes, and the presence of an impoverished Cruziana- Skolithos Ichnofacies. Irregular echinoid structures are abundant mainly in open-marine environments while those produced by bivalves and crustaceans dominate the open-marine and brackish-water ichnofaunas, refl ecting the peak of the Modern Evolutionary Fauna. Ichnofaunas of modern aspect seem to have been well established in shallow-marine, open environments since the Mesozoic, and this is particularly well exemplifi ed in the Neogene ecosystems from Patagonia, where fi nely tuned climax communities display vertical niche partitioning and a remarkable use of the infaunal ecospace. These observations agree with the trends exhibited by the body-fossil record, which show that for the Late Cenozoic middle-latitude successions, marine paleocommunities include a greater representation of infaunal organisms, especially of deep-burrowers. In addition, local infl uence of nutrient-rich waters brought to the surface during upwelling events along the Patagonian coast may have also contributed to the increasing complexity seen in these Neogene infaunal ecosystems.