Ichnology of 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.

St. John's

Congreso; Ichnia 2012; 2012

Memorial University

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, 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‐influenced, brackish environments show low to moderate ichnodiversity, monospecific associations, generally 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 and brackish‐marine ichnofaunas, reflecting 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 exemplified in the Neogene ecosystems from Patagonia, where finely 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 middle latitude successions for the Late Cenozoic, marine paleocommunities show a greater representation of infaunal organisms, especially of deep‐burrowers. In addition, local influence of nutrient‐rich waters brought to the surface during upwelling along the Patagonian coast may have also contributed to the increasing complexity seen in these Neogene infaunal ecosystems.