Making the most of the Coprinisphaera ichnofacies: evolution of Patagonian middle Cenozoic ichnoassambleges and the South American Paleosol Ichnofossil Ages (SAPIAs).

GENISE, J. F.; BELLOSI, E. S.; SÁNCHEZ, M. V.; KRAUSE, J. M.; CANTIL, L. F.; VERDE, M.; PUERTA, P.

Colonia del Sacramento

Simposio; Tercer Simposio Latinoamericano de Icnología; 2015

TERCER SIMPOSIO LATINOAMERICANO DE ICNOLOGÍA

A recent study on high resolution ichnostratigraphy in the Middle Eocene-Early Miocene Sarmiento Formation at Gran Barranca (Chubut), the world famous type locality for several South American Land Mammal Ages (SALMA), showed that changes in Coprinisphaera density, size and diversity could be used to assess the paleoecological evolution of that locality. Other study showed that diversity of trace fossils associated with Coprinisphaera changed along the sequence too. New research in extended outcrops of the same unit at Sierra Talquino (Chubut) and in older and younger Cenozoic sequences from Patagonia allow us to elaborate a frame on the evolution of ichnoassemblages from the Middle Cenozoic of Patagonia. Changes in ichnoassemblages may be used as indicators of paleoecological evolution within the Coprinisphaera Ichnofacies paleoenvironments. Likewise, other major changes can be still traced by the presence of other ichnofacies. Also these assemblages can be used as age indicators along the Cenozoic (i.e. South American Paleosol Ichnofossil Ages, SAPIAs) in parallel to the SALMAs. SAPIAs would be useful to make predictions not only on ages but also on possible mammal faunas in understudied paleontological localities. The recognized assemblages-SAPIAs named after the dominant trace fossil and their relationships with SALMAs are: 1) Feoichnus assemblage-SAPIA: dominated by Feoichnus challa, few to absent Coprinisphaera, Taenidium isp, Skolithos isp. pre-Casamayoran SALMA (> 43 Ma). 2) Eatonichnus assemblage-SAPIA: dominated by Eatonichnus isp., Feoichnus challa, , Taenidium isp., few Coprinisphaera, and a new ichnogenus. Casamayoran SALMA (43?39 Ma). 3) Small-sized Coprinisphaera assemblage-SAPIA: high density (40-100 specimens per m2) of Coprinisphaera of small sizes (21?60 mm, mean equatorial diameter: 34.5 mm): C. murguiai, C. lazai, C. kheprii, C. tonnii and C. kraglievichi, Feoichnus challa, Teisseirei barattinia, few Rosellichnus patagonicus, Celliforma rosellii, and the new ichnogenus. Mustersan SALMA (38 Ma). 4) Large-sized Coprinisphaera assemblage-SAPIA: appearance of Coprinisphaera of large size (60.5-78.5 mm), disappearance of the smallest specimens (21-27 mm), shift in the mode to larger size classes (mean equatorial diameter: 49 mm) and decrease of density (7 specimens per m2). The ichnodiversity is maintained. Deseadan SALMA (29?24 Ma). It remains with minor changes and some loss of ichnodiversity during the Colhuehuapian SALMA (21?20 Ma) and the Pinturan SALMA (19?17.5 Ma). The ichnoassemblage that corresponds to the Santacrucian SALMA (18?16 Ma) is very poor, with few trace fossils recorded, mostly Celliforma. 5) Rosellichnus assemblage-SAPIA: dominated by Rosellichnus patagonicus, Coprinisphaera tonnii, C. akatanka, C. murguiai, and Teisseirei isp. Fictovichnus gobiensis, Rebuffoichnus casamiquelai, and Taenidium isp. are also present. This assemblage probably corresponds to the Colloncuran SALMA (16.5?14 Ma), but is mainly preserved in the underlying La Pava Formation. This frame is probably also applicable to other ichnofossiliferous Cenozoic paleosols of other regions of Argentina, Chile, Uruguay and Ecuador.