Ichnofacies analysis of the Sarmiento Formation (middle Eocene – early Miocene) at Gran Barranca, central Patagonia

BELLOSI E. S., J. H. LAZA, M. V. SÁNCHEZ AND J. F. GENISE

The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia. Madden, R., A. Carlini, M Vucetich & R. Kay

Cambridge University Press

Lugar: Cambridge; Año: 2009; p. 302 - 313

The ichnofacies analysis of the Sarmiento Formation at Gran Barranca, along with older and younger adjacent Patagonian units, permits an assessment of the early Eocene to middle Miocene evolution of terrestrial ecosystems. Most ichnofossils found in Sarmiento Formation paleosols were made by insects: Coprinisphaera ispp. (dung beetles), Celliforma ispp. (solitary bees), Teisseirei barattinia and Pallichnus dakotensis (beetles), Feoichnus challa (cycads), andcocoons. Thick-walled vertical tubes (Loloichnus baqueroensis) were produced by crayfishes (Parastacidae). The nature of other traces is uncertain: Lazaichnus fistulosus, septate burrows, Beaconites coronus, and large burrows. Different types of root traces are also present. The lower middle Eocene Koluel-Kaike Formation contains Feoichnus, Skolithos, Taenidium, and root traces. In the middle Eocene Gran Barranca Member, Feoichnus is abundant, Coprinisphaera, Teisseirei, Beaconites, Celliforma, and cocoons are less common. The late middle Eocene Rosado Member, a pedogenic calcrete, only contains Celliforma andPallichnus. The Lower Puesto Almendra Member (late Eocene) shows the greatest density and diversity of Coprinisphaera, and includes Lazaichnus and Teisseirei. Large burrows attributed to mammals and very few Coprinisphaera are found in the late Eocene to early OligoceneVeraMember. The Oligocene Upper Puesto Almendra Member records the greatest ichnodiversity in the whole succession, with relative high number of nearly all ichnofossils. The early Miocene Colhue-Huapi Member has two distinctive associations. Ichnodiversity of the lower and middle sections of the member is similar to that of the underlying member; but diversity and abundance decline in the upper section, where a calcrete contains only Celliforma. Elsewhere in west–central Patagonia, the early Miocene Pinturas Formation includes Coprinisphaera, Syntermesichnus, and