Aeolian trace fossil associations from Cretaceous formations of Patagonia, Argentina: stratigraphic and ichnofacies implications

PEREZ, M.; UMAZANO, A.M.; MELCHOR, R.N.

Colonia del Sacramento

Simposio; III Simposio Latinoamericano de Icnología; 2015

We have worked in four Cretaceous formations of Patagonia from the Neuquén and Somuncurá-Cañadón Asfalto basins. They are the Campanian Allen Formation (Río Negro province), the Cenomanian Candeleros Formation (Neuquén province), the Albian Puesto La Paloma Member of the Cerro Barcino Formation (Chubut province) and the Hauterivian Avilé Member of the Agrio Formation (Neuquén province). Logged sections included trace-fossil bearing aeolian deposits, and associated fluvio-lacustrine and primary pyroclastic facies. Three types of deposits were recognized: aeolian dune, dry interdune (comprising low-relief aeolian bedforms and volcanic ash falls) and wet interdune (including sheet-floods and lakes). Endichnial trace fossils like Palaeophycus tubularis, Skolithos isp., and Taenidium barretti are common components in most of deposits, but also diagnostic elements were recognized. Aeolian dune deposits are composed of medium to fine-grained sandstones or tuffaceous sandstones mostly with tabular-planar and tabular-tangential cross-bedding. Skolithos isp. and root traces were found associated to second order surfaces (reflecting dune migration) in the Puesto La Paloma Member. In this member the presence of mammal-like and tridactyl footprints, as well as arthropod trackways in aeolian dune deposit allows a comparison with the Chelichnus-Octopodichnus ichnofacies. In the Candeleros Formation, there is a dune stability surface related with lacustrine facies, with abundant specimens of Taenidium barretti that moved upward parallel to the foreset laminae. In the Allen Formation, two types of aeolian dunes were differentiated; they are complex dunes with sinuous crests and crescent dunes with straight crests. The former have an ichnofabric composed by Skolithos isp. and Palaeophycus tubularis specimens, as well as vertebrate burrows, both associated with a second order surface. Beaconites isp. specimens arranged parallel to dip of foreset laminae suggesting a dominant downward movement, were recognized in the straight crest dune deposits. In the same deposit, the presence of Palaeophycus tubularis, Taenidium barretti and Skolithos isp. can be an indication of the Entradichnus ichnofacies. Dry interdune deposits are dominated by fine-grained sandstones or tuffaceous sandstones with plane-parallel lamination and low-angle cross-bedding. Trace fossil content is scarce and is represented by Skolithos isp. and Palaeophycus tubularis. Wet interdune deposits are mainly composed by plane-parallel and massive siltstones or tuffaceous siltstones, and fine-grained sandstones or tuffaceous sandstones with different structures. A tridactyl footprint and Archaeonassa fossulata were recognized in a muddy surface in the Avilé Member, the last one indicates sub-aqueous conditions and is comparable to the Mermia ichnofacies. Finally, abundant specimens of Skolithos isp. forming a Piperock ichnofabric, were recognized in the Allen Formation. The ichnofauna found in aeolian dune deposits share some ichnofossils with roughly coetaneous aeolian units from Brazil (Upper Jurassic-Lower Cretaceous Guará and Botucatú formations, Paraná basin),including mammal-like and tridactyl tracks, arthropod trackways and meniscate burrows.