Ichnology of the brackish water intervals of the Puesto El Moro Formation, Upper Cretaceous, Austral Basin, Argentina

AUGUSTO N. VARELA; SEBASTIÁN RICHIANO; DANIEL POIRÉ

Santa Rosa

Simposio; II Simposio Latinoamericano de Icnología; 2013

INCITAP (Conicet-UNLPam)

The Puesto El Moro Formation (Upper Cretaceous) was originally described by Turic (1971), as a sequence of continental sediments that overlies the Piedra Clavada Formation. This succession outcropping in the region of Lake San Martin, near the homonymous Outpost belonging to the Estancia La Lila. Puesto El Moro Formation is temporally and spatially correlated with Mata Amarilla Formation, both formations have great interest because they mark the onset of the foreland stage of the Austral Basin. A detailed sedimentological logging at the type locality allow the identification of the three main sections, the lower section corresponds to a littoral palaeoenvironment, and the middle and upper sections were developed in continental palaeoenvironments (fluvial). The Lower littoral section is composed of an alternation of medium-grained sandstone, generally bioturbated, with greyish flaser heterolithic which sometimes also exhibit trace fossils. From this set of sedimentary facies has been recovered an interesting ichnofauna dominated by Thalassinoides isp., accompanied by specimens of Ophiomorpha nodosa, Palaeophycus isp. and Sinusichnus sinuosus. This ichnoassociation corresponds to an impoverished Cruziana ichnofacies developed in a marginal shallow marine palaeoenvironment with salinity stress and / or oxygenation. These ichnotaxa are produced by Callianassidae crustaceans that used the galleries for different purposes, including room (domichnia) and bacteria cultivation (agrichnia).These crustaceans ichnotaxa are the product of the galleries that used callianásidos produced for various purposes, including room (domichnia) and bacterial culture (agrichnia). Similar examples to these deposits, which could be used as analogues for palaeoenvironmental characterization can be found in the Pliocene marginal deposits of France and Spain (the type locality of the ichnogenus Sinusichnus) deltaic deposits of the Oligocene-Miocene of Venezuela and in the Cretaceous of Antarctica.