Ichnological study of the Lower Cretaceous Mulichinco Formation (Neuquén Basin, northern Patagonia): preliminary results

DIANA ELIZABETH FERNÁNDEZ; PABLO JOSÉ PAZOS

Congreso; Second Latinamerican Symposium on Ichnology (SLIC 2013); 2013

The Mulichinco Formation (Mendoza Group, Neuquén Basin) is a mainly siliciclastic succession of early Valanginian age exposed in the Neuquén province (Argentina), in the area between the Agrio River to the south and the limit with the Mendoza Province to the north. Previous research conducted in this unit reported the presence of certain ichnotaxa. However, the focus of those analyses was mainly sedimentological and/or stratigraphical. During the past few years, the first extensive ichnological study of this unit has been carried out. Along with the work on trace fossils, sedimentological characteristics have been included in the study. The aim of this work is to communicate some preliminary results.             In the central and northern sectors of the Neuquén Province, where the deposits of this unit are mainly marine, four localities along the north-south directed National Route 40 were analysed in detail. The material has been so far assigned to following ichnotaxa: cf. Arenicolites Salter, Asteriacites lumbricalis von Schlotheim, Bolonia lata Meunier, Chondrites ?intricatus (Brongniart), Cochlichnus anguineus Hitchcock, Gyrochorte comosa Heer, cf. Rhizocorallium Zenker, Lockeia siliquaria James, cf. Nereites, ?Ophiomorpha isp., Ophiomorpha nodosa Lundgren, Palaeophycus tubularis Hall, cf. Planolites Nicholson, Rosselia socialis Dahmer, Skolithos verticalis Hall, Teichichnus isp., ?Thalassinoides isp. and cf. Treptichnus Miller. Three types of trace fossils have been described using open nomenclature: arthropod trackways, tetrapod swimming traces and escape structures. The ichnofossils were described and their distribution along the unit carefully noted. Fourteen types of trace fossils have been added to the previously known ichnodiversity of the Mulichinco Formation.             Preliminary results of the sedimentological studies show that in some localities tidally-dominated depositional settings were more widespread than reported in prior studies. Also, in some localities the inferred paleoenvironment for the top of the unit is shallower than previously thought.             The ichnological characteristics found show that these deposits bear complex ethological and paleodiversity information, and their study is to be continued. The new sedimentological information gathered is important for reviewed paleoenvironmental reconstructions.