Ichnological research in Lower Cretaceous marginal-marine facies from Patagonia: outcrop studies, SEM examinations, and paleontological/sedimentological integration

FERNÁNDEZ, DIANA E.

Congreso; 23rd Colloquium on Latin American Earth Sciences (LAK 2014); 2014

During the past few years, the first in-depth ichnological analysis of Lower Cretaceous, mar-ginal-marine facies from the Neuquén basin (Northern Patagonia, Argentina) has been carried out. The Agua de la Mula Member (Agrio Formation) is a mixed carbonate?siliciclastic marine (Spalletti et al. 2001) and marginal-marine (e.g. Pazos et al. 2012) succession. Along with the sedimentological work on this unit, the focus has been made on the study of trace fossils. Several ichnogenera have been identified (e.g. Fernández et al. 2010; Pazos and Fernández 2010; Fernández and Pazos 2012). The ichnological interpretations enhance the paleodiversity; some inhabitants had not been documented through body fossils. Xiphosurid trackways (Kou-phichnium) and dinosaur tracks (Therangospodus) indicate exposure in areas considered basinal facies in paleocoastline reconstruction maps. The scale of the analyses goes from outcrop stu-dies up to SEM examinations. Microbially induced sedimentary structures (MISS) are present in some trace fossil-bearing levels. The presence of microbial mats was confirmed through SEM analyses (Fernández and Pazos 2013). This is an example of the importance of sedimentologi-cal-ichnological data integration The ichnological and sedimentological characteristics found show that:?    The ichnodiversity is greater than shown by previous works. This has consequences on the paleodiversity and ethological information for the unit.?    Microbial mats are a necessary condition for the exceptional preservation of certain traces.?    The inferred paleoenvironment for the top of the unit is shallower than traditionally thought. Trace fossil studies are key for reviewed paleocoastline reconstructions and can be applied in the oil industry as paleobathymetric controls. Fernández, D.E. and Pazos, P.J. 2012. Ichnology of marginal marine facies of the Agrio Formation (Lower Cretaceous, Neuquén Basin, Argentina) in its type locality. Ameghiniana. Ameghiniana 49(4), 505-524.    Fernández, D.E. and Pazos, P.J. 2013. Xiphosurid trackways in a Lower Cretaceous tidal flat in Patagonia: Palaeoecological implications and the involvement of microbial mats in trace-fossil preservation. Palaeogeography, Palaeoclimatology, Palaeoecology 375, 16-29.Fernández, D. E., Pazos, P. J. and Aguirre-Urreta, M. B. 2010. Protovirgularia dichotoma ? Protovirgularia rugosa: an example of a compound trace fossil from the Cretaceous (Agrio Formation) of the Neuquén Basin, Argentina. Ichnos 17(1), 40-47. Pazos, P.J., Lazo, D.G., Tunik, M.A., Marsicano, C.A., Fernández, D.E. and Aguirre-Urreta, M.B. 2012. Paleoenvironmental framework of dinosaur tracksites and other ichnofossils in Early Cretaceous mixed siliciclastic-carbonate deposits in the Neuquén Basin, northern Patagonia (Argentina), Gondwana Research 22, 1125-1140.Pazos, P.J. and Fernández, D.E. 2010. Three-dimensionally integrated trace-fossils from shallow marine deposits in the Lower Cretaceous of the Neuquén Basin: Hillichnus agrioensis isp. nov. Acta Geologica Polonica, 60 (1), 105-118. Spalletti, L.A., Poiré, D., Pirrie, D., Matheos, S. and Doyle, P. 2001. Respuesta sedimentológica a cambios en el nivel de base en una secuencia mixta clástica-carbonática del Cretácico de la cuenca Neuquina, Argentina. Revista de la Sociedad Geológica de España 14, 57-74.