Resumo

BRESSAN, Graciela S.  e  PALMA, Ricardo M.. Taphonomy and ichnology from storm deposits in Bardas Blancas Formation (Lower-Middle Jurassic), Mendoza, Argentina. Ameghiniana [online]. 2008, vol.45, n.3, pp.513-528. ISSN 1851-8044.

The Bardas Blancas Formation (Toarcian-Bajocian) of the Neuquen Basin in rio Potimalal area is characterized on the basis of sedimentologic, taphonomic and ichnologic criteria. The taphonomic attributes and their relation to the lithofacies allow us to distinguish five different bioclastic deposits (BD): (1) BD1, hummocky cross-stratified shell concentrations; (2) BD2, lenticular or tabular shell concentrations in hummocky cross-stratified sandstones; (3) BD3, shell "lags"; (4) BD4, complex shell beds; (5) BD5, shell beds in massive fine-medium grained sandstones. BD3 have been interpreted as storm relaxation flows, whereas BD1-BD2 has been interpreted as proximal tempestites and BD4-BD5 as distal tempestites. Molluscs taxa recorded include bivalves, cephalopods and gastropods, in order of decreasing of his relative abundance. Pholadomya cf. abbreviata Hupé, Meleagrinella cf. echinata (Sowerby) and Neocrassina andium (Gottsche) are present in sandstone facies while, Pholadomya laevigata Hupé and Trigonia (Trigonia) sp. are abundant in mudstone facies. Ichnofauna includes Skolithos and Ophiomorpha that may be assigned to the Skolithos ichnofacies, and Thalassinoides, Palaeophycus, Planolites and Chondrites, assigned to the Cruziana ichnofacies. In the study area, there are three deepening upward successions averaging 26, 17 and 25 m in thickness. The analysis and interpretation of sedimentologic, taphonomic and ichnologic features suggests a storm-dominated shelf, in a zone comprised from shoreface and outer shelf areas.

Palavras-chave : Bardas Blancas Formation; Jurassic; Storms; Bioclastic deposits; Ichnofacies.