The ichnological diversity of the Yacoraite Formation (Salta Group, Cretaceous-Paleogene): The first approach to its complexity and paleoenvironmental significance

CARLOS A. CÓNSOLE GONELLA, ROSA A. MARQUILLAS Y FLORENCIO G. ACEÑOLAZA

Mendoza, Argentina

Congreso; International Sedimentological Congress; 2010

International Association of Sedimentologists

The Yacoraite Formation (Maastrichtian-Danian) is a one of the most extensive units in northwestern Argentina and is coeval with several units located along of South America, as part of the typical late cretaceous transgressions systems. Represents a carbonate deposit that comprises a set of carbonate and clastic marine and coastal lithofacies, resulting from environmental changes during its accumulation, as part of the initial stage of thermal subsidence of the Salta rift distributed principally in five subbasins (Tres Cruces, Sey, Lomas de Olmedo, Metán and Alemanía) (Salfity y Marquillas 1994; Marquillas et al., 2005). The ichnological framework of the unit has been poorly analyzed, probably by the importance of the Precambrian-Paleozoic trace fossils in northwestern Argentina that has captured the main focus of the researches in the last decades. We present subsequently for the first time, the more extensive integration of the ichnological diversity from the Yacoraite Formation. With this purpose we have relieved the trace fossils of nine stratigraphic profiles of the Tres Cruces, Metán and Alemanía subbasins. As result we are defined a cyclical set of traces that comprises loose, softground ichnofacies Skolithos-Cruziana transition (Skolithos, Arenicolites, Diplocraterion, Rizocorallium, Thalassinoides, Ophiomorfa, Chondrites, Lockeia and Teichichnus) facies crossing traces (Planolites, Paleophycus), and firmground-hardground traces characterized by Glossifungites-Trypanites-Entobia ichnofacies (Gastrochaeonlites, Glossifungites, Trypanites, Entobia, Caulostrepsis). This cyclical alternance of the ichnofacies suite allow us to define a complex variation of the shore line along the stratigraphic sequence, which has generated a succession of recurrent environmental conditions. The correlation of several omission surfaces has been used to detect hiatuses characterized by lowest sedimentation rates. The ichnological diversity is mainly controlled by environmental energy, availability of nutrients, salinity and the variations of texture. Finally we emphasize the coincidence between the sedimentological-stratigraphic framework and the ichnological settings that is typical to a shallow marine environment.