Trace fossils and paleoenvironments of the ?Green section? of the Complejo Don Otto Member (Yacoraite Formation, Maastrichtian-Danian) at Quebrada el Tapón site, Tonco Valley, Salta (Argentina)

DE VALAIS, SILVINA; DÍAZ-MARTÍNEZ, IGNACIO; NOELIA CÓRDOBA ; CITTON, PAOLO; CARLOS A. CONSOLE GONELLA; ALFREDO ZELAYA

Nueva Delhi

Congreso; 36 International Geological Congress; 2020

Organizing committee 36 International Geological Congress

The Quebrada el Tapón (25°36´25.27´´S - 65°55´8.94´´W) is a key locality of the Tonco Valley, a conspicuous area of the Late Cretaceous Central Andes, as an important uranium deposit, besides its rich ichnological background. There, the Yacoraite Formation exhibits three members: Caliza Amblayo (74 m), Complejo Don Otto (67 m) and Arenisca Pedro Nicolás (9 m). We analyzed 18 m of the ?Green section?, at the top of the Complejo Don Otto Member, and recognized three subenvironments: I) A lower intertidal to subtidal zone dominated by centimeter-scale cycles made up of wackestones-packstones, ooidal grainstones and fine sandstones. Subcircular trace fossils (1-2 cm in diameter) from which from 3 up to 12 radiated structures (0.5 to 1 cm wide, with an average length of 6 cm) branch out, characterize the sandstones. The morphology is similar to Dactyloidites and Haentzschelinia ichnogenera. This record is assigned to the Skolithos Ichnofacies. II) A supratidal body of ephemeral ponds, far away from direct wave influence. Facies are made up of mudstones, with jelly roll structures. There are avian tracks (Gruipeda filiportatis) and invertebrate trace fossils (cf. Palaeophycus isp.) in a surface with jelly roll structures. III) A landward position, beyond water direct influence. Facies are composed of calcareous sandstones, with traces of gypsum. There are two ichnoassemblages: i- integrated by Ardeipeda cf. A. egretta, cf. Uhangrichnus isp. associated with Taenidium isp., and ii- cf. Alaripeda isp., cf. Gruipeda filiportatis, and cf. Gruipeda isp. Ichnoassemblages of II and III are included within the shorebird ichnosubfacies, as a subset of the Scoyenia Ichnofacies.