A new continental ichnofabric from Lower Cretaceous Puesto La Paloma Member, Cerro Barcino Formation, Chubut

MASSA, L.; BEDATOU, E.; UMAZANO, A.M.

General Roca

Otro; XVI Reunión Argentina de Sedimentología; 2018

Asociación Argentina de Sedimentología

Pedogenized fluvial volcaniclastic rocks from Lower Cretaceous Puesto La Paloma Member of the Cerro Barcino Formation have yielded a new type of ichnofabric. It consists of two different ichnofossils that could not be classified ichnotaxonomically. Most common specimens are rounded section burrows, 6 to 7 mm in diameter, smoothly walled, commonly passively filled but in some cases, they also show meniscate portions. Its paths are tortuous and random forming a tangled group of burrows. This is the overall appearance of the ichnofabric. The other component is one burrow with rounded section and probable meniscate filling, as seen through CT scan. This burrow follow an arcuate path, and is much bigger than the others and its poor preservation do not allow a more detailed description. Ichnofabric probable producers would have been common earthworms, mainly of endogeic type. The presence of these organisms indicates that the soil was wet enough as to support them but well drained to avoid permanent waterlogging. Climate was seasonal, but after ichnofabric development became dryer, at least locally. It is in agree to previous paleoenvironmental interpretations for this unit. This ichnofabric is different to others from Patagonia, particularly to those produced by earthworms. It was informally named ?spaghetti ichnofabric?. Considering the evolution of paleosol ichnofabrics in Patagonia from Jurassic times, ?spaghetti ichnofabric? emplaced coetaneously with the first records of insect activity, the beginning of diversification of earthworms trace fossils, and the decrease in dominance of crayfishes in the ichnological record.