The Río Loro Formation is a geological formation of the Sierras Pampeanas in Tucumán Province Argentina whose strata date back to the Late Paleocene of the Paleogene, or Riochican in the SALMA classification.
The formation has been deposited in a meandering fluvial environment and has a maximum noted thickness of .
The formation has provided fossils of several mammals and reptiles. The crocodylian genus Lorosuchus and mammal species Eoastrapostylops riolorense were named after the formation which is correlated with the Mealla Formation of the Salta Basin to the northwest of Tucumán Province.
Description The Río Loro Formation crops out in the Sierra Medina, north of Tucumán city. The formation, first defined by Bossi in 1969,Babot et al., 2017, p.732 reaches a thickness of ,Georgieff, 2014, p.6 and comprises red sandstones and siltstones deposited in a fluvial meandering environment.
The Río Loro Formation unconformably overlies the Cretaceous Los Blanquitos Formation and is overlain by the Río Nío Formation. The Río Loro Formation is correlated with the Mealla Formation of the Salta Basin to the northeast.
Fossil content The following fossils were reported from the formation:Río Loro Formation at Fossilworks.org Mammals Notoungulates Satshatemnus bonapartei Eutheria Notonychops powelliSoria, 1989 Xenungulata Rodcania kakanGelfo et al., 2020 Placentalia Eoastrapostylops riolorenseSoria & Powell, 1981 Reptiles Turtles Podocnemis cf. argentinensisDe Broin & De la Fuente, 1993 Crocodylians Lorosuchus nodosus
See also South American land mammal ages Itaboraí Formation
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