Huayquerías Formation

The Huayqueriás Formation, present in the Frontal Cordillera and the neighboring Cuyo Basin, was described in 1934 by Kraglievitch as the basis for the Huayquerian South American land mammal age. The name Huayquerías means "badlands".[1] The formation comprises reddish mudstones with mudcracks, paleoburrows and ichnofossils of vertebrates. Thin sandstone layers of up to 12 centimetres (4.7 in) thick exist in the formation. An ashfall bed exists at 83 metres (272 ft) below the contact with the slightly angular unconformably[2] overlying Tunuyán Formation in a total section of 126 metres (413 ft).[3] The tuff has been dated using ⁴⁰K/⁴⁰Ar analysis to 5.84 ± 0.41 Ma.[4]

The Huayquerías Formation has been used to define the Huayquerian South American land mammal age, ranging from 9.0 to 6.8 Ma. However, later analysis of the ashfall bed in the formation, provided a much younger age of 5.84 ± 0.41 Ma, extending the temporal range of the Huayquerian SALMAans until near the Miocene-Pliocene limit. The Huayqueriás Formation has provided fossils of Cyonasua pascuali,[5] and the litoptern Huayqueriana cristata, the latter of which, named after the formation.[1]

• South American land mammal age