Cerro Azul Formation

The Cerro Azul Formation is a geological layer in northeastern Argentina spanning La Pampa and Buenos Aires provinces. It consists of river deposits with siltstone, sandstone, and volcanic ash layers that together reach several hundred meters in depth.

This layer formed after the retreat of the Parana Sea roughly 10 million years ago and was first systematically documented by scientists in the 1980s. The deposits reveal important environmental changes across Argentina over extended geological time periods.

Researchers from multiple scientific institutions study this formation to understand Argentina's prehistoric environments through its extensive fossil collection.

Researchers reach this layer via country roads connecting various study sites including Barrancas Coloradas, Cerro Patagua, and Estancia Re. The locations require good planning since they are spread out and clear orientation is necessary.

The layer contains fossils of Argentavis, the largest flying bird in Earth's history, alongside many bones from extinct mammals and reptiles. These discoveries offer glimpses into the wildlife of a vanished landscape.