Petrified Forest “Florentino Ameghino”
The set of geological and paleontological data allows us to elaborate the history of the origin of the Petrified Forest Florentino Ameghino (known by its Spanish acronym BPFA), which is part of the Salamanca Formation.
The petrified logs corresponded to trees that were part of an extensive forest of Lauraceae and Fagaceae, which existed 60 million years ago and was located west of the place where is, nowadays, the Petrified Forest FA. Those trees were carried by rivers to the sea coast of that time.
Evidence of this is the presence of trace fossils (also called ichnofossils) of an undisputed marine environment (Ophiomorpha icnsp.) of the Salamanca Formation and the levels with marine invertebrate fossils in the shales, overlaying the sandstone with petrified logs. This would be a first step of the incursion of the Palaeocene Sea, a bay in which the rivers, crossing the plains covered by vast forests, flew into it.
The area assigned to the BPFA is in the contiguous areas of the hills located north of the Chubut River and 3.5 km south of the 112 km (National Route No. 25). This area is located in the Lower Valley of the Chubut River, downstream of the dam Dique Florentino Ameghino, and it is nestled in an important mining district of kaolin and clay, as well as of paleontological and archaeological sites.
The petrified logs -the reason for our interest- are nestled in rocks assigned to the Salamanca Formation which unconformably underlie on the Marifil Formation and equivalents, ranging from the Lower Jurassic to the Middle Jurassic period. In turn, it underlies conformably Río Chico (Palaeocene) Formation and unconformably with Sarmiento (Eocene-Oligocene) Formation, with Montemayor (Pliocene) Formation or it is truncated by ancient terraced levels of the Chubut River.