Geoparque Unesco

13 The most ancient rocks in Sobrarbe (Plan)

A red and blue planet (Plan)

Localización: En Plan, próximo a la oficina de turismo

Coordenadas. 281534 4717894 31 N

Textos Esperanza Fernández (Geopage)

If you look at the landscape around Plan, you might notice the presence of rocks with a deep red colour. These are rocks that come from sediments generated about 200 million years ago, during the Triassic, a time when the Earth was very different from today.

Rocas rojizas del Triásico en los alrededores de Plan. Foto: Marta Montmany.

200 million years ago

All the land above the sea formed a single continent, Pangea, which was surrounded by two great oceans, the Panthalassa and the Tethys.

Geografía de la Tierra durante el Triásico, con todas las tierras emergidas en un continente único

The Earth's climate was very dry and hot. Sporadic, torrential rain fell heavily, eroding the bare land. Large amounts of gravel, sand and silt were transported and deposited along broad and sometimes deep river valleys.

There was very little biodiversity. The only animal and plant species alive were the few which had survived the mass extinction of the late Paleozoic. Most of these would appear strange to us today, but over time they evolved into present-day groups such as mammals, birds and flowering plants.

The reddish conglomerate, sandstone and siltstone rocks near to Plan were produced by the consolidation of gravel, sand and silt. These sediments were transported and deposited by rivers during the early Triassic. Although the landscape was dry, a few wetlands provided shelter for herds of Lystrosaurus, the most abundant herbivore at that time, whose only enemies were some carnivorous reptiles such as the two Proterosuchus that are leaning over the water.

Recreación artística de lo que pudo haber sido el paisaje de Sobrarbe durante el Triásico más antiguo. Un continente desértico en el que habitaban organismos hoy extintos y que, por los restos fósiles hallados en diversos lugares del planeta, eran muy abundantes en este periodo geológico. Dibujo de Óscar Rubio basado en diversos trabajos científicos.

A little later in the Triassic, the Tethys Ocean invaded what is now the Comarca de Sobrarbe and the landscape was transformed into a shallow sea. Large marine reptiles lived on its shores, such as these Nothosaurus, which measured up to 3 m long and caught big fish, such as the Saurichthys. Limestones and marls were deposited at the bottom of this sea, and these now form part of the landscape around Plan and give us information about this lost world.

Recreación artística de lo que pudo haber sido el paisaje de Sobrarbe durante el Triásico medio. En este caso, la Comarca de Sobrarbe estaría bajo un mar somero en el que la vida comenzaba a desarrollarse tras la gran extinción de finales del Pérmico, generando algunas formas que, con el tiempo, darían lugar a los actuales peces, reptiles y anfibios. Dibujo de Óscar Rubio basado en diversos trabajos científicos.

Did you know…?

The reddish colour of these rocks is due to the presence of non-hydrated iron oxides, such as goethite or hematite, which are formed in dry conditions. Therefore, this colour reflects the desert conditions of the Earth in the Triassic.

Aspecto de las rocas triásicas de los alrededores de Plan. El color rojizo es debido a la presencia de minerales de hierro oxidados, que evidencian unas condiciones de formación bajo un clima árido. Fotografía: Marta Montmany.

Recomentations in your visit to Sobrarbe-Pirineos Geopark

  • Safe visits, unforgettable experiences. There are companies who collaborate with the Geopark where you can hire specialized guides to make your tour a unique and safe experience.
  • Respect the geological outcrops. Do not break off samples of rock, mineral or fossils.

Avda. Ordesa 79. 22340 Boltaña. Huesca. 974 518 025.