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Geology in Sobrarbe

Fossils

Fossils are the remains of ancient organisms that are preserved in rock, especially parts of skeletons, or traces of their activity (footprints, feeding marks, etc.).

Many are still to be discovered in Sobrarbe, though already discovered fossils show us an astonishing biological diversity through geological history. We do not find many fossils from the Paleozoic and Mesozoic, but the fossil records from the Cenozoic, especially those related to the Eocene Basin, are very rich both in marine and land organisms: plants, vertebrate and invertebrate animals, etc..

Paleozoic rocks have suffered two important orogenies: the Hercynian and the Alpide. In addition regional metamorphism has affected most of them almost erasing any fossil evidence. However, invertebrate marine fossils from the Devonian have been discovered in the Otal and Ara Valleys: cephalopods (Goniatites, Orthoceras), crinoids (Cyathocrinus), brachiopods (Atrypa, Spirifer, Orthis), anthozoa (Pleurodictium, Calceola, Favosites), trilobites (Phacops), etc.

Crocodile jaw in Lamata. (Image by Jesús Cardiel).

During the Mesozoic, there are scant fossil records until the Cretaceous. In the Upper Cretaceous, marine invertebrate were abundant in warm waters. Large bivalves (Inoceramus) have been discovered between Cotiella and Peña Montañesa, in the La Larri Valley (Hippurites) and in Saravillo (Pecten). Brachiopods (Terebratula) have been discovered nearby Cortalaviña. In the Monte Perdido Massif, several samples of ostreidae (Ostrea), foraminifera (Lacazina, Orbitolites), echinoderms (Ananchites), etc. have also been discovered.

The Cenozoic was more prolific in fossils, especially during the marine domain period (Paleocene and most of the Eocene).

During the Paleocene, tthe presence of foraminifera (Operculina, Discocyclina) and a new crocodile species, dating from 57 million years ago, in the Ordesa and Monte Perdido National Park is of particular interest.

In the marine Eocene, foraminifera (Alveolina, Assilina, Discocyclina and especially Nummulites) are very abundant in the Mediano and Santa María de Buil areas. We can find marine invertebrate in the Fiscal area: bivalves (Chama), gastropods (Cerithium, Turritella, and Fusus), etc. Echinoderms (Ditremaster and Linthia) are also represented in the area surrounding Santa María de la Nuez, and gastropods (Velates, Campanile, Potamides, etc.) in Eripol..

In many strata of deep marine origin, from Guaso to Arro, we can find evidence of the activity of invertebrates (footprints, tracks, etc.). .

In Old Sobrarbe, we find several sites with vertebrates from the Eocene, which are being currently researched. Transition environment fossils are particular interest, such as fish, turtles, crocodiles and mammals. Near a target="_blank" href="http://fosilesdesobrarbe.blogspot.com/">Lamatasome fossils of palm tree leaves and wood fragments have been discovered, proving the tropical and subtropical climate during that period..

From the Eocene and on, the process of active sedimentation in Sobrarbe diminished, in favour of the erosive processes which make fossilization more difficult.

During the Quaternary, some fossils can be observed along the fluvial terraces and on karstic formations. However, in some cases we cannot refer to them as fossils, since the fossilization process has not been completed.Thecave-dwelling bear Cave/near Tella is especially remarkable, since it is the highest site (1600m above sea level) in western Europe where this species has been discovered (Ursus spelaeus).