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PATRIMONIO MUNDIAL PYRÉNÉES-MONT PERDU

Paisaje: naturaleza y cultura

Palaeontology

The term 'fossil' applies to the remains of shells, bones and other morphological elements of animals and plants, as well as any mark or trace of their activity. Consequently, galleries, the marks left by roots, tubes, traces of their travel, footprints, etc. are also fossils and so can be described as heritage.

Most of the fossils in the sedimentary rocks in the area we are concerned with are Foraminifera, which are small in size but even so can be seen and identified using a simple 10x magnifying glass.

Foraminiferans are protozoans and are able to evolve extremely quickly over time.

Sudden changes in environmental conditions very often result in an enormous abundance or the almost complete disappearance of some species. This means that the various geological ages and stages can be determined by their foraminiferal content.

It is to this characteristic that we owe the existence of what are known as biostratigraphic tables. For example, the foraminiferan known as lacazina is almost exclusive to the Santonian Stage. Orbitoid foraminiferans are found only in the Campanian and Maastrictian stages. Alveolinas and nummulites are exclusive to the Tertiary, with numerous forms characteristic of the Ilerdian and Cuisian stages.

It is easy to see in the rocks in the Ordesa and Monte Perdido Park how orbitoids are common in the Marboré sandstone formation but are never found in other types of rock.

Nummulites and alveolinas are extremely abundant after the Faja de las Flores terrace, which marks the lower limit of the Ilerdian Stage. In fact, it corresponds to two very different phenomena, one an extinction and the other a radiation.

The Cretaceous-Tertiary boundary, the limit between the Maastrichtian-Palaeocene stages, is the point at which the dinosaurs disappear because they became extinct. The same is also true of the fossils of orbitoids and ostreids in the Marboré sandstone,

In contrast, from the Palaeocene-Eocene boundary onwards, or the limit between the Thanetian-Ilerdian stages, we find a radiation or a sudden appearance of numerous species of nummulites, alveolinas, other Foraminifera and of course large numbers of new fossils.