GlossaryPrint

Oligocene (34-23 Ma)

last Epoch of the Paleogene Period meaning 'not much new'. The beginning of this epoch is marked by changes in the European fauna and emergence of new species, such as the first horses.

Olivine

normally green mineral constituted by iron and magnesium silicates. It is very common in volcanic and metamorphic rocks.

Operational chain (reduction sequence)

sequentially organised set of technical processes, used for the reconstruction of all the anthropic actions on a certain block of raw material, from its selection to the final disposal of the resulting elements.

 

Ordovician (488-444 Ma)

period of the Paleozoic Era, marked by the appearance of the first vertebrates. The fragmentation of Paleogondwana continued as well as the separation of the continents of Paleolaurentia, Baltica and Siberia, due to the expansion of the Iapetus Ocean. A cooling of the planet occurs, evidenced by ice caps on South Pole lands and a lowering of about 100 m of the sea level. The drifting of the continental plates leads to the formation of an island-arc between the existing continents and Paleogondwana, resulting in a new ocean – the Paleothetys. Geological register of this geological period is conserved in the Mount Saint Gabriel (Castelo Melhor).

 

Ornamental rock

all the rocks used for decorative purposes (sculptures for example) or as building material. It is common to use limestones, marble and granite, among others.

Orogeny

process of mountain chain formation, including the fracture and deformation of the most superficial rocks, metamorphism and appearance of magmatic rocks at the deepest levels. Several orogenies occurred in the planet's geological history. The Hercinian and Alpine orogeny, and posterior erosional processes, were responsible for the deformation of rocks and creation of relief in the Foz Côa region.

 

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