About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
Le Devonien du Portugal
Devonian outcrops in Portugal are scarce and small; both Lower and Upper Devonian occur; Middle Devonian has not yet been recognized although Couvinian might be present at Sao Mamede.
Lower Devonian (Gedinnian and Coblenzian) lies conformably on the Silurian. At some places there was no break in sedimentation from the Silurian to the Coblenzian; elsewhere a stratrigraphic gap corresponding to the Gedinnian seems to occur. This and the petrographic facies (sandstones, shales, greywackes, limestones and even conglomerates) point to very different conditions of depostion, certainly related to the ardennian diastrophism.
At the end of the Coblenzian sedimentation was interrupted except at Sao Mamede where it continued during the Couvinian. Devonian and older strata were folded together and the emergence of the portuguese country north of the Evora igneous-metamorphic massif was accomplished.
The only Upper Devonian, of which the age is established by its fossils, is the outcrop near Pomarao (Alentejo). Nevertheless, until recent years some regions to the south of the country (Shales with Nereites of Sao Domingos, etc.) were given the same age. However, their stratigraphic position is doubtful; they appear to continue into those of the marine Lower Carboniferous and may belong to it.
Intensive igneous activity took place during the Devonian and continued throughout the Lower Carboniferous.
There are no important mineral deposits related to the Devonian. The remarkable cupriferous pyrite deposits of Sao Domingos and Aljustrel, as well as the numerous but small manganese deposits of Alentejo, are found in the “Shales with Nereites of Sao Domingos” of still unestablished age.
While the portuguese Lower Devonian is fairly well known, since fossils are generally abundant in it, the Upper Devonian presents some unsolved problems.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
|Watermarked PDF Document: $14|
|Open PDF Document: $24|