Lower Silurian outcrop

Geossítio 27 Lower Silurian outcrop

With primitive colonial organisms from the Paleozoic seas!

During the Silurian Period (443 to 419 million years ago), the sea level around the ancient continent of Gondwana, located near the South Pole, deepened. The depth of the ocean favored the deposition on the seabed of very fine sediments composed, for example, of clay. This deposition gave rise to the black shales that are found at this geosite, where some fossils of colonial beings that are now extinct – graptolites – have been preserved.

Este geossítio faz parte do itinerário C: Paiva, the surprising valley.
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Informação Geológica

During the Silurian Period (443 to 419 million years ago), the sea level deepened on the Gondwana paleocontinent, which favored the deposition of fine sediments in low oxygen conditions, giving rise to black shales, where some colonial planktonic fossils called graptolites have been preserved. The geosite consists of an outcrop of very fissile phytanites, where it is possible to find and observe a graptolite fauna from the Telychian (Llandovery – Lower Silurian), about 439 million years old.

Graptolites are planktonic colonial forms of hemichordate organisms, similar to the evolutionary basis of vertebrates. The only part that fossilizes is the colonial exoskeleton (rhabdosome), which was originally flexible and proteinaceous in nature.

The paleontological record of graptolites found at this site reveals their high importance, as it allows the age of the strata in which they are found to be determined (paleontological and stratigraphic interest). The high degree of preservation of these fossils was due to the conditions of deposition of very fine sediments and very low oxygen conditions (sedimentological interest), on the margins of the Gondwana paleocontinent (paleogeographical interest). This “open page” of the Paleozoic album has a high educational value for the reasons listed above, as there is a wide range of scientific content that can be explored here.