The glaciation that caused the extinction of marine species
This geosite is characterized by the presence of some evidences of the glaciation occurred in the end of the Ordovician period (Hirnantian), about 445 million years ago, one of the most intense glaciations on record, responsible for the extinction of 50% of the marine species. It is known as the “Hirnantian glaciation”, centered in the northwest Africa, and it was responsible for the significant lowering of the sea level, as well as for the depositional hiatus, with approximately 15 million years. Therefore, in the post-glacial period, about 445 million years ago, sands were deposited in paleo-antarctic latitudes, originating quartzite massifs of the Sobrido Formation basis that locally forms a residual relief called “Galinheiros”. The place name “Galinheiros” (chicken coop, in English) is related to the hypothetical great amount of woodcocks that existed here in the past. In the medieval era, this was a reference point and a landmark of limitation of the territorial influences, as evidenced by documents dated from 1153: “in uilla quos uocitant Canelas subtus mons Galliero discurrente ribulo Pauia territorio [de Arauka (?)]”. These quartzite levels were later covered by silt and clay that originated the sandy-schists where the dropstones were inserted, in the medium and superior part of the Sobrido Formation. Here, it is possible to find clasts inserted in the schist-sandy matrix, that testify the occurrence of a “clasts rain” resulted from the fusion of the icebergs that were drifting in the Rheic ocean, as the result of the biggest glaciation of the Phanerozoic.