Gruta da figueira brava (Arrabida): Geological setting

• Author(s): Pais, João ; Legoinha, P.
• Date: 2000
• Persistent ID: http://hdl.handle.net/10362/1874
• Origin: Repositório Institucional da UNL
• Subject(s): Miocene; Pleistocene; Portinho da Arrabida; Figueira Brava cave; Portugal
• Document Type: Article
• Language: English

Description

Separata do Tomo XXXVIII das Memories da Academia das Ciencias de Lisboa (Classe de Ciencias) The Arrabida Mountain Range is the best example in Portugal of alpine movements. During Miocene times the Arrabida chain acquired the present structural set up: overthrusting accidents striking ENE-WSW and N-S or NNE-SSW sinistral lateral ramps. The main tectonic phases occurred about 17 Ma and somewhat less than 16 Ma. The Miocene deposits, mainly biocalcarenites, are middle Burdigalian and Langhian in age. During the Pleistocene the sea erosion cut several terrasse levels. Scattered remnants of conglomerates corresponding to the 12-15 and to 5-8 meters marine terrasses are ascribed to the last interglacial and to the beginning of the Wiirm glaciation (= 100000 years, Tyrrhenian II and III). The 5-8 meters terrasse, which is of particular interest, was deposited in a narrow marine erosion platform; the corresponding deposits tend to fill the entry of the caves excavated in the sea cliffs during the Upper Pleistocene such as Lapa de. St" Margarida and Figueira Brava Cave. These holes, protected by overhanging parts of the cliffs as a sort of ceiling, were good shelters forman. With the advance of the Wiirm glaciation the sea level was progressively going down. About 30000 years ago, the 5-8 meters platform and the caves dug in the cliffs were elevated as related to an extensive coastal plain. The sea level was ca. 60 meters below the present level (Miskovski, 1987). The human communities found in these territories an excellent hunting ground. The Santa Margarida and Figueira Brava caves were thus natural shelters. A large number of remnants of their occupation are preserved such as shells, animal bones, a few Neanderthal remnants as well as lithic and bone implements. 14C (and U series) dating indicate an age about 30000 years for level 2 where archaeologic remnants were exploited.