ESTRATIGRAFIA E EVOLUÇÃO DE UM ESPORÃO ARENOSO EM AMBIENTE MACROMARÉ: PONTA DA AREIA - SÃO LUÍS - MARANHÃO - BRASIL
Sand spit stratigraphy and evolution in macrotidal environment: Ponta da Areia, São Luis - Maranhão - Brazil
DOI:
https://doi.org/10.5016/geociencias.v39i04.13993Abstract
In the Island of Maranhão, coastal barrier systems can be divided into two main morphotypes: (i) Headland Spit Barriers, which are characterized by a beach attached transversely to the previous topography showing a steep gradient where there is continuous loss of sand on the eroded coast; and (ii) Mailand Beach Barriers, which are characterized by a lagoon-barrier-spur system anchored longitudinally to the previous topography. This latter morphotype originates from a large sediment transport via the coastal drift, whose extension is usually interrupted by the hydraulic spike effect, together with high tide prisms in the river mouths. The present study uses percussion and vibrocore drills to recover the sedimentary record, which is described in terms of its sedimentation, texture, structure and sedimentation facies. The results obtained demonstrate the stratigraphic nature of the coastal barrier in the Ponta da Areia Beach as a retrogradation sequence characterized by the migration towards the continent of a sandy spur. The radiometric dating of lagoon sediments on the beach attested the age of 7,240 ± 30 years AP indicating that at this time, this lagoon-barrier-spur system extended out to sea. Recently, the construction of a coastal spire has changed this stratigraphic nature, and it has a progradational system in the immediate vicinity of the spike, where distal environments (backshore) are sotopostos by proximal environments (foreshore).
