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Evolução geomorfológica da Nave de Santo António (Serra da Estrela) através de técnicas geomorfológicas, sedimentológicas e geofísicas
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Resumo(s)
A Serra da Estrela tem uma morfologia e clima que contribuíram para a sua glaciação
Plistocénica, caracterizada por um campo de gelo de planalto que alimentava vários glaciares de
vale. A área estudada centra-se na Nave de Santo António (NSA) e pretende-se com esta
dissertação contribuir para a caracterização da dinâmica glaciária e pós-glaciária e consolidar o
conhecimento acerca dos geossítios NSA e Poio do Judeu e dos vales glaciários adjacentes. A
metodologia multidisciplinar baseou-se em métodos geomorfológicos, de datação relativa,
sedimentológicos e geofísicos, desenvolvidos a partir de cartografia geomorfológica de pormenor,
datações relativas com martelo de Schmidt e análise morfométrica de pias, cinco perfis
sedimentológicos e cinco perfis de tomografia de resistividade elétrica e nove perfis de georadar.
A dinâmica glaciária e de deglaciação definiu-se em quatro fases: fase 1 – máximo glaciário local
(glaciares a preencher a NSA); fase 2 – primeira fase de deglaciação (recuo do glaciar do Alforfa);
fase 3 – segunda fase de deglaciação (recuo do glaciar do Zêzere); fase 4 – terceira fase de
deglaciação (continuação do recuo do glaciar do Alforfa). A dinâmica geomorfológica holocénica
traduziu-se, principalmente, no enchimento sedimentar da bacia da NSA, com até 60 m de
espessura, possuindo diversas formas associadas à dinâmica hídrica. Este caracteriza-se,
predominantemente, por sedimentos de areia cascalhenta argilosa, na bacia, e de cascalho argiloso
e arenoso, no glacis. Datações em dois perfis revelaram que o enchimento mais recente se
enquadra no Holocénico Médio ou posterior (8380±30 B.P. entre 140 a 145 cm e 5780±30 B.P.
entre os 190 e os 200 cm de profundidade). A estratificação dos sedimentos é irregular e
descontínua, com estruturas horizontais ou concavas associadas a incisões hídricas. O faseamento
da dinâmica sedimentar na bacia é mais marcado no glacis do Teleférico, caracterizando-se,
inicialmente, pela acumulação sedimentar, seguindo-se a incisão e progressão dos sedimentos
para jusante.
The Serra da Estrela’s morphology and climate contributed to its Pleistocene glaciation, characterized by a plateau ice field that fed several valley glaciers. The area studied is centered on Nave de Santo António (NSA) and the aim of this dissertation is to contribute to the characterization of the glacial and post-glacial dynamics and to consolidate knowledge about the NSA and Poio do Judeu geosites and the adjacent glacial valleys. The multidisciplinary methodology was based on geomorphological, relative dating, sedimentological and geophysical methods, developed on detailed geomorphological mapping, relative dating with a Schmidt hammer and morphometric analysis of gnammas, five sedimentological profiles and five electrical resistivity tomography profiles and nine ground penetrating radar profiles. The glaciation and deglaciation dynamics were defined in four phases: phase 1 - local glacial maximum (glaciers filling the NSA); phase 2 - first phase of deglaciation (retreat of the Alforfa glacier); phase 3 - second phase of deglaciation (retreat of the Zêzere glacier); phase 4 - third phase of deglaciation (continued retreat of the Alforfa glacier). The Holocene geomorphological dynamics were mainly reflected in the sedimentary infill of the NSA basin, which is up to 60 meters thick, and has various landforms associated with hydrological dynamics. It is predominantly characterized by gravelly muddy sands in the basin and muddy sandy gravel in the glacis. Dating on two profiles revealed that the most recent infill fits within the Middle Holocene or later (8380±30 B.P. between 140 and 145 cm and 5780±30 B.P. between 190 and 200 cm deep). Sediment stratification is irregular and discontinuous, with horizontal or concave structures associated with water incisions. The phasing of the sedimentary dynamics in the basin is most marked in the Teleférico glacis, initially characterized by sedimentary accumulation, followed by incision and progression of the sediments downstream.
The Serra da Estrela’s morphology and climate contributed to its Pleistocene glaciation, characterized by a plateau ice field that fed several valley glaciers. The area studied is centered on Nave de Santo António (NSA) and the aim of this dissertation is to contribute to the characterization of the glacial and post-glacial dynamics and to consolidate knowledge about the NSA and Poio do Judeu geosites and the adjacent glacial valleys. The multidisciplinary methodology was based on geomorphological, relative dating, sedimentological and geophysical methods, developed on detailed geomorphological mapping, relative dating with a Schmidt hammer and morphometric analysis of gnammas, five sedimentological profiles and five electrical resistivity tomography profiles and nine ground penetrating radar profiles. The glaciation and deglaciation dynamics were defined in four phases: phase 1 - local glacial maximum (glaciers filling the NSA); phase 2 - first phase of deglaciation (retreat of the Alforfa glacier); phase 3 - second phase of deglaciation (retreat of the Zêzere glacier); phase 4 - third phase of deglaciation (continued retreat of the Alforfa glacier). The Holocene geomorphological dynamics were mainly reflected in the sedimentary infill of the NSA basin, which is up to 60 meters thick, and has various landforms associated with hydrological dynamics. It is predominantly characterized by gravelly muddy sands in the basin and muddy sandy gravel in the glacis. Dating on two profiles revealed that the most recent infill fits within the Middle Holocene or later (8380±30 B.P. between 140 and 145 cm and 5780±30 B.P. between 190 and 200 cm deep). Sediment stratification is irregular and discontinuous, with horizontal or concave structures associated with water incisions. The phasing of the sedimentary dynamics in the basin is most marked in the Teleférico glacis, initially characterized by sedimentary accumulation, followed by incision and progression of the sediments downstream.
Descrição
Palavras-chave
Glaciação Dinâmica geomorfológica Sedimentologia Prospeção geofísica Serra da Estrela