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Evolution of the Aveiro Cretaceous aquifer (NW Portugal) during the Late Pleistocene and present day:: evidence from chemical and isotopic data

By
M. T. Condesso De Melo
M. T. Condesso De Melo
Departamento de Geociências, Universidade de Aveiro, 3810-193 Aveiro, Portugal (email: tmelo@geo.ua.pt)
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P. M. M. Carreira Paquete
P. M. M. Carreira Paquete
Departamento de Química, Instituto Tecnológico e Nuclear, 2686-953 Sacavém, Portugal
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M. A. Marques Da Silva
M. A. Marques Da Silva
Departamento de Geociências, Universidade de Aveiro, 3810-193 Aveiro, Portugal (email: tmelo@geo.ua.pt)
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Published:
January 01, 2001

Abstract

A combined hydrogeological, geochemical and isotopic investigation was performed in the Aveiro Cretaceous coastal aquifer in order to investigate the rock-water interaction and the evolution of palaeowaters. The results indicate an aquifer with well-defined freshwater (<50 mg l−1 Cl) throughout most of the aquifer as far as the coastline and with very slow chemical kinetics for the water–rock interactions. The low mineralization may be explained by the mainly siliciclastic composition of the aquifer sediments, while calcite dissolution and cation exchange were also considered to be involved in the groundwater chemical evolution. This interpretation is in agreement with lithology and facies changes, and was validated by the PHREEQC-2 modelling results. Radiocarbon ages indicate a smooth gradient across the aquifer, implying continuous flow during the late Pleistocene and Holocene. Noble gas ratios indicate that the mean annual air temperatures were lower by 5–6°C at the last glacial maximum (LGM). In contrast to most areas with continental palaeowaters, the environmental isotopes indicate enrichment (0.8–1.0‰ in 18O), interpreted as reflecting the composition of the oceans at the time of the LGM at this maritime site, as well as the constancy of the air mass circulations over the period to the present day. An outlet for the aquifer is inferred offshore to account for the observed geochemical data, with the possibility that freshwater could still also be found offshore.

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Geological Society, London, Special Publications

Palaeowaters in Coastal Europe: Evolution of Groundwater since the Late Pleistocene

W. M. Edmunds
W. M. Edmunds
British Geological Survey, Wallingford, UK
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C. J. Milne
C. J. Milne
British Geological Survey, Wallingford, UK
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Geological Society of London
Volume
189
ISBN electronic:
9781862394377
Publication date:
January 01, 2001

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