XVI Reunión Científica de la Sociedad Española de Arcillas - Libro ...

Comunicaciones SEA 2001 – Baeza (Jaén)
SOCIEDAD
ESPAÑOLA DE ARCILLAS
MINERALOGICAL CHARACTERIZATION OF THE CLAY FRACTION
OF THE SEDIMENTS OF THE CONTINENTAL SHELF AND UPPER
SLOPE BETWEEN ESPINHO AND AVEIRO (PORTUGAL)
Abrantes I a , Rocha F b , Dias J c
a
E.S.E./Instituto Superior Politécnico de Viseu. Portugal.
b Dpto. de Geociencias. Universidade de Aveiro. Portugal.
c UCTRA. Universidade do Algarbe. Faro. Portugal.
Introduction
In the studied area the continental shelf is narrow, with a width between 38
km (near Aveiro Canyon) and 50 km (off Furadouro) and corresponding to a
gently westward plunging monoclinal of cretaceous and cenozoic formations
(Musellec 1974). Mesozoic limestones outcrop in the mid and outer shelf. The
shelf break lies at a mean depth of 160 m.
Between centuries X and XVIII, alongshore currents transported sediments
southward developing a sandy spit that closed the bay where the Vouga river
discharged into, forming the Aveiro lagoon which discharges to the study area.
The shelf sedimentary cover is dominated by sand. Gravel occurs in the
middle and outer shelf and consists of relict sediments correlated with paleolitorals.
The mud (silt and clay) content is generally low, with an average content
of 5%, and shows an increasing to the open sea (Figure 1). This distribution point
out to the effectiveness of the lagoon as a natural sediment trap (Dias et al. 1984,
Abrantes et al. 1994) and to hydrodynamics conditions which do not allow the
deposition of this particles.