HIGH-RESOLUTION SEISMIC ANALYSIS IN THE RÍA DE VIGO (NW SPAIN)

The Ría de Vigo is located on the NW Atlantic coast of Spain. It is partially blocked from the open shelf towards the west, by a north ridge composed of Palaeozoic rocks (mainly granitic and metamorphic rocks). The Post-Hercynian tectonics is characterised by the generation of important fractures systems, following lineations SW-NE, N-S and WNW-ESE.

The study of high-resolution seismic reflection profiles of the Ría de Vigo (Uniboom and a 3.5 kHz sub-bottom seismic profiler), has allowed to distinguish seven seismic units: Bg and Bm (interpreted as granitic and metamorphic basement rocks respectively), and the other five corresponding to the sedimentary infill of the ría. The identification of the sequences boundaries (L2 and L3) allow to recognise three sedimentary sequences (S1, S2 and S3).

A lower sequence S1 found in the deepest parts of the ría. A prominent erosive surface L2 at its top is tentatively ascribed to erosion during the glacially-induced Würm regression.

A middle sequence S2, resting unconformably on the S1. Within this sequence, it can be distinguished: unit “a”, the lower one, which onlaps the above mentioned unconformity surface; and unit “b”, which is more extensive and overlies both, unit “a” and the basement side slopes. Its top is marked by an erosion surface L3, correlated with the Younger Dryas event.

An upper sequence S3 developed on the smooth erosive surface L3, at the top of S2. This S3 is composed by two seismic units: unit “c”, characterised by strong and continuous reflectors that onlap the basal surface; and unit “d”, the most extensive within the rías.

Contribution to: PGIDT00PXI30105PR, REN2000-1102 MAR and 437 IGCP Spanish Projects.