Seismic reflection measurements with a pneumatic sound source in the Ría de Arosa (NW Spain)

In 1968 continuous seismic profiles with a total length of 150 km were made in the Ría de Arosa (Galicia, NW Spain). They were executed by the Bundesanstalt für Bodenforschung (Hannover) with the assistance of two members of the Department of Geology of the University of Leiden (The Netherlands). The pneuflex (airgun) system used for profiling is described. The transformation of travel-time profiles into depth profiles was done automatically with the aid of a computer program. The profiles reveal the presence, below some 7—12 m of Holocene marine muds, of bedded deposits with a thickness of about 30 m (and in the outer part of the ria even more than 60 m), which are interpreted as being of fluvial origin. They are underlain by what is assumed to be colluvium and weathered granite. The bedded deposits must have been formed in times when the sea-level was low, presumably during the Riss and/or Würm glacials. They may originate in part from deposits of the Ulla River, but to a greater extent may represent fluvial fans of its tributaries.