Combination of HR & GP seismic records in continental margin sequence stratigraphic studies: the north-catalonia margin

TASSONE, A

Palma de Mallorca

Otro; 3rd Mercator Intensive Course on "Continental Margin Sequence Stratigraphy".; 1993

Erasmus. UE

Combined single channel, high resolution and multichannel, great penetration seismic records allow to establish the seismic stratigraphic evolution, onshore and offshore, of the North-Catalonia margin (Emporda area), Northwestern Mediterranean Sea, during Tertiary and Plio-Quaternary times. The acoustic basement is shaped by two NE-SW and N-S trending systems of horsts and grabens developed during Upper Oligocene/Lower Miocene periods. Later NW-SE tot WNW-ESE trending faults of likely lower Miocene age, mainly represented in onshore and proximal offshore areas, constitute the North and South boundaries separating onshore Alt and Baix Emporda grabens. In offshore distal areas, the NE-SW trending structures define several semi-grabens and progressively deepen the basement towards the central basin. Pliocene deposits overlie a regional erosive unconformity identified as reflector K in seismic records. This unconformity formed during the Messinian salinity crisis, when the Mediterranean basin dried and a subaerial paleodrainage system developed in areas which are now offshore. Some of other Messinian valleys have been obliterated by Plio-Quaternary sedimentation, while others have evolved towards submarine modern canyons. These canyons coexists with other formed more recently, in Quaternary times. Three main seismic sequences are recognized in the Pliocene record, the oldest corresponding to a transgressive event, with the intermediate and the youngest reflecting a regressive episode which produced two consecutive shelf break shift The Quaternary record overlies a local unconformity, identified as reflector G in seismic records, which is an erosive surface produced by a sea level fall below the shelf break. It is marked by canyon incision on the margin. Three main relative sea level changes are identified in the Quaternary record, each represented by the corresponding erosional surface. The entire Quaternary sequences build a progradational margin. This contribution will also discuss with "more detail the relative importance of local morphology, differential subsidence and eustatic cycles on the organization and thickness of Plio-Quaternary deposits. Emphasis will be also made on the importance of combining different scales of observation, i.e. high resolution/ weak penetration and great penetration/poor resolution seismic records.