The building of the North Catalonia continental margin

TASSONE, A; CANALS, M.; ROCA, E.; MUÑOZ, A.; CABRERA, LLUIS

Gent

Conferencia; . 2nd International Conference on the Geology of siliciclastic shelf seas.; 1994

RCMG. Universiteit Gent

The North Catalonia inner continental margin has been studied through the interpretation of multichannel seismic records. This work stresses the tectonic control on the distribution and geometry of Neogene deposits. Two main tectonic regimes are recognized in the study area. The first is related tot the Pyrenean Range building which produced NW-SE Paleogene compressive onshore and offshore structures. The second is of Paleogene-Neogene age and is linked to the extensional tectonics which determined the opening of the Valencia Trough; NE-SW to N-S and NW-SE to WNW-ESE faults define proximal and distal morphostructural domains. While in the proximal domain the fault system results in a horst and graben structure, in the distal domain a semi-graben structure with easterly dipping blocks bounded by NE-SW to N-S trending faults appears. The Neogene sediment record shows a general gradual thickening towards the basin, although locally it reaches up to 3000 meters in some grabens of the proximal domain. Four main seismic units are identified in the Neogene fill: -      Late Oligocene-Lower Miocene Unit, which is only present in structural depressions bounded by NW-SE faults. -      Middle to Upper Miocene Unit which also fills structural depressions and progrades towards the basin, thinning landward. -      Pliocene Unit, which together with the Pleistocene fourth unit builds a prograding margin characterized by paleochannel development. Pliocene sediments 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. In the study area, the Messinian erosion was channeled along NW-SE oriented faults. From uppermost Miocene-Lower Pliocene to Quaternary rimes, the main conduits of the Messinian paleodrainage system evolved to fault controlled submarine valleys resulting from the interplay amongst extensional tectonics and subsidence, and submarine erosional processes. However, in a later phase, some of these valleys were obliterated by sediments, while some others still persist as submarine canyons coexisting with some new ones formed in Quaternary times. Two main seismic sequences are recognized in the Pliocene record, respectively corresponding to an oldest transgressive event and to a regressive episode which produced a shelf break shift. In the continental rise, faults with detachment planes within the Pliocene record are quite common, as well as related gravitational slides. Quaternary Unit which overlies a local unconformity identified as reflector G in seismic records. It corresponds to an erosive surface produced by a sea level fall below the shelf break or very close to it. The G event is marked by canyon incision in the margin. The Quaternary deposits thicken easterly, the maximum consisting of paleocanyon infills.