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The Karstic Systems of the Vallès-Penedès half-graben (onshore of the Valencia Trough, NW Mediterranean)

Vinyet Baqués, Anna Travé, and Irene I. Cantarero

The Vallès-Penedès half-graben is the onshore equivalent of the major petroleum system of the Iberian Peninsula located on the Valencia Trough. The Mesozoic rocks outcropping along the footwall block of the Vallès-Penedès fault are extensively overprinted by different stages of deformation and karstification. Four different karstic events have been identified using structural, petrological and geochemical data: (1) the first event is related to the subaerial exposure of the Mesozoic carbonates after the Paleogene compression. The sediments filling the vug and cavern porosity comes from the erosion and reworking of the Mesozoic host rock; (2) the second event is related to the early stages of the syn-rift Neogene extension. Random fractures were formed at expenses of fault propagation favouring dissolution processes. The geochemistry of the karstic cements indicates that they precipitated from meteoric fluids in an open hydrological system. However, the 87Sr/86Sr ratio of the dolomitized karstic sediments indicates that dolomitization occurred later from marine late Burdigalian-Langhian waters; (3) the third event occurred during the Neogene syn-rift. The fillings related to the NE-SW normal faults that bounds the north-western part of the Vallès-Penedès half-graben are mixtures of tectonic and karstic processes and resulted from multi-stage fault movements. The geochemistry of the cements together with the highly radiogenic values of the karstic pisoliths indicate that meteoric waters, not equilibrated with the host rock, were responsible for precipitation of these cements; (4) the fourth event was favoured by the late post-rift NNW-SSE to NNE-SSW trending fractures. The fractures walls are covered by sediments and cements interpreted as speleothems. The low δ13C of these speleothems indicates a higher involvement of soil-derived CO2 and precipitation in the vadose meteoric environment.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013