EVIDENCE FOR THE MULTISTAGE FORMATION OF THE SOUTH-WESTERN VALENCIA TROUGH

A basin evolution model for the south-western Valencia Trough is established using thermal and palaeo-thermal data. Bottomhole temperature and drillstem test data from oil wells have been used to determine the geothermal gradient in the study area. A combination of well log data and X-ray diffractometry analyses carried out on rock samples from the lbiza Marino well has allowed an estimation of the bulk thermal conductivity and heat flow density. Integrating these data with previous seafloor heat flow measurements yields a regional surface heat flow density of about 90- 100 mW m-2. Vitrinite reflectance data available from the Ibiza Marino well have been used as a palaeo-thermal constraint for the proposed tectonic models. Two different modelling approaches are tested: a single rift phase model and a multi-phase formation model. The single rifting phase, which considers different eroded thicknesses, is ruled out as it does not match the observed data. A multi-stage evolution coherent with the geological and geophysical data is proposed and consists of three Mesozoic rifting events, Palaeogene compression (to which erosion of about 5 km of Late Jurassic and Cretaceous sediments is related) and a Neogene rifting event that gave rise to the present day Valencia Trough. Surface heat flow, vitrinite data and eroded thickness are successfully integrated in the proposed model.