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

A basin evolution model for the south-western Valencia Trough is estab lished using thermal and palaeo-thermal data. Bottomhole temperature a nd 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 condu ctivity and heat flow density. Integrating these data with previous se afloor heat flow measurements yields a regional surface heat flow dens ity of about 90- 100 mW m-2. Vitrinite reflectance data available from the Ibiza Marino well have been used as a palaeo-thermal constraint f or the proposed tectonic models. Two different modelling approaches ar e tested: a single rift phase model and a multi-phase formation model. The single rifting phase, which considers different eroded thicknesse s, is ruled out as it does not match the observed data. A multi-stage evolution coherent with the geological and geophysical data is propose d and consists of three Mesozoic rifting events, Palaeogene compressio n (to which erosion of about 5 km of Late Jurassic and Cretaceous sedi ments is related) and a Neogene rifting event that gave rise to the pr esent day Valencia Trough. Surface heat flow, vitrinite data and erode d thickness are successfully integrated in the proposed model.