The tectonothermal evolution of the Lower-Cretaceous Cameros basin is characterized from the analysis of dimensions and orientation of quartz-filled tension gashes and study of fluid inclusions within them. In the four sites studied in the eastern part of the basin the direction of tension gashes is N120E and most of them are perpendicular to bedding, what allows to relate them with synsedimentary extension. Local extension determined from thickness of quartz veins varies from 2 to 12%, w ith the lo w e st extension rates in strata where ductile boudinage linked to pseudo-cleavage development in incompetent beds occurs. Paleotemperatures obtained from the study of primary fluid inclusions indicate a v aria tion o f 3 0 ° C (80° C with pressure correction) between the bottom and top of the Urbion Croup, separated by 2.500 m of stratigraphic thickness. From these data it can be inferred that (1) the present-day northdipping geometry of beds is not a syn-sedimentary feature but was acquired during the Tertiary inversion and (2) the geothermal gradient was normal during the syn-rift stage