Abstract
Abstract The northern margin of the Basque-Cantabrian Basin was analysed combining stratigraphic and structural data from both surface and subsurface together with reflectance of vitrinite data from oil wells. The use of cross-section balancing techniques in addition to thermal modelling enabled us to reconstruct the tectonic, burial and thermal evolutions of the basin margin as well as those of the Landes High to the N in two different periods. The section restoration at the end of the Cretaceous shows a northern basin margin structure influenced by evaporites related to south-dipping normal faults. The reconstruction in middle Eocene times yielded up to 1 800 m of Paleocene-middle Eocene deposits on top of the basin margin. Subsequent tectonic inversion related to the Pyrenean compression led to the north-directed thrusting of basement units and to the formation of thrust slices or inverted folds in the cover along the northern margin of the basin. Tectonic subsidence analysis together with maturity data provided evidence that oil was generated in the basin during the late syn-rift and post-rift stages in the Late Cretaceous and became overmature during the period of incipient inversion after 55 Ma. In the autochthonous Landes High, the oil was generated after the tectonic inversion period 37 Ma.
Highlights
The Basque Cantabrian Basin, located in the northern margin of Spain, is a Mesozoic extensional basin which was inverted during the Pyrenean orogeny in Paleogene times
The lower Cretaceous rocks outcropping on the northern margin of the basin and imaged at the Cormorán-1 borehole present a high level of maturity of organic matter
The tectonic inversion of the northern margin of the Basque-Cantabrian Basin has been dated as Eocene [Soler et al, 1981; Cuevas et al, 1999], latest Eocene-Oligocene [Derégnaucourt and Boillot, 1982; Rat, 1988] and late Cretaceous-Eocene [Cámara, 1997]
Summary
Key words.– Inversion tectonics, Subsidence analysis, Thermal modelling, Western Pyrenees, Basque-Cantabrian Basin. – The northern margin of the Basque-Cantabrian Basin was analysed combining stratigraphic and structural data from both surface and subsurface together with reflectance of vitrinite data from oil wells. The use of cross-section balancing techniques in addition to thermal modelling enabled us to reconstruct the tectonic, burial and thermal evolutions of the basin margin as well as those of the Landes High to the N in two different periods. Tectonic subsidence analysis together with maturity data provided evidence that oil was generated in the basin during the late syn-rift and post-rift stages in the Late Cretaceous and became overmature during the period of incipient inversion after 55 Ma. In the autochthonous Landes High, the oil was generated after the tectonic inversion period 37 Ma. Mots clés.– Inversion tectonique, Analyse de la subsidence, Modélisation thermique, Pyrénées Occidentales, Bassin Basque-Cantabrique. L’analyse combinée de la subsidence tectonique et des données de maturité indique que la formation du pétrole a commencé dans l’allochtone à l’étape finale du syn-rift et post-rift pendant le Crétacé supérieur et à l’autochtone après la phase d’inversion au Tertiaire à partir de 37 Ma
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