A geological cross-section along the Basque Pyrenees and the Parentis Basin (Western Pyrenees)

Abstract

A new geological cross- section along the North Iberian Margin shows a complete image of the Western Pyrenees and the Parentis Basin as well as the geometric differences and age constraints between both Pyrenean fronts. The South Pyrenean front, developed during Uppermost Cretaceous- Middle Miocene, is represented by a major thrust which accumulates around 20 km of southward displacement. The Basque- Cantabrian basin is a mesozoic extensional basin which was inverted during Paleogene times as a consequence of the Pyrenean orogeny. A basement- involved thrust wedge with an upper south- directed back- thrust characterizes the North Pyrenean Frontal Thrust. The main thrust, emplaced during Late Eocene- Miocene times, shows a displacement around 2 km whereas the back- thrust detached in Paleocene materials shows a displacement about 1.5 km. Northwards, the Landes High, is interpreted as an uplifted plateau where a thick wedge of Upper Cretaceous- Cenozoic synorogenic deposits overlay unconformably the Hercinian basement. This package corresponds with the North Pyrenean foreland basin. More to the north, the Landes fault is the southern margin of the Mesozoic Parentis Basin, a semigraben infilled with a thick package of Triassic to Albian synrift sequence overlied by Cretaceous and Cenozoic deposits. There, inversion structures were poorly developed.