The Lusitanian Basin is a rift basin located on both the mainland and continental shelf off the west-central coast of Portugal. It covers an area measuring 20,000 square kilometres (7,700 sq mi) and extends north-south from Porto to Lisbon. The basin varies between approximately 130 kilometres (81 mi) and 340 kilometres (210 mi) in width and belongs to a family of periatlantic basins such as the Jeanne d'Arc Basin. To the east of the Lusitanian Basin lies the Central Plateau of the Iberian Peninsula. A marginal horst system lies to the west. The Alentejo and Algarve Basins connect to the southern end of the Lusitanian Basin. In the north, it connects to the Porto and Galicia Basins via an undersea ridge.

The Lourinhã Formation is a fossil rich geological formation in western Portugal, named for the municipality of Lourinhã. The formation is mostly Late Jurassic in age (Kimmeridgian/Tithonian), with the top of the formation extending into the earliest Cretaceous (Berriasian). It is notable for containing a fauna especially similar to that of the Morrison Formation in the United States and a lesser extent to the Tendaguru Formation in Tanzania. There are also similarities to the nearby Villar del Arzobispo Formation and Alcobaça Formation. The stratigraphy of the formation and the basin in general is complex and controversial, with the constituent member beds belonging to the formation varying between different authors.