Abstract At the beginning of the Jurassic period, southern European areas formed a single continental mass open to the east (western Tethys), and the Iberian plate lay between latitude 25°N and 35°N. It was separated from the larger European plate to the north by a narrow trough corresponding to the early rifting of the Bay of Biscay. To the NW it was separated from the Laurentia–Greenland Plate by an epicontinental sea showing a typical horst and graben structure, which would eventually become the palaeogeographical connection between the northern and central Atlantic. The opening of the Bay of Biscay took place between latest Jurassic and early Campanian times, giving rise to SE-directed movement and anti-clockwise rotation of the Iberian plate (e.g. Ziegler 1988 b ; Osete et al . 2000 ). Jurassic palaeogeography was characterized by a large part of the central and western Iberian plate forming an emergent massif (the so-called Iberian Massif), whilst the surrounding areas were occupied by intracratonic basins that formed shallow epicontinental seas, predominantly filled with marine carbonate deposits (Fig. 11.1 ). Those areas, located to the north and NE of the Iberian Massif, correspond from west to east to Asturias, the Basque-Cantabrian basin, and the South Pyrenean basin. To the east extended the Iberian basin, whereas the southern margin of the Iberian Massif was occupied by a wide carbonate platform parallel to a narrow oceanic trough connecting Tethys with the central Atlantic Ocean. These areas together comprised the south Iberian margin basin, whose proximal