Abstract

The detailed study of the sediments that fill the depositional complex of Late Eocene and Early Oligocene age, W of the Segre thrust, has allowed the recognition of five major depositional cycles. These cycles are bounded by angular unconformities, particularly in the borders of the basins, and by sharp changes of facies in the more central areas, where the cycles tend to be conformable. The major cycles consist of minor cycles reflecting relative changes of basinal base level. The major cycles are regarded as depositional sequences containing both continental and marine deposits.

The five major cycles are considered to be responses to eustatic sea-level changes. However, tectonism also operated during the sedimentation of these units. The displacement of the Pyrenean thrust sheets enhanced the angular unconformities in the conglomerates that border the thrusts. The emplacement of these thrust sheets caused a paleogeographic change in the orientation of the Basin. During the Middle and Late Eocene, continental deposits formed in the south, while marine conditions existed in the north (Oliana area). In the latest Eocene, and even more clearly in the Early Oligocene, proximal deposits, sourced in the Pyrenees, formed in the north, whereas distal fluviatile and lacustrine sediments formed in the south, towards the centre of the Ebro Basin.