Sedimentology and tectonic record of Late Cretaceous deposits in the western High Atlas, Morocco

Abstract

Late Cretaceous sediments frequently record the paleoenvironmental and paleogeographic changes, which precede the Tertiary Alpine orogeny. The age of the Late Cretaceous deposits of the Moroccan Western High Atlas, has been refined thanks to few paleontological findings and to chemostratigraphical (¹³C) correlations. Coniacian and Santonian shallow marine deposits are dominated by the development of eustacy-controlled carbonate shelves, whereas Campanian and Maastrichtian deposition recorded mainly clastic deposits showing important facies and thickness variability, suggesting a tectonic instability. The appearance of sandstone beds and the fragmentation of the basin in the middle(?) Santonian (≈84 Ma) are interpreted as a result of a mild tectonic event. A significant tectonic event of Late Campanian age (≈77-74 Ma) is marked by the deposition of 50-100m-thick nearshore sandstones, by clastic dykes and mild angular unconformities in the South and by a probable widespread hiatus to the North. The latter area may have been uplifted by at least a few tens of meters. A new, major tectonic event of middle(?) Maastrichtian age (≈70 Ma) is marked, specially to the South and West of the study area, by deposition of up to 300 m-thick shallow marine sandstones, associated with slumps, breccias, clastic dykes and erosions. The absence or reduction of Paleocene deposits in the study area seems to be rather related to eustatic low sea level.