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The Ouarzazate Basin is the southern foreland basin to the High Atlas Mountains in Morocco. The sedimentary fill records a sequence dating from the Eocene to Pleistocene that records the interplay between tectonics and climate. This study presents the first stable isotope and fades analyses of the Middle to Late Miocene Ait Ibrim lacustrine Member (Ait Kandoula Formation). These data test whether the basin was internally draining and enable the development of palaeoenvironmental models for the Middle to Late Miocene. Five sedimentary fades of lacustrine and palustrine limestones are interbeddded with extensive sequences of palaeosols and fluvial sand-stones and conglomerates, often associated with evaporite (gypsum) development. These facies can be divided into two fades associations related to water depth and sub-aerial exposure within the basin. In the Serravalian and early Tortonian shallow water successions dominate the stratigraphy, typical of underfilled foreland basin settings. Furthermore, carbonate delta O-18 and delta C-13 isotopes from the sections show covariance confirming that these carbonates were deposited within a hydrologically closed basin. However, late Tortonian to Messinian carbonates do not demonstrate the covariance typical of endorheic basins. Additionally, the fades association indicates the presence of deeper water lake systems demonstrating that the basin was externally draining at this time. These results question the established view of tectonic stagnation in the Late Miocene and suggest that the Cenozoic sediments of the Ouarzazate Basin contain a rich and untapped record of climate change and tectonic evolution on the edge of the Sahara desert. (C) 2019 Elsevier B.V. All rights reserved.