The Cretaceous Etjo Sandstone Formation is a mixed aeolian and fluvial unit exposed over 5000 km2 in the Huab Basin of Damaraland, northwest Namibia. The distribution of fluvial and aeolian facies reveals complex spatial and temporal variations in depositional style that may be related to four distinct phases of sedimentary evolution. The Krone Member forms the base of the formation and comprises coarse clastic material deposited in an and wadi system by flash floods. This is conformably overlain by a mixed aeolian-fluvial unit that is interpreted to represent a transition from ephemeral fluvial to aeolian sandsheet deposition, with the development of small barchan dunes as aeolian sediment supply increased. Repetitive cycles of alluvial plain to dune sedimentation are common and may indicate climate or subsidence controlled variations in the level of the water table relative to the level of the depositional surface. During deposition of the Main Aeolian Unit, sediment supply increased and large transverse draa bedforms migrated across the basin, rapidly filling available accommodation space. Preservation of isolated barchan dunes in the Upper Aeolian Unit indicates a rapid decrease in sediment supply and a return to restricted aeolian activity, following the emplacement across much of the region of Etendeka flood basalts related to continental break-up of West Gondwana at around 132 Ma. Synsedimentary faulting appears to have been a major control on the geometry and distribution of the Etjo Formation. Extrabasinal controls on depositional style include an initially increasing and subsequently decreasing external supply of aeolian sand to the basin, and a gradual transition from semi-arid to hyperacid climatic conditions.