Deep within the hyper-arid Namib Desert at Narabeb, which is today isolated by 100-m high linear dunes, is a 36-m section of lacustrine mudstones and interbedded sands. The slightly calcareous and laminated sands of this sequence are composed mainly of rounded to subrounded, lightly stained quartz that is similar to the sands of the underlying Tertiary Tsondab Sandstone Formation and the surrounding dunes of the Namib Sand Sea. The six calcareous mudstone units in this sequence are variably laminated and sandy, contain halite-filled fractures, and have been radiocarbon dated at 20,000–26,000 yr B.P. The interrelationship of sediments at this site with Middle to Early Stone Age implements suggests an age of more than 20,000 years, whereas 234U/ 230Th dating of the basal mudstone gave an age of 210,000–260,000 yr B.P. The calcareous mudstones were deposited in a lake at the former end point of the Tsondab River, which was prevented from reaching the Atlantic Ocean by N-S trending linear dunes of the Namib Sand Sea. The interbedded sands were deposited during low water or dry stages of the lake. Sometime before 14,000 yr B.P. the terminus of the Tsondab River shifted eastward from Narabeb in response to the northward encroachment of linear dunes, and the present end point was eventually established at Tsondab Vlei, 38 km to the east. Lacustrine deposition at Narabeb, just as at Tsondab Vlei today, probably occurred mainly in response to precipitation in the headwaters of the Tsondab River. Although no major climatic change is necessary to explain the sequence at Narabeb, the clustering of radiocarbon dates on carbonate from the Namib Desert in the periods 20,000–35,000 yr B.P. and 10,000–14,000 yr B.P. suggests an increase in precipitation during those times.