The late Neogene Sahabi rivers of the Sahara and the hamadas of the eastern Libya–Chad border area

This paper contributes to the concept that during the late Tortonian, Messinian and early Pliocene (c. 7.5–4.6 Ma) in addition to the Nile the Sahabi rivers also crossed the Sahara, having originated from tropical Neogene Lake Chad. Examination of two hamadas lying just to the north of the Libya–Chad border using Landsat images and SRTM topographic data enables one of them, Hamada Ibn Battutah West, to be recognised as an uplifted palaeosurface which preserves late Miocene/early Pliocene fluvial activity. This surface is referred to as the Yangara Palaeosurface. Of particular interest on the hamada are two long (c. 50 km), wide (c. 4 km) channels, a 50 km2 relic landscape and a short well defined 5 km channel about 1 km wide. The location of Hamada Ibn Battutah West is significant because the hamada provides evidence of extensive fluvial activity part way between the place of origin of the Sahabi rivers and their preserved record at the Gulf of Sirt. The Yangara Palaeosurface is considered to extend southwards to the adjacent hamada in northeastern Chad. The total palaeosurface extends 165 km in an approximate north–south direction and averages 45 km in width. It lies in the central part of an area of complex post-Miocene uplift involving four hamadas at the Libya–Chad border.

► Two adjacent hamadas in SE Libya each have a distinctive geomorphology.
► The west hamada shows fluvial effects from north flowing late Neogene Sahabi rivers.
► This adds well placed evidence for a past river between Chad Basin and Mediterranean.
► A palaeosurface produced by the Sahabi rivers straddles the SE Libya/Chad border.
► This area is now a local divide between the Chad Basin and Mediterranean drainage.