First-order reconstructions of a Late Ordovician Saharan ice sheet

Synthesis of outcrop and subsurface sedimentological and geomorphological datasets across North Africa allows a tentative palaeo-glaciological model of the flow dynamics and recessional character of a 440 Ma old (Hirnantian) ice sheet to be proposed. A system of eight cross-shelf trough depocentres is identified from the Late Ordovician of the Sahara region. These are interpreted to have been carved and occupied by ice streams, providing evidence for widespread heterogeneous flow within the ice sheet. During retreat, two key geological features were produced: (1) laterally extensive, sinuous to linear piles of sediment dumped parallel to the ice margin; (2) large meltwater channels (tunnel valleys) cut near the grounding line.