An exhumed Paleozoic glacial landscape in Chad

Abstract

In northern Chad, an outcrop belt of Paleozoic rocks occurs in the Ennedi-Bourkou range. There, satellite image interpretation reveals a series of clearly expressed paleo-ice stream pathways, which are encased in sandstone plateaux. At least five paleo-ice stream pathways are recognized, measuring 5-12 km wide. Each contains well-expressed belts of mega-scale glacial lineations (MSGLs) with occasional drumlins. The paleo-ice stream tracks are confined to present-day low-lying areas, representing ancient valley networks, and have sinuous geometries. The features occur on multiple plateau and/or stratigraphic levels. Their dissection by late Neogene rivers discounts a modern-day origin as eolian features, and offset suites of MSGLs by east-west-striking faults confirms their geologic antiquity. The paleo-ice stream pathways appear to have drained a newly discovered late Paleozoic paleo-ice sheet of probable Visean age that flowed northward toward presentday Libya, with an estimated < 250-m-thick tidewater ice margin. This discovery has wide-ranging implications, increasing the known extent of late Paleozoic ice sheets, and potentially their effects on sea-level changes.