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.

Ice‐margin fluctuation sequences and grounding zone wedges: The record of the Late Palaeozoic Ice Age in the eastern Karoo Basin (Dwyka Group, South Africa)

“…Hence, in KwaZulu‐Natal Province, in areas where glaciogenic deposits have been entirely eroded away, the modern topography exhibits Dwyka‐aged polished and striated surfaces as well as roches moutonnées carved into the ancient basement and hence corresponds to the exhumed Permo‐Carboniferous glacial landscape that prevailed at the onset of the deposition of the Dwyka sediments (von Brunn, , ; see also Guillocheau et al , ). Such an exhumed LPIA glacial landscape echoes those of the same age found in Namibia (Andrews et al , ), Chad (Le Heron, ) and in South America (Assine et al , ).…”

“…These successive ice sheet waxing and waning events probably depended on parameters such as the wander of the South Pole (Opdyke et al , ), variable concentration of atmospheric CO 2 (Frank et al , ; Montañez et al , ; Myers, ), and/or the erection of mountain belts (Isbell et al , ; Goddéris et al , ). Investigations on correlative glaciogenic deposits across Gondwana have been carried out in South America (Dykstra et al , ; Vesely et al , ; Tedesco et al , ; Fallgatter and Paim, ; Valdez Buso et al , ; Assine et al , ), the Middle East (Martin et al , ; Stephenson et al , ), India (Wopfner and Jin, ), Madagascar (Wescott and Diggens, ), Australia (Fielding et al , ), Antarctica (Isbell, ; Cornamusini et al , ) and North Africa (Le Heron et al , ; Bussert, ; Le Heron, ), where spectacular, glacially related palaeoreliefs (fjords, ice stream corridors) have been discovered.…”

Exhumed subglacial landscape in Uruguay: Erosional landforms, depositional environments, and paleo-ice flow in the context of the late Paleozoic Gondwanan glaciation

“…Exhumed glacial landscapes and paleo-ice stream pathways provide valuable information on glacial spreading centers and ice sheet dimensions. Recently, an outstanding late Carboniferous exhumed glacial landscape was recognized in Chad using satellite imagery (Le Heron, 2017).…”

First description of subglacial megalineations from the late Paleozoic ice age in southern Africa

“…Many parts of Gondwana exhibit bedrock features including striations and glacial valleys formed during the LPIA, including Argentina [1], southern Australia [2], southern Brazil [3], Ethiopia, [4], Namibia [5, 6], South Africa [7, 8], and Uruguay [9]. Evidence for ice streams draining the LPIA ice sheets, however, is reported only rarely and mostly from the peripheries (Chad [10], Ethiopia [4]), but never before from southern Africa despite being at or close to the South Pole throughout the Carboniferous and early Permian [11].…”