A world-class example of a Late Palaeozoic glaciated landscape in Chad

• Published in: Sedimentary Geology
• Main Authors: Kettler, Christoph, Wohlschlägl, Ricarda, Russell, Catherine, Scharfenberg, Lars, Ghienne, Jean-François, Le Heron, Daniel Paul
• Other Authors: Institut de physique du globe de Strasbourg (IPGS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), Ecole et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: LPIA; Glacial landforms; Carboniferous; Gondwana; Geomorphology; Earth Science; [SDU]Sciences of the Universe [physics]; Ice Sheet
• Online Access: https://insu.hal.science/insu-04198296; https://insu.hal.science/insu-04198296/document; https://insu.hal.science/insu-04198296/file/1-s2.0-S0037073823001422-main.pdf; https://doi.org/10.1016/j.sedgeo.2023.106470

International audience Continental glacial deposits are rarely preserved in nature. Recent studies of the LPIA reveal the presence of periglacial deposits in Northern Chad covering an area of 20,000 km 2 . Using satellite maps, this project managed to examine the entirety of the Ennedi Plateau. 3D reconstructions of this mountain range reveal complex glacial morphological features. This paper presents large-scale subglacial features interbedded with proglacial fluvial features and discussed the variables at play during the progressive, repetitive, and perhaps cyclical nature of the Carboniferous glaciation. Using remote sensing techniques, this paper shows that there are three major ice advance-retreat cycles that led to the deposition of mega-scale glacial lineations with a complex fluvial channel belt. Palaeo-geomorphological mapping of satellite images in northern Chad reveals that the Late Carboniferous Chadian ice sheet covered at least 20,000 km 2 , a much greater extent than previously thought (ca. 6000 km 2 ). Glacial lineations (GLs) are dominant and extensive on the plateau. They are arranged in widespread ice stream networks and developed at multiple stratigraphic levels. This broadly indicates palaeo-ice flow to the north. We report a newly discovered pristine channel belt, covering at least 300 km 2 of a plateau in the Ennedi Plateau. A swarm of N-S trending channels, up to 250 m wide, is recognised. These are of both braided and meandering characters and are organised into channel belts of up to 500 m width. The mapped palaeo-morphology shows complex crosscutting relationships. The channel belt is intercalated with zones of GLs; hence, ice activity preceded and succeeded fluvial activity. Preserved planform sinuous channel geometries show distinctive point bar deposits and scroll bar geometries therein, which testify to a terrestrial, subaerial environment, rather than to their evolution in the subglacial realm, e.g. as eskers. Therefore, we find that cross-cutting, amalgamated channel systems ...