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

Abstract

We identify late Paleozoic ice age (LPIA) subglacial megalineations from field and geospatial imagery of the Twyfelfontein area of northern Namibia, and present the results of a geomorphometric analysis of those data. Asymmetric 0.1–1.5 km-long megawhalebacks indicate a paleo-ice flow to the northwest. We infer that an ice stream draining the LPIA Kaokoveld ice sheet existed within the proto-Huab River valley and that was comparable to ice streams in modern Antarctica. Recognition of a paleo-ice stream in northern Namibia supports interpretations of glaciogenic sedimentary successions (Itararé Group) in southern Brazil that suggest the presence of major, terrestrial glacial outlet systems in southern Africa during the LPIA.

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, 1994(von Brunn, , 1996 see also Guillocheau et al, 2018). Such an exhumed LPIA glacial landscape echoes those of the same age found in Namibia (Andrews et al, 2019), Chad (Le and in South America (Assine et al, 2018).…”

“…Asymmetrical bedforms are interpreted as Roches moutonnées and confirm that ice was flowing towards the SSE. Oriented parallel to the inferred deepening axis of the basin, and eroded into the central palaeobathymetric domain interpreted as a coastal‐platform domain (see above and Figure A), the U‐shaped trough might be regarded as a small‐scale cross‐shelf trough carved by subglacial processes probably linked to flowing ice, as also evidenced by streamlined forms and polished pavements (Krabbendam et al , ; Newton et al , ; see also Andrews et al , ).…”

“…In southern Africa, research on the Dwyka Group has predominantly focused on the well‐exposed western part of the South African Main Karoo Basin and the Namibian Kalahari‐Karoo Basin, where the LPIA is now relatively well‐constrained both in time and space (Visser, , , , , ; Grill, ; Bangert et al , , ; Stollhofen et al , ,; Himmler et al , ; Andrews et al , ). Here, four phases of ice growth and decay have been proposed on the basis of interstratifed glaciogenic (diamictites) and non‐glaciogenic (Ice Rafted Debris (IRD)‐free mudstones) deposits.…”

Bird’s-eye view of an Ediacaran subglacial landscape

“…In the past 15 yr, major advances in understanding the flow behavior of deep-time ice masses have been made by combining tradi-tional geologic fieldwork with the analysis of satellite image data (Moreau et al, 2005;Assine et al, 2018;Andrews et al, 2019). While UAV technology is widely applied at modern (Tonkin et al, 2016) ice margins, or in the study of Quaternary subglacial bed-form geomorphology (Ely et al, 2018;Chandler et al, 2018), it has never been used in the description of pre-Pleistocene glacial landforms, yet it provides a vital bridge in scale between outcrop and satellite image interpretation.…”

A conceptual model for glaciogenic reservoirs: From landsystems to reservoir architecture

“…Recent studies indicate that ice streaming in ancient deposits is more common than previously thought and can be recognized from glaciogenic successions of Ordovician and Late Palaeozoic age (Andrews et al, 2019;Assine et al, 2018;Elhebiry et al, 2019;. Identification of such features in the subsurface can aid understanding sediment transport mechanisms, mode of deposition, resulting reservoir distribution and fluid migration pathways.…”