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.
Highlights
We infer the presence of a late Paleozoic ice age (LPIA) paleo-ice stream in the Huab River valley based on the occurrence, shape, and size of elongate bedforms exposed on a Carboniferous-Permian glacial erosional surface
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]
Ice streams are channels filled with ice flowing faster than the surrounding ice sheet, and are the principle arteries for ice flow from the sheet’s center to the margin [12], often forming flow networks 103 km in length and with catchments of 106 km2 [13]
Summary
We infer the presence of a late Paleozoic ice age (LPIA) paleo-ice stream in the Huab River valley based on the occurrence, shape, and size of elongate bedforms exposed on a Carboniferous-Permian glacial erosional surface. Megalineations form a size-shape continuum from meter-scale roche moutonees, through rock drumlins and megawhalebacks, to kilometer-scale MSGLs [16] Because they are bedrock features, they have a high preservation potential through repeated glacial advances and retreats [17], and are reliable indicators of paleo-ice flow directions. The bedforms in Saskatchewan, Baffin Island, and Scotland are generally longer (Fig 3C) and more elongate (Fig 3D) than at Twyfelfontein; the Namibian examples are partburied in modern sand, and their dimensions are minima Those in the Canadian examples are classified as megawhalebacks, whereas those at Ullapool are more elongate ‘megaridges’. This range of morphologies is typical of megalineations where there is a continuum between different bedforms (e.g., [16]), and especially between drumlins and whalebacks (10)
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