Paleofjords that drained glaciers 300 million years ago still preserved in the desertic landscape of NW Namibia

Boulder, Colo., USA: The Kaokoland region of northwest Namibia is a desertic land: Vast barren plateaus are deeply dissected by several hundred-meter-deep U-shaped valleys in which ephemeral streams flow. The hard floors and walls of these valleys surprisingly display abundant glacial erosion features characteristic of flowing glaciers such as scratches, striae, grooves, and smooth, elongated hills called whalebacks.

Such features are usually found in Canada or Scandinavia that were recently (20,000 years) covered by huge ice sheets. Discovering such marks of ice flow in Namibia, which did not undergo any recent glaciation, is therefore thrilling and challenging.

These glacial erosion features are sealed in place by remnants of less-resistant sedimentary rocks—conglomerate, sandstones, and mudstones encompassing large, far-traveler lonestones—which indicate that these valleys were inundated by the sea, on which icebergs drifted, after the flowing glaciers retreated.

The dating of these sedimentary rocks indicates an age of 300 million years, corresponding to an icehouse period. Africa, and therefore Namibia, was at that time part of the Gondwana Supercontinent located close to the south pole. Thus, as foreseen as early as the 1950s by the German geologist Henno Martin, famous for having shared his experience of his two years spent in the Namibian desert (Sheltering Desert), a French-American-Austrian joint team demonstrated yesterday in the journal Geology that 300-million-year-old glaciers drained through—and likely carved—these valleys, which, after glaciers vanished, were inundated by the sea and therefore turned into fjords.

These fjords were subsequently filled with sediments for 130 million years before being exhumed in more recent times. Owing to preferential erosion of the less-resistant sedimentary rocks filling up the valleys, these ancestral fjord morphologies are now shaping the desertic landscape of NW Namibia.

Although modern fjords are abundant on continental shelves at high latitude, these Namibian fjords are the unique example of preserved ancient fjord morphologies and therefore serve for tackling climate changes associated to the penultimate icehouse our planet experienced.

Fjords network in Namibia: A snapshot into the dynamics of the late Paleozoic Glaciation
Pierre Dietrich and colleagues
Contact:, Université de Rennes 1–CNRS, Géosciences Rennes UMR 6118, Rennes, France

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For Immediate Release
31 August 2021
GSA Release No. 21-50

Kea Giles

Dietrich U-shaped Valley
Dietrich sedimentary rocks
Fjord morphologies and associated glacial erosion features attesting that glaciers flowed through the desertic landscape of NW Namibia 300 million years ago. Top: this U-shaped valley is carved into hard bedrock and represents an intact fjord morphology, carved 300 million years ago, and subsequently filled up with sediment and later exhumated. At the foreground, one can observe remnants of sedimentary rocks (mudstones and sandstones). Bottom: Glacial scratches and striations carved by direct glacial action onto the vertical walls of the U-shaped valleys seen above. At the background, reddish sedimentary rocks lie upon these vertical straited walls. Credit: Pierre Dietrich. Click on the images for larger versions.