1GR - Géosciences Rennes (Bâtiment 15 - Université de Rennes 1 - Campus de Beaulieu -263 Av du général Leclerc- CS 74205 - 35042 Rennes Cedex - France - France)
Abstract : Fjords are glacially carved estuaries that profoundly influence ice-sheet stability by draining and ablating ice. Although abundant on modern high-latitude continental shelves, fjord-network morphologies have never been identified in Earth’s pre-Cenozoic glacial epochs, hindering our ability to constrain ancient ice-sheet dynamics. We show that U-shaped valleys in northwestern Namibia cut during the late Paleozoic ice age (LPIA, ca. 300 Ma), Earth’s penultimate icehouse, represent intact fjord-network morphologies. This preserved glacial morphology and its sedimentary fill permit a reconstruction of paleo-ice thicknesses, glacial dynamics, and resulting glacio-isostatic adjustment. Glaciation in this region was initially characterized by an acme phase, which saw an extensive ice sheet (1.7 km thick) covering the region, followed by a waning phase characterized by 100-m-thick, topographically constrained outlet glaciers that shrank, leading to glacial demise. Our findings demonstrate that both a large ice sheet and highland glaciers existed over northwestern Namibia at different times during the LPIA. The fjords likely played a pivotal role in glacier dynamics and climate regulation, serving as hotspots for organic carbon sequestration. Aside from the present-day arid climate, northwestern Namibia exhibits a geomorphology virtually unchanged since the LPIA, permitting unique insight into this icehouse.
https://hal-insu.archives-ouvertes.fr/insu-03331205 Contributor : Isabelle DubigeonConnect in order to contact the contributor Submitted on : Wednesday, September 1, 2021 - 3:16:06 PM Last modification on : Thursday, June 2, 2022 - 2:48:17 PM Long-term archiving on: : Thursday, December 2, 2021 - 7:19:38 PM
Pierre Dietrich, Neil P Griffis, Daniel P Le Heron, Isabel P Montañez, Christoph Kettler, et al.. Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation. Geology, Geological Society of America, 2021, 49 (12), pp.1521-1526. ⟨10.1130/G49067.1⟩. ⟨insu-03331205⟩