Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation

• Published in: Geology
• Main Authors: Dietrich, Pierre, Griffis, Neil, P, Le Heron, Daniel, P, Montañez, Isabel, P, Kettler, Christoph, Robin, Cécile, Guillocheau, François
• Other Authors: Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), University of California Davis (UC Davis), University of California (UC), Berkeley Geochronology Center (BGC), Universität Wien, South Africa–Austria joint project of the National Research Foundation (NRF) of South Africa, Österreichischer Austauschdienst (OEAD project ZA 08/2019), U.S. National Science Foundation (grant EAR-1729882)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; Ice Sheet
• Online Access: https://insu.hal.science/insu-03331205; https://insu.hal.science/insu-03331205/document; https://insu.hal.science/insu-03331205/file/g49067.pdf; https://doi.org/10.1130/G49067.1

International audience 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.