266-12 Reconstructing a Cryogenian Shelf-to-Slope Transect: Facies and Isotopic Evidence from the Western Margin of the Congo Craton, NW Namibia

Session: The Neoproterozoic Earth and Life Co-evolution (Posters)

Poster Booth No.: 118

Presenting Author:

Ellery Renger

Authors:

Renger, Ellery¹, Koran, Isabel², Macdonald, Francis³, Tasistro-Hart, Adrian⁴, Rose, Catherine⁵, Prave, Tony⁶, Uahengo, Collen-Issia⁷, Geingos, Ama⁸

(1) Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA, USA, (2) Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA, USA, (3) Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA, USA, (4) Earth and Planetary Science, University of California, Berkeley, Berkeley, CA, USA, (5) School of Earth and Environmental Sciences, University of St Andrews, St Andrews, United Kingdom, (6) School of Earth and Environmental Sciences, University of St Andrews, St Andrews, United Kingdom, (7) Geosciences, University of Namibia, Keetmanshoop, Namibia, (8) Geosciences, University of Namibia, Keetmanshoop, Namibia,

Abstract:

The Otavi Group in northern Namibia hosts Cryogenian glacial deposits within a carbonate-dominated succession. Although a shelf-to-slope transition has been documented on the southern margin of the Congo craton, the existence of a Cryogenian western margin has not been previously recognized. Prior studies proposed that the apparent lack of a western shelf-to-slope transition was due to Cryogenian transform faulting or Ediacaran structural detachments. Here we present new mapping and measured stratigraphic sections of the Cryogenian Abenab Subgroup in northwest Namibia. We document a gradational transition from the classic platform facies assemblage to deeper water slope deposits, which primarily consist of mixed siliciclastic and carbonate turbidites. This facies change is documented across multiple south-to-north and east-to-west transects that are consistent with a Cryogenian embayment, the Ombazu Trough, on the western margin of the ancient Congo craton. We informally refer to these deeper-water facies as the Ondole sequence to distinguish them from the platform facies of the Abenab subgroup. Correlation between the Ondole sequence and the platform facies is established through a combination of mapping, sequence stratigraphy and chemostratigraphy. These slope deposits offer valuable insight into deeper-water Cryogenian deposits relative to the shallow-marine and stromatolitic reef settings recorded by the Otavi carbonate platform. By expanding the stratigraphic and geochemical framework, we can explore facies dependence and depth gradients through some of the largest carbon isotope excursions in the geological record. Additionally, we find no evidence of either Cryogenian transform faults or Ediacaran detachments along the western margin. The outcrop data presented here will be augmented by an upcoming project under the International Continental Scientific Drilling Program.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8546

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.