Geochemical-mineralogical constraints on the provenance of sediment supplied from South African river catchments draining into the Southwestern Indian Ocean

Pryor, E. J., Hall, I. R. ORCID: https://orcid.org/0000-0001-6960-1419, Simon, M. H., Andersen, M. ORCID: https://orcid.org/0000-0002-3130-9794, Babin, D., Starr, A., Lipp, A. and van der Lubbe, H. J. L. 2025. Geochemical-mineralogical constraints on the provenance of sediment supplied from South African river catchments draining into the Southwestern Indian Ocean. Geochemistry, Geophysics, Geosystems 26 (4) , e2024GC011869. 10.1029/2024GC011869

PDF - Published Version Available under License Creative Commons Attribution. Download (4MB)

Abstract

This study utilizes the radiogenic isotopes of neodymium (Nd) and strontium (Sr) measured in river mud —which serves as a proxy for the suspended load—to examine how source-rock lithology and weathering intensity impact the composition of material delivered to marine sediments along the Southeast African continental margin. Sediments were sampled from 22 river catchments between Durban and Cape Town in South Africa. Two distinct endmembers (i.e., geographical source areas) characterizing the regional river systems were identified. According to endmember modeling, rivers of the Eastern Cape drain soils weathered of the Karoo Supergroup and Drakensberg basalts (87Sr/86Sr of 0.74049 and εNd of −8.53), whereas rivers of the Southern Cape drain the Cape Supergroup, exhibiting more radiogenic 87Sr/86Sr ratios (0.74596) and unradiogenic εNd values (−10.09). River sediments from the Karoo Supergroup are finer-grained compared to those from the Cape Supergroup. We analyzed clay mineralogy and two grain size fractions (<2 μm; 2–32 μm) from co-registered samples, and the results suggest that the spatial variability in the 87Sr/86Sr values is due to the lower degree of chemical weathering of silicate rocks and increased illite abundances toward the south, which a simple mixing model can explain. Kaolinite abundance decreased from Northeast to Southwest within South African coastal river catchments. In contrast, illite abundances increased due to diminished chemical weathering in the southern regions driven by the weaker rainfall regime. As demonstrated in this study, combining geochemical tools provides a reliable foundation for provenance studies of offshore marine sediment studies.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Wiley
ISSN:	1525-2027
Funders:	NERC
Date of First Compliant Deposit:	25 April 2025
Date of Acceptance:	8 April 2025
Last Modified:	19 May 2025 11:23
URI:	https://orca.cardiff.ac.uk/id/eprint/177910

Actions (repository staff only)

Edit Item