A Caltech Library Service

Benthic redox conditions and nutrient dynamics in the ca. 2.1 Ga Franceville sub-basin

Aubineau, Jérémie and El Albani, Abderrazak and Chi Fru, Ernest and Kipp, Michael A. and Ngwal'ghoubou Ikouanga, Julie and Bekker, Andrey (2021) Benthic redox conditions and nutrient dynamics in the ca. 2.1 Ga Franceville sub-basin. Precambrian Research, 360 . Art. No. 106234. ISSN 0301-9268. doi:10.1016/j.precamres.2021.106234.

[img] MS Word (Supplementary data) - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


The co-existence of motile macroorganisms and mat-building cyanobacteria in the Paleoproterozoic FB2 Member of the Franceville sub-basin, Gabon, points to the possible emergence of multi-trophic-level biological interaction by 2.1 billion years (Ga) ago. However, it is uncertain how these shallow-marine communities acquired and cycled nitrogen, a key, biolimiting nutrient required to sustain life at all trophic levels. Here, we use carbon and nitrogen isotope data from ancient microbial mats and host sediments, in combination with bottom-water redox proxies, to constrain biogeochemical processes operating in these settings. In this shallow-marine upwelling zone, iron speciation data and redox-sensitive metal concentrations point to oxygen-deficient bottom waters, which were episodically renewed with upwelling deep anoxic waters rich in nutrients and manganese. Organic carbon and nitrogen isotopes show little difference between the mat-related structures (MRS) and host sediments, suggesting either that similar metabolisms operated in benthic and planktonic microbial communities or that benthic carbon fixation contributed organic matter to the host sediments. The isotopic fractionation between organic and inorganic carbon is as large as 44‰, implying the involvement of multiple levels of heterotrophic carbon processing, linked to phototrophy, secondary productivity, and methanotrophy. Whole-rock nitrogen isotope values in the range of −3.5 to + 1.9‰ are consistent with microbial community nitrogen fixation in a nitrate-limited ecosystem. These data suggest that nitrogen fixation, common in photosynthetic microbial mats in modern environments, operated in benthic settings in the coastal area of the mid-Paleoproterozoic Franceville sub-basin. The upwelling of deep, anoxic waters invoked for deposition of the upper part of the underlying FB1 Member suggests that basin-scale redox structure modulated nitrate availability in this otherwise oxic, shallow-marine basin shelf environment.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kipp, Michael A.0000-0003-1844-3670
Additional Information:© 2021 Elsevier B.V. Received 6 November 2020, Revised 2 March 2021, Accepted 15 April 2021, Available online 4 May 2021. We acknowledge the support of the Gabonese Government, CENAREST, General Direction of Mines and Geology, and Agence Nationale des Parcs Nationaux of Gabon. This work was supported by La Région Nouvelle Aquitaine, the University of Poitiers, Théodore Monod Doctoral School, and the French Embassy in Libreville, Gabon. We are grateful to Prof. P. Mouguiama Daouda, J.C. Balloche, L. White, and R. Oslisly for their support during field trips. For assistance, we acknowledge C. Laforest, C. Lebailly, Y. Lin, L. Magad-Weiss, A. Meunier, A. Oldroyd, P. Recourt, C. Reedman, and X. Tang. J.A. is particularly thankful to T. Lyons for scientific discussions. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
Gabonese GovernmentUNSPECIFIED
Agence Nationale des Parcs Nationaux of GabonUNSPECIFIED
La Région Nouvelle AquitaineUNSPECIFIED
University of PoitiersUNSPECIFIED
Théodore Monod Doctoral SchoolUNSPECIFIED
Subject Keywords:Mat-related structures; Paleoproterozoic; Nitrogen isotopes; Paleoredox; Basinal structure; Francevillian biota
Record Number:CaltechAUTHORS:20210512-093451126
Persistent URL:
Official Citation:Jérémie Aubineau, Abderrazak El Albani, Ernest Chi Fru, Michael A. Kipp, Julie Ngwal'ghoubou Ikouanga, Andrey Bekker, Benthic redox conditions and nutrient dynamics in the ca. 2.1 Ga Franceville sub-basin, Precambrian Research, Volume 360, 2021, 106234, ISSN 0301-9268, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109091
Deposited By: Tony Diaz
Deposited On:12 May 2021 16:44
Last Modified:12 May 2021 16:44

Repository Staff Only: item control page