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Calcium carbonate in terrestrial environments: the enigmatic tropical carbonate mounds

English title Calcium carbonate in terrestrial environments: the enigmatic tropical carbonate mounds
Applicant Verrecchia Eric
Number 147038
Funding scheme Project funding
Research institution Institut de géologie et de paléontologie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geology
Start/End 01.05.2013 - 30.04.2015
Approved amount 238'590.00
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All Disciplines (2)

Discipline
Geology
Other disciplines of Earth Sciences

Keywords (7)

Africa; Calcium carbonate; Calcium cycle; Calcium oxalate; Bio-precipitation; Carbon pools; Terrestrial carbonates

Lay Summary (French)

Lead
L'objectif de ce projet est double: i) étudier les monticules carbonatés tropicaux dont l'origine reste incertaine (sont-ils liés à l'action de termites et/ou de plantes?), et ii) de proposer un nouveau modèle du temps de résidence des carbonates en milieu tropical. Ces deux aspects sont associés aux cycles couplés à temps court et millénaire du carbone et du calcium des sols tropicaux et à leur rôle dans la séquestration du carbone.
Lay summary

Le long de la ceinture sahelo-soudanienne, des cercles et des monticules énigmatiques sont observés dans les formations sédimentaires des pédiments. L’érosion permet d’observer leur structure qui peut être décrite comme un cône tronqué à large base. Ces monticules sont enrichis en nodules de carbonate de calcium, à forme souvent tubulaire, ce qui est pour le moins surprenant puisque le premier affleurement de calcaire est à plusieurs centaines de kilomètres. Quelle pourrait donc bien être l’origine de ces formes géomorphologiques si particulières, sont-elles liées à des plantes et/ou des termites ? Où sont les sources de carbone et de calcium, alors que ces formes s’observent dans des milieux où dominent essentiellement le fer et la silice, issus des granites et des grès précambriens ? L’objectif principal de  ce projet est donc de proposer un modèle de formation de ces objets en relation avec les cycles couplés du carbone et du calcium, dans un contexte d’interactions complexes entre le vivant et le minéral. Cette recherche devrait permettre de souligner toute l’importance de ces interactions dans des milieux appauvris en carbone et en calcium, comme les milieux tropicaux semi-arides à sub-humides. Elle souscrira aussi à mieux circonscrire les temps de résidence des carbonates en domaine tropical et à leur quantification en tant que puits de carbone. Enfin, les conclusions de ces travaux pourraient être utilisées à des fins de reconstruction des contextes paléo-environnementaux qui ont présidé à la mise en place de paléosols carbonatés dans les paysages non-calcaires et à leur relation avec la pCO2 et la vie passée.

Direct link to Lay Summary Last update: 25.03.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Can mima-like mounds be Vertisol relics (Far North Region of Cameroon, Chad Basin)?
Diaz Nathalie, Dietrich Fabienne, Cailleau Guillaume, Sebag David, Ngounou Ngatcha Benjamin, Verrecchia Eric (2016), Can mima-like mounds be Vertisol relics (Far North Region of Cameroon, Chad Basin)?, in Geomorphology, 261, 41-56.
Pedogenic carbonate nodules as soil time archives: Challenges and investigations related to OSL dating
Diaz Nathalie, King Georgina, Valla Pierre, Herman Frederic, Verrecchia Eric (2016), Pedogenic carbonate nodules as soil time archives: Challenges and investigations related to OSL dating, in Quaternary Geochronology, 36, 120-233.

Collaboration

Group / person Country
Types of collaboration
Institut de Recherche pour le Développement (IRD) France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Université de Ngaoudéré Cameroon (Africa)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Université de Montpellier - IRD France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
The Environmental History of Africa Since the Last Ice Age: Climate, Humans, and Biogeochemistry Talk given at a conference Tracking the calcium over the last 20 ky: the meaning of calcitic pedogenic nodules in a silicate watershed (northern Cameroon) 14.09.2016 Lausanne, Switzerland Verrecchia Eric; Dietrich Fabienne; Diaz Nathalie;
The Environmental History of Africa Since the Last Ice Age : Climate, Humans, and Biogeochemistry Talk given at a conference Evolution of a Sudano-Sahelian paleoenvironment since late MIS-2 (Far N Cameroon, Chad Basin) 14.09.2016 Lausanne, Switzerland Diaz Nathalie; Verrecchia Eric; Dietrich Fabienne;
Goldschmidt Conference Talk given at a conference Origin of pedogenic carbonate nodules in silicate settings by using 87Sr/86Sr and ε(Nd) 26.06.2016 Yokohama, Japan Dietrich Fabienne; Verrecchia Eric; Diaz Nathalie;
European Geosciences Union General Assembly 2016 Talk given at a conference A 20-ka reconstruction of a Sahelo-Sudanian paleoenvironment using multi-method dating on pedogenic carbonate 17.04.2016 Vienna, Austria Diaz Nathalie; Dietrich Fabienne; Verrecchia Eric;
Congrès annuel de la Société Suisse de Pédologie Talk given at a conference What do pedogenic carbonate accumulations tell? 05.02.2016 Geneva, Switzerland Diaz Nathalie; Dietrich Fabienne; Verrecchia Eric;
Swiss Geoscience Meeting Talk given at a conference Reconstruction 20 ka of history using multi-dating on pedogenic carbonate nodules 21.11.2015 Basel, Switzerland Dietrich Fabienne; Verrecchia Eric; Diaz Nathalie;
Goldschmidt Conference Poster Ca sources for pedogenic carbonate nodules in a silicate watershed (Far-North Cameroun) 16.08.2015 Vienna, Austria Verrecchia Eric; Diaz Nathalie; Dietrich Fabienne;
UK Luminescence and ESR meeting Talk given at a conference Luminescence and radiocarbon dating of pedogenic carbonate nodules: palaeo-climatic implications for the Lake Chad Basin 07.07.2015 Glasgow, Great Britain and Northern Ireland Dietrich Fabienne; Verrecchia Eric; Diaz Nathalie;
Dan Yaalon International Symposium Talk given at a conference Are the Mima-like mounds from Far-North Cameroon Palaeo-Vertisols inherited from Late Pleistocene-Holocene climatic variations? 08.04.2015 Vienna, Austria Verrecchia Eric; Diaz Nathalie; Dietrich Fabienne;
International Congress of Sedimentology Poster Geomorphological and geochemical evidence of palaeo-Vertisols in relationship with Quaternary climatic changes (Far North Cameroon) 18.08.2014 Geneva, Switzerland Diaz Nathalie; Dietrich Fabienne; Verrecchia Eric;
Swiss Geoscience Meeting Poster Origin of unexpected terrestrial carbonate formations (TCF) in northern Cameroon: hypotheses and challenges 15.11.2013 Lausanne, Switzerland Diaz Nathalie; Dietrich Fabienne; Verrecchia Eric;


Awards

Title Year
Outstanding reviewer for Catena - Elsevier 2016
Prix SANU - Société Suisse de Pédologie 2016
Student Oral Prize - UK Luminescence and ESR meeting 2015, Glasgow, UK 2015

Associated projects

Number Title Start Funding scheme
118130 The role of plants, bacteria, and fungi in carbon transfer from atmospheric CO2 to calcium carbonate through the oxalate-carbonate pathway 01.11.2007 Interdisciplinary projects
159901 Calcium carbonate in terrestrial environments: the enigmatic tropical carbonate mounds 01.05.2015 Project funding
101564 Calcium carbonate cycle in soils and surficial sediments: a multidisciplinary approach to the role of fungi and bacteria 01.10.2003 Project funding

Abstract

All along the Sahelo-Soudanian belt, enigmatic circles and mounds are observed in pediment formations. The present-day erosion shows that superficial circles have the shape of flattened and truncated cones (the mounds), with a large base. One of the most intriguing characteristics of these mounds, and the most important in terms of biogeochemical cycles, is their extreme abundance in carbonate nodules of various shapes, in a place where the closest carbonate outcrop is several thousands of kilometres away. Although identified by French researchers a many years ago, these tropical carbonate mounds (TCM) have not been studied in detail, and their origin is still unknown, although similar features have been observed associated with termites and plants. So what could be the origin of such strange geomorphological forms? Where are the carbon sources for carbonates? Where are the Ca sources, as these mounds are observed in environments dominated by iron and silica and where the surrounding bedrocks are mainly composed of granite and Precambrian sandstones? This project aims to understand the way TCM could have formed as they must obviously be the result of complex interactions between life and minerals. Characterized by an unexpected presence of organic matter and important accumulations of carbonate nodules, they can be explained neither by simple sedimentological processes (e.g. palustrine limestones) nor by purely physicochemical and abiotic pathways. The two most pertinent hypotheses related to these particular accumulations are related to life, i.e. termites and plants.The proposed research is conducted at various scales: (i) geographical distribution of TCM as well as evaluation of the mass of carbonates in them, (ii) characterization of carbonate nodules and parent matrix in terms of geochemistry (minor and major elements, C, Ca, and Sr isotopes) and petrology (including SIMS analyses), (iii) characterization of residual organic matter. All of these three topics will be used to propose a potential genetic model and compared to termite and oxalate-carbonate pathway ecosystems, which are active today. In addition, it is instrumental to circumscribe the past and present-day Ca cycle, its impact on both the past and present-day landscapes (e.g. is it contributing to a carbon sink?). Finally, dating TCM is also one the objectives of the proposal as well as the understanding of the way they will evolve in the future. The research plan is conceived as a strategy to link and address the following challenges: 1) Characterization of tropical carbonate mounds AND 2) Evolution of present-day $Ca$ cycle, 3) Genetic model of TCM formation AND 4) Reconstruction of Ca paleo-cycle, 5) Dating, evaluation of CaCO3 mass AND 6) Calculations of potential reservoirs and residence times.This research will improve our knowledge on the crucial role of life-mineral interactions in the carbon-calcium coupled cycle at the surface of continents, particularly in tropical carbonate-free environments. The conclusions drawn from this research can possibly be applied to the Earth's past in order to explain the presence of some surprising carbonate paleosols in carbonate-free landscapes and their potential relationships with atmospheric pCO2 and life.
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