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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 159901
Funding scheme Project funding (Div. I-III)
Research institution Institut des sciences de la Terre Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geology
Start/End 01.05.2015 - 30.09.2017
Approved amount 291'337.00
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All Disciplines (2)

Discipline
Geology
Other disciplines of Earth Sciences

Keywords (7)

Calcium cycle; Vertisols; Terrestrial carbonates; Calcium carbonate; Stable isotopes; Africa; Dating methods

Lay Summary (French)

Lead
Ce projet a deux objectifs majeurs: i) étudier les monticules carbonatés tropicaux dont l'origine serait liée à l’évolution des paléo-environnements de la Période Humide Africaine, ii) proposer un nouveau modèle de formation des carbonates en milieu tropical en s’intéressant aux sources de calcium et de carbone. Ces aspects sont associés aux cycles couplés du carbone et du calcium des sols tropicaux et à leur rôle dans la séquestration du carbone.
Lay summary

Le long de la ceinture sahélo-soudanienne, des formations énigmatiques, fortement enrichies en carbonate de calcium, sont observées sous des pédiments. L’érosion ayant cours aujourd’hui révèle des formes de monticules tronqués ou aplatis. L’une des caractéristiques la plus intrigante, et sans aucun doute la plus importante en termes de cycles biogéochimiques, consiste en une abondance extrême de nodules calcaires de formes très diverses, alors que le premier affleurement calcaire est à plus de 1000 km. Bien qu’observés dès les années 50 par des chercheurs français, ces formations carbonatées tropicales n’ont fait l’objet d’aucune étude approfondie. Leur origine reste donc inconnue, bien que leurs caractéristiques puissent être associées à celles observées en présence de plantes, de termites, ou de sols particuliers appelés Vertisols (sols contenant de fortes proportions d’argiles gonflantes). Les résultats préliminaires pointent vers la présence de paléo-vertisols (donc des sols fossiles) qui auraient été associés à une végétation tout à fait spécifique.

Les recherches qui vont être conduites proposent de viser plusieurs objectifs à différentes échelles : i) évaluer la répartition géographique du phénomène, ii) s’intéresser aux sources des matériaux, en particulier le carbone et le calcium, iii) de proposer un cadre chronologique absolu en utilisant les datations au carbone 14, les séries isotopiques Uranium-Thorium, et une technique récente, la luminescence par stimulation optique sur certains silicates. De plus, cette approche se complète de l’étude fondamentale du cycle du calcium et du carbone au moment de la génération des nodules, de façon à établir si ces formations ont agi ou non comme puits de carbone. Les résultats serviront indubitablement à résoudre certaines questions soulevées par les paléosols carbonatés qui se sont formés dans le passé dans des environnements dénués de tout apport de calcaire, et ce, en relation avec les anciennes pressions partielles de gaz carbonique atmosphérique.

 

Direct link to Lay Summary Last update: 02.04.2015

Responsible applicant and co-applicants

Employees

Publications

Publication
Origin of Calcium in pedogenic carbonate nodules from silicate watersheds in the Far North Region of Cameroon: Respective contribution of in situ weathering source and dust input.
Dietrich Fabienne, Diaz Nathalie, Deschamps Pierre, Ngounou Ngatcha Benjamin, Sebag David, Verrecchia Eric P. (2017), Origin of Calcium in pedogenic carbonate nodules from silicate watersheds in the Far North Region of Cameroon: Respective contribution of in situ weathering source and dust input., in Chemical Geology, 460, 54-69.
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 P (2016), Can mima-like mounds be Vertisol relics (Far North Region of Cameroon, Chad Basin)?, in Geomorphology, 261, 41-56.
Pedogenic carbonate nodules as soils time archives: Challenges and investigations related to OSL dating
Diaz Nathalie, King Georgina, Valla Pierre, Herman Frédéric, Verrecchia Eric (2016), Pedogenic carbonate nodules as soils time archives: Challenges and investigations related to OSL dating, in Quaternary Geochronology , 36, 120-133.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Goldschmidt Conference 2017 Poster U-Th isochron dating of pedogenic impure carbonate: a first attempt using density separations 13.08.2017 Paris, France Dietrich Fabienne;
5th Open Science Meeting, PAGES Poster Calcium transfer over the last 20 ka : from sources to trapping in carbonate nodules (silicate watershed of northern Cameroon) 09.05.2017 Zaragoza, Spain Dietrich Fabienne; Diaz Nathalie;
5th Open Science Meeting PAGES Poster Quaternary palaeo-environmental reconstruction of the southwestern Chad Basin: the invaluable legacy of soil relics. 09.05.2017 Zaragoza, Spain Dietrich Fabienne; Diaz Nathalie;
Swiss Geoscience Meeting 2016 Talk given at a conference Switzerland. Talk: Evolution of a Sudano-Sahelian paleoenvironment since late MIS-2 (Far N Cameroon, Chad Basin) 19.11.2016 Genève, Switzerland Verrecchia Eric; Dietrich Fabienne; Diaz Nathalie;
Swiss Geoscience Meeting 2016 Talk given at a conference Tracking the calcium : the meaning of calcitic pedogenic nodules in a silicate watershed (northern Cameroon) 19.11.2016 Genève, Switzerland Dietrich Fabienne; Diaz Nathalie; Verrecchia Eric;
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 Dietrich Fabienne; Diaz Nathalie; Verrecchia Eric;
The Environmental History of Africa Since the Last Ice Age: Climate, Humans, and Biogeochemistry Talk given at a conference Tracking the calcium : the meaning of calcitic pedogenic nodules in a silicate watershed (northern Cameroon) 14.09.2016 Lausanne, Switzerland Diaz Nathalie; Dietrich Fabienne; Verrecchia Eric;
Goldschmidt Conference 2016 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;
EGU 2016 Vienna Talk given at a conference A 20-ka reconstruction of a Sahelo-Sudanian paleoenvironment using multi-method dating on pedogenic carbonate 17.04.2016 Vienne, Austria Diaz Nathalie;
Swiss Soil Science Society Meeting Talk given at a conference What do pedogenic carbonate accumulations tell? 04.02.2016 Genève, Switzerland Diaz Nathalie; Dietrich Fabienne;
Swiss Geoscience Meeting 2015 Talk given at a conference Reconstruction 20 ka of history using multi-dating on pedogenic carbonate nodules 21.11.2015 Basel, Switzerland Dietrich Fabienne; Diaz Nathalie; Verrecchia Eric;
Goldschmidt Conference 2015 Poster Ca sources for pedogenic carbonate nodules in a silicate watershed (Far-North Cameroun) 16.08.2015 Prague, Czech Republic Dietrich Fabienne;
UK Luminescence and ESR meeting 2015 Talk given at a conference Luminescence and radiocarbon dating of pedogenic carbonate nodules: palaeo-climatic implications for the Lake Chad Basin. 08.07.2015 Glasgow, Great Britain and Northern Ireland Diaz Nathalie;


Self-organised

Title Date Place
The Environmental History of Africa Since the Last Ice Age: Climate, Humans, and Biogeochemistry 14.09.2016 Lausanne, Switzerland

Awards

Title Year
SANU Prize, Swiss Soil Science Society Meeting, 2016, 4-5.02.2016, Geneva, CH. What do pedogenic carbonate accumulations tell? Nathalie Diaz, Fabienne Dietrich, David Sebag, Pierre Deschamps, Benjamin Ngounou Ngatcha and Eric P. Verrecchia 2016
Student Oral Prize to Nathalie Diaz UK Luminescence and ESR meeting 2015, 08-10.07.15, Glasgow, UK. Talk: Luminescence and radiocarbon dating of pedogenic carbonate nodules: palaeo-climatic implications for the Lake Chad Basin. N. Diaz, G.E. King, P.G. Valla, F. Dietrich, D. Sebag, F. Herman, E.P. Verrecchia 2015

Associated projects

Number Title Start Funding scheme
172944 Assessing the coupled cycles of C and Ca in tropical environments: the significance of terrestrial carbonate deposits in limestone-free watersheds 01.10.2017 Project funding (Div. I-III)
147038 Calcium carbonate in terrestrial environments: the enigmatic tropical carbonate mounds 01.05.2013 Project funding (Div. I-III)
101564 Calcium carbonate cycle in soils and surficial sediments: a multidisciplinary approach to the role of fungi and bacteria 01.10.2003 Project funding (Div. I-III)

Abstract

All along the Sahelo-Sudanian belt, enigmatic formations enriched in carbonate are observed in pediments. The present-day erosion shows that these deposits have the shape of imperfect flattened, truncated mounds. One of their most intriguing characteristics, and the most important in terms of biogeochemical cycles, is their extreme abundance of carbonate nodules of various shapes, in a place where the closest carbonate outcrop is several thousands of kilometres away. Identified by French researchers a many years ago, these tropical carbonate formations (TCF) have not been studied in detail, and their origin is still unknown, although similar features have been observed associated with termites, plants, and Vertisols. The preliminary results obtained during the first phase of this project seem to show that these unexpected accumulations of calcium carbonate may originate from the development of paleo-Vertisols associated with a specific paleo-vegetation. Although the general pedogenic context is recognized, sources of the vast amount of needed calcium remain unidentified. In addition, mechanisms responsible for the nodule formation, as well as for the carbonate accumulation and preservation are still unknown. Consequently, this project aims to understand the way TCF could have formed, when, and in which paleoenvironmental conditions they evolved.The proposed research is conducted at various scales to tackle different objectives : (i) the geographical distribution of TCF will give an evaluation of the extent of such carbonate deposits; (ii) the characterization of carbonate nodules and parent matrix in terms of geochemistry (trace - REE -, minor, and major elements, C, O, Ca, and Sr stable isotopes) and a precise petrographical study (including micromorphology and microprobe analyses) will provide clues regarding the original processes involved in their formation; (iii) an assessment of the Ca and Sr (associated with Nd) isotope contents in the features constituting the TCF, as well as in the regional potential sources of material, will bring information on the sources of matter providing Ca to the system; (iv) finally, a chronological setting will be proposed using 14C, U-Th series and recent methods of OSL (Optically Stimulated Luminescence on feldspar) dating of the sediments. All of these topics will be used to propose a potential genetic model of such an unexpected accumulation of calcium carbonate in carbonate-free and acidic landscape. In addition, it is instrumental to assess the past Ca cycle to clearly state if such TCF constituted or not a carbon sink. The aims are the following: 1) precisely characterize tropical carbonate formations; 2) identification of the potential past calcium sources; 3) dating of CaCO3 concretions and host material; 4) Reconstruction of the paleo-dynamics and evolution of TCF.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 will contribute to the explanation of carbonate deposits found in unexpected settings and can possibly be applied to the Earth's deep 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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