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Assessing the coupled cycles of C and Ca in tropical environments: the significance of terrestrial carbonate deposits in limestone-free watersheds

English title Assessing the coupled cycles of C and Ca in tropical environments: the significance of terrestrial carbonate deposits in limestone-free watersheds
Applicant Verrecchia Eric
Number 172944
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 01.10.2017 - 31.10.2021
Approved amount 281'304.00
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All Disciplines (2)

Discipline
Geology
Other disciplines of Earth Sciences

Keywords (8)

Calcium cycle; Calcium carbonate; Calcium oxalate; Dating methods; Stable isotopes; Terrestrial carbonates; Africa; Quaternary

Lay Summary (French)

Lead
Ce projet vise à proposer un nouveau modèle génétique expliquant la présence inattendue de carbonate de calcium dans des paysages endorheiques acides et exempts de carbonate durant le Quaternaire tardif.Ce travail améliorera nos connaissances sur les relations entre variabilité climatique à l'échelle régionale et forçage climatique en Afrique australe.Ses conclusions contribueront à expliquer la présence paléosols carbonatés dans des paysages exempts de carbonate au cours de l’histoire de la Terre et leurs relations potentielles avec la pCO2 atmosphérique et la vie.
Lay summary
Dans le désert du Kalahari, au nord du Botswana, des formations quaternaires énigmatiques sont observées dans le paysage. Ces dépôts se situent dans la zone géographique des grands (paléo-)fleuves ayant leur source dans la zone équatoriale. L'une des caractéristiques les plus intrigantes de ces dépôts est leur grande abondance de lits de carbonate continentaux, dans un endroit où l'affleurement calcaire le plus proche se trouve à plusieurs centaines voire milliers de kilomètres. En effet, au Botswana, de vastes zones sont recouvertes de sables du Kalahari, mais à certains endroits, des couches épaisses de carbonate s’observent de façon inattendue dans un environnement à prédominance de quartz. Ces formations semblent être des dépôts lacustres peu profonds ou palustres, probablement liés à la dynamique des (paleo-)rivières Zambezi-Chobe et/ou Linyanti durant le Quaternaire tardif, fournissant ainsi des informations cruciales sur l'évolution du paysage au cours des dernières millénaires.
La première tâche (i) vise à étudier les différents types de dépôts dans l'Enclave de Chobe, y compris les diatomites, les sables fluviaux et éoliens, sur la base de méthodes modernes et conventionnelles utilisées en sédimentologie / biogéochimie. (ii) L'objectif suivant concerne les sources de Ca: comment le Ca s'est-il accumulé en si grande quantité pour pouvoir contribuer à la précipitation des phases de carbonate de Ca presque pures? (iii) La troisième tâche, en conséquence, évalue les origines/conditions de cette succession inattendue de phases riches en silicate et en carbonate: serait-elle climatique, tectonique, tectono-climatique, lacustre, palustre, éolienne? (iv) Enfin, la datation des différents dépôts dans l'Enclave de la Chobe mènera à proposer une séquence chronologique locale et permettra de comparer les résultats au cadre chronologique de l'Afrique australe.
Direct link to Lay Summary Last update: 31.03.2017

Responsible applicant and co-applicants

Employees

Project partner

Publications

Publication
Soil diversity and major soil processes in the Kalahari basin, Botswana
Romanens Rémy, Pellacani Federico, Mainga Ali, Fynn Richard, Vittoz Pascal, Verrecchia Eric P. (2019), Soil diversity and major soil processes in the Kalahari basin, Botswana, in Geoderma Regional, 19, e00236-e00236.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Swiss Geoscience Meeting Poster Origin of calcium in Ca-carbonate deposits from a sandy siliceous basin (Chobe Enclave, North Botswana): first results. 23.11.2019 Fribourg, Switzerland Verrecchia Eric; Rigoussen Dimitri;
Swiss Geoscience Meeting Poster Occurrence and significance of sepiolite deposits in the Chobe enclave (Northern Kalahari Basin, Botswana) 30.11.2018 Bern, Switzerland Verrecchia Eric; Rigoussen Dimitri;


Associated projects

Number Title Start Funding scheme
159901 Calcium carbonate in terrestrial environments: the enigmatic tropical carbonate mounds 01.05.2015 Project funding (Div. I-III)
137994 The oxalate-carbonate pathway: measuring biological interactions and dynamics in a natural C sink ecosystem 01.01.2012 Interdisciplinary projects

Abstract

In the northern Kalahari desert in Botswana, enigmatic Quaternary formations enriched in carbonate are observed in the landscape. These deposits are in the geographical area of large (paleo-) rivers having their source in the Equatorial zone. In the past, the watershed was related to an inland lacustrine basin, the Makgadikgadi Lake. One of the most intriguing characteristics of these deposits is their large abundance of carbonate nodules and/or beds, in a place where the closest limestone outcrop is several hundreds to thousands of km away. Indeed, in Botswana, large areas are covered with Kalahari sands, but in some places, thick carbonate layers and paleosols unexpectedly outcrop in this predominantly quartz environment. These formations, incorrectly identified as "calcrete" in the past, seem to be palustrine/shallow lacustrine deposits, probably related to the dynamics of the (paleo-)Zambezi-Chobe and/or Linyanti rivers during the Late Quaternary.The proposed research will be conducted to tackle these objectives :(i) The various carbonate deposits need to be properly studied, as they are usually considered as calcrete instead of palustrine limestones. Consequently, the first task targets the study of the various types of deposits in the Chobe Enclave, including diatomites, fluvial and eolian sands, based on modern and conventional methods used in sedimentology/biogeochemistry. (ii) The next aim concerns the Ca sources. How did Ca accumulate enough to contribute to the precipitation of almost pure Ca-carbonate phases? (iii) The third task, as a consequence, assesses the origin/conditions of the unexpected succession of silicate- and carbonate-rich phases: climatic, tectonic, tectono-climatic, lacustrine, palustrine, eolian ? (iv) Finally, dating of the various deposits in the Chobe Enclave will be assessed in order to propose a chronological sequence based on various methods, i.e. 14C on carbonate and organic matter, OSL, ESR, U-Th, and compare results to the Southern African chronological framework.In conclusion, the aim of the project is to propose a genetic model that can explain the unexpected presence of calcium carbonate in carbonate-free and acidic endorheic landscapes during the Late Quaternary. This research will improve our knowledge of the relationships between regional scale climatic variability and externally-forced climate change in Africa. In addition, conclusions will contribute to understanding some surprising carbonate paleosols in carbonate-free landscapes from the Earth’s deep time and their potential relationships with atmospheric pCO2 and life.
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