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Molecular and isotopic biogeochemistry of Neoproterozoic sediments from SW-Gondwana - insight into early palaeoclimatic changes and evolution of life

Applicant Spangenberg Jorge
Number 109421
Funding scheme Project funding (Div. I-III)
Research institution Institut de Minéralogie et Géochimie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geochemistry
Start/End 01.11.2005 - 31.10.2008
Approved amount 184'430.00
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Keywords (15)

neoproterozoic; global changes; glaciations; metabolic evolution; acritarchs; stable isotopes; hydrocarbon biomarkers; carbonates; kerogen; GC-MSD; GC-C-IRMS; CSIA; Gondwana; Isotopes; Biomarkers

Lay Summary (English)

Lay summary
The main goal of this project is to perform a combined inorganic and organic, isotopic and molecular study of Ediacaran/Cambrian (E/C) sediments from the Rio de la Plata Craton (Brazil, Uruguay, Argentina). The continuous and unmetamorphosed succession of E/C strata with well preserved fossil record provides excellent conditions for studying significant events in Earth history, namely the occurrence of the most severe glaciations, drastic changes in climate and chemistry of oceans, and the evolution of multicellular life forms. During the second year of the project we have analysed samples from two units: Corumba (Brazil) and Arroyo del Soldado (Uruguay) by stable isotopes in carbonates (?13Ccarb and ?18Ocarb) and associated kerogen (?13Cker and ?15NKer) as well as the molecular isotopic composition of the bitumen (GC/MS, ?13CEOM).
The ?13Ccarb values range from -5.7 to 5.7‰, and display coeval excursions in the two units coinciding with global curves. The lowest values recorded for cap dolostones (Bocaina Formation) of the Corumbá Group are typical in cap carbonates worldwide. The ?13Cker values varying from -26.4 to -22.8‰ in Corumbá samples and from -27.4 to -12‰ in Arroyo del Soldado, suggest variations in the primary composition of organic matter as well as in the productivity rate. The ?15Nker values range between -3.3 to 3.1‰, suggesting primary contribution of molecular nitrogen fixers (cyanobacteria). An increase of ~5‰ of ?13Ccar-ker in bioclastic limestones from both groups indicates a period of higher primary bioproductivity. Higher concentrations of redox sensitive elements (Mn, Fe, U and V) and REE in this level indicate reducing conditions, which ensured the preservation of organic carbon.
The main resolvable compounds in the gas chromatograms of the hydrocarbons saturated fraction are n-alkanes in the C12-30 range (maxima at C21) for Corumbá and C14-35 range (maxima at C26) for Arroyo del Soldado samples. The predominance of C>18 n-alkanes in the Arroyo del Soldado samples confirm a marine planktonic input. The biomarker distribution (C29 to C34 hopanes, 7- and 8-Methyl-heptadecane, acyclic isoprenoids, branched alkanes, alkybenzenes and traces of steranes) reflects a mainly microbial (cyanobacteria, bacteria not strictly anaerobic) ecosystem based on photosynthetic primary production.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
121808 Molecular and isotopic biogeochemistry of Neoproterozoic sediments from SW-Gondwana - insight into early palaeoclimatic changes and evolution of life 01.11.2008 Project funding (Div. I-III)