Research project CG/DD1/12 (Research action CG)
Context
Records from North Atlantic deep-sea and Greenland ice cores showed a very stable climate during the Holocene (i.e. the last 11,000 years), instead of a cold event between 9.000 and 8.000 years B.P. (Before Present). However, studies of continental sedimentary deposits, e.g. in Belgium, revealed variation in humidity and temperature conditions during the Holocene. The following question therefore arises: was the Belgian climate stable or not, during the Holocene?
Objectives
The main objective of the project is the reconstruction of the natural climate variability during the Holocene. The study focuses on calcareous tufa deposits from Southern Belgium. The selected deposits are characterised by high sedimentation rates. The reconstruction of climatic and environmental changes is based on a qualitative approach in order to detect local and regional modifications of the environment. Moreover, quantitative methods allow us to tentatively propose palaeotemperature and palaeoprecipitation curves. Quantification of palaeoclimatic data is required to compare the magnitude and the spatial and temporal evolution of climate changes.
Method
Tufa deposits are carbonate sediments precipitated from Ca-rich, bicarbonate waters. The Holocene period was particularly favourable for the rapid formation of thick tufa sequences. This fact highlights the link between tufa formation and climate evolution. Some authors consider the level of atmospheric CO2 as the main factor controlling the precipitation rate of tufa, while for other researchers temperature should be the primary cause of huge tufa deposits. In Belgium, tufa formation was active in small valleys, mainly during the first ~6,000 years of the Holocene. For this project, the following sites were chosen: Annevoie-Rouillon, Treignes and Villers-devant-Orval
The main methods are sedimentary facies analysis, pollen analysis, and faunal analysis of ostracods and geochemical study of their shells. 14C datations are provided to establish the chronological framework for the observed environmental changes.
l. The study of the sedimentary facies provides the local sedimentary conditions. Such analyses also contribute to detect possible sedimentary discontinuities and reworked sections.
2. Pollen analysis records changes in the vegetation cover. It allows detecting the main climate changes during the Holocene.
3. Ostracods are aquatic micro crustaceans. They secrete a calcite shell often well preserved in tufa deposits. Ostracod assemblages provide information on palaeoecological and palaeohydrological conditions at the time of deposition. Moreover, the geochemistry of ostracod shells offers the opportunity to quantify these conditions. The quantification is based on the relationships between trace elements (Sr & Mg) incorporated in the shells and the temperature and chemistry of the host water.
To assess the results of the chemical analyses of fossil ostracods, the research focuses on the geochemical and ecological responses of ostracods to natural and laboratory controlled conditions. Laboratory experiments provide accurate quantification of the relationships between ostracod chemistry and environmental conditions. Laboratory results are compared to the data obtained on ostracods living in natural conditions (i.e. spring environment).
Deliverables and expected results
- Quantified data for modelling purposes.
- Contribution to the PAGES- PEP III (Past Climate Variability Though Europe and Africa) programme.
- Contribution to E.L.D.P. (European Lake Drilling Programme) research programme, E.S.F.
- Methodology development: relevant recommendations for using ostracod chemistry method. with the aim of reconstructing palaeoenvironmental changes.
Scientific collaboration
National:
- Institut royal des Sciences naturelles de Belgique, Biologie des eaux douces.
- Faculté polytechnique de Mons, Département de Géologie et de Minéralogie.
International:
- Valencia University (Spain), Department of Microbiology and Ecology.
- Geological Institute of Barcelona, C.S.I.C. (Spain).
- Canberra University (Australia), Department of Geology.
- Université d’Angers (France), Laboratoire de Géologie.
- University of Minnesota (U.S.A.), Limnological Research Center.
