Sedimentation in the “varzea” floodplain systems as a potential tool for the study of past natural perturbation events in Amazonia.
Patricia
Moreira-Turcq, Intitut de Recherche pour le Développement (IRD-LMTG), Departamento de Geoquímica-Universidade Federal Fulmínense, pturcq@geoq.uff.br
(Presenting)
Renato
Campello
Cordeiro, Departamento de Geoquímica-Universidade Federal Fulmínense, rccordeiro@geoq.uff.br
Bruno
Turcq, Intitut de Recherche pour le Développement (IRD-LMTG), Departamento de Geoquímica-Universidade Federal Fulmínense, bturcq@geoq.uff.br
Patrick
Seyler, Intitut de Recherche pour le Développement (IRD-LMTG), pseyler@lmtg.ups-tlse.fr
Arnaldo
Carneiro, INPA, carneiro@inpa.gov.br
Marcello
Bernardes, Departamento de Geoquímica-Universidade Federal Fulmínense, bernardes@geoq.uff.br
Lilian
C. dos Santos
Carlos, Departamento de Geoquímica-Universidade Federal Fulmínense,
Renata
Lima da
Costa, Departamento de Geoquímica-Universidade Federal Fulmínense,
Perturbations of forest ecosystems and hydrological regimes in Amazon basin are relatively known for the last tenth of years by the instrumental records and for the last thousands of years by quaternary studies. An observational time scale from the century to the last millennium is still lacking and this scale corresponds probably to the scale needs for studying the rhythm of the largest events of perturbation (largest fires, extreme floods, extreme dryness).
The “varzeas” floodplains present high sedimentation rates, reaching 1 cm/yr, which made possible the record of perturbation events during the last centuries. The sedimentation in the varzea systems is formed by a superposition of metric sedimentary sequences. These sequences are characterized by fining-up sediments that may include gravel, sands, silts and clays with a variable content of organic matter. The first cause of the sequence deposition is the migration of the channels supplying sediments to the varzeas. As observed in other fluvial systems, the initiation of each sedimentary sequence is probably due to a strong perturbation in the hydrological regime.
Inside the sedimentary sequences the sediment are frequently finely laminated. Different perturbation events can be evidenced: the fires may be recorded by levels of charcoal fragments, the major floods by clayey layers,... Other sediment characteristics, as, for example, organic geochemistry biomarkers can bring information on the rainforest itself.
Due to the high dynamics and hydrological complexity of these systems, such studies need to be based on several cores for each of the studied sites.
Submetido por Patricia Moreira-Turcq em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)