Petrographical and geochemical study of modern lacustrine sedimentary organic matter (Lagoa do Caçò, Maranão, Brazil): Relationship between early diagenesis, organic sedimentation and lacustrine filling

Mohammed Boussafir (1) , Abdelfettah Sifeddine (2, 3, 4) , Jérémy Jacob (1) , Merouane Foudi (1) , Renato Campello Cordeiro (3, 4) , Ana Luiza Spadano Albuquerque (4, 5) , Jorge Abrão (5, 4) , Bruno Turcq (5, 2)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 PALEOPROXUS - Paléoclimats, proxies, processus
3 Departamento de Geoquímica
4 LMI "PALEOTRACES"
5 DEPARTAMENTO DE GEOQUIMICA - Departamento de Geoquimica

Lagoa do Caçò is an equatorial lake in northeast Brazil, where the Inter-Tropical Convergence Zone (ITCZ) enters the South American continent, and so at a key position for deciphering Quaternary climatic variation. Preliminary results have shown that the sedimentary organic matter (OM) in the lake records the shifts in the ITCZ since the Last Glacial Maximum. The nature and fate of the OM have been determined by studying surface sediments and potential OM sources. We present here the results of organic petrographic and Rock-Eval pyrolysis analytical assessments of the biological origin and preservation state of the OM in modern sediments from two deep transects of the lake. The results led us to understand how an oligotrophic lake has accumulated 6 m of OM-rich sediment during the last 20 kyr. Palaeoenvironmental studies have shown that the lake level fluctuated during this time. Our results explain the influence of lake bathymetric variation on early diagenesis and enable interpretation of the corresponding sedimentary OM record, which is dependent on the bathymetric variation.

Keywords: Caço Lake; Early diagenesis; Palynofacies; Organic geochemistry; Brazil; Organic sedimentation

Domains: Sciences of the Universe [physics]; Continental interfaces, environment; Environmental Sciences; Global Changes

Mohammed Boussafir, Abdelfettah Sifeddine, Jérémy Jacob, Merouane Foudi, Renato Campello Cordeiro, et al.. Petrographical and geochemical study of modern lacustrine sedimentary organic matter (Lagoa do Caçò, Maranão, Brazil): Relationship between early diagenesis, organic sedimentation and lacustrine filling. Organic Geochemistry, 2012, 47, pp.88-98. ⟨10.1016/j.orggeochem.2012.03.013⟩. ⟨insu-00686432⟩