Trace metal elements as paleoenvironmental proxies: Why should we account for sedimentation rate variations?

Vincent Crombez (1) , Sébastien Rohais (1) , Tristan Euzen (1) , Laurent Riquier (2, 3) , François Baudin (2, 3) , Eider Hernandez-Bilbao (4)

1 IFPEN - IFP Energies nouvelles
2 ISTEP-PPB - Paléoenvironnemements Paléoclimats, Bassins
3 SU FSI - Sorbonne université - Faculté des Sciences et Ingénierie
4 Total E&P

Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present during the deposition of organic-rich sediments. For example, TME concentrations controlled by changes in primary productivity and redox conditions are widely used in paleoenvironmental studies. Recently, these proxies have undergone a resurgence of interest and are commonly used in large-scale (10–1000 km) studies. However, applying these geochemical proxies at basin scale while ignoring variations in sedimentation rates (SR) may lead to misinterpretation of paleoenvironmental conditions. Here, we show how SR can affect the geochemical records and may lead to incorrect interpretations of TME evolution. Accounting for SR, we computed the authigenic fraction accumulation rates of key TMEs in the Upper Montney Formation and Doig Phosphate (Triassic, western Canada), and we correct the concentration of these elements in the Vaca-Muerta Formation (Jurassic–Cretaceous, Argentina). Our SR-corrected TME proxies require a different interpretation of paleoenvironmental conditions (e.g., primary productivity, basin restriction) compared to conventional TME results and highlight that elementary enrichments commonly interpreted as indicative of anoxic depositional environments may reflect low SR and the formation of condensed intervals. This work also introduces a new workflow to account for SR in paleoenvironmental studies at basin scale and over long time periods.

Domaines: Sciences de la Terre

Vincent Crombez, Sébastien Rohais, Tristan Euzen, Laurent Riquier, François Baudin, et al.. Trace metal elements as paleoenvironmental proxies: Why should we account for sedimentation rate variations?. Geology, 2020, 48 (8), pp.839-843. ⟨10.1130/G47150.1⟩. ⟨hal-02888651⟩