The expression of early Aptian to latest Cenomanian oceanic anoxic events in the sedimentary record of the Briançonnais domain

RSTE enrichments associated with the highest TOC values (up to 5.4 and 4.8 wt%) and with the lowest Mn contents in sediments equivalent to the Selli and Paquier OAEs (1a and 1b) indicate the presence of intermittent anoxic to euxinic conditions during these events. Sediments equivalent to Bonarelli OAE2 near the Cenomanian-Turonian (CT) boundary are also characterized by significant trace-element enrichments in comparison to average shale values. Mo and U enrichment factors (EFs) in the lower Aptian and lower Albian intervals are characteristic of an unrestricted marine environment, and in the Cenomanian-Turonian boundary interval they indicate a relationship with a particulate Fe-Mn-oxyhydroxide shuttle within the water column. In the OAE1a interval the elevated total P content associated with higher Corg/Ptot ratios and maxima in TOC values suggests that a part of the remobilized P remained trapped in the sediments. By contrast, the lower Ptot values associated with RSTE and Corg/Ptot enrichments in the OAE1b and OAE2 intervals indicate that a significant part of P was remobilized and escaped to the bottom water. Our results highlight the combined roles of regional and global parameters in the development of oxygen-deficient conditions that may lead to anoxia and increase in organic matter preservation during the OAEs. The differentiated topography of the Briançonnais domain associated with global climate and sea-level change and its influence on weathering in general, and more specifically on the mobilization of sediments on the adjacent ridge, modulated nutrient availability in different proportions during the different “mid”-Cretaceous OAEs.