oa IDENTIFYING CONTROLS ON ORGANIC MATTER ENRICHMENTS IN HEMIPELAGIC SETTINGS: A BIOMARKER APPROACH

The biomarker content of several dark coloured and/or organic-rich levels from the Marnes Bleues Formation (Aptian-Albian) from the Vocontian Basin (South-eastern France) was analysed in order to compare the modes of formation of such deposits in a hemipelagic, basinal setting. The studied levels include the Goguel and Paquier Levels, deposited during oceanic anoxic events (OAE) 1a and 1b, respectively. Unexpectedly, most studied samples show comparable biomarker contents, regardless of their richness in organic matter. The data indicates an organic matter of marine algal origin, deposited under oxygenated conditions. The Paquier level, however, shows an abundance of archaea-derived biomarkers and of organo-sulfur compounds in the extract, indicating deposition under reducing conditions. The Paquier level excepted, the biomarker content indicates that depositional conditions remained overall stable during deposition of the Marnes Bleues formation, including during OAE1a. Nevertheless variations of the relative proportions of steranes, hopanes, terrestrial plant biomarkers and fire-derived polyaromatic hydrocarbons, suggest that minor environmental changes occurred and occasionally favoured organic matter enrichment in the sediment. In the end, no unique mechanism explaining the deposition of these dark coloured and/or organic-rich levels can be identified.