Assessing controls on organic matter enrichments in hemipelagic marls of the Aptian-Lower Albian Blue Marls of the Vocontian Basin (France): an unexpected variability observed from multiple “organic-rich” levels

Abstract

The Marnes Bleues Formation from the Vocontian Basin (Southeastern France) shows many organic rich levels, some concomitant to oceanic anoxic events OAE1a and OAE1b. These organic-rich levels are scattered through a thick homogeneous succession of marls, poor in organic matter (OM). Through a multi-parameter approach, the organic-rich levels from the Aptian-Albian were characterized. Our results show that all OM-rich levels exhibit variable characteristics, such as OM nature (marine vs. continental), sedimentation and accumulation rates, redox conditions, surface-water productivity and relative sea level, but they all show low to modest enrichments in OM. Furthermore, all the levels share in common the fact that they formed under conditions of normal to low productivity and oxic to suboxic conditions. Thus, our results strongly suggest that, in the absence of high productivity and anoxic bottom conditions, the other factors reputed to favor OM accumulation only led to sporadic and low enrichments in organic contents. It is as if such factors could only enhance OM accumulation but could not induce it alone. What was true for the Vocontian Basin may be extended to other settings, regardless of their time of deposition or location.

Molecular fossils of Aptian–Albian blue marls of the Vocontian Basin (France), depositional conditions and connections to the Tethys Ocean

“…), only caused modest OM enrichments in the sediment [Caillaud et al, 2022]. We here present the continuation of the work by Caillaud et al [2022] with detailed molecular fossil results of the same six OLs. These data complement the previous dataset and allow to reconsider the depositional model of some of these OLs.…”

“…. ), only caused modest OM enrichments in the sediment [Caillaud et al, 2022]. We here present the continuation of the work by Caillaud et al [2022] with detailed molecular fossil results of the same six OLs.…”

“…The mid-Cretaceous Blue Marls Formation of the Vocontian Basin (SE-France) is a thick sequence (650-800 m cumulated thickness) dominated by grey-colored pelagic to hemipelagic marls that were 192 Armelle Riboulleau et al Marls Formation. One of the most remarkable features of the Blue Marls Formation is the recurrence of pluridecimetric dark colored layers, which have been collectively termed "organic levels" (OL), though the organic matter (OM) enrichment in these levels is highly variable [Bréhéret, 1995, Caillaud et al, 2022. All Cretaceous oceanic anoxic events (OAEs) were recorded in the Vocontian Basin [Leckie et al, 2002, Föllmi, 2012, but in particular OAEs 1a to 1d and OAE2 are characterized by organic-rich deposits within the Blue Marls Formation.…”

“…Using sedimentation rate, grain size analysis, Rock-Eval analysis, trace metal content, and preliminary biomarker data, Caillaud et al [2022] compared six of these OLs, namely the Goguel Level, Niveau Noir, Fallot Interval, Jacob Level, Kilian Level, and Paquier Level (Supplementary Figure 1). They concluded that the OLs were formed under variable conditions, but that in the absence of high primary productivity and bottom water anoxia, the supposedly "favorable" factors (e.g.…”

New insights into the palaeoenvironmental–palaeoclimatic significance and sedimentary dynamics of carbonate Lagerstätten: The lower Albian of Pietraroja (Southern Italy)

“…The OAE1b deposits are referred to as reliable key‐markers for dramatic palaeoceanographic changes in the Aptian–Albian of the Tethys, Atlantic and Pacific oceans (Wagner et al ., 2008; Trabucho‐Alexandre et al ., 2011; Zhang et al ., 2016; Benamara et al ., 2020; Caillaud et al ., 2022). However, contrary to other Cretaceous OAEs (Huck et al ., 2011; Jenkyns et al ., 2017; Graziano & Raspini, 2018), the control of early Albian OAE1b subevents on the biosedimentary dynamics of the Tethyan carbonate platforms is still barely assessed.…”