\makeatletter
\@ifundefined{HCode}
{\documentclass[screen,CRGEOS,Unicode,Thematic]{cedram}   
\renewcommand\bibsection{\section*{\refname}}
\newenvironment{noXML}{}{}
\def\thead{\noalign{\relax}b\hline}
\def\endthead{\noalign{\relax}\hline}
\def\tbody{\noalign{\relax}\hline}
\def\hyphen{\mbox{-}}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\0{\phantom{0}}
\def\mn{\phantom{$-$}}
\def\botline{\\\hline} 
\usepackage{amssymb,wasysym}
\usepackage[figuresright]{rotating}
\RequirePackage{etoolbox}
\def\jobid{crgeos20230049}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\newcounter{runlevel}
\let\MakeYrStrItalic\relax
\def\refinput#1{}
\csdef{Seqnsplit}{\\}
\def\back#1{}
\def\para{\par}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\gappto{\UrlBreaks}{\UrlOrds}
\makeatother
\DOI{10.5802/crgeos.233}
\datereceived{2023-01-16}
\daterevised{2023-08-23}
\dateaccepted{2023-09-06}
\ItHasTeXPublished
\def\og{\guillemotleft}
\def\fg{\guillemotright}
}{
\PassOptionsToPackage{authoryear,comma}{natbib}
\documentclass[crgeos]{article}
\def\CDRdoi{10.5802/crgeos.233}
\def\xxtabnote#1{\tabnote{#1}}
\let\newline\break
\makeatletter
\def\CDRsupplementaryTwotypes#1#2{}
\def\selectlanguage#1{}
\def\href#1#2{\url[#1]{#2}}
}
\makeatother

\def\0{\phantom{0}}

\usepackage{upgreek}
\usepackage[T1]{fontenc} 

\dateposted{2023-10-03}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Tribute to Jean Dercourt}
%\def\cdr@specialtitle@french{Hommage \`a Jean Dercourt}
%\makeatother

\title{Molecular fossils of Aptian--Albian blue marls of the Vocontian
Basin (France), depositional conditions and connections to the Tethys
Ocean}

\alttitle{Fossiles mol\'{e}culaires des Marnes Bleues
Aptiennes--Albiennes du bassin vocontien (France), conditions de
d\'{e}p\^{o}t et connexions avec la T\'{e}thys}

\author{\firstname{Armelle} \lastname{Riboulleau}\CDRorcid{0000-0002-2717-8330}\IsCorresp}
\address{Laboratoire d'Oc\'{e}anologie \& G\'{e}osciences,
Universit\'{e} de Lille, UMR LOG 8187 Univ Lille-CNRS-ULCO-IRD, 59000,
Lille, France}
\email[A. Riboulleau]{armelle.riboulleau@univ-lille.fr}

\author{\firstname{Melesio} \lastname{Quijada}\CDRorcid{0000-0001-7300-983X}}
\addressSameAs{1}{Laboratoire d'Oc\'{e}anologie \& G\'{e}osciences,
Universit\'{e} de Lille, UMR LOG 8187 Univ Lille-CNRS-ULCO-IRD, 59000,
Lille, France}
\email[M. Quijada]{melesioquijada@gmail.com}

\author{\firstname{Alexis} \lastname{Caillaud}}
\addressSameAs{1}{Laboratoire d'Oc\'{e}anologie \& G\'{e}osciences,
Universit\'{e} de Lille, UMR LOG 8187 Univ Lille-CNRS-ULCO-IRD, 59000,
Lille, France}
\email[A. Caillaud]{caillaud.alexis@gmail.com}

\author{\firstname{Fran\c{c}ois} \lastname{Baudin}\CDRorcid{0000-0003-3180-459X}}
\address{Sorbonne Universit\'{e}, CNRS, ISTeP, 75005, Paris, France}
\email[F. Baudin]{francois.baudin@sorbonne-universite.fr}

\author{\firstname{Jean-No\"{e}l} \lastname{Ferry}}
\address{TOTAL S.A., CSTJF, 64000 Pau, France}
\email[J.-N. Ferry]{jean-noel.ferry@total.com}

\author{\firstname{Nicolas} \lastname{Tribovillard}\CDRorcid{0000-0003-3493-5579}}
\addressSameAs{1}{Laboratoire d'Oc\'{e}anologie \& G\'{e}osciences,
Universit\'{e} de Lille, UMR LOG 8187 Univ Lille-CNRS-ULCO-IRD, 59000,
Lille, France}
\email[N. Tribovillard]{nicolas.tribovillard@univ-lille.fr}

\shortrunauthors

\begin{abstract}
The Mesozoic witnessed some episodes of marked accumulation and burial
of organic matter (OM) in the Tethys Ocean and satellite basins, such
as the Vocontian Basin (SE-France). These famous episodes, termed
Oceanic Anoxic Events (OAEs), resulted from various factors, acting in
complex synergies; the consensus about the key factors has not been
reached yet. The Aptian--Albian Blue Marls Formation (Fm.) of the
Vocontian Basin recorded the various substages of OAE1, plus additional
organic-rich levels of regional extension. The semi-pelagic marlstones
of the Blue Marls Fm. allow to carry out a detailed examination of the
molecular fossils, to assess the respective weights of the factors
involved in the OM storage process. In this work, we examined the lipid
biomarkers of six organic-rich levels ranging from the Goguel Level to
the Paquier Level in stratigraphic order. Biomarkers reputed to be
characteristic of some OAEs are observed here: 2-methylhopanoids in the
Goguel Level (OAE1a) and archaeal lipids in the Jacob, Kilian and
Paquier Levels (OAE1b). This study shows that, in the Vocontian Basin,
OM deposition resulted mostly from local factors and that each level
has its own peculiarities; however, overarching connections with the
Tethys Ocean were critical for the recording of global anoxic events.
\vspace*{-1pt}
\end{abstract}

\begin{altabstract}
Le M\'{e}sozo\"{i}que a connu des \'{e}pisodes d'accumulation et
d'enfouissement marqu\'{e}s de mati\`{e}re organique (MO) dans la
T\'{e}thys et les bassins satellites, comme le bassin vocontien
(SE-France). Ces fameux \'{e}pisodes, appel\'{e}s Oceanic Anoxic Events
(OAE), r\'{e}sultent de diff\'{e}rents facteurs, agissant en synergies
complexes ; le consensus sur les facteurs cl\'{e}s n'a pas encore
\'{e}t\'{e} atteint. La formation des Marnes Bleues Aptiennes--Albiennes
du bassin vocontien a enregistr\'{e} les diff\'{e}rentes
sous-\'{e}tapes de l'OAE1, ainsi que des niveaux riches en MO
suppl\'{e}mentaires d'extension r\'{e}gionale. Ces marnes
h\'{e}mip\'{e}lagiques se pr\^{e}tent \`{a} un examen d\'{e}taill\'{e}
des fossiles mol\'{e}culaires, afin d'\'{e}valuer les poids respectifs
des facteurs impliqu\'{e}s dans le processus de stockage de la MO. Dans
ce travail, nous avons examin\'{e} les biomarqueurs lipidiques de six
niveaux riches en MO allant du niveau Goguel au niveau Paquier par
ordre stratigraphique. Des biomarqueurs r\'{e}put\'{e}s
caract\'{e}ristiques de certains OAE sont observ\'{e}s ici :
2-m\'{e}thylhopano\"{i}des dans le niveau Goguel (OAE1a) et lipides
d'arch\'{e}es dans les niveaux Jacob, Kilian et Paquier (OAE1b). Cette
\'{e}tude montre que, dans le bassin vocontien, le d\'{e}p\^{o}t de MO
r\'{e}sulte principalement de facteurs locaux et que chaque niveau a
ses propres d\'{e}terminismes ; cependant, les connexions du bassin
avec la T\'{e}thys ont \'{e}t\'{e} cruciales pour l'enregistrement des
\'{e}v\'{e}nements anoxiques globaux. 
\end{altabstract}

\keywords{\kwd{Vocontian basin}\kwd{Organic matter}\kwd{Lower
Cretaceous}\kwd{OAE1a}\kwd{OAE1b}\kwd{Biomarkers}}

\altkeywords{\kwd{Bassin vocontien}\kwd{Mati\`{e}re
organique}\kwd{Cr\'{e}tac\'{e}
inf\'{e}rieur}\kwd{OAE1a}\kwd{OAE1b}\kwd{Biomarqueurs}}

\maketitle

\vspace*{-2pt}

\twocolumngrid

\end{noXML}

\section{Introduction}\label{sec1}

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
deposited in a fast subsiding basin \citep{Breheret1995,Fries1986}. 
These deposits very well recorded both local and global environmental
changes \citep{Breheret1995,Fries1986}. Consequently, two~Global
\mbox{Boundary} Stratotype Sections and Points (GSSPs), namely the Col de
Pr\'{e}-Guittard section for the base of the Albian Stage
\citep{Kennedyetal2017} and the Mont Risou section for the base of the
Cenomanian stage \citep{Kennedyetal2004} are located in the Blue 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
\citep{Breheret1995,Caillaudetal2022}. All Cretaceous oceanic anoxic
events (OAEs) were recorded in the Vocontian Basin
\citep{Leckieetal2002,Follmi2012}, but in particular OAEs 1a to 1d and
OAE2 are characterized by organic-rich deposits within the Blue Marls
Formation. Nevertheless, additional OLs not related to global events
are also observed.\looseness=-1

Using sedimentation rate, grain size analysis, Rock-Eval analysis,
trace metal content, and preliminary biomarker data,
\citet{Caillaudetal2022} 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. rapid burial, sediment condensation,
dominance of refractory terrestrial OM,\,\ldots), only caused modest OM
enrichments in the sediment \citep{Caillaudetal2022}. We here present
the continuation of the work by \citet{Caillaudetal2022} 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.

{\vspace*{-2pt}}

\section{Materials and methods}\label{sec2}

{\vspace*{-2pt}}

\subsection{Sampling and bulk analysis}\label{ssec21}

{\vspace*{-2pt}}

For bulk analysis, more than 130 samples were collected from 8 sections
located in the Vocontian Basin (Figure~\ref{fig1}, Supplementary
Figure~2). Detailed information on the different sampled OLs and
sections can be found in Supplementary text~1 and in
\citet{Caillaudetal2022}.  For each sample, 500~g--1~kg of rock were
sampled. The surface sediment was removed on a thickness of 30--50~cm,
in order to sample material not affected by weathering. The rock
samples were kept in aluminum foils to avoid contamination. All samples
were characterized by Rock-Eval analysis at Sorbonne University (ISTeP)
using a RE6 device and the bulk rock method \citep{Caillaudetal2022}. 

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig1}(a) Paleogeographic map of Late Aptian 
\citep[simplified from][]{Golonka2007}
showing the location of the Vocontian Basin
(VB) and the main other areas cited in the text. Central Atlantic
Ocean: ODP Sites 1049 and 1276, DSDP Site 545; UMB: Umbria-Marche
Basin; IB: Ionian Basin. (b) Map of the geological context of the
Vocontian Basin during the Aptian times. Modified from 
\citet{FriesParize2003}. AB: l'Arboudeysse; Br: les Briers;  GL:
Glaise; ND: Notre Dame; PG: Pr\'{e}-Guittard; Ra: Ravel; SA: les
Sauzeries; SC: Serre Chaitieu; SJ: Saint Jaume; St:
Saint-Andr\'{e}-les-Alpes; TA: Tarendol.}
\end{figure*}

{\vspace*{-2pt}}

\subsection{Biomarker analysis}\label{ssec22}

{\vspace*{-2pt}}

64 samples, corresponding to black shales, dark-colored marls and
bioturbated marls (Supplementary Figure~2), were selected for molecular
fossil analysis. The procedure for lipid biomarker analysis is detailed
in Supplementary text~2. Briefly, between 50 and 70~g of sediments were
extracted using a mixture of dichloromethane and methanol 2:1~v/v with
an accelerated solvent extractor. Maltenes-like fractions were
recovered after reducing the total extracts to dryness by rotary
evaporation and solubilisation in cyclohexane. The maltenes-like were
separated in three fractions over an activated silica column using
solvents of increasing polarity. The aliphatic and aromatic fractions
were analyzed by gas chromatography--mass spectrometry (Supplementary
text~2).

{\vspace*{-2pt}}

\section{Results}\label{sec3}

{\vspace*{-2pt}}

\subsection{Bulk OM}\label{ssec31}

{\vspace*{-2pt}}

The total organic carbon (TOC) and results of Rock-Eval analysis of the
total sample set were previously described \citep{Caillaudetal2022}.
Only the most important features of the samples selected for the
present study are briefly recalled here. The highest TOC contents are
observed in the samples from the Goguel Level at les Sauzeries section
(av. 3.3\%), followed by the Paquier Level (av. 2.7\%). The Goguel
Level at Saint Jaume and Notre Dame sections, part of the Fallot
Interval, the Jacob Level, and the Kilian Level show TOC contents
between 1 and 2\%. The Goguel Level at Glaise section, the upper part
of the Fallot Interval, and the Niveau Noir show TOC contents lower
than 1\%, which are comparable to the TOC content of the surrounding
marls. Generally, the Hydrogen Indices (HI) are positively correlated
with the TOC contents (Figure~\ref{fig2}; Supplementary Figure~3). The
highest HI are observed in the Goguel Level at les Sauzeries (387
mgHC/gTOC on average) and Paquier Level (290 mgHC/gTOC), \mbox{indicating}
type~II kerogen. The other sections are characterized by low to very
low HI (67--202 mgHC/gTOC), reflecting type III to type II--III
kerogen. The majority of samples bears $T_{\max}$ values below
435~\textdegree C suggesting thermal immaturity. However, the
$T_{\max}$ values from Glaise and les Sauzeries sections are generally
higher (435 and 439~\textdegree C, respectively), indicating that the
OM has reached early oil-generating window. 

\begin{figure}
{\vspace*{6pt}}
\includegraphics{fig02}
{\vspace*{6pt}}
\caption{\label{fig2}Cross plot of the total organic carbon (TOC)
content and Hydrogen Index (HI) for the rock samples of the Blue Marls
Formation. The two trends depicted by the arrows are discussed in the
text. See electronic version for\break colors.}
\end{figure}

Two parallel trends are observed for the positive correlation between
TOC content and HI (Figure~\ref{fig2}; Supplementary Figure~3). They
are termed as ``high HI'' and ``low HI'' for the sake of simplicity.
The high HI trend includes samples from the Goguel Level at all
sections plus a few samples from the Paquier Level. The low HI trend
includes samples from the Kilian Level, Fallot Interval, Niveau Noir,
part of the Paquier Level, and some samples from the Goguel Level at
Saint Jaume section. The few samples from the Jacob Level are located
in between these two trends. These two trends are also visible when
Rock-Eval data from other studies of the Blue Marls Formation
\citep{Breheret1994, Giraudetal2018,Westermannetal2013} are included.

\subsection{Molecular fossils}\label{ssec32}

A large variety of lipid biomarkers was found in the saturated and
aromatic fractions of the studied samples. The molecular fossil content
is similar in all samples. However, a few samples contain additional
compounds, as will be described below. A detailed description of
compounds distributions is presented in Supplementary text~3. 

\subsubsection{Linear and branched alkanes}\label{sssec321}

Linear alkanes ($n$-alkanes) generally dominate the saturated
fractions. $n$-Alkanes comprise short chain compounds from C\tsub{13}
to C\tsub{22}, with a maximum in C\tsub{16} or C\tsub{17}
(Figure~\ref{fig3}), which are generally ascribed to phytoplanktic
sources \citep{Blumeretal1971, Gigeretal1980}, and long chain compounds
from C\tsub{23} to C\tsub{33}, presenting a predominance of
odd-carbon-numbered compounds. Though odd-carbon-numbered long-chain
$n$-alkanes may originate from micro- or macroalgae 
\citep[e.g.][]{Aichneretal2010, AllardTemplier2000}, these compounds mainly
derive from the epicuticular waxes of terrestrial plants
\citep{EglintonHamilton1967}. The terrestrial {vs.} aquatic
ratio  \citep[TAR;][]{BourbonniereMeyers1996} is generally lower than
0.4, reflecting a low contribution of long chain $n$-alkanes
(Supplementary Table~1). Marl samples at Pr\'{e}-Guittard have an
average TAR of 5, and TAR $>$ 0.4 are observed in the Fallot Interval
and Paquier Level. The lowest TAR values are observed in the Goguel
Level at les Sauzeries and Saint Jaume. The predominance of
odd-carbon-numbered long $n$-alkanes, as indicated by OEP\tsub{27}
\citep{ScalanSmith1970}, is present in the majority of samples
(Supplementary Table~1). The highest OEP\tsub{27} are observed in the
Fallot Interval (av. 1.9) and Paquier Level (av. 1.8). In the samples
of the Goguel Level at les Sauzeries and Glaise, the OEP\tsub{27}
$\sim$1 is ascribed to the high thermal maturity of the OM in these
sections.

\begin{figure*}
{\vspace*{-2pt}}
\includegraphics{fig03}
{\vspace*{-2pt}}
\caption{\label{fig3}Mass chromatogram $m/z$ 57 of selected aliphatic
fractions showing the distribution of acyclic compounds. (a) Sample
TAFE2OG003---Kilian Level; (b) sample ARBOG002A---Paquier Level. Pr:
pristane; Ph: pyhtane; TMI: 2,6,15,19-tetramethylicosane; PMI:
2,6,10,15,19-pentamethylicosane; ETMI:
10-ethyl-2,6,15,19-tetramethylicosane; PMH: pentamethylhenicosane, 
C$_{x}=$\ number of carbon atoms.}
{\vspace*{-2pt}}
\end{figure*}

Series of 2-methyl- and 3-methyl-alkanes, ranging from C\tsub{15} to
C\tsub{21}, maximizing around C\tsub{17}, are observed in most of the
samples. These compounds generally derive from branched \textit{iso}-
and \textit{anteiso}- fatty acids of gram positive bacteria
\citep{Goossensetal1986,Kaneda1991}. The highest relative abundances of
branched alkanes are observed in the Niveau Noir while low abundances
are observed in the Fallot Interval (Supplementary Table~1). 

\subsubsection{Acyclic and monocyclic isoprenoids}\label{sssec322}

Acyclic isoprenoids mainly consist of a series of head-to-tail linked
(regular) compounds ranging from C\tsub{14} to C\tsub{21} and are
dominated by pristane (Pr) and phytane (Ph). Regular isoprenoids are
generally less abundant than short $n$-alkanes (Supplementary Table~1;
Figure~\ref{fig3}a). In the Paquier and Jacob Levels, however, the
relative abundance of regular isoprenoids is higher (Figure~\ref{fig3},
Supplementary Table~1) and 2,6,10-trimethyltetradecane (C\tsub{16}) is
the dominant regular isoprenoid in the samples of the Jacob Level. The
samples from the Paquier Level also contain a series of tail-to-tail
linked C\tsub{24}--C\tsub{26} irregular isoprenoids (TMI, PMI and ETMI)
which were previously described by  \citet[Figure 3]{Vinketal1998} in
the same interval. An additional compound belonging to this series,
pentamethylhenicosane (PMH), is also tentatively identified
(Supplementary Figure~4). Three isoprenoid compounds with a
cyclohexyl ring ranging from C\tsub{17} to C\tsub{19} previously
described by \citet{Vinketal1998} are also present with significant
contents in the samples of the Paquier Level. Numerous other compounds
showing comparable structures were tentatively identified based on
their mass spectra (Supplementary Figure~5). The latter compounds,
ranging from C\tsub{14} to C\tsub{20}, are also present in one sample
of the Jacob\break Level. 

Pristane and phytane are often related to chlorophyll 
\citep{Didyketal1978}, which is present in many photosynthetic
organisms, but can also originate from the degradation of tocopherols,
carotenoids or biphytane structures \citep{Goossensetal1984,Lietal1995,
tenHavenetal1987}, so they are not source-specific. PMI derives from
the membrane lipids of archaea \citep{Holzeretal1979,
Brasselletal1981}. PMI and other archaea-derived isoprenoids, such as
biphytanes, presenting a highly depleted carbon isotopic signature
point to methanotrophic archaea as the source of these compounds 
\citep[e.g.][]{Elvertetal1999,Birgeletal2006}. Nevertheless, in deposits
coeval to the Paquier Level, phytane, PMI and biphytanes have a heavy
carbon isotopic signature \citep{Kuypersetal2002}.  Isotopically heavy
PMI is present in the deep part of the chemocline of the Black Sea and
Cariaco Basin, and is related to chemoautotrophic archaea
\citep{Wakehametal2007,Wakehametal2012}.  \citet{Vinketal1998}
suggested that TMI and ETMI originated from the same source as PMI.
Similarly, we consider likely that the other isoprenoids, including
monocyclic compounds, present in abundance in the samples of the
Paquier and Jacob Levels, also originate from chemoautotrophic\break archaea.

Most of the samples have a Pr/Ph ratio higher than~1
(Figure~\ref{fig4}, Supplementary Table~1). The highest values of
Pr/Ph, up to 8.6, are observed in the marl samples at Pr\'{e}-Guittard,
followed by the Fallot Interval. Only some samples from the Jacob and
Paquier Levels have Pr/Ph close to or lower than 1 (Figure~\ref{fig4},
Supplementary Table~1).

\begin{figure}
\includegraphics{fig04}
\caption{\label{fig4}Pristane/$n$C\tsub{17} {vs.}
phytane/$n$C\tsub{18} cross plot of samples from the Vocontian Basin.
Partially filled symbols correspond to marls collected close to the
organic levels.}
\end{figure}

\subsubsection{Steroids}\label{sssec323}

A wide variety of steroids is observed in most of the samples. The
compounds include diaster-13(17)-enes, diasteranes, regular steranes,
ring-C monoaromatic steroids and triaromatic steroids, as well as
methylated counterparts. The highest relative abundances of steroids
are observed in the Paquier Level and the Goguel Level at Notre Dame.
Low relative abundances of steroids are generally observed in the
marls.

Regular steranes are generally dominated by C\tsub{29} compounds
(Figure~\ref{fig5}, Supplementary Figure~6). In the Paquier Level,
however, C\tsub{27} isomers are dominating regular steranes. The
relative abundance of C\tsub{27}, C\tsub{28} and C\tsub{29} regular
steranes \citep{HuangMeinschein1979} suggests a mixed contribution of
algal and terrestrial OM for all samples (Figure~\ref{fig5}).
Nevertheless, 24-$n$-propylcholestanes are observed in significant
proportion in most of the samples (Supplementary Table~1). Precursors
of 24-$n$-propylcholestane have been observed in marine algae
\citep{RaederstorffRohmer1984}, desmosponges \citep{Zumberge2019} and a
foraminifer \citep{Grabenstatteretal2013}. 24-$n$-Propylcholestane
could also result from diagenetic methylation of C\tsub{29} sterols
\citep{Bobrovskiyetal2021}. Nevertheless, 24-$n$-propylcholestanes are
generally considered as indicative of deposition under marine
conditions \citep{Moldowanetal1985}. The highest abundances of
24-$n$-propylcholestanes are \mbox{observed} in the Paquier Level
(Supplementary Table~1).

\begin{figure}
\includegraphics{fig05}
\caption{\label{fig5}Ternary plot showing the distribution of
C\tsub{27}, C\tsub{28}, and C\tsub{29} regular steranes in the
aliphatic fractions. Legend of symbols as in Figure~\ref{fig4}.}
\end{figure}

Methylsteroids comprise saturated and aromatic compounds methylated at
position 2-, 3-, and \mbox{4-,} as well as dinosteroids (based on the
4,23,24-trimethylcholestane skeleton; Supplementary Figures~6, 10).
2-Methyl- and 3-methyl-steroids originate from diagenetic
rearrangements in the sediment 
\citep{SummonsCapon1988,SummonsCapon1991} and seem present in
relatively stable proportion in the samples. Conversely,
4-methylsteroids and dinosteroids mainly originate from dinoflagellates
\citep{Summonsetal1987}, and are present in variable proportion in the
samples. The highest proportions of 4$\upalpha$-methyl-steranes,
dinosteranes and triaromatic dinosteroids are observed in the Paquier
and Goguel Levels at Notre Dame and Saint Jaume. 

\subsubsection{Hopanoids}\label{sssec324}

A wide variety of hopanoids is observed in the samples (Supplementary
text~3). The dominant hopanoids are saturated $\upalpha\upbeta$-hopanes
ranging from C\tsub{27} to C\tsub{35} (C\tsub{28} absent) with a
maximum in C\tsub{30} and a progressive decrease of the abundance of
homohopanoids with increasing chain length (Figure~\ref{fig6}). The low
abundance of C\tsub{34} and C\tsub{35} hopanes is indicative of a
deposition in non-hypersaline conditions  \citep{tenHavenetal1985}. The
distribution of hopanoids isomers is comparable in most of the samples
and reflects the thermal immaturity of the OM; however, the
distribution differs at les Sauzeries and Glaise sections, reflecting
the higher thermal maturity at these locations (Supplementary\break Table~1).

\begin{figure*}
{\vspace*{3pt}}
\includegraphics{fig06}
\caption{\label{fig6}Partial mass chromatograms showing the
distribution of (a) hopanes and moretanes ($m/z$ 191) and (b)
methylhopanes ($m/z$ 205). Sample NDOG003---Goguel Level.}
{\vspace*{3pt}}
\end{figure*}

2-Methyl hopanes ranging from C\tsub{28} to C\tsub{35}, with a maximum
in C\tsub{31}, are present in significant proportion in most of the
studied samples from the Goguel Level, with 2-methyl hopane index
\citep[2-MHI;][]{Andoetal2022} ranging between 6 and 23
(Figure~\ref{fig6}; Supplementary Table~1). If present in the other
OLs, the abundance of 2-methyl hopanes is very low. 2-Methyl hopanes
are absent from the extract of marl samples (Supplementary Table~1).
Traces of 3-methyl-hopanes are detected in many samples
(Figure~\ref{fig6}).

Desmethyl hopanoids mostly originate from biohopanoids present in the
cell walls of many bacteria, including cyanobacteria
\citep{OurissonRohmer1992, Talbotetal2008,KuschRush2022}, so desmethyl
hopanes are poorly specific bacterial markers. In contrast,
methyl-hopanes are more specific: though their origin is still
discussed, 2-methyl-hopanes mainly originate from cyanobacteria and
alphaproteobacteria \citep{Summonsetal1999,Naafsetal2022,
KuschRush2022}, while 3-methylhopanes originate from \mbox{aerobic}
\mbox{methanothrophs} \citep{NeunlistRohmer1985,CordovaGonzalezetal2020}.

\subsubsection{Aryl isoprenoids}\label{sssec325}

Aryl isoprenoids are detected in most of the OLs, though generally in
low abundance. This series ranges from C\tsub{13} to C\tsub{20}, with
the C\tsub{24} and C\tsub{29} compounds also often present in low
proportion. Values of the aryl isoprenoid ratio 
\citep[AIR;][]{SchwarkFrimmel2004} are generally higher than 1, reflecting
the dominance of short aryl isoprenoids (C\tsub{13}--C\tsub{15});
nevertheless, AIR are lower than 1 in the Paquier Level (Supplementary
Table~1). The highest proportions of arylisoprenoids are observed in
the Paquier Level, as well as the Goguel Level at Glaise and Notre
Dame.\looseness=1 

Aryl isoprenoids are often considered to derive from carotenoids of
anoxygenic photosynthetic bacteria \citep{SummonsPowell1987,
BrocksSchaeffer2008}. Nevertheless, other sources, in \mbox{particular}
the aromatisation of carotene, are also likely when these compounds are
observed in rocks deposited in well oxygenated environments 
\citep{Koopmansetal1996b}. From the very low abundance of aryl
isoprenoids longer than C\tsub{20}, the absence of C\tsub{40} aryl
isoprenoids as well as of commonly observed isorenieratene derivatives
\citep{Koopmansetal1996a},  the arylisoprenoids observed in the
sediments of the Vocontian Basin likely do not originate from
anoxygenic photosynthetic bacteria. In particular, the abundant aryl
isoprenoids and substituted alkylbenzenes (Supplementary text~3)
observed in the samples from the Paquier Level could originate from the
degradation and aromatisation of archaea-derived biphytanyl compounds.

\subsubsection{Other terpenoids}\label{sssec326}

Terpenoids of microbial origin, namely dammar-13(17)-enes and
13${\upbeta}$,17${\upalpha}$(H)-dammaranes 
\citep{MeunierChristmannetal1991} are observed in the samples of the
Paquier Level only, while \mbox{cheilanthanes} \citep{Petersetal2005}
are widespread in the samples from the Goguel Level, Niveau Noir, and
the Paquier Level. 

The aromatic terpenoids retene, cadalene, and
6-isopropyl-1-isohexyl-2-methylnaphthalene are detected in most of the
samples. These three compounds mainly derive from higher plant
terpenoids and are thus generally related to a terrestrial source 
\citep{vanAarssenetal2000}. Their relative abundance is maximum in the
marl samples from Pr\'{e}-Guittard and minimum in the Goguel Level at
Glaise and les Sauzeries. High relative abundances are also observed in
the Paquier Level (Supplementary Table~1). Cadalene, a non-specific
terrestrial plant biomarker \citep{vanAarssenetal2000} is largely
dominant in all the samples, though its relative abundance is slightly
lower in the Goguel Level at les Sauzeries\break section.

Series of methylated 2-methyl-(trimethyltridecyl)-chromans (MTTC) are
present in most of the samples, except those from Pr\'{e}-Guittard, les
Sauzeries and Glaise sections. These compounds likely originate from
the rearrangement of the phytol side chain of chlorophyll
\citep{Lietal1995} but are widely used as paleosalinity indicators. The
dominance of the 5,7,8-trimethyl-isomer in the samples from the
Vocontian Basin indicates normal salinity conditions
\citep{SinningheDamsteetal1993}.

\subsubsection{Polycyclic aromatic hydrocarbons}\label{sssec327}

Condensed polycyclic aromatic hydrocarbons ranging from triaromatic
(phenanthrene and anthracene) to heptaaromatic (coronene) are detected
in most of the samples (Supplementary Table~1, Supplementary Figure
13). These compounds generally have a pyrogenic origin 
\citep{Wakehametal1980,binAbasetal1995} and can be used as tracers of
terrigenous inputs. The highest relative abundances of PAHs are
associated to a predominance of benzo[\textit{ghi}]perylene and
coronene, and are observed in the marl samples from Pr\'{e}-Guittard
section, Tarandol (Kilian and Jacob Levels), and Serre Chaitieu
sections (Fallot Interval). Low relative abundances of PAHs are
observed in the samples of the Goguel Level, Niveau Noir and Paquier
Level. 

Dibenzofuran is detected in most of the samples, except the marls from
Pr\'{e}-Guittard. Its highest abundance is observed in the Niveau Noir.
Dibenzofuran and its alkylated counterparts have been related to
lichens and can be used as tracers of \mbox{terrigenous} \mbox{inputs} 
\citep{Radkeetal2000}. Nevertheless, our data suggest that dibenzofuran
here results from the degradation of an algal or microbial biomass (see
Section~\ref{sec4}).

\subsubsection{Sulfur containing compounds}\label{sssec328}

Organo-sulfur compounds (OSCs) are present in all the samples from the
Paquier Level. They correspond to a C\tsub{20} isoprenoid thiophene and
several isomers of C\tsub{20} isoprenoid benzothiophenes. OSCs are not
observed in the other samples. 

\section{Discussion}\label{sec4}
\subsection{Thermal maturity}\label{ssec41}

Based on Rock-Eval analysis and molecular indicators (Supplementary
Table~1), the majority of the studied outcrops are thermally immature,
allowing to compare the biomarker content with each other in these
different settings. Nevertheless, consistent with previous studies
\citep{Breheret1995}, our data indicate that the oil-generating
window was reached at les Sauzeries and Glaise sections (Supplementary
Table~1). The biomarker content of the Goguel Level at these two
outcrops must therefore be considered in the light of this higher
thermal maturity.

\subsection{Comparison of the different OLs}\label{ssec42}

Previous characterisations of the OM in the Blue Marls Formation based
on palynofacies, palynology or organic geochemistry, showed that the OM
was mainly of marine origin, with variable contributions of terrestrial
plant debris \citep{Bodinetal2023,Breheret1994,Friedrichetal2003,
Heimhoferetal2006,Herrleetal2010,Herrleetal2003b,
Kuypersetal2002,Okanoetal2008b,TribovillardGorin1991}. The biomarkers
identified in the present study confirm the mainly autochthonous origin
of the OM, while the contributions from higher plants are present, but
are low in most of the samples. According to previous studies (op.
cit.), the variations of the organic content reflect several factors:
sea-level evolution during the Aptian to Albian interval, variations of
primary productivity, orbitally induced climate fluctuations, and
oceanic anoxic events. In addition, turbiditic corridors are well
documented in the western part of the Vocontian Basin
\citep{Breheret1995,Fries1986,FriesParize2003},  so that the location
within the basin might also influence the organic content.

The Blue Marls Formation is characterized by alternations of ligh and
dark levels related to orbitally induced climate oscillations 
\citep{AitIttoetal2023,Charbonnieretal2023,Galeetal2011}. These
orbitally induced oscillations are also visible in the OLs, as the
latter frequently present alternations of black shales or dark-colored
laminated marls and bioturbated marls (Supplementary Figure~2). Since
the sampling for molecular fossil analyses was mainly focussed on the
darkest sub-levels, the discussion below concentrates on the conditions
most prone to OM deposition.

\subsubsection{Hemipelagic marls}\label{sssec421}

Though located in the west part of the Vocontian Basin, the
Pr\'{e}-Guittard section does not show major turbidites in the sampled
interval (Supplementary Figure~2) and can therefore be considered as
representative of the hemipelagic sedimentation. The very low TOC
content and HI, as well as high OI \citep{Caillaudetal2022, 
AitIttoetal2023}, are typical for highly degraded OM (type IV). Such
observation is consistent with the high Pr/Ph ratio and the absence of
C\tsub{35} homohopanes, indicative of well oxygenated conditions in the
sediment \citep{Didyketal1978,PetersMoldowan1991}. The very low
abundance of steroids, the notable contribution of resistant compounds,
such as long $n$-alkanes from terrestrial plant waxes and fire-derived
PAHs, and the CPI of $n$-alkanes close to 1, are also consistent with
extensive biodegradation \citep{Hoefsetal2002,Petersetal2005}.
Dibenzofuran is hardly observed at Pr\'{e}-Guittard, while other
land-sourced compounds, e.g. long-chain $n$-alkanes, cadalene and PAHs
are relatively abundant. The latter compounds are mainly delivered to
the marine environment as aerosols \citep{SimoneitMazurek1982,
Simoneit1984}, while dibenzofuran could be delivered by rivers, thus
explaining this discrepancy. Nevertheless, an alternative source for
dibenzofuran is suggested by our data (see below). It should be noted
that in the marl samples from the Pr\'{e}-Guittard section, the
terrestrial signature is higher than in the marl samples from the other
sections (Supplementary\break Table~1).

\subsubsection{Goguel Level}\label{sssec422}

The Goguel Level is recording the Oceanic Anoxic Event (OAE) 1a in the
Vocontian Basin. The OAE1a is a global event characterized by a
carbonate crisis, deposition of organic-rich sediments in marine
settings and a marked negative carbon isotope excursion in both
carbonates and OM \citep[see][for a review]{Follmi2012}.

The Goguel Level was sampled at four different outcrops
(Figure~\ref{fig1}, Supplementary Figure 2). Les Sauzeries was in a
distal setting, far from detrital influences \citep{Breheret1995}. 
Nevertheless, the OM is thermally mature. Glaise section is as well
supposed as a distal setting, but was influenced by detrital inputs, as
indicated by the fine turbidites. The OM is thermally mature, as for
les Sauzeries. Saint Jaume and Notre Dame sections were located in a
more proximal setting and contain more detrital deposits, as indicated
by the numerous turbidites, though the turbidites are thin at Saint
Jaume and relatively thick \`{a} Notre Dame. As a result of the
detrital influence, lower TOC and HI are observed at Glaise, Notre Dame
and Saint Jaume compared to les Sauzeries (Supplementary  Figure~3);
still, the four outcrops all belong to the ``High HI'' trend, the same
trend as observed in the coeval Selli Level, in the Umbria-Marche Basin
\citep{Baudinetal1998}.%\looseness=1

Consistent with previous molecular fossil studies
\citep{Heimhoferetal2004,
Okanoetal2008a,Okanoetal2008b,Andoetal2022,Andoetal2017}, the molecular
signature of the Goguel Level is marked by the predominance of
autochthonous algal and microbial OM, without marked difference in the
four studied sections (Supplementary Table~1). In particular, all four
sections show a similar low abundance of land-derived inputs. The
moderate amounts of dibenzofurans in these sections suggest that this
compound is not land-derived. The high sterane/hopane ratio in the
least thermally mature sections reflects an important contribution of
eukaryotes and in particular a significant contribution of
dinoflagellates, which can be related to the observation of dinocysts
and acritarchs in the palynofacies \citep{Heimhoferetal2006,
Andoetal2022}. A high abundance of dinosteroids was similarly observed
in the coeval mid-Pacific organic-rich deposits of Shatsky Rise 
\citep{DumitrescuBrassell2005}.\looseness=1 

Though indicators of severe water column anoxia were described in the
coeval deposits from northern Tethys \citep{Pancostetal2004,
vanBreugeletal2007}, and sediment anoxia at Shatsky Rise 
\citep{DumitrescuBrassell2005}, molecular fossils of euxinia or anoxia,
like aryl isoprenoids are not observed in the Vocontian Basin. The
Goguel Level presents a ``paper shale'' texture, and the benthic fauna
is overall rare \citep{Fries1986,Breheret1995,Giraudetal2018}.
Moreover, the dominance of fluorescing amorphous OM in the palynofacies
and the high HI indicate a good degree of OM preservation 
\citep{Heimhoferetal2004,Heimhoferetal2006,Andoetal2022}.  These data
point to anoxic conditions at the sediment water interface
(Figure~\ref{fig7}a), consistent with the high values of the C\tsub{35}
homohopane ratio \citep{PetersMoldowan1991}.  Episodic oxygenation is
indicated by the intermittent presence of benthic foraminifera or
bioturbation in the Goguel Level
\citep{Fries1986,Breheret1995,Giraudetal2018}, but the low enrichments
of redox-sensitive trace elements \citep{Westermannetal2013,
Caillaudetal2020} could reflect a basin reservoir effect
\citep{Caillaudetal2020}. Despite the dominance of anoxia in the
sediment, high Pr/Ph are observed in the Goguel Level 
\citep[this study;][]{Okanoetal2008b,Andoetal2017};
it thus appears that the Pr/Ph
ratio is not a good indicator of oxygenation conditions in this level.
The high Pr/Ph ratio could be related to an abundance of pristane
precursors, such as tocopherols, in the organic flux to the sediment
\citep{Goossensetal1984}, or to peculiar diagenetic conditions, as also
suggested by the abundance of MTTC \citep{Lietal1995}. 

\begin{figure*}
{\vspace*{2pt}}
\includegraphics{fig07}
{\vspace*{2pt}}
\caption{\label{fig7}Depositional model for the different OLs.}
{\vspace*{2pt}}
\end{figure*}

The abundance of 2-methylhopanoids at the four studied sections is
distinctive of the Goguel Level compared to the other OLs of the
Vocontian Basin. The abundance of 2-methylhopanoids has been previously
described in different organic-rich deposits of OAE1a
\citep{Kuypersetal2004b,
DumitrescuBrassell2005,DumitrescuBrassell2006,
Karakitsiosetal2018,Castroetal2019}, but also in the deposits of the
Toarcian OAE
\citep{Farrimondetal1994,BlumenbergWiese2012,Ruebsametal2018,
Ajuabaetal2022}, and OAE2 \citep{Farrimondetal1990,Kuypersetal2004a,
Forsteretal2008}. The significance of elevated concentrations of
2-methyl hopanoids is still highly discussed \citep{KuschRush2022}.
Nevertheless, a recent review suggests that the abundance of
2-methylhopanoids during these events reflects an expansion of \mbox{marine}
anoxygenic photoautotrophic ${\upalpha}$-proteobacteria as a response to
water column deoxygenation \citep{Naafsetal2022}. A high contribution
of ${\upalpha}$-proteobacteria during deposition of the Goguel Level is
consistent with the oligothrophic conditions indicated by the
nannofossil content \citep{HerrleMutterlose2003,Giraudetal2018}. 
Oligotrophic conditions are generally not prone to favor deoxygenation
of the water column or sediment. Conversely, high productivity is
documented at the beginning of OAE1a in the Tethys Ocean
\citep{Aguadoetal2014,Sabatinoetal2015}. For this reason, it appears
more likely that the deoxygenation in the Vocontian Basin resulted from
the spreading of oxygen-poor waters originating from the Tethys Ocean
(Figure~\ref{fig7}a). The Goguel Level was deposited during a
transgressive period \citep[Supplementary Figure~14;][]{Rubino1989,
FriesParize2003,Ferryetal2022}, which favored communications between
the Tethys Ocean and the Vocontian Basin. The gradient of the
phosphorus content in the sediment \citep{Westermannetal2013},  and the
observation of maximum 2-MHI in the most basinal section at les
Sauzeries, are consistent with this scenario. Sedimentary condensation
likely also favored OM enrichment  
\citep[Supplementary Figure~14;][]{Caillaudetal2022,Caillaudetal2020}.

\subsubsection{Niveau noir}\label{sssec423}

The Niveau Noir has not been correlated with other organic-rich levels
outside the Vocontian Basin and is considered a local event. In the
present study, only the two upper sub-levels of the Niveau Noir were
analyzed (NN3 and NN4, Supplementary Figure~2). The biomarker content
of these two samples indicate that the OM is mainly of algal to
bacterial origin. The low abundances of continent-derived long-chain
$n$-alkanes and cadalene, as well as fire-derived PAHs, are consistent
with the absence of turbidites from the Niveau Noir, though turbidites
are present in other parts of Saint Jaume section. Molecular indicators
of the redox state of the water column and sediment (homohopane ratio,
AIR,\,\ldots) indicate oxygenated conditions, consistent with the
absence of redox-sensitive trace metal enrichment
\citep{Caillaudetal2022}. The abundance of branched alkanes suggests
efficient bacterial activity under aerobic conditions. Nevertheless,
the sterane/hopane ratio indicates significant input of eukaryotic
biomass, including algae producing 4-methyl-steranes. The chain length
distribution of steranes in the Niveau Noir is characterized by a high
proportion of the C\tsub{27} compounds (Figure~\ref{fig5}). C\tsub{27}
sterols are produced by a variety of marine algae as well as
zooplankton \citep{Volkman1986}, and thus are not specific biomarkers.
Nevertheless, cholesterol dominance was observed in the upper sediment
or settling particles of several high productivity environments 
\citep[e.g.][]{Volkmanetal1987, Colomboetal1996}. The high proportion of the
C\tsub{27} steranes in the Niveau Noir could therefore reflect high
primary productivity, despite the low enrichment of trace elements
sensitive to productivity \citep{Caillaudetal2022}. Consistent with
our interpretation, the nannofossil content of the NN4 level \mbox{indicates}
higher primary productivity than for the surrounding marls
\citep{Herrleetal2010}. 

To summarize, the Niveau Noir resulted from an increase in surface
primary productivity (Figure~\ref{fig7}b, Supplementary Figure~14),
possibly resulting from orbitally induced increases of nutrient
delivery associated to continental runoff \citep{Herrleetal2010}.
Nevertheless, this increase in primary productivity was not sufficient
to significantly alter the concentration of oxygen in the water column
and sediment (Figure~\ref{fig7}b). As a result, OM preservation was
ultimately low. The Niveau Noir was deposited during a high sea level
interval \citep{Rubino1989,FriesParize2003}, sediment condensation
likely also contributed to OM enrichment 
\citep[Supplementary Figure~14;][]{Caillaudetal2022}. 

\subsubsection{Fallot interval}\label{sssec424}

The Fallot Interval has no recognised lateral equivalent outside the
Vocontian Basin and is considered a local event. Though the biomarker
content of the Fallot Interval is dominated by an algo-bacterial
signature, the influence of terrestrial OM is more pronounced than in
the other OLs. A progressive increase of the terrestrial influence from
the base to the top of the Fallot Interval is indicated by the increase
of TAR and of the relative abundance of PAHs, mirroring a decrease of
the proportions of the marine steroids and of dibenzofuran
(Supplementary Table~1). Consistently, several authors consider that
the Fallot Interval was deposited during a period of falling relative
sea level 
\citep[Supplementary Figure~14;][]{Rubino1989,FriesParize2003}.
The values of the AIR and
C\tsub{35} homohopane ratio, as well as the absence of isorenieratane
\citep{Reitneretal2015}, point to dysoxic to well oxygenated
conditions, consistent with the presence of bioturbations and benthic
foraminifera in most of the Fallot Interval
\citep{Breheret1995,Friedrichetal2003}. The low HI and low abundance of
steroids consitently indicate efficient OM degradation. The moderate
sterane/hopane ratio suggests a moderate input of eukaryotic biomass,
consistent with the mesotrophic conditions indicated by planktic
foraminifera \citep{Friedrichetal2003}. The latter authors suggested
that OM enrichment in the sediment was related to moderately high
primary productivity for the lower part of the Fallot Interval, but was
linked to water column stagnation in the upper part. The molecular
fossil content of the lower part of the Fallot Interval is consistent
with the ``productivity'' model of  \citet{Friedrichetal2003} and
points to depositional conditions comparable to the Niveau Noir, but
with a higher input of terrestrial OM (Figure~\ref{fig7}b).
Nevertheless, for the second part of the Fallot Interval, the
stagnation model \citep{Friedrichetal2003} is not supported by the
redox proxies. Taking account of the lower hydrocarbon extraction
yields from leaves and wood of terrestrial plants compared to algae
\citep[e.g.][]{Cranwelletal1990,BushMcInerney2013,JambrinaEnriquezetal2018},
the biomarker content likely underestimates the proportion of
terrestrial OM in the sediment. Though a detailed palynofacies analysis
is needed to further \mbox{support} this hypothesis, the more pronounced
terrestrial signature suggests that the upper part of the Fallot
Interval results from efficient burial of terrestrial OM
(Figure~\ref{fig7}b, Supplementary Figure~14), as proposed by
\citet{Caillaudetal2022}. 

\subsubsection{Jacob Level}\label{sssec425}

The Jacob Level is the first organic-rich deposit associated to OAE1b
in the Vocontian Basin \citep{Leckieetal2002,Coccionietal2014}. Lateral
equivalents of the Jacob Level have been mostly recognised in the
Tethys Ocean and in the Pacific Ocean; it could correspond to a global
event \citep[see][for a review]{Bodinetal2023}.

Debris of higher plants have been described in the Jacob Level
\citep{BaraleBreheret1995}, as well as abundant spores and pollen
grains in the palynofacies \citep{Breheret1995,Heimhoferetal2006}. 
Consistent, PAHs, retene and cadalene are relatively abundant.
Nevertheless, only the highest sample from the Jacob Level shows a high
TAR, and the molecular signature is overall dominated by the algal
contribution (Supplementary Table~1). Low proportions of dinosterane
and medium values of the triaromatic dinosteroid (TADS, Supplementary
text~2) ratio suggest medium to low contribution of dinoflagellates.
Average C\tsub{27} triaromatic steroids (TAS, Supplementary text~2)
values also suggest an average productivity of coccolithophorids or
prasinophytes. Consistent, the microfaunal content suggests mesotrophic
conditions \citep{Erbacheretal1998,Heimhoferetal2006}. The samples of
the Jacob Level plot between the ``high HI'' and ``low HI'' trends
(Figure~\ref{fig2}), which suggests intermediate OM preservation, and
is consistent with the variable proportion of amorphous OM in the
palynofacies \citep{Heimhoferetal2006}. The same conclusion can be
reached based on the molecular signature: steranes and hopanes are
relatively abundant but the homohopane index is null, suggesting OM
degradation in an oxygenated sediment. The presence of benthic
foraminifera in the Jacob Level \citep{Erbacheretal1998} gives support
to this latter interpretation. 

A peculiar feature in the extracts of the Jacob Level is the abundance
of acyclic and monocyclic isoprenoids. Though PMI and TMI are not
observed in the Jacob Level 
\citep[this study;][]{Andoetal2022,Andoetal2017}, we consider that the abundant
isoprenoids likely derive from lipids of planktic chemoautotrophic
\mbox{archaea}. The archaeal biomarkers PMI and TMI have been described in
Livello 113, a lateral equivalent of the Jacob Level in Umbria-Marche
Basin \citep{Coccionietal2014,Ferraro2017}. Livello 113 was deposited
as a result of moderate to high primary productivity and anoxia to
dysoxia of the bottom water \citep{Coccionietal2014,Sabatinoetal2015,
Ferraroetal2020}. Planktic chemoautotrophic archaea could have been
driven in the Vocontian Basin through intrusions of anoxic intermediate
waters originating from the northern Tethyan margin. The presence of
the Tethyan taxon \textit{Nannoconus} in the Jacob Level 
\citep{HerrleMutterlose2003}, is consistent with this scenario.
Nevertheless, the water column was oxygenated in the Vocontian Basin,
which led to efficient degradation of the archaeal lipids
(Figure~\ref{fig7}d). 

Previous models have proposed that OM enrichment in the Jacob Level was
the result of sediment condensation, low sea level, elevated detrital
input, or water column anoxia \citep{Breheret1995, Erbacheretal1998,
Heimhoferetal2006, Caillaudetal2022}. A short episode of temperature
increase during this interval is documented in the Umbria-Marche Basin
\citep{Ferraroetal2020}. Increased continental runoff associated to a
more humid climate could have increased the delivery of terrestrial OM,
but also favoured primary productivity and bottom water stagnation in
the Vocontian Basin [Figure~\ref{fig7}d; \citealp{Heimhoferetal2006}].
The Jacob Level was deposited during a period of low sea level, which
also favoured the delivery of continental OM to the Vocontian Basin
[Figure~\ref{fig7}d, Supplementary Figure~14;
\citealp{FriesParize2003}]. Nevertheless, the surrection of the west
margin of the Vocontian Basin during the late Aptian--early Albian
\citep{Ferryetal2022} could have further contributed to the increased
detrital flux. 

\subsubsection{Kilian Level}\label{sssec426}

The Kilian Level is the second organic-rich deposit associated to OAE1b
in the Vocontian Basin \citep{Leckieetal2002,TrabuchoAlexandreetal2011,
Coccionietal2014}. The Kilian Level is associated to a negative carbon
isotope excursion, which has been recognised in numerous settings
\citep{TrabuchoAlexandreetal2011,Bodinetal2023}. It corresponds to a
global event.

Two samples from the Kilian Level were analyzed for their biomarker
content and they show contrasting results: the lower one is comparable
to the marls below, with a marked terrestrial signature (TAR, PAHs) and
abundant hopanes, while the second sample has a reduced terrestrial
contribution and a more marine affinity, but high abundance of plant
terpenes. The relative abundance of steroids in the Kilian Level is
low, but is higher than in the surrounding marls. The sterane/hopane
ratio is high in the upper sample. Based on TADS values, the
dinoflagellate contribution is low in both samples, but higher than in
the surrounding marls, and lower than in the Jacob Level (Supplementary
Table~1). The C\tsub{27}TAS ratio indicates a contribution of
coccolithophorid or prasinophyte comparable in the Kilian Level and
surrounding marls. The sterane distribution in the upper sample is
dominated by cholestane, interpreted as indicative of increased primary
productivity. Despite the differences between the two studied samples,
the biomarker content is consistent with the notable occurrence of
terrestrial palynomorphs in the palynofacies \citep{Herrleetal2003b}.
It also suggests low to medium primary productivity, consistent with
the oligo- to mesotrophic conditions indicated by nannofossils
\citep{Herrleetal2003b}.  No molecular indicators of water column
anoxia are observed, though the small and poorly diversified planktic
foraminifera suggest water column stratification or deoxygenation
\citep{Breheret1995, Kennedyetal2000}. Though the Kilian Level is often
laminated, the low C\tsub{35} homohopane ratio indicates a relatively
oxygenated sediment, consistent with the presence of benthic
foraminifera \citep{Herrleetal2003b} and modest enrichments in
redox-sensitive trace elements \citep{Caillaudetal2022,Wangetal2022}.
Our observations differ from previous molecular studies of the Kilian
Level at Saint-Andr\'{e}-les-Alpes, located to the east of the
Vocontian Basin, in a more basinal setting (Figure~\ref{fig1}). A
higher contribution of dinoflagellates was observed
\citep{Andoetal2017}, with a general increase from the Jacob to the
Kilian and Paquier Levels. In addition, PMI and TMI were present in
significant concentration \citep{Okanoetal2008b}. 

In the Umbria-Marche Basin and in the Central Atlantic Ocean, the
equivalents of the Kilian Level are dominated by marine OM and resulted
from increases in surface productivity
\citep{TrabuchoAlexandreetal2011, Coccionietal2014}. They were
deposited under anoxic bottom waters, though trace elements are not
systematically enriched in the rocks
\citep{TrabuchoAlexandreetal2011,Sabatinoetal2015}. The Italian
equivalent of the Kilian Level contains TMI and PMI, but no
isorenieratane \citep{Ferraro2017}. 

Recent studies of les Briers outcrop, located to the east of the
Vocontian Basin, suggest that the Kilian Level resulted from an episode
of increased primary productivity and OM preservation, associated to
pulses of continental runoff in the Vocontian Basin
\citep{Bodinetal2023}. The molecular data do not conflict with this
model, but the presence of archaeal biomarkers in the eastern part of
the basin suggest that the Vocontian Basin was also influenced by
intrusions of reducing water from the Tethyan margin
(Figure~\ref{fig7}d, Supplementary Figure~14). These intrusions led to
higher surface productivity, high abundance of dinoflagellates,
presence of planktic archaea and possibly more reducing conditions in
the water column in the eastern part of the Vocontian Basin, but not to
the west (Figure~\ref{fig7}d). The east--west decrease of TOC content
in the Kilian Level \citep{Caillaudetal2022, Bodinetal2023} and the
absence of \textit{Nannoconus} in the Kilian Level at Pr\'{e}-Guittard
and Palluel \citep{Breheret1995}, in the west part of the Vocontian
Basin, give support to this scenario. 

\subsubsection{Paquier Level}\label{sssec427}

The Paquier Level is the most prominent of the organic-rich deposits
associated to OAE1b in the Vocontian Basin \citep{Breheret1995,
Coccionietal2014}. Equivalents of the Paquier Level are recognised
worldwide, in particular by its marked negative carbon isotope
excursion in carbonate [\citealp{TrabuchoAlexandreetal2011,
Coccionietal2014}; also see \citealp{Bodinetal2023} for a review]. The
Paquier Level is the only level in the OAE1b that records global ocean
deoxygenation  \citep{Wangetal2022}.

The molecular fossil content of the Paquier Level is characterized by
the abundance of archaea-derived acyclic and monocyclic isoprenoids
(Supplementary text~3). This feature was previously observed in Ravel
section, located in a more basinal part of the Vocontian Basin
\citep{Vinketal1998,Kuypersetal2002,Okanoetal2008b}. The high abundance
of archea-derived phytane in the samples of the Paquier Level explains
the low Pr/Ph, which are the lowest of our dataset (Supplementary
Table~1). The Paquier Level is also characterized by a high abundance
of steranes, a high sterane/hopane ratio and the highest abundances of
$n$-propyl cholestanes, indicative of a high flux of a diversified
eukaryotic biomass. The relative abundance of dinosteroids is high, as
indicated by the TADS values \citep{Andoetal2017}, which can be related
to the abundance of dinocysts in the palynofacies
\citep{TribovillardGorin1991, Kennedyetal2000}. The chain length
distribution of steranes in the Paquier Level is characterized by the
dominance of the C\tsub{27} compounds, which we interpret as indicating
high primary productivity. This interpretation is consistent with the
microfaunal content indicating eutrophic conditions
\citep{Erbacheretal1998, Kennedyetal2000,Herrleetal2003b}. Though the
molecular signature of marine organisms is dominant, the terrestrial
contribution, indicated by the TAR, abundance of PAHs and of higher
plant aromatic terpenoids, is also notable (Supplementary Table~1).
These molecular data can be related to the presence of abundant
terrestrial palynomorphs in the palynofacies
\citep{TribovillardGorin1991,Herrleetal2003b}, and of occasional plant
remains in the rocks \citep{Breheret1995}. The contribution of
terrestrial OM in the Paquier Level has been observed in different
locations of the Vocontian Basin, and cannot be ascribed to the
relatively proximal setting of the studied section. 

The high homohopane ratio and the presence of OSCs indicate sulfidic
conditions in the sediment, possibly associated with bottom water
anoxia (Figure~\ref{fig7}f). This is consistent with the rarity of the
benthic fauna \citep{Breheret1995, Erbacheretal1998}, abundance of
amorphous OM in the palynofacies \citep{TribovillardGorin1991}, and
trace metal enrichment in the sediment \citep{Benamaraetal2020,
Caillaudetal2022,Wangetal2022}. Nevertheless, no indicator of photic
zone anoxia was detected, consistent with previous data
\citep{Kuypersetal2002}. 

Molecular fossil analyses were performed in several lateral equivalents
of the Paquier Level, in the Umbria-Marche Basin
\citep{Coccionietal2014},  in the Ionian Basin \citep{Tsikosetal2004}
and in the Central Atlantic Ocean \citep{Kuypersetal2002}. All these
levels are characterized by the abundance of biomarkers derived from
archaeal lipids, including PMI and TMI, and by the absence of
isorenieratane \citep{Kuypersetal2002,Tsikosetal2004,Ferraro2017}.
While in the Central Atlantic Ocean samples the steranes are dominated
by the C\tsub{29} compounds and 2-methylhopanes are present
\citep{Kuypersetal2002},  the biomarker content in the Umbria-Marche
Basin is more comparable with that of the Paquier Level, with a
dominance of C\tsub{27} steranes and possible absence of
2-methylhopanes \citep{Ferraro2017}.  These lateral equivalents of the
Paquier Level are all characterized by heavy organic carbon isotopic
ratios ($\delta^{13}\mathrm{C}_{\mathrm{org}} = -22$ to $-17\permil$),
indicative of a high contribution of chemoautotrophic archaea
\citep{Kuypersetal2002,Tsikosetal2004, Sabatinoetal2015}. In the
Paquier Level, however, heavy organic carbon isotopic ratios are only
observed sporadically \citep{Benamaraetal2020,
AitIttoetal2023,Bodinetal2023}, indicating that archaea were rarely
dominant in the Vocontian Basin.

Because of the high proportion of terrestrial OM, several authors
proposed that the Paquier Level deposited as a result of increased
input of nutrient to the ocean associated to a warm, humid climate and
continental runoff \citep{Herrleetal2003a,Herrleetal2003b,
Benamaraetal2020,Bodinetal2023}. The highest levels of primary
productivity and water stratification would have been reached under
favourable orbital conditions, at the peak of a long period of
progressive warming  \citep{Wangetal2022,Bodinetal2023}. The surrection
of the west margin of the Vocontian Basin during the late Aptian--early
Albian \citep{Ferryetal2022} possibly also contributed to the increased
inputs of continental material during this period. The molecular fossil
content does not conflict with the influence of terrestrial runoff.
Nevertheless, the similarity of biomarker composition in the northern
Tethyan margin and in the Vocontian Basin, as well as the abundance of
the Tethyan nannofossil \textit{Nannoconus} in certain layers of the
Paquier Level \citep{Breheret1995}, are consistent with the
establishment of good connections between the Tethys Ocean and the
Vocontian Basin (Figure~\ref{fig7}f). The Paquier Level is interpreted
as a 3{rd} order maximum flooding surface [Figure~\ref{fig7}f,
Supplementary Figure~14; \citealp{Rubino1989,FriesParize2003}].
Sediment and bottom water anoxia in the Vocontian Basin could therefore
have resulted from the high primary productivity, nevertheless, an
expansion of the Tethyan oxygen minimum zone associated to the eustatic
rise also seems possible.{\vspace*{-3pt}} 

\section{Conclusion}\label{sec5}
{\vspace*{-1pt}} 

Basing on sedimentation rate, grain size analysis, Rock-Eval analysis,
trace metal content, and preliminary biomarker data,
\citet{Caillaudetal2022} came to the conclusion that organic matter
(OM) enrichment within the Blue Marls Formation (Aptian--Albian) was
only modest because the conditions in the Vocontian Basin were overall
not favorable to massive burial of OM. This detailed study of the
biomarker content in the Organic Levels confirms that surface
productivity fluctuated mainly between oligotrophic and mesotrophic and
that bottom waters were rarely reducing. As a result, the OLs of
regional extension only show modest OM enrichments, associated to small
increases of productivity (Niveau Noir) or of terrestrial OM inputs
(Fallot Interval). 

Larger-scale events are fundamentally different: the Goguel Level
(OAE1a) and Jacob, Kilian, and Paquier Levels (OAE1b) present the same
molecular peculiarities (abundance of 2-methylhopanoids and of archaeal
lipids, respectively) as coeval deposits located outside the Vocontian
Basin. These are strong arguments in favor of good connections between
the Tethys Ocean and the Vocontian Basin during the deposition of these
levels. In particular, a lateral spreading of the Tethyan oxygen
minimum zone into the Vocontian Basin could explain the low sediment
oxygenation despite moderate increases of surface productivity.
Sea-level variations were previously considered as an important factor
influencing OM enrichment, through sediment condensation and water
column stratification. The present biomarker study highlights how
sea-level variations also impact OM enrichment in a given sedimentary
basin, through connections with surrounding basins. Such feature, well
known in modern settings, such as the Cariaco Basin off Venezuela, are
more difficult to document in ancient sedimentary basins.

\section*{Declaration of interests}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Acknowledgements}

We thank TOTAL S.A. (now TotalEnergy) for funding this research, M.
Gentric for administrative management, M. Delattre and R. Abraham for
technical support. P. Adam and P. Schaeffer (Institut de Chimie de
Strasbourg) are acknowledged for their help in identifying compounds. 

\back{}

\section*{Supplementary data}

Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crgeos-233-suppl.pdf}}
\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{Table-S1.xlsx}}

\bibliographystyle{crgeos}
\bibliography{crgeos20230049}
\refinput{crgeos20230049-reference.tex}

\end{document}
