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%\def\cdr@specialtitle@english{Tribute to Jean Dercourt}
%%\def\cdr@specialtitle@french{Hommage \`a Jean Dercourt}
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\title{A tribute to Jean Dercourt (1935--2019) --- Editorial}

\alttitle{Hommage \`{a} Jean Dercourt (1935--2019) --- Editorial}

\author{\firstname{Fran\c{c}ois} \lastname{Baudin}\CDRorcid{0000-0003-3180-459X}}
\address{Institut des Sciences de la Terre (ISTeP),
Sorbonne-Universit\'{e}/CNRS, 4 place Jussieu 75005 Paris, France}
\email{francois.baudin@sorbonne-universite.fr}

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\noindent
Jean Dercourt was born in Boulogne-Billancourt on March 11th
1935\footnote{Some elements of Jean Dercourt's biography summarized
here have been translated---with the authors' agreement---from an
article by De Wever and Cadet (2019) published in G\'eochronique,
$\text{n}^{\circ}$150, June 2019, p.~17.}. Pressed by his mother to take
over the family pharmacy, he began higher studies in pharmacy, and at
the same time studied natural sciences, which he found more appealing.
He successfully completed this dual training before finally choosing
geology. At university, he met Anne-Marie, who became his wife and they
had four children.

He began his career in 1957 as a ``stagiaire de recherche'' (research
fellow) at the National Centre for Scientific Research (CNRS) and he
came out first at the ``Agr\'{e}gation de Sciences Naturelles'' (the
diploma to teach in secondary schools) in 1958. Under the supervision
of Jean Aubouin, he worked in Greece to draw up a cross-section of the
northern Peloponnese and a 1:200,000 map, while he was an associate
professor at Sorbonne from 1959 to 1965. He defended his ``Th\`{e}se
d'Etat'' (professoral thesis) in 1964 \citep{Dercourt1964}.

He was appointed professor of geology at Lille University when he was
29, and was there from 1964 to 1979. This period was interrupted by a
sabbatical year in Canada in 1969 where he was a visiting researcher at
the University of Edmonton (Alberta). On his return he taught the new
revolutionary theory of plate tectonics, being one of the first in
France to do so. With his friend Jacques Paquet, he wrote a textbook
\citep{DercourtPaquet1974} which, 50 years later and in its 12th
edition, is still a reference for undergraduates. In 1979 Jean Dercourt
returned to Paris to teach at Pierre and Marie Curie University (UPMC),
where he remained to the end of his career. His dynamic and charismatic
personality attracted many students. His qualities as an enthusiastic
teacher have left their mark on generations of students training for
teaching or research.

Jean Dercourt's scientific work is marked by the study of sedimentary
basins and mountain ranges built over the last 250 million years in the
ancient ocean that opened up in Pangea during the Permian and
disappeared when the Alps collided. Jean Dercourt directed several
international scientific programmes (Tethys and Peri-Tethys) from 1985
to 2004, focusing on the paleodynamics and paleoenvironments of the
Tethyan region. Convinced that the paleogeographic map is the ultimate
synthesis of an area's geological knowledge, he set out to map the
periods from the opening to the closing of the Tethys Ocean, thereby
identifying the marine and terrestrial environments of this important
region on a global scale. The programmes have mobilised hundreds of
researchers from dozens of countries, generating more than a thousand
scientific articles.

Jean Dercourt held many important positions, in the academic world
(such as Lille University Vice-President), at the ministry of
universities, at the French Geological Society (SGF, as president in
1984--1985) and, of course, at the French Academy of Sciences, where he
was a correspondent in 1987, a member in 1991 and then Perpetual
Secretary from 1996 to 2010. As Perpetual Secretary, Jean Dercourt was
constantly concerned with the transmission of knowledge and the quality
of scientific teaching.{\break} He was responsible for overseeing the
publication of the Comptes Rendus de l'Acad\'{e}mie des sciences. He
supported the development of the Nobel prize and academician Georges
Charpak's ``La main \`{a} la p\^{a}te'' educational activities
initiated in 1995. In 2005, he supported the creation of an education
and training delegation within the academy. He made the
Ch\^{a}teau-observatory of Abbadie, near Biarritz, owned by the
academy, a place open to the public and to teachers.

I have lost count of the number of positions he held on boards of
directors and scientific councils in a wide variety of fields,
including ocean exploration and exploitation (IFREMER), the French
geological survey (BRGM), the French petroleum institute (IFP),
radioactive waste (ANDRA), environment and energy management (ADEME),
and even Sea fisheries. At international level, his involvement and
responsibilities were just as numerous and important. Let me only
mention his chairmanship of the Tectonics Commission of the
International Union of Geological Sciences (IUGS) and the Commission
for the Geological Map of the World (CGMW).

The Society acknowledged the quality of Jean Dercourt's commitments, as
demonstrated the awards he has received: several national and
international scientific prizes, membership of six academies in
different countries, four honoris causa doctorates, as well as national
distinctions (L\'{e}gion d'honneur, Ordre national du M\'{e}rite).

Very much diminished after a stroke, he had retired to his family
setting. He closed his eyes on this world on 22th March 2019, aged 84.

Here, we mean to praise him as a colleague and with this special volume
of articles as a tribute. But it is the man, the friend, whose lessons
and memory we will always remember. Many are aware that it they have
been very lucky to cross his path.

I will now briefly introduce the content of the articles of this
volume, situating them as regards Jean Dercourt's research and
scientific interests.

``The lost Tethys Ocean was the favourite topic of Jean Dercourt's
research'' said \citet{Jolivet2023} as incipit of his paper. Indeed,
Jean Dercourt's first attempts at reconstructing the evolution of the
Tethys were carried out with Bernard Biju-Duval and Xavier Le Pichon
and presented at the international symposium on the structural history
of the Mediterranean basins in 1976 \citep{BijuDuvaletal1977}.{\break}
The series of maps, limited to the Mediterranean domain, caused quite
a~stir. This attempt was then detailed and completed in the form of
9~maps extending from Atlantic to Pamir and covering the period from
Triassic to the present-day \citep{Dercourtetal1985,Dercourtetal1986b}.
On the basis of these maps Jean Dercourt built the Tethys programme and
its successors (Peri-Tethys, MEBE/Middle-East Basin Evolution), a
series of projects organised around large consortia bringing together
more than a hundred scientists from academia and industry. The initial
paleogeographic maps were extended to all the remains of the Tethys
Ocean, from the Caribbean to Indonesia \citep{Ranginetal1990,
Stephanetal1990}, with details to the northern margins of the Tethys
\citep{Rakusetal1988, Rakusetal1989, Rakusetal1990, Dercourtetal1990}.
Based on these paleogeographic data, depositional paleoenvironments
were then reported for the Tethyan realm \citep{Dercourtetal1993} and
finally for the Peri-Tethyan realm \citep{Dercourtetal2000}. Thanks to
Jean Dercourt, Tethys joined the collection of books published by
Plenum on ocean basins and their margins, as the first to be devoted to
an extinct ocean \citep{Nairnetal1996}. In addition, this volume
introduced the concept of \textit{seuils lithospheriques},
physiographic cratonic barriers that influenced Tethyan ocean dynamics
\citep{Vrielyncketal1994}. The Apulia, a micro-continent that drifted
away from Africa and then shortened to form a part of the Alpine
chains, was one of these ``\textit{seuils}''.

In his article, entitled ``\textit{Tethys and Apulia (Adria), 100 years
of reconstructions}'', \citet{Jolivet2023} reviews the main
reconstructions of the Mediterranean Tethys published since 1924,
following the evolution of concepts and methods. He also discusses the
importance of this type of synthesis for understanding large-scale
geodynamic processes.

Five years after defending his professoral thesis on the Hellenides,
Jean Dercourt spent a sabbatical year in Canada where he travelled
through the Rocky Mountains. He went there to study a different orogen
model from that of the Mediterranean Alpine ranges. Familiar with the
new theory of plate tectonics, proposed the previous year, he quickly
understood how this new vision of the dynamics at the surface of Earth
accounted for the formation of these two types of orogens. He then
wrote two articles, one in French \citep{Dercourt1970} and the other in
English \citep{Dercourt1972}, comparing the formation of these two
orogens within the framework of plate \mbox{tectonics}. Both articles
were successful and won him an international audience. This is probably
why he was elected Member and then Chairman of the Tectonics Commission
of the International Union of Geological Sciences (IUGS) from 1980 to
1992, and subsequently Chairman of the Commission for the Geological
Map of the World (CGMW) from 1992 to 2000.

In their article, entitled ``\textit{Rifting and seafloor spreading in
the South China Sea: a subduction related-extension on the down-going
plate?}'' \citet{ChangPubellier2023}, the latter being currently
Chairman of CGMW, examined the stages of rifting, spreading and
termination of activity in the South China Sea basin during the
Cenozoic. The rifting-to-drifting history of the South China Sea, which
took place between 45~Ma and 16~Ma, may be correlated in terms of
stratigraphic boundaries with the subduction-collision history of the
Proto South China Sea observed in the NW Borneo and Palawan Island.
This evolution illustrates how the process of subduction can have an
impact on regional \mbox{tectonics}.

Micropaleontology is particularly useful for establishing a precise
biostratigraphic framework in sedimentary basins and for dating
geodynamic events. Jean Dercourt quickly realised the value of bringing
together tectonicians, geodynamicians and micropaleontologists to
propose a timetable for the opening of oceanic domains that are now
integrated into mountain ranges. Among microfossils, radiolarians are
particularly useful for dating siliceous sediments that are often
associated with submarine lavas. In his quest for geodynamic
reconstructions of the Tethys, Jean Dercourt led research in this area,
in particular with Patrick De Wever \citep{DeWeverDercourt1985} and
Luc-Emmanuel Ricou \citep{Knipperetal1986}. Such approaches were
subsequently pursued and expanded by Jean Dercourt's disciples,
providing valuable information on the geodynamics of complex areas such
as the Canadian Rocky Mountains and several parts of the Alpine chain
\textit{sensu lato}, from Caribbean to Indonesia.

In their paper, entitled ``\textit{Synthesis of micropaleontological
age constraints for the reconstruction of the Tethyan realm in the
Lesser Caucasus (Armenia, Karabagh)}'', \citet{Danelianetal2023}
provide new biostratigraphic results from two ophiolite outcrops in
Armenia. The discovery of the upper Tithonian--lower Berriasian
radiolarian allows to date submarine lava eruptions and block sliding
from a nearby shallow-water carbonate platform more accurately.
Moreover, the discovery of the Upper Coniacian--Santonian calcareous
nannofossils refine the timing of ophiolite obduction in the Lesser
Caucasus.

Jean Dercourt was convinced that the geological map is an irreplaceable
document that summarises the data acquired on a given study area.
Together with Jean Aubouin and Bernard Labesse, they published a handbook
for students to introduce them to the geological mapping
\citep{Aubouinetal1970}. When he became a member of the Academy of
Sciences, Jean Dercourt gave up the traditional presentation of a sword
by his students and friends to dedicate this fund to the creation of a
prize for geological cartography. Jean Dercourt was also convinced
that, in sedimentary environments, the stratigraphy of the studied
succession should be as detailed as possible. As Chairman of the
Committee of the Geological Map of France from 1986 to 1992, then
Chairman of the Earth Sciences Council at the Geological Survey of
France (BRGM), he met the geologists from this geological survey who
were producing the geological maps of the western edge of the Saudi
Arabian platform. He convinced them and their supervisors that their
work deserved to be widely broadcast and could lead to a doctoral
thesis. Thanks to their work, the stratigraphy of the Lower Paleozoic
to Upper Jurassic of the Arabian Platform made enormous progress in the
late 1980s and early 1990s.

Work has continued since and in their complementary articles, entitled
``\textit{The Middle to Late Triassic of Central Saudi Arabia with
emphasis on the Jilh Formation. Parts~I and~II}'',
\citet{LeNindreetal2023a, LeNindreetal2023b} provide a magnificent
stratigraphic and paleoenvironmental synthesis of this formation and
discuss both its sequence stratigraphic interpretation and its
paleogeographic significance.

Although Jean Dercourt himself did not study much geology of the French
territory, with the exception of his postgraduate dissertation
(``Dipl\^{o}me d'Etudes Sup\'{e}rieures'') on the Seine fault in
Normandy, he was always keen on French geology. As Chairman of the
Scientific Committee for the 6th edition of the geological map of
mainland France at 1:1,000,000 scale (published in 1996), he was eager
to include the most recent results and innovative concepts, along with
Jean Chantraine and the BRGM colleagues involved in the project.
Drawing on this \mbox{experience} and the knowledge he has acquired of
French geology, he produced an educational book \citep{Dercourt1997} in
which, following his guiding principle, he takes the reader on a search
for the oceans that have disappeared in mainland France and
\mbox{overseas}.

In their paper, entitled ``\textit{Insights on the Permian tuff beds
from the Saint-Affrique Basin (Massif Central, France): an integrated
geochemical and geochronological study}'', \citet{Poujoletal2023} study
several volcanic ash beds of this basin using an integrated
petrological, geochemical and geochronological approach. Their results
highlight the existence of two different groups of felsic
volcanoclastic rocks. Although the first cannot be dated due to the
absence of zircon, the second is of late Early Permian age
(Cisuralian), demonstrating that the sedimentary filling of the
Saint-Affrique Basin is younger than previously assumed.

In their paper, entitled ``\textit{The Br\'{e}cy depocenter as part of
a new reference late Variscan basin (northern Massif Central,
France)}'' \citet{BeccalettoBourquin2023} re-interpret 115~km of
seismic lines and several deep wells in this Carboniferous-Permian
basin covered by Mesozoic deposits in the SW Paris Basin. The geometry,
depositional environments and tectonic evolution of the Br\'{e}cy basin
are considerably updated compared with previous work. The alluvial to
lacustrine environments, characterising the sedimentary filling, show a
transgressive--regressive--transgressive pattern. The current geometry
of the Br\'{e}cy basin is controlled by several east-dipping normal
faults, some of which being connected to deep detachment levels active
during the late Carboniferous and Permian times.

After returning to Paris as a professor in the early 1980s, Jean
Dercourt, together with Eric Fourcade, set up a laboratory devoted to
Stratigraphy associating UPMC with the CNRS and the Museum national
d'Histoire Naturelle (MNHN). With this new team, they developed
integrated stratigraphy combining the most modern approaches of
sedimentology, (micro)paleontology, chemostratigraphy,
magnetostratigraphy, geochronology and the emerging sequential
stratigraphy. Their researches were focused on the Tethyan region, from
Turkey \citep{Fourcadeetal1991} to Spain \citep{Rasplusetal1997}. Their
results have provided an opportunity to decipher the traces of
geodynamic, oceanic or climatic events in the sedimentary series
\citep{Dercourtetal1986a},
in particular the oceanic anoxic events of the Mesozoic. The Toarcian
anoxic event that Jean Dercourt spotted in Greece was clarified
\citep{Baudinetal1988, Baudinetal1990}.

In their paper, entitled ``\textit{Molecular fossils of Aptian--Albian
blue marls of the Vocontian Basin (France), depositional conditions and
connections to the Tethys Ocean}'', \citet{Riboulleauetal2023} examine
the lipid biomarkers of six organic-rich levels of global or regional
extension and discuss their depositional controlling factors. This
study demonstrates that, in the Aptian--Albian succession from SE
France, organic-matter deposition resulted mostly from local factors
and that each level has its own peculiarities. Nevertheless,
connections with the Tethys Ocean were critical for the recording of
global oceanic anoxic events.

In their paper, entitled ``\textit{The contrasting origins of
glauconite in the shallow marine environment highlight this mineral as
a marker of paleoenvironmental conditions}'',
\citet{Tribovillardetal2023} challenge the paradigm of a constantly
slow formation of the authigenic mineral ``glauconite'' in outer shelf
domain. Comparing glauconites formed in contrasting environments from
the Jurassic and Cretaceous succession of Boulonnais (NW France), the
authors hypothesise that isolated oyster reefs harboured anoxic
micro-environments favouring the authigenic formation of glauconite in
shallow waters. These results support the idea that the ``glauconite
factory'' is not restricted to outer shelf but may also be formed in
very shallow areas of the shelf.

Jean Dercourt himself had never worked on the origin of Man, but he was
fascinated by the question. Several major waves of \textit{Homo
sapiens} migration from Africa to the Arabian Peninsula and the Levant
took place between 59,000 and 29,000 years ago, in the general glacial
context of Marine Isotope Stage~3 (MIS~3). However, the environmental
conditions at the origin of these migrations are poorly known, and the
scarcity of continental data covering this period has been interpreted
as reflecting arid conditions. This conclusion has been challenged, as
the intense aeolian deflation that occurred during the last glacial
maximum (20,000 years ago) could have destroyed or seriously damaged
lake or river sediments, which could have reflected humid climatic
conditions conducive to the migration of human populations. Another
difficulty in studying this period is the \mbox{methodological}
limitation of ${}^{14}\text{C}$ radiocarbon dating, which reaches its
limit of use around 50,000 years ago.

In their paper ``\textit{Data and models reveal humid environmental
conditions during MIS~3 in two of the world's largest deserts}'',
\citet{Lezineetal2023} compare 245 continental discrete records and 11
long-term continental and marine core records, dated using
${}^{14}\text{C}$, U/Th or luminescence methods. These data are
compared with results from the Institut Pierre-Simon Laplace (IPSL)
general circulation model to discuss hydrological changes between
59,000 and 29,000 years in Northern Tropical Africa, North Africa and
the Arabian Peninsula. Despite a general glacial context, wet
conditions were widely, creating numerous lakes, rivers and wetlands.
This study shows that humid conditions appeared much earlier and were
more prevalent in the Arabian Peninsula than in Africa, due to the
combination of monsoon rains in summer and Mediterranean rains in
winter.

This collection of articles, published as a tribute to Jean Dercourt,
includes many useful contributions, which I hope will be of interest to
readers. I would like to thank the colleagues who agreed to submit
these choice pieces to C.~R.~G\'{e}oscience---Sciences de la
Plan\`{e}te, and Fran\c{c}ois Chabaux for supporting and encouraging me
in my mission as guest editor of this special issue. Some of these
contributions were presented at conferences organised by the Academy of
Sciences and the French Geological Society on December 7th and 8th,
2021. Our warmest thanks go to Philippe Taquet, Patrick De Wever and
Jean-Paul Cadet, who organised the December 7th event. Special thanks
to Fran\c{c}oise Cadet for her careful proofreading of the English of
this editorial.\vspace*{-.4pc}

\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.

\vspace*{-.4pc}

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