Volume 18 - Numéro 2 - 2007
Q5 Le Quaternaire, Limites et spécificités - Deuxième Partie
Colloque organisé par le cnf-INQUA et l'AFEQ,
Muséum national d'Histoire Naturelle de Paris ( 1-3 Février 2006)

Brigitte VAN VLIET-LANOË 
Le prélude au Quaternaire : les modalités d'entrée en glaciaition (65 Ma - 2,2 Ma). 111-128.
The dawn of Quaternary: cause of the entrance in the Ice Age (65 Ma-2.2 Ma)

RÉSUMÉ :  Le Cénozoïque enregistre une englaciation croissante par étapes, d’abord dans l’hémisphère sud puis, depuis le début du Néogène, dans l’hémisphère nord. Cette évolution est en relation surtout avec le rifting et la tectonique des plaques qui ouvrent ou ferment des détroits. La création de reliefs de collision ou de reliefs de décharge isostatique par érosion crustale ou superficielle, après le Crétacé, favorise l’englaciation. L’extension du plancher océanique et le stockage croissant de glace amènent une baisse eustatique importante. Les modifications des circulations océaniques et atmosphériques, que les reliefs entraînent, accentuent le refroidissement par le biais de la consommation du CO2 atmosphérique. La Terre passe d’un régime d’englaciation unipolaire à un régime bipolaire à partir du Néogène, d’une circulation océanique zonale à la circulation thermohaline que nous connaissons aujourd’hui. À partir de 3 Ma, en relation avec la configuration particulière des océans et des continents, le régime glaciaire est mondial, contrôlé préférentiellement par l’intensité de l’insolation, avec également un retour de la convergence intertropicale en position équatoriale. L’augmentation de l’aridité a influencé la biodiversité et la production de poussières. À la veille du Pléistocène, l’ère glaciaire est largement commencée : l’Antarctique passe par un maximum d’englacement au Miocène alors qu’il faut attendre le Pliocène pour voir de vraies calottes s’installer dans l’hémisphère nord.

ABRIDGED ENGLISH VERSION: The Cainozoic era records a step-like glacierization, first on the southern hemisphere and since the onset of Neogene on the northern hemisphere. This evolution is linked to the rifting and to plate tectonic that opened or closed several straits. Since the Cretaceous, the creation of collisional or isostatic deloading reliefs thanks to underplating or superficial erosion favoured the glacierization. Sea floor spreading and ice storage induced an important sea-level drop. Modifications of the marine and atmospheric circulations induced by the new-born reliefs intensified the cooling trend. The Earth shifted from an unipolar glaciation to a bipolar one from the Neogene, from a zonal oceanic circulation to the present thermohaline circulation throughout CO2 consumption. From 3 Ma, in relation with the land masses and oceans configuration, the glacierization is global with a strong control by insolation strength, and an equatorial positioning of the Intertropical convergence zone (ITCZ). The increasing aridity influenced the biodiversity and dust production at least since the Oligocene. At the onset of the Pleistocene, the glacierization is mostly completed : the Antarctic ice maximum occurred during the Miocene, although true ice sheets only developed from the Pliocene in the northern hemisphere



Jean-Philip BRUGAL & Roman CROITOR
Evolution, ecology and biochronology of herbivore associations in Europe during the last 3 million years. 129-152
Évolution, écologie et biochronologie des associations d'herbivores en Europe sur les 3 derniers millions d'années.

ABSTRACT:   A study of the evolution of the herbivore community during the last three million years in Europe is proposed in this paper. The study includes the analysis of evolutionary changes of systematic and ecological structure (taxa diversity, body mass, diet specializations) related both with eco-physiological and environmental factors. Several biochronological phases can be envisioned. The most drastic change in the herbivore community structure coincides with the onset of the global glacial/interglacial cycle. It marks the emergence of the zoogeographical Palearctic region in Northern Eurasia that may be correlated with the base of Gelasian (2.6 Ma) and indicates the beginning of the Quaternary. This period (considered as an era/erathem) is specific in terms of the recurrent, relatively cyclic, faunal turnover. The two following stages of faunal evolution mark a beginning and the end of complex continuous changes in the taxonomic and structural composition of the herbivore associations that resulted in a dominance of large-sized ruminant herbivores of modern type. They are mostly opportunistic mixed-feeders and grazers that can endure a high content of cellulose in forage. Quaternary herbivore associations in Western Europe demonstrate a high ecological polyvalence and adaptive tolerance to a broad variation of environmental and climatic conditions

RÉSUMÉ: L’analyse de l’évolution des communautés d’herbivores européens est proposée pour les trois derniers millions d’années sur la base de la diversité, de la composition taxonomique et sur les structures écologiques (taille corporelle et stratégies alimentaires), mis en relation avec des facteurs éco-physiologiques et environnementaux. Plusieurs phases biochronologiques sont reconnues. Le plus important changement de structure des communautés d’herbivores coïncide avec l’installation au niveau global des cycles glaciaires/interglaciaires. Il est synchrone de l’émergence d’une nouvelle région paléarctique dans le Nord de l’Eurasie, corrélé à la base du Gélasien (2,6 Ma) qui indiquerait alors le début du Quaternaire. Cette période (considérée comme une ère) montre la spécificité de changement faunique régulier et relativement cyclique. Les étapes suivantes indiquent des renouvellements dans la structure et la composition des associations d’herbivores résultant dans la dominance d’espèces de grande taille de type moderne. Ce sont essentiellement des brouteurs et des ‘mangeur-mixtes’ qui tolèrent de grosses quantités de cellulose dans leur alimentation. Les associations d’herbivores du Quaternaire ouest-européen se caractérisent par une grande polyvalence écologique et une souplesse adaptative aux modifications importantes des environnements et des climats.


Vincent LEBRETON, Anne-Sophie LARTIGOT, Elena KARATSORI, Erwan MESSAGER, Laurent MARQUER & Josette RENAULT-MISKOVSKY
Potentiels et limites de l'analyse pollinique de spéléothèmes quaternaires : applications à la reconstitution de l'environnement végétal de l'Homme préhistorique sur le pourtour Nord-Méditerranéen.  153-174
Potentials and limits of pollen analysis on Quaternary spelothems: an attempt to reconstruct the vegetal environment of prehistoric human in the Northern Mediterranean.

RÉSUMÉ :   En contexte archéologique, l’analyse pollinique de spéléothèmes offre l’opportunité de caractériser la composition de l’environnement végétal de l’Homme préhistorique. L’évaluation des processus taphonomiques affectant la pluie pollinique lors du dépôt dans la calcite souligne les limites et les potentiels de ce type de support. Les résultats obtenus sur des sites préhistoriques du pourtour nord-méditerranéen sont confrontés et corrélés à l’ensemble de l’information paléoécologique livrée par les données multidisciplinaires. Ces études palynologiques tentent aussi d’estimer la distribution spatiale des écosystèmes végétaux, la composante locale étant souvent la plus significative. Quand la formation des spéléothèmes coïncide avec des niveaux archéologiques, l’environnement local de l’Homme préhistorique peut être précisé.

ABSTRACT: Pollen analysis on speleothems carry out detailed vegetal environment data in archaeological context. Pollen rain recorded in calcite is subject to a variety of taphonomic processes, pointing out limits and potentials of pollen analyses on speleothems. These records are evaluated in the light of multidisciplinary palaeoecological information from Northern Mediterranean prehistoric settlements. A main contribution of local vegetation with regard to spatial distribution of the different vegetal ecosystems is observed. When speleothem growths and archaeological layer deposits are synchronous, local environment of the prehistoric populations can be accurately documented.

Jean-Jacques BAHAIN, Christophe FALGUÈRES, Pierre VOINCHET, Matthieu DUVAL, Jean-Michel DOLO, Jackie DESPRIÉE, Tristan GARCIA & Hélène TISSOUX
Electron Spin resonance (ESR) dating of some European Late Lower Pleistocene sites. 175-186
Datation par résonance de spin électronique (ESR) de quelques sites pléistocène inférieur d'Europe. 

ABSTRACT: InWestern Europe, most of the oldest prehistoric sites (ranging from 2 Ma to 500 ka) are associated with clastic or carbonated karstic environments. Here, the electron spin resonance (ESR) dating method is often the only one method permitting to place these localities in the global Quaternary framework, which is mainly based on marine isotopic data and palaeomagnetical record. ESR can be applied on different materials frequently recovered in archaeological sites such as tooth enamel, quartz grains or carbonates. In this paper, we present the results, which have been obtained for more than ten years on different archaeological sites of the late Lower Pleistocene or the early Middle Pleistocene, which are crucial for the understanding of the first human settlements of Europe: Pont-de-Lavaud and Grâce-Autoroute (France), Atapuerca Gran Dolina (Spain), Monte Poggiolo and Isernia La Pineta (Italy). Wherever possible, the ESR results were compared with those of independent dating methods, including 39Ar/40Ar, palaeomagnetism and biostratigraphy. In some cases, the ESR method applied on bleached quartz extracted from fluvial sediments and the ESR/U-series method on tooth enamel were the only available methods to provide geochronological data


 RÉSUMÉ : En Europe occidentale, la plupart des sites préhistoriques les plus anciens (compris entre 2 millions d’années et 500 000 ans) se trouvent en contexte détritique ou carbonaté karstique. Dans de tels cas, la méthode de datation par résonance de spin électronique (ESR) est souvent la seule
méthode géochronologique permettant de replacer ces gisements dans le cadre chronologique du Quaternaire établi notamment à partir des données isotopiques marines et du paléomagnétisme. Cette méthode a également pour avantage d’être applicable sur plusieurs types de supports que l’on retrouve fréquemment sur les sites préhistoriques : émail dentaire, grains de quartz ou carbonates. Nous présentons dans ce travail les résultats obtenus depuis une dizaine d’années sur des sites préhistoriques de la fin du Pléistocène inférieur ou du début du Pléistocène moyen, sites importants pour la compréhension des premiers peuplements de l’Europe : Pont-de-Lavaud et Grâce-Autoroute (France), Atapuerca Gran Dolina (Espagne), Monte Poggiolo et Isernia La Pineta (Italie). Chaque fois que cela était possible, les résultats ESR ont été comparés avec ceux obtenus par des méthodes indépendantes, comme le paléomagnétisme, la biostratigraphie ou la méthode 39Ar/40Ar mais, dans certains cas, les méthodes ESR sur grains de quartz extraits de sédiments fluviatiles et ESR/U-Th sur émail dentaire se sont révélées comme les seules méthodes utilisables pour fournir des points de repère chronologiques.


Hervé CUBIZOLLE, Pierre BONNEL Christine OBERLIN, Arnaud TOURMAN & Jérôme PORTERET
Advantages and limits of radiocarbon dating applied to peat inception during the end of the Lateglacial and the Holocene: the example of mires in the Eastern Massif Central (France). 187-208
Intérêts et limites de la datation par le radiocarbone pour le calage chronologique de l'apparition des tourbières à la fin du Tardiglaciaire et au début de l'Holocène : l'exemple du démarrage de la turfigenèse dans le Massif Central oriental (France).

ABSTRACT: The origins of mires and the initiation of peat inception during the last 12 000 years has been widely interpreted in terms of macroclimatic change or land-use changes associated with human activities. One objective of our palaeoenvironnemental studies in the eastern Massif Central in France was to accurately date basal peat layers at a great number of sites. These radiocarbon dates of peat inception must then be confronted with palaeocological and archaeological data. Although radiocarbon dating is currently used to date peat initiation, various difficulties can be encountered when attempting to identify and sample the oldest basal layers in amire, and these problems are rarely addressed. This paper proposes amethodology based on detailed investigation
by means of stratigraphical, sedimentological and micromorphological analyses. Five mires were studied: 3 bogs, and 2 fens. As a main result we illustrated the great importance of micromorphological analysis. We also show that many radiocarbon dates are required to obtain accurate age estimations of the chronology of peat inception, precise enough to be confronted with other palaeoenvironmental data.

RÉSUMÉ  : L’apparition des tourbières au cours des 12000 dernières années est révélatrice de changements environnementaux importants, tant d’origine climatique que d’origine anthropique. Aussi, est-il fondamental, dans le but d’une reconstitution paléoenvironnementale, de pouvoir caler chronologiquement le démarrage de la turfigenèse sur un grand nombre de sites. La répartition dans le temps des dates obtenues peut ensuite être confrontée aux données géomorphologiques, paléoécologiques et archéologiques locales et régionales pour tenter de retracer l’évolution des paysages et des sociétés humaines qui les ont façonnés. Néanmoins, si la datation par le radiocarbone est l’outil le plus adapté au travail de calage chronologique des couches basales des tourbières, l’entreprise est complexe et pose un certain nombre de problèmes méthodologiques très rarement abordés dans la bibliographie. Une première difficulté est d’identifier le faciès qui, sur la stratigraphie, matérialise le démarrage de la turfigenèse. Il convient ensuite de déterminer le ou les secteurs de la tourbière où la tourbe a commencé à s’accumuler. Cet article propose une méthode d’échantillonnage des couches basales de tourbe fondée sur un travail minutieux de restitution des stratigraphies couplé à des analyses sédimentologiques et à des examens micromorphologiques. Cinq sites pilotes ont été retenus: trois tourbières bombées et deux tourbières basses. Parmi les résultats notables de l’étude, on insistera sur l’apport de l’analyse micromorphologique. Par ailleurs, le grand nombre de datations par le radiocarbone qui ont été réalisées a permis d’apprécier la précision que l’on est en droit d’attendre d’un tel travail de calage chronologique, une information déterminante avant d’entreprendre la confrontation avec les autres données paléoenvironnementales

Marie Pierre QUESSADA & Pierre CLÉMENT
Le quaternaire dans l'enseignement secondaire français : sa disparition aujourd'hui à la lumière des enjeux socioculturels de son introduction au 19ÈME siècle. 209-214
The Quaternary in French secondary school: its disappearance today in light of the sociocultural stakes of its introduction during the 19TH century.

ABRIDGED ENGLISH VERSION: The Quaternary is disappearing from French syllabi. The current Earth and Life Sciences curriculum for the French seventh grade (pupils from 13 to 14 years old) includes the example “of the paleogeographic and climatic changes of the Quaternary Era.” Historical Geology will disappear completely from the future seventh grade syllabus. From 1994 to 2001, in the twelfth grade science track class (pupils from 17 to 18 years old), the teaching proposed “to reconstruct the paleo-environments in which the human line evolved during the Quaternary”. It was replaced in 2001 by a topic entitled “From the geological past to the future evolution of the planet,” in which the past planetary climates are studied. We are currently witnessing an upheaval in the conceptions presented in French secondary school programs. Since 1966, with the reintroduction of the teaching of Human Evolution in the twelfth grade, the study of the Quaternary has been linked to the study of human origins. This corresponds with what we will call the quaternarist anthropocentric conception. Today, education is oriented toward what we will call an environmentalist conception, centred on climatic studies.
Following the model of Bachelard (1938), our didactic approach includes both an epistemological and a historical approach. By comparing the conceptions in secondary school curricula with scientists’ conceptions, it is possible to develop hypotheses to explain the dynamics of the didactic transposition of knowledge. We have shown in a work based on the teaching of Human Evolution during the 19th and 20th centuries (Quessada & Clément, 2006), that the syllabi changes follow the changes in scientific references. However, the delay in the transposition of these changes is heavily influenced by the values promoted by the academic institution as well as by the socio-political issues of the day. Using a similar approach, we will attempt to identify the values associated with teaching the Quaternary. Given the previous research, we have chosen to focus the current study on the 19th century, during which the Quaternary was introduced into the curricula.
From 1814 to 1864, before the introduction of the Quaternary to the curricula, the teaching of Historical Geology develops following catastrophist and creationist conceptions, even though a full blown scientific controversy is raging at the time. The actualist and evolutionist conceptions are not transferred to secondary education. Neither the Quaternary nor quaternaryman is included even though the term Quarternary is defined by the geologist Jules Desnoyers in 1829 and the concept of the Pleistocene is established in 1839 by the English geologist Charles Lyell.
This directed transposition can be explained by both the scientific and political influence of Cuvier as well as by the educational system’s objectives and the socio-political context of the time. This quote from Victor Cousin,Minister of State Education in 1840 testifies: “it (the teaching of Natural History) generates, so to speak, a natural theology which shows to pupils the hand of Divine Providence, impressed everywhere in the design of this world and the organization of the beings which live in it. Thus presented, the teaching of Natural History will leave deep marks on the intelligence and even in the soul of pupils”.
From 1865 to 1912, we witness the entry of the Quaternary and prehistoric man into the syllabi with a progressive movement towards evolutionary actualist ideas. The programs of 1912 represent a breaking point with the abandonment of the teaching of Human Evolution in the twelfth grade, followed by the disappearance of the term Quaternary from middle school education. The introduction of the Quaternary in secondary education during the second half of the 19th century is certainly related to scientific advances. The division of time is refined with the introduction of the Holocene in 1867 by Paul Gervais. After the 1856 discovery of Neanderthal man, the idea of quaternary man is accepted by the scientific community. The transfer to the syllabi is rapid however, which may be explained by the socio-cultural context of the moment: developments in education; popularisation of scientific knowledge, notably with respect to prehistoric man, inciting immense interest; and the importance of humanistic values associated with those of progress and faith in science.We can also link this change in the syllabi with the project to secularise republican schools. At this time, Edmond Perrier, zoologist and evolutionist wrote in Buisson’s pedagogical dictionary (1882): “Natural history … has fought in close combat with ancient philosophies, doing away with old legends one by one, and is now preparing for its toughest battle yet, the most profound revolution ever achieved in the philosophical, political and religious orders”. The struggle for the secularisation of thought relies heavily on a scientific approach to the origins of man, reinforced by the temporal framework of a specific geological era: the Quaternary.
We have demonstrated the relationship between the rapid introduction of the Quaternary Period into 19th century curricula and the socio-political context of the times. How then is the contemporary socio-political situation related to the disappearance of the Quaternary from the most recent curricula?
We must consider the debates and current issues occurring within the quarternarist community (Gradstein & Ogg, 2004). The geological time scale is not the expression of strict, general rules of nomenclature but rather the juxtaposition of periods presenting different tools of dating, the legacy of Historical Geology’s complex history (Odin G.S et al., 2005). The inclusion or exclusion of the Quaternary period in or from stratigraphic charts depends on the recognition of a major geological event at the end of the Cenozoic. The rank of the Quaternary within the geological time scale is partly related to the acceptance or denial by the scientific community of the emergence of the genus Homo as a major event. G.S. Odin’s daring proposal during the conference “Le quaternaire, limites et spécificités” in February 2006 to divide Geological time into three major periods (a time without the biosphere; a time when the biosphere is present and its evolution is related to nonhuman factors; and an anthropozoic time, corresponding to the Quaternary, where mankind’s influence dominates the biosphere) would have the advantage of epistemological clarity. The risk of such an approach, however, is that it may appear anthropocentric. But by attempting to avoid this finalistic, anthropocentric trap, don’t we risk falling into the trap of denying the singularity of the human species and its impact on the rest of the biosphere?
The disappearance of the quaternaristic, anthropocentric conception from French curricula is almost simultaneous with the questioning of the existence of the Quaternary by the authorities of the international commission of stratigraphy. The delay in the transposition is therefore extremely short. In this case, the struggle against didactic obsolescence, one of the rules of didactic transposition, cannot be the only explanation for the curricula modifications. Other explanatory hypotheses must be sought which take into account the values which the educational system seeks to promote. Since the mid-20th century, global conflicts and ecological catastrophes have modified the conception of man and science that was in effect at the end of the 19th century. Humankind may now be perceived negatively, as a threat to the planet. Consequently, the curricula have been refocused on the study of the planet, incorporating the objectives of Environmental Education for sustainable development presented in national and international publications. Moreover, the beginning of the 21st century has seen a renewal of spiritualistic tendencies, refuting Darwinism to the benefit of finalistic theses. Human evolution could disappear from middle school education to avoid creationist reactions from students and their families.
The current trends in curricula dealing with teaching the Quaternary correspond both to new scientific references and to new values within not only the educational system but also on the wider scale of the current socio-political context (alarmist media coverage of climatic changes, a resurgence of spiritualism, the struggle against creationism and finalism, the decline of humanism). Rather than erasing the Quaternary from the syllabi, shouldn’t we use it as an example of the dynamic nature of scientific knowledge construction and the relationships between science and values? By avoiding a dogmatic approach to science, this proposal would promote the development of students’ critical skills.