Abstract. Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunisia) traces the climatic and environmental dynamics in the lower arid bioclimatic zone over the last 8000 years. During the Mid- to Late Holocene transition, between 8 and 3 ka, a succession of five wet/dry oscillations is recorded. An intense arid event occurs between 5.7 and 4.6 ka. This episode marks the onset of a long-term aridification trend with a progressive retreat of Mediterranean woody xerophytic vegetation and of grass steppes. It ends with the establishment of pre-desert ecosystems around 3 ka. The millennial-scale climate change recorded in the data from Sebkha Boujmel is consistent with records from the south and east Mediterranean, as well as with climatic records from the desert region for the end of the African Humid Period (AHP). Eight centennial climatic events are recorded at Sebkha Boujmel and these are contemporary with those recorded in the Mediterranean and in the Sahara. They indicate a clear coupling between the southern Mediterranean and the Sahara before 3 ka. The event at 4.2 ka is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic Cooling events is clearer from 3 ka onwards. These variations indicate the importance of climatic determinism in the structuring of landscapes, with the establishment of the arid climatic conditions of the Late Holocene. It is only from 3 ka onwards that the dynamic of plant associations is modified by both human activity and climatic variability. The climatic episodes identified during the historic period indicate strong regionalisation related to the differential impact of the North Atlantic Oscillation (NAO) and the Mediterranean Oscillation (MO) on the Mediterranean basin. The local human impact on regional ecosystems is recorded in the form of episodes of intensification of pastoral and/or agricultural activities. The development of olive production and of several taxa associated with agriculture attest to increasing sedentism among human populations during Classical Antiquity. The significant increase in Artemisia (wormwood) between 1.1 and 0.8 ka (850–1150 AD) is linked to intensive pastoral activity, associated with heightened interannual and/or seasonal climatic instability. A complete re-shaping of the landscape is recorded during the 20th century. The remarkable expansion of the olive tree, and the deterioration of regional ecosystems with the spread of desert species, is linked to recent local socio-economic changes in Tunisia.

The objectives were to retrace the eolian and fluvial terrigenous supplies in a sediment core from the Sicilian-Tunisian Strait by coupling mineralogical, grain-size and geochemical approaches, in order to get informations on the atmospheric versus riverine contributions to sedimentation on the southern side of central Mediterranean since the last glacial. The eolian supply is dominant over the whole interval, excepted during the sapropel S1 when riverine contribution apparently became significant, and particles provenance has been modified since Last Glacial. Saharan contribution increased during the Bølling-Allerød, evidencing the persistence of aridity over North Africa although the northern Mediterranean already experienced moister and warmer conditions. The Younger Dryas is marked by proximal dust inputs highlighting intense regional eolian activity. A southward migration of dust provenance toward Sahel occurred at the onset of the Holocene, likely resulting from a southward position of the Inter Tropical Convergence Zone, probably associated with a large-scale atmospheric reorganization. Finally, a peculiar high terrigenous flux associated with drastic modifications of the mineralogical and geochemical sediment signature occurred during the sapropel S1, suggesting the propagation of fine-particles derived from major floodings of the Nile River – resulting from enhanced rainfall on northeastern Africa – and their transportation across the Sicilian-Tunisian Strait by intermediate water-masses

Major ophiolitic thrust sheets are widespread within the internal Hellenides, particularly in the Pelagonian domain (Greece and Albania). The ophiolitic sheets are notably well exposed in western Othris mountains of continental Greece. In that area, the structural stacking of oceanic nappes obducted in the Jurassic is particularly well constrained. New sedimentological and structural data from recently studied outcrops, together with new micro-paleontological data, allow to reconsider the architecture of the ophiolitic nappes and their evolution in the Othris mountains. Our new data set includes notably the description of a Mid-Late Jurassic sedimentary succession, from basal litharenites and radiolarites to syn-obduction mélange, on top of the uppermost Mega Isoma ophiolitic Unit. These results are crucial in the perspective of constraining the Jurassic contractional evolution of the Maliac Ocean from the beginning of the subduction and intra-oceanic obduction to the final obduction on the Pelagonian continental crust. Another major result concerns the dating of primary conformable series of Middle and Late Triassic age on top of the pillow-lavas of the Fourka unit. Since this lava unit, with MORB affinities, is one of the syn-obduction Jurassic nappes, we propose that this very large Fourka nappe represents the major reference unit of the initial (Triassic) Maliac oceanic crust.

Glauconite is an authigenic mineral reputed to form during long-lasting contact between a nucleus (a pre-existing phyllosilicate) and seawater. This protracted contact makes it possible to subtract the ions necessary for the construction of the neoformed phyllosilicate, here, glauconite (a mineral very close to an illite, rich in K and Fe). As a result, glauconite is often associated with sediments deposited in a transgressive context with a strong slowdown in the rate of sedimentation and a relatively large water layer thickness. This is the case of the Cenomanian chalk of Boulonnais (north of France). Being chemically and physically resistant, glauconite is a mineral that is often reworked, like quartz grains. This is frequently the case of the Jurassic deposits of the Boulonnais, where glauconite, almost ubiquitous, either in traces or in significant proportions of the sediments, presents a grain size sorting attesting to its transport and reworking. However, these Jurassic deposits are shallow (shoreface, upper offshore), which supports the idea that the "glauconite factory" was itself in the shallow areas of the Boulonnais. The only identified Jurassic facies of the Boulonnais where glauconite is both relatively abundant, large in size and unsorted (non reworked) are oyster reefs that formed at the outlet of cold seeps linked to a late-Jurassic synsedimentary tectonic (Kimmeridgian, Tithonian). Our work makes it possible to hypothesize that isolated oyster reefs were environments combining the redox conditions and in contact with seawater favoring the authigenic formation of glauconite. The weakly reducing conditions necessary for the formation of glauconite here are attested by the contents of metallic trace elements sensitive to redox conditions (vanadium, germanium, arsenic, in this case). Our work thus adds a new element to the understanding of the mechanisms of formation of glauconite in shallow environments.

Le maar d'Alleret (Massif central, France) contient une séquence lacustre couvrant les stades isotopiques marins (SIM) 17 à 15. La partie étudiée, comprise entre 40,5 et 24,25 m de profondeur, enregistre la présence de téphras du Mont Dore (phase Sancy) qui permettent d'établir une téphrochronologie à partir de datations 40 Ar/ 39 Ar laser comprises entre 683 ± 5 et 718 ± 6 ka. Les analyses géochimiques et minéralogiques de ces téphras montrent une mésostase vitreuse à composition trachytique à rhyolitique. Des analyses sédimentologiques (granulométrie laser, susceptibilité magnétique, carbone et azote total) permettent de proposer une reconstitution des dynamiques morphosédimentaires et de comprendre la géodynamique externe dans le bassin versant pendant la phase lacustre. Une étude palynologique complète cette étude et apporte des informations sur la dynamique de la végétation autour du maar. Dans la partie inférieure de la séquence, le développement successif de forêts riparienne, caducifoliée, puis montagnarde est caractéristique d'un interglaciaire, attribué au SIM 17. Cet interglaciaire est suivi par une phase glaciaire corrélée au stade SIM 16. Le début de cette période glaciaire montre dans la séquence d'Alleret une grande variabilité cyclique, avec la présence de trois cycles stade/interstade. La comparaison avec les données paléoenvironnementales issues de forages glaciels, marins et continentaux montrent une bonne adéquation avec le cadre chronostratigraphique de cette partie de la séquence d'Alleret et confirme le remarquable intérêt des maars du Massif central comme enregistreurs des variations climatiques et environnementales en milieu continental au cours du Quaternaire.