Jean-François Pastre

Identification and dating of tephra layers from Quaternary sedimentary sequences of Inner Anatolia, Turkey

Abstract Results presented here are part of a research programme to investigate the environmental evolution in central Anatolia during the Pleistocene. In this study, tephra are used as chronostratigraphical markers between lacustrine sequences studied in cores or in sections surrounding eruptive centres of the Central Anatolian Province. At different locations in the Konya Plain and Cappadocia, tephra have been identified, characterized and linked to eruptions of the nearby volcanoes. Seven different tephra have been clearly identified in lacustrine sequences of the Konya Plain. 14 C dates on shells or organic matter, as well as 230 Th / 234 U ages on gypsum, give a chronological framework to the tephra layers. In addition, the study of the sediment fill of the Eski Acigol maar near Nevsehir has allowed the recognition of several eruptions during Late Glacial and Holocene in the vicinity of Acigol. The results show the first tephra to be identified in lacustrine sequences of Anatolia; they also show the Cappadocian volcanism to be very young (≤35 ka). This young volcanism is often of a basaltic type and does not include thick differenciated pyroclastic deposits.

River system evolution and environmental changes during the Lateglacial in the Paris Basin (France).

Abstract Lateglacial sequences from the Paris Basin floodplains provide a general overview of the valleys evolution related to climatic changes from the Weichselian Upper Pleniglacial to the beginning of the Holocene. Comparison between morphostratigraphical and palaeobiological data allows discussion of fluvial dynamics and related palaeoenvironmental conditions. The Upper Pleniglacial/Oldest Dryas transition remains poorly documented. It is represented by sands and silts deposited by a braided channel network. The Bolling begins with a significant incision related to a meandering system which is followed by local organic and minerogenic deposition, contemporaneous with vegetation development. The Older Dryas is evident in several sequences. The Allerod appears more stable and the forest extension is accompanied by a thin soil formation on the banks. The Younger Dryas is characterised by a strong infilling of the valleys by calcareous silts. This last sharp event precedes a second major downcutting phase which takes place in the early Postglacial and is followed by a decline in river flow and sediment supply. This evolution reflects a broad regional pattern of fluvial response which illustrates its sensitivity to climatic change. The study of various morphosedimentary contexts shows their influence on the fluvio-dynamic record and bio-proxies which complicates the detection of minor phases.

A 36,000-Year-Old Volcanic Eruption Depicted in the Chauvet-Pont d'Arc Cave (Ardèche, France)?

Among the paintings and engravings found in the Chauvet-Pont d’Arc cave (Ardèche, France), several peculiar spray-shape signs have been previously described in the Megaloceros Gallery. Here we document the occurrence of strombolian volcanic activity located 35 km northwest of the cave, and visible from the hills above the cave entrance. The volcanic eruptions were dated, using 40Ar/39Ar, between 29 ± 10 ka and 35 ± 8 ka (2σ), which overlaps with the 14C AMS and thermoluminescence ages of the first Aurignacian occupations of the cave in the Megaloceros Gallery. Our work provides the first evidence of an intense volcanic activity between 40 and 30 ka in the Bas-Vivarais region, and it is very likely that Humans living in the Ardèche river area witnessed one or several eruptions. We propose that the spray-shape signs found in the Chauvet-Pont d’Arc cave could be the oldest known depiction of a volcanic eruption, predating by more than 34 ka the description by Pliny the Younger of the Vesuvius eruption (AD 79) and by 28 ka the Çatalhöyük mural discovered in central Turkey.

Évolution morphostructurale du plateau volcano-sédimentaire de Gergovie au Miocène inférieur : implications géodynamiques sur la phase tardi-tectonique du rift de Limagne (Massif central, France)

The Gergovie plateau is a Lower Miocene topographically inverted volcano-sedimentary system located in the monogenetic volcanic field of the Limagne rift Tertiary basin. It is composed of three east–west aligned maars partly covered by a basaltic lava flow. The eruption of the central maar (maar 1) occurred at the Oligocene–Miocene transition, during the first volcanic phase. This phreatomagmatic structure was almost totally cut through by the opening of a second maar (maar 2) during the next eruptive phase. The basaltic lava flow at the summit and the eastern maar (maar 3) were placed during a third and last eruptive phase during the Middle or Upper Burdigalian (∼19–16 Ma). Between these periods of volcanism, three fluvial to fluviolacustrine sedimentation episodes, separated by two erosive stages, followed one another. A bedrock thickness of 100–300 m was eroded from maar 2 during the upper Aquitanian and (or) the lower Burdigalian (∼22–19 Ma). This erosion is partly due to a volcano-tectonic uplift in ...