2018-03-15-NAC-Jelgersma-Bsc
Abstract Montagne Noire, part of the southern Massif Central in France, is the border between two climate types and therefore, it has always been subject to major and minor changes in temperature, rainfall and vegetation. This study aims to reconstruct the local paleoclimate of southern France by using a multi-proxy approach based on mineralogical (X-ray diffraction), geochemical (stable isotopes: C, O, H) and microscopic (scanning electron, petrographic and colour) analyses in a speleothem from Mélagues, located on the northern side of Montagne Noire. Temperature, rainfall and vegetation changes over time in the Mélagues region have been studied using the stable isotopic composition recorded in the speleothem. Although no dating of this speleothem is available yet, this study also examined possible relations with other regions and climate oscillations. Microscopic analyses of thin sections together with XRD analyses allowed us to determine the morphology, texture and mineralogy of the speleothem, which is composed of a mixture of magnesium calcite (∼70%), dolomite (∼25%, possibly formed through diagenetic processes) and a very low content of quartz (∼5%). Partial dissolution (∼5%) of the speleothem led to small voids (<40 µm) that were subsequently (partially) refilled by bacteria and microorganisms. Four columnar fabrics (compact, open, elongated and spherulitic) are observable in the studied speleothem, along with micrite, microsparite and mosaic fabrics. All these fabrics reflect (post-)depositional and environmental changes. The average temperature (∼14.8 °C) and vegetation (C3 plants) during deposition resemble the present-day temperature (14.8 ± 0.9 °C) and vegetation around our study site. Relatively high average 18O values (-4.38‰, 1σ ≈ 0.37) and relatively low average 13C values (-9.36‰, 1σ ≈ 0.55) of the stalagmite led us to interpret that the stalagmite was mainly deposited in a relatively warm and dry period, while seasonal precipitation from the Mediterranean Sea dominates the record.
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