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Clinopyroxene rim geochemistry: A tephrochronological proxy in maar-lake sediments of the Eifel, Germany

Frederik Krebsbach, Roman Botcharnikov, Regina Mertz-Kraus, Stephan Buhre, Frank Sirocko

Abstract

Geochemical differences in clinopyroxene rims are utilised as potential differentiators of volcanic eruptions in the Eifel, Germany. This provides the possibility of geochemical tie-points for the tephrochronology of the Eifel Laminated Sediment Archive, i.e. the ELSA-23 chronology and tephra stack. In maar lake sediments of the Eifel with seasonal oxic and anoxic bottom water, volcanic glass fragments are prone to weathering and therefore not always found in sufficient quantities in the lake sediments. To deal with the lack of volcanic glass, we used clinopyroxenes, which are more weathering resistant and present in larger amounts in Eifel eruptions. Only the rims of these clinopyroxenes were analysed, because they represent a geochemical fingerprint closely related to the final magmatic composition prior to the eruption. A total of 13 potential marker tephra of the Eifel Laminated Sediment Archive were analysed with EPMA and LA-ICP-MS. Five of these marker tephra can be uniquely characterised by the geochemistry of clinopyroxene rims. Accordingly, geochemical analysis of clinopyroxene rims represents a promising tool for differentiating tephra and for creating robust stratigraphical tie-points across different archives such as lake sediments and loess, which will be a subject of future studies.