Tephras in lacustrine sediments of the Sarliève marsh (French Massif Central): age and preservation

Abstract

The Sarliève marsh sediments (Massif Central, France) contain two tephras. The first tephra [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>13.7</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.4</mml:mn> <mml:mspace width="0.25em"/> <mml:mtext>ka</mml:mtext> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> <mml:mspace width="0.2em"/> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> , ca. 12 000 BP], regionally well known, enables to date the beginning of lacustrine infill to the Lateglacial. The second tephra, the ‘tephra de Sarliève’, the emitting volcano of which is unknown, would be dated to around the Early Subboreal from pollen data. This occurrence, after the discovery of the ‘tephra de Beaunit’, emphasizes that volcanic eruption(s) occurred in the ‘Chaîne des Puys’ or in the volcanic Cézallier more than 1000 years after the last known eruption (Pavin) in the ‘Chaîne des Puys’ at around 6.6/6.7 ka (5800/5900 BP). In the Sarliève piles, these tephras, well preserved in thick and more silicated deposits of deltas, were not observed in carbonated basin sediments where they were altered. The abundance of authigenic zeolites formed during the Lateglacial in restricted depocentre lacustrine waters allows us to detect initial CF1 tephra occurrence.