Lake Pavin History, geology, biogeochemistry, and sedimentology of a deep meromictic maar lake

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sites. The tephra is distributed in vast lobes: (1) the southern
lobe is oriented southwards and it was delimited at La
Godivelle by Bourdier ( 1980 ). The identifi cation of the
tephra layer in lakes and peat bogs outside that lobe has
enabled its known distribution to be extended at least as far
as the Planèze de Saint-Flour (Cantal), where the tephra bed
is still 2 cm thick; (2) the northern lobe of the tephra was
only identifi ed by thin tephra beds in two peat bogs and one
lake as far as the Gour de Tazenat in the northernmost part of
the Chaîne des Puys. For both lobes, the tephra materials cor-
respond to Plinian fall-out deposits.

A. Southern lobe

Tephra occurrences were described in the vicinity of the

volcano by Bourdier ( 1980 ) and in distal lacustro-palustrine

sites by Juvigné and Gilot ( 1986 ). Juvenile magma is repre-

sented by highly vesiculated pumice clasts which are essen-

tially yellowish in dry terrains, but light grey in peat bogs.

Their size reaches 20 cm across on the edge of the volcano,

and decreases to ash size towards the western and southern

margins of the lobe, while centimetre-thick lapilli are still

present in the easternmost peat bogs. The trend is similar for

Fig. 8.2 Tephra age model after investigation of cores taken from peatbogs and lakes of the Massif Central (after Juvigné 1991 , p. 166, Fig. 1,
updated). T = recognized tephra; S = sandy layer (detrital or tephra; see below)

8 Distribution, Tephro- and Chronostratigraphy of the Widespread Products of Pavin Volcano