14 4
(Fig. 8.2 ). Altogether, 10 distinct tephras were found in
stratigraphic positions distributed from the Late Glacial
(Allerǿd) through the mid-Holocene (Atlantic) (Juvigné
1992a ). The tephras of the volcanoes Montcineyre-
Estivadoux- Montchal- Pavin (MEMP group hereafter) are
part of them: Juvigné and Gilot ( 1986 ), Juvigné et al. ( 1986 ,
1988b , 1994 ), Etlicher et al. ( 1987 ), Gewelt and Juvigné
( 1988 ), Juvigné ( 1992b , 1993 ), Juvigné and Bastin ( 1995a ,
1996 ), Juvigné and Stach- Czerniak ( 1998 ). The application
of^14 C-dating method on samples from several sites has
allowed Juvigné and Gillot ( 1986 ) to show that the series of
eruptions have occurred within a time range of about fi ve
centuries around 6000 B.P. (we use the standard notation
B.P. for non-calibrated^14 C dates).
8.2 Description of Tephras from MEMP
Volcanoes
The current paper focuses on the tephras of the MEMP vol-
canoes, and more specifi cally on the Pavin tephra. Bourdier
( 1980 ) realized petrographic and geochemical analyses of
these tephras and he produced a map of the distribution of
relevant lobes based on outcrops in road-sides and various
excavations (Fig. 8.3a ). Later on, the investigation of the
cores taken from lake and peat-bogs (see above) has enabled
maps of each lobe to be extended (Fig. 8.3b ) since millimetre-
thick tephra beds can be easily identifi ed in lacustro-
palustrine sediments where they have not been disturbed nor
altered by pedological processes.8.2.1 Pavin TephraVarious activities during the eruptive phases were described
by Bourdier ( 1980 ) and later refi ned by Boivin et al. ( 2010 )
and Leyrit et al. ( 2016 ). Base surges linked to phreatomag-
matic explosions have accumulated products in the vicinity
of the volcano, while Plinian activity was responsible for the
widespread distribution of pumice. Due to the high amount
of pale grey to yellowish pumices, a tephra bed is easily rec-
ognizable to the naked eye up to tens of kilometres far from
the volcano as decimetre- to millimetre-thick beds in dark
organic material of peat bogs and lakes. The spatial distribu-
tion of pumices in the tephra beds in peat bogs is strongly
asymmetrical due to fl oating and drift on lacustrine areas at
the time of the ash-fall, so that the ratio ‘pumices/(miner-
als + lithics)’ does not confi rm with normal patterns in suchFig. 8.1 The evolution of the Late Glacial to Holocene tephrostratigraphical model in the Massif Central (After Gewelt and Juvigné 1988 , p.26,
Fig. 1)
E. Juvigné and D. Miallier