Calcareous tufa as indicators of climatic variability: a case study from southern Tuscany (Italy) - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 269

Giraudi's reconstruction with the available data of
the aggradational/erosional phases of the Valdelsa
terraced sequence it is possible to appreciate the
correspondence of events (Fig. 8).
In particular, radiometric data obtained from the
CAL Synthem show that this depositional phase
can be readily related to the high lake-level stage
connected with the 1st terrace of Mezzano Lake
and the oldest terrace recognized in the Vico Lake.
The radiometric data from the FOC Synthem corre-
lates with the 2nd terrace of the Mezzano Lake and
the youngest terrace of the Vico Lake. The same
high lake-level event has been recognized in the
Accesa Lake (southern Tuscany) (Fig. 1a) where a
coeval rapid rise of the water table is attested by a
remarkable peak of Chara oogonia production
(Magny et al. 2006). The age obtained for the BEL
Synthem coincides with the high lake-level stage
recognized in the Fucino Lake and assumed in the
Mezzano Lake.
Even though the ABB, the POG Synthems, and
all the interposed erosive stages lack actual dating,
the correspondence between the succession of
events reconstructed in Central Italy by Giraudi
(2004) and those recognized in Valdelsa Basin
enables the correlation of the two sequences.
Consequently the erosional phase between CAL
and FOC Synthems can be correlated with the low
lake-level at about 17-20 ka BP of the Mezzano,
Vico and Fucino lakes (Giraudi 1989).
The FOC-BEL erosional phase appears to be
coeval with the fall of the lake-level recorded in the
three Central Apennine lakes about 10-12 ka BP.
The BEL-POG transition represents the last
major erosional phase recognized in the Valdelsa
Basin. The correlation between this erosive stage
and the low lake-level recognized in the Mezzano
and Fucino lakes at c. 4 ka BP is likely. A coeval
depositional phase at about 4,000 years BP (uncal.
14 C age) has been also recognized in the low-stand
limestones of Accesa Lake by Magny et al.
(2006). The last POG Synthem comprises the most
recent alluvial deposits of the area. Unfortunately,
no data are available for the oldest Valdelsa
Synthem (ABB) and the associated erosional
phase (ABB-CAL).

around high-temperature springs are considered
good indicators of extensional tectonic activity.
The strict relationship between travertine deposition
and faulting, recently recognized and termed 'Travi-
tonics' (Hancock et al. 1999), suggests that the age of
travertine can be taken as a proxy for the age of fault-
ing (Altunel 2005; Hancock et al. 1999). A similar
tectonic control has been recognized in the Hungar-
ian Danube area where several orders of terraces
made of travertine have been interpreted as succes-
sive river incisions resulting from the combined
uplift of theHungarianMountainRange and periodic
climate changes (Ruszkiczay-R¨diger et al. 2005).
The assumed tectonic activity in the Valdelsa
Valley could be related to the extensional tectonic
movements affecting Southern Tuscany since the
Early-Middle Miocene (Bossio et al. 1995a; Car-
mignani et al. 1994). The tectonic evolution of the
Pliocene-Quaternary basins in Southern Tuscany
and in the Valdelsa Basin itself, appears to be
mostly controlled by a rapid regional uplift (Dall-
meyer & Liotta 1998) triggered by a widespread,
mainly intrusive Middle Pliocene magmatism
(Brogi et al. 2005b).
The laminated carbonates, even if finally would
be demonstrated to be caused by thermal waters,
seem to be very limited and not sufficient to
explain a significant tectonic control on the local
fluvial deposition. In fact, the physical and geochem-
ical features of the present day active low tempera-
ture springs suggest that the superficial aquifer is
fed by waters coming from the 'Calcare cavernoso'
reservoir (Casagli et al. 1990; Barazzuoli et al.
2002). The slight thermalism of the springs can be
easily related to the local geothermal gradient,
which is about 57 8C/km (Del Chicca et al. 1988).
Moreover, during the Late Pleistocene-
Holocene there are only minor evidences of tectonic
activity in this area (Capezzuoli & Sandrelli 2006)
and in other areas of Tuscany (Boccaletti et al.
1999). Certainly the Late Pleistocene-Holocene
tectonic activity seems to be less significant than
the Middle-Late Pleistocene movements of uplift
that resulted in the rearrangement of the Arno
Basin drainage, recognized by Bartolini & Pranzini
(1981). This latter uplift phase has been recognized
as a major event that changed an area of rather low
relief into the Northern Apennine mountain chain
(Bartolini 2003).

Tectonic involvement

The presence of travertine-like facies in the basal
part of the calcareous sequences exposed in the
proximal part of the Valdelsa terraces suggests an
alternative interpretation to climate being the domi-
nant control on the genesis of continental carbonates
in this area. In fact, according to some authors
(Altunel & Hancock 1993a, b; Hancock et al.
1999; Atabey 2002; Brogi et al. 2005a; Brogi &
Capezzuoli 2008),

Depositional/erosional phases and late
Quaternary climatic events: a tentative
correlation

Assuming that the Valdelsa carbonate deposition
was mainly controlled by climate, a tentative corre-
lation between the depositional/erosional Valdelsa travertine bodies deposited