Page 14 - 15 New data on the Holocenic sea-level

136 F. Antonioli et al. / Global and Planetary Change 34 (2002) 121–140
In the coastal zone of the Capo San Vito Promon-
tory where submerged speleothems were sampled
(sector F), the post-Tyrrhenian average uplift rate
obtained on the base of the inner margin of the
Eutyrrhenian terrace (0.024 mm/year) is even smaller
than that calculated for the northern Castelluzzo Plain.
However, considering the age ranges obtained for the
speleothems, it introduces an error due to vertical
dislocation which is of the order of 0.18 –0.40 m,
respectively, for the speleothem located at À 0.3 and
À 1.3 m. Since the continental layers of the speleo-
thems just provide indication about the time before the
sea level rose (i.e. when it was not present yet) to the
level of the speleothems, these errors do not affect the
sea-level rise curve.
The limited vertical dislocation shown by the
Eutyrrhenian wave-carved notches at Marettimo (see
Section 3.2) suggests that errors for the neotectonic
mobility of the coastal tracts of the island should be
lower than the instrumental errors related to the
measurement of submerged speleothem depths and
than the analytical error related to U/Th radiocarbon
dating. The 1-m long speleothem sampled in the Punta
Martini Cape submerged cave shows the presence of
marine overgrowth of organic material encrusting the
continental inner portion of the speleothem, and this
makes it particularly suitable for the reconstruction of
the Holocenic sea-level rise. Both the marine and
continental layers have been radiometrically dated
(Table 2) and, following the methodology by Alessio
et al. (1992, 1998), the following considerations have
been derived. Samples 1007 and 1006 belong to two
different inner layers of the stalactitic core. The results sampled at the Capo San Vito Promontory and the
suggest that the continental growth of the speleothem
began around 40 ka BP and continued undisturbed
until about 24 ka ago (i.e. part of the isotopic stage 3),
a period during which the sea level was beyond the
depth of the speleothem. During the Holocene, the
carbonatic continental growth was abruptly interrup-
ted by the arrival of the sea to the speleothem level.
This stage is witnessed by the early colonization from
Lithophaga, which bored into the speleothem soon
after the marine submergence. The 14C AMS datings
on Lithophaga shells collected from the speleothem at
about À 24 m of depth mark at around 9 – 10 ka BP
the beginning of the marine encrusting deposition,
which continued by means of biobuilding organisms
(such as Serpulids) later on, to the present-day.
Fig. 11. Sea-level rise curve for the Holocene for Northwestern
Sicily. Tide gauge data are from recent IPCC estimations (global
data, 10 – 25 cm, in gray, and Mediterranean data 12 – 15 cm, in
black, from Tsimplis and Baker, 2000).
On the basis of the data obtained from Vermetid
reefs and submerged speleothems in Northwestern
Sicily, sea-level rise curves for the last 10 ka have
been reconstructed (Figs. 11 and 12), considering also
sea-level data averaged from tide-gauges for the last
century (Tsimplis and Baker, 2000). For the obtained
detail and for the very recent (in geological terms)
time range involved (last 500 years), especially the
younger part of the curve represents an interesting
result, although it has been based on a few dated
samples and should be supported by further sampling
and datings. Relative sea-level data on a similar time
range are reported by Laborel et al. (1994), which
dated biologically constructed marine rims from the
rocky coasts of southwestern France and northern
Corsica; but the two sets of data are not exactly
comparable (absolute ages reported by Laborel et al.
are uncalibrated 14C datings; moreover the data are
not supported by a check on the recent neotectonic
evolution of the studied coastal tracts).
Fig. 12 compares the sea-level rise data obtained
by Alessio et al., 1998 (based on marine overgrowths
and Litophaga shells on submerged speleothems from
Palinuro and Argentarola, Central Tyrrhenian Sea)
with the curve published by Bard et al., 1996 (based
on coral reefs from Tahiti) and with the results
obtained, in the present work, from the Vermetid reefs
speleothem from Marettimo cave.
Recently, the glacio-hydroisostatic theories and
modelling (Lambeck and Johnston, 1995; Peltier,