Imp.Colorti_Barca_Melis


87

1. INTRODUCTION

The new Sheet “557” Cagliari (CARG Project) pro-
duced a map of the Quaternary Syntems, however the
results of the new radiometric datings were not exhau-
stive and sometimes contradictory. The groups working
on continental and marine areas reached different con-
clusions on the chronology of the deposits: some coa-
stal deposits have been included in the subsynthem of
Cala Mosca (Tyrrhenian) although we should refer them
to the Holocene. However, the distribution of the
Tyrrhenian deposits was reduced and the Is Arenas
beach ridge grouped within the Holocene. We report
the elements supporting a Holocene age for the coastal
deposits. 

2. GEOLOGICAL SETTING

The Campidano is a Plio-Pleistocene NNW-SSE
oriented subsiding basin. Early Pliocene marine sedi-
ments crop out on the western side at Capo Frasca and
Capo S.Marco up to 50 m asl. Early Pliocene sediments
with Globorotalia margaritae, puncticulata and cras-
saformis have been found at depth in the Cagliari Gulf
(MURRU, 1983) and in the Oristano 1 and 2 boreholes (-
727 and -666 m respectively; (POMESANO-CHERCHI, 1971)
(Fig.1a). In the Oristano 1, these sediments are covered
with basalts, similar to those dated at 3 Ma in the Sinis
Peninsula. They are in turn overlaid by continental
deposits suggesting a great mobility of the Campidano.
Along the Cagliari coast, NNE-SSE normal faults, that in
the nearby Villacidro Sheet cut Late Pleistocene alluvial
fan deposits, drove the river network. 

3. LITHO-, MORPHO-, BIO- AND PEDO-STRATI-
GRAPHIC CHARACTERISTICS

The quaternary deposits have been subdivided
into the Late Pleistocene Porto Vesme Sinthem (PVM),
comprising the Cala Mosca (PVM1; “Tyrrhenian” Auct.)
and the Portoscuso Subsynthem (PVM2a), and the
Holocene Sinthem. The PVM2a consists of gravelly
alluvial fans, up to ca 10 m in thickness, that are trunca-
ted by marine cliffs and river incision. The top of the
Late Pleistocene Rio Corongiu terraced alluvial fan, to
the east of the Poetto beach, is preserved for ca 10 km
from the apical zone (205 m), to the rear of the coastline
(m. 28). Soil with well developed argillic horizons and

with profiles A-Bt-C, A-Btc-C and A-Btg-Cg (Typic,
Ultic e Aquic Paleoxeralf, APAT, 2005) are locally pre-
served. The argillic horizons in places overlie carbona-
te-rich horizons but the latter develop also on top of the
argillic horizons (A-Bt-Ck e A-Btk-Ckm, Calcic and
Petrocalcic Paleoxeralf). These are Early Holocene soils
because their degree of weathering is not comparable
with the Last Interglacial soils of the Apennines (COL-
TORTI & PIERUCCINI, 2005). The PVM1, crop out only at
Cala Mosca (Capo S.Elia), that is the type locality of the
“Tyrrhenian”, the penultimate high standing marine
stage (ISSEL, 1914; SPANO, 1980; ULZEGA et alii, 1982)
and at Marina Piccola (Fig.1a). A few decimetres of gra-
vels and bioclastic sands, including Strombus
bubonius, lay unconformably on a rocky marine
platform whose elevation varies from ca + 1 m to + 4 m
asl. They are sealed with over 7 m of debris and aeolian
sands. At Cala Mosca, these sediments are also found
inside a coastal cave with mussel boreholes up to 3.8
m asl.

The Holocene deposits that after the recommen-
dations of geologists dealing with the marine areas,
have been mapped as “Tyrrhenian” in age, crop out at
Sa Illetta and at Foxi (Fig. 2). At Sa Illetta sands and cal-
carenites constitute the remains of an inner beach ridge
up to ca. 1,5 m asl while at Foxi they crop out along the
beach. Molluscs are typical of coastal and lagoon envi-
ronments. Small colonies of Cladocora coespitosa in
living position are present in both sites.

Incised into the Pleistocene terraced deposits,
there is a Holocene alluvial gravelly terrace locally con-
taining polmonates and thin buried soil (A1C or A1Ck
profile). It is cut by a coastal cliff sealed with alluvial or
beach deposits. Nowadays, most rivers are bordered
by artificial levees but in the past they had a braided
pattern associated with a high solid load due to accele-
rated slope erosion. Laterally, they interlayer with allu-
vial fan deposits. Prior to this braided pattern, air-pho-
tos reveal that meanders occupied the plain. Close to
the coastline the Riu Corongiu create a small fan delta
whilst the Flumini Mannu generated cuspidate deltas
inside the S.Gilla lagoon. In the Quartu bay the rivers
enter the Molentargius swamp, originated by the Is
Arenas beach ridge made with even laminated sands
and gravels up to ca. 5 m asl,. Organic lagoon mud has
recently been dredged at a depth of 8 m. We recogni-
sed only present-day mollusc fauna but ULZEGA et alii
(1982) mention the presence of Strombus bubonius,
although it is possible that it was reworked from older
layers. 

STABLE OR MOBILE SEA-LEVEL, STABLE OR MOBILE SARDINIA DURING 
THE HOLOCENE: EVIDENCE FROM THE CAGLIARI GULF 

Mauro Coltorti 1, S. Barca 2, E. Melis 3
1 Dipartimento di Scienze della Terra, Via di Laterina, 8 53100 Siena –coltorti@unisi.it

2 Dipartimento di Scienze della Terra, Via Trentino, 51 - 09100 Cagliari
3 PROGEMISA S.p.A  Via Contivecchi, 7  - Cagliari



88

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89

4.  CHRONOSTRATIGRAPHIC  DATA

A new U/Th dating on Cladocora found in Cala
Mosca gave 122,11+5,3/-5,01 ka (EM-216-6375) but
the low isotopic 230Th/232Thratio suggests contamina-
tion. A date of 138 ± 8 ka was obtained by HEARTHY et
alii (1986) but the sample had a percentage of calcite
exceeding 9%. When calcite exceeds 5%, the
230Th/234Uratio or the 230Th/238Uratio ratio are not mea-
sured, samples have to be rejected (KAUFFMANN, 1986).
BELLUOMINI et alii (1986) utilising the isoleucine epimeri-
zation, report an age of over 250 ka. HEARTY et alii
(1986) utilises the ratio between Arca/Glicimeris, becau-
se the results from a single species are unreliable. The
Last Interglacial shells would have a ratio close to 1,31
but at Cala Mosca it varies between 1,37 (lower part)

and 0,86 (top). However, this method is unreliable
because the decaying ratio varies with the temperature
(MCCARROLL, 2002; WALKER, 2005).

The chronology of the PVM2a fluvial deposits is
based on a date of 34.810 + 2880/-2120 BP (AMS-
KIA24070) of organic material found 10 m below terra-
ced alluvial fan gravels at Samassi. The Holocene terra-
ced deposits have been dated at Sa Matta Manna.
Polmonate shells found in silty layers in the lower part
of the sequence gave 8.680 ± 60 BP (AMS, Beta-
150624). In the S.Lorenzo area and at S.Michele
Cemetery (Fig.1a) rolled fragments of pottery testify that
the incision occurred after the Early Neolithic. At Foxi
the whole rock dating of calcarenites gave 23.140 ± 90
BP (Beta-138678) while a U/Th of corals gave 53,3
+0,8/-0,7 ka (EM-130-6376). At Sa Illetta, a sample of

Fig. 2 - The seismic profile (A) located to the south of La Playa beach ridge (Fig.1) used by ORRÙ et al. (2004) to establish an unconfor-
mity between Holocene and Tyrrhenian deposits (B). Interlayering is evident in our interpretation (C).



90

shell was dated at 40.420 ± 1.120 BP (AMS, Beta-
138680) while the whole rock was 18.880 ± 50 BP
(AMS, Beta-138675). ULZEGA & HEARTHY (1986) also
obtained an unreliable U/Th dating of  Cladocora of 149
± 10 ka because stratigraphy, calcite content and isoto-
pic ratios are unknown. At Is Arenas a sample of shells
was dated at 26.740 ± 360 BP (AMS, Beta-138676).
Isoleucine epimerization allowed BELLUOMINI et alii
(1986) and HEARTHY et alii (1986) to attribute the depo-
sits to the Neo-Tyrrhenian. ULZEGA & HEARTHY (1986)
report corals, never published in a comprehensive way,
coming from the Poetto and La Playa beaches, dated
respectively at 6,5 and 7 ka. Holocene datings also
come from marine shells found in the clay filling in front
of the Cagliari port (ORRÙ et alii, 2004).

5. DISCUSSION AND CONCLUSIONS

Cala Mosca and Marina Piccola constitute the
older units cropping out below debris and aeolian
deposits (Fig.1b). Terraced Late Pleistocene alluvial
fans are the older deposits inland. Their incision was fil-
led with alluvial deposits later incised and filled with the
actual fluvial sediments. The latter unit shows a transi-
tion to coastal deposits subdivided into a number of
beach ridges and lagoon deposits similar to the Adriatic
(COLTORTI, 1997) and Tyrrhenian coasts (BOSCHIAN et al.,
2006). The reliability of radiometric dates of organic
matter and polmonates in Late Pleistocene and
Holocene alluvial deposits is confirmed by the rolled
pottery. The dating of the shell remains at Sa Illetta, Is
Arenas and Foxi is evidently unreliable. These are
Holocene beach ridges lying at the base of marine and
fluvial escarpments that affect the Late Pleistocene ter-
raced deposits (Fig.1b). Aeolian deposits or paleosoils
are absent. Shells found in lagoon deposits at + 6 m asl
at the Vascone site (Matzaccara, Carbonia Sheet) dated
to 36.220 ± 730 B.P. (Beta-138698) but at the same
layer with a few pieces of rolled pottery confirm a syste-
matic error for these Holocene deposits. The older ages
of the shells could be due to the hard water effect or
diagenetic processes. Also the marine deposits of
Santa Reparata (Fig.1a), attributed to Last Interglacial
with isoleucine epimerization (ULZEGA & HEARTHY, 1986),
are Holocene in age. In fact, they overlie (and not
underlie) aeolian deposits that in the nearby Cala
Spinosa contain polmonate shells dated to 20.010 ± 60
BP (AMS; Beta 138687). The Sa Illetta and Is Arenas
beach ridges were attributed to the “Tyrrhenian” also
because, following an eustatic model, a series of deep
narrow valleys would have cut the “Tyrrhenian” depo-
sits during the Last Glaciation. However, a deposition
dominated by climatic processes follows an eventual
erosion as a consequence of sea level fall (PLINT et al.,
1992) and seismic profiles demonstrated a strong sedi-
mentation before 18 ka down to the shelf break (LECCA
et alii, 1998). In particular Is Arenas beach ridge com-
pletely dams the valley and if it is Tyrrhenian in age, no
later erosion and limited sedimentation occurred in the
basin. The erosional valleys that in the model of PECORI-
NI (1986) and ORRÙ et alii (2004) were carved during the
cold period in our idea were modelled during the Late
Glacial/Early Holocene, after the reduction of the solid
load resulting from reforestation while the sea level was

still low. This is confirmed by the Holocene age of the
valley filling and by the interlayering visible in our re-
interpretation of the Orrù’s seismic profile (Fig. 2).
Barrier beaches are the result of long-shore drifting of
river sediments after Neolithic soil erosion. 

The high elevations of the Sa Illetta and Is Arenas
coastal deposits was also used to support a
“Tyrrhenian age because Holocene storm deposits are
not expected above 4 m asl (ISSEL, 1914; ULZEGA et alii,
1982). However, elevation must not aprioristically repre-
sent a proof. If elevation and not stratigraphy should be
the criteria, new discoveries are impossible.
Stratigraphy suggests that the Holocene sea-level rose
higher than the present day and/or that some parts of
Sardinia are affected by positive tectonic movements.
Sardegna is considered a stable region but the geologi-
cal setting and the faults cutting the Late Pleistocene
deposits suggest otherwise. The “Tyrrhenian” tidal not-
ches in the Orosei Gulf (CAROBENE & PASINI (1973) also
demonstrated differential uplift. Moreover, if the dating
of Cladocora found at the sea level and dated ca 7 ka
at La Playa and Poetto (ULZEGA & HEARTHY (1986) are
reliable they confirm a higher sea level during the Early
Holocene or tectonic movements. In fact, today
Cladocora grow between 4 and 10 m bsl. If the
Holocene sea level never exceeded the present day
one (LAMBECK et alii, 2004) the Cagliari area is affected
by uplift. However, it is our opinion that the curve of the
Holocene sea level rise is still far from resolved.

ACKNOWLEDGEMENTS

The work is the result of the CARG Project Sheet
557, Cagliari, Legge 305/89, Convenzione APAT -
Serv.Geol.D’It. - Regione Autonoma Sardegna. We
thank the Progemisa for the continued logistic and
technical support.

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