THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 51
GEOLOGICA CARPATHICA, 55, 1, BRATISLAVA, FEBRUARY 2004
STRATIGRAPHY OF THE MIOCENE SYN-RIFT VOLCANO-
SEDIMENTARY SUCCESSION IN A SECTOR OF THE
CENTRAL-SOUTHERN SARDINIA TROUGH ( ITALY)
, MICHELE MATTIOLI
, FRANCISCO SERRANO
and GIULIANA RAFFAELLI
Institute of Geology, University of Urbino, Campus Scientifico Loc. Crocicchia, 61029 Urbino, Italy; email@example.com
Institute of Volcanology and Geochemistry, University of Urbino, Campus Scientifico Loc. Crocicchia, 61029 Urbino, Italy;
Department of Geology, University of Malaga, Campus de Teatinos s/n, 29071 Malaga, Spain; firstname.lastname@example.org
Institute of Geodynamics and Sedimentology, University of Urbino, Campus Scientifico Loc. Crocicchia, 61029 Urbino, Italy;
*Corresponding author: Francesco Guerrera, Istituto di Geologia, Università di Urbino, Campus Scientifico, Località Crocicchia,
61029 Urbino, Italy; email@example.com
(Manuscript received September 23, 2002; accepted in revised form June 23, 2003)
Abstract: The Miocene sedimentation in the Sardinia Trough has been controlled by tectonic activity, also respon-
sible for strong, basic-intermediate and silicic calc-alkaline volcanism. The volcano-sedimentary succession cropping
out near the Villanovaforru village (Marmilla Basin, central-southern Sardinia Trough) is the object of this study.
The succession has been subdivided into nine new stratigraphic intervals and it is characterized by abundant volcaniclastic
materials. In the lower part of the succession some basaltic pillow lavas are interbedded. The nine stratigraphic intervals
extend from Early Burdigalian (Zone N5 and N6) to Late Burdigalian (Zone N7) and the microfossil assemblages indi-
cate hemipelagic sedimentation. A deepening of the basin seems to occur in correspondence to the beginning of the
volcanic activity. The reconstructed stratigraphic succession of the Villanovaforru area, which is considered representa-
tive of the Early Miocene sedimentation within the southern sector of the Marmilla Basin, shows that a transition from
a continental to a marine environment occurred during the Sardinia Trough rifting and the drift of the Sardinia-Corsica
Block. The extensional tectonics is also confirmed by the high-Mg composition of the basaltic lava flows interbedded in
Key words: Burdigalian, Sardinia-Corsica Block, lithostratigraphy, biostratigraphy, extensional tectonics, syn-tectonic
deposition, volcano-sedimentary succession, Sardinia Trough.
Introduction, geological setting and objectives
The study of Sardinian geology is an important tool to recon-
struct the stratigraphic, tectonic and magmatic events, which
occurred during the Neogene geodynamic evolution of the
Western Mediterranean area. Between the Late Oligocene and
the Early Miocene, rifting of the European Margin caused the
opening of the oceanic Algero-Provençal Basin (cf. Gattacce-
ca 2001 and references therein) and the connected Apennine
deformation. Normal faulting also affected the area corre-
sponding to the present day Western Sardinia (Cherchi &
Montadert 1984; Assorgia et al. 1997a) and originated a NS-
striking depression, up to 200 km in length, named the Sar-
dinia Trough (Vardabasso 1963; Fig. 1). The coexistence be-
tween the extension occurring in the Sardinia Trough and
the compression originated by the drift and counterclockwise
rotation of the Sardinia-Corsica Block towards the east, sug-
gests a strong genetic link between the extensional deforma-
tion (internal areas) and the compressional one (external ar-
eas), which may be related to a N-NW subduction
(Carmignani et al. 1995). The extensional tectonics caused the
development of many sub-parallel basins and ridges, bounded
by normal faults and cut by transversal minor tectonic features
(Oggiano et al. 1995). These tectonic basins are usually asym-
metric in shape and they are related to master faults (in the
eastern margin) and antithetic faults (in the western margin).
However, during the extensional deformation, some compres-
sional events have been recorded by some unconformities and
hiatus within the sedimentary successions; compressional
mesostructures such as joints, faults, pebbles with stylolitic
striae and gentle folds have also originated. In its southern
sector the Sardinia Trough has been overprinted by a minor
extensional Pliocene-Pleistocene NW-SE trending structure
(the Campidano Graben, Fig. 1).
The Early Miocene rifting originating the Sardinia
Trough involved the whole of Central-Western Sardinia,
causing a deep paleogeographical change. Several authors
proposed interesting geodynamic and paleogeographical
models (Coulon 1977; Cherchi & Montadert 1982; Guerrera
et al. 1993; Maillard & Mauffret 1993; Carmignani et al.
1995; Vigliotti & Langenheim 1995; Assorgia et al. 1997b;
Gattacceca 2001), but little attention has been given to the
collection of detailed stratigraphic data, which are of high im-
portance to calibrate the different events. The sedimentation
within the Sardinia Trough ranges from a fluvio-lacustrine
to a marine environment, with abundant volcaniclastic inter-
vals and it shows a marked facies variability which does not
allow easy lithostratigraphic correlations. Therefore the de-
52 GUERRERA et al.
Fig. 1. Geological sketch of Sardinia (after Cherchi & Montadert 1984; modified) (A); schematic geological map of the Villanovaforru
area (B). Asterisc (
) indicates the location of the studied stratigraphic section.
THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 53
tailed integrated stratigraphic analysis represents the most use-
ful correlation method; the study and correlation of the strati-
graphic successions may give important information about the
development of the Sardinia Trough since the Early Mi-
In this paper we give a detailed stratigraphic characteriza-
tion of the volcano-sedimentary succession cropping out in
the Villanovaforru area (Fig. 1), which can be considered rep-
resentative of the most important depositional area of the
southern sector of the Sardinia Trough known as the
Marmilla Basin (Fig. 2). The reconstructed stratigraphic col-
umn (ca. 650 m thick, Fig. 3) provides detailed information
about the different volcanic and sedimentary processes.
The Miocene sedimentation in the different depositional ar-
eas of the Sardinia Trough was strongly influenced by con-
temporaneous tectonic activity, which was also associated
with a wide calc-alkaline basic to acid volcanism (Cherchi &
Montadert 1982; Cherchi 1985; Assorgia et al. 1997b, and ref-
erences therein) as testified by the widespread volcanic and
volcanogenic materials interbedded within the sedimentary
successions. The complex Neogene geodynamic evolution of
Western Sardinia is outlined by different sedimentary cycles,
which are separated by unconformity surfaces and by coeval
widespread volcanic events (Assorgia et al. 1997b). These au-
thors recognized four main sedimentary cycles: a Lower Oli-
goceneMiddle-Upper Burdigalian cycle; an Upper Burdiga-
lianMiddle-Upper Serravallian cycle; an Upper Serravallian
Lower Messinian cycle; a Pliocene cycle. During marine sed-
imentation, two main Cenozoic volcanic events (Oligocene-
Miocene and Pliocene-Pleistocene) are also recognizable
(Assorgia et al. 1997b). The oldest one is calc-alkaline in na-
ture and it may be further subdivided into four minor events:
1 Lower Basic-Intermediate Lavic Series (LBLS): Oli-
gocene (33/2823 Ma);
2 Lower Acid-Intermediate Explosive Series (LAES):
Aquitanian (2320 Ma);
3 Upper Basic-Intermediate Lavic Series (UBLS): Burdi-
galian (1916 Ma);
4 Upper Acid-Intermediate Explosive Series (UAES):
Upper Burdigalian-Serravallian pro parte (1713 Ma).
The studied Burdigalian Villanovaforru volcano-sedimenta-
ry succession can be referred to the oldest sedimentary cycle
defined by Assorgia et al. (1997b). This succession contains
abundant volcaniclastic materials and primary lava flows
which can be related to the UBLS defined by the same au-
Owing to its complex tectonic evolution, the sedimentation
in the Sardinia Trough results in a marked lateral and verti-
cal lithofacies variability and it does not allow an easy correla-
tion of the geological events, also at the scale of the single mi-
nor basin. A good example of this variability is represented by
the Burdigalian stratigraphic evolution of the Lugodoro Ba-
sin (northern part of the Sardinia Trough; Funedda et al.
2000), which is completely different from that of the coeval
Marmilla Basin (central-southern Sardinia Trough).
According to previous authors the stratigraphic succession
of the Marmilla Basin is characterized by the following,
mostly partially heteropic, formations: Ussana Formation,
Ales Marls, Gesturi Sandstones, Isili Limestones and
Marmilla Formation. (Fig. 2). The stratigraphic units recog-
nized in the Marmilla Basin and their stratigraphic relation-
ships are here briefly described.
The marine transgressive cycle, including the studied Vill-
anovaforru volcano-sedimentary succession, overlies the up-
Fig. 2. Stratigraphic relationships of the main sedimentary units of the Marmilla Basin in the central-southern Sardinia Trough
(from Cherchi 1985; Assorgia et al. 1997b). Sedimentary environments: Ussana Formation, continental to littoral; Gesturi Sandstones,
shallow-water marine deposits; Isili Limestones, carbonate platform; Ales Marls and Marmilla Formation, littoral to pelagic.
54 GUERRERA et al.
per Oligocene-Aquitanian Ussana Formation (Pecorini &
Pomesano Cherchi 1969). This formation is constituted by
clastic deposits (ruditic and reddish silty-arenitic beds) with
varying thickness, indicating upward a transition from a conti-
nental (fan and alluvial plain system) to a marine littoral envi-
ronment (Cherchi 1985; Assorgia et al. 1997b). The Gesturi
Sandstones, which represent the first shallow marine sandy
deposition, unconformably lie above the Ussana Formation.
They are heteropic with the Isili Limestones, which represent a
carbonate platform unit laterally grading also into the Ales
Marls. The Marmilla Formation overlies the Ales Marls but it
can also rest directly above the Ussana Formation and the
Gesturi Sandstones. All the described formations are consid-
ered the result of a syn-rift deposition by Cherchi (1985). In
the adjacent sectors of the Sardinia Trough other units are
comprised within the same cycle (Assorgia et al. 1997b). In
the marine succession volcanic (primary) products and more
frequently volcanogenic (secondary) materials are locally in-
terbedded in different stratigraphic intervals.
A stratigraphic log (about 650 m thick) of the volcano-sedi-
mentary succession cropping out SW of Villanovaforru vil-
lage (Figs. 1 and 3) has been reconstructed. According to lit-
erature in this area the succession consists of the following
stratigraphic units (from the base): a) uppermost part of the
Ussana Formation auctorum, cropping out at the base of the
reconstructed log; b) the heteropic Gesturi Sandstones (auct.)
and Ales Marls auct., lying above the Ussana Formation in the
lower part of the log; c) the Marmilla Formation auct., charac-
terizing the middle-upper part of the log. However, the bound-
aries among these formations are not well recognizable in the
measured section. It has been possible to recognize only the
top of the Ussana Formation, which has been observed in a lit-
tle outcrop below the marine succession (Figs. 1 and 3) and
probably a part of the Ales Marls, in the lower part of the
same. In this way, the studied stratigraphic interval represents
a characteristic sedimentation that corresponds to the literature
formations. Moreover, the Marmilla Basin depositional
style was also strongly influenced by contemporaneous explo-
sive and effusive volcanism during the UBLS of Assorgia et
al. (1997b); the high abundance of the related volcanogenic
materials contributes to the origin of a variety of facies which
are not easily correlable with those of the other formations rec-
ognized in the surrounding areas. Nevertheless, it cannot be
excluded that some stratigraphic intervals, especially those
characterized by evident marker beds, could be recognized in
all of the other sectors of the Marmilla Basin. In this case,
they can represent an important tool to understand the evolu-
tion of the whole Sardinia Trough depositional system.
The Villanovaforru succession has been analysed from the
lithostratigraphic, sedimentological and biostratigraphic
points of view. Although it is not possible to arrange the dif-
ferent lithofacies according to the stratigraphic units defined in
literature, the outcrop-scale observations allow us to distin-
guish some intervals which may be referred as local members,
whose lateral extension is still to be verified. This subdivision
is particularly useful because of the peculiar characters of the
different lithofacies assemblages and, especially, because the
unit boundaries recorded in the literature are not recognizable
in the field for the examined succession.
The volcano-sedimentary succession of the Villanovaforru
area widely crops out along the road linking the SS N. 131
Carlo Felice to Villanovaforru village (Fig. 1). The study of
this succession allowed us to reconstruct a stratigraphic sec-
tion about 650 m thick. The succession shows a constant geo-
metrical setting with layers uniformely dipping towards the
north-east; however, the presence of several often syn-sedi-
mentary faults which have been recognized in the surround-
ing areas (e.g. Collinas village; Cipollari & Cosentino 1997)
and the covered intervals does not allow us to exclude the
presence of faults. On the other hand, some minor faults have
been pointed out as shown in Fig. 3. In spite of this, the bios-
tratigraphic results testify to a continuous sedimentation and
this leads us to consider as not remarkable the possible faults
affecting the studied stratigraphic section.
The studied Villanovaforru succession (Fig. 3) is made up
of generally well-layered lithofacies with dominant medium-
to coarse-grained volcanogenic sandstones and subordinate
silicified marls with highly variable amounts of volcanic ma-
terial (Figs. 4 and 5). Marls, calcareous marls, siltstones and
marly limestones also occur, always with various amounts of
volcanic material and often with abundant foraminifers. Sub-
ordinate microconglomerates are also present in the middle-
upper part of the succession. Occasionally, thin volcaniclastic
beds such as bentonitic, diatomaceous-tripolaceous and
ochraceous layers occur, whereas some intervals are charac-
terized by high concentrations of vegetable and bivalve re-
mains forming characteristic beds. Subacqueous basaltic lava
flows have also been recognized in the middle-lower part of
the succession, already defined as high-Mg basalts with
tholeiitic affinity by Mattioli et al. (2000).
The dominant volcaniclastic sandstones consist of three
lithofacies corresponding to distinct depositional and/or erup-
Lithofacies A, represented by medium- to thick-bedded (20
to 50 cm thick) lithic-rich volcanogenic sandstones with fine-
to coarse-grained laminae (5 to 10 mm thick). This lithofacies
contains dense volcanic lithic grains of pilotaxitic basalt and
porphyric andesite, angular to subangular crystal fragments of
plagioclase and subordinate amphibole, clinopyroxene and
pumice. Grain-size ranges from 0.2 to 10 mm. Lithofacies A
is framework-supported and matrix-poor.
Lithofacies B, consists of thin bedded (5 to 20 cm) vitric-
rich volcanogenic sandstones with parallel lamination (2 to
10 mm thick) and subordinate undulose bedding. Its frame-
work composition is made up by comparable proportions of
vitric shards and basaltic-andesitic lithic grains and minor
amounts of euhedral plagioclase, pyroxene, amphibole and
biotite crystals. The vitric component includes pumice frag-
ments and glass shards. Grain size ranges from 0.1 to 2 mm.
Lithofacies C, consists of distinctive darker layers of crys-
tal-rich volcanogenic sandstones (4 to 15 cm thick) with par-
allel lamination well-defined by biotite flakes and grain size
variations. Grain-size ranges from coarse to fine sand, from
the bottom to the top, up to laminated and yellow-grey silt-
stones. This lithofacies contains very abundant framework
grains of plagioclase, clinopyroxene and amphibole crystals,
THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 55
Fig. 3. Stratigraphy of the volcano-sedimentary succession of the Villanovaforru area showing the nine identified lithostratigraphic in-
tervals (roman numbers), collected samples and chronostratigraphy. See text for further details about petrographic features of the volca-
niclastic sandstones. 1 Sandy and conglomeratic deposits of continental and transitional environment (Ussana Formation); 2a marls
with varying amounts of volcaniclastic materials and subordinate foraminifer-rich beds; 2b silicified marls; 3a microconglomer-
ates; 3b coarse-grained sandstones; 3c fine-grained sandstones and rare siltstones with volcaniclastic material; 3d thin volcanic
epiclastic layers; 3e reddish sandstone level; 4a marly limestones and silicified calcareous marls; 4b silicified limestones;
5 partially silicified marls containing thin volcaniclastic siltstones and sandstones; 6 thin fine- and medium-grained sandstones
(rarely coarse-grained) with interbedded bentonitic layers; 7 interval with basaltic pillow lavas; 8 diatomaceous-tripolaceous lev-
els; 9 bentonitic levels; 10 ochraceous levels; 11 layers with vegetable remnants and small bivalves; 12 discontinuous/un-
dulating bedding; 13 faults; 14 vegetable remnants; 15 bivalves; 16 unexposed; 17 partially exposed; 18 deepening;
56 GUERRERA et al.
THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 57
with lesser amounts of pumice, lithic grains of pilotaxitic and
scoriaceous basalt, andesite and trachyte.
On the basis of lithostratigraphy and petrographic charac-
ters nine peculiar intervals (Fig. 3) have been recognized
within the volcano-sedimentary succession of the Vill-
anovaforru area. However, preliminary field observations car-
ried out in different areas of the central-southern sector of the
Sardinia Trough suggest that the recognized intervals
should still be regarded as local members which may be con-
nected to vertical facies evolutions.
A summary of the nine stratigraphic intervals features is re-
ported in Table 1. It is worth noting that all the intervals are
characterized by a variable amount of volcanogenic materials.
In particular, volcanogenic marls with subordinate lithic-rich
volcanogenic sandstones characterize Interval I, whereas si-
licified marls with crystal-rich volcanogenic sandstones and
marly limestones are the main lithotypes of Intervals II, V
and VII. Interval III corresponds to the only primary volca-
nics (prevailing basaltic pillow lavas) recognized in this area.
The Intervals IV, VI and IX are characterized mainly by vit-
ric-rich volcanogenic sandstones with minor amount of marly
limestones and bentonites. Lithic-rich volcanogenic sand-
stones and microconclomerates with silicified marls are the
prevailing lithotypes of Interval XIII.
VVS with subordinate bentonites
LVS and microconglomerate with silicified marls
silicified calcareous marls with CVS
marls with subordinate limestones and VVS
silicified and calcareous marls with CVS
VVS with marly limestones
primary volcanics (prevailing basaltic pillow lavas)
silicified marls with CVS and marly limestones
volcanogenic marls with subordinate LVS
LVS lithic-rich volcanogenic sandstones; VVS vitric-rich volcano-genic
sandstones; CVS crystal-rich volcanogenic sandstones
New biostratigraphic data from the lower part of the Vill-
anovaforru succession indicate an age comparable to that
pointed out in the same area for the Marmilla Formation
(Sardara-Villanovaforru succession of Iaccarino et al.
1984). However, the different scale of observations does not
allow us detailed litho- and biostratigraphic correlations be-
tween our reconstructed succession and the stratigraphic sec-
tion of these authors, which also appears to be highly simpli-
fied. As an example, Iaccarino et al. (1984) describe the
Sardara-Villanovaforru succession as only constituted by
marls with interbedded tuffitic layers.
Starting from the base of the studied succession (lower lev-
els of Interval I, sample A1; Fig. 3), the planktonic foramin-
iferal assemblages (Table 2) containing Globigerinoides altia-
perturus Bolli and Globigerinoides trilobus (Reus), are
evidence that they belong to N5 Zone (Blow 1969) or to a
younger interval. Among the samples from these basal levels,
there are no other components that might provide greater bios-
tratigraphic precision, except for the presence of Globigerina
venezuelana Hedberg. This species does not seem to exist be-
yond the top of N6 Zone, although some authors extended its
presence up to considerably higher levels (Kennett & Srini-
vasan 1983; Bolli & Saunders 1985). Also noteworthy is the
absence of Globigerinoides subquadratus Brönnimann and of
Globorotalia praescitula Blow in these levels, which could
indicate that they were deposited before the levels in which
they currently appear, close to the base of N6 Zone. The ab-
sence of typical specimens of Catapsydrax dissimilis (Cush-
man et Bermúdez) is noteworthy, though we have observed
examples of a morphology similar to C. dissimilis or Catapsy-
drax unicavus Bolli, Loeblich et Tappan in which bulla
have not developed. This component is frequently encoun-
tered in the hemipelagic marine deposits of the lower Miocene
prior to N7 Zone. Iaccarino et al. (1984) have also noted this
fact, suggesting that the absence of Catapsydrax may be due
to the shallowness of the environment. However, the compo-
sition of the microfauna seems to indicate there is sufficient
depth for C. dissimilis to develop, at least in most of the sec-
At higher levels (Intervals I to V) the succession still con-
tains very similar assemblages of planktonic foraminifers.
Noteworthy among the differences here is the appearance of
isolated specimens of Globigerina tripartita Koch (sample
A5), some atypical specimens of C. unicavus (samples A18,
A21 and A22) and Globigerinoides with three chambers in
the final whorl and a single dorsal aperture (samples A6 to
A24), which could be considered transition forms between G.
altiaperturus and G. subquadratus (in Table 2 these are re-
ferred to as cf. G. subquadratus).
At the highest levels of Interval V (samples A25 and
A25bis) typical specimens of G. subquadratus appear. The
first appearance datum (FAD) of G. subquadratus seems to be
close to that of Globigerinatella insueta Cushman et Stain-
forth (zonal marker of the base of N6 Zone) although this lat-
ter species is very rare in the Mediterranean domain and it has
Table 1: Summary of lithological features of the recognized strati-
Fig. 4. Representative lithofacies of the lower part (Intervals IIII)
of the volcano-sedimentary succession of the Villanovaforru area.
a Sandy and conglomeratic deposits of the top of the Ussana For-
mation; b view of the lower portion of the Villanovaforru succes-
sion; c reddish sandstone level in the lower part of Interval I;
d marls of the lower part of the succession (Interval II); e
volcaniclastic beds in the lower part of the succession (Interval II);
f silicified marly limestones in the lower part of the succession
(Interval II) interbedded with volcanic epiclastic and diatoma-
ceous levels; g) view of Interval III containing basaltic pillow la-
vas; h and i pillow lava with multiple-rind structures.
58 GUERRERA et al.
THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 59
Fig. 5. Representative lithofacies of the intermediate-upper part
(Intervals IVIX) of the volcano-sedimentary succession of the
Villanovaforru area. a and b silicified calcareous marls in-
cluding frequent volcaniclastic beds (Interval VII); c partially
silicified marls containing thin volcaniclastic siltstones and arenites
(lower part of Interval VIII); d coarse-grained arenite beds (In-
terval VIII); e arenites and marls of the upper part of Interval
VIII; f arenites with interbedded bentonite layers and thin micro-
conglomeratic levels (Interval IX) with a detail g.
not been found in this succession. Some specimens of C. dis-
similis (sample A25) and C. unicavus (sample A27bis from
Interval VI) have also been observed. The presence of these
species shows that this part of the succession still lies below
According to the zonation of Iaccarino (1985), established
for the Mediterranean domain, Intervals IVI belong to the
zone of Globigerinoides altiaperturusCatapsydrax dissimi-
lis. According to the zonal scheme of Molina (1979) the sub-
zone of G. altiaperturus and the lower part of the
G. subquadratus Subzone are distinguished.
Above Interval VI the microfauna is poorly preserved. In
Interval VII (samples VF16 to VF22 and VF1 to VF15)
G. trilobus, G. altiaperturus, G. subquadratus (very scarce),
G. venezuelana, G. tripartita, Globorotaloides suteri Bolli
and atypical specimens of C. dissimilis are still present. Thus,
Interval VII belongs to the same biostratigraphic interval as
the upper levels of Interval V and those of Interval VI (N6
Zone, Blow 1969; or the upper part of the zone of
G. altiaperturusC. dissimilis, Iaccarino 1985).
The middle-upper part of Interval VIII (samples VF100 to
VF114) contains scarce and poorly preserved planktonic fora-
minifers. In the assemblages we have noted the absence of the
species that disappear at the top of N6 Zone (C. dissimilis, C.
unicavus, G. suteri and the G. venezuelana group, Blow
1969). This seems to suggest that the middle-upper part of In-
terval VIII belongs to N7 Zone (Blow 1969; or G. trilobus
Zone, Iaccarino 1985); however, some doubt still remain due
to the poor preservation of the microfauna.
In the highest part of the succession corresponding to Inter-
val IX (samples VF23 to VF30) C. dissimilis and other spe-
cies indicating the N6 Zone are absent, while specimens of the
G. trilobus group with a strongly embracing final chamber ap-
pear, which can be assigned to Globigerinoides bisphaericus
Todd. These assemblages seem to indicate that the uppermost
part of the succession corresponds to the N7 Zone (Blow
1969). Nevertheless, we did not detect the predominance of
Globoquadrina and of G. trilobus group, which usually char-
acterize the higher part of the N7 Zone in the Mediterranean
In the bio-chronostratigraphical correlation used by many
authors working in the Mediterranean domain (Demarcq et al.
1974; Molina 1979; Iaccarino 1985) the Aquitanian-Burdiga-
lian boundary is placed at the FAD of Globigerinoides altiap-
erturus. Thus, the upper Aquitanian could be characterized by
assemblages without G. altiaperturus, but including G. dehis-
cens and little-evolved morphotypes of the G. trilobus group,
mainly G. quadrilobatus and G. inmaturus forms.
The Burdigalian would lie between the FAD of G. altiaper-
turus and that of Praeorbulina, and could be divided into two
parts, separated by the last occurrence datum (LOD) of C. dis-
similis (e.g. Serrano 1992). The Lower Burdigalian would be
characterized by the joint presence of G. altiaperturus and C.
dissimilis. This biostratigraphic interval has frequently been
used in the Mediterranean domain (Bizon & Bizon 1972; Cita
1976; Bizon 1979; Molina 1979; Iaccarino & Salvatorini
1982; Iaccarino 1985) and corresponds to part of N5 and the
whole of the N6 Zone (Blow 1969). Within this interval Moli-
na (1979) distinguishes two subzones limited by the FAD of
G. subquadratus. The Upper Burdigalian is limited to the N7
Zone (Blow 1969), between the LAD of C. dissimilis and the
FAD of Praeorbulina. In the upper part of this interval, the as-
semblages are frequently dominated by Globoquadrina and
the G. trilobus group, with abundant specimens of the G.
According to this bio-chronostratigraphic correlation, the
succession comprising Intervals IVI was completely depos-
ited during the Early Burdigalian. From the level correspond-
ing to sample A25 (upper part of Interval V), in which the
first specimens of G. subquadratus appear, deposition oc-
curred during the upper part of the Early Burdigalian (Fig. 3).
Interval VII was also deposited in the upper part of the Ear-
ly Burdigalian. Above this interval, the transition to the Late
Burdigalian cannot be accurately identified, but it seems like-
ly that starting from sample VF100 (Interval VIII) the Late
Burdigalian occurs (Fig. 3).
Most of the samples collected in Intervals IVI (A1 to
A27bis) contain abundant microfauna sufficiently well pre-
served to enable precise identification. In the 125
the microfauna mainly comprises planktonic foraminifers, al-
though the relative abundance varies within the succession.
In the basal levels (samples A1 to A4; Fig. 3) the relative
abundance of planktonic foraminifers ranges from 60 to 70 %.
The accompanying benthic microfauna is mainly composed of
Florilus (only in the first level), Lenticulina, Heterolepa, No-
dosaria and abundant radioles of Echinoidea. These as-
semblages are characteristic of upper bathyal hemipelagic de-
Above samples A7 and A9, where no microfauna are
present, the predominance of the planktonic foraminifers be-
comes even more pronounced, exceeding 90 % of all the mi-
crofauna present; only in few layers (e.g. sample A13) the
planktonic foraminifers are scarce and show traces of dissolu-
tion, while radiolarians are found in greater numbers. These
deposits seem to reflect a deepening of the basin, coincident
with intra-basinal volcanic activity related to extensional
The upper levels of Interval V and those of Interval VI
(samples A25 to A27bis) show somewhat lower abundances
of planktonic foraminifers (around 75 %), with a varied
60 GUERRERA et al.
Table 2: Distribution and relative abundance of planktonic foraminifers in the recognized stratigraphic intervals. The corresponding
zones and age are also indicated.
THE SYN-RIFT VOLCANO-SEDIMENTARY SUCCESSION IN SARDINIA TROUGH (ITALY) 61
benthic assemblage including Nodosaria, Lenticulina, Het-
erolepa, Cibicides, Bulimina, Oridorsalis, Nonion and Pulle-
nia, in addition to remains of Echinoidea. It is likely that these
levels reflect a slight shallowing of the basin.
In Intervals VIIIX the microfauna mainly consists of
planktonic foraminifers, usually exceeding 80 %, although in
many levels the microfauna is very scarce. Within these inter-
vals radiolarians often exceed 10 %. This group, however, in-
creases considerably in levels where there is evidence of high
carbonate dissolution (samples VF112, VF114, VF24 to
VF28). Carbonate dissolution could have been facilitated by
the intense volcanic activity and a certain degree of confine-
ment of the bottom waters. The remaining constituents of the
microfauna are calcareous benthic foraminifers (mainly No-
dosaria and Lenticulina) and agglutinants (e.g. Reophax,
These observations lead us to conclude that Intervals VII to
IX must have been deposited in a relatively deep marine envi-
ronment comparable to the lower part of Interval II or per-
haps somewhat deeper.
The Early Miocene geodynamic evolution of Central-West-
ern Sardinia has been investigated by several authors (Coulon
1977; Cherchi & Montadert 1982; Guerrera et al. 1993; Mail-
lard & Mauffret 1993; Carmignani et al. 1995; Vigliotti &
Langenheim 1995; Assorgia et al. 1997b; Gattacceca 2001),
as well as the whole stratigraphic succession. However, a de-
tailed stratigraphic analysis of the different formations con-
nected with the sedimentation in the Sardinia Trough is still
undefined. The lack of these data does not allow detailed
lithostratigraphic correlations across the basin and makes it
difficult to calibrate the different depositional events. Filling
this gap, the studied stratigraphic section of the Villanovafor-
ru area can be considered as well representative of the Early
Miocene sedimentation in the central-southern sector of the
Sardinia Trough (Marmilla Basin).
The Villanovaforru succession is dominated by fine- to
coarse-grained volcaniclastic deposits whose different lithofa-
cies are related to depositional (mainly epiclastic), diagenetic
and alteration processes. The facies recognized in the studied
stratigraphic section show differences in thickness and
amount of volcanogenic materials which may be explained
supposing a complex physiographic setting and source areas
characterized by a varying amount, in space and time, of
available volcanic materials. This provides an example for the
influence, on marine sedimentation, of a coeval volcanism.
The coeval volcanic activity is also testified by the presence
of high-Mg basaltic pillow lavas interbedded in the lower part
of the succession (Mattioli et al. 2000).
The whole studied stratigraphic section extends from the
Early to the Late Burdigalian (Zone N5 to N7, Blow 1969)
and it seems to be characterized by a continuous sedimenta-
tion, without hiatus at least at the scale of the biostratigraphic
resolution. The deposition is certainly controlled by a strong
syn-sedimentary tectonic activity and, on the basis of the
Fig. 6. Paleogeographic and paleotectonic evolutional sketch of the Sardinia-Corsica Block during the Late Oligocene-Early Miocene
(from de Capoa et al. 2002, modified) with the location of the Sardinia Trough.
62 GUERRERA et al.
litho- and biostratigraphic reconstructions, it is possible to es-
timate a sedimentation rate of about 200 m/My.
Lithostratigraphic, petrographic and biostratigraphic analy-
ses allowed us to identify and characterize nine stratigraphic
intervals (Intervals I to IX), which could represent an impor-
tant sedimentary record of the overall environmental basin
evolution in the Sardinia Trough. In fact, at the basal levels
(lower marly portion of Interval I, which overlies continental
deposits) the microfossil assemblages indicate hemipelagic
deposition, corresponding to an upper bathyal environment.
Above these levels, a deepening of the basin seems to occur
(IIIV Intervals, cf. arrow in Fig. 3) and this is probably con-
nected with a climax of the volcanic activity related to exten-
sional faulting. The upper levels of the Interval V and the In-
terval VI reflect a slight shallowing of the basin (cf. arrow in
Fig. 3), whereas the VIIIX Intervals must have been depos-
ited in a relatively deep marine environment, similar to that of
the lower part of the Interval II.
According to the collected data, a schematic model of the
Late OligoceneBurdigalian evolution of the Sardinia-Corsica
Block is here proposed and the different phases are schemati-
cally shown in Fig. 6. A continental deposition (Ussana For-
mation, not indicated in Fig. 6 for a scale problem), which is
Late OligoceneAquitanian in age, occurs during the first
stages of crustal thinning, before the starting of the drift of the
Sardinia-Corsica Block (Fig. 6A). During the Burdigalian, the
volcano-sedimentary marine succession of Villanovaforru de-
posited during the drift towards east of the block and it was
strongly influenced by the contemporaneous volcanic activity
which occurred in the area of the Sardinia Trough (Fig. 6B).
In this way, the reconstructed stratigraphic succession com-
prises the transition from a continental (Fig. 6A) to a marine
(Fig. 6B) syn-rift deposition environment and it was deposited
during the extensional tectonics which caused the develop-
ment of the Sardinia Trough and its lenghtening towards the
north (Rossi et al. 1997). This is in agreement with the exten-
sional deformation suggested by the high-Mg composition of
the interbedded basaltic lava flows (Mattioli et al. 2000),
which are also similar to those described in the NW Sardinia
Trough (Morra et al. 1997). These results favour the hypoth-
esis that, during the deposition of the volcano-sedimentary
succession of Villanovaforru (Burdigalian p.p.), the rifting of
the Sardinia-Corsica Block was not yet accomplished.
This study allows us to point out the following main results.
1) The reconstruction of a new detailed stratigraphy of the
volcano-sedimentary succession outcropping in the Vill-
anovaforru area, which is considered as representative of the
Early Miocene sedimentation within the central-southern sec-
tor of the Sardinia Trough (Marmilla Basin).
2) The litho- and petrographic descriptions of the fine- to
coarse-grained volcaniclastic lithofacies, as well as the char-
acterization of the primary volcanics (basaltic pillow lavas)
interbedded in the measured section. This provides a good ex-
ample for the influence on marine sedimentation of a coeval
3) A detailed biostratigraphic analysis of the whole studied
succession, which extends from Early to Late Burdigalian
without hiatus (continuous sedimentation) and is character-
ized by an estimated sedimentation rate of about 200 m/My.
4) The paleoenvironmental reconstruction of the succes-
sion, which reveals a transition from a continental (upper Oli-
gocene-Aquitanian) to a marine (Burdigalian) depositional
5) The presence, in the Burdigalian, of an extensional tec-
tonics which caused the development of the Sardinia
Trough and a contemporaneous effusive volcanic phase with
peculiar basaltic high-Mg composition. This extensional tec-
tonics also suggests that, during the deposition of the volcano-
sedimentary succession of Villanovaforru, the rifting of the
Sardinia-Corsica Block was still in progress.
Acknowledgements: Thanks are due to M. DAtri and C.
Bucci for their assistance in editing and drafting. We also
thank the students of the University of Urbino who took part
in one of the Scientific Field Trips on the Sardinia Trough
for their cooperation during a part of the log measurement in
the Villanovaforru area. The constructive comments by M.
Kováè, G. Moratti and D. Puglisi considerably improved the
quality of the paper. This research was supported by the fol-
lowing grants: MIUR Urbino University Cofin/2003
(resp. F. Guerrera); Ricerca Scientifica Urbino Univer-
sity (resp. M. Tramontana) and B97.1063-RNM-202 (resp.
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