Permian-Triassic continental sequences of Northwest Sardinia and

Boll. Soc. Geol. It., Volume speciale n. 2 (2003), 119-129, 4 ff., 2 tavv. n.t..
Permian-Triassic continental sequences of Northwest Sardinia
and South Provence: stratigraphic correlations
and palaeogeographical implications
G. CASSINIS (*), M. DURAND (**) & A. RONCHI (*)
ABSTRACT
Detailed stratigraphical-sedimentological investigations have
recently focused on the Permian to Triassic continental sequences of
Nurra (NW Sardinia) and Provence (SE France) with the shedding
of new light on the chrono- and lithostratigraphical correlations
between these two distant areas today. The target of this research is
to reconstruct the paleogeography of this western Mediterranean
sector during the Late Palaeozoic-Early Mesozoic transition, and to
make inferences on the most reliable palaeoposition of the CorsicaSardinia block before its drift toward the Tyrrhenian area. The
investigated successions are presently and mainly exposed in Sardinia, along the coastal area of Cala Viola-Porto Ferro, up to Punta Lu
Caparoni (N of Alghero) and in France, between Sanary and Carqueiranne (W and E of Toulon). Facies and palaeoenvironmental
analysis, enhanced by the outstanding quality of outcrops, allowed
us to correlate both the successions and, consequently, to highlight
three main stratigraphic sequences which are recognisable at a
regional scale. The stacking pattern of these sequences is as follow:
The first sequence shows reduced thicknesses and lies unconformably on the Variscan metamorphic basement. It is initially represented by a Basal Conglomerate entirely composed of basement
lithoclasts and later by alluvial-to-lacustrine deposits, named the
Punta Lu Caparoni Fm. in Sardinia and the Les Pellegrins Fm. in
Provence. The first «Formation» is rich in Autunian mega- and
microfloras, while for the second, new palynological research is in
progress. In both areas, volcanic rocks of presumed calc-alkaline
affinity are discontinuously associated within and above these sediments.
The second sequence is the most represented both in Sardinia
and France. It consists of an alluvial megacycle which begins with
tens of metres of channelised quartz-conglomerates and arenites,
deposited in a braided alluvial setting. These deposits, represented
in Nurra by the Pedru Siligu Fm. and in Provence by the Transy
Fm., unconformably overlie the first sedimentary and volcanic
sequence.
Further volcanic activity, ascribed to the Bron Fm. in Provence
and identified possibly with that of the Casa Satta volcaniclastics in
Nurra, followed the above-mentioned quartz-rich formations. The
sequence passes upwards into reddish alluvial sediments with very
similar facies (Porto Ferro and Les Salettes Fms). A terminal lacustrine event in the latter unit yielded rich macro- and microflora,
which allowed us to relate these deposits to post-Kungurian/preTatarian times. The first episodes of undoubtedly alkaline volcanism
(basalts) also occur in the Salettes Fm.
The overlying St.-Mandrier and Fabregas Fms in Provence, and
the Cala del Vino Fm. in Nurra, are represented again by very thick
alluvial, mainly meandering deposits, locally grading, as in the second unit, into playa sediments. Volcanic rocks crop out moderately
in both regions. The top of this second, mainly siliciclastic succession probably pertains to undefined Late Permian (Tatarian?) times.
The third sequence begins with a thin quartz-conglomerate
band, which includes wind-worn clasts testifying to an arid climate,
named Poudingues de Port-Issol in Provence and Conglomerato del
(*) Università di Pavia, Dipartimento di Scienze della Terra,
Via Ferrata 1, I-27100 Pavia.
(**) Université Henri Poincaré, Nancy I, Sciences de la Terre et
UMR G2R, F-54506 Vandœuvre cedex.
Porticciolo in Nurra. These basal layers rest unconformably on the
previous formations and are followed by over 50 m of medium to
fine reddish sandstones and siltstones, laid down in a floodplain by
terminal fans, which are known as the Grès de Gonfaron in the former area and the Arenarie di Cala Viola in the latter. The age of this
sequence, which reaches up to the Middle Triassic marine Muschelkalk, is generally delimited between the Olenekian and the Anisian.
Later, the authors of this paper highlight some preliminary
results about the stratigraphic position and petrographic affinity of
the Permian volcanics in Nurra, which have been long debated. In
particular, a conspicuous mainly ignimbritic body was in places
identified between the Punta Lu Caparoni and the Pedru Siligu
Fms.; the volcaniclastic products of Casa Satta, more than 20 m
thick, appear intercalated between the Pedru Siligu and the Porto
Ferro Fms, and thus they pertain to the second sequence; a third and
younger volcanic episode, which is represented by some metre-thick
tuffs and cinerites cropping out within the Cala del Vino Fm. at the
Ponte Crabolu locality, occurs below the Triassic Buntsandstein,
though is as yet lacking in a clear stratigraphic position.
The serial affinity of the aforementioned volcanics, which
appear generally affected by heavy hydrothermal alteration or induced by significant secondary depletion of mobile elements, needs
further research. Only the alkaline affinity of the welded tuffs at M.
Santa Giusta has been recently confirmed. As a consequence, in
order to define appropriately their petrographic and geochemical
composition, a comparative study of these Permian volcanics of
Nurra with the relatively well known igneous sequences of SouthProvence is in progress.
KEY WORDS: siliciclastic deposits, volcanics, Permian, Triassic, stratigraphy, Sardinia (Nurra), Provence (Toulon), correlation, palaeogeographical implications.
RIASSUNTO
Successioni continentali permiane e triassiche della Sardegna nordoccidentale e della Provenza meridionale: correlazioni
stratigrafiche ed implicazioni paleogeografiche.
Di recente sono state condotte ricerche stratigrafiche e sedimentologiche sulle successioni continentali permiane e triassiche
della Nurra (NW Sardegna) e della Provenza (SE Francia) allo scopo di delucidare il quadro lito- e cronostratigrafico tra queste due
aree ora distanti. L’obiettivo della ricerca è di ricostruire la paleogeografia di questo settore del Mediterraneo occidentale tra il tardo
Paleozoico e il Mesozoico inferiore, nonché di trarre indizi sulla più
sicura paleoposizione del blocco Sardo-Corso prima della sua deriva verso l’area Tirrenica. Le successioni indagate sono essenzialmente esposte in Sardegna, lungo la fascia costiera compresa tra
Cala Viola e Porto Ferro, da cui s’innalzano fino alla Punta Lu Caparoni (a N di Alghero) ed in Francia, tra Sanary e Carqueiranne (ad
W e ad E di Tolone). L’analisi di facies e quella paleoambientale, fortemente favorite dall’ottima esposizione degli affioramenti, ci ha
condotto a correlare entrambe le successioni e, conseguentemente, a
riconoscere la presenza di tre principali sequenze stratigrafiche che
sono riconoscibili a scala interregionale. Le caratteristiche di queste
sequenze sono qui di seguito date.
La prima sequenza mostra uno spessore ridotto e poggia in discordanza sul substrato metamorfico Ercinico. Essa è contraddistinta da un Conglomerato Basale interamente costituito da clasti li-
120
G. CASSINIS ET ALII
tici del basamento e più sopra da depositi alluvio-lacustri, noti sotto il nome di Fm. di Punta Lu Caparoni in Sardegna e di Fm. di Les
Pellegrins in Francia. La prima «Formazione» include numerose macro- e microflore Autuniane, mentre la seconda è oggetto di studi palinologici ancora in corso. In entrambe le aree affiorano irregolarmente, all’interno ed al di sopra di questi prodotti sedimentari, rocce
vulcaniche di presunta affinità calcalcalina.
La seconda sequenza è la più ampiamente distribuita sia in
Sardegna che in Francia. Essa forma un megaciclo caratterizzato da
depositi alluvionali, che inizia con alcune decine di metri di conglomerati quarzosi canalizzati e alternati ad arenarie d’analoga composizione, depositatisi in un ambiente «braided». Questi sedimenti,
rappresentati in Nurra dalla Fm. di Pedru Siligu ed in Provenza dalla Fm. di Transy, giacciono in discontinuità sopra la prima sequenza sedimentaria e vulcanica.
Alle sopracitate formazioni ricche in quarzo seguono i prodotti di
una più recente attività vulcanica, ascritta alla Fm. di Bron in Provenza e identificabile possibilmente con quella di Casa Satta in Nurra.
La sequenza in corso d’esame passa verso l’alto a sedimenti fluviali rossastri con facies assai simili (Fm. di Porto Ferro e Fm. di Les
Salettes). Un evento lacustre finale, avvenuto nell’ambito della seconda unità, favorì la comparsa di una ricca macro-microflora, che
ha portato a correlare i rispettivi depositi ad un intervallo di tempo
post-Kunguriano/pre-Tatariano. Nella Fm. di Les Salettes si registrano inoltre i primi episodi di un’attività vulcanica d’indiscussa natura alcalina (basalti).
Le sovrastanti Formazioni di St.-Mandrier e di Fabregas in Provenza, nonché la Fm. di Cala del Vino in Nurra, sono anch’esse rappresentate da depositi fluviali, soprattutto d’ambiente meandriforme,
molto potenti, che graduano localmente, come ad es. nella seconda
unità sopracitata, a sedimenti di playa. In tutt’e due le regioni prese
in esame affiorano altresì subordinati depositi vulcanici. Il «top» di
questa seconda, essenzialmente silicoclastica successione appartiene
con ogni probabilità ad età tardo-permiane imprecisate (Tatariano?).
La terza sequenza inizia con una sottile unità di conglomerati
quarzosi, con frammenti clastici smussati dall’azione del vento a testimonianza di un clima arido, e definiti come Poudingues de PortIssol in Provenza e Conglomerato del Porticciolo in Nurra. Questi
termini basali poggiano in discordanza sulle precedenti formazioni
e sono a loro volta seguiti da oltre 50 m di arenarie medio-fini e siltiti rossastre, depositatesi in una piana d’inondazione ad opera di
«terminal fans», e note sotto il nome di Grès de Gonfaron in Provenza e di Arenarie di Cala Viola in Nurra. L’età di questa sequenza, che si protrae sino al Muschelkalk marino medio-triassico, è in
genere delimitata tra l’Olenikiano e l’Anisico inclusi.
Nel lavoro sono successivamente messi in evidenza alcuni risultati preliminari sulla posizione stratigrafica e sull’affinità petrografica delle vulcaniti permiane della Nurra, già da tempo dibattute. In
particolare, è stata confermata in alcuni luoghi la presenza, tra le
Formazioni di Punta Lu Caparoni e di Pedru Siligu, di un cospicuo
corpo vulcanico costituito essenzialmente da ignimbriti; i noti prodotti vulcanoclastici di Case Satta, potenti oltre 20 m, appaiono invece intercalati più sopra, tra le Formazioni di Pedru Siligu e di Porto Ferro, e rientrano pertanto nella seconda sequenza descritta;
infine, un terzo e più giovane episodio vulcanico, caratterizzato da
pochi metri di tufi e cineriti riconoscibili a Ponte Crabolu entro la
Formazione di Cala del Vino, sottostà al Buntsandstein triassico,
senza tuttavia poterne indicare una più precisa posizione stratigrafica a causa della discontinuità degli affioramenti e dell’abbondante
copertura di quest’area.
L’affinità seriale di queste rocce vulcaniche, che sono state generalmente interessate da una notevole alterazione idrotermale o da
una significativa perdita secondaria di elementi mobili, richiede ulteriori ricerche per una loro chiara definizione. Solo l’affinità alcalina delle ignimbriti di M. Santa Giusta è stata di recente confermata. Allo scopo di chiarire questi problemi petrografici e geochimici,
sono stati pertanto condotti studi di confronto tra le vulcaniti permiane della Nurra e quelle relativamente meglio conosciute della
Provenza meridionale.
TERMINI CHIAVE: depositi silicoclastici, vulcaniti, Permiano, Triassico, stratigrafia, Sardegna (Nurra), Provenza
(Toulon), correlazione, implicazioni paleogeografiche.
INTRODUCTION
The accepted model of Sardinia in the Permian is
similar in most aspects to that of nearby Corsica, and is
also reminiscent of conditions in Provence and northeastern Spain, with which Sardinia and Corsica were joined
before beginning their drift toward the Tyrrhenian area.
Recent palaeogeographical studies tried to identify a
more reliable palaeoposition for the Sardinia-Corsica
microplate, through a chrono- and lithostratigraphical
correlation between the Carboniferous to Triassic continental sequences of Nurra (NW Sardinia; fig. 1) and Provence (SE France; fig. 2).
The (late) post-Variscan basins examined for such
correlations are those of Lu Caparoni-Cala Viola and Toulon-Cuers, respectively: their volcanosedimentary infills
appear to be impressively similar and can be subdivided
into three stratigraphic sequences.
PREVIOUS STUDIES
Nurra (NW Sardinia)
The post-Variscan siliciclastic and volcanic deposition
in Nurra has been investigated for more than a century.
Due to the lack of fossils, it was roughly subdivided by
some authors (LOVISATO, 1884; OOSTERBAAN, 1936),
mainly for its similarities with the German successions,
into two poorly defined intervals: the older characterised
by Permian sedimentary and volcanic deposits, the younger with Buntsandstein-like sediments (or Grès bigarré).
LOTTI, in 1931, first pointed out the presence of macrofloral fossils, subsequently determined by PRINCIPI as
pteridosperm seeds of «Samaropsis fluitans Dawson»,
within reddish siltstones 300 m deep in a well (Cuili Mola
Casu) drilled near Cala Viola. Nevertheless, the first significant palaeontological datum was found by PECORINI
(1962), who shed new light on the chronostratigraphical
attribution of the base and top of the siliciclastic
sequence. He collected a megaflora in the dark shales just
a few metres above the Variscan basement at the Punta
Lu Caparoni. The forms hereafter listed allowed the
recognition for the first time of Autunian deposits in
the Nurra region: Lebachia (Walchia) piniformis Florin
(Schloth. pars), L. (Walchia) cf. gallica Florin, L. (Walchia)
cf. laxifolia Florin, Walchia linearifolia Goepp., Ernestiodendron (Walchia) filiciforme Florin (Schloth. pars), Callipteris nicklesi Zeill., C. conferta Sternb., C. bergeroni Zeill., C.
cf. flabellifera Zeill., C. cf. raymondi Zeill., Taeniopteris
multinervis Weiss., Odontopteris subcrenulata Rost.,
Annularia stellata Schloth., A. sphenophylloides Zenk.,
Linopteris cf. brongnarti Gutb., Pecopteris sp. and Cordaites sp. In particular, the high percentage of Lebachia
and callipterid genera and the simultaneous absence of
typical Early Autunian elements led PECORINI to compare
these deposits to the Germanic Lebach strata and to
ascribe them to the late Autunian.
PECORINI (1962) also found estherias and plant
remains that were ascribed to Equisetum mougeotii
Brongt., near the uppermost portion of the Cala Viola
siliciclastic succession (see fig. 2 in VARDABASSO, 1966, p.
297), and attributed these deposits to the Lower Triassic.
Brief descriptions of the stratigraphic framework of the
Permian basins of the island, including Nurra, can also be
found in GASPERI & GELMINI (1977), GANDIN et alii
(1977) and FONTANA et alii (1982).
Later, due to this overview, litho- and chronostratigraphical subdivisions were proposed by GASPERI & GELMINI (1980), who defined the lower portion of the Nurra
PERMIAN-TRIASSIC CONTINENTAL SEQUENCES OF NORTHWEST SARDINIA AND SOUTH PROVENCE
sequence as Formazione di Punta Lu Caparoni and all the
overlying siliciclastic succession as Verrucano Sardo.
This name was taken from VARDABASSO (1966), even if
the author meant, with this term, only the Permian or
older basal conglomerates unconformably deposited over
the Variscan basement.
In the 1990s, further geological research on the Late
Palaeozoic basins of Sardinia (AA.VV., 2000, and references therein) unravelled the age and described in detail
the stacking patterns and facies of the Permian and Triassic siliciclastic successions of Nurra. BROUTIN et alii
(1996), CASSINIS et alii (1996, 1998a, 1998b) and CASSINIS
& RONCHI (1997) gave additional data, particularly on the
sandstone petrography of the detrital units and the nature
of the intercalated volcanic rocks.
A detailed lithostratigraphical revision, with facies
interpretations and new observations on the composition
of the arenites, was proposed by NERI et alii (2000 a,b)
and FONTANA et alii (2001) respectively.
Subsequently, SCIUNNACH (2001) focused on the heavy
mineral content of the sandstones belonging to the upper
part of the sequence (units 3 and 4 of GASPERI & GELMINI, 1980) in the Porticciolo and Cala Viola area. However, in our opinion, the stratigraphical framework and
the correlations proposed by this author with other Nurra
sections, such as Monte Santa Giusta, require further
research for a general consensus.
Recently, Nurra’s Permian stratigraphy was also highlighted by RONCHI (2001a, b) in two syntheses on the Late
Palaeozoic continental basins of Sardinia. Furthermore, a
preliminary comparison between the debated PermianTriassic siliciclastic and volcanic sequences of Nurra and
Provence was also presented, for the first time, during an
AGP meeting in Paris (CASSINIS et alii, 2000).
Provence (SE France)
Compared with the other more easterly Provencal
basins, and especially the Estérel, the Toulon-Cuers area
remained the least studied for a long time. Nevertheless,
a clear distinction was made very early, within the post-
121
Argentiera
Jurassic to
Quaternary
covers
Upper Triassic
(Keuper) evaporites
Middle Triassic
(Muschelkalk)
carbonates
Punta Lu
Caparoni
C. Pedru
Siligu
Casa
Satta
Ponte
Crabolu
Torre Negra
Permian
volcanic rocks
M. de
s’Abe
Porto Ferro
Lower Permian to
Middle Triassic
continental deposits
Variscan Basement
Lago
Baratz
Cala del
Vino
40’
Sassari
N
Il Porticciolo
Cala Viola
0
2
Guardia
Grande
Km
Alghero
Capo Caccia
Fig. 1 - Location of Nurra, NW Sardinia, and geological sketch map
of the Permian Lu Caparoni-Cala Viola Basin and surrounds (After
BARCA et alii, 1996, redrawn and modified).
– Posizione della Nurra nella Sardegna nord-occidentale e schizzo geologico semplificato del bacino permiano compreso tra la Punta Lu Caparoni-Cala Viola e dintorni (Secondo BARCA et alii, 1996, ridisegnato
e modificato).
Variscan continental succession, between two series supposed to be respectively Permian and Triassic in age.
The prominent oligomictic conglomerate forming the
basal part of the Triassic series was compared to the Grès
des Vosges in general, and especially the Poudingue de
Sainte-Odile from northeastern France, while the main
part, made up of sandstones which yielded some Voltzia
Mesozoic
Tanneron
Permian
Upper Carboniferous
Le Muy
Variscan basement
Frejus
Le Luc
Vidabaum
Maures
Complex
opez
r
St-T
f
Gul
Cuers
Fig. 2 - Geological outline of Provence
(SE France). Box area: Toulon-Cuers
Basin. (From TOUTIN-MORIN & VINCHON, 1989, redrawn and modified).
– Schizzo geologico della Provenza marittima (Francia sud-orientale). L’inserto a
sinistra corrisponde al Bacino di ToulonCuers. (Da TOUTIN-MORIN & VINCHON,
1989, ridisegnato e modificato).
Sollies-Pont
Toulon
Pierrefeu
N
Le Pradet
Giens Gulf
0
5
10
Km
ANISIAN
E
A u c t .
1. PROVENCE
COMPOSITE
SECTION
(Toulon-Cuers
Basin)
2. NURRA
COMPOSITE
SECTION
(Lu CaparoniCala Viola Basin)
GRØS
DE GONFARON
ARENARIE DI
(>80 M)
SEQUENCE CALA VIOLA
(> 50 M)
POUDINGUE
DE PORT-ISSOL
III
FABREGAS FM.
?
CONGLOMERATO
DEL PORTICCIOLO
(CA. 5 M)
(CA.8M)
(50-150 M)
PC
?
SAINTMANDRIER FM.
CALA DEL
VINO FM.
(Broutin & Durand, 1995)
(>700 M)
POST-KUNG.
PRE-TATAR. (1)
" S A X O N O - T H U R I N G I A N "
U P P E R
R
?
R
M
I
A
N
p . p .
OLENEKIAN?
"Buntsand."
G. CASSINIS ET ALII
TRIASSIC
122
(> 400 M)
SEQUENCE
CALCAIRES DU
BAU ROUGE
(CA. 25 M)
II
LES SALETTES
FM.
PORTO FERRO
FM.
(100 M)
(CA.150-200 M)
?
BRON FM.
(CA. 200 M)
(> 20 m)
TRANSY FM.
PEDRU
SILIGU FM.
CS
W
E
?
(CA. 50 M)
ORDOVICIANLOWER CARB.
(Ronchi et al., 1998)
"UPPER"
AUTUNIAN Auct. (2)
L
O
P
(> 40 M)
(> 30 m)
PUNTA LU
LES PELLEGRINS SEQUENCE
CAPARONI FM.
FM.
(50-80 M)
I
(CA.15 M)
BC
BC
Variscan Basement
Alkaline volcanic rocks
Macrofloras
Calc-alkaline volcanic rocks
Palynomorphs
Volcanics of uncertain affinity
Regional unconformities
Minor rank unconformities
Fig. 3 - Schematic and composite logs of the Permian and Triassic sequences of Lu Caparoni-Cala Viola (Nurra) and Toulon-Cuers Basins.
Columns are not to scale. ABBREVIATIONS: CS and PC: Casa Satta and Ponte Crabolu volcanic rocks, respectively. In the time column, the
dating (1) pertains to the Provence section, whilst (2) to the Nurra section.
– Colonne schematiche e composite delle successioni permiane e triassiche dei Bacini di Lu Caparoni-Cala Viola (Nurra) e di Toulon-Cuers. Le due
colonne stratigrafiche non sono in scala. ABBREVIAZIONI: BC indica il Conglomerato Basale, mentre CS e PC corrispondono rispettivamente ai
prodotti vulcanici di Casa Satta e di Ponte Crabolu (il punto interrogativo a lato di quest’ultimi sta ad indicarne la posizione stratigrafica incerta).
A sinistra, nella colonna cronologica, le datazioni poste tra parentesi con i numeri 1 e 2 si riferiscono rispettivamente alla Provenza ed alla Nurra.
PERMIAN-TRIASSIC CONTINENTAL SEQUENCES OF NORTHWEST SARDINIA AND SOUTH PROVENCE
and Equisetum in the neighbourhood of Hyères, was related to the Grès bigarré from the same area (JAUBERT,
1859; CHARLES, 1949; THÉOBALD, 1952). The subsequent
sedimentological and palynological studies confirmed
that point of view (DURAND et alii, 1989). The Permian
series, where Callipteris conferta and Walchia piniformis
would have been found (BOUILLET & LUTAUD, 1958),
were subject to less attention, with the result that the Permian series remained undifferentiated in the 2nd Edition
of the «Toulon» sheet of the Geological Map of France
(GOUVERNET, 1969). Rhyolitic tuff beds were pointed out
in several places, as well as seven basalt lava flows in the
Carqueiranne area (COULON, 1967).
Stratigraphic research on the Permian succession
began in the 1970s with a prospecting campaign by
COGEMA (1973-74), the results of which were not published, and a hydrogeological study (TRAVI, 1976) in the
northern part of the basin (Cuers). These studies led to the
definition of the six presently recognised formations (AREVIAN et alii, 1979). In 1989, TOUTIN-MORIN & VINCHON
proposed new names for the southern part of the basin
(Toulon), which was supposed to be separated by a swell
during Permian times. As there is no sedimentological evidence for such a swell (DURAND, 1993), the formation
names herein (fig. 3) are valid for the whole basin.
STRATIGRAPHICAL SEQUENCES
SEQUENCE I
In both northwestern Sardinia and southwestern Provence (fig. 3), the first sequence lies unconformably on
the Variscan basement, locally through a palaeosol. It is
represented by an irregular and very thin Basal Conglomerate, made up of basement metamorphic clasts, and a
reduced alluvial-to-lacustrine succession composed of
dark shales, sandstone sheets and conglomerate bodies,
informally named (like all the others within this paper)
the Punta Lu Caparoni Fm. in Sardinia and the Les Pellegrins Fm. in Provence.
As mentioned above, the basin deposits of this oldest
cycle in Nurra, which reach up to approximately 15
metres in thickness, generally pertain to the Punta Lu
Caparoni Fm. (GASPERI & GELMINI, 1980). The most representative section in this area, recently revised by CASSINIS et alii (1996), NERI et alii (2000a) and FONTANA et alii
(2001), begins with very scarce clast-supported and
poorly sorted conglomerates (Basal Conglomerate),
which are upwardly capped by blackish laminated shales
and sandstones; decimetre- to metre-scale conglomerates,
which contain volcanic quartz and rare metamorphic
fragments, also occur (plate 1A). A unit of about 10 m of
light, weathered massive strata follows, with frequent
finer intercalations interpreted as kaolinised cinerites.
Their scattered ochrous ferruginous crusts could have
been formed in a pedogenetic environment.
Ten of metres of volcaniclastic acidic deposits (rhyolitic ignimbrites and tuffs), with unknown series affinity,
crop out locally on the top, not only in the Lu Caparoni
area but also nearby (Lake Baratz).
In the lower portion of this section two shaly-silty
horizons are rich in Autunian megafloras. As already
recorded, the first finds of such flora were made by
123
PECORINI (1962) and later by GASPERI & GELMINI (1980).
New collections by RONCHI and DIEZ led BROUTIN
(BROUTIN et alii, 1996, 2000) to identify the following
plants: Autunia conferta, Odontopteris cf. subcrenulata,
Pecopteris polymorpha, Ernestiodendron filiciforme, Taeniopteris sp., Walchia piniformis, Rhachiphyllum lyratifolia,
etc., and microfloras, such as Potonieisporites novicusbhardwaji, Florinites diversiformis, F. mediapudens, Nuskoisporites cf. klausii, Vesicaspora ovata, Gardenasporites
leonardii, Illinites tectus, Limitisporites spp., Protohaploxypinus samoilovichii, Hamiapollenites sp., Vittatina ovalis,
Costapollenites sp., and other forms.
BROUTIN compares the macrofloral association to
that recorded in the Assise de Surmoulin-Millery («Upper
Autunian») of the typical Autun Basin (Massif Central
Français; CHÂTEAUNEUF et alii, 1992), and the palynological assemblage with biozone «A3» as defined by DOUBINGER (1974) for the Autunian of Europe.
The Toulon-Cuers Basin basal formation is represented by the alluvial-lacustrine to flood-plain Les Pellegrins Fm., whose thickness is estimated, in the Maupas
graben, at about 50-80 m (plate 1B). In this locality,
poorly-sorted basement breccias (Basal Conglomerate)
grade into alternating thick sandstone lenses with thinner
dark-grey silt and clay layers. Paludal carbonated paleosols, grey lacustrine limestones and massive fine rocks,
interpreted as kaolinised cinerites, crop out in other sections of the same area.
Allowing for close lithological analogies with the
Punta Lu Caparoni Fm., and a structural context very different to that of the clearly Stephanian deposits of the
same region, this «Formation» is inferred herein to be
Early Permian in age, although palaeontological data
reported by differing authors (BOUILLET & LUTAUD, 1958;
PARENT, 1932; BASSO, 1987), from the Pierrefeu area and
Collobrières, are in conflict with this interpretation
(DURAND, 2001).
In southern France, between Cannes and Toulon, only
the local, sandy-to-pelitic Avellan Fm. (Estérel), which is
unconformably covered by the only calc-alkaline volcanic
body known in that region (CABANIS & TOUTIN-MORIN,
1992), has so far been attributed to the Autunian (TOUTIN-MORIN & VINCHON, 1989; DEROIN et alii, 2001). In
contrast, calc-alkaline volcanism occurred widely in Corsica and Sardinia.
On the whole, according to a palaeogeographicalstructural point of view, this «Autunian» sequence, which
began locally during «Stephanian» times (such as in the S.
Giorgio Basin, Sardinia) was related to a moderate transtensional-transpressional regime, generating small strikeslip or pull-apart basins. In contrast, the Upper Carboniferous (Westphalian?-Stephanian) basins lacking Permian
deposits (such as those of Le Reyran and Plan-de-la-Tour
in Provence) display evidence of a distinct E-W compressive phase (TOUTIN-MORIN & BONIJOLY, 1992).
SEQUENCE II
The second sequence starts with some tens of metres
of channelised quartz-conglomerates and arenites laid
down in a braided alluvial setting. These deposits are represented in Nurra by the Pedru Siligu Fm. (corresponding
to unit 1 of GASPERI & GELMINI, 1980), and in Provence
124
G. CASSINIS ET ALII
Plate 1 - Field photographs of the sedimentary facies of sequences I and II from Nurra (NW Sardinia) and Toulon-Cuers area (Provence),
respectively. Sequence I: A. Punta Lu Caparoni Section (Nurra): the fluvio-lacustrine deposits of the Punta Lu Caparoni Fm. (PLC) and, separated by a marked unconformity, the coarse sandstone-conglomerate bodies of the Pedru Siligu Fm. (PS). B. Le Maupas Graben (Pierrefeu): the pale conglomeratic sandstones of the Transy Fm. (T), which unconformably overlie the fluvio-lacustrine to flood-plain deposits of
the Les Pellegrins Fm. (LP). Sequence II: C. Channelised braided deposits in the Porto Ferro Fm. (Torre Bianca, Porto Ferro). D. Pebbly
sandstones in the Les Salettes Fm. (Beau Rivage, Carqueiranne). E. Crevasse splays and overbank deposits in the Cala del Vino Fm. (Cala
Viola, Nurra). F. Meandering-channel setting of the Saint-Mandrier Fm. (Marégau Point, St. Mandrier).
– Foto di alcune facies sedimentarie delle sequenze I e II, relative sia alla Nurra (Sardegna nord-occidentale) che all’area di Toulon-Cuers (Provenza meridionale). Sequenza I: A, Sezione di Punta Lu Caparoni (Nurra): i sedimenti fluvio-lacustri della Formazione di Punta Lu Caparoni
(PLC) e, separati da una marcata discontinuità stratigrafica, i depositi arenaceo-grossolani e conglomeratici della Formazione di Pedru Siligu
(PS). B. La depressione di Maupas (Pierrefeu): le arenarie conglomeratiche chiare della Formazione di Transy (T), sovrapposte in discordanza
stratigrafica ai sedimenti lacustri e di piana d’inondazione della Formazione di Les Pellegrins (LP). Sequenza II: C. Depositi braided canalizzati
nella Formazione di Porto Ferro (alla Torre Bianca, nella baia di Porto Ferro). D. Arenarie a ciottoli nella Formazione di Les Salettes (Beau Rivage,
Carqueiranne). E. Depositi di rotta (crevasse spays) e depositi di tracimazione (overbank) nella Formazione di Cala del Vino (a Cala Viola in
Nurra). F. Assetto di canali a forma di meandro nella Formazione di Saint-Mandrier (alla Marégau Point, St. Mandrier).
PERMIAN-TRIASSIC CONTINENTAL SEQUENCES OF NORTHWEST SARDINIA AND SOUTH PROVENCE
by the Transy Fm. (plate 1A, B). In NW Sardinia this
lower unit is overlain by the Porto Ferro Fm. (unit 2 of
GASPERI & GELMINI), represented by up to 150-200 m of
fossil-barren red beds, rich in porphyric pebbles and
characteristic of a braided-to-alluvial plain setting (plate
1C). The uppermost part of the second Sardinian
sequence is again represented by prevalent red beds, defined as the Cala del Vino Fm. (unit 3 of GASPERI & GELMINI). They mainly crop out along the coastal area and
consist of stratified greenish to reddish sandstones and
siltstones deposited by meandering rivers (plate 1E). Field
measurements allowed us to estimate this last formation
at about 400 m in thickness, thus increasing the presumed vertical development of the entire Permian-Triassic succession of Nurra to more than 700 m. Along the
cliffs south of Punta Lu Caparoni and west of Punta
Belardinu it is possible to appreciate the angular unconformity that separates the Porto Ferro Fm. from the overlying Cala del Vino Fm.
In the Toulon-Cuers area, these two lithostratigraphical units correspond to the Salettes Fm. (plate 1D) and
the Saint-Mandrier Fm. respectively; the latter, which
crops out with a 700 m thick exposure east of Marégau
Point (plate 1F), is also superimposed locally by playa
deposits corresponding to the Fabregas Fm.
The Porto Ferro Fm. includes, in places at its base,
some weathered volcaniclastic rocks of uncertain origin,
which are reminiscent of the widespread acidic tuffs and
local rhyolite flows known within the Bron Fm. of the
Toulon Basin (TOUTIN, 1980), and probably in a similar
stratigraphic position. The first episodes of undoubtedly
alkaline volcanism (basalts) occur in the Salettes Fm.
(LEROY & CABANIS, 1993). In this context, we underline
that the appearance in northern Nurra, near Mt. Santa
Giusta, of clearly alkaline magmatic rocks in the form of
ignimbrites and pyroclastics, and in other Sardinian
extra-basinal areas in the form of dykes of bimodal composition, is important for geodynamic interpretation and
correlations with Corsica and Provence.
The ages of all the aforementioned Sardinian red
deposits of the Sequence II are as yet undetermined; they
can generally be related to a post-«Autunian» interval,
probably ranging from Early to Late Permian times. On
the other hand, the Bau-Rouge limestones (a local uppermost member of the Salettes Fm., cropping out along the
cliffs of Cap Garonne) yielded the following macroflora
taxa: Ullmannia frumentaria (dominant), U. bronnii, Pseudovoltzia liebeana, Lesleya (al. Taeniopteris) eckardtii,
«Sphenopteris» dichotoma and Odontopteris osmundaeformis. The best-preserved microfloras, found in black mudstones interlayered with carbonaceous arkoses, include
Potonieisporites «novicus-bhardwaji», Lueckisporites virkkiae, Nuskoisporites dulhuntyi, Vesicaspora-Scheuringipollenites complex, Gardenasporites leonardii, Protohaploxipinus
microcorpus, Vittatina costabilis, Costapollenites ellipticus,
Lunatisporites sp., Falcisporites cf. zapfei, and other forms
(BROUTIN & DURAND, 1995). According to these authors,
this palaeofloristic association, which is very similar to that
described from the Tregiovo Fm. (central Southern Alps,
Italy, between the Bolzano and Trento provinces; CASSINIS
& DOUBINGER, 1992), suggests a post-Kungurian to preTatarian time-interval, i.e. an early Late Permian age.
In the other basins of Provence (Estérel, Bas-Argens,
Le Luc) the coarse-to-fine clastic red beds, up to 2000 m
125
thick, were ascribed to the «Saxonian» and «Thuringian».
These red beds include alkaline volcanics, from acidic
(rhyolites, tuffs) to basic (basalts) composition, which are
intercalated in the form of flows, ignimbrites, dykes and
pyroclastic products, mainly in the Estérel and BasArgens basins. Palaeontological and radiometric investigations lead us to relate the French «Saxono-Thuringian»
succession to a post-«Autunian» period, probably ranging
from the Artinskian to the Tatarian (DEROIN et alii, 2001).
As already mentioned, a distinct unconformity marks the
lower boundary of this stratigraphic interval.
In the two considered areas, Provence and Nurra, the
second sequence is consistent with broader extensional
conditions, which were accompanied by widespread
braid-plain and flood-plain deposition.
SEQUENCE III
The third sequence begins with a few metres of conglomerate, made up exclusively of quartz pebbles and
cobbles, including wind-worn clasts, and with arenitic
intercalations: Poudingues de Port-Issol in Provence
(GLINZBOECKEL & DURAND, 1984; DURAND, 1988) and the
herein-named Conglomerato del Porticciolo in Nurra. The
first unconformably overlies the Saint-Mandrier Fm. and
is well exposed in the south of Port-Issol Point (Bau
Rouge), Fabregas (plate 2B), and Carqueiranne Point
(Cap Garonne). The second, which rests disconformably
over the Cala del Vino Fm., comprises a continuous and
evident bank in the Porticciolo-Cala Viola area (plate 2A).
These deposits testify to a clearly arid period, also occurring in many other parts of Europe around middle
«Scythian» times: late Induan-early Olenekian (DURAND
et alii, 1989).
The main part (over 50 m thick) of the Triassic siliciclastic succession consists of medium-to-fine reddish
sandstones and siltstones laid down in flood plains by terminal fans, which are known as the Arenarie di Cala
Viola (unit 4 of GASPERI & GELMINI) in Nurra (plate 2C)
and the Grès de Gonfaron in Provence (plate 1D). These
two formations probably indicate, with respect to the
quartz-conglomerates below, the occurrence of new climatic conditions, from arid to semi-arid, responsible for
the formation of these floodplain-to-playa deposits rich in
pedogenetic carbonate nodules (in situ and reworked).
According to PITTAU (2000), in the subsurface siliciclastics (i.e. the Cugiareddu well), similar to those cropping out in the Cala Viola coastal area, two differing
sporomorph assemblages occur. The older one bears
Olenekian?-early Anisian taxa such as Enzonalasporites
leschikii, cf. Stellapollenites muelleri, Sulcatisporites splendens, Voltziaceosporites heteromorphus, Triadispora crassa
and Microcachryidites fastidiosus, whereas the younger
association yields typical forms from late Anisian times,
such as Stellapollenites muelleri, Dyupetalum vicentinense
and Cristianisporites triangulatus. In Provence only one
palynological association, mainly characterised by the
presence of Hexasaccites muelleri (syn. Stellapollenites
thiergartii) and Illinites kosankei, and ascribed to a Lower
Anisian age, was found within the upper part of the Grès
de Gonfaron Fm. (ADLOFF in DURAND et alii, 1989).
In Sardinia and Provence, sedimentological and palynological studies suggest that the deposition of the third
sequence (Buntsandstein) started probably in the Olenekian but developed during the Anisian, giving rise to a
126
G. CASSINIS ET ALII
Plate 2 - Field photographs of sedimentary aspects of Sequence III, respectively from Nurra (NW Sardinia) and the Toulon-Cuers area
(Provence). A. Conglomerato del Porticciolo (CP) unconformably deposited over the Cala del Vino Fm. (CV), which belongs to Sequence II
(Il Porticciolo). B. Whitish oligomictic conglomerates of the Poudingue de Port-Issol (PI), below the Grès de Gonfaron (GG), in Fabregas.
C. Arenarie di Cala Viola in the type locality (Cala Viola, Nurra). D. Flood-plain to playa deposits of the Grès de Gonfaron Fm. (Fabregas).
– Foto di aspetti sedimentari della sequenza III, sia in Nurra (Sardegna nord-occidentale) che nell’area di Toulon-Cuers (Provenza meridionale).
A. Conglomerato del Porticciolo (CP) depostosi in discordanza sulla Formazione di Cala del Vino (CV), che appartiene alla sequenza II (località
«il Porticciolo»). B. Conglomerati oligomitici biancastri della Puddinga di Port-Issol (PI), al di sotto dell’Arenaria di Gonfaron (GG). C. Le arenarie
di Cala Viola nella località-tipo (Cala Viola, Nurra). D. Depositi di piana d’inondazione e di playa nell’Arenaria di Gonfaron (a Fabregas).
regional unconformity with Permian and older rocks, and
a progressive onlap on to the metamorphic basement.
This Triassic Buntsandstein marks the onset of the second first-order eustatic cycle during the Phanerozoic
(VAIL et alii, 1991).
In both areas, the end of siliciclastic sedimentation is
heralded by an interlayering of thin greenish sandstone
slabs, displaying halite-crystal casts, with variegated mudstones.
STRATIGRAPHICAL POSITION AND PETROGRAPHIC
AFFINITY OF THE PERMIAN VOLCANISM IN NURRA
(NW SARDINIA)
The stratigraphic position and the series affinities of
the Nurra Permian-Triassic volcanics have long been debated.
The presence of «quartz porphyries» at the base of
Mt. Santa Giusta siliciclastic deposits and in the Baratz
Lake (Monti de s’Abe) area was first pointed out by
LOVISATO (1884), who ascribed them to a basal Permian
age. Later, OOSTERBAAN (1936), in his pioneering work
on the geology and stratigraphy of Nurra, grouped the
Permian-Triassic siliciclastics into two units: the older
one (p1) made of «schistose graywackes, compact conglomerate and dolostones», and the younger (p2) composed of «coarse sandstones and conglomerates, foliate
micaceous sandstones and variegated conglomeratic
sandstones». These last deposits grade upwards into the
typical Germanic Buntsandstein facies (the so-called
French «Grès bigarré»). According to this author, in the
Casa Satta-Cuile Puddighinu area, some «quartz porphyries and tuffs» are intercalated in the lowermost part of
the above-mentioned p2 and probably separate the two
subunits. We suggest that OOSTERBAAN rightly placed
these volcanic rocks as interspaced between the U1 and
the U2 of GASPERI & GELMINI (1980).
Permian-Triassic volcanic activity, alternating with
the siliciclastic deposition, was also highlighted in the
Nurra subsurface: one well (Cuili Mola Casu; LOTTI,
1931) near Guardia Grande (east of Cala Viola) and a second one (Cugiareddu well; POMESANO-CHERCHI, 1968)
further to the north showed two differing volcanic epi-
PERMIAN-TRIASSIC CONTINENTAL SEQUENCES OF NORTHWEST SARDINIA AND SOUTH PROVENCE
sodes. The direct correlation of these logs (briefly described and, unfortunately, by now destroyed) with field data
is likely to be very misleading.
As a consequence, recent investigations by the authors
of this paper highlight the following results:
(A) A more than 30-metre-thick mainly ignimbritic
body, deposited between the Punta Lu Caparoni Fm. and
the Pedru Siligu Fm. (M. de S’Abe, Punta Belardinu and
SW of Punta Lu Caparoni). These volcanic rocks, currently under study, clearly belong to the first sequence
and can be considered as the main source of the lithoclasts in the Pedru Siligu Fm., and probably a subordinate source for those in the Porto Ferro Fm.
(B) Volcaniclastic products (probably pertaining to
pyroclastic flows and fall deposits), more than 20 m thick,
crop out in the Casa Satta area, and should not be correlated to the previous volcanic rocks. As already stated by
OOSTERBAAN (1936) and by GASPERI & GELMINI (1980),
these products appear intercalated between the Pedru
Siligu and the Porto Ferro Fms. (respectively U1 and U2
of GASPERI & GELMINI, 1980), and thus they belong to
the second sequence. Some of the volcanic lithoclasts in
the Porto Ferro Fm. seems to relate to this type, but the
provenance of the major fraction remains unknown.
In their study on the Late Palaeozoic volcanism in
Sardinia, LOMBARDI et alii (1974) identified these last volcanic rocks as tuffs with pisolitic layers lying on quartzitic sandstones and conglomerates, while those occurring
at the base of variegated sandstones at the eastern and
northern side of Mt. Santa Giusta were classified as
alkali-rhyolitic pyroclastic rocks and ignimbrites. Furthermore, these authors interpreted the two episodes as
coeval and related to the same magmatic input.
Fig. 4 - Palaeogeographically inferred scenario between Nurra and southern Provence throughout the latest Palaeozoic to
earliest Mesozoic times. The position of
the Sardinia-Corsica Block is in accordance with a 60° clockwise rotation with
respect to the present-day position (dotted
lines). Dashed contours indicate hypothetical limits of other continental and marine
domains.
– Tentativo di ricostruzione paleogeografica,
tra il tardo-Paleozoico ed il Mesozoico inferiore, dell’area compresa tra la Nurra e la
Provenza meridionale. La posizione del
Blocco Sardo-Corso è compatibile con una
rotazione oraria di 60° rispetto alla sua
attuale posizione (in puntinato). Le linee
tratteggiate indicano limiti ipotetici di altri
domini continentali e marini.
127
(C) A third and younger volcanic episode, which is only
represented by some metre-thick tuffs and cinerites cropping out within the Cala del Vino Fm. in the Ponte Crabolu
locality (PC in fig. 3). In a similar fashion, several tuff beds
were reported within the Saint-Mandrier Fm. (DURAND,
1993), but no geochemical study has so far been done.
Even though the alkaline affinity of the welded tuffs
at M. Santa Giusta has recently been confirmed by some
research (CASSINIS et alii, 1996, 1998b; CORTESOGNO &
GAGGERO, 2000), doubts were raised about the nature of
the pyroclastic products in the Casa Satta-Cuile Puddighinu area (CS in fig. 3), as well as for the lithoclasts yielded from the Porto Ferro Fm. (Torre Bianca and Torre
Negra). In the opinion of CORTESOGNO & GAGGERO, the
calc-alkaline-type pattern probably shown by the Casa
Satta pyroclastic fall and flow deposits may be either primary or induced by significant secondary depletion of
mobile elements, whereas the pebbles in the latter unit,
even though involved in heavy hydrothermal alteration,
exhibit a more typically dacite to rhyolite composition
and an average calc-alkaline affinity.
It is worth mentioning that a geochemical study of
the rhyolite pebbles in the Les Salettes and Saint-Mandrier Fms. also showed a calc-alkaline affinity (LEROY &
CABANIS, 1993); according to these authors, the volcanic
source of the above lithoclasts was related to a poorly
defined area to the south (Sardinia?).
CONCLUDING REMARKS
AND PALAEOGEOGRAPHICAL INFERENCES
In conclusion, the above regional overview highlights
further the Early Permian to early Middle Triassic affin-
128
G. CASSINIS ET ALII
ities between Sardinia and Provence. In this context, they
are mutually emphasised by a good stratigraphical and
palaeogeographical picture of the considered (late) postVariscan continental evolution according to three main
tectonosedimentary sequences.
On the basis of numerous palaeomagnetic data, collected over the last 30 years by many authors (see the review
by SPERANZA, 2000), the amount of counterclockwise rotation of the Corsica-Sardinia block is today inferred to be
about 60° (fig. 4). In particular, the remarkable similarities
between the Permian-Triassic successions of the Nurra and
Toulon basins allow us to place them closely facing one
another, and consequently to place the southern part of Sardinia near the eastern Pyrenees, and northwest Corsica in
front of Estérel. Furthermore, strict analogies between the
palaeofloristic associations from the SE Sardinia Perdasdefogu Basin and the Gerri de la Sal (Sierra del Cadì, in the
Catalan Pyrenees) have recently been emphasised (RONCHI
et alii, 1998). Thus, from this standpoint, the microplate palaeopositions that match best for the Late Palaeozoic-Early
Mesozoic times are those proposed by WESTPHAL et alii
(1973), OLIVET (1996) and BROUTIN et alii (1994).
ACKNOWLEDGEMENTS
This paper represents a contribution to the activities of the
«Continental Permian Working Group» of the Subcommission on
Permian Stratigraphy, and of the Permian Geologists Association
from France. This work was supported by Italian (CNR and MURST)
and French grants. The authors are indebted to Alfredo Arche and
Jean-Jacques Châteauneuf for their helpful suggestions.
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Manoscritto pervenuto il 10 Giugno 2002; testo approvato per la stampa il 3 Luglio 2002; ultime bozze restituite il 3 Aprile 2003.