Rivista Italiana di Paleontologia e Stratigrafia volume I uz numero 3 pagine 353-362 Dicembre 1996

GEOLOGICAL OUTLINE, COMMUNITYTHE SILURIAN

' ANNALISA FERRETTI &

Key-trords: Silurian, Sardinia, communities.

Riassunto. I due distinti tipi di successioni siluriane affiorantiin Sardegna (Italia) sono qui analizzati e confrontati tra 1oro. Panico-lare attenzione viene rivolta alla loro età, al loro contenuto faunisticoed al loro significato globale nel tentativo di fornire un ulteriore con-

tributo alf interprerazione degli eventi verificatisi ne1 Siluriano.

Abstract. Two distinct types of Silurian successions from Sardi-

nia fitaly) are described and compared each other. Their age, {aunal

content and significance are briefly summarized in the attempt ofgiving a contribution to the global view of Silurian events.

Introduction and geological outline.

Sardinia is the second largest Mediterranean island

located just in the heart of the Thyrrenian Sea at equal

distance between Italy, France and Spain. A rich Paleo-

zoic Îavna, already reported about 140 years ago (Mene-

ghini, 1857) and which provided also the oldest Italianfossils, is there exposed.

Together with Corsica, Sardinia is a segment ofthe European Flercynian collisional Chain which was

affected by strong deformation, metamorphism and in-tense magmatic activity. Paieontological and geological

evidences locate these two regions almost adjacent toSpain and southern France until late Oligocene (Art-haud & Matte, 1966; Cherchi 6c Schroeder, 7973, 1976;

\íestphal et al., 1,976). The suture between Armoricaand Gondwana is expressed in the northern part of theisland by a SE-NSí tectonic contact ("Posada-Asinara

Line'), regarded as a segment of the south EuropeanHercynian Suture Zone. It separates the northern "HighGrade Metamorphic Complex" (Corsica and northernSardinia) from the "Medium to Low Grade Metamor-phic Compiex" (central and southern Sardinia) (Fig, 1).

These units represent two terranes, fused together byFlercynian events, which geometrically acted as the

overthrusting continentai margin and the overthrust

continental margin respectively (Carmignani et al.,

1992). The sedimentary cover rocks of Cambrian-early

SEQUENCE ANDOF SARDINIA

PALEOECOLOGY OF

ENRICO SERPAGLI*

Carboniferous age, belonging to the undedying margin,are detached from their basement and accumulated in a

pile of allochthonous nappes exposed between the Posa-

da-Asinara Suture Line and the autochthonous rocks ofthe External Zone of the chain in SV Sardinia. Strati-graphic and structural features allow to divide this al-

lochthonous complex into Internal Nappes (from thePosada-AsinaraLíne to the overthrust External Nappe$and External Nappes (between Barbagia and Iglesiente)(Carmignani et al., 1992).

The geotectonic picture of the region has been wi-dely discussed and different interpretations have been

proposed (e,g. Vai, 1980a, 1980b, l99L; Yai & Cocozza,

1986; Carmignani et a1., 1992). To these works we referfor further information.

South-central Europe is supposed to have been Io-cated in the Silurian at high latitudes in the southernhemisphere adlacent to the northern margin of Gond-wana, being mostly populated by low-diversity tempera-

te shelf faunas (Scotese Ec McKerrow, 1990).

The Silurian in Sardinia.

Silurian rocks are exposed, discontinuously, onlyin southern Sardinia. Two distinct and peculiar situa-tions occur in the S\fl part (Iglesiente and Sulcis sub-re-

gions) and in the SE part (Gerrei and Sarrabus sub-re-

gions) of the island. They remind mainly to the Siluriansequences exposed in Bohemia and Thuringia respecti-

vely. Their mutual relation is still unclear and this justi-fies a separate treatment and the use of different correla-tion charts Fig. Z). In addition, formal lithostrati-graphic units were proposed for the Silurian-eady Devo-nian of S\l Sardinia (Gnoli et al., 1990) which are nowcommonly used (e. g. Siveter et al., t991; Bechstadt,

199a). Still informal names are in use in SE Sardinia,

directly adopted from Thuringia (Helmcke, t973; Jaeger,1976, 1977). Formal names are going to be proposed byBarca, Corradini, Ferretti & Serpagli (work in progress).

'r Dipartimento di Scienze del1a Terra, Via Università 4, 477A0 Modena (Italy).

354 A. Fenetti G E. Serpagli

lilll I

f*-:Tl 2

IsE lq

f ilsf----lo

Fig. 1 - Primary structural elements of the Sardinian Basement. 1:

Post-Hercynian coverl 2: Hercynian batholith; 3: HighGrade Metamorphic Complex; 4: Internal Nappes; 5: Ex-

ternal Nappes; 6: External Zone;7: Posacia-Asinara Line.Modified after Carmignani et a1. (1992).

The strong tectonic activity which affected Sardi-

nia during all the geological history of the island is

mainly responsible for the fact that no continuous sec-

tions expose the full Silurian. This is reflected also inthe definition of lithostratigraphic units, mostly derivedfrom the study of several discontinuous outcrops. Furth-ermore, references both to graptolites and conodonts as

zonal fossils are necessarily made, due to the peculiarlithology of the exposed formations, The left-band co-

lumn reported in the 1995 issue of "Silurian Times" is

here used, even if we believe that some of the modifica-

tions proposed in the conodont zonation and in the

correlation with graptolites must be further tested.

The Silurian starts in Sardinia with graptolitic sili-

ca-argillaceous and siltitic shales, rich in carbon and py-

rite especially in SE Sardinia ("alum slates"; Jaeger,1977)and interbedded by lydites in the lower part. The Genna

Muxerru Fm. of SV Sardinia Q0-25 m; Fig. 2) provided

the Llandovery graptolite acuminatug'uesiculosus, q)phus,

triangulatus-pectinatus, conoolutus, turriculatus-crispus

and griestoniensis-crenulata biozones (Gnoli et al., 1990;

Storch & Serpagli, 1993). The lower and upper bounda-

ries of the formation are never clearly exposed but bothappear gradational. The recovery in many sections of

the acunrinatus Biozone (Fig. 2) makes highiy possiblethat this formation extends up to the base of the Silu-rian. The "I-ower Graptolitic Shales" of SE Sardinia (30-

40 m; Fig. 2 and 3) cover a longer time interval, revea-

ling how shaly deposition persisted in this area also inlùTenlock and early Ludlow times. No undisturbedlower contacts of the formation with Ordovician rocksare known. Lydites, very rare in SV Sardinia, are welldeveloped here in the Llandovery up to fhe turriculatus-crispus Zone with thick individual beds, bearing fre-quent radiolarian lenses, separated by thin shaly layers.

Phosphori.tes occur in the middle-upper part of the for-mation (Fig. 2) from the lundgreni to the nilssoni Zoneas nodules, lenses or proper layers (Barca & Jaeger,1990). Llandovery graptolites of the vesiculosus, triangu-latus-pectinatus and argenteus (=gregariu), conoolutus,

turriculatus-crispus, griestoniensis-crenulata and spiralisbiozones are reported. This unit extends into the earlyLudlow; at least up to the nilssoní Biozone (Barca & Jae-ger, 1990) as also recently confirmed by the recovery at

the base of the overlying calcareous formation of the A.ploeckensis conodont Zone (Barca et al., 1995), whoselower part seems to be equivalent to the uppermost partof the scanicus graptolite Biozone.

The Flrrminimrqoiore Fm lFiq 2ì overlies theGenna Muxerru Fm. in SV Sardinia and roughly corre-sponds to the "calcarí a Orthoceras, Cardiola, Monograp-

tus, ecc." of the early authors. Its thickness, estimatedonly indirectly due to the strong tectonism, is 45-50 m.The formation spans from late Llandovery to earliest

Lochkov. Black calcareous lenticular layers (Fig. 4) alter-nate with dark non calcareous pelites and shales. Plastic

deformation and cleavage strongly aiterated the shales

while limestone blocks preserve fossils mostly in fullthree dimensions (Gnoli et a1., 1980). The black colourand the peculiar bituminous smell reveal high contentof organic matter. Fauna is dominated by cephalopods,

associated with bivalves, pelagic ostracodes, graptolites,conodonts, forams, chitinozoans and muellerisphaeridswhereas gastropods, brachiopods, trilobites, the proble-matic organism Kolibaia and eurypterid fragments are

extremely rare. Graptolites are frequently found packed

together in pseudo-lenticular calcareous bodies Fig. S).

Bivalves are the only significant indicators of a benthicepifauna vrhile almost no trilobites and brachiopodshave been found, revealing the presence of anomalousoxygen conditions which could not be tolerated by the-se organisms. Phyllocarids and pelagic crinoids are occa-

sionally present towards the top. The crinoid bioclasticpackstone horizon associated with Sryphocrinites and

spreading over many other regions of Gondwana caps

the Fluminimaggiore Fm. The P amorphognathoides, O.

sagita sagita, O. bohernica, A. ploeckensis, P siluricus, O.

remscheidensis, O. eosteinhornensis-O. e. detortus and L

uoschrnidti utoschmidti conodont biozones have been do-

z1É.

l

ja

aLU

Í.LU<J)

0LU(,I6

GRAPTOLITES

=ooú.o_

bou ce ki4ransg ted Ie ns

b ran ik e nsi s-lach kove nsis

pa rultimus-ultimus

=alJolJ

ot

6fJ

formosus

bohemicus tenuis-kozlowskii

leintwardensis

ztsacco(,

scantcus

n tlssant

)<

a'lJzI.IJI

zEU

oI

ludensis

praedeubell-de ubell

parr'us-nassa

lundgreni

zoo3zUIa

tigidus-perneri

nccanonensts-belophorus

centrilugu s-mu rchi son i

cfLU

aloz)J

zI(J

JUF

lapwot'thi-insectus

splralls interval zone

g ri e ston e n si s -cre n u la t a

lurriculatus-ctispus

gueilchi

zzocu

sedgwickii

convolulus

argenteus

t ri a ng u I atu s- p e ct i natu s

g

oolIE

cyphus

vesrculosus

acuminatus

aIIJ

ÒT

LITHOLOGY&

Fomalions

GRAIN SIZEOR

TEXTURE"t,.,.f^-t^-l

s

I

\

=:rrTlt_

_l

=trt I t^flNil--

MAGGIORE

=ll

rt,l

C.J

N

=qs!:VUXERR

Silurian of Sardinia

SW SARDINIA SE SARDINIA-Gerrei

-r F;-Y', H#1. m+ ffis:1 t---rl

Stratigraphic column of the Silurian exposed in S$l and SE Sardinia (Gerrei) respectively. 1:shales; 2:lydites; 3:phosphorites;4-bedded limestone; 5:màssive limestone. Stratigraphic scale used here is the one recently proposed by the Silurian Subcommission

on Stratigraphy (1995), even if funher testing is probably needed.

Dunham's classification: m.s:mudstone; w.s:wackestone; p.s:packstone; g.s:Brainstone. Udden-Wentwonh scale: sh.:c1ay; si.:silt;v.f.s.:vey fine sand; f.s.:fine sand; m.s. medium sand; c.s.:coarse sand; v.c.s.:very coarse sand; g.:granules.

355

CONODONTS

O. remscheldensislnterval zone

u. cnspa

Interval zone

P. siluticus

A. ploeckensis

NOT ZONED

K. slauros

O. bohemicus

O. sagitta sagitta

NOT ZONEDO. sagitta rhenana

K. DatulaK. ranulilormisìntor\/rl 7^nó

P. amorphognathoides

P. celloni

P. tenuis -

D. staurognathoides

D. kenluckyensis

O.? nathani

356 A. Fenetti & E. Seryagli

cumented (Gnoli et al., 1990). Late Ludlow is probablyrepresented in SV Sardinia by dark shales as 'the O. sna-

jdri Intewal Zone and the O. crispa Bíozone have never

been found. Such biozones, however, occur in SE Sardi-

nia (Barca et al., 1995). Graptolites from the calcareous

bodies provided so far the lwndgreni, niksoni, scanicus,

leintwardensis, paruhimus-ultimus graptolite zones (H.

Jaeger, comm. pers. 1987; Rickards et al., 1995). Carbo-nate deposition is characterised by dominant fossilife-

rous wackestone-packstones that pass to fossiliferous

mudstones at the top of the formation.The nautiloid limestones of SW Sardinia are main-

ly represented in SE Sardinia (Gerrei sub-region) by theuppermost part of the "l-ower Graptolitic Shales", by a

calcareous unit ("Ockerkalk') and probably by thelowermost part of another shaly unit, the "Upper Grap-tolitic Shales". The "Ockerkalk" (30 m thick; Fig. 2 and

6) is an argillaceous limestone with a blue-grey colour

"Lower Graptolitic Shales"exposed in the Beccu Scortissection (SE Sardinie, Gerreisub-region).

weathering to ochre (so the name) and having a typicalirregular flaser texture. The poor fauna is mainiy com-posed of few nautiloids (Gnoli, L993), rare osrracodes,brachiopods, thin-shelled bivalves, trilobite fragments,gastropods, sponge spiculae, phyllocarids (mainly man-

dible$ and crinoids. Trace fossils and very small soiitarycorals were reported from the "Ockerkalk" by Jaeger(1977). All these organisms are scattered in a micriticlimestone, only locaily concentrated in thin wackestonebands of disarticulated debris. A rich conodont faunaspanning from the A. p/oeckensls to the O. remscheiden-

sis-O. e. detortus Biozone has been reported, documen-ting the A. ploeckensis, P silurícus, (Pe. latialata), O. sna-

jdri, O. crispa, O. remscheidensis, O. eosteinhornensis-O. e.

detortus conodont biozones (Barca et aI., 1995). The O.

snajdri Interval Zone and the O. rispa Biozone have

been therefore for the first time reported in Sardinia.The precise stratigraphic definition so achieved is in

Black lens-shaped limestone rich in cephalopods of theFluminimaggiore Fm. exposed at Fluminimaggiore-Galem-mu ISV Sardinid.

Graptolite limestone with beautifully preserved three-di-mensional specimens at Fluminimaggiore-Perd'e Fogu (S\7

Sardinia) ; approximately 0.6x.

Fie 4

qI

Fig. 6 - The "Ockerkalk" limestone exposed in the lower pan ofthe SIL Io section (SE Sardinia, Gerrei sub-region). The

interuJ represented here belongs to the P. siluricus Biozo'ne. Stratigraphic distance between samples 5 and 6 is about

1m.

good agreement with the graptolite data derived fromthe embedding shales at the base and the top of the for-

mation (|aeger, t976). The lobolith-horizon with the

giant pelagic crinoid Scypbouinites well known along

the northern Gondwana margin across the S/D bound-

ary and already recorded in the early Devonian of SVSardinia (Gnoli et al., 1988) extends aiso to the late Silu-

rian of SE Sardinia (Gerrei sub-region; Helmcke, 1923;

Jaeger, 1976, 1,977; Barca Ec Jaeger, 1990; Barca et al.,

t995). To point out that, at least in Sardinia, late Silu-

rian loboliths are apparently smaller than those of early

Devonian age. In the Sarrabus sub-region of SE Sardinia,

Silurian olistolithes and olistostromes embedded inflysch-type silico-clastic sediments of probably early

Carboniferous age were described (Barca, 1991; Barca &

357

Olivieri, 1991). Graptolitic alum slates with interbeddedlydites (like those described in Barca Ee Jaeger, 1990) as

well as calcareous blocks (described in Barca et a1., L986;

Barca & Olivieri, 1.991) are part of this complex (S. Bar-

ca, comm. pers. 1996), deposited in a foredeep basin,

with many analogies with the Culm-type Hercynian fly-sches of southern Europe (Spalletta & Vai, 1982; Yai &.

Cocozza,1986).The Silurian/Devonian boundary occurs in SV Sar-

dinia sti1l in the calcareous Fluminimaggiore Fm. (Gnoliet a1., 1988), whereas it seems to develop in SE Sardinia

(Gerrei sub-region) at the base of the "Upper GraptoliticShales" whose first layers bear the index species M. unifor-mis (Jaeger, 1976). These are composed of alum slates

without lydites or phosphorites. According to the compo-site section prepared by Barca & Jaeger (1990, fig. 9),

Scyphouinites occurs also in the lower part of this forma-tion. These shales grade continuously to nodular lime-

stones of late I-ower to Middle Devonian ase.

Paleoecological remarks.

As expressed by lithological columns (Fig. 2), the

Silurian started in Sardinia with a more or less uniformdiffusion of dark lyditic shales rich in graptolites. The

same deposition occurs at the base of many other south-European sequences, indicating the establishment of a

common circuit along northern Gondwana after the

marked provincialism of the Upper Ordovician. The

shaly deposition occurred in a reducing euxinic saprope-

litic basin (faeger, 1977; GnoIi et a1., 1990) and was in-terrupted diachronously by a calcareous sedimentationwhich started sporadically already in late Llandoveryand more definitelv in Wenlock times in SW Sardinia

Silurian of Sardinia

Fluminimaggiore Fm. "Ockerkalk"

Frg.7 - Calcareous deposition in the Silurian of Sardinia: the Fluminimaggiore Fm. occurs in S\f Sardinia and the "Ockerkalk" in SE

Sardinia.

358 A. Ferretti & E. Serpagli

encrinitic packstone

dark laminaîemudstone

SW

\sARDrNrASE

SARDINIA

íSsi -'

,r'il:i*,irl,'ì :{llilfÀì

oY

OoJ

-1,olol-iEi:'fLi

3oJo3

crinorcal waakcstone

;]|w

YooJz|'IJ

=

bioclasttL. iJ;:ìi Kcslorle

cephalopod-ostracodepackstone-wackesÎone

ìuffik;::ffiffi?wJ

ilscate 0ar

Fig.8 - Comparison between the calcareous sedimentation and microfacies of SSI Sardinia and SE Sardinia (Gerrei sub-region). Scale barreference - 2x (for white bars) or 1Ox (for dark bar$. Microfacies photographs partly from Ferretti (1989) and Barca et al. (1995).

g

e(

and only in late Ludlow in SE Sardinia (Fig. 7). Cepha-

lopod limestones from S\l Sardinia are lens-shaped beds

which always intercalate to shales. They probably repre-

sent short sedimentation events in the quiet depositio-nal environment of the shales. A very pronounced dou-b1e alignment of orthoconic shells, comparable to thecrest and the trough of ripple marks and to the typicaibimodal orientation pattern of wave accumulation, was

revealed by examination of large cephalopod plates and

blocks and by laboratory experiments (Gnoli et al.,

1930). A constant SSE-NNSí cephalopod orientationwas recently described from a new upper Wenlock loca-

lity (Ferretti et a1., t995a), suggesting the existence of at

least a connection with the globai current carrying ce-

phalopods over many parts of northern Gondwana.Even displaced blocks bearing random oriented orthoco-nes were found.

Five different microfacies (Fig. 8) were recognised

in the \Tenlock-upper Ludlow limestones from S'V Sar-

dinia, indicative of two main different regimes: a shal-

low high-energy deposition for the cephalopod-ostraco-

de packstone-wackestones (typical of the Ortboceras

limestone), the graptolitic packstones and the "coated

grains" grainstone-packstones, and a deposition below

normal wave-base but probably in areas within storm

wave-base for rare Ludlow pre-nodular mudstones withintercalated shellJags and for dark laminated fossiliferous

mudstones found locally. The Pridoli sedimentation in-dicates a shift to deeperwaters being represented bydark fossiliferous mudstones with occasional disarticula-

ted winnowed sheli lags of thin-shelled and convex-up

bivalves and ostracodes, small orthocones and rare cri-noid fragments (Ferretti, 1989).

Limestones from SE Sardinia are mostly repre-

sented by massive sequences of fine micritic limestones

with millimetric shelllags of disarticulated debris (Fig.

8). A quiet pelagic environment below wave-base was

supposed (Barca et al.,1995).As already noted, the transition to the Devonian

occurs still in calcareous facies in SV Sardinia while inSE Sardinia it appears to correspond to the lithologicalchange from the "Ockerkalk" limestone to the overlying"Upper Graptolitic Shales".

Community sequence.

Eight communities and assemblages, both benthicand pelagic owing to the peculiar nature of the fauna,

were described from the Silurian of southern Sardinia

(Ferretti et al., 1995b, in Boucot Ec Lawson, Eds.). Thatstudy was completed in 1989, when the latest informa-

tion on the "Ockerkalk" and the new faunal discoveries

from the Fluminimaggiore Fm. were not yet emerged.

Subsequent investigations respectively of the nautiloid

359

(Gnoli & Serpagli, I99l) and of the bivalve fauna (Kriz& Serpagli, t993) lrom SW Sardinia provided a detailedintra-taxa community definition. The communitysketch given here (Fig. 9) is an attempt of summarize alldata nowadays available on the Silurian Communities ofSardinia. Many of them, like the Orthocera.s lmst. and

Cardiola Communities, have a widespread distributionin the circum-Mediterranear- area.

The "Graptolitic Shale" Community covers mostof the Llandovery, being only sporadically associated

with the P amorphognathoides Community reported inSW Sardinia. In \íenlock times, the Orthoceras Imsf.and Cardiola Communities developed in SW Sardinia,

being strongly related each other and interfingering and

alternating to the "Graptolitic Shale" Community. Thevery rich O. sagitta sagitta Community and a first"Graptolitic Limestone" Community were also present

at that time.The ostracode Entomis migrans and Bolbozoe bohe-

mica Communities flourished in Ludlow times; the Or-thoceras lmst., Cardiola, "Graptolitic iimestone" and"Graptolitic Shale" Communities were still present. Theconodont Ko ckelella-Ancyrodella-Po lygnath oides Commu-nity developed both in SW and in SE Sardinia. The O,

crispa-O. snajdri Community from SE Sardinia is the

only present at the end of the Ludlow. A further "Grap-tolitic iimestone" and the Orthocera.s lmst. Communitiesare reported in the early Pridoli of SW Sardinia, whilethe conodont O. remscheidensis Community .was present

on both sides of the island. The phyllocarid Ceratiocaris

Community, a peculiar forams Community from S\lSardinia and the Scyphocrinites Community from bothsides of Sardinia developed close (the former two) orcrossed the Silurian/Devonian boundary.

Twelve Silurian-I-ower Devonian Bivalvia-domina-ted communities were recognised at distinct strati-

graphic levels inside the Fluminimaggiore Fm. (Kriz &Serpagli, 1993). The strong affinity of SV Sardinia and

Bohemia was stressed once more by the occurrence ofalmost 80 common bivalve species. Four medium-diver-sity communities were described within the Cardiola

Community Group of late 'ùTenlock to late Ludlow age.

Adaptation to the cephalopod limestone biofacies was

achieved by these communities mainly composed ofabundant epibyssate bivalves living on a substrate repre-

sented by cephalopod shells. Pridoli communities adju-

sted to the soft bottom conditions of the micritic facies

with low-diversity infaunal and seminfaunal popula-

tions. Monospecific or almost monospecific communiti-es developed at restricted living conditions (e. g. iimitedcurrent activity and low oxygen content) while in the

most favourable regions relatively higher diversity and

lower population density communities still grew (Kriz& Serpagli, 1993).

Silurian of Sardinia

360 A. Fenetti & E. Serpagli

SARDINIA SW SARDINIA SW SARDINIBENTHIC & SHALLOW DEEPER

PELAGIC ASSEMBI.AGES PELAGIC ASS BIVALVIA-DOMINATEDCOMMUNITIES

NAUTILOIDASSEMBLAGESBA1 I BA2 I BA3 I BA4 I BA518A6 AND PELAGIC

i *ffilffifc]

| scYPhocinites c'

O. remscheidensis C.

Q rthoce ras Graptolitici lmst C lmst C

'aLe.gnOllt V.l|a.CYD.neS. v$Jn. raLvar.v

Kopaninoce ras ? thy rsus-Orthocycloeras ?

fltrnin*assemblage

Uctrn

Ch.bndgei C.lJoa.falcata C.lSn.insolita C.

Cardiolinka sardiniana C.

=oJol

O. snaidri-O. críspa

'tEntomis Bolbozoermiorans C. bohemica C.j -

Graptolitic Polygnathoidest,

-o.t65 lmst.C. -,4u1crndella

| ,.r6no-!"O. .,. -Kod<elella C.

| " \fsP'' .,1ie\a G, ou'"' RT-It. Orthoceras lmst. C.I

I

I

I

I

I

APT

TCardiola C.

-Erapioiìii-Cm-sl. c.O. saoitta C.

SH

I

E

Graptolitic Shale C.

Cardiola

I Carc

Cardiolz

clocens C.,-;4 Merocvdoeras declive-Crybtocycloceras ?

deludens'\ asèemblage /'\/\?t

Cardiota sibbosa"l-

YOozlrJ

=

Pseudrcydocerast/?tngens

-Columeno@ras gnndeassemblage

r agna figusi C.

-------LKriz & Serpagli, 1993 Gnoli & Serpagli, 1991

GRAPTOLITE COMMUNITIESNOT YET ESTABLISHED

ct!oozJ

Fie. 9 - General sketch of Silurian Communities in Sardinia. Data of the left column are modified after Ferretti et al. (1995b).

Silurian of Sardinia Jbl

Three nautiloid assemblages with potential strati-graphic value were recognised in the middle-late Silurianof SV Sardinia (Gnoli & Serpagli, 1991). The Pseudory-

cloceras transiens-Coluftlenocerds grande assemblage occur-red in the O. sagitta sagitta-O. bobemica Zones, the Me-

roqcloceras declizte-Cryptocycloceras ? deludens assemblage

developed in the A. ploeckensis-P siluricus Zones and theKopanino ceras ? tlryrsus-Ortbo cyclo ceras ? fl uminese assem-

blage extended from the O. eosteinhornensis to the L uwoschmidti Zone. Each of them has a widespread distri-bution and is closely linked again to the nautiioid fauna

from the Prague Basin.

New data are still emerging from Sardinia andinteresting projects are running on. Major attentionhas been recently paid towards "minor" fossil groups(i. e. chitinozoans or muellerisphaerids) or unusual fa-

cies like the graptolitic limestones of SW Sardinia; cono-dont evidences from additional "Ockerkalk" sequencesare coming. So, the picture here Jrawn is just a preli-minary synthesis based on previous studies and cur-rent researches on the Silurian of Sardinia. This re-gion will certain provide in the near furure new pie-ces of information to understand more clearly Silu-rian events.

A cknotaledgements.

Our sincere and grateful rhanks ro Sebastiano Barca

(University of Cagliari) for helpful discussions and imponantsuggestions (providing us also unpublished data), and for criticalreading of the manuscript. Piero Vezzani and Giancarlo Leonardi(University of Modena) are deepiy acknowledged respectively fortheir photographic and graphic suppon. This project has been

funded by C.N.R. and MURST (40ok and 600lo) grants.

REFERENCES

Arthaud F. & Matte Ph. (1966) - Contribution à l'étude de la

tectonique superposée dans la chaîne hercynienne: étu-

de microtectonique des séries métamorphiques du Mas-

sif des Maures. C. R. Acad. Sc. Paris, v.262, pp. 436-439,

Paris.

Babin C., Cocks L. R. R. 6. \lalliser O. (1980) - Faciès faunes

et paléogéographie antécarbonifère de I'Europe. 26o

Congr. Géol. Intern. Coll. 6 "Géol. de l'Europe", Paris

7-17 fuillet 1980, pp. l9l-202, Parìs.

Barca S. (1981) - Contributo alla stratigrafia del Siluriano-De-voniano del Sarrabus (Sardegna sud-orientale). Boll. Soc.

Geol. It., v. 100, pp. 85-92, Roma.

Barca S. (1991) - Phénomènes de resédimentation et flyschhercynien à faciès Culm dans le "synclinal du Sarrabus"(SE de la Sardaigne, Italie). C. R. Acad,. Sc. Paris,v.373,pp. i051-1057, Paris.

Barca S., Corradini C., Ferretti A., Olivieri R. Ec Serpagli E.

(1995) - Conodont biostratigraphy of the "Ockerkalk"(Silurian) from southeastern Sardinia. RioL. It. Paleont.

Strat.,v. 100 (1994), n.4, pp. 459-476, Milano.Barca S., Gnoli M., Olivieri R. & Serpagli E. (1986) - New

stratigraphic data and evidence of Lower and Upper De-

vonian based on conodonts in Sarrabus area (Southea-

stern Sardinia). Rip. It. Paleont. Strat., v.92, n.3, pp.

299-320, Milano.Barca S. Er Jaeger H. (1990) - New geological and biostrati-

graphical data on the Silurian in SE-Sardinia" Close affi-

nity with Thuringia. Boll. Soc. Geol. It., v. 108 (1989),nn \A\-\Xl ì R^ffa

Barca S. & Olivieri R. (1991) - Age and source of calcareous

blocks resedimented into Hercynian flysch type sedi-

ments of the Sarrabus area (Southeastern Sardinia). ,4rlSoc. Nat. Mat. Mod.ena, v. 122, pp.49-66, Modena.

Bechstàdt T. (1994) - Short remarks on the Silurian to Devo-

nian series. In Bechstàdt T. & Boni M. (Eds.) - Sedimen-

tological, stratigraphical and ore deposits field guide ofthe autochthonous Cambro-Ordovician of southwesternSardinia. Mem. Descr. Carta Geol. Italia, v. 68, pp. 1,47-

148, Roma.

Carmignani L., Barca S., Cappelli B., Di Pisa A., GattiglioM., Oggiano G. & Pertusati P. C. (1992) - A tentativegeodynamic model for the Hercynian basement of Sar-

dinia. In Carmignani L. & Sassi F. P. (Eds.) - Contribu-tions to the Geology of Italy with special regard to thePaleozoic basements. A volume dedicated to Tommaso

Cocozza. IGCP N" 276, Newsletter, v. 5, pp. 61-82, Sie-

Cherchi A. & Schroeder R. (1973) - Sur la biogéographie de

l'association à Vakerina du Barrémien et la rotation de

1a Sardaigne. C. R. Acad.. Sc. Paris, v.277, pp.829-832,Paris.

Cherchi A. Ec Schroeder R. (1976) - Présence de galets duVraconien supérieur-Cénomanien basal de provenance

ibérique dans le Paléogène continental du Sud-Ouest de

la Sardaigne. Bull. Soc. Géol. France, v. 18, n. 5, pp.

1.217-121.9, París.Ferretti A. (1989) - Microbiofacies and constituent analysis of

Upper Silurian-l-owermost Devonian limestones {romSouthwestern Sardinia. Boll. Soc. Paleont. Ital.. v. 28. n.

1, pp. 87-100, Modena.

Ferretti A., Gnoli M., Kriz J. & Serpagli E. (1995a) - TheSilurian and early Devonian in south-western Sardinia.

In Cherchi A (Ed ) - 6th Paleobenthos InternationalSymposium. Rend. Sem. Fac. Sci. Univ. Cagliarl, supple-

mento v. 65, pp. 106-117, Cagbarì.

Ferretti A., Gnoli M. & Vai G. B. (1995b) - Silurian to LowerDevonian Communities of Sardinia. In Boucot A.J. &Lawson J. D. (Eds.) - Palaeocommunities. A Case Studyfrom the Silurian and lower Devonian, CambridgeUniversity Press.

J6Z A. Fenetti G E. Serpagli

Gnoli M. (1993) - Occurrence of middlelate Silurian Nautiloids from S. Basilio area (Gerrei, SE Sardegna). Bol/.

Mus. Reg. Piemonte, v. 10 (1992), n. 2, pp. 265-269, Tori-no.

Gnoli M., Kríz J., kone F,, Olivieri R., Serpagli E. Er Storch P.

(1990) - Lithostratigraphic units and biostratigraphy ofthe Silurian and early Devonian of Southwest Sardinia.Boll. Soc. Paleont. Ital., v. 29, n. 7, pp. 1.1-23, Modena.

Gnoli M., Leone F., Olivieri R. & Serpagli E. (1988) - TheMason Porcus Section as reference section for Upper-most Silurian-I-ower Devonian in S\7 Sardnia. Boll.Soc. Paleont. Ital., v. 27, n. 3, pp. 323-334, Modena.

Gnoli M., Parea G. C., Russo F. Er Serpagli E. (1980) - Pa-

laeoecological remarks on the "Ortboceras limestone" ofSouthwestern Sardinia (Middle-Upper Silurian). Mem.

Soc. Geol. It., v. 20 (1979), pp.405-423, Roma.Gnoli M. & Serpagli E. (1991) - Nautiloid assemblages from

Middle-Late Silurian of Southwestern Sardinia: a propo-sal. Boll. Soc. Paleont. Ital., v.30, n.2, pp. 187-195, Mo-dena.

Helmcke D. (1973) - Schichtgebundene NE-Metall-und F-Ba-

Lagerstdtten im Sarrabus-Gerrei-Gebiet, SE Sardinien.II. Bericht: Zur Stratigraphie des Silur und lJnterdevonder Lagerstàtten-provinz Sarrabus-Gerrer, N. Jb. Geol.

Palàont. Mh., v. 9, pp. 529-544, Stuttgart.

Jaeger H. (1976) - Das Silur und lJnterdevon vom thuringi-schen Typ in Sardinien und seine regionalgeologische

Bedeutung. Noaa Acta Leopoldina, v. 45, n. 224, pp.263-299, Halle.

Jaeger H. (1977) - The Silurian-Devonian boundary in Thu-ringia and Sardinia. In Martinsson A (Ed ) - The Silu-rian,/Devonian boundary. IUGS, s. A, n. 5, pp. 117-125,

Stuttgart.KrizJ. & Serpagli E. (1993) - Upper Silurian and lowermost

Devonian Bivalvia of Bohemian type {rom South-'We-

stern Sardinia. Boll. Soc. Paleont. Ital., v.32, n.3, pp.289-347, Modena.

Meneghini G. (1857) - Paléontologie de l'Ile de Sardaigne. InLa Marmora A, (Ed.) - Voyage en Sardaigne. ImprimerieRoyal, 58+ pp., Turin.

Rickards R. B., Holland C. H. 8c Serpagli E. (1995) - Aspects

of Silurian and Lower Devonian graptolite faunas andstratigraphy in Southern Sardinia. Boll. Soc. Paleont.

Ital., v. 34, n. 7, pp. 67-8A, Modena.

Scotese C. R. 6. McKerrow \7. S. (1990) - Revised 'llorld

maps and introduction. In McKerrow \f. S. Sa Scorese

C. R. @ds.) - Palaeozoic Palaeogeography and Biogeo-graphy. Geol. Soc. Mem., n. 12, pp. 1-21, London.

Siveter D. J., Vannier J. M. C. & Palmer D. (1990 - SilurianMyodocopes: Pioneer pelagic ostracods and the chrono-logy of an ecological shift. I micropalaeontol., v. lO, n.2, pp. 151.-173, London.

Spalletta C. & Vai G. B. (1982) - Conrarro Devoniano pelagi-co-flysch ercinico a Villasalto (Gerrei). In CarmignaniL., Cocozza T., Ghezzo C., Pertusati P. C. & Ricci C.A. (Eds.) - Guida alla Geologia del Paleozoico sardo.

Guide Geol. Reg., Soc. Geol. It., pp. 117-118, Roma.Storch P. E< Serpagli E. (1993) - I-ower Silurian Graptolites

from Southwestern Sardinia. Boll. Soc. Paleont. Ital.. v.

32, n. l, pp. 3-57, Modena.Vai G. B. (1976) - Stratigrafia e paleogeografia ercinica delle

Alpi. Mem. Soc. Geol. It., y. 1.3, pp. 7-37, Roma.Vai G. B. ( 1980a) - Tracing the Hercynian srrucrural zones

across "Neo-Europa": an introduction. Mem. Soc. Geol.

It., v. 2A (1979), pp.39-45, Roma.Vai G. B. Ed. (1980b) - Paleozoico e basamento in Italia: ag-

giornamenti e problemi. Mem. Soc. Geol. It., v. 20

(1979), 464 pp., Roma.Vai G. B. (1982) - Fasi di "rifting", nuovi dati stratigrafici e

conseguenze paleogeografiche nel Paleozoico inferiore.In Carmignani L., Cocozza T., Ghezzo C., Pertusati P.

C. & Ricci C. A. (Eds.) - Guida alla Geologia del Paleo-

zoico sardo. Guide Geologiche Regionali, Soc. Geol. It.,pp. 193-195, Roma.

Vai G. B. (1990 - Palaeozoic strike-slip rift pulses and palaeo-

geography in the circum-Mediterranean Tethyan realm.Palaeogeogr., Palaeoclimatol., Palaeoecol., v. 87, pp. 223-

z)2. Amsterdam.

Vai G. B. &. Cocozza L. (1986) - Tentative schematic zonarionof the Hercynian chain in Italy. Bull. Soc. Géol. France,

s. 8, v. 1, n. 1, pp. 95-114, Paris.

V'estphal M., Orsini J. & Vellutini P. (1976) - Le microconti-nent corso-sarde, sa position initiale: données paléoma-gnétiques et raccords géologiques. Tectonoplrysics, v. 30,

pp. 141-157, Amsterdam.

Receioed March 29, 1996; accepted JuLy 18, 1996