Radiolites and D - Società Paleontologica Italiana

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Bollettino della Società Paleontologica Italiana, 44 (3), 2005, 185-192. Modena, 30 novembre 2005
New data on the relationship between shape and palaeoenvironment
in Late Cretaceous Rudists from Central Italy:
Radiolites and Distefanella (Radiolitidae)
Riccardo CESTARI
R. Cestari (present address), ENI E&P, Unità Geografica Italia, Via del Marchesato 13, I-48023 Marina di Ravenna (RA), Italy;
riccardo.cestari@agip.it
KEY WORDS - Bivalves, Rudists, Radiolitidae, Palaeoenvironment, Late Cretaceous, Central Italy.
ABSTRACT - Analyses on the shell shape and structure of some rudist bivalves belonging to the Radiolitidae family have been
performed on specimens from carbonate successions cropping out in central Italy and from Museums’ collections.
Radiolites trigeri (Coquand) and R. darìo (Catullo) have a conical to slender cilindrical right valve provided with a flat and little
developed left valve, the shell structure may have a well developed cellular network. These species are mainly found in Late TuronianSantonian mud-supported carbonates of inner platform and ramp settings with medium to low hydrodynamic regime.
Distefanella salmojraghii Parona, D. bassanii Parona, D. douvillei Parona and D. guiscardii Parona have an extremely elongate
right valve provided with a cupular and well developed left valve, the shell is extremely thin and made of compact calcite. They are mainly
found in Santonian grain-supported bioclastic limestones of platform margin settings with medium to high hydrodynamic conditions.
The occurrence of these radiolitid species shows an asymmetric geographic distribution, caused by a complex physiography of the
carbonate platforms in the Mediterranean Tethys during the Turonian-Santonian (Late Cretaceous) when the East-West driven
Circumglobal Tethys Current favoured the diffusion of bioclastic Distefanella facies in the successions today facing the Adriatic side of
the Apennine chain. On the other hand, Radiolites assemblages set in mud-supported limestone were widespread in the successions
today facing the Tyrrhenian Sea. This asymmetric distribution should be assumed as reminiscence of a windward-leeward control on
carbonate platform growth.
RIASSUNTO - [Forma del guscio e struttura dei bivalvi Rudiste nel Cretaceo Superiore: Radiolites e Distefanella (Radiolitidae) in
Italia centrale] - Nel Cretaceo Superiore le Rudiste, bivalvi appartenenti all’ordine Hippuritoidea, colonizzarono gran parte degli
ambienti di piattaforma carbonatica raggiungendo la loro massima diversità con specie appartenenti alle famiglie Radiolitidae e
Hippuritidae. In questo lavoro, vengono prese in considerazione l’organizzazione, l’assetto morfostrutturale del guscio e la distribuzione
di alcune specie appartenenti alle radiolitidi che danno utili informazioni riguardo l’ambiente di sedimentazione delle piattaforme
carbonatiche che si svilupparono nell’area mediterranea della Tetide nel Turoniano-Santoniano (Cretaceo Superiore). In particolare
sono stati riesaminati alcuni dati già pubblicati sull’area dell’Appennino centrale (Italia centrale), integrati con osservazioni originali
nelle successioni di M. Rotondo e M. Orsello-Inghiottitoio nei Monti d’Ocre, le serie di Trevi e Fiuggi nei M.ti Simbruini, nell’area di
Sonnino nei M.ti Ausoni, a S. Polo Matese nei M.ti del Matese e nella Montagna della Majella.
In generale, le radiolitidi sono caratterizzate da una valva destra con forma da conica a cilindrica e valva sinistra solitamente poco
sviluppata ed appiattita. La struttura del guscio è tipicamente cellulare, costruita dalla sovrapposizione ritmica di laminae e muri.
Le specie Radiolites trigeri (Coquand) e R. darìo (Catullo) sono caratterizzate da forma da conica allungata a cilindrica e valva
sinistra appiattita e poco sviluppata, con struttura del guscio da prevalentemente cellulare nelle forme a minore tasso di accrescimento
a prevalentemente compatta in quelle ad elevato tasso di crescita. Esse risultano essere ben rappresentate nelle successioni fangosostenute
a idrodinamismo medio-basso di piattaforma interna e di rampa del Turoniano-Santoniano.
Tra le distefanelle, le specie Distefanella salmojraghii Parona, D. bassanii Parona, D. douvillei Parona e D. guiscardii Parona sono
caratterizzate da una valva destra estremamente allungata, guscio molto sottile composto da calcite compatta e da una valva sinistra
cupuliforme ben sviluppata. Esse sono ben rappresentate nelle successioni prevalentemente granosostenute ad idrodinamismo medioalto di margine di piattaforma del Santoniano.
Considerando il medesimo intervallo cronostratigrafico, le specie di radiolitidi esaminate risultano avere una distribuzione geografica
asimmetrica: le distefanelle sono ben rappresentate nelle successioni affioranti nei M.ti d’Ocre, nella Majella e nei M.ti del Matese
mentre Radiolites trigeri e R. darìo sono ben rappresentate nelle dorsali carbonatiche più ad occidente, quali i M.ti Simbruini e i M.ti
Ausoni. La distribuzione geografica asimmetrica di queste rudiste viene messa in relazione al complesso assetto fisiografico delle
piattaforme carbonatiche nell’area mediterranea della Tetide nel corso del Turoniano-Santoniano. In questo intervallo temporale la
crescita dei sistemi carbonatici era condizionata dalla corrente paleooceanica tetisiana che, spingendosi da est verso ovest, favoriva lo
sviluppo di biofacies a rudiste (come la Distefanella) bioclastiche e granosostenute nelle successioni della catena appenninica che oggi
guardano verso l’Adriatico. Verso la parte occidentale, invece, sono diffuse le associazioni oligotipiche a Radiolites (come Radiolites
trigeri e R. darìo) in successioni fangosostenute. Questa distribuzione asimmetrica deve essere attribuita al controllo sopravento e
sottovento che ha condizionato la crescita delle piattaforme carbonatiche nell’area italiana.
INTRODUCTION
In Late Cretaceous times, Rudist bivalves flourished
in carbonate platform environments, reaching their peak
diversity with the extraordinary diffusion of taxa
belonging to the Radiolitidae and Hippuritidae families.
ISSN 0375-7633
They colonized diverse environments of the
Mediterranean Tethys becoming significant organic
builders and sediment constituents of neritic carbonates
(Philip, 2003). Well-exposed successions yielding rudist
bivalves have been already studied extensively in central
Italy (e.g. Chiocchini & Mancinelli, 1977; Mariotti,
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
Fig. 1 - Studied localities in central Italy. a)
Ocre Mts. (Rotondo Mt. and M. OrselloInghiottitoio successions); b) Simbruini Mts.
(Trevi and Fiuggi); c) Ausoni Mts. (Sonnino
and Amaseno); d) Matese Mt. (S. Polo
Matese); e) Majella Mt.
1982; Accordi & Carbone, 1988; Damiani et al., 1992;
Pons & Sirna, 1992; Chiocchini et al., 1994; Simone et
al., 2003).
This study focuses on some slender taxa belonging
to Radiolites and Distefanella of the Radiolitidae family
reported from the Turonian-Santonian (Late
Cretaceous) carbonate successions cropping out in
central Apennines (central Italy) (Fig. 1). These taxa
have been taken into account among the others as they
show similar general shell features but different
relationship with the sedimentary substrate. Radiolites
trigeri (Coquand) and R. darìo (Catullo) are mainly
found in mud-supported limestone of inner platform
and ramp environments while Distefanella salmojraghii
Parona, D. bassanii Parona, D. douvillei Parona and
D. guiscardii Parona are found in grain-supported
sediments of outer platform settings.
The aim is therefore to give an interpretation of the
main factors that shaped the shell architecture of these
radiolitids and that favoured their asymmetric
distribution on carbonate platforms, eventually under
the influence of the Circumglobal Tethys Current
(Hotinsky & Toggweiler, 2003).
(Accordiella conica-Rotorbinella scarsellai Zone and
Nezzazatinella picardi-Nummoloculina heimi pars Zone
in Chiocchini et al., 1994). Analyses have also been
performed by studying specimens housed in museum
collections (Bassani Collection housed at the Centro
Musei delle Scienze Naturali di Napoli, Parona Collection
at the University of Turin, rudist collections at “La
Sapienza” University of Rome and at the Museum of
Geology and Palaeontology of the University of Padua.
Figured samples are housed at the Departamento de
Geologia, Universidad Autònoma de Barcelona (label
PUAB).
MATERIALS
Assemblages yielding Radiolites and Distefanella
have been considered from carbonate successions
cropping out in the Ocre Mts. (Rotondo Mt. and M.
Orsello-Inghiottitoio sections in Chiocchini et al., 1994;
Damiani et al., 1992) (Fig. 1a), in the Simbruini Mts.
(Trevi and Fiuggi sections in Cestari et. al. 1992) (Fig.
1b), in the Ausoni Mts. (Sonnino and Amaseno area;
Chiocchini & Mancinelli, 1977; Damiani et al., 1992)
(Fig. 1c), in the Matese Mt. (at S. Polo Matese and
Piano di Corte in Accordi et al., 1990a) (Fig. 1d) and in
the Majella Mt. (Accordi et al., 1990b; Stössel, 1999;
Stössel & Bernoulli, 2000) (Fig. 1e). The inferred age
of these species is Late Turonian-Santonian
Fig. 2 - Main shell features of a radiolitid bivalve. The right valve
is conical to cylindrical while the left valve is usually opercular
(modified from Cestari & Sartorio, 1995).
R. Cestari - Occurrence of Radiolites and Distefanella (Hippuritoidea) in central Italy
Fig. 3 - Radiolites sp. transverse section of the right valve. The
outer shell layer shows the cellular network (a) and a well
developed ligament ridge (b). Simbruini Mts. Base width = 2 cm.
PUAB-74.402.
SHELL SHAPE AND STRUCTURE
Over the last years, rudist palaeontology focused
on the relationship between morphology and substrate
(Gili et al., 1995; Sanders & Pons, 1999) also basing
on the comparison with other fossil groups (Seilacher,
1998; Johnson et al., 2002). In particular, radiolitids’
unusual morphology is the product of a peculiar
constructional pattern of the shell that could generate
extremely varied shapes from conical to more or less
elongate cylindrical, characterized by a well developed
right valve and usually by a smaller and operculiform
left valve (Fig. 2).
Shell structure is composed by a thin aragonitic inner
layer and by a thick outer low-Mg calcite layer, this
last often with cellular network (Fig. 3) formed during
the vertical growth of laminae (or lamellae) delimitating
growth rhythms, separated by muri (Fig. 4). The
complex laminae stacking and their orientation during
vertical growth give rise to the cellular structure (Pons
& Vicens, 2005). The genus Radiolites is marked by a
right valve with conical to cylindrical shape,
predominant cellular structure in the outer shell layer
and with a left valve little developed. Among the nearly
150 species and subspecies assigned to the genus
(Sánchez, 1981; Steuber T., www.ruhr-uni-bochum.de/
sediment/rudinet, A palaeontological database of Rudist
Bivalves (Mollusca: Hippuritoidea, Gray 1848 - accessed
may 2005)), two species well represented in the study
area have been taken into account: Radiolites trigeri
(Coquand) and R. darìo (Catullo), with this last one
grouping great part of “Gorjanovicia” taxa (Cestari,
1992).
In these species, the shape of the left valve is flat
and provided with a weak cardinal apparatus that is
interpreted to be related to muddy substrate with
medium to low hydrodynamism (Cestari & Pons, 2005).
In the Trevi and Fiuggi successions (Simbruini
Mts.), Radiolites trigeri (Coquand) (Radiolites sp. 1
in Cestari et al., 1992) is found in beds formed by
scattered specimens or organized in bouquets or small
clusters, set in mud-supported limestone with other
radiolitids e.g. Durania arnaudi (Choffat), Sauvagesia
187
sp. and a fossil assemblage indicative of the Late
Turonian. Above in the same succession, Radiolites
darìo (Catullo) is found in bouquets and clusters made
of elongate specimens in mainly mud-supported
limestone with Bournonia sp. and Sauvagesia sp. and
a microfossil assemblage of Santonian age.
Near Amaseno and Sonnino villages and in the
adjacent area (Ausoni Mts.), slender radiolitids with
little developed, flat opercular left valve belonging to
Radiolites trigeri (Coquand) show well developed
vertical growth rates marked in the ornamentation by
“lames externes” (Pl. 1, figs. 1-2). They form small
bioconstructions made of bouquets and small clusters
of specimens (Pl. 1, fig. 3) with shells made of cellular
and compact calcite outer shell layer (Pl. 1, figs. 4-6),
of Late Turonian age. In the same area conical to
cylindric-shaped radiolitids (Pl. 2, fig. 1) belonging to
Radiolites darìo (Catullo), spread on inner platform
environments during the Coniacian-Santonian through
different ecomorphotypes. Here, oligotypic and
monotypic assemblages occur in mud-supported, partly
dolomitized, limestone. R. darìo is found in bouquets
and clusters often made of slender specimens (Pl. 2,
figs. 2-3); low growth rates produced conical
specimens dominated by cellular shell structure while
higher growth rates favoured conically shaped
specimens with thin compact-dominated outer shell
layer. These species are usually represented by
monotypical to oligotypical communities in low to
moderate energy mud-supported deposits, with
moderate to high sedimentation rate, mainly in inner
platform to ramp settings.
Twenty-five species are currently assigned to the
genus Distefanella (Sánchez, 1981; Steuber, 2005),
among these four species instituted by Parona (1900,
1911) at S. Polo Matese village in the Matese Mts. have
been considered: Distefanella salmojraghii Parona, D.
bassanii Parona, D. douvillei Parona and D. guiscardii
Parona. The left valve is cupuliform and provided with
a well developed cardinal apparatus that is related to a
Fig. 4 - Radiolites sp. radial section of the right valve showing
the superimposition of stacked laminae (L1, L2, Ln outlined
lines) and muri (M1, M2, Mn) delimitating growth rhythms
(GR1, GR2, GRn). Simbruini Mts. Base width = 0.5 cm. PUAB74.403.
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
substrate with medium to high hydrodynamism and
significant bioclastic input (Cestari & Pons, 2005) (Pl.
2, fig. 5). The right valve has an extremely elongate
cylindric shape and a shell structure made of a very
thin outer layer with compact calcite. Their elongate
shape, the thin shell and the rapid growth favoured to
their diffusion in grain-supported and unstable bottoms
with high sedimentation rates. In the type locality of
the type species of the genus the age is Late Turonianearly Campanian (Accordi et al., 1990a; Carannante et
al., 1993) or limited to the Santonian for the lack of
radiolitids with canaliculate upper valves (Cestari &
Sartorio, 1995). Distefanella generally occurs in
moderate to high energy grain-supported deposits, with
high sedimentation rate, in platform margin to distal
ramp environment. Distefanella is also reported in
Scaglia type pelagic deposits of northern Italy (Cestari
& Trevisani, 2005).
In the Inghiottitoio succession (Ocre Mts.),
Distefanella beds are found in grain-supported
limestone intercalated to mud-supported facies bearing
radiolitid assemblages composed of Biradiolites
angulosus (d’Orbigny), Radiolites sp., Sauvagesia sp.
among others (Pl. 2, fig. 4). These beds have been
observed in a condensed succession few tens meters
thick, following the Cenomanian emersion. The
depositional settings is referred to shelf margin
bioclastic deposits of Late Turonian-Coniacian age
(Damiani et al., 1992).
At San Polo Matese these taxa form oligo- and
monotypic banks and are in assemblages with
Biradiolites canaliculatus (Pejovic), Sauvagesia
tenuicostata Polšak, Plagioptychus paradoxus
(Matheron), Milovanovicia sp., Jerinella sp. among
others. These taxa flourished in marginal areas of
carbonate platform (barrier banks in Accordi et al.,
1990a).
In the Majella Mt., well exposed rudist assemblages
with Distefanella are reported (Accordi et al., 1990b;
Stössel, 1999; Stössel & Bernoulli, 2000) along with
other taxa such as Radiolites, Praeradiolites,
Plagioptychus, Hippurites, Vaccinites, and Hippuritella.
Distefanella form nearly oligotypic assemblages that
can laterally extend for hundred meters. Assemblages
are set in medium to coarse bioclastic limestone (Pl.
2, fig. 6).
Fig. 5 - Sketch of an elongate Radiolites, provided with a flat left
valve, set in mud-supported sediment (on the left) and of a
Distefanella, with a robust left valve, inserted in grain-supported
deposit (on the right). LV = left valve; RV = right valve.
DISCUSSION
Great part of the shells of the considered taxa were
deeply inserted in soft carbonate sediment and they
can be considered as sediment stickers (Gili et al., 1995)
of semi-infauna. They could have a slender right valve
with the left valve flat and little developed as in Radiolites
or cupuliform and well developed as in Distefanella,
well suited for different water regimes. The inferred
rapid vertical shell accretion appears as particularly
suited for distancing the commissure and its related
biological activity from the substrate in a valve almost
completely inserted in soft sediment, under high
sedimentation rate conditions (Fig. 5). The different
shell shape of the left valve has to be related to the
EXPLANATION OF PLATE 1
Figs. 1-6
- Radiolites trigeri (Coquand).
1 - Lateral view of the right valve, radial bands are partially broken due to compaction. Cyclic vertical shell growth reflected
in the external ornamentation. Late Turonian. Amaseno (Ausoni Mts.). Sample PUAB-74.397.
2 - Dorsal lateral view of a curved right valve indicating unstable substrate. Clionid sponge borings can be observed. Late
Turonian. Amaseno (Ausoni Mts.). Sample PUAB-74.398.
3 - Oblique sections of partly recrystallized right valve. A bouquet made of young specimens is attached (left). Late
Turonian. Amaseno (Ausoni Mts.). Polished slab. Base width is 4 cm. Sample PUAB-74.399.
4 - Transverse section of the right valve of two specimens with well preserved cellular network. The ligament ridge can be
observed in both of them. Late Turonian. Amaseno (Ausoni Mts.). Polished slab. Base width is 6 cm. Sample PUAB74.400.
5 - Detail of the shell structure made of compact calcite layers passing into cellular network. Amaseno (Ausoni Mts.).
Polished slab. Base width is 0.7 cm. Sample PUAB-74.400a.
6 - Detail of the outer shell layer with cellular network. Late Turonian. Amaseno (Ausoni Mts.). Polished slab. Base width
is 1.2 cm. Sample PUAB-74.400a.
R. Cestari - Occurrence of Radiolites and Distefanella (Hippuritoidea) in central Italy
1891
Pl.
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
different sedimentary environments: Radiolites could
colonize mud-supported bottoms with medium to low
hydrodynamic regime of inner platform and ramp
settings while Distefanella flourished in grain-supported
deposits with medium to high hydrodynamic conditions
where common winnowing and sediment reworking
by waves and currents were a typical feature of shelf
margin settings.
As stated by Cestari & Pons (2005), the general
growth and distribution of rudist biofacies should have
been driven, among other factors, by the atmospheric
and oceanic patterns.
During great part of the Cretaceous, the
Circumglobal Tethys Current flowed westward
favouring the diffusion of bioclastic Distefanella
biofacies (among others) in the carbonate successions
today cropping out along the eastern (or Adriatic) side
of the Apennine chain. On the other hand, rudist
biofacies with Radiolites trigeri (Coquand) or Radiolites
darìo (Catullo), are commonly set as oligotypical
assemblages in mud-supported limestone that are
widespread in the carbonate successions today facing
the western (or Tyrrhenian) side. Apart the complex
and intense geodynamic history, this general asymmetric
distribution of Rudist biofacies can be assumed as
reminiscence of a windward-leeward control on
carbonate platform growth.
CONCLUSIONS
The analysis of some rudist bivalves belonging to
the Radiolitidae occurring in central Italy carbonate
successions and the examination of museum rudist
collections indicate that shell shape and structure of
these radiolitids are intimately linked to the sedimentary
environment. Radiolites trigeri (Coquand) and R. darìo
(Catullo), with this last one grouping great part of
“Gorjanovicia” taxa, are reported in Late TuronianSantonian mud-supported carbonates of inner platform
and ramp settings, pertaining to isolate carbonate
platform of the central Mediterranean area during the
Late Turonian-Santonian times.
Four species of Distefanella - i.e. D. salmojraghii
Parona, D. bassanii Parona, D. douvillei Parona, and
D. guiscardii Parona - have been taken into account;
these are reported in mainly Santonian grain-supported
bioclastic limestone of shelf margin settings with
medium to high hydrodynamic regime. It has to be noted
that the geographic distribution of these taxa is
asymmetric, with the Distefanella species well
represented in carbonate successions cropping out in
the Ocre Mts., Matese Mt. and Majella Mt., while the
other two Radiolites species are well represented in
muddy deposits of the western carbonate successions
as in the Simbruini Mts. and in the Ausoni Mts.
This distribution has to be referred to the complex
physiography of the carbonate platforms in the
Mediterranean Tethys during the Turonian-Santonian
(Late Cretaceous) that favoured the spreading of certain
taxa in the different carbonate platform environments.
The diffusion of bioclastic rudist biofacies, such as
the Distefanella biofacies, in the carbonate successions
today cropping out along the eastern (or Adriatic) side
of the Apennine chain should have to be related to the
atmospheric and oceanic patterns linked to the
Circumglobal Tethys Current that, during great part of
the Late Cretaceous, flowed westward. On the other
hand, rudist biofacies with Radiolites trigeri or R. darìo,
are commonly set as oligotypical assemblages in mudsupported deposits that are widespread in the carbonate
successions today facing the western (or Tyrrhenian)
side.
Apart the complex and intense geodynamic history,
this general asymmetric distribution of rudist biofacies
can be assumed as reminiscence of a windward-leeward
control on carbonate platform growth.
ACKNOWLEDGEMENTS
Many thanks to Prof. R. Matteucci of the “La Sapienza”
University of Rome and Prof. J.M. Pons of the Universitat
Autònoma de Barcelona, who kindly followed and improved
this work. I am also indebted to Prof. J. Pignatti for his review of
a draft of this paper. Review by Prof. A. Laviano and suggestions
by the Board of the Bollettino della Società Paleontologica Italiana
are gratefully acknowledged. Thanks are due to Dott.ssa I. Del
EXPLANATION OF PLATE 2
Figs. 1-3
- Radiolites darìo (Catullo).
1 - Lateral view of two right valves with conical shape. Sonnino, Ausoni Mts. Base 7 cm. “La Sapienza “ University
collection.
2 - Shell concentration in mud-supported limestone. Sonnino area, Ausoni Mts. Hammer on the left as size reference.
3 - Slender specimen with multigeniculate growth in soft sediment. Sonnino area, Ausoni Mts. Pen in the upper right corner
as size reference.
Figs. 4-6
- Specimens of the genus Distefanella.
4 - D. douvillei Parona. Transverse section of the right valve set in bioclastic grainstone made of fragments of other
radiolitids. Inghiottitoio succession, Ocre Mts. Base width is 10 cm.
5 - D. salmojraghii Parona side view of the holotype with both the valves. Note the left (upper) valve with cupular shape.
Bassani Collection, CMSN-17006.
6 - Distefanella thicket made of tens slender specimens in bioclastic limestone, also with multigeniculate growth indicating
soft bottoms (e.g. specimens on the right upper corner). Focalone Mt., Majella Mt.
R. Cestari - Occurrence of Radiolites and Distefanella (Hippuritoidea) in central Italy
1912
Pl.
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
Re of the Centro Musei delle Scienze Naturali di Napoli for the
facilities given in studying the Bassani collection.
Work presented at the final meeting of the COFIN Project
2002-2004 “La risposta delle piattaforme carbonatiche alle
variazioni climatiche: esempi dal Triassico e dal Terziario
mediterraneo”, held in Modena on 8 July 2005.
This work is dedicated to the memory of my father Generoso.
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Manuscript received 01 September 2005
Revised manuscript accepted 21 October 2005