Bollettino della Società Paleontologica Italiana, 44 (3), 2005, 185-192. Modena, 30 novembre 2005185

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; [email protected]

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 Turonian- Santonian 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 medio- alto 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 They colonized diverse environments of the Mediterranean Tethys becoming significant organic In Late Cretaceous times, Rudist bivalves flourished builders and sediment constituents of neritic carbonates in carbonate platform environments, reaching their peak (Philip, 2003). Well-exposed successions yielding rudist diversity with the extraordinary diffusion of taxa bivalves have been already studied extensively in central belonging to the Radiolitidae and Hippuritidae families. Italy (e.g. Chiocchini & Mancinelli, 1977; Mariotti,

ISSN 0375-7633

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Fig. 1 - Studied localities in central Italy. a) Ocre Mts. (Rotondo Mt. and M. Orsello- Inghiottitoio 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; (Accordiella conica-Rotorbinella scarsellai Zone and Pons & Sirna, 1992; Chiocchini et al., 1994; Simone et Nezzazatinella picardi-Nummoloculina heimi pars Zone al., 2003). in Chiocchini et al., 1994). Analyses have also been This study focuses on some slender taxa belonging performed by studying specimens housed in museum to Radiolites and Distefanella of the Radiolitidae family collections (Bassani Collection housed at the Centro reported from the Turonian-Santonian (Late Musei delle Scienze Naturali di Napoli, Parona Collection Cretaceous) carbonate successions cropping out in at the University of Turin, rudist collections at “La central Apennines (central Italy) (Fig. 1). These taxa Sapienza” University of Rome and at the Museum of have been taken into account among the others as they Geology and Palaeontology of the University of Padua. show similar general shell features but different Figured samples are housed at the Departamento de relationship with the sedimentary substrate. Radiolites Geologia, Universidad Autònoma de Barcelona (label trigeri (Coquand) and R. darìo (Catullo) are mainly PUAB). 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).

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; Fig. 2 - Main shell features of a radiolitid bivalve. The right valve Stössel & Bernoulli, 2000) (Fig. 1e). The inferred age is conical to cylindrical while the left valve is usually opercular of these species is Late Turonian-Santonian (modified from Cestari & Sartorio, 1995).

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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 Fig. 3 - Radiolites sp. transverse section of the right valve. The and compact calcite outer shell layer (Pl. 1, figs. 4-6), outer shell layer shows the cellular network (a) and a well of Late Turonian age. In the same area conical to developed ligament ridge (b). Simbruini Mts. Base width = 2 cm. PUAB-74.402. 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 SHELL SHAPE AND STRUCTURE monotypic assemblages occur in mud-supported, partly dolomitized, limestone. R. darìo is found in bouquets Over the last years, rudist palaeontology focused and clusters often made of slender specimens (Pl. 2, on the relationship between morphology and substrate figs. 2-3); low growth rates produced conical (Gili et al., 1995; Sanders & Pons, 1999) also basing specimens dominated by cellular shell structure while on the comparison with other fossil groups (Seilacher, higher growth rates favoured conically shaped 1998; Johnson et al., 2002). In particular, radiolitids’ specimens with thin compact-dominated outer shell unusual morphology is the product of a peculiar layer. These species are usually represented by constructional pattern of the shell that could generate monotypical to oligotypical communities in low to extremely varied shapes from conical to more or less moderate energy mud-supported deposits, with elongate cylindrical, characterized by a well developed moderate to high sedimentation rate, mainly in inner right valve and usually by a smaller and operculiform platform to ramp settings. left valve (Fig. 2). Twenty-five species are currently assigned to the Shell structure is composed by a thin aragonitic inner genus Distefanella (Sánchez, 1981; Steuber, 2005), layer and by a thick outer low-Mg calcite layer, this among these four species instituted by Parona (1900, last often with cellular network (Fig. 3) formed during 1911) at S. Polo Matese village in the Matese Mts. have the vertical growth of laminae (or lamellae) delimitating been considered: Distefanella salmojraghii Parona, D. growth rhythms, separated by muri (Fig. 4). The bassanii Parona, D. douvillei Parona and D. guiscardii complex laminae stacking and their orientation during Parona. The left valve is cupuliform and provided with vertical growth give rise to the cellular structure (Pons a well developed cardinal apparatus that is related to a & 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 Fig. 4 - Radiolites sp. radial section of the right valve showing the superimposition of stacked laminae (L1, L2, Ln outlined scattered specimens or organized in bouquets or small lines) and muri (M1, M2, Mn) delimitating growth rhythms clusters, set in mud-supported limestone with other (GR1, GR2, GRn). Simbruini Mts. Base width = 0.5 cm. PUAB- radiolitids e.g. Durania arnaudi (Choffat), Sauvagesia 74.403.

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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 Turonian- early 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 Fig. 5 - Sketch of an elongate Radiolites, provided with a flat left depositional settings is referred to shelf margin valve, set in mud-supported sediment (on the left) and of a bioclastic deposits of Late Turonian-Coniacian age Distefanella, with a robust left valve, inserted in grain-supported (Damiani et al., 1992). deposit (on the right). LV = left valve; RV = right valve. At San Polo Matese these taxa form oligo- and monotypic banks and are in assemblages with Biradiolites canaliculatus (Pejovic), Sauvagesia DISCUSSION tenuicostata Polšak, Plagioptychus paradoxus (Matheron), Milovanovicia sp., Jerinella sp. among Great part of the shells of the considered taxa were others. These taxa flourished in marginal areas of deeply inserted in soft carbonate sediment and they carbonate platform (barrier banks in Accordi et al., can be considered as sediment stickers (Gili et al., 1995) 1990a). of semi-infauna. They could have a slender right valve In the Majella Mt., well exposed rudist assemblages with the left valve flat and little developed as in Radiolites with Distefanella are reported (Accordi et al., 1990b; or cupuliform and well developed as in Distefanella, Stössel, 1999; Stössel & Bernoulli, 2000) along with well suited for different water regimes. The inferred other taxa such as Radiolites, Praeradiolites, rapid vertical shell accretion appears as particularly Plagioptychus, Hippurites, Vaccinites, and Hippuritella. suited for distancing the commissure and its related Distefanella form nearly oligotypic assemblages that biological activity from the substrate in a valve almost can laterally extend for hundred meters. Assemblages completely inserted in soft sediment, under high are set in medium to coarse bioclastic limestone (Pl. sedimentation rate conditions (Fig. 5). The different 2, fig. 6). 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 PUAB- 74.400. 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.

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different sedimentary environments: Radiolites could Four species of Distefanella - i.e. D. salmojraghii colonize mud-supported bottoms with medium to low Parona, D. bassanii Parona, D. douvillei Parona, and hydrodynamic regime of inner platform and ramp D. guiscardii Parona - have been taken into account; settings while Distefanella flourished in grain-supported these are reported in mainly Santonian grain-supported deposits with medium to high hydrodynamic conditions bioclastic limestone of shelf margin settings with where common winnowing and sediment reworking medium to high hydrodynamic regime. It has to be noted by waves and currents were a typical feature of shelf that the geographic distribution of these taxa is margin settings. asymmetric, with the Distefanella species well As stated by Cestari & Pons (2005), the general represented in carbonate successions cropping out in growth and distribution of rudist biofacies should have the Ocre Mts., Matese Mt. and Majella Mt., while the been driven, among other factors, by the atmospheric other two Radiolites species are well represented in and oceanic patterns. muddy deposits of the western carbonate successions During great part of the Cretaceous, the as in the Simbruini Mts. and in the Ausoni Mts. Circumglobal Tethys Current flowed westward This distribution has to be referred to the complex favouring the diffusion of bioclastic Distefanella physiography of the carbonate platforms in the biofacies (among others) in the carbonate successions Mediterranean Tethys during the Turonian-Santonian today cropping out along the eastern (or Adriatic) side (Late Cretaceous) that favoured the spreading of certain of the Apennine chain. On the other hand, rudist taxa in the different carbonate platform environments. biofacies with Radiolites trigeri (Coquand) or Radiolites The diffusion of bioclastic rudist biofacies, such as darìo (Catullo), are commonly set as oligotypical the Distefanella biofacies, in the carbonate successions assemblages in mud-supported limestone that are today cropping out along the eastern (or Adriatic) side widespread in the carbonate successions today facing of the Apennine chain should have to be related to the the western (or Tyrrhenian) side. Apart the complex atmospheric and oceanic patterns linked to the and intense geodynamic history, this general asymmetric Circumglobal Tethys Current that, during great part of distribution of Rudist biofacies can be assumed as the Late Cretaceous, flowed westward. On the other reminiscence of a windward-leeward control on hand, rudist biofacies with Radiolites trigeri or R. darìo, carbonate platform growth. are commonly set as oligotypical assemblages in mud- supported deposits that are widespread in the carbonate successions today facing the western (or Tyrrhenian) CONCLUSIONS side. Apart the complex and intense geodynamic history, The analysis of some rudist bivalves belonging to this general asymmetric distribution of rudist biofacies the Radiolitidae occurring in central Italy carbonate can be assumed as reminiscence of a windward-leeward successions and the examination of museum rudist control on carbonate platform growth. collections indicate that shell shape and structure of these radiolitids are intimately linked to the sedimentary ACKNOWLEDGEMENTS environment. Radiolites trigeri (Coquand) and R. darìo (Catullo), with this last one grouping great part of Many thanks to Prof. R. Matteucci of the “La Sapienza” “Gorjanovicia” taxa, are reported in Late Turonian- University of Rome and Prof. J.M. Pons of the Universitat Santonian mud-supported carbonates of inner platform Autònoma de Barcelona, who kindly followed and improved and ramp settings, pertaining to isolate carbonate 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 platform of the central Mediterranean area during the by the Board of the Bollettino della Società Paleontologica Italiana Late Turonian-Santonian times. 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.

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