Radiolites and D - Società Paleontologica Italiana
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Radiolites and D - Società Paleontologica Italiana
185 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; [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 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, 186 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. 188 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. 190 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. 192 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. REFERENCES Accordi G. & Carbone F. (1988). Sequenze carbonatiche mesocenozoiche. 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Manuscript received 01 September 2005 Revised manuscript accepted 21 October 2005