Microbial–Serpulid Build-Ups in the Norian–Rhaetian

Paper 245 Disc

Microbial±serpulid build-ups in the Norian±Rhaetian of the Western Mediterranean area: ecological response of shelf margin communities to stressed environments Simonetta Cirilli1*, Alessandro Iannace2, Flavio Jadoul3 and Valeria Zamparelli2 1Dipartimento di Scienze della Terra, Piazza UniversitaÁ, 06100, Perugia, Italy, 2Dipartimento di Scienze della Terra, Largo San Marcellino, 80138 Napoli, Italy, 3Dipartimento di Scienze della Terra, Via Mangiagalli, 20133 Milano, Italy

ABSTRACT Microbial±serpulid communities are the main reef-builders of roughly parallel to the Piedmont±Ligurian Ocean spreading axis most Norian±Rhaetian carbonate platforms of Italy.They during the Jurassic.Dysoxic and mesosaline waters are the main represent minor, yet significant communities in the shallow cause of the success of the Norian microbial±serpulid build-ups; western Tethys, in contrast with the highly diversified sponge- whereas, from the late Norian to the Rhaetian, eutrophication and coral-dominated Dachstein reefs widespread from Eastern and climate change control their distribution.These environ- Alps to Australia.The microbial±serpulid build-ups are ments acted during Norian±Rhaetian times as refuges, where systematically associated with narrow intraplatform troughs opportunitistic organisms could survive and build frameworks and developed on the outer margin±upper slope area under during a period otherwise dominated by coralgal reefs. marine conditions unsuitable for the development of coralgal reefs.The development of these settings can be related to Terra Nova, 11, 195±202, 1999 transtensional tectonics affecting an elongate belt which was

marine conditions were unsuitable for spread along most of the Italian penin- Introduction the development of coral±sponge reefs. sula, from the Southern Alps through Phanerozoic reef history is character- During the Norian, the western part to the southern Apennines. ized by a succession of evolutionary of the Tethys gulf was characterized by a In this paper Rhaetian is used in the pulses, mainly interrupted by mass ex- wide carbonate platform system (Bosel- sense recommended by the Subcom- tinctions, with each pulse dominated by lini, 1973; Laubscher and Bernoulli, mission of Triassic Stratigraphy (Gae- a different type of metazoan group reef. 1977; Marcoux et al., 1993). Inner plat- tani, 1992), as a stage with S. reticulatus The abundance of these skeletal com- form facies (Hauptdolomit/Dolomia zone as lower boundary. Where possi- munities was the controlling factor in Principale) were bordered to the east ble, Norian has been distinguished the occurrence of microbial reef and in by marginal facies (Dachstein Lime- from the Rhaetian; otherwise a generic the absence of ecological competition stone) passing laterally to various kinds Norian±Rhaetian age has been used. from metazoans, microbial commu- of open marine basinal sediments (i.e. nities dominated Precambrian plat- Hallstatt, Lagonegro and Imerese ba- Norian platform facies distribution forms (Grotzinger, 1989). Following sins) (Fig. 1). Wide areas were also the appearance of metazoans, microbial characterized by carbonate-evaporitic The Dolomia Principale (DP) is the build-ups only dominated either after sedimentation (e.g. Burano Anhydrite typical facies of Norian platforms that mass extinctions or in particular ecolo- Fm.). Landward, the inner platform was are represented by thick (up to 2000 m), gical niches which became their `refuges' bordered by clastic±evaporitic facies of well-bedded successions of peritidal do- against competition from the larger me- the German Keuper. Transtensional lomites mainly arranged in shallowing tazoans (Pratt, 1995; Webb, 1996) tectonics starting in the uppermost Nor- upward cycles. The subtidal facies are The Late Triassic shallow marine ian±Rhaetian, affected a belt adjacent to characterized mainly by the presence of facies of western Tethys illustrate this the future opening axis of the Piedmont± gastropods, megalodontid bivalve and variant ecological behaviour against a Ligurian Ocean, and started to dissect dasycladacean algae. background of Norian±Rhaetian reefs the wide carbonate shelves whilst cli- The eastern border area between the that were dominated by sphinctozoan- mate shifted towards more humid con- shallow inner platform of western coral build-ups (FluÈ gel and Senowbari- ditions (Cirilli et al., 1993, 1994; Jadoul Tethys and the basinal facies (Hall- Daryan, 1996). However, as will be et al., 1994; Cirilli, 1995). statt-type facies of Western Alps and documented in this paper, microbial This early rifting stage culminated Dinarides) were dominated by calcar- communities associated with serpulids with the drowning of most carbonate eous megalodon-bearing back-reef cyc- were a significant, yet subordinate, platform systems during the middle± lic facies (Dachstein Limestone of component of reefs during Norian± late Jurassic as the Piedmont±Ligurian Zankl, 1971) (Fig. 1) and massive Rhaetian times in the shallow western ocean opened. These depositional sys- Dachstein reefs (Tollmann, 1976; Se- Tethys. These peculiar build-ups devel- tems are now preserved in tectonic units nowbari-Daryan, 1980). These reefs oped on the margins of epicontinental, belonging to a number of different do- have been studied intensively in several intraplatform, suboxic basins, where mains (Southern Alps, Northern Cal- classic localities of the Northern Cal- careous Alps, Central Austroalpine, careous Alps and Slovenia. The main *Correspondence: Fax: +39/075-5853203; Apennines, Transdanubian Central reef-builders were sponges and corals E-mail: [email protected] Range, etc.). The studied areas (Fig. 2) associated with a highly diversified

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SOUTHERN * ALPS Milano APENNINES Sestri-Voltaggio lineament NORTHERN

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Fig.1 Late Triassic palaeogeography of Western Tethys (modified after Fig.2 Main structural domains of Italy and geographical Stampfli and Marchant, 1997) with location of the intraplatform location of the studied successions. troughs containing marginal microbialite±serpulid build-ups; Im, Imerese; La, Lagonegro; Cal, Calabria; Ap, Alpujarride; Lo, Lombar- dia; Ca, Carnia; Au, Austroalpino; Bu, Burano. fauna and flora, as well as microbial facies contain bioclastic grainstones teristic serpulid bafflestone is present, crusts. Similar reefs occur also in Sicily, and bindstones with fenestral fabrics consisting of clusters of vertically grow- Greece and eastward to Australia (Cirilli and Tannoia, 1985; Jadoul, ing serpulids (Cirilli and Tannoia, 1985; (FluÈ gel, 1982; Fagerstrom, 1987; FluÈ gel 1985; Cirilli, 1993; Berra and Jadoul, Cirilli, 1993; Claps et al., 1996; Iannace and Senowbari-Daryan, 1996). 1996; Climaco et al., 1997); mega-tee- and Zamparelli, 1996; Climaco et al., pee structures are common and host 1997) (Fig. 5). The serpulid aggregates, large amounts of laminated early ce- ranging in diameter from 10 cm up to 50 Norian microbial serpulid mounds ments (Climaco et al., 1997). The slopes cm, sometimes directly encrust large Within the extensive shallow platform facies comprise various kind of talus bioclasts, mostly represented by gastro- of the Dolomia Principale, narrow and mass-flow deposits interfingering, pods and brachiopods (Cirilli, 1993). troughs started to open up during the basinward, with organic-rich turbiditic Associated facies are thin-shelled, ar- middle±late Norian (Jadoul et al., 1992; dolomites and tempestites (Cirilli and ticulated pelecypod-or brachiopod- Zappaterra, 1994) as a consequence of Tannoia, 1985; Jadoul, 1985; Cirilli, bearing packstones. Locally, corals the earliest Alpine Tethyan rifting. 1993; Claps et al., 1996). In all these and calcareous sponge, `problematica' Most of these intraplatform basins basin±platform systems, boundstone and solenoporaceae can be present show similar facies associations and facies are developed in the outer plat- (Cirilli, 1993; Climaco et al., 1997). In depositional patterns (Cirilli and Tan- form margin and the middle±upper Northern Calabria (Climaco et al., noia, 1985; Jadoul, 1985; Cirilli, 1993; slope area, just below storm wavebase. 1997) the fauna frequently include as- Berra and Jadoul, 1996; Claps et al., Build-ups show lenticular shapes and semblages of small (5 1cm) sponges 1996; Iannace and Zamparelli, 1996; can reach about 10 m in thickness. Reef and rare, larger sphinctozoan sponges Climaco et al., 1997; Zamparelli et al., complexes reach thicknesses ranging (Deningeria iannacei, Colospongia sp., 1997; Zamparelli et al., 1999). They between a few tens to several hundreds Amblysiphonella sp.; Senowbari-Dar- were quite limited in extent (a few to of metres. They consist of massive do- yan and Zamparelli, 1999). some 20 km in length and some 5±8 km lomites dominated by microbial±serpu- The reefs are associated with abun- in width) and characterized by well- lid boundstones (Fig. 5). Microbialites dant floatstones and rudstones which bedded, laminated organic-rich muddy display mammillary stromatolitic and are more or less regularly dispersed limestones/dolostones in their axial thrombolitic textures (Cirilli, 1997; Ian- within the boundstone and laterally to part. Fossils are generally absent or nace and Zamparelli, 1996) (Figs 3, 4); it, representing talus breccias (Fig. 6). are represented only by ostracods, but they are generally predominant quanti- The breccia clasts have the same com- fishes and terrestrial reptiles were tatively in the organic boundstone, position as the boundstones, consisting found in some horizons within the Cal- with serpulids confined to the core of of microbialite±serpulid fragments care di Zorzino Auct. (Lombardian the framework something coated by mixed with bioclasts of various organ- pre-Alps) (Tintori, 1995). The marginal thick microbial crusts. Locally, charac- isms (corals, calcareous sponges, gas-

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started in the middle Norian (Cirilli et al., 1993, 1994; Jadoul et al., 1994; Cirilli, 1995). Associated with this siliciclastic input, a large amount of organic matter was deposited and preserved in these sediments (Cirilli, 1995). In the more eastern and southern part of the Adria plate (Southern Alps and South- ern Apennines), the restricted and com- pletely dolomitized facies of the DP are replaced by Dachstein-type carbonate platforms which are generally dolomitized only in their intertidal±supratidal portions (Zankl, 1971; Iannace and Fri- sia, 1994; and references therein). The shallow marine Dachstein-type reefs were still flourishing in the easternmost areas (Senowbari-Daryan-B. 1980; FluÈ - gel, 1981), and are generally transgres- sive over DP facies. A partial recovery of carbonate pro- Fig.3 Boundstone consisting of serpulid shells surrounded by microbial crusts with duction in the Lombardy Basin and clotted microfabrics. Two thin-shelled pelecypods are present. Dolomitization has Northern Apennines is achieved in the obscured most microtextural details (Norian, northern Calabria; field view 3.5 cm). Rhaetian, with the establishment of homoclinal carbonate±siliciclastic ramps. Some of these ramps are colonized by coral-dominated patch reefs associated with small serpulid aggregates (Jadoul et al., 1994; Lakew, 1994). Only locally in the Northern Apennines have true microbial±serpulid reefs been found within muddy ramp sediments (Cirilli, 1997).

Palaeoenvironmental settingof microbial-serpulid reefs Microbial±serpulid association and the coeval diverse Dachstein-type reefs (Fig. 7), colonized wide areas characterized by different palaeoenvironmental parameters and geodynamic evolution. The microbial±serpulid build-ups occur in a subbioprovince whose location was controlled indirectly by the Late Triassic transtensional tectonics which generated the pull-apart basins. Fig.4 Field view of a microbial boundstone with characteristic thrombolitic texture. The dendroid light-coloured patches represent fine-grained infill of framework cavities However, the oceanographic and eco- (Northern Calabria; scale bars in cm). logical parameters which influenced their unusual setting and peculiar biological composition are less clear. tropods, megalodonts, foraminifers, important facies and biofacies changes The reefs always occur on the slopes calcareous algae and ostracods) and over the entire Western Tethys area. A and margins of dysoxic±suboxic basins intraclasts. The rudstone clasts are lo- decrease in carbonate accumulation is and in association with basinal dys- cally coated by microbial laminae and recorded in most of the northernmost aerobic biofacies. by sessile foraminifers. areas, which became sites of marine In recent settings, the mass occur- mixed siliciclastic±carbonate sedimen- rence of serpulids is recorded mainly in tation. This clay input is considered to ecologically extremely-stressed envir- Upper Norian±Rhaetian mixed be the expression of a fluvial±deltaic onments, related to either very low tem- siliciclastic-carbonate ramps development coming from Western peratures (Antarctica, Kirkwood and The geodynamic and climatic changes Eurasia in response to a shift towards Burton, 1988) or very high tempera- outlined in the introduction led to some a more warm and humid climate, which tures (308 in the Tunis Lake, Ten Howe

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stressed environments (Leeder, 1973; Mistiaen and Poncet, 1983; Palma and Angeleri, 1992; Ten Howe and Van den Hurk, 1993). In summary, the mass occurrence of serpulids seem to be related to a number of different factors all arising from conditions that have limited competition from other organisms for food and space. Present-day microbial carbonates also develop in those marine environments where they are not in ecological competition with other benthic organisms such as cryptic, dysphotic to apho- tic environments and under dysaerobic to anoxic conditions (Sageman et al., 1991; Zankl, 1993; Reitner and Neu- weiler, 1995). Large microbial build- ups have also been observed in such extreme environments as alkaline lakes Fig.5 Outcrop view of a serpulid bafflestone showing the vertical growth of most tube aggregates. The space between the individual shells is filled party by microbial, peloidal (Kempe et al., 1991; Kempe and Kaz- material and partly by cement (Monti Lattari, Southern Italy; scale bar in cm). mierczak, 1993). In the geological record microbial communities play more significant carbonate-producing roles, i.e. during the Early Triassic in post- mass extinction and recovery periods, when metazoan competition in near- shore normal marine environments was reduced and microbial communities recolonized the vacant normal marine settings (Baud et al., 1997). The co-occurrence of serpulids and microbes as the main reef builders in the Late Triassic restricted basins suggests the following stress factors: . low oxygen (dysaerobic) concentra- tions in sea water; . anomalous salinities (mainly meso- haline); . eutrophic conditions. Low oxygen trends within these basins, and in particular on the sea bot- toms, are not difficult to envisage in these Late Triassic depositional systems. Regional facies distribution and Fig.6 Field detail of a talus breccia with rounded pebbles of microbial boundstones (Northern Calabria; scale bars in cm). their relationships show that these basins were relatively deep troughs within a large epicontinental shelf. Within a warm climate, a stable pycnocline and Van den Hurk, 1993) and to a very viour and reef-building capabilities of might be easily established in these broad range of salinities (Hedgpeth, these suspension-feeding organisms is basins (Tyson and Pearson, 1991), lead- 1957; Mastrangelo and Passeri, 1975; favoured by larval retention which ing to the formation of low-oxygen Davaud et al., 1994). Significantly, they may occur in environments with re- waters at the basin depocentre and along have also been observed to dominate duced sea water exchange and high the slopes. On the upper part of the benthic communities formed after mass primary productivity (Bosence, 1979). slope, microbial±serpulid communities mortality in suboxic shelf environment In the geological record serpulids are appear to have been the only organisms (Stachowitsch, 1991; Harper et al., commonly found as accessory consti- able to thrive. Occasionally, better bot- 1991). In fact, serpulids are amongst tuents of shallow water communities. tom conditions, particularly in the shal- the most tolerant organisms to low Only in some instances have they been lowest areas, allowed the repopulation oxygen bottom-water conditions (Sage- described as the main consituent of by pelecypod or brachiopod commu- man et al., 1991). The gregarious beha- carbonate sediments in anomalously nities rich in small-sized individuals. In

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Dachstein-type reefs which would have induced water stra- tification. This is witnessed in the Constructors uppermost Norian and Rhaetian of the Alps and Northern Apennines by Sphinctozoa Sphinctozoa Scleractinia Sphinctozoa the fine terrigenous input and by the death type and preservation of organic matter Binders death Bafflers (Jadoul et al., 1994). Cyanophyta Inozoa The high detrital input and likely Solenoporacea Spongiomorphida Problematica Crinoidea associated nutrients might also have Bryozoa fossil Serpulida reef induced eutrophication of the water diagenesis community diagenesis mass and an increase in the amount of particulate organic carbon in the eco- system, with a reduction of water trans- Destroyers Dwellers parency. Both of these factors would Brchiopoda, Mollusca Bivalvia, Algae Fishes, Reptilia, Dasycladacea have prevented the growth of the nor- Crustacea, Echinodermata death mally oligotrophic coralgal reef system. Foraminiferida However, invertebrate suspension fee- Microbial–Serpulid reefs ders (i.e. serpulids) would appear to be favoured by eutrophic conditions (cf. Constructors Braiser, 1995). Eutrophic conditions

Microbialites Serpulida might also have inhibited the distribu- Microbialites Serpulida tion of dinoflagellates which are inter-

death preted to have been symbionts of Trias- Binders Bafflers death sic corals (Bucefalo Palliani and Cyanophyta Sphinctozoa Riding, 1998). Problematica Spongiomorfida Serpulida Serpulida fossil reef Palaeogeographic implications diagenesis community diagenesis The palaeogeography of the Mesozoic Tethys has been the subject of several Dwellers Destroyers research projects (Dercourt et al., 1986; Brachiopoda, Mollusca Fishes, Reptilia, Dasycladacea Bivalvia, Algae Ziegler, 1988; Dercourt et al., 1993; Crustacea Foraminiferida death Stampfli and Marchant, 1997) which aim to find the `best fit' of all the available palaeomagnetic, palaeogeographic, geodynamic, petrological and geological data. Our challenge is to find, Fig.7 Comparison betweeen the guild community structure of typical Upper Triassic within the framework provided by these Dachstein reef from Northern Calcareous Alps, Austria and Bavaria (above, from studies, a reliable palaeoceanographic Fagerstrom, 1987) with that of the microbial±serpulid build-ups of the Southern Alps, explanation for the development of the Apennines and Betic Cordillera (below). microbial±serpulid build-ups. In all the available palaeogeographic maps for the Norian±Rhaetian, the ba- shallow-water areas, fair weather and pered water circulation and increased sins we have discussed in this paper storm wave activity was sufficient to salinity. Thus, a marine environment occupied a continuous belt from the mix the water column, and the facies with widespread mesosaline conditions Southern Alps through to the Northern and biota of the typical cyclic peritidal was likely to have been established on and Southern Apennines (Zamparelli and light-coloured facies of the DP in- most of the DP shelf; only in particular et al., 1999) (Fig. 1). An interesting dicate a very shallow to emergent envir- areas (Apulia) and in transitional en- point is that this belt may be extended onment with normal marine oxygen le- vironments to the Eurasian continent to the Betic Cordillera to the south- vels at the sediment±water interface. (Keuper evaporites) did water concen- west, where build-ups with analogous The surface water composition, how- trations exceed the threshold for sul- features have already been described ever, was likely to have been affected by phate precipitation (Fig. 1). Such a (Martin and Braga, 1987). The data evaporation given the arid climate scenario has been suggested previously summarized here show that this palaeo- which has been inferred by the facies to explain also the anomalous massive geographic sector of the Western of the DP and the palaeolatitude calcu- dolomitization and positive d18O va- Tethys was affected in the late Triassic lation (Marcoux et al., 1993). In addi- lues which characterize DP sediments by transtensional tectonics leading to tion, the complicated physiography, (Iannace and Frisia, 1994). pull-apart basins which formed the in- comprising flat emergent islands and These palaeoceanographic condi- trashelf troughs. This geodynamic set- shallow basins dispersed on a shelf tions were stable until the upper Norian ting is reflected in the Newark Basin on covering many thousands of square when they changed dramatically be- the North American passive margin kilometres would have further ham- cause of periodic fresh water influx (Olsen, 1988).

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In this scenario, the Dachstein-type in the internal parts of the shelves, on (G. Larwood and B.R. Rosen, eds). Spec. reefs that developed on the margins of the margin of restricted intrashelf Publ. Syst. Ass.,11, 299±318. shelves with good connections to open troughs with limited water exchange Braiser, M. and D., 1995. Fossil indicators seas and coastal downwelling, caused with open seas. These peculiar commu- of nutrient levels. 1: Eutrophication and climate change. In: Marine by westerly winds, provided the opti- nities represent an ecological adapta- Palaeoenvironmental Analysis from Fossils mum oligotrophic life conditions for tion to restricted conditions induced by (D.W.J. Bosence and P.A. Allison, eds). Sphinctozoa±coral±algal communities. the interplay of hydrodynamic and cli- Spec. Publ. Geol. Soc. London, 83, In contrast, rift-related intrashelf matic factors. 113±132. troughs were isolated from the open 3 The intraplatform troughs extended Bucefalo Palliani, R. and Riding, J.B., 1998. marine basins and microbial±serpulid from the easternmost Southern Alps, The influence of palaeoenvironmental communities thrived as an ecological via the western side of Apulia to south evolution on dinoflagellate cyst- response to the peculiar environmental of the Iberian massif. These troughs distribution: an example from the Lower conditions therein developed through were related to early extensional±trans- and Middle Jurassic of Quercy, southwest the mechanisms outlined above. tensional tectonics preceding the Juras- France. Bull. Cent. Rech. Expl.-Prod. Elf- Aquitaine, 21(1), 107±123. The relative abundance of sphinc- sic Piedmont±Ligurian Ocean opening, Cirilli, S., 1993. Il Trias di Filettino- tozoan sponges in Calabria, coupled which occurred immediately to the Vallepietra (Monti Simbruini, Appennino with the existence of Dachstein-type north and west of this belt. Centrale). Boll. Soc. Geol. Ital., 112, reefs in the Triassic of Sicily, may relate 4 During the Late Triassic, microbial 371±394. to more open marine conditions and build-ups were subordinate to coral± Cirilli, S., 1995. Upper Triassic black shales closely matches the recent palaeogeo- sponge reefs, being confined to ecolo- in the western Tethys and their graphic model proposed by Stampfli gical niches inhospitable to metazoans. palaeoclimatological meaning. In: Black and Marchant (1997). In fact, the biota Following the mass extinction event Shales Models (W. Oscmann, ed.), 3rd present in Calabria can be seen as tran- affecting reefs at the Triassic±Jurassic EPA Workshp, Europal, 8, 63. Cirilli, S., 1997. Environmental versus sitional between the more simple mi- boundary (Stanley, 1988), microbial organic controls on biogenic mud crobial±serpulid assemblages described reefs temporarily resurrected the domi- mounds: examples from the Upper in this paper and the highly diversified nant role they had in every period of Triassic of the Northern and Central reefs of Sicily. This would suggest that Earth history devoid of skeletal me- Apennines (Italy). In: Biosedimentology of the isolation of the intraplatform tazoan reef-builders (Webb, 1996). Microbial Buildups (F. Neuweiler, J. troughs occurring from Southern Alps Reitner, C.L.V. Monty, eds), IGCP to Betic Cordillera was interrupted Project N. 380 Proceedings of 2nd Acknowledgements around Calabria and Sicily by a more Meeting, Gottingen/Germany 1996. open seaway which can be seen in the The authors wish to tank Prof. D. Bosence Facies, 36, Part. XVIII, 257±262. western prolongation of Eastern Med- (Royal Holloway University of London Cirilli, S. and Tannoia, G., 1985. Studio stratigrafico e sedimentologico di un iterranean ocean of Stampfli and Egham, surrey) and Prof. A. Hallam (Uni- versity of Birmingham), for the suggestions particolare sistema di margine e bacino Marchant (1997). nella Dolomia Principale dell'area di An analogous facies transition is re- which improved the quality of this paper. This work was financial supported by Italian Menaggio (Lago di Como). Mem. Soc. corded also in the Eastern Alps when CNR (Zamparelli V; 1997±99 project). Geol. Ital., 30, 313±326. the eastern oceanic basins are ap- Cirilli, S., Bucefalo, R. and Pontini, R., proached. These connections became 1993. Palynolstratigraphy and even better established during Upper References palynofacies of the Late Triassic R. Norian±Rhaetian times in the South- contorta facies in the Northern ern±Eastern Alps as a result of the Baud, A., Cirilli, S. and Marcoux, J., 1997. Apennines: (I) The La Spezia Formation. Â westward-spreading ocean (Zamparelli Biotic response to mass extinction: the Rev. Paleobiogr., 12(1), 179±192. Cirilli, S., Bucefalo, R. and Pontini, R., et al., 1999). lowermost Triassic Microbialites. In: Biosedimentology of Microbial Buildups 1994. ±Palynolstratigraphy and (F. Neuweiler et al., eds), Proceedings of palynofacies of the Late Triassic R. Conclusions 2nd Meeting, IGCP Project No. 380, contorta facies in the Northern Apennines: (II) The Monte Cetona 1 In the Upper Triassic of the western Gottingen, Germany, 1996. Facies, 36, 238±242. Formation. Rev. PaleÂobiogr., 13(2), Tethys, two main reefal communities Berra, F. and Jadoul, F., 1996. Norian 319±339. were present. Alongside the widespread Serpulids and microbial bioconstructions: Claps, M., Trombetta, G.L. and Picotti, V., and well-known Dachstein-type sphinc- implication for the platform evolution in 1996. Il bioerma del Monte Zenone tozoan/coral dominated reefs, micro- the Lombardy basin, Southern Alps. (Norico, Prealpi bresciane): facies, bial±serpulid build-ups developed in Facies, 36, 143±162. geometrie e ambiente deposizionale. Atti areas now represented by carbonate Bosellini, A., 1973. Modello geodinamico e Ticin. Sci. Terra (Serie. spec.) 3±18. successions of Southern Alps, Apen- paleotettonico delle Alpi Meridionali Climaco, A., Boni, M., Iannace, A. and Zamparelli, V., 1997. The depositional nines and the Betic Cordillera. durante il Giurassico-Cretacico: sue system of the Upper Triassic carbonates 2 The Dachstein-type reefs had the possibili implicazioni agli Appennini. Quaderno 183. Accad. Naz. Lincei, 183, of `Verbicaro Unit' (Lucania and palaeoecological characteristics of 163±205. Calabria, Southern Italy. Facies, 36, highly diverse communities and devel- Bosence, D.W.J., 1979. The factors leading 37±56. oped on the shelf margins facing open to aggregation and reef formation in Davaud, E., Strasser, A. and Jedoui, Y., basins. In contrast, the microbial±ser- Serpula vermicularis L. In: Biology 1994. Stromatolite and serpulid bioherms pulid communities and reefs developed and Systematics of Colonial Organisms in a Holocene restricted lagoon, Sabkha el

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