Dasycladalean green algae from the Upper Triassic of Mt. Rotonda (Verbicaro Unit, Calabria-Lucania Border, Southern Italy)

Summary A rich and diverse dasycladalean algae association is described from the Upper Triassic succession of Mt. Rotonda (Calabria-Lucania border, Southern Italy). This association consists of:Neoteutloporella rajkae n.sp.,Griphoporella bechst?dti n.sp.,Physoporella zamparelliae n.sp.,Spinaporella andalusica Flügel & Flügel-Kahler, 1984,S.? granadaensis Flügel & Flügel-Kahler, 1984,Chinianella? sp.,Gyroporella sp.,Griphoporella? sp. andPhysoporella aff.leptotheca. Neoteutloporella rajkae n.sp. is characterised by an undulated calcareous skeleton with short acrophore primary laterals bearing a tuft of 4–6 elongate, segmented, trichophore secondary laterals. This species allows to extend back to the Upper Triassic the stratigraphic range of the genusNeoteutloporella, previously known only from Upper Jurassic levels. Griphoporella bechst?dti n.sp. has a cylindrical calcareous skeleton and primary laterals only, consisting of a thin proximal part followed by a swollen portion that pinches out distally and finally opens outward with a cup-like swelling. Physoporella zamparelliae n.sp. is characterised by a calcareous skeleton made by partly welded thin individual sheaths enclosing the laterals. The laterals are piriferous, vertically compressed, roughly triangular both in vertical and in verticillar section. In some specimens they end with a spine-like thin apophysis. This species confirms that the typical Middle Triassic genusPhysoporella survived up into the Norian. The dasycladalean algal association of the Norian of Mt. Rotonda shows some similarities with the algal association found in the Upper Triassic of the Betic Cordillera whereas it is markedly different from the rich association occurring in the Upper Triassic of Sicily and of the Northern Calcareous Alps. This pattern is coupled with a different composition of the platform margin communities: microbial/serpulids bioconstructions in the Upper Triassic of the Calabria-Lucania border and of Alpujarridevs. Dachstein-type reefs in Sicily and the Northern Calcareous Alps. This indicates that the palaeoceanographic and palaeogeographic conditions controlled both the development of the different platform margin and of the different algal assemblages.     

Facies patterns of a tectonically-controlled Upper Triassic platform-slope carbonate depositional system (Carnian Prealps, Northeastern Italy)

Summary Upper Triassic (Middle-Upper Norian) shallow-water carbonates of the Dolomia Principale and its deep-water counterparts (Forni Dolomite) have been studied in the Carnian Prealps (northeastern Italy). The Dolomia Principale was a storm-dominated carbonate platform; in the Mt. Pramaggiore area, along a well-preserved 3.5 km-long platform-to-basin transition, the inner platform facies of the Dolomia Principale, characterized by m-scale shallowing upward cycles, give way seaward to open marine storm-dominated shallow subtidal lagoon deposits with frequent hardgrounds and evidence of microbial stabilization of the bottom sediment. The margin of the Dolomia Principale platform was colonized by meter-scale stromatolites and serpulid-microbial mounds that thrived due to the local highly stressed environment, characterized by drastic salinity fluctuations and turbid waters, that excluded the Upper Triassic coral-sponge communities. The Forni Dolomite slope-basin complex was characterized by an upper slope facies with debris flows, megabreccias, turbidites and serpulid-microbial mounds. The lower slope and basinal facies show thinning and fining trends. After restoring the original geometry of the slope, the depositional angles of the clinoforms range between 11 and 36 degrees, reflecting closely the coarse-grained character of the Forni Dolomite slope complex, which can be interpreted as a slope apron that, as a model, can be extended to steeply inclined carbonate slopes. The onset of synsedimentary extensional tectonics at the Middle-Late Norian boundary affected the platform-slope depositional system via: 1) localized inner platform collapses and the formation of an intraplatform anoxic depression at Mt. Valmenone, 2) a switch from platform lateral progradation during the Middle Norian to vertical aggradation in the Late Norian, reflected in an increase in platform relief, steeper foreslope angles and coarser-grained slope facies, and 3) controlling the spatial orientation of the margin of the Dolomia Principale.     

Dasycladalean algae distribution in ammonoid-bearing Middle Triassic platforms (Dolomites, Italy)

This paper gives an account of distribution of Dasycladales in ammonoid-bearing Middle Triassic carbonate platforms of the Dolomites. A ca. 600-m-thick section was investigated within the Latemar platform interior and Dasycladales from correlated ammonoid-bearing samples of the Marmolada platform were studied for comparison. At Latemar, the dense sampling allowed, with some confidence, the identification of the first occurrences of Diplopora nodosa and Gyroporella ladinica, and the last occurrences of D. annulatissima and D. comelicana. Their stratigraphic range was found to be in agreement with literature. Other first or last occurrences could not be reconciled with known distributions, and were considered as environmentally or palaeogeographically controlled. All four algal events occur within a narrow interval of two Illyrian (Upper Anisian) ammonoid subzones (avisianum and crassus subzones). This study demonstrates the biostratigraphic potential of Dasycladales in platform settings, and highlights the necessity of detailed stratigraphic studies to determine their distribution.     

Norian serpulid and microbial bioconstructions: Implication for the platform evolution in the Lombardy Basin (Southern Alps,Italy)

Summary The development of peculiar margin facies and abundant talus breccias within the Dolomia Principale inner platform is commonly observed in the Lombardy Basin during the Norian. The organisms building these margins are mainly serpulids, benthic microbes, subordinate porostomata and other encrusting forms; typical margin organisms, as sponges or corals, are extremely rare or absent. The build-ups form narrow rims along the borders of tectonic-controlled intraplatform basins. Regional back-stepping and progradation of the margin facies on the talus breccias produced by the erosion of the reef is commonly observed in the uppermost Dolomia Principale depositional system. Widespread occurrence of serpulids and microbial margins in middle-late Norian times is indicative of stressed environmental conditions—fluctuation of salinity and temperature on the inner platform and in the intraplatform basins—controlled by palaeogeographic setting. Physical characteristics allowed the bloom of forms able to develop in a wide range of environmental conditions, such as serpulids. In the Late Norian, major input of fine-grained clastics is recorded; close to the Norian-Rhaetian boundary, carbonate ramps were regionally restored. Locally, small serpulid and microbial bioconstructions still persist in the lowermost part of the shaly succession, even if they are less abundant with respect to the Dolomia Principale. Patch-reefs generally do not build a platform margin, but represent isolated mounds within shaly deposits. These build-ups occur on the edge of former structural highs; the communities survived the environmental change responsible for the siliciclastic input and locally managed to produce mounds during the deposition of the lower part of the upper depositional system (Riva di Solto Shale).     

Dasycladales from the Upper Maastrichtian of Salento Peninsula (Puglia, southern Italy)

Summary A rich dasycladalean assemblage, mainly consisting of new taxa, has been discovered in upper Maastrichtian coarse bioclastic limestones of shelf margin facies cropping out along the southeastern coast of Salento peninsula (Puglia, Southern Italy). It consists of 8 species grouped into 6 genera:Cymopolia decastroi Parente 1994;C. barattoloi Parente, 1994;Zittelina fluegeli n.sp;Jodotella koradae (Dieni, Massari & Radoicic, 1983) nov. comb.;Barattoloporella salentina n. gen. n. sp.;Morelletpora dienii n. sp.;Neomeris spp. (two different species). Zittelina fluegeli n. sp. is characterized by an ovoid thallus with calcification made by a calcareous wall enveloping only the proximal part of the branches (except in basal whorls) and by closely packed, and partly coalescent, calcified ampullae arranged all around the median and distal portion of branches. The transferral ofNeomeris (Larvaria) koradae Dieni, Massari & Radoicic, 1983 into the genusJodotella, with the new combinationJodotella koradae, is proposed on the basis of new observations on the number and arrangement of fertile ampullae. The new genusBarattoloporella, type-speciesBarattoloporella salentina n. gen. n. sp., is erected for dasycladalean algae characterized by a segmented thallus. Each segment consists of: a) basal and apical sterile whorls made by primary branches only, b) central fertile whorls made by primary branches bearing in terminal position one fertile ampulla and one or two secondary branches. morelletpora dienii n. sp. is characterized by a segmented thallus with barrel shaped to pear shaped repetitive elements, consisting of simple whorls of first order branches only. Shape of the branches varies from regularly phloiophorous to more or less differentiated in a stalk and a swollen portion, with or without a subterminal constriction. This is by far the most diverse dasycladalean assemblage ever found in the Maastrichtian. Its diversity supports the conclusion that, within the Late Cretaceous, the Maastrichtian represents a maximum in dasycladalean diversity. Its taxonomic composition strenghtens the hypothesis that dasycladaleans were hardly affected by K/T mass extinction.     

Norian calcareous Algae from the Matese Mountains (northern Campania,Italy)

The Norian portion of the Costa dei Frascari succession (Matese Mountains, northern Campania) provides an example of a calcareous algae association dominated by the family Pseudoudoteaceae; subordinately, Gymnocodiaceae and Dasycladaceae also occur. The present study deals with the record of Garwoodia maxima Dragastan, Garwoodia toomeyi Dragastan, Pseudoudotea magna Dragastan et al., Jabrianella sp., and Asterocalculus heraki Sokac and Grgasovic, from the open-lagoon carbonate deposits which were referred to the portion of the Norian below the Triasina hantkeni Zone.Riassunto. Vengono presentati i risultati di uno studio sistematico condotto sulle alghe calcaree del Norico dei Monti del Matese (Campania settentrionale), per la prima volta segnalate in Italia. La ricca associazione è composta da prevalenti pseudoudoteacee e precisamente: Garwoodia maxima, Garwoodia toomeji, Pseudoudotea magna, Jabrianella sp., oltre a Asterocalculus heraki, Heteroporella zankli e Probolocuspis espakhensis, recentemente attribuito alle Dasycladales da Senowbari-Daryan and Majidifard. I campioni analizzati provengono dalla porzione inferiore della successione della Costa dei Frascari (versante meridionale dei Monti del Matese) i cui 160 m basali sono costituiti da prevalenti calcari granulo-sostenuti e da rare intercalazioni di calcari fango-sostenuti, talora loferitici, spesso dolomitizzati e stromatolitici. Labbondanza di antozoi, chetetidi, gasteropodi di grandi dimensioni e, in particolare, di resti di echinodermi indica che tali sedimenti si sono deposti in un ambiente di open-lagoon caratterizzato da continui scambi con il mare aperto che garantivano condizioni di salinità e ossigenazione delle acque idonee a questo tipo di organismi. In base allassociazione micropaleontologica e considerata lassenza di Triasina hantkeni e di Griphoporella curvata, la cui comparsa avviene a circa 160 m dalla base della successione, questi sedimenti sono stati riferiti alla porzione di Norico sottostante la Zona a Triasina hantkeni (sensu Marcoux et al. 1993).     

Calcareous algae from the Triassic (Anisian reef boulders and Norian reef limestones) of Karaburun, western Turkey

Invertebrate Anisian and Norian reef boulders were found in the Gerence and Güvercinlik Formations, respectively, exposed in northeastern part of the Karaburun Peninsula, western Turkey. Halimedacean green algae and solenoporacean red algae, usually associated with other reef building organisms are described in this paper. The following taxa were determinated: halimedaceans: Egericodium hungaricum Flügel, Velledits, Senowbari-Daryan and Riedel, Aternasus irregularis n. gen., n. sp.; solenoporaceans: Solenopora cf. alcicornis Ott, Solenopora triasina Vinassa de Regny, Solenopora vachardi n. sp., Solenopora concentrica n. sp., Solenopora paraconcentrica n. sp., Tauristorea parallela Senowbari-Daryan and Link, Tauristorea discursa n. sp., and Parachaetetes cassianus (Flügel). The monospecific genus Aternasus n. gen. is the most abundant alga within the Anisian reef boulders. The solenoporaceans are represented by several taxa but the individual species are less abundant. E. hungaricum, T. parallela Senowbari-Daryan and Link, and S. triasina Vinassa de Regny are described from the Norian reef limestones embedded in Güvercinlik Formation, all other taxa from the Anisian reef boulders embedded in the Gerence Formation.     

Scinderella scopuliformis nov. gen., nov. sp. (Dasycladales, green algae) from the middle Triassic of Croatia

Scinderella scopuliformis nov. gen., nov. sp. is identified in the Anisian (Middle Triassic) reef limestones from the Belski dol quarry (Ivanš?ica Mt., NW Croatia). The new alga is characterised by claviform thallus, curved in the basal part, and very narrow central cavity. Thallus is often disintegrated into fragments. Laterals swell from a thin basal part, and have uniform (rarely slightly increasing) diameter along most of their length. Distally, they are flattened and probably touch each other, forming an irregular cortex. Laterals are arranged densely in close whorls and oblique to the longitudinal axis. Euspondyl arrangement is readily visible in the proximal part of the laterals, but distally, the arrangement seems more or less irregular, i.e. ruffled (Lat. scindere = ruffle, dishevel) and resembling a broom (Lat. scopulae = small broom; forma = form, shape).     

Middle Triassic carbonate deposits and calcareous algae from the Sasca zone (Southern Carpathians,Romania)

Summary The Sasca zone situated in the innermost part of the Getic Domain from the South Carpathians comprises mainly Triassic deposits of Scythian-Anisian (?Ladinian) age that can be ascribed to four different members forming the Sasca Formation. Three of the members consist of carbonate deposits. Their study permitted a brief characterization of the main microfacies types, and especially in the Valea Susara Limestone Member the identification of a relatively rich association of foraminifers and calcareous algae. The assemblage withMeandrospira dinarica, Pilammina densa, Oligoporella pilosa andPoncetella hexaster identified in these limestones indicates a Middle Anisian age (Pelsonian-Lowermost Illyrian). Difficulties arise in differentiating between the forms belonging to theOligoporella-Physoporella group for which a taxonomic revision is necessary. The morphologic characteristics of the three varieties ofDiplopora subtilis allow a splitting into different species.Teutloporella peniculiformis Ott, 1963 is regarded as anomen nudum.     

Upper Triassic (Norian) hypercalcified sponges from the Musandam Peninsula (United Arab Emirates and Oman)

Supercalcified sponges, including sphinctozoans, inozoans, chaetetids, spongiomorphids, occurring in Upper Triassic (Norian-Rhaetian) shallow-marine limestones of Musandam Mountains in United Arab Emirates (UAE), are described. The following taxa were determined: sphinctozoans: Hajarispongia osmani Senowbari-Daryan and Yancey, Nevadathalamia arabica n. sp., Nevadathalamia conica n. sp., Fanthalamia milahaensis n. sp., Iranothalamia incrustans (Boiko), Cinnabaria regularis n. sp.; inozoans: Cavsonella triassica n. sp., Molengraaffia regularis Vinassa de Regny, Peronidella? sp., Circopora cf. caucasica Moiseev, Circopora? sp.; spongiomorphids: Spongiomorpha sp.; chaetetids: Lovcenipora chaetetiformis Vinassa de Regny, Lovcenipora musandamensis n. sp., Lovcenipora sp., chaetetid sponge gen. et sp. indet. The most abundant sponge in the studied material is Nevadathalamia arabica n. sp. The described sponge association of the Arabian shelf (Musandam Mountains) shows close affinity to the sponge association known from age-equivalent terranes in the Panthalassa Ocean (Sonora Mountains in Mexico; Pilot Mountains in Nevada, USA), but is remarkably different from sponge associations in carbonates bordering the Tethys. This difference goes along with the biogeography of wallowaconchid bivalves and is most likely attributed to climatic, palaeogeographic or oceanographic factors.     

Late Triassic (Late Norian) gastropods from the Wallowa Terrane (Idaho,USA)

A diverse Late Triassic (Late Norian) gastropod fauna is described from the Mission Creek Limestone of the Wallowa terrane (Idaho, USA). Sample standardization by rarefaction analysis indicates that the fauna is even more diverse than the Late Triassic gastropod fauna from the Pucara Formation (Peru) which represents the most diverse gastropod fauna from South America. The gastropod fauna consists of 66 species; several genera are reported for the first time from North America. A high percentage of the species are highly ornamented and several have distinct siphonal canals. This suggests that the appearance of truly Mesozoic elements among the gastropods began before the Mesozoic Marine Revolution in other clades. The fauna is dominated by high-spired strongly ornamented procerithiids, a group more characteristic for the Jurassic. Comparison of the present fauna and the Iranian Nayband Formation gastropod fauna show that the procerithiids underwent a first global radiation in the Late Triassic. The high number of new species in this fauna suggests that sampling of Late Triassic gastropod faunas is still incomplete and hinders palaeobiogeographic considerations. Previous suggesions that gastropod faunas from the Wallowa and Wrangellia terranes resemble each other and are distinct from those of Alexander, Chulitna, and Farewell terranes are basically corroborated. The gastropod fauna of the Mission Creek Limestone differs considerably from that of the western and central Tethys but shares several taxa with the Late Triassic gastropod fauna of the Pucara Formation in Peru. Thus, the Hispanic corridor was probably not present in the Norian but opened only in the Early Jurassic. The subfamily Andangulariinae is introduced and placed in the Zygopleuridae. The generaSpiniomphalus, Nodoconus, Gudrunella, Blodgettella, Idahospira, andSiphonilda and the subgenusCryptaulax (Wallowax) are introduced. 27 species are erected. A lectotype is designated forCryptaulax rhabdocolpoides Haas, 1953.      

A new dasycladalean alga from the Middle Triassic carbonates of Northern Calabria (Southern Italy)

Summary A new dasyclad alga—Acicularia boniae n.sp.—is discribed from Middle Triassic (?Ladinian) of the Piano del Minatore Formation, outcropping in the Cozzo del Pellegrino area (Calabria, southern Italy). The systematic position of this species, with respect to the genusAcicularia and morphogeneraAciculella andTerquemella, is discussed.

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Riassunto Viene descritta una nuova specie di dasicladale—Acicularia boniae—proveniente dal Triassico Medio della formazione del Piano del Minatore affiorante nel massiccio del Cozzo del Pellegrino (Calabria, Italia meridionale). Viene discussa la posizione sistematica rispetto al genereAcicularia ed ai morfogeneriTerquemella edAciculella.

     

Filograna (colonial serpulid worm tubes) from Upper Triassic (Norian) reef boulders of Taurus Mts. (southern Turkey)

Two colonial serpulid worm tubes—Filograna taurica n. sp. and Filograna serialis n. sp.—from the Upper Triassic (Norian) reef boulders occurring in Taurus Mts. (south Turkey) are described. As bafflers, both species of Filograna build microbioherms reaching dimensions of up to 15 cm. Both species were not known either in Turkey or in any other Triassic localities of the Tethyan realm.     

Middle Triassic basin evolution and stratigraphy in the Carnic Alps (Austria)

Summary A local intraplatform basin developed in the Gartnerkofel-Zielkofel area of the Carnic Alps (southern Carinthia, Austria) during the Middle Triassic (Ladinian). This basin was filled with a transgressive basinal sequence composed of the Uggowitz Formation and overlying Buchenstein Formation. At the northwestern slope of the Gartnerkofel, the platform carbonates of the Schlern Dolomite interfinger with the Buchenstein Formation, causing the formation of two depositional sequences. The Uggowitz Formation consists of the Uggowitz Breccia and the Kühweg Member. Sediments of the Uggowitz Breccia were formed by different types of gravity induced processes. The Kühweg Member is a thin sequence of silt-and fine-grained sandstones which were deposited in a slope to basin margin environment by turbidity currents. The overlying Buchenstein Formation consists of hemipelagic to pelagic limestones of Fassanian age with intercalated pyroclastic rocks (Pietra verde). Nodular limestones were deposited under slow rates of accumulation during a relative sea-level highstand. The uppermost Buchenstein Formation is composed of hemipelagic limestone beds with intercalated graded calcarenites and breccias of platform-derived debris, showing characteristics features of a fore-reef slope of the prograding Schlern Dolomite. Uggowitz Formation and basal Buchenstein Formation are interpreted as a transgressive systems tract, nodular limestones from the middle part of the Buchenstein Formation mark an early highstand systems tract, forereef slope sediments of the upper Buchenstein Formation formed during the beginning regression of a late highstand systems tract, the basal part of the overlying Schlern Dolomite probably reflects a lowstand systems tract. The intercalated bedded limestone facies within the Schlern Dolomite is characterized by large, platform derived blocks, slump structures, breccia beds, graded calcarenites and hemipelagic limestones indicating a forereef slope environent. This intercalated facies belongs to the Buchenstein Formation and interfingers with the Schlern Dolomite. Conodonts from this intercalated slope facies point to Late Fassanian age. Therefore, the two Middle Triassic depositional sequences of the Gartnerkofel area can be correlated with the depositional sequences ‘Ladinian 1’ and ‘Ladinian 2’ of the Dolomites, proposed byDe Zanche et al. (1993). A brief comparison with the basinal sequences of similar age of the karawanken Mountains and the Carnia is presented.     

Carbonate facies dominated by syndepositional cements: a key component of Middle Triassic platforms. The Marmolada case history (Dolomites, Italy)

Summary This article deals with the discussion of the role of the syndepositional cementation for the growth of the Middle Triassic pre-volcanic carbonate platforms of the Dolomites (Southern Alps, Northern Italy). The study is concentrated on the Marmolada Buildup, which escaped the facies destroying dolomitization which affected many surrounding platforms. The investigations took place within an almost isochronous uppermost Anisian palcogeographic transect, ranging from the platform-top to the margin and the upper slope. Methods used include geological mapping, sedimentological and paleontological studies, evaluation of the microfacies, as well as SEM and EDS epifluorescence analyses. The well bedded platform-top succession consists of intra-bioclast calcarenites and calcirudites, interbedded with subordinate boundstones, and organized in shallowing upward, meter scale depositional cycles, sometimes capped by subaerial surfaces. The platform margin belt is rich in boundstones and lacks a primary framework formed by organisms; metazoan skeletons form less then 5% of the rock volume. The outer margin and the uppermost slope are characterized by decimeter-scale boundstone blocks, coated and linked to each other by huge amounts of radiaxial fibrous calcite cements, arranged in concentric crusts. These cements (“evinospongiac”) represent the main component of the margin and upper slope facies. Epifluorescence analyses suggest the existence of abundant organic residual matter associated not only with the bioclasts and peloids, but also with the syndepositional cements. Organic matter likely played a significant role in carbonate cementation and was a key factor for the early lithification of the platform as well as for the sediment production. Minor element microanalyses reveal an uniform Mg content in different calcite types (2–4 Mole % MgCO₃), independently from the primary nature of the components. Late diagenetic sparry calcites exhibit similar Mg values but no iron. These data point to a homogenization of minor element distribution, probably associated with a slow but long-lasting semi-closed fluid circulation, possibly related with the Neogene uplifting of the Dolomite Mountains.     

Extremely distal fluvial sandstone within the playa system of Arnstadt Formation (Norian,Late Triassic), Central Germany

The Wachsenburg Sandstone of Thuringia (Central Germany) occurs within playa deposits of the Arnstadt Formation (Late Triassic, Norian) and furnishes an example of ephemeral river metamorphosis under dryland conditions. Characterized by high flow regime features, the sand-dominated lithofacies constitution exhibits sedimentation by channel processes under the influence of recurring flash floods. Bearing signatures of subaerial exposures, the fining-upward lithofacies cycles are bound by low-angle lateral accretion elements suggesting deposition in a meandering stream. Channel migration in response to point bar expansion and active bank erosion, led to the development of four laterally shifting point bar events. Unimodal palaeocurrent patterns with low variance and azimuthal dispersion support the point bar origin of the Wachsenburg Sandstone. With reduced water budget under largely semi-arid climate, the river progressively became smaller, highly sinuous and ultimately abandoned. The resulting point bar succession was finally covered with sheet flow deposits of over bank origin. The sandstone was deposited during a period of low base-level when the playa system temporarily fell dry.     

Note on Sestrosphaera liasina (Pia, 1920) from the Lowermost Jurassic of Malga Mandrielle (type-locality, Southern Alps - Italy)

New paleontological data on Sestrosphaera liasina (Pia) based on material collected in the type-locality, Malga Mandrielle (Italian Southern Alps) are supplied. All the features of the alga are reexamined; the occurrence in the stalk region of an unusual primary lateral inner swelling is confirmed. The structure formed by the inner enlarged portion of the laterals is here indicated as inner pseudocortex. A new diagnosis of S. liasina is proposed and a lectotype is chosen from Pia's material. Finally, a paleontological reconstruction is supplied taking into account all the main biometrical values.     

New endothyrids (Foraminifera) from the Upper Visean of the northern Ural Mountains

New endothyrids from the Upper Visean of the western slope of the northern Ural Mountains are described and assigned to the new species Eoendothyranopsis (Ninella) extremus and E. (N.) poststaffelliformis.     

The mud mound nature of the Cassian Platform Margins of the Dolomites A case history: the Cipit boulders from Punta Grohmann (Sasso Piatto Massif, northern Italy)

Summary The sedimentological features and the microbiofacies of the Cassian platforms (Late Ladinian-Carnian) of the Dolomites can be studied only on the basis of the socalled “Cipit boulders”, that are platform-derived olistoliths and clasts fed to the basin and escaped to the extensive dolomitization affecting the buildups. Our paper deals with the Cipit boulders occurring in the Punta Grohmann section (Wengen and S. Cassiano formations, Late Ladinian, Archelaus and Regoledanus Zones). The dominant microfacies are represented by boundstone, consisting of nearly 60% of micritic limestone occurring both as peloidal or aphanitic micrite, mostly organized into stromatolitic laminites of thrombolites. The skeletal organism (Tubiphytes, skeletal cyanobacteria, sphinctozoan sponges, etc.) represent only a minor component of the rock (usually less than 10%). Early cements are widespread and consist both of fan-shaped calcite (replacing former aragonite), bladed isopachous magnesian calcite and radial-fibrous calcite (neomorphic after Mg-calcite). The carbonate platforms from which the olistoliths derive were made up mainly of carbonate mud that underwent early lithification, as witnessed by the considerable amount of early cements: therefore they may be regarded to as mudmounds, and more precisely as microbial mud-mounds, due to the clearly accretionary, organic-controlled nature of most micrites. The micrites, subdivided into auto- and allomicrite on the basis of micromorphological and fabric characteristics, have been tested for epifluorescence. The results confirm the organic control on the deposition of automicrite, also in the cases in which a microbial influence is not obvious (i.e. aphanitic micrite without internal organization).