Adelaide Mastandrea

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)

SummaryThe 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).

THE PRATI DI STUORES/STUORES WIESEN SECTION (DOLOMITES, ITALY): A CANDIDATE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASE OF THE CARNIAN STAGE

The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy) is proposed as a candidate Global Stratotype Section and Point for the base of the Carnian Stage. In addition to being a famous, richly fossiliferous locality, it includes the type-section of the Cordevolian substage. The section is located near Pralongia, along the southern slope of the crest separating the Badia/Abtei and Cordevole valleys. Below the levels with Trachyceras aon , the section contains a rich ammonoid fauna that chacterizes the lower part of the Regoledanus Subzone and subsequently records the first appearances of the mid-high latitude genus Daxatina ( Daxatina sp., D. cf. canadensis ) and of traditional Trachyceras with species different from T. aon . Moreover, the Daxatina cf. canadensis Subzone is recognised above the Regoledanus Subzone. Very rare conodonts of the Budurovignatus group and species of Gladigondolella from the diebeli Assemblage Zone occur. Gondolella polygnatyformis, already known from the Aon Subzone, is absent. Palynomorphs, foraminifers, gastropods, bivalves, brachiopods, microcrinoids and holothurian sclerites were studied. Variations in frequency and taxonomic diversity of these faunas suggest anaerobic-disaerobic bottom conditions for the lower-middle part of the section (0-105 m), followed by a more stable oxygen content in the upper portion. Magnetostratigraphy showed four intervals with normal polarity and three intervals with reversed polarity. The Daxatina cf. canadensis Subzone falls close to the normal polarity interval S2n. The present study proposes the FAD of the cosmopolitan genus Daxatina as a marker of the base of the Carnian Stage, placing it at a lower stratigraphic level than previously indicated in the Stuores area. The Prati di Stuores section is proposed as GSSP of the Ladinian-Carnian boundary.

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

SummaryThis 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.

Depositional and diagenetic history of the Alpe di Specie (Seelandalpe) fauna (Carnian, Northeastern Dolomites)

SummaryThe fauna from Alpe di Specie (Seelandalpe) is one of the most important Carnian faunas in the world. Unfortunately it has never been found in situ; it is only known from erratic boulders embedded in peaty soil in the meadows of the Alpe di Specie, where they are distributed along a continuous beltabove the deep-water S. Cassiano Fm andbelow the shallow water Dürrenstein Dolomite. Wide unexposed zones and strong tectonics make it difficult to determine their stratigraphic setting.Our research carried out in the Alpe di Specie area enabled us to reconstruct of the stratigraphic sequence at the S. Cassiano/Dürrenstein boundary. A bioclastic limestone horizon, just at the bottom of typical Dürrenstein Dolomite (Rifugio Vallandro—Dürrensteinhutte—section), contains at least three frame-builder horizons, with corals (Retiophyllia sp. and other indeterminate colonial forms), sponges and stromatoporoids in life position. Although this unit is strongly recrystallized and dolomitized, its faunal content and facies patterns show strong affinities with those of the erratic boulders. From these facts, and on the basis of the geometrical and stratigraphic relationships recognized in the study area, we think that these beds can be correlated with the erratic boulders.We propose to include the frame-builder horizons of the Rif. Vallandro section, and the isochronous erratic boulders within the Dürrenstein Dolomite, on the basis of sequence stratigraphy.From a biostratigraphic point of view, the erratic boulders and the frame-builder horizons of Rif. Vallandro can be correlated with the Austriacum Zone.In order to understand the different diagenetic histories of the dolomitized frame-builder horizons of Rif. Vallandro and of the well preserved erratic boulders, we have studied minor elements distribution and micromorphology of tissues and cements using EDS microanalyses, digital X-ray maps and SEM observations on polished and etched samples from five erratic boulders and two frame-builder horizons.The main results of these diagenetic studies are:1)the erratic boulders underwent very little diagenetic change, generally retaining the original mineralogy of their tissues and primary cements; this indicates that they remained as almost closed systems after their early diagenesis. All subsequent changes occurred without external flux of diagenetic fluids;2)by contrast, the frame-building horizons of Rif. Vallandro section are deeply recrystallized, with the matrix substituted by fine dolomite and the skeletons by blocky coarse crystalline calcite; geochemical data suggest that dolomitization and recrystallization occurred very late. These two different diagenetic histories can be explained by assuming lateral changes in the amount of shaly sediment interbedded with the boundstone. This would account for differences in diagenetic fluid flux, both primary and tectonically induced.RiassuntoLa fauna dell’Alpe di Specie è una delle più importanti faune carniche del mondo. Sfortunatamente non è mai stata rinvenuta in situ; è conosciuta esclusivamente in blocchi erratici dispersi nei prati dell’Alpe di Specie, in una fascia più o meno continua localizzata tra il tetto della Formazione di S. Cassiano e la base della Dolomia di Dürrenstein. La presenza di ampie coperture e di numerosi disturbi tettonici rende difficile la ricostruzione della loro precisa posizione stratigrafica.Recenti ricerche condotte dagli scriventi hanno permesso una miglior definizione della successione stratigrafica al limite S. Cassiano/Dürrenstein. Una sottile unità calcareo-dolomitica alla base della Dolomia di Dürrenstein (sezione del Rif. Vallandro) contiene almeno tre livelli biocostruiti, con coralli in posizione di vita, associati a spugne e stromatoporidi. Nonostante la ricristallizzazione e dolomitizzazione subita, il contenuto faunistico e le facies sedimentarie mostrano grande affinità con i blocchi erratici. Queste affinità, e i rapporti geometrici e stratigrafici tra blocchi e serie affiorante, indicano che le faune in situ e blocchi erratici sono correlabili.Sulla base della stratigrafia sequenziale, si propone di inquadrare queste due unità isocrone nella Dolomia di Dürrenstein.Dal punto di vista biostratigrafico, esse appartengono alla Zona ad Austriacum (Julico).La ricostruzione delle differenti storie diagenetiche dei blocchi erratici e degli orizzonti biocostruiti della sezione del Rif. Vallandro è stata affrontata mediante l’analisi della distribuzione degli elementi minori e lo studio della micromorfologia dei tessuti e dei cementi carbonatici, attraverso microanalisi puntuali EDS, mappe digitali della distribuzione degli elementi e osservazioni al SEM.I principali risultali relativi alla diagenesi sono:1)i blocchi erratici hanno conservato in generale la mineralogia originale sia dei tessuti sia dei cementi primari marini; questo indica che essi rimasero un sistema isolato dopo la diagenesi precoce, subendo soltanto minori trasformazioni diagenetiche senza l’apporto di fluidi esterni;2)al contrario, gli orizzonti biocostruiti del Rif. Vallandro risultano fortemente ricristallizzati, con la matrice sostituita da una dolomite finemente cristallina e i tessuti scheletrici da calcite spatica a grossi cristalli; i dati geochimici suggeriscono una dolomitizzazione e ricristallizzazione tardiva. Le due differenti storie diagenetiche possono essere spiegate in termini di variazioni laterali nella quantità di pelite alternata ai carbonati, molto maggiore nella futura ‘fascia degli erratici’ rispetto agli orizzonti biocostruiti della serie Rif. Vallandro. Ciò condizionò fortemente la permeabilità (sia primaria, sia secondaria da fratturazione tettonica) delle due unità in esame alle soluzioni diagenizzanti.

Commensal symbiosis between agglutinated polychaetes and sulfate-reducing bacteria.

Pendant bioconstructions occur within submerged caves in the Plemmirio Marine Protected Area in SE Sicily, Italy. These rigid structures, here termed biostalactites, were synsedimentarily lithified by clotted-peloidal microbial carbonate that has a high bacterial lipid biomarker content with abundant compounds derived from sulfate-reducing bacteria. The main framework builders are polychaete serpulid worms, mainly Protula with subordinate Semivermilia and Josephella. These polychaetes have lamellar and/or fibrillar wall structure. In contrast, small agglutinated terebellid tubes, which are a minor component of the biostalactites, are discontinuous and irregular with a peloidal micritic microfabric. The peloids, formed by bacterial sulfate reduction, appear to have been utilized by terebellids to construct tubes in an environment where other particulate sediment is scarce. We suggest that the bacteria obtained food from the worms in the form of fecal material and/or from the decaying tissue of surrounding organisms and that the worms obtained peloidal micrite with which to construct their tubes, either as grains and/or as tube encompassing biofilm. Peloidal worm tubes have rarely been reported in the recent but closely resemble examples in the geological record that extend back at least to the early Carboniferous. This suggests a long-lived commensal relationship between some polychaete worms and heterotrophic, especially sulfate-reducing, bacteria.

Deep-water coral banks: an example from the “Calcare di Mendicino” (Upper Miocene, Northern Calabria, Italy)

SummaryThe “Calcare di Mendicino” is a mixed carbonatesiliciclastic informal unit of Miocene (Late Tortonian-Early Messinian age), that crops out extensively in the northwestern part of the Calabria. In the Scannelle quarry near Belsito (Cosenza), four stratigraphic sections were studied to define the sedimentological and paleoecological setting. The carbonate body records the development of a deep-water coral bank characterized by a low-diverse community of azooxanthellate scleractinian (Oculina andDendrophyllia) and stylasterine hydrozoans colonies. Two main stages of bioconstruction development can be distinguished: a thicket and a bank stage. Among the biostromal dwellers the more common are bryozoans, echinoids, benthic foraminifers, gastropods, and bivalves. A higher content of planktonic foraminifers occur in the thicket stage. The coral bank flourished within the aphotic zone, with deep currents loaded with nutrients and siliciclastic sediments.The upper part of the “Calcare di Mendicino” carbonate body has been affected by a pervasive dolomitization destroying almost completely the sedimentary structures and the biofacies. The lower part, the main object of this paper, preserves the microfacies but it experienced a widespread recrystallization obliterating the primary geochemical characteristics. The diagenetic history, partly hidden, reveals three main stages: primary marine with isopachous fibrous cements, deep burial with cavities infilled by sparry calcite, and meteoric-phreatic with dog-tooth cements.

The Characterisation of Sedimentary Organic Matter in Carbonates with Fourier-Transform Infrared (FTIR) Spectroscopy

The characterisation of the insoluble macromolecular fraction of sedimentary organic matter preserved in carbonate sediments (also known as kerogen; Durand B, Kerogen: Insoluble Organic Matter from Sedimentary Rocks. Editions Technip, Paris, 1980) allowed for the identification of fossil organisms that were not otherwise preserved.

Morphological and mineralogical evolution of microfossils during the heating process: a contribution to the archaeometric study of ceramics

The role of microfossils for the ceramic paste characterization has been revealed through firing experiment. Ceramic samples were prepared with the clay of Monte San Giorgio (Sicily, Italy), that contains many microfossils that suffered relevant changes in the microstructure and chemical composition during firing temperature. The samples were fired at different conditions according to the presumed ancient techniques. The alteration and/or decomposition of mineral phases with temperature was observed with optical and electron microscopy by monitoring the mineral modifications at different firing conditions. In order to validate our approach on archaeological material, the analyses were performed also on ceramic fragments, furnished by the Ceramics Regional Museum “Antonino Ragona” of Caltagirone. The micropaleontological study, as component of the archaeometric analyses, seems to be a useful archaeothermometry for the evaluation of firing processes and sometimes decisive to distinguish the characteristics of the clay used in a given production.

Micromorphological, geochemical, and diagenetic characterization of sirenian ribs preserved in the Late Miocene paleontological site of Cessaniti (southern Calabria, Italy)

The site of Cessaniti (Vibo Valentia, Italy) has been well known since the 19th century for the richness and good preservation of its Miocene fauna and flora. The sedimentary succession of the site represents a paralic system that evolved toward an open-marine environment recording the Tortonian transgression. The fossil assemblage contains rich invertebrate (corals, bivalves, gastropods, brachiopods, echinoids, benthic and planktonic foraminifers) and vertebrate faunas (proboscideans, rhinoceroses, giraffids, bovids, sirenids, marine turtles, and fish remains). The fossils recovered at the Cessaniti site have a relevant role in phylogenetic studies and paleogeographic reconstructions of Late Miocene environments of the southern Italy. This research is focused on the microstructure and preservation state of the fossil bones. Samples of Metaxytherium sp. bones have been analyzed to understand the diagenetic profile of the bone assemblages that characterizes the taphonomic history of the Cessaniti site. The analyses provided a comprehensive account of how bone mineral (bioapatite) has been altered and demonstrated that the post-burial processes did not significantly affect the micromorphological and biogeochemical features of the bones. The excellent preservation state of the bones strengthens the importance of the Cessaniti site for studies of the Mediterranean Miocene vertebrate fauna.

Importance of Rare Earth Element Patterns in Discrimination Between Biotic and Abiotic Mineralization

Rare earth element (REE) patterns have been used to discuss the origin of rocks and minerals and the evolution processes that occurred during their formation (Goldschmidt 1954; Henderson 1996).