Western Dolomites Research Articles

THE GEOLOGICAL TRAVELS OF ACHILLE DE ZIGNO IN THE DOLOMITES DURING THE SPRING OF 1846

ABSTRACT The nobleman Achille De Zigno (1813–1892) was an Italian geologist and naturalist who studied the geological and paleontological features of the Veneto and Tirol regions. His field notes were accompanied by a great number of extremely detailed drawings. His eight notebooks were written between 1841 and 1890, starting when he was 28 until shortly before his death in 1892. He sketched mountain sections, maps, geological outcrops, and he made ink drawings of fossils together with archeological and landscape views. The most impressive features in De Zigno's notebooks are the illustrations of a great number of ‘strati’. These testify to the great effort he made to understand the age and stratigraphic order of the main geological sections in the mountains which he visited. In the spring of 1846, De Zigno crossed the already renowned Dolomites and described in detail in his notebooks the geology of the area, providing a state-of-the-art account of the geological kowledge of the Dolomites during the mid-nineteenth century. Using a geological map prepared by Leopold von Buch, De Zigno travelled from Auer (Ora) to Bozen (Bolzano), walking through all the western Dolomites, including a site in the village of Predazzo. The former locality, described by Giuseppe Marzari Pencati in 1819, was renowned for its rock layer sequence which contradicted neptunism, a dominant stratigraphic theory of the early 19th century. De Zigno, in sketching the ‘Stratified rocks’ underlying the so-called ‘Primitive rocks’ that therefore were not placed at the base of the entire stratigraphic sequence, made a significant contribution to the history of geology of the Dolomites of that time.

Bivalves from the Changhsingian (upper Permian) Bellerophon Formation of the Dolomites (Italy): ancestors of Lower Triassic post‐extinction benthic communities

AbstractDiverse shallow marine fossil assemblages from the Changhsingian Bellerophon Formation (Dolomites) record late Palaeozoic marine life immediately before the end‐Permian mass extinction. We classified c. 6500 bivalves from western Dolomites localities, identifying 26 species including one new family (Ladinomyidae), three new genera (Ladinomya, Lovaralucina, Gardenapecten) and 10 new species: Acharax frenademezi, Bakevellia (Bakevellia) preromangica, Edmondia hautmanni, Etheripecten stuflesseri, Ladinomya fosteri, Lovaralucina covidi, Palaeolima badiotica, Promytilus merlai, Tambanella? stetteneckensis and Volsellina carinata. The occurrence of three Eumorphotis species with different stratigraphic distributions, leads us to propose an upper Permian ‘Lower Eumorphotis Zone’, divided into E. praecurrens, E. striatocostata and E. lorigae subzones, and distinct from the existing Lower Triassic Eumorphotis Zone (here renamed ‘Upper Eumorphotis Zone’). Palaeoecological analysis produced six biofacies and four ecofacies, based on richness, dominance and ecological lifestyle. The bivalves inhabited lagoonal to nearshore environments affected by stressed conditions: high temperatures, high salinity, shallow water depths, low oxygen and high terrigenous input. The upper Bellerophon Fm is characterized by increasingly fully marine conditions, although eurytopic taxa still suggest stressed conditions. Bivalve richness of the upper Permian Bellerophon and Lower Triassic Werfen formations was compared to estimate the genus‐level extinction rate. The disappearance of almost half (47%) of Bellerophon Fm genera is remarkably low compared with other, coeval bivalve faunas. Pre‐extinction bivalve faunas were dominated by stress‐adapted taxa (Unionites, Eumorphotis, Bakevellia, Towapteria) able to thrive in extreme environmental conditions, survive the end‐Permian mass extinction, and become the dominant biotic component of Lower Triassic benthic communities globally.

Small mammals in a mountain ecosystem: the effect of topographic, micrometeorological, and biological correlates on their community structure

An increasing number of studies have investigated spatial and temporal patterns in species richness and assemblage composition in mountain ecosystems along altitudinal gradients. Small mammals have been successfully used as indicators of environmental health and as proxies of biodiversity. However, information about the composition and distribution of species assemblages in the mosaic of habitat and rocky landform types at a high altitude is still lacking for most of the mountain regions. Through the use of live traps and camera trapping, we described the small mammal community living above the treeline of the Western Dolomites (Italian Alps), investigating the species richness, abundance of individuals and community composition in relation to topographic, micrometeorological, mesohabitat, and biological correlates. A total of five species and 50 individuals were sampled, analysed, and released. At the extremes of the analysed altitudinal range (i.e. 1900 vs 2900 m a.s.l.), community composition was completely different and species richness was related to elevation, steepness, and vegetation cover. At the same time, the taxonomic distinctness of ground-dwelling arthropods (namely carabid beetles and spiders), a proxy of habitat complexity, showed higher values in areas with a greater small mammal species richness. We found a positive effect of steepness and rocky landform type “carsism” on the number of captured individuals, showing the importance of the availability of shelters and underground burrows for the sampled species. As a confirmation of the altitudinal shift for these species in relation to the ongoing climate change, we detected a negative impact of sub-surface ground temperature on small mammal abundance during the monitoring period. In conclusion, small mammals represent an excellent model for understanding the evolutionary processes of ecosystems, population dynamics under changing environmental conditions, and habitat vulnerabilities.

Habitat and Landform Types Drive the Distribution of Carabid Beetles at High Altitudes

The high altitude mountain slopes of the Dolomites (Italian Alps) are characterized by great habitat and landform heterogeneities. In this paper, we investigated the effect of Nature 2000 habitat and landform types in driving the high altitude ground beetle (Carabidae) distribution in the Western Dolomites (Brenta group, Italy). We studied the carabid assemblages collected in 55 sampling points distributed in four Nature 2000 habitat types and four landform types located between 1860 and 2890 m above sea level (a.s.l.). Twenty-two species, half of them Alpine endemics, were sampled. Species richness and taxonomic distinctness did not show any significant difference among habitat types; conversely, these differences became significant when the landform type was considered. Total activity density and the frequency of brachypterous, endemic and predatory species showed significant differences between both habitat and landform types. Indicator species analysis identified twelve species linked to a specific habitat type and thirteen species linked to a specific landform type. Canonical correspondence analysis showed that altitude and vegetation cover drove the species distribution in each habitat and landform type while the aspect had a weak effect. Our results highlight the need for a geomorphological characterization of the sampling points when high altitude ground-dwelling arthropods are investigated.

Underground warehouses for food storage in the Dolomites (Eastern alps – Italy) and energy efficiency

Underground food storage represents an interesting solution to the increasing demand for new food storage space, combining this demand with sustainable land exploitation. It also reduces the energy demand for food conservation, therefore limiting storage costs and greenhouse gas emissions. Moreover, atmospheric conditions can be easily controlled in underground warehouses, ensuring optimal long-term maintenance of the stored food.This paper presents a case study located in the Western Dolomites (Val Di Non, Trento, Italy), where mining activity is followed by the creation of storage space not only for food, but also for groundwater and a data hosting center. After the extraction of the dolomitic rock used in construction, underground excavated spaces are converted into warehouses, whose storage capability is improved once the inner surfaces have been protected by a gas-proof mineral hydraulic lime material, developed for this purpose.The thermal behavior of the rock mass over the first few years is analyzed by means of a Finite Element Model and compared with on-site monitoring data. Laboratory measurements of the thermal properties of the dolomite rock and the temperature data registered in the field permitted the development of a preliminary numerical model, in order to describe the heat exchange between the cavern and the rock mass and supply data to support future developments. Finally, the specific energetic consumption is compared with the one required by an aboveground deposit.

Origin of Triassic magmatism of the Southern Alps (Italy): Constraints from geochemistry and Sr-Nd-Pb isotopic ratios

During Middle-early Late Triassic (∼243–235?Ma) a diffuse igneous activity developed in the Southern Alps (Italy). Sparse lava flow and pyroclastic succession remnants of such Southern Alps Triassic Igneous Rocks (SATIR) crop out in the Brescian Prealps, the Vicentinian Alps (Recoaro-Schio-Posina), Non Valley, Dolomites and Julian Alps. Plutonic rocks are found in two main plutonic complexes (Monzoni and Predazzo) and a small stock (Cima di Pape). Coeval igneous products can be traced eastward to Austria and Dinarides, for a total length of ∼450?km.The coeval formation of major late Anisian-late Ladinian carbonate platforms in the subsiding eastern Dolomites, and significant uplift and subaerial erosion in the western Dolomites suggest, for these areas, the occurrence of large-scale strike-slip and extensional tectonics with the development of horst-and-graben structures.This study reports the first complete review of the SATIR activity, including new mineral chemical data on 14 samples, 61 major and trace element whole rock analyses and 7 Sr-Nd-Pb isotopic ratios for volcanic and plutonic samples from Dolomites (lavas plus Monzoni and Predazzo plutonic rocks) and Vicentinian Alps lavas. Despite the variable post-magmatic modifications, the large areal distribution of the products and their wide spectrum of chemical compositions, these samples show rather common geochemical and mineralogical characteristics and define major and trace element trends that can be associated with nearly close-system magmatic evolution. Minor upper crustal contaminations can be observed in specific cases, mostly in the most differentiated products (SiO2 >70?wt%).A specific characteristic of SATIR is their calcalkaline to shoshonitic affinity, resembling the derivation from subduction-modified mantle sources, a feature at odds with the coeval strike-slip and extensional tectonics. Geochemical modelling, petrological considerations and geological constraints allow us to propose a model in which the SATIR mantle sources reflect previous subduction metasomatism (likely occurred during Variscan times). These metasomatised mantle sources were reactivated ∼90–100 Myr after the end of the subduction, when continental rifting caused a raise of the geotherms and passive upwelling of asthenospheric mantle.

Phylogenetic position of Geitleribactron purpureum (Synechococcales, Cyanobacteria / Cyanophyceae) and its implications for the taxonomy of Chamaesiphonaceae and Leptolyngbyaceae

Over the last decades, the taxonomy of cyanobacteria has been considerably improved and restructured due to the increase in data output from molecular phylogeny. Recently, a new protocol was developed that enables reliable sequencing of 16S rRNA genes in cultivation-resistant cyanobacteria using analysis of single cells, filaments, or colonies. In the current study, we examined a sample of a heteropolar unicellular cyanobacterium, Geitleribactron purpureum, from the holotype material (deep epilithon of Lake Tovel, Western Dolomites, Italy). We isolated and purified single colonies of G. purpureum, and subjected them to direct PCR and 16S rRNA gene sequencing. We obtained a congruent set of sequences that formed a unique, isolated cyanobacterial lineage, showing phylogenetic clustering among simple filamentous genera of the family Leptolyngbyaceae. We provide evidence for deep polyphyly in Chamaesiphonaceae, and suggest that Geitleribactron should be re-classified in the Leptolyngbyaceae.

Unveiling trampling history through trackway interferences and track preservational features: a case study from the Bletterbach gorge (Redagno, Western Dolomites, Italy)

Unveiling trampling history through trackway interferences and track preservational features: a case study from the Bletterbach gorge (Redagno, Western Dolomites, Italy)

Burial history and thermal maturity of Mesozoic rocks of the Dolomites, Northern Italy

Thermal maturity analyses provide a valid basis to reconstruct the burial and temperature history of sedimentary rocks. In combination with computer based modeling it is possible to quantify former overburden and erosional thickness. This study was carried out to analyze thermal maturity and elaborate the burial history of Permo-Mesozoic sediments of the Western Dolomites, Northern Italy. Based on their location in the non-metamorphosed Southern Alps of the Alpine realm, the Dolomites are well suited to study thermal maturation in a complex orogenic setting. Determination of maturity was carried out by vitrinite reflectance and solid bitumen reflectance measurements on a large number of samples as well as by Rock–Eval pyrolysis. Vitrinite reflectance commonly ranges between 0.5 % VRr for Triassic and 0.76 % VRr for Permian sediments allowing an analysis of the lateral and vertical maturation patterns. Several 1D basin models were developed and calibrated by maturity measurements. Results show that deepest burial probably occurred at the end of Cretaceous times, followed by erosion of about 1800 ± 200 m. The estimated heat flows were moderate with 75 mW/m2 for Jurassic rifting, 46 mW/m2 for times of deepest burial and 41 mW/m2 for present day.

Palynology of the Permian and Triassic of the Tesero and Bulla sections (Western Dolomites, Italy) and consideration about the enigmatic species Reduviasporonites chalastus

A palynological study of two Permian–Triassic sections of the Southern Alps (Tesero and Bulla sections) was carried out in order to correlate the palynological data with the available conodont zones. Both the sections crop out in the Western Dolomites, the Tesero section in Fiemme Valley and the Bulla section in Badia valley.The two sections include the uppermost Bellerophon Formation and the overlying Werfen Formation. In the latter the Permian/Triassic boundary (Farabegoli et al., 2007) has been defined by conodonts. The palynological assemblages collected in both sections throughout the Bellerophon up to the Werfen formations show compositional variation marked by: a) a dominance of taeniate and non-taeniate bisaccates in the Bellerophon Formation dated as Late Permian; b) a bloom of the organic microfossil incertae sedis Reduviasporonites chalastus in the lower Tesero Member (Werfen Formation), found only in the Tesero section. This interval should stratigraphically lie below the Permian/Triassic boundary, as defined by conodonts recorded in the Bulla section; c) poorly preserved acavate and bisaccate taxa in the upper Tesero Member, above the Permian/Triassic boundary, and in the overlying Mazzin Member of the Tesero section. The origin and the ecological preferences of Reduviasporonites chalastus and the implications of its worldwide distribution across the Permian/Triassic boundary are also discussed.

EVIDENCE FOR LADINIAN (MIDDLE TRIASSIC) PLATFORM PROGRADATION IN THE GYULAKESZI AREA, TAPOLCA BASIN, WESTERN HUNGARY: MICROFACIES ANALYSIS AND BIOSTRATIGRAPHY

A shallowing-upward carbonate sequence was studied from the outcrop at Gyulakeszi, Tapolca Basin (western Hungary), and it is interpreted as a Middle Triassic ( Curionii or younger) platform progradation. Two lithostratigraphic units are distinguished. Microfacies analysis and micropaleontological investigation conducted on the red nodular, cherty limestone (Vaszoly and Buchenstein formations) suggest that the lower unit was deposited during the Reitzi and the Secedensis ammonoid zones. The overlying white platform limestone (upper unit) is typical of a prograding platform and includes gravity-driven deposits at the base followed by periplatform facies deposited in shallow marine warm waters around the fair-weather wave base. The section at Gyulakeszi was unaffected by fabric-destructive dolomitization, which is uncharacteristic of similar platform facies in the Balaton Highland. Isopachous and radiaxial fibrous calcite cement found in the grainstone and boundstone facies are indicative of early lithification and diagenesis in the marine phreatic zone. “Evinospongiae”-type cement is described for the first time from the Balaton Highland and it is similar to the outer platform cements published previously from the Alps (Italy and Austria). The progradation could have advanced over the pelagic limestones as early as the Curionii zone, which is an undocumented event in the Veszprem Plateau. Similar event, however, is well known from the Western Dolomites, where aggradation was followed by intense progradation during the Gredleri and Archelaus ammonoid zones. The length of this progradation event at Gyulakeszi, however, is ambiguous since proven Ladinian (Longobardian) rocks are not exposed in the study area and were not penetrated by boreholes in the Tapolca Basin.

Geological map of the Middle Triassic Latemar platform (Western Dolomites, Northern Italy)

The Latemar is a Middle Triassic isolated carbonate buildup with a diameter of approximately 3 km, that crops out in the western Dolomites, northern Italy. The platform is an important case study and potential analogue for carbonate hydrocarbon reservoirs. Detailed field mapping of the platform has been carried out on a high-resolution topographic base extracted from airborne LIDAR to produce a geological map at 1:5000 scale. Remote sensing was used for the recognition of structural features and then validated in the field. In addition, high-resolution digital photographs were used to interpret the geology of inaccessible rock walls. This work represents a up-to-date detailed geologic map of the Middle Triassic Latemar platform that enhances its internal units subdivision and highlights its complex shape, characterized by gulfs and internal basins and strongly controlled by synsedimentary tectonics.

Runout analysis of a large rockfall in the Dolomites/Italian Alps using LIDAR derived particle sizes and shapes

ABSTRACTLiDAR data were used to quantify and analyse a rockfall event which occurred in 2003 in the Western Dolomites (Italian Alps). In addition to previously existing airborne laserscanning (ALS) data, high resolution terrestrial laserscanning (TLS) data were collected. By using the original point clouds, the volume, axial ratio and runout length of single boulders as well as the surface roughness in the runout zone of the rockfall were derived. The total volume of the rockfall event of approximately 10 000 m³ was estimated by a reconstruction of the pre‐event surface at the detachment zone. The analysis of the laser scanning data of the accumulation zone revealed a power law scaling for boulder volumes larger than 8 m³. The dependence of runout length on boulder volume is complex; it is moderated by particle sphericity.In addition, we used ALS and TLS data to derive the spatial distribution of surface roughness on the talus cone. TLS allow for more accurate roughness mapping than ALS data, but for most applications the point density of ALS data seems to be sufficiently high to derive measures of roughness. Different sampling approaches for plane fitting on the scale of 5 m did not show significant effects besides the computational time. The results of our analyses provide important perspectives for rockfall modelling and process understanding with potential applications in both ‘applied’ (natural hazards) and ‘pure’ geomorphological research. Copyright © 2012 John Wiley & Sons, Ltd.

Biogeochemical characterization of automicrites building the Cipit Boulders of the Ladinian-Carnian platforms in the Dolomites (northeastern Italy)

The sedimentological features and the microfacies of the Cassian platforms (Late Ladinian – Early Carnian) of the Dolomites (northeastern Italy) can be studied only on the basis of the so called Cipit boulders, that are platform-derived olistoliths and clasts fed to the basin and escaped to the extensive dolomitization affecting the platform limestone.The Punta Grohmann section (Sassolungo, Western Dolomites) is one of the most classical Late Ladinian – Early Carnian basin successions (Wengen and S. Cassiano Formations) of Dolomites in which several levels containing gravity-displaced carbonate olistoliths occur. The carbonate platforms, from which the olistoliths derive, were made up mainly of carbonate mud, interpreted as microbialite, and therefore they can be regarded as mud mounds (Russo et alii, 1997, 1998).Skeletal organisms (Tubiphytes, skeletal cyanobacteria, sphinctozoan sponges, etc.) represent a minor component of the rock (usually less than 10%). On the contrary the composition of Cipit boulders is dominated by the micritic fraction (about 60%), mainly represented by automicrite, with subordinate amounts of micrite interpreted as detrital (allomicrite).The microbialites or automicrites, which may exhibit both dense microcrystalline (aphanitic) or peloidal microfabric, are sometimes organized in stromatolitic laminae or thrombolitic fabric. The organic-induced nature of microbialite was supposed on the base micromorphological evidence and epifl uorescence observations (Russo et alii, 1997).To corroborate the microbialitic model of Russo et alii (1997) for the Late Ladinian – Early Carnian platforms buildups, biogeochemical analyses have been carried out on selected samples of carbonate boulders. Fourier Transformed Infra-Red (FT-IR) spectroscopy and Gas Chromatography Mass Spectrometry (GC-MS) analyses have been performed to confirm the presence of organic matter remains and identify the metabolic signature of bacteria/cyanobacteria.The geochemical characterization of extracted organic matter shows a great prevalence of the aromatic fraction over the aliphatic and carboxylic ones.The FT-IR spectra reveal the presence of stretching C=C vibrations attributable to alkene and/or unsaturated carboxylic acids, that may be synthesized by microbes. GC-MS investigations indicate the presence of extended hopane series, short chain methyl-steranes (C22, C23), straight chain saturated (C14, C16), monounsaturated (C17:1, C18:1), and diunsaturated C18-acids, diagnostic of microbial activity.All data confi rmed the presence of bacteria/cyanobacteria communities during platform deposition, indicating that microbes have played a prominent role in the genesis of these carbonates. These communities created the chemical conditions that triggered the induced precipitation of great volumes of syndepositionally-cemented automicrites, which stabilized the carbonate bodies controlling their depositional geometries.

The Latemar: A Middle Triassic polygonal fault-block platform controlled by synsedimentary tectonics

Detailed field mapping of a Middle Triassic carbonate buildup, the Latemar in the western Dolomites, northern Italy, has been carried out. The Latemar is an isolated carbonate buildup that nucleates on a fault-bounded structural high (horst) cut into the underlying late Anisian carbonate bank of the Contrin Fm. This study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase. In an early phase, slopes were mostly composed of well bedded, clinostratified grainstones and rudstones. In a later stage, the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias. The upper portion of slopes is a microbial boundstone with abundant Tubiphytes and patches or lenses of grainstone. Boundstones may occasionally expand into the platform interior and downward to the base of the slope. The depositional profile was that of a mounded platform. The buildup is dissected by a dense framework of high angle fractures and faults, and by magmatic and sedimentary dikes, exhibiting two principal directions trending NNW–SSE and ENE–WSW. Faults trending WNW–ESE were also observed. Magmatic dikes are related to the emplacement of the nearby Predazzo intrusion and are thus upper Ladinian. Kinematic indicators of strike-slip activity were observed on fault planes trending NNE–SSW and NNW–SSE, that can be attributed to Cenozoic Alpine tectonics. Faults, magmatic dikes and sedimentary dikes show systematic cross-cutting relationships, with strike-slip faults cutting magmatic dikes, and magmatic dikes cutting sedimentary (neptunian) dikes. ENE–WSW and WNW–ESE faults are cut by all other structures, and record the oldest tectonic activity in the region. Structural analysis attributes this tectonic phase to an extensional stress field, with a direction of maximum extension oriented ca. N–S. Several lines of evidence, including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional, and to date it to the latest Anisian ( avisianum and crassus ammonoid biochronozones). The horse-shoe shape of the platform and its margins, rectilinear for long tracts, are explained by the existence of a network of extensional faults, whose activity lasted for part of the growth of the platform. The Latemar is thus a polygonal, fault-block platform controlled by synsedimentary tectonics. The resulting sedimentary architecture is that of a growth wedge, deposited probably on the uplifted side of a submerged half graben. Continuous reactivation of faults at platform margins locally determined anomalous facies transitions, with well layered platform interior directly in contact with the clinostratified slopes.

Marine biotic events in the Lopingian succession and latest Permian extinction in the Southern Alps (Italy)

AbstractThe Upper Permian in the eastern Southern Alps consists of an overall transgressive sedimentary succession of continental red beds (Val Gardena Sandstone), which are overlain and interfingered by the marine Bellerophon Fm, consisting of sulphate evaporites, dolomites and neritic limestones. In the western Dolomites, a key‐area for analysing the stratigraphic framework and biotic events connected with the Permian‐Triassic boundary and related mass extinction studies, the Bellerophon Fm is followed by oolitic limestone of the Werfen Fm, where the end‐Permian mass extinction and the erathem boundary, are located a few centimetres and a few metres, respectively, above the formational contact.The marine events presented here are located in three historical sections in the western Dolomites (Bletterbach, Seceda‐Monte Balest and Putia). Bioevents mostly concern brachiopod and cephalopod assemblages, discussed herein in terms of biodiversity changes and bio‐chronostratigraphic value. Recent data on cephalopod and conodont biostratigraphy have improved significantly the chronostratigraphic framework of the upper part of the succession and its correlation with other Tethyan localities. As far as nautiloids are concerned, the Tirolonautilus beds (T. crux and Tirolonautilus sebedinus lineage zone) are Changhsingian in age; while, all the Comelicania‐bearing brachiopod beds are late Changhsingian in age.The extinction pattern of the Dolomites is compared with that which occurred in the GSSP Meishan (South China) section. In both regions, the main extinction phase is probably synchronous, whereas the ultimate extinction of relicts is slightly diachronous. However, in the Dolomites the extinction seems to have been more catastrophic, because of the lack of the Chinese prelude phase, which is also characterized by miniaturization. On the other hand, the supposed coeval Dolomites assemblages have a high biodiversity, both in richness and abundance, and include gigantic brachiopod species. Copyright © 2010 John Wiley & Sons, Ltd.

PTB (Permian-Triassic Boundary) succession in the western Dolomites of the Southern Alps

PTB (Permian-Triassic Boundary) succession in the western Dolomites of the Southern Alps

Contact metamorphism and selective metasomatism of the layered Bellerophon Formation in the eastern Monzoni contact aureole, northern Italy

The Monzoni intrusive complex in the central Western Dolomites comprises a series of small monzogabbro, monzodiorite and pyroxenite intrusions, which were emplaced in previously unmetamorphosed Permo-Triassic sediments during the mid-Triassic. Intrusion depth was less than five kilometres, and solidus temperatures were 900–1000 °C. An about one kilometre wide contact aureole developed in the country rocks for which peak metamorphic temperatures of about 800 and 500 °C are derived for the immediate intrusive contact and for a distance of 380 m from the contact, respectively. The Upper Permian Bellerophon Formation is an alternating sequence of dolomite-poor and dolomite-rich limestone layers. These two lithologies behaved differently during contact metamorphism. Whereas the layers derived from dolomite-poor precursors behaved as closed systems, the layers derived from dolomite-rich lithologies were much more susceptible to the infiltration of fluids or melts. The supply of substantial amounts of silica, alumina and ferric iron from the nearby intrusions lead to high temperature metasomatism of these lithologies. Substantial chemical alteration is discernible up to 65 m away from the intrusive contact and produced clinopyroxene rich skarns, which preferentially replaced the layers derived from dolomite-rich protoliths. The presence of clintonite and melilite in the skarn assemblages indicates formation temperatures in excess of 750 °C. In contrast, the high-grade equivalents of the originally dolomite-poor lithologies largely preserved their original chemical and stable isotope compositions and do not show any evidence of pervasive fluid or melt infiltration at high-grade conditions. The syn-metamorphic permeability structure of the Bellerophon Formation appears to have been largely controlled by the lithological layering and was heterogeneous on a decimetre scale. Together with a complex folding of the country rocks this makes large scale syn-metamorphic thermally driven fluid circulation unlikely in the Bellerophon Formation.

Lateral variations in sediment composition and bedding in Middle Triassic interplatform basins (Buchenstein Formation, southern Alps, Italy)

ABSTRACT Hemipelagic deposits are widespread in Triassic sequences of the Alpine belt and provide important data for stratigraphy and the study of bedding rhythms. The area of the western and central Dolomites of northern Italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting. The Buchenstein Formation, the object of this study, was deposited in up to 1000 m deep, Middle Triassic interplatform basins, which extend over an area of 500 km2 within the Dolomites. Excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated (anoxic) and bioturbated facies down to a bed scale, and show its relationship to coeval carbonate platforms. Correlation of lithostratigraphically well‐constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow‐water debris in the succession and is a function of the distance to coeval carbonate platform sources. In the laminated background deposit, thickness variations in limestones and marls parallel the thickness variations in ash layers, and were caused by local redeposition of sediment on the basin floor. Lateral persistence of laminae indicates that bottom currents were weak in the Buchenstein basin, but were able to redeposit mud in a significant way. In the area around Seceda and Geisler (western Dolomites), a lateral transition from dark‐grey laminated to grey bioturbated to red bioturbated facies is observed, which is probably linked to local relief with different oxygenation conditions on the sea floor. A comparison shows that decimetre‐scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis. Correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin, and decrease in thickness and contain less micrite towards the east, further away from the main shallow‐water areas. Nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin. These observations point to a platform source of lime mud in the Buchenstein basin.

Erratum to: Facies interfingering and synsedimentary tectonics on late Ladinian-early Carnian carbonate platforms (Dolomites, Italy)

A stratigraphic model for carbonate platform evolution in the Dolomites during the late Ladinian–early Carnian is presented. New light on pre-Raibl growth of individual carbonate platforms of the western Dolomites was shed by biostratigraphic data combined with a revised lithostratigraphy. At the Schlern, Langkofel and Sella, the carbonate factory (Upper Schlern Dolomite) remained productive into the lowermost Carnian (Cordevolian = Aon Zone), and caused a levelling-out of the former steep platform-to-basin relief. In the eastern Dolomites, platforms were producing till basal Julian 2 (Austriacum Zone). At the Sella and Langkofel, the sedimentation pattern after deposition of the Upper Schlern Dolomite was strongly influenced by synsedimentary tectonics. A first phase of extensional tectonics led to local fissures, block-tilting, graben structures and breccia deposits. Composition and fabric of the reworked clasts argue for local-source sediments and short transport distances. The extensional structures are sealed by sediments of Lower Carnian age. Two facies belts (Schlernplateau beds and Durrenstein Dolomite), which interfinger at the western side of the Sella, reflect the shallow marine environment with terrigenous–volcanoclastic input in the western Dolomites. A second generation of breccias at the Sella documents local fracturing of the Durrenstein and Upper Schlern Dolomite. Depositional environments across the western and eastern Dolomites were largely dependent on differential subsidence. The sediments of early Carnian age on top of the Schlern platform are a few metres thick only, whereas, in the eastern Dolomite, up to 400-m-thick carbonate sediments ('Richthofen reef' and Settsass platform) were deposited. The most incomplete stratigraphic record is present at the Mendel platform in the west, where Ladinian volcanics are unconformably overlain by late Carnian 'Raibl beds'. The increase in sediment thickness towards the eastern Dolomites becomes partly visible at the eastern flank of the Sella platform. Differential subsidence across western and eastern Dolomites caused local fracturing of platform sediments. Synsedimentary extensional tectonics was a significant controlling factor to the lithofacies and thickness variations of early Carnian platform sediments in the Dolomites.