Formazione di Wengen

Definizione e formalizzazione unità litostratigrafic

The start-up of the Dolomia Principale/Hauptdolomit carbonate platform (Upper Triassic) in the eastern Southern Alps

Wide carbonate platform environments developed on the western passive margin of the Tethys during the Late Triassic, after a major climate change (Carnian Pluvial Episode) that produced a crisis of high-relief microbial carbonate platforms. The peritidal succession of this epicontinental platform (Dolomia Principale/Hauptdolomit, Dachstein Limestone) is widespread in the Mediterranean region. However, the start-up stage is not fully understood. The original platform to basin depositional geometries of the system have been studied in the north-eastern Southern Alps, close to the Italian/Slovenian boundary where they are exceptionally preserved. Sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile. The analysis of the facies architecture allowed reconstruction of the palaeoenvironments of the Dolomia Principale platform during its start-up and early growth stages in the late Carnian. The carbonate platform was characterized by an outer platform area, connected northward to steep slopes facing a relatively deep basin. Southward, the outer platform was connected to inner sheltered environments by a narrow, often emerged shelf crest. Behind this zone, carbonate sedimentation occurred in shallow lagoons and tidal flats, passing inward to a siliciclastic mudflat. The Dolomia Principale platform was initially aggrading and able to keep pace with a concomitant sea-level rise, and then prograding during the late Carnian. This stratigraphic interval was correlated with the Tuvalian succession of the Dolomites, allowing depiction of the depositional system on a wide scale of hundreds of kilometres. This large-scale depositional system presents features in common with some Palaeozoic and Mesozoic carbonate build-ups (for example, the Permian Capitan Reef complex, Anisian Latemar platform), both in terms of architecture and prevailing carbonate producers. A microbial-dominated carbonate factory is found in the outer platform and upper slope. The recovery of high-relief microbial carbonate platforms marks the end of the Carnian Pluvial Episode in the Tuvalian of Tethys

Conglomerato di Richthofen

Definizione e formalizzazione unità litostratigrafic

Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, Foglio 016, Dobbiaco

Note illustrative di un foglio geologico 1:50.000 del progetto CAR

Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, Foglio 029 Cortina d'Ampezzo

descrizione della geologia del foglio Cortina d'Ampezzo, con carta geologica alla scala 1:50.000 allegat

Correlation potential of Middle Triassic hemipelagic carbonate successions using carbon isotopes

Stable isotope studies of the marine Triassic have previously focused on two intervals, the Permian/Triassic and Triassic/Jurassic boundaries. The potential of stable carbon and oxygen isotopes as chemostratigraphic correlation tools, however, is largely untapped for Triassic carbonate successions. The present study was launched to explore the usefulness of carbon isotope data in correlating Middle Triassic deep-water, hemipelagic carbonate sediments of the Livinallongo Formation of the Dolomites (Southern Alps, Northern Italy). The samples come mostly from the Knollenkalke Member consisting of greenishgrey, bioturbated, nodular limestones. We analyzed the micritic calcite within individual nodules and compared its composition to that of matrix calcite as well as late diagenetic calcite veins. Thin-section examination aided by cathodoluminescence petrography and scanning electron microscopy suggest that the fine grained calcite cement in the nodules formed near the sediment-water interface and has not been diagenetically altered since then. Its carbon isotopic composition therefore most likely reflects the initial seawater isotopic composition. The carbon isotope data from the Knollenkalke Member show a secular trend of increasing values upsection which coincides with a similar trend in biostratigraphically correlated sections in eastern Romania (Atudorei et al., 1997) and Oman (Hauser et al., 2001). These preliminary results suggests the presence of a possibly Tethys-wide chemostratigraphic marker in the Middle Triassic. Hauser M. et al., 2001, Eclogae geol. Helv., 94, 29-62 Atudorei V. et al., 1997, Extended scientific report of the project 95-32 “The Triassic of north-Dobrogea”, Geological Museum, Lausanne, Switzerland