Analisi stratigrafiche della sezione di Forcella China, Monte Clapsavon (Alpi Carniche – Udine). = Stratigraphic analyses of the Forcella Chiana section, Mount Clapsavon (Carnic Alps).

The stratigraphic research made on M. Clapsavon has the purpose of obtaining a stratigraphic column of “Forcella Chiana” section, where was surveyed the following formations: Calcari Dolomitici del M. Tiarfin: these are massive grey limestones with facies of carbonatic platform, precisely of a reef environment. Looking at the microfacies into the thin sections, is recognizable the typical configuration of a microbial boundstone with trombolitic structure, to be more precise is a bioconstructed limestone built by encrusting microbes. Into the sections can be observed several fossils organism like dasicladacean algae, foraminifers and ostracods, all encrusted into the biogenic micrite. The formation contains also some heavily dolomitizated layers, in which the substitution from calcite to dolomite obliterated the previous structures. Calcari Rossi ad Ammoniti del Monte Clapsavon: these are thin grained red limestones, deposed in a pelagic environment, enriched in re-crystallizated radiolarian, echinoderms and bivalves fragments immersed into a micritic matrix; the rock is grain-substained and can be defined like a packstone. At the bottom of the formation there is a breccias with clasts < 3 cm belonging to the underlying formation, that are the “Calcari Dolomitici del M. Tiarfin”. The clasts are immersed into a reddish matrix belonging to “Calcari Rossi” full of bivalvs and echinoderms’ flakes. Wengen Formation: these sandstones derive from terrigen material settled into a basin, enriched of volcanogenic products especially volcanic crystals. Moreover, portions of volcanic rocks can be included into these sandstones like isolated clasts. The colour of this rock is greenish for the occurrence of volcanic elements, sometimes with dark red halos caused by weathering. Looking at the thin sections is possible to see volcanic crystals within biological elements like radiolarian and sponges’ spiculas. Into a sample there is a volcanic clast that seems an effusive igneous rock, probably a basalt. The analysis with thin sections gave us more information about depositional environments. The “Calcari del Tiarfin” formation are typical rocks of reef zone, therefore during Middle Triassic a carbonatic platform was active. The presence of a basal breccias confirms the reef zone, but is possible that this rocks have been formed into an upper slope zone. The “Calcari Rossi ad Ammoniti del Monte Clapsavon” formation was deposed during the latemost Anisian to Late Ladinian; these limestones derives from a pelagic environment, that means the platform was pulled down by extensional tectonic activity, until the drowning of the platform. The presence of Wengen Formation indicates the following passage to open basin conditions, with heavy terrigen and volcanogenic contribution. Usually the Livinallongo Formation is stratigrafically lower then Wengen Formation; in Forcella Chiana the Livinallongo Formation is absent because is replaced by “Calcari Rossi ad Ammoniti”, which is stratigrafically equivalent.