The Pre-Variscan sequence of the Carnic Alps

The Pre-Variscan sequence of the Carnic Alps includes rocks deposited between the Middle Ordovician and the early Late Carboniferous, and represents one of the most continuous sequence of the world in that time interval. In a relatively small area it is possible to distinguish rocks deposited at various latitudes and climate (from cold in the Ordovician to tropical in the Devonian), and in different sedimentary environments (from shallow water, including reef deposition, to basin). The lithostratigraphy of the sequence has been recently revised and formalised, and 36 formations have been discriminated

Insight into the development of a carbonate platform through a multi-disciplinary approach - A case study from the Upper Devonian slope deposits of Mount Freikofel (Carnic Alps, Austria/Italy)

The development and behavior of Million year-scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. Therefore, the understanding of palaeoenvironmental changes that occur in geological past is still limited. We herein undertake a multi-disciplinary approach (sedimentology, conodont biostratigraphy, magnetic susceptibility and geochemistry) of a long-term succession in the Carnic Alps which offers new insights into the peculiar evolution of one of the best example of Palaeozoic carbonate platform in Europe. The Freikofel section, located in the central part of the Carnic Alps represents an outstanding succession in a fore-reef setting, extending from the latest Givetian (indet. falsiovalis conodont Zones) to the early Famennian (Lower crepida conodont Zone). Sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore-reef slope deposits. The most distal setting is characterized by an autochthonous pelagic sedimentation showing local occurrence of thin-bedded turbiditic deposits. In the fore-reef slope, in a more proximal setting, there is an accumulation of various autochthonous and allochthonous fine- to coarse-grained sediments originated from the interplay of gravity-flow currents derived from the shallow-water and deeper-water area. The temporal evolution of microfacies in the Freikofel section evolves in two main steps corresponding to the Freikofel (Unit 1) and the Pal (Unit 2) Limestones. Distal slope to fore-reef lithologies and associate changes are from base to top of the section: (U1) thick bedded litho- and bioclastic breccia beds with local fining upward sequence and fine-grained mudstone intercalations corresponding, in the fore-reef setting, to the dismantlement of the Eifelian – Frasnian carbonate platform during the early to late Frasnian time (falsiovalis to rhenana superzones) with one of the causes being the Late Givetian major rift pulse; (U2) occurrence of thin-bedded red nodular and cephalopod-bearing limestones with local lithoclastic grainstone intercalations corresponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin, in relation with late Frasnian sea-level rise. Magnetic susceptibility and geochemical analyses were also performed along the Freikofel section and demonstrate the inherent-parallel link existing between variation in magnetic susceptibility values and proxy for terrestrial input. Interpretation of magnetic susceptibility in term of palaeoenvironmental processes reflect that even though distality remains the major parameter influencing magnetic susceptibility values, carbonate production and water agitation also play an important role.Grants IGCP 580 and NAP0017 (DP, ACDS), the FWF P 23775-B17 (TS and EK

Late Ludfordian correlations and the Lau Event

Changes in whole conodont faunas and δ13C values are combined to achieve highresolution correlations of Upper Silurian successions in many areas (primarily Gotland, Skåne, Lithuania, Bohemia, Austria, Sardinia and Queensland); other areas are correlated with lower precision. Four of the widely recognised subzones average considerably less than 0.1 Ma and a fifth interval less than 0.01 Ma. The main constraints on resolution and precision now achievable are the amount of, and the precision in, new or previously published data from each local section; centimetric scale collecting would be worthwhile in many sections. Some stratal characters are more widespread during certain intervals than might have been expected, for example, the presence of oncolites and algal coatings in the Icriodontid Zone and the lower part of the O. snajdri Zone. Similarly, the Dayia navicula bloom in the Upper P. siluricus Subzone was widespread. So also were muddy-sandy sediments followed by oolite low in the O. snajdri Zone; crinoids flourished widely when the lower part of the Lower Icriodontid Subzone was formed. Closely spaced samples show that, in some intervals, the now well-known δ13C spike was modified considerably by fluctuations; that is, it is not a smooth plateau. The best-documented fluctuations (19 analyses) are 2.5 smooth cycles with up to 2.7‰ in amplitude during ca 12,000 years or less in the base of the O. snajdri Zone. An enigma is the depletion of the spike in some sections, especially in the best Bohemian section