Lochkovian (Lower Devonian) marine-deposits from the Rio Malinfier West section (Carnic Alps, Italy)

Annalisa Ferretti,Carlo Corradini,Luca Simonetto,Maria G Corriga,Monica Pondrelli,Paolo Serventi

doi:10.3301/ijg.2018.33

Abstract

The Rio Malinfier West section in the central Carnic Alps provides important data on the evolution of the Lochkovian (Lower Devonian) sedimentary basins of the Variscan belt. An exposure of about 100 m documents five lithostratigraphic units (Alticola, Rauchkofel, Nolbling, La Valute and Findenig formations) spanning in age from the latest Silurian to the Early Devonian. The complex structural setting of the section results from a main fault dividing the succession in two separate segments. A precise lithological characterization was carried on at a macro- and micro-scale. Macrofauna includes, among others, abundant cephalopods and crinoids (loboliths). The biostratigraphic assignment to the uppermost Silurian-lowermost Devonian (Lochkovian) was possible basing on a moderately abundant conodont fauna, that provided thirty-two taxa belonging to thirteen genera, among which the new species Zieglerodina schoenlaubi. The Rio Malinfier West section testifies that a differentiation between shallow and deep water parts of the Devonian basin was already present during Lochkovian times, prior to the establishment of the conditions enabling the colonization of the well-known upper Lower-Middle Devonian reef buildings.

Highlights

The Carnic Alps are located on both sides of the ItalianAustrian border
This interval is crucial in understanding the evolution of the Carnic basin, as it was just in this time frame that patch reefs evolved for the first time
We focused our attention to a geographic sector in the proximity of the Rio Malinfier creek, in the central Carnic Alps (Fig. 1), where distal deposits were accumulating throughout the Early Devonian, in order to contribute with a punctual and integrated analysis to the reconstruction of the evolution of the entire basin

Summary

INTRODUCTION

The Carnic Alps are located on both sides of the ItalianAustrian border. Here, one of the best exposed and most complete Palaeozoic successions in the world, ranging in age from the Middle Ordovician to the Late Permian, is documented. The Variscan sequence is laterally uniform across the Cason di Lanza Pass area with the exception of the Eifelian-Frasnian interval, when the basin differentiated in a shallow water sector (dominated by back-reef and reef deposits) and a more distal part (with pelagic deposits interlayered by gravity driven re-deposited material coming from the shallow water units) (Pondrelli et alii, 2015) In this area, the Variscan orogeny generated a top to the south detachment, leading to the formation of a pluri-kilometric asymmetric NW-SE trending fold with an overturned flank which includes the Zermula and Pizzul mountains and the Rio Malinfier-Rio Sglirs area (Venturini, 1990). A good biostratigraphy of these units based on graptolites was provided by Jaeger & Schönlaub (1977, 1980)

MATERIAL AND METHODS

CONCLUSIONS