GNGTS 2013 - Atti del 32° Convegno Nazionale

The Quaternary successions within the Meduna valley are discontinuous and lacking in chronological data. Better preserved successions are located in the lower reach of the valley, at Ponte Racli with the occurrence of lacustrine bodies interbedded with deltaic or fluvial deposits, ascribed to downstream damming by moraines (Venturini, 1985) and at Del Bianco village, where fluvial conglomerates, glacial and glaciolacustrine sediments were described by Feruglio (1929). However, no specific studies are so far available for the terraces at the outlet of the valley. On the contrary, the geological surveys for the CARG-FVG Project (Zanferrari et al. , 2008) let the reconstruction of the late Quaternary evolution of the Meduna alluvial fan (Avigliano et al. , 2002). From a structural point of view, the JM gives rise to a kmWSW-ENE striking, S-vergent M. Ciaurlec anticline that involves both the Upper Jurassic-Upper Cretaceous Friulian Carbonate Platform and its Tertiary siliciclastic roofing. Moreover the prevailing siliciclastic Tertiary succession (Scaglia Rossa, Clauzetto Flysch and Miocene succession) gives rise to a WSW- ENE anticlines-synclines tight fold-system. East of Meduno locality, this structural framework shows a noticeable ondulation, probably reflecting a Cretaceous or Eocene paleostructure and causing a NW-SE striking transpressive transfer zone. Evidence of JM Quaternary activity is shown near Maniago locality, where the terraced Middle-upper Pleistocene units (respectively Maniago gravels and Maniago conglomerates: Zanferrari et al. , 2008) are uplifted and suspended on the present piedmont plain by the activity of the M. Jouf thrust; moreover, along the Colvera creek lacustrine deposits (9090 ± 90 years 14C BP) are gently folded and fractured (Zanferrari et al. , 2008). South of the JM, the Miocene succession is thrust and folded by the Arba-Ragogna thrust- system (AR in Fig. 1). It shows evidence of Quaternary activity, as testifies the angular unconformity between the Lower Messinian (Montello conglomerate) and the Early Quaternary Fig. 1 – Structural sketch of NE Italy and W-Slovenia. In the red rectangle the study area. JM: M. Jouf-Maniago thrust-system; AR: Arba Ragogna; PE: Periadriatic thrust (mod. after Zanferrari et al. , 2013). 194 GNGTS 2013 S essione 1.2