THE PLEISTOCENE EVOLUTION OF ARZINO ALLUVIAL FAN AND WESTERN PART OF TAGLIAMENTO MORAINIC AMPHITHEATRE (FRIULI, NE ITALY)

Abstract

The Pleistocene evolution of Arzino alluvial fan and western part of Tagliamento morainic amphitheatre (Friuli, NE Italy) - The geologic
survey of the sheet 065 “Maniago” (CARG Project) allowed to gain founded data for attempting a reconstruction of Pleistocene evolution of this portion of Friuli piedmont plain, located in left hydrographic slope of Tagliamento River. Units recognised by bounding
discontinuity are Unconformity-bounded Stratigraphic Units in the meaning used in CARG Project. Eight units have been distinguished:
four related to Arzino alluvial fan, three to Tagliamento Morainic Amphitheatre and one to Ragogna Hill southern slope evolution. These units outcrop along Tagliamento left slope and inside Ponte brook valley. Arzino alluvial fan is made by stratified gravel and sandy deposits, Tagliamento basin units are made by glacial (lodgement till and melt-out till) and fluvioglacial sediments (mainly sandy gravel), while the units of Ragogna Hill southern slope are colluvial (muddy diamicton) and alluvial (sandy gravel and sand).
Relationships between Arzino alluvial fan and Tagliamento endmorain system, happened during Quaternary age, let to understand the
relative chronology of events, erosive and sedimentary, that has interested Pinzano narrow area during this time span. During early and middle Pleistocene through it Arzino Stream flew down and built an alluvial fan; then from middle Pleistocene glacial advances in
Tagliamento basin began to interfere with alluvial fan till it was completely covered during last glacial maximum in Tagliamento basin,
for which a find provided the age 19.075±160 14C yr BP.
As regards older units, probably many events are juxtaposed without recognisable and classifiable bounding surfaces, whereas chronological reconstruction becomes more reliable for late Pleistocene units.