Evoluzione quaternaria della Laguna di Marano (Friuli Venezia Giulia)

Abstract

Wells (drilled to a depth of about 30 m) in the Marano Lagoon (Northern Adriatic Sea) have pointed out a succession of continental sediments covered by transgressive lagoonal-littoral deposits derived from the Isonzo drainage basin. 14C datings of peat, bivalves and organic matter have given an age of 20,200 ± 270 years S.P., for the "basali" continental deposits, of 5,540 ±225 years B.P., for the lower lagoonal deposits and 1,400 ±290 years B.P., for the upper lagoonal deposits.The continental sequence is dominated by sandy, subordinately pelitic alluvial deposits, alternating with recurrent marsh episodes, from Würm IIIIII to Upper Atlantic or up to the Present. Lagoonal deposits are pelitic-sandy to sandy-pelitic-organogenous indicating proximity to a lagoon mouth (inlet). The lagoonal facies has tourned out to be roughly contemporary to analogous environments of the Northern Adriatic Sea, notably in the Venice and Caorle Lagoon; its formation shows to be mainly related to the Holocene eustatic rise of the sea level. Littoral deposits have only been found in corrispondence with the modern barrier island of the Marano Lagoon. They are made up of sands and shell horizons marking the gradual transition, from bottom to top, from shoreface-foreshore to backshore facies. The position of the present shoreline has to be considered, with the exception of local fluctuations, the northernmost reached by the sea, after the last glacial period. The present configuration of the lagoon was reached during the historical age (late-Roman), by the connection of the barrier island with the prograding delta of R. Tagliamento.