Younger Dryas to Early Holocene palaeoenvironmental evolution of the Lake Terlago (Southern Alps)

Abstract

At Terlago lake (near Trento, 415 m a.s.l.) lake sediments were drilled to a depth of 22,2 m where the bedrock was reached. Sedimentological, malacological and stable isotope analyses of freshwater shells were carried out on the recovered core. These analyses, in conjunction with 14C dating, allow the reconstruction of environmental change at Lake Terlago from the Younger Dryas to Holocene. The oldest age, 11,890±90 yr B.P. coincides with the first appearance of Pisidium sp. at 1410 cm and testifies to the complete deglaciation of the area by that time, linked to the rapid glacial retreat in the Southern Alps almost completely accomplished at beginning of the Late Glacial. The mollusc assemblage of the lower part of the core indicates deep water condition. During this interval a progressive rise in d18O from 1268 to 1090 cm has been tentatively correlated with Younger Dryas/Pre-Boreal climatic transition according to ¹⁴C ages and the d18O variation. The interval between 1090-930 cm, with enriched d18O values, may represent the Pre Boreal climatically favourable phase. In the following core section a progressive lowering of the water level and infilling of the lake is suggested from malacological analyses. Another shift in the oxygen stable isotope composition occurred just before 9310±80 ¹⁴C yr B.P. at 930-683 cm in concomitance with lithological and molluscan assemblage changes. d18O values progressively shift toward mean values found at the top of the core representative of a lake with isotopic composition similar to present-day precipitation. The change in lake level and temperature of calcification of the shell, hydrological factors, and the effect of meteoric precipitation probably all contribute to this isotopic drift.