Preliminary results on the "Grotta del Lago" Holocene deposits (Triponzo, Nera River Valley, Umbria, central Italy)

Abstract

The results of geological, paleontological, archeological investiga-tions and of radiocarbon dating on the cave filling deposits of Grotta del Lago (a cave near Triponzo, in the Nera River Valley, Umbria, central Italy) are presented. These allow for a first reconstruction of the Holocene evolution of the Triponzo Lake. Data show that the lake level progressively rised after the damming of the Nera and Corno rivers because of the development of a travertine threshold (probably triggered by the climatic amelioration at the Pieistocene/Holocene boundary). Man occupied the cave about 6,500 years BP, during the Atlantic chronozone, when the lacustrine sediments were being deposited some 10-15 m below the cave entrance. The lake deposits sealed the archeological site during the Subboreal chronozone, probably about 4,000 years BP and the lake reached its maximum level (417 m a.s.l.) ca. 3,100 years BP. The climatic deterioration of this period is recorded by the limnetic ostracod assemblages which are characterized by oligothermophilous species. After this time, the rivers started the erosive action, and about 50 m of Holocene sediments were eroded, down to the present talweg elevation, at a rate of 1.7 cm/year.