Late -pleistocene and holocene ephemeral lakes of Campo Imperatore and the Gran Sasso d’Italia Massif (Abruzzo-Central Italy)

Abstract

On the Gran Sasso Massif some sediments of several ephemeral lakes have been found, dated to the last gladal maximum, to the late-gladal and to the Holocene. The sediments point out the presence of lakes outside the frontal moraines (in one of these have been deposited sediments dated 22.6S0±530 and 22.350±300 years BP), behind that moraines or in depression formed by the melting of dead ice during the glacial retreat. The presence of lakes testifies a water surplus, clearly produced by the low temperature, that partially inhibited the evaporation, and by the melting of the glaciers. A small lake appeared in Val Venacquaro, far a shart periad beginning from i1.760±160 years BP: according to the etJemical ori gin of the sediments, it formed during a humid but mild phase, probably during the B0l1ing-Allemd interstade. A smalllake appeared around S035±i 40 years BP in a depression, on the debris of the former rock glacier of Sorgente Fontari: the lake point out the melting of the permafrost, and one can inter a temperature increase. During the Glocene, other three phases of development of ephemeral lakes, Iinked to climatic factors, are known: the first is dated around 6,000-5,000 years BP; the second and third, shorter than the first one, begun at 3790±90 years BP and after the development of a soil dated 3440±65 years BP. The climatlc conditions during the three periods of the Glocene in which were present the lakes, had to favor a positive water budget in the depressions. The positive budget could derive from factors as the variations in the amount or in the distribution of the precipitations, or tram oscillations in the mean annual temperature. The dating of the lacustrine sediments of the Gran Sasso Massif has allowed to establish that they have the same age of other sediments of ephemerallakes found on other massif in Central ltaly. AUTHOR KEYWORDS: Upper Pleistocene, Holocene, ephemeral lakes, Gran Sasso Massif.