Grèzes litées e falde detritiche stratificate di origine crionivale

Grèzes litées and stratified slope deposits

Abstract

A group of stratified slope deposits are examined that were observed in different places: in the Cismòn valley (Southern Dolomites); on Prealps plateaux in the provinces of Vicenza and Verona; on the Apennines in the province of Ancona. They are described in their essential features and interpreted as deposits of periglacial environment, probably of Wurm age or late Wurm in some cases. As to considered deposits, the waste comes from the calcareous-marly rocks of the Cretaceous formations Biancone and Scaglia. Frost-weathering on these rocks produces smalì fragments and a silty-clayey material. Depositional processes of the detrital beds, often alternatively poor or rich in silty-clayey material (« lean » and « fat » beds respectively) are discussed. The grain-size analyses have shown in some deposits a large quantity of fragments whose sizes vary between 12 and 64 mm, in other ones a prevalence of those between 1 and 12 mm; the latters are to be considered grèzes litées. The shape of the slopes and the ways of deposition have influenced the attitude of the strata; most likely phenomena connected with snow melting, congelifluction and slipping intervened in transport processes. Moreover several cases of displacement of strata in these deposits, as small faults, large folds and crevasses filled up with waste are also described.