SR-ISOTOPE-STRATIGRAPHY OF THE GONFOLITE-LOMBARDA-GROUP (SOUTH-ALPINEMOLASSE, NORTHERN ITALY) AND RADIOMETRIC CONSTRAINTS FOR ITS AGE OF DEPOSITION

Sr isotope ratios in mollusc shells from the deep water sediments of t he Oligocene Chiasso Formation and of the Oligo-Miocene Gonfolite Lomb arda Group are in fine with the biostratigraphically established depos itional ages for the different formations. They show that Sr isotope d ating can be a valuable tool also in marine depositional setting domin ated by clastic input of recycled continental crustal material. Radiom etric signatures in clasts of Tertiary intrusive rocks further constra in the depositional age of non-fossiliferous deep sea conglomerates (V illa Olmo Conglomerate [max. age 31.7 +/- 0.5 Ma], Como Conglomerate [ 29.2 +/- 3.2 Ma] and Lucino Conglomerate (21.0 +/- 2.4 Ma]). Radiometr ic dating of the cooling history of pebbles (FT on apatite: 20.4 +/- 2 .0 Ma) derived from the Novate intrusion (almost-equal-to 26 Ma) sugge st a possible correlation of the southernmost outcrops of conglomerate s of the Gonfolite Lombarda Group (Castiglione Olona) with the Lucino Conglomerate. This would imply a north-vergent thrust, similar to the Monteolimpino thrust, between Castiglione Olona and Gurone.