Abstract

The stratigraphic section of Mt. Ramaceto is 1.015 m thick; measured layers are 2.027. It is located in the Mt. Gottero Sandstone Formation. Its lower and upper stratigraphic boundaries are defined by hemipelagic shaly units of Campanian-Maastrichtian and Paleocene age, respectively. Four members can be distinguished: 1) a lower member (140 m thick), with prevailing fine/very fine sandstones and occasional coarse-grained layers, thin layers (average thickness 12 cm), arenite-to-pelite ratio < or =1, but ratio > or =1 is well represented (41,5%), facies Mutti & Ricci Lucchi (1975) D <sub>1</sub> -D <sub>2</sub> , starting Bouma intervals d and c, prevailing thickening upward depositional sequences; 2) an intermediate member (400 m thick), with prevailing coarse-grained turbidites, average thickness 69 cm, prevailing arenite-to-pelite ratio < or =1 and remarkable amount of > or =1 (24,2%), facies D <sub>2</sub> and C <sub>1</sub> -C <sub>2</sub> , starting Bouma intervals d and subordinately a (26%), symmetric depositional sequences in which sets of coarse-grained and thicker layers alternate with sets of fine-grained and thicker layers alternate with sets of fine-grained and thinner layers; 3) an A-upper member (250 m thick), transitional, with characteristics of both the contiguous members; 4) a B-upper member (200. m thick), formed by dominant siltstone and more than 5% of isolated layers of marl with a thin calcarenaceous base, average thickness 84 cm, dominant arenite-to-pelite ratio < or =1, facies D <sub>2</sub> , starting Bouma intervals d, random depositional sequences alternate with symmetrical sequences. About twenty paleocurrent measurements from the intermediate and A-B-upper members show a wide dispersion on 160 degrees with a mean northerly flow + or -30 degrees . These characters lead to identify a succession of facies associations of lobe fringe (lower member)-->distal lobe and interlobe (intermediate member)-->fan-fringe/basin-plain (A-B-upper members). Such a sequence suggests a complete cycle of progradation-->retrogradation, which is embraced between two hemipelagic units of starved basin-plain. Therefore, the whole section is comparable with a "turbidite system sensu stricto" (Mutti & Normark, 1987) and it testifies a period of activity of the deep-fan between two quiescent periods.

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