NEW OUTCROP AND SUBSURFACE DATA IN THE TERTIARY PIEDMONT BASIN(NW-ITALY): UNCONFORMITY-BOUNDED STRATIGRAPHIC UNITSAND THEIR RELATIONSHIPS WITH BASIN-MODIFICATION PHASES

摘要

This paper deals with the regional stratigraphy aroundthe Alps-Apennines junction during late Eocene-Miocene. The basin-fill architecture and its relation to changes in structural style weredeciphered through the integration of subsurface and outcrop data onthe basis of seismic- and sequence-stratigraphy principles, respectively. During late Eocene-Oligocene, the study area hosted a mosaicof partially interconnected sub-basins, and the Torino Hill area markedthe junction towards the western apex of the Southern Alps foredeep(Gonfolite Basin). Since the latest Oligocene, the uplift of the north-verging Monferrato arc provided the separation from the adjacent Gon-folite Basin and the Tertiary Piedmont Basin behaved as a larger andmore regularly subsiding thrust-top basin. The upper Eocene-Miocene successions record a long-term, ma-jor transgressive-regressive cycle, consisting of seven large-scale uncon-formity-bounded stratigraphic units, whose stacking pattern was con-trolled by changes in the rate of tectonic subsidence and whose bound-aries were generated by basin-modification phases. During the Oligo-cene-lower Miocene deepening-upward sequence set, the marginalmarine systems show a marked diachronism associated with the SW-ward change of coastal onlap, punctuated by drowning-platform uncon-formities generated in relation to basinward tilting and high-angle syn-sedimentary faults. The maximum transgression coincides with the lateBurdigalian tectonic space creation phase, when a basinwide, highlyefficient turbidite system was deposited. The middle-upper Mioceneprogradation, punctuated by forced regression pulses, was driven bythe inversion and uplift of the southern basin margin, so that a northwardshift and progressive narrowing of the turbidite depocentre occurred.