Stratigraphic vs structural contacts in a late orogenic basin: the case of the Tertiary Piedmont Basin in the Sassello area (Ligurian Alps, Italy)

This geological map (1: 10.000 scale) of the 'Sassello Basin' remnant covers an area of about 33.4 km(2) of Liguria (NW Italy); it highlights the occurrence of two main types of contacts between the sediments of the Tertiary Piedmont Basin and the metamorphic substratum (Voltri Unit): (i) stratigraphic and (ii) structural (thrust or steeply dipping faults). (i) Stratigraphic contacts are represented by the main transgressive surface and the nonconformity between the metamorphic rocks of the substratum and the subaerial deposits. They are locally folded and occur along the steeply dipping short limbs of asymmetric folds related to the late-alpine/apennine tectonics. (ii) Structural contacts are related to the late-alpine/apennine tectonics (thrust faults) or (mostly) to Plio-Quaternary extensional/transtensional faulting.