Subsidence, stress regime and rotation(s) of a tectonically active sedimentary basin within the western Alpine Orogen: the Tertiary Piedmont Basin (Alpine domain, NW Italy)

Abstract

The Oligocene to Miocene Tertiary Piedmont Basin (TPB) is located in the NW part of Italy at the junction between the Apennine and the Alpine thrust belts. The position of the TPB on top of the Alpine/Apennine Orogen poses fundamental questions as to the tectonics of the basin subsidence. Having undergone little deformation, the TPB sediments provide an insight into the stress regime and rotations in the kinematically very complex area surrounding the basin itself. In this study we integrate subsidence and structural analysis with measurements of magnetic susceptibility anisotropy (AMS) and natural remanent magnetization (NRM) in order to better constrain the tectonic kinematics of the basin evolution. A major important period of subsidence occurred in the Middle Miocene involving the whole basin. During this period the TPB experienced NE-SW-directed compression and limited shortening. Some NW-SE-directed compressional features have been identified and they were probably active during post Tortonian times. Structures associated with north-south tension are quite common, but the amount of strain that they accommodate is minor. In addition this research provides new preliminary data suggesting counterclockwise rotation in the TPB by c. 20° which has taken place during Middle Miocene time.

Provenance of Oligocene synorogenic sediments of the Ligurian Alps (NW Italy): inferences on belt age and cooling history

“…The second hypothesis is supported by data regarding the geohistory of the TPB succession (Dela Pierre et al 1995;Bersezio et al 1997;Carrapa et al 2003a). These data in conjunction with the results reported here suggest a sudden switch from fast cooling/exhumation to subsidence around the Eocene-Oligocene boundary, an overall subsidence of the basin since Early Oligocene-Late Miocene and consequent latest Miocene-Quaternary uplift responsible for the present TPB elevation (~600 m above sea level).…”

“…Subsidence started in the latest EoceneEarly Oligocene and caused the progressive drowning of the chain. The related onset of sedimentation on the belt occurred mostly in the Early Oligocene (Dela Pierre et al 1995) and continued until Late Miocene time with strong subsidence during the Langhian (Gelati et al 1993: Carrapa et al 2003a) followed by Pliocene-Quaternary uplift (Lorenz 1984) allowing the entire stratigraphic series to crop out at present.…”

New Frontiers in Integrated Solid Earth Sciences

“…The dominant source region for sediments deposited in a basin cannot be neglected, as there is a clear genetic link between the geomorphic, tectonic and sedimentological evolution of the sediment source and sink areas (Carrapa et al, 2003). This, together with sediment volumes, provides a powerful tool for estimating regionally averaged mechanical denudation rates over long time scales.…”

Pro‐ vs. retro‐foreland basins

“…Tectonic subsidence within the basin accelerated at 5–6 Ma, and either remained steady or decelerated since that time as predicted above for retro‐foreland basins. Similar examples of decelerating subsidence histories are documented for the Miocene history of the Tertiary Piedmont basin, which from Oligocene through early Miocene times was part of the western Po Basin compressional system (Carrapa et al , 2003). Hence, this basin remnant records the retro‐foreland basin of the southern French Alps, although this is complicated by Apennine deformation and loading from the south.…”