The Tertiary-Piedmont Basin (NW Italy) is an episutural basin that developed from the late Eocene on the Alps-Apennines tectonic junction. Several coeval geodynamic processes, including the loading and exhumation of the Western Alps, the outward migration of the Apennine accretionary wedge and the opening of the Liguro-Provençal rift basin, controlled the basin evolution. We integrate fluid-inclusion microthermometry, low-temperature thermochronology and burial history with numerical modelling to constrain the palaeo-geothermal gradients required and evaluate the mechanisms that governed the basin thermal history. Apatite fissiontrack and (U-Th-Sm)/He analyses of the basal late Eocene turbidites show reset ages of ca. 25 and 20 Ma, respectively, which require temperatures to be >120°C.Homogenization temperatures up to ca. 130°C from fluid inclusion analyses from authigenic minerals confirm the thermochronometric data, supporting a significant post-depositional heating in the lower sequence of the basin. Stratigraphic reconstructions and decompaction of the basin fill indicate that the maximum burial experienced by the basal strata at 25 Ma is 2.3 ± 0.1 km, which is not sufficient to reset the AFT thermochronometric system when applying a typical geothermal gradient (ca. 20-30°C/km). An elevated geothermal gradient of 45 ± 5°C/km is thus necessary to explain the thermochronometric dates and the elevated thermal signature at shallow depths. 2D numerical simulations indicate that such an elevated palaeogeothermal gradient can be best explained by mantle upwelling, consistent with crustal thinning caused by the inception of the Liguro-Provençal rift basin and related outward migration of the Alpine and Apennine fronts during the Oligocene.

<p>The Tertiary Piedmont Basin (TPB) in NW Italy represents an episutural basin developed since the Late Eocene in the retrobelt of the Western Alps and in the foreland of the Northern Apennine. During Oligo-Miocene time, up to 3 km-thick clastic deposits filled the basin recording the tectonics associated with the shift from the Alpine collisional thickening and the progressive NE-migration of the Apennine. The continental thickening was also accompanied by the opening of the Liguro-Provençal Basin and the drift of the Corsica-Sardinia block. Because of this key-position, the tectono-sedimentary and thermochronological history of the TPB has been the object of extensive investigations (Maino et al., 2013 and reference therein). However, several questions regarding its burial-exhumation history are still open. In order to define the thermal history of the source-sink system, we combined literature data with new detrital apatite fission-track analyses and zircon U-Pb dating from Upper Priabonian to Lower Miocene syn-tectonic deposits. Results from AFT analysis show: i) a single reset population at 24.8 ± 1.2 Ma (Late Chattian) in the lowermost Late Priabonian sample; ii) partially annealed apatite grains from Early Rupelian sample; iii) unannealed Late Rupelian-Miocene samples with AFT age populations spanning from Late Cretaceous to Late Oligocene in time. Data from the Ligurian Alps crystalline massifs report similar AFT cooling ages between 22.9 ± 5.3 - 24.0 ± 1.4 Ma. This, combined with our data, shows that the bottom of the TPB sequence experienced ~110 °C heating and subsequent cooling together with its nearby margin. The heating experienced by the basin combined with reconstructed sedimentary thickness (before the exhumation/cooling event) of ca. < 3 km, implies an elevated geothermal gradient of about 60 °C/Km, which is anomalous for a thickened orogenic crust. Furthermore, one sample from Upper Oligocene sedimentary rocks contains an AFT detrital population age (33.6 ± 2 Ma) consistent with a youngest U-Pb age peak of 33.6 Ma from co-magmatic zircon grains, which likely reflects the age of volcanites today buried under the Po Plain (Di Giulio et al., 2001). Detrital zircon U-Pb ages show two main populations at ca. 290 and ca. 460 Ma, which are expected products of a Variscan source now exposed in the Ligurian Alps and Southern Alps. Our new geo-thermochronological data overall suggests a distributed Oligocene thermal signal, the origin of which is discussed. Possible explanations are: 1) a > 3 km of focused erosion associated with tectonic deformation occurred in the TPB and nearby margin and/or 2) an anomalously high heat flow event driven by asthenospheric rise as a consequence of the Liguro-Provençal rifting.</p><p>Maino M., Decarlis A., Felletti F., Seno S. (2013) Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo–Miocene central Mediterranean geodynamics. Tectonics, 32, 593–619.</p><p>Di Giulio, A., Carrapa B., Fantoni R., Gorla L., Valdisturlo L. (2001) Middle Eocene to Early Miocene sedimentary evolution of the western segment of the South Alpine foredeep (Italy). Int. J. Earth Sci., 90, 534-548.</p>

The sedimentary architecture of channelized turbidites can be highly complex as it reflects the response of submarine channels to several interplaying factors. Although intensively investigated through seismic imaging, turbidite channel fills are not convincingly calibrated for sedimentary facies at a sub‐seismic scale. This contribution addresses the sedimentary architecture and the controls on the evolution of a ca 20 m thick channel‐levee complex of the Tachrift turbidite subunit (Upper Miocene, the Melloulou Formation), which accumulated along the southern slope of the Neogene Taza‐Guercif Basin (Rifian Corridor of north‐east Morocco). Facies and architectural analyses indicate that the studied channel‐levee complex is the result of three‐fold evolution. From base to top, it is comprised of: (i) a ca 7 m thick lower mud‐prone interval containing relatively small and vertically stacked channel fills with poorly developed muddy levees; (ii) a ca 4 m thick and >1 km wide sandstone‐rich middle interval made of lateral accretion packages that become progressively less amalgamated and fine‐grained and is overlain by ca 5 m of thin‐bedded mud‐rich turbidites intercalated with hemiplegic marlstones; and (iii) an up to ca 9 m thick upper interval constituted by aggradational channel fills with well‐developed levees and variously directed lateral accretion packages. This organization suggests that, following a phase of inception (lower interval), the channel underwent extensive meandering with very minor vertical aggradation, prior to being blanketed by ‘retrogressive’ muddy lobes (middle interval) during a phase of reduced sediment input. In turn, the uppermost interval records a late phase of channel re‐establishment and aggradation that likely terminated as a result of up‐dip avulsion. It is suggested that the observed change of architectural style reflected the feedback of changing sediment input, slope equilibrium profile and channel morphodynamics.