A Small Polyhistory Foreland Basin Evolving in a Context of Oblique Convergence: The Venetian Basin (Chattian to Recent, Southern Alps, Italy)

The Venetian basin evolved in two distinct stages: (a) from the Chattian to the Langhian it behaved as a foreland basin of the Dinaric range and evolved under rather weak tectonic control, due to low rates of thrust propagation. Positive features related to the growth or rejuvenation of structural highs acted as a focus for the localization of shelf sand ridges during transgressive stages, while major regressive stages are marked by progradation of significantly diachronous sandstone bodies (during the late Aquitanian and the late Burdigalian) and by evidence of partial basin isolation and faunal endemism. Such events can be correlated with major discrete pulses of thrust activity in the outer Dinarides. From Chattian to Langhian an important ‘external’ source of clastics was represented by the axial zone of the Alpine range (Austroalpine and Penninic units) subjected to rapid uplift and denudation; (b) from Serravallian onwards a drastic change in the tectonic framework of the Venetian basin occurred: the axis of subsidence shifted in position and trend, and the basin was thereafter incorporated in the South Alpine kinematic system. The latter evolved in a context of oblique convergence which resulted in a migration of thrusting and of foreland subsidence around the South Alpine compressional belt from the west (Lombard foredeep) toward the east (Venetian foredeep) during the time span from late Oligocene to Recent. This shifting pattern was accommodated by wrenching along the Insubric (Periadriatic) lineament and along sets of conjugate transverse faults which segmented the Southern Alps in a number of sub-areas with significantly diachronous tectono-sedimentary evolution. On a larger scale, the South Alpine and Apenninic domains show a close correspondence in timing of major events and in stepwise eastward shifting of deformation and foredeep subsidence, suggesting an evolution within the same megashear system. From Serravallian onwards an imbricate stack of overthrusts rapidly ‘prograded’ SSE-wards in the eastern South Alpine area and shed a huge amount of clastics into the Venetian basin. Unconformity-bounded sequences developed in response to discrete pulses of thrust progradation, with localized angular unconformities and along-strike differential subsidence resulting from the interplay of thrust pulses with strike-slip motion along transverse faults. Although tectonic control is pervasive, especially in the second stage of basin evolution, the effect of major eustatic events can still be recognized in the trend of sedimentation.