Activation of deep seated slope gravitational deformations in complex tectonic settings: the Corno Zuccone sackung, Val Taleggio

Deep-seated slope gravitational deformations (DSGD) are described for the first time in the western sector of the Taleggio Valley (Bergamo, Italy) within the Middle-Late Triassic successions of the Southern Alps. Most of them occur at rigid carbonatic platforms (Corno Zuccone: Dolomia Principale Fm.; Corno del Bruco: Calcare di Esino Fm.) thrusted upon the more ductile shales of the Late Triassic Argillite di Riva di Solto Fm. (ARS). Other DSGD occur in the parautocthonous succession of W-SW Taleggio valley (Dolomia a Conchodon of I Canti). The sackung of Corno Zuccone, located near the village of Vedeseta, is here described in detail through geological, geomorphological and morphometrical analyses based on field and photo-geological surveys, integrated within a Geographical Information Systems. The main morpho-structures of Corno Zuccone consist of a spectacular set of sub-vertical E-W and ENE-WSW trending fractures developed especially within the uppermost part of the carbonatic massif. The main scarp suggests a vertical throw of at least 100m, as small throws are also recognizable along the secondary fractures. The analysis of these systems suggests that also the upper member of the ARS, present below the Corno Zuccone klippe, is affected by the DSGD. This idea has been also confirmed through 2-d numerical modelling of the sackung. Superficial landslides active especially at the foot of the slope around Vedeseta within the ARS may be related to the uplifting induced by southward motion of the entire slope and by a general lowering of the mechanical properties of the rock mass. The peculiar geological and structural setting of the area, together with a rapid deep erosion of the valley bottom, possibly related to the post-Early Quaternary deepening of the Enna gorge in the eastern part of Val Taleggio, may be responsible for the activation of the phenomenon.