Geologia

From the stratigraphic point of view the Tretto and Mount Summano area belongs to the so called “Recoarese”, a region including the upper Agno, the Leogra and the Posina valleys. The Recoarese differs from the neighbouring areas because it contains the southernmost outcrop of the Southalpine crystalline basement. On the basement a thick mainly sedimentary succession lies, which represents the time interval from the upper Permian to lower Miocene. The Triassic system makes exclusive the Recoarese: during the Triassic time this area was mainly a marine environment located on the northern border of a wide emerged area, at present buried beneath the Po Plain alluvial deposits. Detrital inputs from the continent fed the basin, while marginal marine environments were favourable to ecological niches. Marine, coastal and continental facies alternated continuously with time. This was due to the special paleogeographic location, which registered also slight sea level fluctuations. The recent recognition that most of these fluctuations are eustatic oblige to re-interpret the Recoaro Triassic rocks in terms of sequence stratigraphy. The contribution given by our area is surprising, if we consider that the sequence stratigraphy can interpret global scale events. The outcrop of the crystalline basement and Permo-Triassic units in the Recoarese results from erosion of a block tectonically uplifted during the Neogene shortening of the Southalpine chain. The Mount Summano is carved on an anticline with a steep southern limb developed in the hanging wall of the Bassano Line, which is a SSE-verging thrust. The Tretto valley results from selective erosion of the relatively low resistant rocks underlying the Dolomia Principale. The north-dipping steep arcuate scarp delimiting towards the south the Tretto valley is a spectacular example of the control on the landscape exerted by inclined rocks with selective erosion.