The epi-Ligurian Sequence of the Val Marecchia thrust sheet (Northern Apennines) crops out in several "slabs". Ligurian deposits, belonging to the Monte Morello tectonic Unit, are mostly composed by clayey and shaly "argille varicolori" (basal complex of the Monte Morello Formation). Four epi-Ligurian formations (Antognola, Bismantova, Termina and Monte Sabatino - Upper Oligocene to Lower Pliocene), separated by erosional surfaces, occur in the "slabs", which, on the base of structural data, can be subdivided in three groups: 1) "arcuate slabs", 2) "tabular slabs" and 3) small "slabs" slumped in Upper Tortonian sediments of the Ghioli di Letto Formation. The "arcuate slabs", occurring in frontal parts of the Val Marecchia thrust sheet, dip uphill and display vertical cliffs on the NE side facing the Adriatic Sea. The arcs, elongated to the direction of the Apenninic chain, are characterized by distinctive fracture sets: A) perpendicular to the curvature, B) fan-shaped and intersecting the previous one, C) parallel to the length of arc. Syntectonic sedimentary wedges were deposited in "arcuate slabs" from Tortonian to Lower Pliocene and sedimentation was strongly controlled by movement of arcuate thrust-system of the Val Marecchia sheet. The "tabular slabs", outcropping in internal parts of the Val Marecchia thrust sheet, show margins located nearly at the same altitude and are constituted only by a shelf carbonate unit (San Marino Formation). These "slabs" are characterized by subhorizontal stratification and dense network of fracture sets directed parallel to the margins. The position of two main "slabs" seems to be controlled by a transversal tectonic line running parallel to the course of the River Marecchia, 3-4 km east of it. Different structural patterns of "arcuate" and "tabular slabs" could be related to the influence of the "substratum" (Umbro-Marchean-Romagna Sequence) overthrusted by the Val Marecchia thrust sheet. The fracture system control the dismemberment of the two kinds of "slabs" and the evolution of the mass-movements. The latter affect both the clay substratum and the overlying rocks with different patterns of evolution according to structural elements.
|Data di pubblicazione:||1992|
|Titolo:||Caratteristiche geologico-strutturali delle placche epiliguri della coltre della Val Marecchia e loro riflessi sulla franosità.|
|Appare nelle tipologie:||Articolo su rivista|
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