A selected area was studied to evaluate the hypothesis of far-traveled gravity slides in a part of the Northern Apennines.
The backbone of the Northern Apennines south of Passo della Cisa consists of strong, autochthonous macigno sandstone (Oligocene); it is a horst, devoid of structural cover. Adjoining on the west, a lower macigno block is structurally overlain by allochthonous remnants. North and east of the horst, widespread allochthonous materials form a thick cover which presumably once mantled the entire area prior to block faulting.
The complex allochthon comprises argille scagliose and dispersed masses of competent limestone, sandstone, and sandy siltstone. The shale matrix and the enclosed competent masses are remnants of Cretaceous, Eocene, and Oligocene formations of various penecontemporaneous facies. One extensive mass of black shale in the argille scagliose represents a single semi-coherent formation. This shale shows appreciable structural homogeneity, and small overturned folds within it indicate movement of the allochthon toward the north, east, and southeast.
The writer is convinced that gravity is the only agent that could have moved the allochthon. One plate of rock more than 4 by 7 km is apparently separated from its sources by intervening weak shale, so that it could hardly have been pushed laterally. Most of the competent blocks in the allochthon are not in contact with one another and have drifted apart rather than forming a train capable of transmitting a lateral “push from the rear.” This seemingly eliminates any alternative to gravity as the propulsive agent.