Gravity tectonics and sedimentation of the Montefeltro, Italy

Abstract

The tectono-stratigraphic framework of the southern Montefeltro is illustrative of the interaction between thin-skinned shearing and sedimentation in the outer segment of the Apenninic orogenic system during the Neogene. Mesozoic through Paleogene evaporitic-carbonatic-marly terrains constitute the lower part of its autochthonous sedimentary cover. This Umbro-Marchean Sequence compares with deposits of the contiguous Adriatic Foreland. Structural style is characterized by longitudinal chains of brachyanticlines more or less intensely dissected by stepped thrusts rooted in a common sole fault. The Neogene clastics of the overlying Umbro-Romagnan Sequence are arranged in broad synclines separated by complex highs developed over shallow detachment levels. The pronounced lateral variability of these foredeep deposits argues the synsedimentary origin of the structural pattern. More internal detached Umbro-Romagnan terrains define a parautochthonous thrust sheet composed of synclinal elements bounded by listric reverse faults. The formation of these shallow structures was determined by migratory subsidence in consequence of crustal imbrication. The synsedimentary orogenic paroxysm was complicated by the emplacement of a voluminous glide mass. This Montefeltro Colata principally consists of teleallochthonous terrains derived from the innermost segment of the Apenninic system. Semi- and peneallochthonous elements originated on the mobile allochthon as this advanced toward the Adriatic Foreland. The phased progress of the Montefeltro Colata was gUided by bulges bordering a transversal depression which resulted from the interaction between the mobile allochthon and the thin-skinned tectonics of its UmbroMarchean- Romagnan substratum. Neoautochthonous deposits suture the structural edifice on the outer side of the Apenninic orogen.