Pre-orogenic tectonics in the Umbria-Marche sector of the Afro-Adriatic continental margin

The pre-orogenic deformation of the Afro-Adriatic paleomargin during Jurass ic-Paleogene times is recorded in the Umbria-Marche regions of Central Ital y by facies differences, lateral thickness variations and, most importantly , by faults. Structural data suggest the persistence of normal faulting not only during rifting (Late Trias-Bathonian) but also during drifting and mo re precisely in Late Cretaceous times. Syn- and post-rift extension caused the development of mainly NNW-SSE- and ENE-WSW-trending structures. Post br eak-up normal faults are found in several localities of the Apennines and g enerally coincide with older, syn-rift sites of stretching. One-dimensional numerical modelling of subsidence suggests that thinning during rifting wa s about 15%, compatible with the stretching factor reconstructed fr om geol ogical sections. Late Cretaceous thinning was obviously less but still sign ificant and estimated at ca 5%. The acquisition and analysis of the stratig raphic and structural data presented in this study allowed us to correlate the subsidence history of the Umbria-Marche basin with the tectonic events that occurred in pre-orogenic times, in this sector of the Apennines, thus deriving useful indications about the pre-Oligocene evolution of this segme nt of the perimediterranean mountain belt. (C) 1999 Elsevier Science B.V. A ll rights reserved.