Mesostructural analysis on the conglomerates of the outer marchean area (between M. Ascensione and S. Benedetto)

A mesostructural analysis carried out on the conglomerates of the sedimentary sequence (Middle Pliocene-Early Pleistocene) of the coastward area of the Marche is presented. These conglomerates are interbedded in epibathial to neritic clays. The sequence is about 2000 m thick and it constitutes a gentle NE dipping monocline. An unconformity exists between this sequence and the underlying Messinian-Early Pliocene deposits which are involved in the thrusts affecting the Apennines during Miocene-Early Pliocene. Deformational features, due to frictional pebble boundary sliding during deformation (slickolite striae and slickolites, mainly at microscopic scale) are analysed. This analysis suggests the presence of compression which postdates the Early Pleistocene, Late Pliocene and Middle Pliocene deposits from the E towards the W. The different shortening axes are subhorizontal, trending about N-S, NE-SW and NW-SE, and subvertical. There is a good geometric analogy between the compressive fields, in these deposits, and the older ones suggested by the structural features of the Umbria-Marche chain (Miocene-Early Pliocene). Nevertheless we think that is better to associate these findings to a context of downslope gliding and/or gravity spreading within the accretionary Umbria-Marche fold and thrust belt System.