Sedimentary petrography of upper Messinian sandstones in the coastal area of Northern Marche (Italy)

The upper Messinian succession of the coastal area of Northern Marche can be subdivided into two lithostratigraphic units, the San Donato Formation and the Colombacci Formation. The older San Donato Formation can be referred to a foredeep sedimentation, and it consists of arenitic- to pelitic-arenitic turbidites, with at least one volcaniclastic level. The overlying Colombacci Formation is also characterised by a pelitic-arenitic succession, making it difficult to point out a boundary between these formations. However, the Colombacci Formation is locally typified by the occurrence of limestone levels and plane-parallel laminated pelitic intervals, grey-greenish in colour. The studied succession is well exposed along the sea-cliff north of Mt. S. Bartolo, where the San Donato Formation and the Colombacci Formation are separated by a thick transitional horizon of uncertain attribution. In order to characterise the Messinian succession cropping out in this area, arenites belonging to both formations have been studied in thin section. The obtained results show significant differences in the lithic fraction compositions of San Donato vs. Colombacci arenites. These petrographic parameters might be useful to discriminate these formations by their petrofacies, in the whole Northern Marche area