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Conglomerate

Miocene conglomerate containing Jurassic limestone-Moustiers-Sainte-Marie. In petrography, a conglomerate is a detrital rock (resulting from the mechanical degradation of other rocks) composed of pieces linked together by natural cement. To be considered discernible, the pieces must measure more than 2 mm (below this size, we would be dealing with a sandstone and no longer a conglomerate). Conglomerates are most often sedimentary in nature, but they can also be volcanic. Among the conglomerates, we find: - the breccias, composed of angular blocks; - puddingues, made up of rounded pebbles; - and tillites which contain both angular pebbles and rounded pebbles. Many conglomerates were formed when the sea invaded a originally continental surface (transgression), in a low area. Sparnacien pudding from Nemours south of Fontainebleau We call ossiferous conglomerate a conglomerate rich in bones of reptiles, birds and mammals: example of the conglomerates of the lower tertiary discovered at Meudon in 1836