Reflexions sur le facies 'ammonitico rosso'

Abstract

Abstract The 'ammonitico rosso' of limestone formations in the Mediterranean region involve involves problems of age and facies relationships. Two principal facies types occur in the southern Alps, the 'ammonitico rosso' limestone type (known as 'calcare rosso ammonitico di Verona' from the type occurrence in quarries of the Verona region in northern Italy), and the 'ammonitico rosso' marl. Both types are characterized by variable red to green color governed by the valence of the iron content, and the rich ammonite content. In the Alpine cycle of the southern Alps, 'ammonitico rosso' is systematically lacking at certain stratigraphic levels, as the lower Triassic and the Cretaceous, but is characteristic of middle and upper Lias (lower Jurassic) and Malm (upper Jurassic), indicating a relationship to stages of geosynclinal evolution. The limestone type occurs on rides, either as condensed sedimentation on pelagic haut-fonds of the Briancon ride type, or as a belt representing a given depth zone on the flanks of a neritic haut-fond of the Gavrovo ride type. The marl occurs in sillons as an accident in the fundamental marl-limestone series of sediments. 'Ammonitico rosso' facies elsewhere in the Mediterranean region are discussed, with particular attention to those of Hercynian age.