Fig. 6

Characteristic facies of the Mauvoisin marbles. a, b Slightly detrital calcitic marble with siliceous mm-cm thick bands; Mauvoisin [2′592′650/1′094′510]. c Similar lithology at La Tour [2′605′310/1′104′860], Hérens valley. d Detrital calcitic marble with mm-cm thick siliceous bands and sparse cm-dm thick limestone clasts (dolomitic clasts appear out of the picture); Giétro [2′593′690/1′092′930], Bagnes valley. e Alternating layers of detrital calcitic marble and dolomitic microbreccia; 10 m from Fig. c. f, g Details of the outcrops of Figs. a and b. In g sharp borders are observed at the contact between the siliceous bands and the surrounding marble, whereas a progressive transition is visible to the more carbonaceous inner parts of these bands. As this characteristic is typical of cherts that are not fully silicified in their inner parts, it supports the biogenic nature of these siliceous bands