strati.ch - Lessico lithostratigrafico della Svizzera

Rappresentazione e statuto

Varianti storiche: Gipsen von Gessi am Berninapass und in Val Federia (Staub & Cadisch 1921), conca de I Gessi (Godenzi 1963), Val di Gess Mb. (Furrer et al. 1985)

Definizione: Furrer Heinz (Ed.) (1985) : Field workshop on Triassic and Jurassic sediments in the Eastern Alps of Switzerland. Mitt. geol. Inst. ETH und Univ. Zürich (N.F.) 248, 81 S.

p.72: In the upper part [of the Fuorn Fm.] (Val di Gess Mb.) we find characteristic gypsum layers and lenses intercalated in a succession of mostly green siltstones, sandy dolomites, cornieules and carbonaceous sandstones. Lenticular bedding is rather common. The sandstones are often of the greywacke type. Detrital volcanic quartz grains are abundant, especially in the massive sandstone body above a possible erosional surface in the midle of the Val di Gess Mb. Here they dominate and are well rounded. Some very fine placerlike Zirconium/Pyrite layers can be found. Albite, muscovite and chlorite are also common due to regional metamorphism (lower greenschist facies); this metamorphism also caused strong recrystallisation, with destruction of nearly all primary structures.