«Graphitische Einheit» (der Camosci-Decke)
Back to «Kalkige Einheit» (der Camosci-Decke)Representation and status
- Color RGB
- R: 210 G: 170 B: 190
- Rank
- lithostratigraphic Formation
- Validity
- Unit is in Use
- Status
- informal term
Nomenclature
- Deutsch
- «Graphitische Einheit» (der Camosci-Decke)
- Français
- «Unité graphitique» (de la nappe des Camosci)
- Italiano
- «Unità grafitica» (della falda dei Camosci)
- English
- «Graphitic unit» (of the Camosci nappe)
- Historical Variants
-
black phyllitic schists + calcschists complex (Bianchi et al. 1998), Graphitic unit = Toarcian-Aalenian (Carrupt 2003)
Description
- Thickness
- Environ 75 m (Carrupt 2003 Fig.2.4)
Hierarchy and sequence
Age
- Age at top
-
- Aalenian
- Age at base
-
- Toarcian
- Dating Method
-
Ennoyement de la plateforme / black shales au Toarcien-Aalénien (Carrupt 2003).
Palaenography and tectonic
- Tectonic unit (resp. main category)
- Kind of protolith
-
- sedimentary
References
- Definition
-
(2003) :
New stratigraphic, structural and geochemical data from the Val Formazza - Binntal area (Central Alps). Mémoires de Géologie (Lausanne) 41, 103 p.
p.17: Graphitic unit: is characterized by important lateral variations of facies (Fig.10.2).
The clearest succession is found in the western part of the nappe. A black graphitic micaschists (metashale, see microscopic description in paragraph III.4) containing porphyroblasts of garnets, immediately follows the Calcareous unit; the contact is clear-cut. It may contain rare thin levels of a calcareous graphitic micaschist (metamarls). Bianchi et al. (1998) found various heavily recristallized bioclasts in the black micaschist.
The eastern part is more complex. A calcareous graphitic micaschist (metamarls, see microscopic description in paragraph III.4) containing porphyroblasts of plagioclase or epidote overlies the Calcareous unit. The contact is gradual: thin levels (3 cm) of calcareous micaschist alternate with the calcitic marble; the latter becomes thinner upsection, whereas the calcareous micaschist thickens. Some graded bedding can be observed, indicating the local polarity (Fig.2.4). Up sequence, thin levels of black micaschist are interbedded within the calcareous micaschist.
The lateral transition between the western and the eastern part of the Graphitic unit is made over less than 2 m. A very hard and dark 50 cm-thick rock composed of graphite (50%), carbonate (29%), muscovite (12%), opaque (8%) and some accessory minerals, represents the transitional stage between the calcareous micaschist and the black micaschist.