Bifertenfirn-Formation
Back to Aar MassifRepresentation and status
- Index
- P-Bi
- Color CMYK
- (23%,0%,13%,39%)
- Color RGB
- R: 120 G: 155 B: 135
- Rank
- lithostratigraphic Formation
- Validity
- Unit is in Use
- Status
- informal term
Nomenclature
- Deutsch
- Bifertenfirn-Formation
- Français
- Formation du Bifertenfirn
- Italiano
- Formazione del Bifertenfirn
- English
- Bifertenfirn Formation
- Origin of the Name
-
Bifertenfirn (GL), am Tödi
- Historical Variants
-
Anthracitschiefer von Tödi (Paulcke 1906), Bifertenfirn Metasediments (Franks 1968 p.59), Bifertenfirn Formation (Berger et al. 2017)
Hierarchy and sequence
- Superordinate unit
- Units at roof
Age
- Age at top
-
- Middle Paleozoic
- Age at base
-
- Early Paleozoic
References
- Definition
-
(2017) :
Geological Map of the Aar Massif, Tavetsch and Gotthard Nappes. Geological Special Map 1:100'000, Explanatory Notes 129
p.34: OBERHÄNSLI et al. (1988) attribute to FRANKS (1968 b) the definition of the Bifertenfirn Formation, but in fact FRANKS (1968 a, b) refers to this sequence as the “Bifertenfirn metasedimentary rocks”. For the present map sheet, the term Bifertenfirn Formation was chosen since the informal use of the term “ formation” for a distinct sequence of Carboniferous clastic and volcanic rocks has become current in the Aar Massif (e.g., Diechtergletscher and Trift Formations). HÜGI (1941) and FRANKS (1968b) described the rocks outcropping at the northern end of the Bifertenfirn as a well-layered sequence of hornfels and “Knotenschiefer” derived from argillaceous siltstone and fine-grained sandstone. They suggested that the overprint is the result of the intrusion of the Tödi Granite Complex (HÜGI 1941), hence of contact-metamorphic origin. The porphyroblasts occur mainly as replacement structures and were interpreted as former andalusite or cordierite. The matrix is dominated by albite, quartz and white mica. In some places minor amounts of chlorite are present. Primary bedding is visible in form of variations in the quartz/mica content (FRANKS 1968 b). Apophyses and dykes emanating from the Tödi Granite Complex frequently crosscut the metasedimentary rocks. The rocks of the younger, Late Carboniferous Bifertengrätli Formation (hB) unconformably overlie the plutonic rocks of the Tödi Granite Complex (HÜGI 1941, FRANKS 1968 b) permitting reconstruction of the relative chronology of events. Furthermore, FRANKS (1968 b) correctly correlated the Bifertenfirn Formation with the Val Gliems Formation, but unfortunately did not recognise the volcaniclastic character of some of the metasedimentary rocks.