The information on this page is a summary description.
The full formal description is available here: Illy Formation
Abbreviation
ILL
Parent unit
Child units
Lithological description
Black slate and silty slate (called “quartzophyllade” in the older literature), micaceous with not frequently thin sericite laminae; the middle and upper part of the formation show frequent alternations of black slate and quartzite beds never exceeding 0.50 to 1 m in thickness. In the slate beds often microfolds are observed and more rarely millimetric chloritoid crystals (Beugnies, 1960).
Age
The acritarchs in the lower part of the formation belong to the Zone 4b, indicating a Mid to Late Cambrian age (Vanguestaine, 1992). This result confirms at least certain lithostratigraphic correlations of Beugnies (1960) and contradicts those of Graulich (1954) and of Fourmarier (1960) who put the Givonne massif formations at a level below the Deville Group.
Thickness
850 m (Beugnies, 1960).
Area of occurrence
Givonne Massif.
Type locality
Not yet defined; type area in the outcrops along the Ruisseau de la Hatrelle, east of Illy.
Alternative names
Rv3
Authors
Verniers, J., Herbosch, A., Vanguestaine, M., Geukes, F., Delcambre, B., Pingot, J.-L., Belanger, I., Hennebert, M., Debacker, T., Sintubin, M. & De Vos, W.
Date
01/01/2001
Cite as
Verniers, J., Herbosch, A., Vanguestaine, M., Geukes, F., Delcambre, B., Pingot, J.-L., Belanger, I., Hennebert, M., Debacker, T., Sintubin, M. & De Vos, W., 2001. The Illy Formation, 01/01/2001. National Commission for Stratigraphy Belgium. https://ncs.naturalsciences.be/lithostratigraphy/Illy-Formation
