6.1 La Chapelle Formation - LCH (old: Rv2)
Author: Beugnies, 1960.
Description: Formation subdivided into two members. The unnamed lower member (old: Rv2a), is an alternation of black quartzite in 1 to 4 m thick beds and thin bedded black roofing slate. The Olly Member (OLL, old: Rv2b) is a vein of black roofing. The lower boundary of the formation is not observed (Beugnies, 1960).
Stratotype: Not yet defined; type area in the outcrops north of the village La Chapelle and close to Illy; the Olly Member has its type area in the outcrops along the Ruisseau de la Hatrelle, east of Illy.
Area: Givonne Massif.
Thickness: At least 100 m, with the Olly Mbr only a few meters thick (Beugnies, 1960).
Age: The acritarchs in the Olly Mbr and the upper part of the lower member belong to the Zone 4b, dated as Mid to Late Cambrian. The acritarchs in the lower part of the lower member belong to the Zone 3 dated as probable Middle Cambrian (Vanguestaine, 1992); see also discussion on the ages at the Illy Fm.
(M. VANGUESTAINE)