Re art Pe

Figure 22.

Bedding style of the Alex Allan Formation at its type locality on the road to Bowron

Lake Provincial campsite, approximately 200 m north of where the road crosses Alex Allan Creek.

(GSC 191021)

exposed in isolated outcrops locally with Greenberry and
Guyet formations. A good type locality is a roadcut
(Fig. 22) near the intersection of Allex Allan and Summit
creeks; hence the name, Alex Allan Formation. The unit
is given formation status, although it would not appear
on most regional scales, because its conodont fauna dis-
tinguish it as unconformable on the Greenberry Forma-
tion. At its type locality it is 5 m thick, the maximum seen.

Contacts with underlying units are not exposed except
at Summit Creek where the limestone is interbedded with
black slate indistinguishable from slate apparently con-
tinuous with muddy conglomerate of the Guyet Forma-
tion. From relationships and fossil data from other areas
there must be an unconformity concealed in the slate
succession.

Grey to black micritic limestone, shaly and silty lime-
stone and graphitic shale dominate the unit. Several beds
at the Summit Creek locality contain wisps of shale
(Fig. 23) and others have accumulations of fine grained
bioclastic debris. Beds of limestone vary from 3 to 70 cm
in thickness with thinner interbeds of shale and are com-
monly disrupted into augen-like lenses. Secondary pyrite
appears throughout most of the unit.

Age and correlation. The age of the Alex Allan Forma-
tion is Middle Pennsylvanian as determined from cono-
donts examined by M.J. Orchard (see Appendix A, and
Orchard and Struik, 1985). There is a mixture of age
specific conodonts within the unit, representing Latest
Mississippian to Middle Pennsylvanian. The mixing is
thought to be due to either reworking or extremely slow

deposition. Reworking is favoured (Orchard and Struik,
1985) because the same mixed fauna can be extracted
from several beds within the unit (Fig. 22). No attempt
is made to correlate beyond the field area.

Paleoenvironments of the Greenberry and
Alex Allan formations

The Greenberry Formation contains abundant macro-
fossil debris and yields a conodont fauna indicative of
a shallow-water environment. The conodont Mestogna-

Figure 23. Wisps of pelite, which may be fossil ripples,
in the black micrite of the Alex Allan Formation; Cana-
dian quarter for scale. (GSC 191022)

35