Page 133 - Carbonate Facies in Geologic History

120 The Advent of Framebuilders in the Middle Paleozoic

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MASSIVE STROMATOPOROIDS
6 AlVEOLITES, HEXAGONARIA, PHllliPSASTREA
MASSIVE STROMATOPOROIDS

BRACHIOPODS, OSTRACODS
5 MASSIVE STROMATOPOROIDS 40?

BRACHIOPODS
OSTRACODS

1
1-20

Fig.IV-1S. Biofacies in carbonate buildups in Mercy Bay Member at Manning River, N.W.T.,
Canada. From Embry and Klovan (1971, Fig.4). Numbers 1 D to 9D refer to Devonian
microfacies types described in Chapter IV. Illustration courtesy of authors and Canadian
Society of Petroleum Geologists

tent and varied geographical settings of the Middle and Late Devonian buildups
make it impossible to list all types of their microfacies. Surprisingly, however, a
group of about a dozen types recur in areas where careful study has been made.
These are listed below in order from basin to shelf with comments on special
characteristics and environmental interpretations. The list includes numbers I-D
to 13-D, the letter desgination for Devonian to distinguish these microfacies from
the standard types (SMF-). The types are chosen with particular attention to
examples from western Canada where the most detailed petrographic study has
been done. Photomicrographs of most of these facies are found in Klovan (1964),
Fischbuch (1968), and Jenik and Lerbekmo (1968). From study of almost perfectly
exposed beds in the Arctic Banks Island, Northwest Territories, Canada, Embry
and Klovan (1971) were able to position some of these facies in terms of absolute
water depth along slopes of organic carbonate accumulations assumed to have
built up in a situation of stable sea level. Their water depth estimates are given
below. Some of the microfacies are "keyed in" to the idealized diagram of Arctic
Banks Island buildup described by Embry and Klovan (Fig. IV-IS). A classifica-
tion of Devonian faunal assemblages based simply on wave relationships was
given by Lecompte (1970) and is also noted in the outline.
Basinal facies
1 D. Brown-black organic rich shale with Styliolina, Buchiola, Tentaculites, conodonts, gon-
iatites. Deposits around buildups in deep, less aeriated waters. Typical in Duvernay of
Alberta, and interreef deposits of Canning Basin, Australia, and Dinant Basin, Belgium.
Waters as deep as a few hundred meters are estimated from the thickness of the section
onlapping against the buildups. Lecompte's "deep zone".
2D. Gray-green shale with ostracods, Tentaculites, Buchiola and some foraminifera. The
Ireton shale blanket which fills in around banks in Alberta, Canada is characteristic,
perhaps in water more than 100 m deep.