Geologic Studies in Alaska by the U.S. Geological Survey, 1992

LITHOFACIES AND CONODONTS OF CARBONIFEROUS STRATA IN THE IVOTUK HILLS, BROOKS RANGE
The upper unit of the Lisburne Group was deposited
chiefly below wave-base in deeper water, middle to outer
shelf environments that received little input from carbonate
banks. Well-laminated dolomitic mudstone, spiculite, and
lesser shale characterize this unit. Rare packstone layers
rich in brachiopods probably represent storm deposits;
shells in these layers are locally bored, probably by algae
prior to tempestite deposition. A conodont collection from the
uppermost part of this unit produced exclusively gnathodids,
forms typical of outer shelf and slope environments.
- C 0 0.5 MILLIMETER
0
CORRELATION
KAYAK SHALE
The Kayak Shale in the Ivotuk Hills resembles the
Kayak Shale elsewhere in the Killik River-Howard Pass
area, but also has some lithologic and faunal similarities to
the Kuna Formation of the Lisburne Group. Both the
Kayak Shale and the Kuna Formation consist chiefly of
black to dark-gray shale, but shale in the Kuna Formation
0.5 MILLIMETER
u
Figure 7. Sedimentary features, upper unit of Lisburne Group. scattered dolomite crystals (m) overlain by layers of spiculitic
A, Thin-bedded dolostone with shale partings, 262 m above base chert (s) and dolomite (d). D, Photomicrograph of silicified bra-
of section. B, Laminae rich in siliceous spicules weather out of chiopod packstone (probable tempestite), 199.2 m above base of
dolomitic mudstone, 180 m above base of section. C, Photomi- section. Brown mud-filled borings (b) rim shell on right side of
crograph of interval shown in 7B; dark mudstone layer with photograph.
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