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

GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992
Figure 8. Mississippian conodonts from measured section of uppermost part of the Kayak Shale and the Lisburne
Group, Ivotuk Hills, Killik River B-5 quadrangle, western Brooks Range, Alaska (scanning electron micrographs).
See figures 1 and 3 for location of samples and stratigraphic column and table 1 for conodont species distribution.
A-C, Latest Mississippian (latest Chesterian) conodonts from 11 m below top of the Lisburne Group (sample of
grayish-black micrite to sparite collected by J.P. Siok, field no. 85ASi14-18), USGS colln. 29892-PC.
A, Gnathodus bilineatus (Roundy), incomplete Pa element, upper view, x60, USNM 473816. Specimens
of G. bilineatus in this collection are juveniles or, like this specimen, lack diagnostic posterior part of
platform and thus cannot be identified to subspecies. G. bilineatus subspp. range from the early
Chesterian into the earliest Morrowan (into the noduliferus-primus Zone).
B, Gnathodus defectus Dunn, Pa element, upper view, x40, USNM 473817. This species ranges from
within the Chesterian (probably latest Chesterian) into the earliest Morrowan (into the noduliferus-
primus Zone).
C, Gnathodus girtyi simplex Dunn, Pa element, upper view, x50, USNM 473818. This latest Chesterian
species extends to the very top of the Chesterian, and probably not into the Morrowan. It restricts the
highest sample of the Lisburne Group in the Ivotuk Hills to the Chesterian.
D, P-T, Early Osagean conodonts from crinoidal packstone bed in the Kayak Shale, 43 m below the base of the
Lisbume Group, and 1.7 m above base of the measured section, USGS colln. 31734-PC, x40.
D, Synclydognathus geminus (Hinde), Pa element, outer lateral view, USNM 473819. The species ranges
from the Osagean into the early Chesterian.
P, Q, Polygnathus lacinatus circaperipherus Rhodes, Austin, and Druce, Pa element, upper and lower
views, USNM 473820. The species occurs in strata equivalent to the Osagean in the British Avonian
(Rhodes and others, 1969).
R, Polygnathus communis communis Branson and Mehl, Pa element, oblique upper view, USNM 473821;
a long-ranging Famennian through Osagean species.
S, Hindeodus crassidentatus (Branson and Mehl), Pa element, outer lateral view, USNM 473822. Late
Kinderhookian through at least Osagean species.
T, Bisparhodus aculeatus anteposicornis (Scott), Pa element, inner lateral view, USNM 473823. Latest
Famennian to early Osagean species. The occurrence of this species with Synclydognathus gemin~~s
(fig. 8D) possibly restricts the age of the sample to the early Osagean.
E, F, N, 0, Late Meramecian conodonts from crinoidal packlgrainstone, 9 m above the base of the lower unit of the
Lisbume Group and 54 m above the base of the measured section, USGS colln. 31735-PC, x40.
E, F, Synclydognathus geminus (Hinde), Sa and Sb elements, posterior and inner lateral views, USNM
473958, 59.
N, 0, Cavusgnathus sp. indet., Pa element fragments, lateral and upper views, USNM 473960, 61. This
form combined with conodonts from underlying and overlying beds restricts the collection to the
upper half of the Meramecian.
G, H, L, Late Meramecian conodonts from bryozoan-crinoidal wackestone, 20 m above the base of the middle
massive unit of the Lisburne Group and 115.4 m above the base of the measured section, USGS colln. 31737-
PC, x40.
G, H, Bispathodus utahensis Sandberg and Gutschick, Pa element, inner lateral and upper views, USNM 473962.
Representatives of this species, mostly incomplete Pa elements, are the most abundant forms in this
collection and in USGS colln. 317736-PC.
L, Kladognathus sp., Sc element, inner lateral view, USNM 473963.
I-K, M, Late Meramecian conodonts from dolomitized crinoidal packlgrainstone, 21 m above the base of the lower
unit of the Lisburne Group and 66 m above the base of the measured section, USGS colln. 31736-PC, x40.
I-K, Bispathodus utahensis Sandberg and Gutschick, Pa and Sb elements, outer lateral, upper, and inner
lateral views, USNM 473964, 65, respectively.
M, Kladognathus sp., P element, inner lateral view, USNM 473966.