Reference Detail of

Report on Referred Fossils
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Stratigraphic range: Carb. - Perm. - Triassic(?)
Kinds of fossils: Marine invertebrates
Quadrangle or area: Misheguk Mtns., Alaska
Shipment No.: A-71-13
Referred by: Tailleur, Irv L.
Report prepared by: Dutro, J. Thomas, Jr.
Date: 05/10/1972

This report covers 41 collections made in 1971 on Nuka Ridge with the aim of revising the stratigraphy of the type Nuka Formation.

The collections are placed in three groups, according to the stratigraphic sections accompanying the material: lower Nuka, middle Nuka and upper Nuka.

Discussions include revisions of earlier collections, where pertinent, and correlation with determinations of microfossils furnished by B. L. Mamet (written communication, April 1, 1972).

Two collections in this shipment are from “member f”, the lowest part of the “Nuka Formation”. They come from the same two levels that were sampled in 1953 by Sable and add no new information of significance.

Mamet reports Zone 14 foraminifers in this member, below the goniatite level, so there is agreement that “member f” is of early late Visean age (middle or upper Meramec).

No fossils of any kind have been reported from “member g” and only microfossils from “member h”. These are also assigned a Zone 14 age by Mamet.

One can conclude then that the beds below “member i” at the east end of the ridge are Mississippian, and not latest Mississippian at that.

The structural relationships of “member i” to the beds below suggest either an unconformity or a fault.

There is no faunal evidence for the age of “member i”, and only microfossils have been recovered from the upper 50 ft. of “member j”. Mamet reports that these are Zone 18, a high Chester or lower Namurian level. As far as I am aware, none of the strata in the Lisburne Group of the DeLong Mountains have yielded fossils this young in the Mississippian, although beds of this age are found in the upper Alapah in the eastern Brooks Range and in the upper 150 ft. of the Kogruk Fm. at Cape Lewis.

The absence of “member j” everywhere except at the eastern end of the ridge suggests to me either unconformity or faulting at the base of “member k”.

“Member k”, essentially a chert-argillite sequence, has very few fossils. The only significant ones appear to be USGS 1455-PC (53ASa29) from about 450 ft. above the base of the member. These are pelecypods that have been examined by N. J. Silberling who states (written communication, Feb. 8, 1972):

“The imperfect impressions of ribbed clams in the collection USGS 1455-PC are suggestive of Monotis in their size, pattern of ribbing, and what can be seen of their shape. However, this is permissive only; I don’t think this generic assignment could be proved from these specimens.”

The possibility, however remote, that these might be Triassic in age is intriguing in view of the suggestion by Tailleur that wacke of possible Cretaceous age is present at the top of the member in this section, about 400 ft. stratigraphically above this pelecopod bed.

Three collections from “member l” contain a characteristic Visean assemblage and two of these (71ATr 16.2 and 16.3) contain mollusks and trilobites like those in collections obtained earlier from this member. The present collections, especially 71ATr16.1, together with the Zone 14 age determined by Mamet, make the early Late Mississippian age of this unit certain. It is an age equivalent to “member f” and a thrust fault within the member as mapped is almost a certainty.

“Member m” – this member is difficult to assess in terms of age. It is these arkosic rocks that yield the most convincing macrofossil evidence of Permian age. The original Permian assignment for the upper part of the Nuka was based on collections from “member m” and later collections by Armstrong, and Grant and Stehli, confirm this assignment, in my opinion. Microfossil evidence is sparse in this part of the sequence, but two collections from section T 71.18 are given as Zone 18 or younger by Mamet and three collections from section T 71.24 are called Zone 18-20? by Mamet. According to Mamet, the collections in section T 71.18 could be any age, younger than 18, but he holds firm on the late Chester-Namurian age for the forams in section T 71.24 (oral communication, May 1, 1972).

Four collections in this shipment are from “member m” (or possibly “n”?). Unfortunately, none of these contains well preserved macrofossils.

Although the macrofossils in this shipment are not diagnostic, earlier collections from “member m” are significant. One of these, made by A. K. Armstrong in 1964, is especially rewarding.

Mamet (oral communication, May 1, 1972) confirms that microfossils from this collection are, indeed, post-Carboniferous.

Another large collection of silicified material was made by R. E. Grant and F. Stehli in 1968. This collection was also from “member m”, in the valley of Nose Creek. Although much of this material consists of large indeterminate productoids, several distinctive Permian forms are present, including: Arctitreta, Horridonia, and Spiriferella.

True “member n” has no fossils of any kind reported from it. This is possibly a thrust slice of chert, or a younger unit lying unconformably on “member m”.

A large number of collections are from “member o” in three sections, 71ATr28, 71ATr4 and 71ATr1. This interval in all three sections consistently yields a foraminiferal Zone 14 assemblage, according to Mamet (oral communication May 1, 1972). I have examined the macrofossils and come to the conclusion that they are also of Late Mississippian age. My original ideas about a Permian age were based on stratigraphic position and an incorrect identification of Licharewia, primarily. It now is clear that I was wrong and that “member o and p” represent yet another thrust slice at the top of the pile on Nuka Ridge.

“Member p” is an enigma. Mamet reports a Zone 17 microfauna in section T 71.28 from about 1440-1530 ft. Other earlier microfossil determinations by Armstrong have indicated a similar age for this part of the sequence. However, I judge several megafossil collections from “member p” to be Permian and a possible Permian microfossil assemblage was identified from about the middle of the member by Armstrong (see report on shipment A-71-5M dated 3/30/71; collection L-48).

From the paleontological evidence, one can assume that structural complications again place Lower Carboniferous above Permian in some complex way near the top of the ridge.

Only 4 collections from “member p” are present in this shipment, although a number of older collections have been re-examined in writing this report.

Although these collections are not definitive, some of the earlier collections from this member contain what I consider to be Permian fossils. These have been re-examined and a pretty certain Permian age can be assigned to 53ATr54 and 53ATr35.

The age problem of “member p” cannot now be resolved. It appears to have yielded both early Namurian and Permian fossils. Perhaps a detailed structural analysis of the ridge crest, where both overturning and faulting seem to be present, may aid in the solution of this problem.

User Note module to be added
71ATr-4-779 (M1039, 23529-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
fenestrate bryozoan impressions, indet.
Inflatia sp.
Echinoconchus sp.
productoids, indet. (small)
Brachythyris sp.
fish tooth, undet.
71ATr 21.2 (23504-PC) , Misheguk Mtn , Nuka Ridge, from "member f", the lowest part of the "Nuka Formation".
Leiorhynchoidea sp.
71ATr 21.6 (23505-PC) , Misheguk Mtn , Nuka Ridge, from "member f", the lowest part of the "Nuka Formation".
Goniatites cf. G. sphaericus (Sowerby)
71ATr16.1 (23506-PC) , Misheguk Mtn , Nuka Ridge, from "member l", middle Nuka.
Sinuatella? sp.
Acanthoplecta sp.
Ovatia sp.
Echinoconchus sp.
Anthracospirifer sp.
Brachythyris? sp.
Cleiothyridina sp. (large)
pectenoid pelecypod, undet.
pelecypod, undet.
71ATr16.2 (23507-PC) , Misheguk Mtn , Nuka Ridge, from "member l", middle Nuka.
productoid, indet.
Brachythyris sp.
pelecypod fragments, indet.
medium-spired gastropod, indet.
goniatite, indet.
trilobites (including Kaskia?)
71ATr16.3 (23508-PC) , Misheguk Mtn , Nuka Ridge, from "member l", middle Nuka.
pectenoid pelecypods, indet.
schizodid pelecypod, indet.
Mourlonia cf. M. reloba Yochelson and Dutro
goniatite?, indet.
Kaskia? sp.
71ATr7.82 (23509-PC) , Misheguk Mtn , Nuka Ridge, from "member m", middle Nuka.
brachiopod, indet.
71ATr18 (23510-PC) , Misheguk Mtn , Nuka Ridge, from "member m", middle Nuka.
large productoid, indet.
71ATr24.46 (23511-PC) , Misheguk Mtn , Nuka Ridge, from "member m", middle Nuka.
productoids, gen. indet.
71ATr24.95 (23512-PC) , Misheguk Mtn , Nuka Ridge, from "member m", middle Nuka.
indet. shell fragments
64B117 (23346-PC) , Misheguk Mtn , Alaska, Misheguk Mtn. quad., approx. 68 deg. 32'30" N., 158 deg. 12' W.; Nuka Fm., Type section, member m. Collector: A. K. Armstrong, Shell Oil Co., 1964
Horridonia cf. H. horrida (Sowerby)
Waagenoconcha sp.
Yakovlevia cf. Y. greenlandica (Dunbar)
Spiriferella cf. S. keilhavi (vonBuch)
Neospirifer? sp.
Brachythyrina? sp.
dictyoclostid, indet.
linoproductid, indet.
71ATr1. (23513-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm., base of section, loose specimen.
Pseudosyrinx? sp.
71ATr1.65 (23514-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm.
Ovatia sp.
dictyoclostid, indet.
Moorefieldella sp.
71ATr1.90 (23515-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm.
Orbiculoidea sp.
Orthotetes? sp.
Ovatia sp.
Buxtonia? sp.
Moorefieldella sp.
Spirifer spp.
gastropod steinkern, indet.
71ATr1.130 (23516-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm.
Orthotetes?
Pseudosyrinx?
71ATr1.141 (23517-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm.
Ovatia sp.
Inflatia? sp.
dictyoclostid, undet.
71ATr1.160 (23518-PC) , Misheguk Mtn , Nuka Ridge, from member o, upper Nuka Fm.
Inflatia sp.
Flexaria? sp.
Spirifer sp.
Anthracospirifer sp.
71ATr1.175 (23519-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
echinoderm debris
fenestrate bryozoan, indet.
trilobite pygidium, indet.
71ATr1.177 (23520-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Cleiothyridina sp.
71ATr1.179 (23521-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Echinoconchus sp.
71ATr4.158-4.162 (23522-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Ovatia sp.
pelecypods, including a pectenoid
71ATr4.184 (23523-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
chonetid, indet. (large)
Ovatia sp.
Spirifer sp.
pectenoid, indet.
71ATr4.235 (23524-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Spirifer sp. (large)
Brachythyris? sp.
Sulcatopinna sp. (very large species)
71ATr4.282-4.285 (23525-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Orthotetes? sp.
Ovatia sp.
Buxtonia? sp.
dictyoclostid, indet.
Moorefieldella? sp.
Pseudosyrinx? sp.
Punctospirifer? sp.
71ATr4."547" (23526-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Inflatia sp.
Flexaria sp.
dictyoclostid, undet.
syringothyrid, indet.
71ATr4.548 (23527-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Orbiculoidea sp.
brachiopod fragment, indet.
pectenoid, indet.
goniatite impression, indet.
fish spine, indet.
71ATr4.704 (23528-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Orthotetes? sp., fragments
productid fragments
71ATr4t (23530-PC) , Misheguk Mtn , float?, basal member o?; Nuka Ridge.
Pseudosyrinx? sp.
loxonematid, indet.
71ATr28.110 (23531-PC) , Misheguk Mtn , Nuka Ridge, talus from member o, upper Nuka Fm.
echinoderm debris, indet.
chonetid, indet. (large)
Inflatia sp.
Echinoconchus sp.
spiriferid, indet.
possible worm trails
71ATr28.135 (23532-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
echinoderm columnals, indet.
ramose and fenestrate bryozoans, indet.
Rugosochonetes sp.
Echinoconchus sp.
productoid, indet. (small)
Brachythyris? sp.
Cleiothyridina? sp.
71ATr28.270-28.275 (23533-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Inflatia sp.
Buxtonia? sp.
Flexaria sp.
Dimegelasma sp.
Pseudosyrinx? sp.
Mourlonia? reloba Yochelson and Dutro
71ATr28.282 (23534-PC) , Misheguk Mtn , Nuka Ridge, talus from member o, upper Nuka Fm.
Rhipidomella sp.
Orthotetes? sp.
Retichonetes? sp.
Flexaria? sp.
71ATr28.295-28.300 (23535-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Inflatia sp.
Dimegelasma sp.
syringothyrid, indet.
Wilkingia sp. (large pelecypod)
71ATr28.305 (23536-PC) , Misheguk Mtn , Nuka Ridge, float, member o, upper Nuka Fm.
crinoid stems, indet.
71ATr28.350-28.365 (23537-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Orbiculoidea sp.
Leiorhynchoidea sp.
Crurithyris sp.
fish plate, indet.
71ATr28.400 (23538-PC) , Misheguk Mtn , Nuka Ridge, talus, member o, upper Nuka Fm.
Orthotetes sp.
Inflatia sp.
Brachythyris sp.
71ATr28.660 (23539-PC) , Misheguk Mtn , Nuka Ridge, member o, upper Nuka Fm.
Schizophoria sp.
Orthotetes sp.
Inflatia? sp.
Brachythyris sp.
71ATr5 (23540-PC) , Misheguk Mtn , Nuka Ridge, gravel, member o, upper Nuka Fm.
ambocoelids
nuculanids
medium-spired gastropods
scaphopods?
71ATr1.555 (23541-PC) , Misheguk Mtn , Nuka Ridge, member p, upper Nuka Fm.
echinoderm debris, indet.
medium-sized productoid
Neospirifer? sp.
syringothyrid
compositid
71ATr4.800 (23542-PC) , Misheguk Mtn , Nuka Ridge, member p, upper Nuka Fm.
Orbiculoidea sp.
71ATr28.850 (23543-PC) , Misheguk Mtn , Nuka Ridge, member p, upper Nuka Fm.
productid, indet. (large)
Spiriferella? sp.
compositid
71ATr28.1126 (23544-PC) , Misheguk Mtn , Nuka Ridge, member p, upper Nuka Fm.
productoid fragments
?echinodermal fragment