Sample Detail of
Sample: Sample No. F6-J-27 -- USGS No. Mesozoic loc. 31260
Locality: Field No. F6-J-27
Description: Divide between Ohio and Copeland Creeks. 5,800 ft. N. 30o E. of B.M. Copeland in Healy (A-6) quad., Upper Chulitna Districti, Alaska Range, Alaska. [N.J. Silberling and D.L. Jones, 1976. On divide between Ohio and Copeland Creek, 5,800 ft (1,768 m) N. 30o E. of VABM Copeland, Healy (A-6) quadrangle, south-central part of Alaska Range, southern Alaska. Unnamed beds. Late early to early middle Sinemurian (description from Imlay, 1981, p. 26)]
Location: Alaska Quadrangle: Healy A-6
Reference
Title: Report on Referred Fossils ,  1976 (11/10)
All the fossil collections listed below, except those from Mesozoic loc. 31261 (F6-J-31), are definitely of early Sinemurian age. Such an age is shown by the presence at four localities of Arnioceras, which genus in Europe ranges from the top of the Arietites bucklandi zone into the Asteroceras obtusum zone (see Dean, Donovan and Howarth, 1961, Bull. of British Museum (Nat. Hist.) v. 4, no. 10, p. 450, 454). The very earliest Sinemurian age for localites 31264 (F6-S-331) and 31266 (F6-S-333) is shown by the presence of Psiloceras? canadense Frebold at both localities and of Vermiceras (Paracaloceras) at loc. 31266. The species Psiloceras? canadense is significant because in British Columbia it has been found in association with the ammonites Vermiceras (Vermiceras), (V.) Paracaloceras, and Charmasseiceras (Frebold, 1967, G.S. Canada Bull. 158, p. 30, pls. 1-9). Those taxa are now known to be characteristic of the basal Sinemurian in Europe and Nevada (unpublished studies by Jean Guex and David Taylor) instead of the highest Hettangian as postulated by Frebold (1967, p. 30-31).

The age of the fossils at locality 31261 (F6-J-31) is definitely Sinemurian. A late Sinemurian age older than the zone of Echioceras raricostatum is indicated by two ammonites that are identical in shape and ribbing with the type specimens of Arctoasteroceras jeletzkyi Frebold (1960, G.S. Canada Bull. 59, pls. 2,3) from Arctic Canada and which likewise have a low, blunt keel on their venters. Such a keel is lacking on the venters of Psiloceras? canadense Frebold which species is otherwise similar.

Frebold dated A. jeletskyi as middle late Sinemurian because of its occurrence with Oxynoticeras oxynotum and below Echioceras sensu lato and because of its close resemblance to Aegasteroceras (Frebold, 1960, p. 14, 26). If Arctoasteroceras is a synonym of Aegasteroceras, as proposed by Hallam (1965, AAPG Bull., v. 49, p. 1495) and by Donovan and Forsey (1973, Univ. Kansas Paleont. Contributions Paper 64, Systematics of Lower Liassic Ammonitina, p. 3), then it could represent the zone of Asteroceras obtusum of earliest late Sinemurian age (Dean, Donovan and Howarth, 1961, p. 454.)

The only other ammonite from locality 31261 resembles both Paltechioceras of latest Sinemurian age and Paracaloceras of earliest Sinemurian age in its highly evolute coiling, its strong simple forwardly arched ribs, and its tricarinate-bisulcate venter. At present this specimen does not permit dating the locality closer than Sinemurian.
Report by: Ralph W. Imlay
Referred by: Bela Csejtey , Jr. , Norman J. Silberling
Age: Sinemurian (early Sinemurian)
Comment:All the fossil collections listed below, except those from Mesozoic loc. 31261 (F6-J-31), are definitely of early Sinemurian age. Such an age is shown by the presence at four localities of Arnioceras, which genus in Europe ranges from the top of the Arietites bucklandi zone into the Asteroceras obtusum zone (see Dean, Donovan and Howarth, 1961, Bull. of British Museum (Nat. Hist.) v. 4, no. 10, p. 450, 454).
Occurrence(s)
No. Group Name Qty Notes
1 Ammonoids Arnioceras cf. A. densicosta (Quenstedt)
2 Bivalves Weyla sp.

Title: Report on Referred Fossils ,  1977 (02/14)
*Revised report.
Identifications of Lower Jurassic ammonites from the Alaska Range have been revised slightly. The species at localities 31264 and 31266 that previously were assigned (A-76-33) to Psiloceras? canadenseFrebold are now assigned to a newly described genus Badouxia Guex and Taylor (1976, La limite Hettangian-Sinemurian, des Prealpes romandes au Nevada: Ecologae Geol. Helvetiae, v. 69, no. 2, p. 525). These authors present evidence (p. 521-526) that some ammonites associated with the new genus Badouxia in British Columbia (Frebold, 1967, Geol. Survey Canada Bull. 158) belong the genera Vermiceras, Paracaloceras, and Charmasseiceras which are characteristic of the early Sinemurian in Eurasia, Indonesia and Nevada and are not known from the Hettangian. This knowledge is useful in dating certain beds at Puale Bay, Alaska, where such genera as Paracaloceras and Badouxia have been found about 650 ft. below the base of the Kialagvik Formation (Mes. locs. 10820, 12396 (part) and ROC 1240 and ROC 1241).

In the Healy (A-6) quadrangle the presence of Arnioceras at Mesozoic locs. 16229, 31260, 31262, 31263, 31265 is good evidence of a somewhat younger early Sinemurian age, although the genus in Europe ranges from the upper part of the Arietites bucklandi zone into the Asteroceras obtusum zone.

The youngest Jurassic fossils found to dae in the Healy (A-6) quadrangle consist of Arctoasteroceras jeletzkyi Frebold in association with Paltechioceras (Orthoechioceras?) at Mesozoic locality 31261. Of these taxa, A. jeletzkyi was dated by Frebold (1960, Geol. Survey Canada Bull. 59, p. 26, table 1) as middle late Sinemurian because of its association with Oxynoticeras oxynotum. Its association with Paltechioceras at loc. 31261 is good evidence, however, of a latest Sinemurian age corresponding to the European zone of Echioceras raricostatum. It is possible, of course, that Arctoasteroceras ranges from the oxynotum into the raricostatum zone.

As a result of these revisions the ammonites found in the south central part of the Alaska Range are now listed as follows:

Badouxia canadense (Frebold) 31264, 31266
Badouxia columbiae (Frebold) 31264
Coroniceras sp. 30908
Arnioceras cf. A. densicosta (Quenstedt) 16229, 31260, 31262, 31263, 31265
Arietitid ammonite 30907, 31264, 31270
Paracaloceras rursicostatum Frebold 31266
Arctoasteroceras jeletzkyi Frebold 31261
Paltechioceras (Orthechioceras?) sp. 31261.

Any comments or corrections that you want to make will be appreciated.
Report by: Ralph W. Imlay
Referred by: Robert L. Detterman
Age: Sinemurian (early Sinemurian)
Comment:In the Healy (A-6) quadrangle the presence of Arnioceras at Mesozoic locs. 16229, 31260, 31262, 31263, 31265 is good evidence of a somewhat younger early Sinemurian age, although the genus in Europe ranges from the upper part of the Arietites bucklandi zone into the Asteroceras obtusum zone.
Occurrence(s)
No. Group Name Qty Notes
1 Ammonoids Arnioceras cf. A. densicosta (Quenstedt)