Reference Detail of

Report on Referred Fossils
Edit Reference Add/Edit Sample Sample List Show Map
Stratigraphic range: Lower Jurassic
Kinds of fossils: Mollusks
Quadrangle or area: Healy (A-6) quad., Alaska Range
Shipment No.: A-76-33
Referred by: Csejtey, Bela, Jr. , Silberling, Norman J.
Report prepared by: Imlay, Ralph W.
Date: 11/10/1976

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 Those taxa are now known to be characteristic of the basal Sinemurian in Europe and Nevada (unpublished studies by Jean Guex and David Taylor) instead of the highest Hettangian as postulated by Frebold (1967, p. 30-31).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.

User Note module to be added
F6-J-27 (Mesozoic loc. 31260) , Healy , Divide between Ohio and Copeland Creeks. 5,800 ft. N. 30 deg. 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. 30 deg. 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)]
Arnioceras cf. A. densicosta (Quenstedt)
Weyla sp.
F6-J-31 (Mesozoic loc. 31261) , Healy , Divide between Ohio and Copeland Creeks. 6,800 ft. N. 39 deg. E. from B.M. Copeland in Healy (A-6) Quad., Alaska Range, Alaska.
Arctoasteroceras jeletzkyi Frebold
Paltechioceras? ........
...... or Paracaloceras?
Belemnite fragment
Weyla sp.
F6-S-322 (Mesozoic loc. 31262) , Healy , Divide between Partin and Little Shotgun Creeks in upper part of small drainage into Partin Creek. 39,850 ft. S. 31.5 deg. W. from B.M. Copeland, Healy (A-6) Quad., Alaska. [N.J. Silberling and D.L. Jones, 1976. Divide between Partin and LIttle Shotgun Creeks in upper part of small drainage into Partin Creek, 39,850 ft (12,147 m) S. 31.5 deg. W. from VABM Copeland, Healy (A-6) quadrangle, south-central part of Alaska Range, southern Alaska. Unnamed calcareous sandstone. Late early to early middle Sinemurian. (description from Imlay, 1981, p. 26-27)]
Arnioceras cf. A. densicosta (Quenstedt)
Pleuromya sp.
F6-S-325 (Mesozoic loc. 31263) , Healy , Divide between Shotgun and Ohio Creeks. 19,800 ft. S. 38 deg. W. from B.M. Copeland. Healy (A-6) Quad., Alaska. [N.J. Silberling and D.L. Jones, 1976. Divide between Ohio and Shotgun Creeks, 19,800 ft (6,035 m) S. 38 deg. W. from 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. 27)]
Arnioceras cf. A. densicosta (Quenstedt)
Weyla sp.
Pleuromya sp.
F6-S-331 (Mesozoic loc. 31264) , Healy , Divide between Shotgun and Little Shotgun Creeks. 28,800 ft. S. 34 W. from B.M. Copeland, Healy (A-6) Quad., Alaska.
Arietitid ammonite
Psiloceras? canadense Frebold
F6-S-332 (Mesozoic loc. 31265) , Healy , Divide between Shotgun and Little Shotgun Creeks, 31,700 ft. S. 33 deg. W. from B.M. Copeland, Healy (A-6) Quad., Alaska. [N.J. Silberling and D.L. Jones, 1976. Divide between Shotgun and Little Shotgun Creeks. 31,000 ft (9,449 m) S. 33 deg. W. from 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. 27)]
Arnioceras cf. A. densicosta (Quenstedt)
Lytoceras? sp.
Belemnite fragment
Pleuromya sp.
F6-S-333 (Mesozoic loc. 31266) , Healy , Crest of ridge on east side of upper Long Creek. 32,700 ft. N. 6 deg. E. from B.M. Copeland, Healy (A-6) Quad., Alaska.
Vermiceras (Paracaloceras) cf. V. (P.) rursicostatum Frebold
Psiloceras? canadense Frebold
Weyla sp.
Lima? sp.
Eopecten? sp.