Sample Detail of
Sample: Sample No. 52AGz61 -- USGS No. Mesozoic loc. 24106
Locality: Field No. 52AGz61
Description: Hoare, Imlay, and Grantz, 1952. Anchorage D-2 quad., on south tributary of Squaw Creek, 2.02 miles N 28 1/2 degrees E of southeast summit of Gunsight Mountain. Talkeetna formation.
Location: Alaska Quadrangle: Anchorage D-2
Reference
Title: Report on Referred Fossils ,  1967 (01/23)
Collections 66AGz31A and B, as well as the others listed below, are of late Pliensbachian age. Among the ammonites the genera Arieticeras, Fontanelliceras, Leptaleoceras and Amaltheus are known in Europe only from the upper Pliensbachian zones of Amaltheus margaritatus and Pleuroceras spinatum. Paltarpites in Europe ranges through these zones into the lowermost Toarcian (lower part of zone of Dactylioceras tenuicostatum). Fanninoceras has been found only in western North America and only in beds of Pliensbachian age. It occurs in the Suplee and Nicely formations in eastern Oregon associated with ammonites of late Pliensbachian age, which will be described in a Prof. Paper that was submitted last year. Fanninoceras at its type locality on Maude Island in the Queen Charlotte Islands is associated with the late Pliensbachian ammonite Arieticeras in a collection made by David Jones (Mesozoic loc. 28724). Previous assignment of Fanninoceras to the early Toarcian (Imlay in Dickinson and Vigrass, 1965, Oregon Dept. Geol. Mineral Industries Bull. 58, p. 37-41) was based on erroneous generic identifications by me and has now been corrected by detailed studies of certain ammonite assemblages from eastern Oregon.

The ammonites present in these collections do not permit a closer age determination than late Pliensbachian. Once I identified an ammonite from Mes. loc. 25941 as Pleuroceras, which would indicate a correlation with the zone of Pleuroceras spinatum, but the specimen now appears to me to be a deformed Fontanelliceras similar to specimens from Mes. loc. 29450. This locality is so near the main highway that re-collection should be easy.
Report by: Ralph W. Imlay
Referred by: Arthur Grantz
Age: Pliensbachian (late Pliensbachian)
Formation: Talkeetna Formation
Comment:Collections 66AGz31A and B, as well as the others listed below, are of late Pliensbachian age. Among the ammonites the genera Arieticeras, Fontanelliceras, Leptaleoceras and Amaltheus are known in Europe only from the upper Pliensbachian zones of Amaltheus margaritatus and Pleuroceras spinatum. Paltarpites in Europe ranges through these zones into the lowermost Toarcian (lower part of zone of Dactylioceras tenuicostatum). Fanninoceras has been found only in western North America and only in beds of Pliensbachian age. It occurs in the Suplee and Nicely formations in eastern Oregon associated with ammonites of late Pliensbachian age, which will be described in a Prof. Paper that was submitted last year. Fanninoceras at its type locality on Maude Island in the Queen Charlotte Islands is associated with the late Pliensbachian ammonite Arieticeras in a collection made by David Jones (Mesozoic loc. 28724). Previous assignment of Fanninoceras to the early Toarcian (Imlay in Dickinson and Vigrass, 1965, Oregon Dept. Geol. Mineral Industries Bull. 58, p. 37-41) was based on erroneous generic identifications by me and has now been corrected by detailed studies of certain ammonite assemblages from eastern Oregon.

The ammonites present in these collections do not permit a closer age determination than late Pliensbachian. Once I identified an ammonite from Mes. loc. 25941 as Pleuroceras, which would indicate a correlation with the zone of Pleuroceras spinatum, but the specimen now appears to me to be a deformed Fontanelliceras similar to specimens from Mes. loc. 29450. This locality is so near the main highway that re-collection should be easy.

Occurrence(s)
No. Group Name Qty Notes
1 Ammonoids Fanninoceras?
2 Bivalves Meleagrinella
3 Bivalves Astarte

Title: Report on Referred Fossils ,  1961 (05/23)
Enclosed is a complete listing of Lower Jurassic mollusks from the Talkeetna Mountains. A letter has been sent to John Wells at Cornell University concerning the Lower Jurassic corals. If he cannot find time to study them, we will try to find some other coral specialist to do so.

The stages of the Lower Jurassic that are represented in the Talkeetna Mountains are based on the European ranges of the ammonites that are present. These ranges and the probable ages of the various fossil collections are listed below. Perhaps with this information you can now determine the ages of the several units of the Talkeetna formation discussed in our recent letter of May 2nd. You will note that most of the collections containing ammonites are of late Toarcian age and that there is no fossil fossil evidence for the Hettangian.

European Ranges of Lower Jurassic Ammonites found in the Talkeetna formation of the Talkeetna Mountains.

Megarietites - Sinemurian, mostly lower
Arnioceras - Sinemurian, most lower
Oxynoticeras - Sinemurian to basal Pliensbachian, mostly upper Sinemurian
Crucilobiceras - upper Sinemurian into basal Pliensbachian
Radstockiceras - lower Pliensbachian
Uptonia - lower Pliensbachian
Acanthopleuroceras - lower Pliensbachian
Protogrammoceras - upper Pliensbachian to lower Turonian
Paltarpites - upper Pliensbachian
Amaltheus - upper Pliensbachian
Pleuroceras - upper Pliensbachian
Catacoeloceras - middle Toarcian
Harpoceras - top of Pliensbachian through Toarcian, but mostly lower & middle Toarcian
Pseudlioceras - middle Toarcian into basal Bajocian (zone of Harpoceras serpentinum to Lioceras opalinum
Phlyseogrammoceras - upper Toarcian
Phymatoceras - upper Toarcian
Haugia - upper Toarcian
Grammoceras upper Toarcian to early Bajocian

Probable ages of Lower Jurassic Fossil Collections from the Talkeetna Mountains

Lower Sinemurian - 24107, 27586
Upper Sinemurian or lower Pliensbachian - 6706, 26722, 24106
Lower Pliensbachian - 3698(?), 6697, 8569, 24108
Upper Pliensbachian - 25941
Lower Toarcian - 24787, 25938(?)
Upper Toarcian - 24109, 24111, 24114, 25316, 25317, 25318, 25319, 25342, 25359, 25939, 25940, 27508, 27509(?)

The basal sandstone of the Tuxedni formation is probably entirely of Bajocian age. In an attempt to determine if any part of it might be of Toarcian age, I examined the fossils from the following localities whiach labeled either as the basal sandstone or from the basal part of the Tuxedni formation.

Fossils from the Basal beds of the Tuxedni formation

[Note by RBB: a list follows of localities with fauna - see locality list]

In summation, the basal sandstone of the Tuxedni formation in the Talkeetna Mountains has furnished ammonites and Inoceramus of early to middle Bajocian age at six localities. The immature ammonite at Mes. loc. 24137 could be either of late Toarcian or early Bajocian age.

I wish that you would let me know if any of the other collections that you have submitted are from the basal sandstone of the Tuxedni formation as I should discuss the age of the basal part of the Tuxedni formation in my forthcoming paper on the Bajocian ammonites.

Also, I would like to have you prepare a very brief statement, or summary of the stratigraphy of the Tuxedni formation in the Talkeetna Mountains that I could use in my paper. You may recall from previous papers that I need a statement concering lithologic features, thicknesses, and stratigraphic positions of the fossils. I could quote your statement as written, or I could use your data in preparing a statement that has some bearing on the fossils. It would be presented as a written communication. I do not need such a statement before next Fall, but would like to have it by December. I am working on the general part of the manuscript now and should complete it by that time. I do not expect the fossil photographs to be available until then, although only about 100 more views are needed.
Report by: Ralph W. Imlay
Referred by: Ralph W. Imlay
Age: Sinemurian-Pliensbachian (late Sinemurian or early Pliensbachian)
Formation: Talkeetna Formation
Comment:Age: Upper Sinemurian or lower Pliensbachian.
Occurrence(s)
No. Group Name Qty Notes
1 Ammonoids Oxynoticeras? sp.
2 Bivalves Meleagrinella sp.
3 Bivalves Astarte sp.

Title: Report on Referred Fossils ,  1953 (01/21)
The collections from the Lower Jurassic show that most of the subperiod is represented. Lot 52AGz63 containing Arnioceras represents the lower part of the Sinemurian stage. Lot 52AGz66 contains ammonites that are slightly younger and represents either the upper Sinemurian or the lower Pliensbachian. The sharp-ventered Oxynoticeras in Europe ranges from the zone of Asteroceras obtusum to the zone of Prodactylioceras davosi. Ammonites with ribbing similar to Grammoceras are not known below the zone of Uptonia jamesoni. I suspect that lot 52AGz66 represents the lower Pliensbachian, but an exact age determination cannot be made with the material in hand. Lot 52AGz61 contains a fragmentary ammonite that is probably an Oxynoticeras and indicates an age similar to that of lot 52AGz66. Since the latter was obtained from beds that appeared to be lower stratigraphically than lot 52AGz63, there must be a fault within the Jurassic sequence that we did not detect. It seems unlikely that the sequence is completely overturned. One thing that needs to be determined in the field is whether the mass of volcanics forming the central part of Sheep Mountain is older or younger than Sinemurian. Establishment of this relationship should help in determining the structure of Sheep Mountain.
Lots 52AGz92 and 52AGz253 represent the upper Toarcian and probably the zone of Lytoceras jurense as shown by the presence of Pseudogrammoceras and Phylseogrammoceras. Beds of this age have not hitherto been reported from Alaska. I hope that you can determine their stratigraphic position with respect to the Talkeetna-Tuxedni contact.
Lot 52AGz98 contains well-preserved specimens of Haugia, which ammonite in Europe occurs in the Lytoceras jurense at the top of the Lower Jurassic and attains its greatest development in the lower part of that zone. It is interesting, therefore, that the field description notes that the specimens come from a siltstone that is transistional between the Talkeetna and Tuxedni formations.
The collections from the Middle Jurassic of the Talkeetna Mountains and Matanuska Valley represents only three faunal zones whereas seven have been recognized in the Cook Inlet area. Whether failure to find the other zones may be explained by inadequate collecting, by structural complications, or by absence of sediments can be determined by future field work.
The lowermost part of the Middle Jurassic is represented by lot 52AGz240. The two species of Erycites in this lot occur in the lowermost exposed beds of the Kialavik formation at Wide Bay in the Alaskan Peninsula where they are associated with the ammonite Tmetoceras. Lot 52AGz284 is probably of the same age as it contains an ammonite probably representing Pleydellia. In Europe this genus ranges through the zones of Lioceras opalinum and Ludwigia murchisonae but is most common at the base of the opalinum zone.
Report by: Ralph W. Imlay
Referred by: Arthur Grantz
Age: Sinemurian-Pliensbachian (late Sinemurian to early Pliensbachian)
Formation: Talkeetna Formation
Occurrence(s)
No. Group Name Qty Notes
1 Ammonoids Oxynoticeras? sp.
2 Bivalves Meleagrinella sp.
3 Bivalves Astarte sp.