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Enclosed is a list of Lower Jurassic ammonite genera and species present in the Talkeetna Mountains. Please note that all ammonite localities of age significance are listed and that the ammonites are grouped under the stages Sinemurian, Pliensbachia and Toarcian. In Europe Paltechioceras occurs only in the highest Sinemurian. Crucilobiceras occurs mostly in the highest Sinemurian but a few species occur in the basal Pliensbachian. Their association at several localities in the Talkeetna Mountains is evidence that the beds in which they occur represent the upper Sinemurian. The ranges of most of the other ammonite genera listed under Pliensbachian and Toarcian are shown on p. C16 (fig. 6) in U.S.G.S. Prof. Paper 593-C (see discussion on p. C17-C21). Genera not listed therein include Uptonia and Apoderoceras from the basal Pliensbachian, Amaltheus from the upper Pliensbachian, Phymatoceras and Brodieia from the upper Toarcian, and Pseudolioceras from lower Toarcian to lower middle Bajocian. On the basis of these ranges the Talkeetna Formation has furnished ammonites of late Sinemurian to late Toarcian age. As explained in your letter of May 2, 1961, these fossil collections cannot reliably be assigned to stratigraphic positions within the Talkeetna Formation. If that conclusion still holds true, please try to make gross assignments to the three units as discussed in that letter. It would be of some value if the middle and upper units can be dated. Your comments will be appreciated.
Lower Jurassic Ammonites in the Talkeetna Mountains Toarcian Dactylioceras cf. D. commune (J. Sowerby) - 24787 and 29198
D. (Orthodactylites) kanense McLearn - 29198
Harpoceras cf. H. exaratum (Young & Bird) - 29198
Pseudolioceras sp. - 25317
Grammoceras? sp. - 25939
Phymatoceras? sp. - 25317, 25342
Brodieia cf. B. tenuicostata (Jaworski) - 25940
Haugia cf. H. variabilis (d'Orbigny) - 25318, 27508
H. cf. H. grandis Buckman - 24111, 24114
H. cf. H. compressa Buckman - 24114
H. sp. - 25316, 25319, 25359 Pliensbachian Leptaleoceras pseudoradians (Reynes) - 29450
Uptonia sp. juv. - 6697
Amaltheus cf. A. stokesi (J. Sowerby) - 25941
A. sp. - M2441
A. sp. - M2441
Fontanelliceras cf. F. fontanellense (Gemmellaro) - 25941, 27586, 29450
Arieticeras cf. A. domarense (Meneghini) - 24107, 27586, 29450
Protogrammoceras cf. P. platum Buckman - 24108, 25941, 29449
P. cf. P. argutum (Buckman) - 24108, 25941
P. sp. - 29450
Fanninoceras kunae McLearn - 24107, 24108, 27586
F. cf. F. carlottense McLearn - 24108, 29449
Apoderoceras cf. A. subtriangulare (Young & Bird) - 6697, M6171 Sinemurian Paltechioceras cf. P. harbledownensis (Crickmay) - 28661, 28663
Crucilobiceras cf. C. densinodulum Buckman - 28661
C. cf. C. muticum (d'Orbigny) - 28661, 28662, 28663
C. cf. C. submuticum (Oppel) - 6706, 28661
C. sp. juv. - 26772 |