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.