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Reference
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| Title: |
Tertiary Stratigraphy and Paleobotany of the Cook Inlet Region, Alaska
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1966
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ABSTRACT--The nonmarine sedimentary rocks of Tertiary age in the Cook Inlet region, once thought to be entirely of Eocene age, are shown by paleobotanical evidence to be most of Paleocene, Miocene, and Pliocene age. Our study of Chickaloon floras confirms the Paleozoic age of the Chickaloon Formation, as suggested by Barnes and Payne (1956). The Wishbone Formation has not yielded fossil plants, but its conformable and gradational relationship to the underlying Chickaloon Formation indicates that it is at least partly of Paleocene age, although some of rocks of Eocene age may be included. Our study of Kenai floras, shown to be most of Miocene and probable Pliocene age, confirms the suggestions of Barnes and Payne that two different coal-bearing rocks sequences of disparate age may be represented in the Chickaloon Formation of the Matanuska Valley and the Kenai Formation of the Cook Inlet-Susitna Lowlands. The Tsadaka Formation, which rests unconformably upon the Chickaloon and Wishbone Formations, represents a marginal conglomeratic facies of the Kenai Formation; the fossil floras indicate that the Tsadaka Formation was deposited during the first half of the Miocene Epoch. Three new provincial time-stratigraphic units--the Seldovian, Homerian, and Clamgulchian Stages--are proposed. These units encompass all plant-bearing strata in Alaska and in adjoining parts of the same ancient floristic provinces that are of approximately the same age as those part of the Kenai Formation represented in the type and reference sections designated in this report. Rocks belong to these stages are recognized and distinguished from one another primarily by fossil plants. The Seldovian Stage is characterized by a rich and diversified warm-temperate flora containing many elements that are now exotic to Alaska but that were widespread during the Miocene. At least 23 fossil plant species appear to be restricted to the Seldovian Stage. Comparisons of different floras suggest that lower and upper subdivisions of the Seldovian Stage may be recognized. Paleobotanical correlations indicate that the Seldovian Stage corresponds approximately to the lower half of the Miocene Series as recognized in northwestern conterminous United States and Japan, but some upper Oligocene rocks may also be included. The Homerian Stage is characterized by a less diversified and relatively provincial flora in which many of the exotic elements are lacking. At least 11 fossil plant species appear to be restricted to the Homerian Stage. The provincialism of the flora makes correlation in traditional Epoch-Series terms difficult, but some paleobotanical evidence indicates that the Homerian Stage corresponds at least in part to the upper half of the Miocene Series; some lower Pliocene rocks may also be included. The Clamgulchian Stage is characterized by an extremely provincial flora that is depauperate in species of woody plants. Nearly all the warm-temperate exotic genera have disappeared. Three species of willow and one species of alder seem to be restricted to the Clamgulchian Stage; all seem to be ancestral to living Alaskan species. The extreme provincialism of the flora makes correlations with deposits outside of Alaska imprecise at the present time; we think, however, that the Clamgulchian Stage corresponds to at least part of the Pliocene Series. |
| Report by: |
Jack A. Wolfe
,
David M. Hopkins
,
Estella B. Leopold
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| | Age: | Early Miocene |
| Formation: | Kenai Group (Kenai Formation) |
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| Comment: | Seldovian Lower(?) Seldovian |
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