MIOCENE POLLEN FROM THE WARM-TEMPERATE HOMERIAN TYPE SECTION NEAR HOMER, ALASKA - AN IN-DEPTH STUDY

Coal from swamps that formed on Neogene flood plains of the Kenai lowlands, Alaska, yields a well preserved pollen and spore flora from the Homerian type section. Stump horizons, abundant wood fragments, wood grain, and amber within the coal attest to forested swamps. Our detailed studies of these pollen assemblages reveal elements of both mixed northern hardwood and warm-temperate mesophytic forests. These assemblages are richer than the flora formerly defining the Homerian type section, which had indicated a less diverse, cooler assemblage. The flora exhibits no definite taxonomic chronology regardless of stratigraphic position. Alnus dominates with up to 45% of the total counts in our samples, followed by Pinaceae and TCT with 25-30%, and up to 15% thermophiles representing at least 25 genera. The thermophiles include Carya, Coylus-type, Ilex, Juglans, Myrica, Ostrya/Carpinus, Pterocarya, Quercus/Quercus-type, and Ulmus/Zelkova; three of these have not yet been reported from the Homerian. Unexpectedly, Podocarpus and Dacrydium are present in at least 85% and 65% of the samples, respectively. They appear to have coexisted with the other taxa, because the nearby sediment-supplying Kenai-Chugach terranes are mostly of oceanic-plate affinity and are unlikely to have provided podocarp pollen that could have been redeposited. Under fluorescent light, all of the pollen, including the podocarps, exhibit a uniform orange-yellow color, also suggesting a contemporaneous origin for all the grains. New, preliminary high-resolution ⁴⁰Ar/³⁹Ar dates of ~6.5-7.8 Ma for the Homerian type section suggest that the upper Homerian is probably younger than previously thought, and consequently, the Homerian-Clamgulchian boundary is probably younger as well. Our flora precedes uplift of the Alaska Range to the north, so comparison with Homerian taxa at more northerly locations will be important. Thus, our study of the Homerian type section has revealed three surprises: (1) warm-loving taxa; (2) the first appearance in the Homerian of a new gymnosperm family, Podocarpaceae; and (3) the apparent youth of the type Homerian.