THE PALEOGENE PALM FORESTS OF ALASKA AND WASHINGTON

The fishy art of Ray Troll is firmly rooted in the drippy Tongass rainforest of southeast Alaska. Although this conifer-dominated temperate coastal rainforest that stretches north from Washington through British Columbia and into south-central Alaska evokes a sense of deep antiquity, the fossil record suggests a different story. A series of Paleocene-Eocene units that include the Chuckanut Formation near Bellingham, Washington; the Chickaloon Formation of the Matanuska Valley of South-Central Alaska; and the Kootznahoo Formation of Kupreanof Island contain fossil floras indicative of warmer climates and floral dominance by angiosperms. Collectively, these floras suggest a very different type of coastal rainforest.

The discovery of the 64 Ma Castle Rock Rainforest in central Colorado documented a type of fossil rain forest characterized by a very high diversity of large-leaved angiosperms with smooth-margins and drip tips. These floras also contained palms, cycads, ferns and cupressaceous conifers. Several distinct angiosperms from the Castle Rock site appeared unique to the site but were subsequently noticed in Arthur Hollick’s 1936 monograph, The Tertiary floras of Alaska. In 2012, we relocated some of Hollick’s Kootznahoo sites on Kupreanof Island and discovered that they also contained abundant palms, ferns and cycads. Comparison with museum collections from the Chuckanut and Chickaloon formations show a diversity of additional angiosperm genera that occur in common with the Kootznahoo and Castle Rock floras. These isolated sites begin to suggest the presence of a strip of coastal rainforest that stretched from 49N to 61N. A number of these species also occur in northeast Asia and are evidence of a warm Paleogene Beringia.