Tertiary Fossil Plants of Alaska's National Parks

The National Park Service's paleontology program works to build a baseline understanding of the natural history of the nation's public lands, and its fossil inventories have been especially productive in Alaska. The state's national parks cover 54 million acres, approximately two-thirds of all the land the Park Service manages, and hold fossils from nearly the whole geologic column.

One highlight is the plant record of the Cenozoic. Alaskan plant fossils have been known for more than 150 years and studied by some of the most famous paleobotanists of the last two centuries. Tertiary plant fossils — Paleocene through Pliocene, 66 to 2.58 million years ago — come from six Alaskan parks and 14 formations spanning approximately 60 million years, and their story is central to paleobotany and plant geography.

Alaska's national park units. NPS.

A century of misdated leaves

• Oswald Heer, the Swiss paleobotanist, published the first illustrated Alaskan plant fossils in Flora Fossilis Alaskana (1869), from Cook Inlet and the Kenai and Alaska peninsulas: 50 taxa, ten of them new. He correctly placed the Coal Cove flora on the Kenai Peninsula in the Miocene, but also linked it to a flora from Atanikerdluk, Greenland, now known to be Paleocene.
• Frank Hall Knowlton in 1904 described a flora from Kukak Bay, now in Katmai National Park and Preserve, collected by De Alton Saunders on E. H. Harriman's expedition of June and July 1899: 26 taxa, nine new. He assigned it to the "Arctic Miocene," which paleobotanists then took to be late Eocene, wrongly assuming that high-latitude Eocene floras should look like temperate mid-latitude Miocene ones because plants had migrated toward the equator as climate cooled.
• Arthur Hollick, in the 1930s, collected new sites in the Yukon Valley and, working from Smithsonian collections, identified more than 300 Tertiary species. Lacking detailed stratigraphic records, he put everything into one "Kenai Formation" of composite late Eocene age — the accepted view until the 1960s and 1970s.

The Arcto-Tertiary Geoflora

The term, coined by Heinrich Gustav Adolf Engler in the 19th century, described the temperate forests of conifers and broad-leaved deciduous trees — firs, maples, hickories, dogwoods, spruces — shared by North America, eastern Asia and Europe. Ralph Works Chaney argued that this Arcto-Tertiary Geoflora had persisted with little change for epochs while shifting its range, and, building on the misdated Alaskan floras, placed its source in the Arctic Eocene. Since Alaska was periodically joined to Asia by the Bering Land Bridge, Eocene forests of Beringia seemed a plausible common origin for the similar modern forests of eastern Asia and eastern North America.

Jack Wolfe's revision

In the second half of the 20th century, Jack Wolfe recollected sites, restudied old collections and brought new methods. He was the first to fit localities from the Alaska and Kenai peninsulas, Cook Inlet and the Gulf of Alaska into one stratigraphic framework, showing that the supposedly uniform Eocene "Kenai flora" actually spanned the early Paleocene to the late Miocene — approximately 60 million years — and included many different forest types.

His methods mattered too. He analyzed floras both floristically, identifying fossils as precisely as possible and inferring climate from the ranges of their nearest relatives, and physiognomically, using leaf traits tied to climate — the share of species with toothed leaves, for instance, falls as mean annual temperature rises — compared against modern forests. By 1966 he concluded that, given Alaska's succession of floras, the Arcto-Tertiary Geoflora concept did not hold. In its place he described two main forest types, with gradations between them.

Paleogene: paratropical rainforest

The early Paleogene was dominated by paratropical rainforest — rainforest outside the tropics — rich in lianas (woody climbers), species with smooth-edged leaves, and plants whose closest living relatives are tropical.

• Kulthieth Formation, near Yakutat Bay (Wrangell-St. Elias): the oldest leaf assemblages of the region, early Eocene, and the warmest and most diverse Alaskan Paleogene flora, with an estimated mean annual temperature of 19.4°C (66.9°F). It includes the custard apple family and type specimens in the moonseed and Icacinaceae families that probably grew as lianas.
• Tolstoi Formation, Aniakchak Crater (Aniakchak): 34 species from the middle Eocene, when climate had cooled somewhat — oaks, elms, dogwoods and maples, plus katsura and Chinese wingnut, trees now native only to Asia.
• Tyonek Formation, Redoubt Point (Lake Clark): after the cooling at the Eocene–Oligocene boundary, the lowest Paleogene temperature estimate — 10°C (18°F) cooler than the Kulthieth flora and 5°C (9°F) cooler than Aniakchak — and only 17 species, dominated by the extinct alder Alnus evidens and dawn redwood (Metasequoia). Similar-aged floras come from the Hemlock Conglomerate at Kukak Bay (Katmai) and the Poul Creek Formation (Wrangell-St. Elias), all sharing Alnus evidens.

Type and other specimens from Alaska's Tertiary floras, including (A) a moonseed-family leaf from Yakutat Bay, (B) Alnus evidens and (C) Populus congerminalis from Kukak Bay, (D) an Icacinaceae fruit from Yakutat Bay, and (E) the extinct beech Fagus antipofi from Seldovia Point. From USGS Professional Papers 182 (Hollick, 1936) and 1105 (Wolfe and Tanai, 1980).

Neogene: mixed northern hardwood forest

Later came mixed northern hardwood forest, rich in broad-leaved deciduous trees and similar to today's temperate forests of eastern Asia and eastern North America. It is best seen in floras from a warm interval of the middle Miocene that Wolfe named the Seldovian, after the Seldovia Point flora on the Kenai Peninsula, approximately 40 km (25 mi) west of Kenai Fjords National Park's southwest corner. With 45 species, it is Alaska's most diverse post-Eocene flora, strong in the willow, walnut, birch, beech, elm and maple families.

Seldovian floras in the parks include the Yakataga Formation on Cenotaph Island (Glacier Bay) and the Frederika Formation along Skolai Creek (Wrangell-St. Elias). Skolai Creek stands out for its needles and seeds of the pine family, absent at other Seldovian sites; one untested idea is that it formed at higher elevation than coastal Seldovia Point, with the flora varying by altitude.

Still being discovered

New finds keep coming. In 2010 a new plant locality turned up in the early Eocene Copper Lake Formation in northwestern Katmai, and the Tolstoi and West Foreland formations of similar age have yielded plants in Aniakchak and Lake Clark. Late Cretaceous plant fossils found in Yukon-Charley Rivers National Preserve and Denali National Park and Preserve may link the Tertiary floras to older ones.

Sources

Rewritten from the National Park Service article "Tertiary Fossil Floras of Alaskan National Parks" by Theodore Matel, NPS–Paleontological Society Paleontology in the Parks fellow and University of Michigan PhD student (public domain), in hubnx's own words. The article names the Seldovia Point flora once as "Seldovian Point"; the page uses Seldovia Point.