LANDSCAPE ECOLOGY OF THE PLEISTOCENE (100 KA) FAUNA OF FOSSIL LAKE, OR

Fossil Lake is a famous locality for Pleistocene fossils in Lake County, Oregon, first collected in 1876 by John Whiteaker and Thomas Condon, and then in 1879 by E.D. Cope. James Martin has established a tephrostratigraphy showing that the fossils are mixed by deflation from several different stratigraphic levels ranging in age from 23-646 ka, but the most productive and extensive horizon is the 47 ka Marble Bluff tuff. Our study of paleosols above and below the Marble Bluff tuff provides a context for the fossil fauna. Four pedotypes were recognized. The most striking of these is a paleosol below the Marble Bluff tuff with very clayey, columnar-structured, Bn horizon, which we identify as a Natrargid paleosol. Directly below is a different clayey paleosol with crumb textured surface horizon 22 cm thick, which we identify as a Xeroll. A third pedotype is brown burrowed sandstone with persistent relict bedding, which we identify as Psamments. A fourth pedotype is sandstone and volcanic ash with a tabular calcareous rhizoconcretions, as evidence of very shallow water table and allowing identification as Aquents. The Aquents and Psamments represent streamside and lakeside early successional communities. The Natriargid on the other hand has scattered silica rhizoconcretions and represents an open alkali shrubland. The Xeroll has fine root traces of a sod grassland, which is significant in light of common grazers, Columbian mammoth (Mammuthus columbi) and horse (Equus scotti), in the mammal fauna. There are also fossil fish and waterbirds in the fossil fauna as evidence for lakes in the past, but there has been concern about how the diverse mammal fauna made so far out into the lake depositional basin. It now is clear that fossiliferous lacustrine sediments and well drained paleosols alternated in the sequence.