2008 Joint Annual Meeting (5-9 Oct. 2008): Similarity of Lacustrine Deposition in the Pleistocene of Oregon and the Oligocene of Australia

A remarkable similarity in the mode of lacustrine deposition occurs in two temporally and geographically separated successions in the Cenozoic. Graded packages occur in two study areas and represent the waxing and waning within ephemeral lake basins. This rhythmic deposition occurs in the classical Fossil Lake Formation of south-central Oregon and in the Etadunna Formation of the Lake Palankarinna region of south-central Australia. Although the stratigraphy is similar, the mechanism for each differs. At Fossil Lake, nine upwardly fining packages represent episodes of lake deposition from 610 to 10 ka in the Pacific Northwest, an area dominated by Pleistocene glaciation. Vertebrate fossils include large mammals such as bison, horse, and camel, as well as smaller ones, such as rodents. Bird fossils are relatively common, whereas amphibians and snakes are rare. At Lake Palankarinna, similar fining upward packages were deposited 24-26 Ma during warm, mesic conditions during the late Oligocene. Vertebrate fossils include expected taxa associated with lacustrine deposits, such as fish, crocodiles, turtles, frogs, and aquatic birds, as well as terrestrial marsupials. Despite the climatic and temporal differences, both formations record ephemeral changes in lake levels resulting in similar upwardly fining sequences.