Cenozoic paleobotany of the John Day Basin, central Oregon
Published:January 01, 2009
Richard M. Dillhoff, Thomas A. Dillhoff, Regan E. Dunn, Jeffrey A. Myers, Caroline A. E. Strömberg, 2009. "Cenozoic paleobotany of the John Day Basin, central Oregon", Volcanoes to Vineyards, Jim E. O’Connor, Rebecca J. Dorsey, Ian P. Madin
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The John Day Basin of central Oregon contains a remarkably detailed and well-dated Early Eocene–Late Miocene sedimentary sequence, known for its superb fossils. This field trip examines plant fossil assemblages from throughout the sequence in the context of their geological and taphonomic setting and regional and global significance. The Early to Late Eocene (>54–39.7 Ma) Clarno Formation contains fossil plants and animals that occupied an active volcanic landscape near sea level, interspersed with meandering rivers and lakes. Clarno assemblages, including the ca. 44 Ma Nut Beds flora, record near-tropical “Boreotropical” rainforest, which was replaced during late Clarno time by more open and seasonal subtropical forest. The overlying John Day Formation (39.7–18.2 Ma) was deposited in a backarc landscape of low hills dotted with lakes and showered by ashfalls from the Western Cascades. Fossils and paleosols record the advent of the “Icehouse” Earth during the earliest Oligocene, with decreasing winter temperature and more seasonal rainfall that supported open deciduous and coniferous forest, much like that of the southern Chinese highlands today. Sixteen and a half million years ago the Picture Gorge flood basalt covered the region. Animals and plants fossilized in the overlying (ca. 16 to >12 Ma) Mascall Formation occupied a relatively flat landscape during a warm and moist period known as the Middle Miocene Climatic Optimum. In total this sequence preserves a detailed series of time slices illustrating regional biotic and landscape evolution during the Cenozoic that is highly relevant for deciphering regional and global biotic, climatic, and geological trends.
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Volcanoes to Vineyards
This volume contains guides for 33 geological field trips offered in conjunction with the October 2009 GSA Annual Meeting in Portland, Oregon. Showcasing the region’s geological diversity, the peer-reviewed papers included here span topics ranging from accreted terrains and mantle plumes to volcanoes, floods, and vineyard terroir. Locations visited throughout Oregon, Washington, and Idaho encompass Astoria to Zillah. More than just a series of maps, the accompanying descriptions, observations, and conclusions offer new insights to the geologic processes and history of the Pacific Northwest insights that will inspire readers to put their boots on the evidence (or perhaps sip it from a glass of Pinot!) as they develop their own understanding of this remarkable and dynamic corner of the world.