Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
Geology Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Geology; April 2004; v. 32; no. 4; p. 297-300; DOI: 10.1130/G20247.1
© 2004 Geological Society of America
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (11)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Retallack, G. J.
Right arrow Articles by Fremd, T. J.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Glacial-interglacial–scale paleoclimatic change without large ice sheets in the Oligocene of central Oregon

Gregory J. Retallack1, Jonathan G. Wynn2 and Theodore J. Fremd3

1 Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA
2 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
3 John Day Fossil Beds National Monument, 32651 Highway 19, Kimberly, Oregon 97848, USA

Abundant late Oligocene paleosols in eastern Oregon compose a paleoclimatic archive rivaling the resolution of deep-sea cores, recording 105 Milankovitch-scale cycles over the 5.1 m.y. duration of the middle John Day Formation. Paleoclimatic cycles are apparent from the fossil record of snails, mammals, trace fossils, soil structure, depth to calcic horizon of paleosols, and carbon and oxygen isotopic composition of pedogenic carbonate. Interpreted Oligocene alternation between semiarid sagebrush steppe and subhumid wooded grassland has the same amplitude as that inferred during accumulation of the Quaternary Palouse Loess in Washington and Oregon. This similar amplitude is surprising because large ice caps like those of the Quaternary did not extend across North America or Europe during the Oligocene. Thus ice-albedo amplification of Milankovitch-scale insolation variation cannot explain the similar magnitude of Oligocene paleoclimatic fluctuation. Weak orbital signals were more likely amplified by greenhouse gases such as CO2 and CH4 due to changing carbon budgets in the sea and on land.

Key Words: paleosols • paleoclimate • Oligocene • Oregon • carbon isotopes • oxygen isotopes




This article has been cited by other articles:


Home page
 GeologyHome page
M. J. Kohn and T. J. Fremd
Miocene tectonics and climate forcing of biodiversity, western United States
Geology, October 1, 2008; 36(10): 783 - 786.
[Abstract] [Full Text] [PDF]

Home page
 PALAIOSHome page
G. J. RETALLACK and M. X. KIRBY
MIDDLE MIOCENE GLOBAL CHANGE AND PALEOGEOGRAPHY OF PANAMA
Palaios, December 1, 2007; 22(6): 667 - 679.
[Abstract] [Full Text] [PDF]

Home page
 GeologyHome page
G. J. Retallack
Pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols
Geology, April 1, 2005; 33(4): 333 - 336.
[Abstract] [Full Text] [PDF]

Home page
 PaleobiologyHome page
Ecological polarities of mid-Cenozoic fossil plants and animals from central Oregon
Paleobiology, December 1, 2004; 30(4): 561 - 588.



JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2009 by Geological Society of America