GLOBAL CLIMATE CHANGE IN THE MIOCENE RECORDED IN COLUMBIA RIVER BASALT-HOSTED PALEOSOLS

HOBBS, Kevin M., Department of Geological Sciences, The University of Idaho, PO Box 443022, Moscow, ID 83844-3022 and PARRISH, Judith Totman, Dept. of Geological Sciences, Univ of Idaho, P.O. Box 443022, Moscow, ID 83844, hobb9170@vandals.uidaho.edu

Paleosols preserved between flows of the Columbia River Basalt Province record hiatuses in basalt emplacement and provide detailed information about paleoclimatic conditions during pedogenesis. Ten paleosols hosted by the Grande Ronde and Wanapum Formations of the Columbia River Basalts were identified on the basis of pedogenic features such as horizon development, root traces, and saprolitization, and studied for their paleoclimatic indicators. A relationship between age of a paleosol and its clay mineralogy suggests that pedogenic processes changed in the eastern Columbia River Basalt Province at ca. 15.8 Ma. Geochemical analysis of the mass balance trends and chemical indexes of alteration of a Grande Ronde Formation-hosted paleosol indicates a warm humid climate was present during the early stage of Grande Ronde basalt eruption. We suggest that the absence of similar warm-humid paleosols and the presence of 2:1 clay-rich paleosols hosted by basalts younger than ca. 15.8 Ma is a representation of a cooling and drying climate change related to the termination of the Middle Miocene Climate Optimum.

Session No. 288

T122. Cenozoic Terrestrial Environmental Change in North America: From Paleosols to Paleobotany

Wednesday, 3 November 2010: 1:30 PM-5:30 PM

Room 607 (Colorado Convention Center)

Geological Society of America Abstracts with Programs. Vol. 42, No. 5, p.672

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