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Abstract Detail

The Miocene vegetation and environment of Western North America

Rember, William C. [1], Manchester, Steven  [2].

Fossil sites associated with flows of the Columbia River Basalt Group with emphasis on the Northwest Quadrant of the Flood Basalt Province.

Ranging in age from in age from 17.5 to 6 Ma, fossiliferous sediments associated with the flows of the Columbia River Basalt Group present an opportunity to study the change in climate on either side of the Mid-Miocene Climatic Optimum 15 to 16 million years ago. The group contains four formations, Imnaha Basalt, Grande Ronde Basalt, Wanapum Basalt, and Saddle Mountains Basalt. Because geology of the northwest quadrant has remained stable for the past 30 million years the, preservation of fossil plants is excellent. The oldest basalt flow in the area is the Onaway Basalt found near the town of Potlatch, Idaho. It was first mapped as being a member of the Wanapum Basalt; however later studies have shown it to be middle Oligocene in age (28 to 29 Ma). This flora is largely unknown as it is represented only by collections made in the 1970’s from sediment blocks found downstream from a meander cutoff in the upper Palouse River. The oldest basalt flows in the area are those of the Imnaha Basalt (17.5 Ma). The lower Salmon River paleobotanical site is stratigraphically near the base of the Imnaha formation. The Grande Ronde Basalt (16.5 to 15.6 Ma.), being the most voluminous, comprises 87% of the total Columbia River Basalt Group. The interbedded sediments include many associated floral localities. Two sites, Musselshell and Jungle Point, are associated with the lowermost flows of the formation with reversed magnetic polarity, R1. Paleobotanical sites near Kendrick, Idaho are between the two lowermost Grande Ronde flows with reversed and normal polarity, R1 and N1. On the north central edge of the province is located the Grand Coulee floral site, associated with the Grande Ronde N1. The Wanapum Formation (15.6 to 14 Ma) contains the uppermost flows around the perimeter of the flood basalt province; hence there are many associated fossiliferous sediments. The most thoroughly investigated of these are those of Miocene lake Clarkia, best known from the Clarkia Racetrack and Emerald Creek localities. The White Bird paleobotanical site is associated with the Basalt of Grangeville, coeval with the Saddle Mountain formation, 14 to 6 Ma. Because of the excellent preservation and abundance of plant remains, both numerically and taxonomically, these sites have the potential to enhance our understanding of the change in vegetation during this critical period of earth history.

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1 - University of Idaho, Department of Geology, Moscow, ID, 83844, USA
2 - University of Florida, Florida Museum of Natural History, PO Box 117800, Gainesville, FL, 32611, USA

Columbia River Basalt

Presentation Type: Symposium or Colloquium Presentation
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 2:30 PM
Number: C2005
Abstract ID:625
Candidate for Awards:None

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