Gray clay (Malpass clay) in the west Eugene Wetlands and the Willamette Valley is weathered and redeposited ash from Mount Mazama / authors: Karin E. Baitis, Gregory J. Retallack, Michael E. James.

Format:

Book

Government document

Author/Creator:

Baitis, Karin E., author.

Retallack, Greg J. (Greg John), 1951- author.

James, Michael E., author.

Contributor:

United States. Bureau of Land Management, issuing body.

National Operations Center (U.S.), publisher.

Series:

Technical note (United States. Bureau of Land Management) ; 447.

Technical note ; 447

Language:

English

Subjects (All):

Volcanic ash, tuff, etc--Oregon.

Volcanic ash, tuff, etc.

Clay soils--Oregon.

Clay soils.

Volcanic eruptions--Oregon.

Volcanic eruptions.

Oregon.

Physical Description:

1 online resource (iv, 21 pages) : illustrations (some color), maps (some color).

Place of Publication:

Denver, CO : U.S. Department of the Interior, Bureau of Land Management, National Operations Center, 2015.

Summary:

The climactic eruption of Mount Mazama approximately 7,600 years ago distributed airfall tuff throughout what is now eastern and offshore Oregon. This distinctive tephrostratigraphic marker had been thought to be absent across the Willamette Valley. X-ray diffraction, examination of pyrogenic mineral suites, and new high-resolution radiometric dating (40AR/39AR) of Malpass clay from tuffaceous marker beds suggest that it is the missing ash from Mount Mazama. Over time and weathering, the ash has transformed into a smectitic gray imogolite and clay. Analysis of this widespread gray clay provided a radiocarbon date of 6,850 ± 70 years before present. Radiometric dating of the clay provided the ages of 7,987 ± 102, 8,451 ± 57, and 8,540 ± 48 years before present. These dates are comparable with that of the climactic eruption of Mount Mazama.

Contents:

Abstract

Introduction

Geologic setting of Malpass clay and Dayton soil

Material and methods

Stratigraphic position of the gray clay in the west Eugene wetlands

Chromatography

Vertic soil and gilgai relief

X-ray diffraction

Transmission electron microscope EDX analyses

Transmission electron microscope images

Mineralogy of gray clay unit

Radiometric ages

Palynology

Conclusions

References.

Notes:

Title from title screen (viewed on July 13, 2015).

"June 2015"--Cover.

"BLM/OC/ST-15/006+7100"--Page 2 of cover.

Includes bibliographical references (pages 19-21).

Other Format:

Print version: Baitis, Karin E. Gray clay (Malpass clay) in the west Eugene Wetlands and the Willamette Valley is weathered and redeposited ash from Mount Mazama

OCLC:

910980879