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Magnetic stratigraphy of the lower middle Eocene (type Ulatsian) Vacaville Shale, Solano County, California

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Abstract

Mallory (1959) designated exposures of the Vacaville Shale on Ulatis Creek, northwest o Vacaville, California, as the type section of his lower middle Eocene Ulatisian benthic foraminiferal stage. Magnetic samples were taken from the 75 m of exposed section, and yielded a stable remanence held mainly in magnetite which passed a reversal test. The section showed two normal zones and three reversed magnetozones. Based on calcareous nannofossils and planktonic foraminifera, we correlate the type Ulatisian with Chron C20r-C22r (45.0-50.5 Ma), which is latest early Eocene to early middle Eocene on the global time scale. Our data calibrate what has been previously suggested by micropaleontologists: the base of the Ulatisian in the Vacaville Shale is 2 million years older (50.5 Ma) than it is in Media Agua Creek in the Temblor Range (48.5 Ma), and that the top of the Ulatisian is a million years younger (46.5 Ma) in the Vacaville section then it is at Media Agua Creek (47.5 Ma). This is another example of the problems with time-transgressive benthic foraminiferal stages.

Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Magnetic stratigraphy of the lower middle Eocene (type Ulatsian) Vacaville Shale, Solano County, California
ISBN 1-878861-84-0
Volume 91
Year Published 2001
Language English
Publisher Society of Economic Paleontologists and Mineralogists, Pacific Section
Description 9 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title Pacific Section, Society of Economic Paleontologists and Mineralogists
First page 56
Last page 64
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