Quaternary tephrochronology and deposition in the subsurface Sacramento-San Joaquin Delta, California, U.S.A.

Quaternary Research
California Department of Water Resources
By: , and 

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Abstract

We document characteristics of tephra, including facies and geochemistry, from 27 subsurface sites in the Sacramento-San Joaquin Delta, California, to obtain stratigraphic constraints in a complex setting. Analyzed discrete tephra deposits are correlative with: 1) an unnamed tephra from the Carlotta Formation near Ferndale, California, herein informally named the ash of Wildcat Grade (<~1.450 - >~0.780 Ma), 2) the Rockland ash bed (~0.575 Ma), 3) the Loleta ash bed (~0.390 Ma), and 4) a middle Pleistocene tephra resembling volcanic ash deposits at Tulelake, California, and Pringle Falls, Bend, and Summer Lake, Oregon, herein informally named the dacitic ash of Hood (<~0.211 to >~0.180 Ma, correlated age). All four tephra are derived from Cascades volcanic sources. The Rockland ash bed erupted from the southern Cascades near Lassen Peak, California, and occurs in deposits up to >7 m thick as observed in core samples taken from ~40 m depth below land surface. Tephra facies and tephra age constraints suggest rapid tephra deposition within fluvial channel and overbank settings, likely related to flood events shortly following the volcanic eruption. Such rapidly deposited tephra are important chronostratigraphic markers that suggest varying sediment accumulation rates (~0.07-0.29 m/1000 yr) in Quaternary deposits below the modern Sacramento-San Joaquin Delta. This study provides the first steps in developing a subsurface Quaternary stratigraphic framework necessary for future hazard assessment.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Quaternary tephrochronology and deposition in the subsurface Sacramento-San Joaquin Delta, California, U.S.A.
Series title Quaternary Research
DOI 10.1016/j.yqres.2014.12.007
Volume 83
Issue 2
Year Published 2015
Language English
Publisher American Quaternary Association
Publisher location New York, NY
Contributing office(s) Earthquake Science Center
Description 16 p.
First page 378
Last page 393
Country United States
State California
Other Geospatial Sacramento-San Joaquin Delta
Online Only (Y/N) N
Additional Online Files (Y/N) N
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