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Volcanic Glass as a Paleoenvironment...

Carlson, Tessa Boe.

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Volcanic Glass as a Paleoenvironmental Proxy: Comparing Preparation Methods on Ashes from the Lee of the Cascade Range in Oregon, USA.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Volcanic Glass as a Paleoenvironmental Proxy: Comparing Preparation Methods on Ashes from the Lee of the Cascade Range in Oregon, USA./
Author:	Carlson, Tessa Boe.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	105 p.
Notes:	Source: Masters Abstracts International, Volume: 58-01.
Contained By:	Masters Abstracts International58-01(E).
Subject:	Geochemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10785064
ISBN:	9780438272095

Volcanic Glass as a Paleoenvironmental Proxy: Comparing Preparation Methods on Ashes from the Lee of the Cascade Range in Oregon, USA.
Carlson, Tessa Boe.

Volcanic Glass as a Paleoenvironmental Proxy: Comparing Preparation Methods on Ashes from the Lee of the Cascade Range in Oregon, USA. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 105 p.

Source: Masters Abstracts International, Volume: 58-01.

Thesis (M.S.)--Portland State University, 2018.

Deuterium ratios (deltaD) of hydrated volcanic glass have been used to reconstruct paleoenvironments, although the reliability and proper sample preparation protocol have been debated. In this study, hydrated volcanic ash samples from the lee of the Cascades were prepared using two separate methods. Method 1 involves sonicating and rinsing samples with hydrochloric acid (HCl) followed by hand-selection of glass shards (125 --212microm). Method 2 requires hydrochloric acid (HCl) and hydrofluoric acid (HF) abrasion as well as heavy liquid separation of shards (70 --150microm). Method 2 produced more consistent results with decreased intra-replicate variability in both water content (-0.92 wt. %) and deuterium values (-2.5‰ deltaD). Method 2 deltaD values of ≥ 99% isotropic glass were also 2.5 -- 10 ‰ more negative relative to Method 1 values, with an increasing discrepancy with age (3.68 -- 32.66 Ma). Method 2 results suggest volcanic glass did not re-equilibrate with modern water, based on 1) < 2‰ discrepancies between samples of the same ash flow taken from unique sample localities and 2) a ~20‰ difference between samples of different ages (~8 Ma apart) from the same locality. These results support the specified use of HF abrasion and heavy liquid separation on 70 -- 150 microm glass shards to minimize the impact of contaminants on reconstructed paleowater deltaD values.

ISBN: 9780438272095Subjects--Topical Terms:

539092
Geochemistry.

Volcanic Glass as a Paleoenvironmental Proxy: Comparing Preparation Methods on Ashes from the Lee of the Cascade Range in Oregon, USA.
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520 $a Deuterium ratios (deltaD) of hydrated volcanic glass have been used to reconstruct paleoenvironments, although the reliability and proper sample preparation protocol have been debated. In this study, hydrated volcanic ash samples from the lee of the Cascades were prepared using two separate methods. Method 1 involves sonicating and rinsing samples with hydrochloric acid (HCl) followed by hand-selection of glass shards (125 --212microm). Method 2 requires hydrochloric acid (HCl) and hydrofluoric acid (HF) abrasion as well as heavy liquid separation of shards (70 --150microm). Method 2 produced more consistent results with decreased intra-replicate variability in both water content (-0.92 wt. %) and deuterium values (-2.5‰ deltaD). Method 2 deltaD values of ≥ 99% isotropic glass were also 2.5 -- 10 ‰ more negative relative to Method 1 values, with an increasing discrepancy with age (3.68 -- 32.66 Ma). Method 2 results suggest volcanic glass did not re-equilibrate with modern water, based on 1) < 2‰ discrepancies between samples of the same ash flow taken from unique sample localities and 2) a ~20‰ difference between samples of different ages (~8 Ma apart) from the same locality. These results support the specified use of HF abrasion and heavy liquid separation on 70 -- 150 microm glass shards to minimize the impact of contaminants on reconstructed paleowater deltaD values.
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