Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology

Simon E. Engelhart; Benajamin P. Horton; Christopher H. Vane; Alan R. Nelson; Robert C. Witter; Sarah R. Brody; Andrea D. Hawkes

doi:10.1016/j.palaeo.2013.02.032

Modern foraminifera, δ¹³C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology

Palaeogeography, Palaeoclimatology, Palaeoecology

By: Simon E. Engelhart, Benajamin P. Horton, Christopher H. Vane, Alan R. Nelson, Robert C. Witter, Sarah R. Brody, and Andrea D. Hawkes

https://doi.org/10.1016/j.palaeo.2013.02.032

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Abstract

We assessed the utility of δ¹³C and bulk geochemistry (total organic content and C:N) to reconstruct relative sea-level changes on the Cascadia subduction zone through comparison with an established sea-level indicator (benthic foraminifera). Four modern transects collected from three tidal environments at Siletz Bay, Oregon, USA, produced three elevation-dependent groups in both the foraminiferal and δ¹³C/bulk geochemistry datasets. Foraminiferal samples from the tidal flat and low marsh are identified by Miliammina fuscaabundances of > 45%, middle and high marsh by M. fusca abundances of < 45% and the highest marsh by Trochamminita irregularis abundances > 25%. The δ¹³C values from the groups defined with δ¹³C/bulk geochemistry analyses decrease with an increasing elevation; − 24.1 ± 1.7‰ in the tidal flat and low marsh; − 27.3 ± 1.4‰ in the middle and high marsh; and − 29.6 ± 0.8‰ in the highest marsh samples. We applied the modern foraminiferal and δ¹³C distributions to a core that contained a stratigraphic contact marking the great Cascadia earthquake of AD 1700. Both techniques gave similar values for coseismic subsidence across the contact (0.88 ± 0.39 m and 0.71 ± 0.56 m) suggesting that δ¹³C has potential for identifying amounts of relative sea-level change due to tectonics.

Additional publication details
Publication type	Article
Publication Subtype	Journal Article
Title	Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology
Series title	Palaeogeography, Palaeoclimatology, Palaeoecology
DOI	10.1016/j.palaeo.2013.02.032
Volume	377
Year Published	2013
Language	English
Publisher	Elsevier
Contributing office(s)	Alaska Science Center Geology Minerals
Description	15 p.
First page	13
Last page	27
Country	United States
State	Oregon
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