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

Engelhart, Simon E.; Horton, Benjamin P.; Vane, Christopher H.; Nelson, Alan R.; Witter, Robert C.; Brody, Sarah R.; Hawkes, Andrea D.. 2013 Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology. Palaeogeography, Palaeoclimatology, Palaeoecology, 377. 13-27. 10.1016/j.palaeo.2013.02.032

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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 fusca abundances 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.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.palaeo.2013.02.032
ISSN: 00310182
Date made live: 20 May 2013 10:32 +0 (UTC)

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