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

TitleModern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology
Publication TypeJournal Article
Year of Publication2013
AuthorsEngelhart SE, Horton BP, Vane CH, Nelson AR, Witter RC, Brody SR, Hawkes AD
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume377
Pagination13-27
Date Published05/2013
KeywordsBulk geochemistry, Cascadia, earthquake, Foraminifera, Oregon, Paleoseismology, Relative sea level, δ13C
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.

URLhttp://www.sciencedirect.com/science/article/pii/S0031018213001181?via%3Dihub
DOI10.1016/j.palaeo.2013.02.032