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Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
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Palaeogeography, Palaeoclimatology, Palaeoecology
j ourna l homepage: www.e lsev ie r .com/ locate /pa laeo
Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshesand their application in paleoseismology
Simon E. Engelhart a,b,⁎, Benjamin P. Horton b,c, Christopher H. Vane d, Alan R. Nelson e, Robert C. Witter f,Sarah R. Brody g, Andrea D. Hawkes h
a Department of Geosciences, University of Rhode Island, Woodward Hall, 9 East Alumni Avenue, Kingston, RI, 02881, USAb Sea Level Research, Department of Earth and Environmental Science, University of Pennsylvania, Hayden Hall, 240 South 33rd St, Philadelphia, PA, 19104, USAc Sea Level Research, Institute of Marine and Coastal Sciences, School of Environmental and Biological Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901, USAd British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UKe Geologic Hazards Science Center, US Geological Survey, 1711 Illinois St., Golden, CO 80401, USAf Alaska Science Center, US Geological Survey, 4200 University Drive, Anchorage, AK 99508, USAg Nicholas School of the Environment, Duke University, Box 90328, Durham, NC 27708, USAh Department of Geography and Geology, University of North Carolina Wilmington, Wilmington, NC 28403, USA
⁎ Corresponding author at: Department of GeosciencWoodward Hall, 9 East Alumni Avenue, Kingston, RI, 02187.
E-mail address: [email protected] (S.E. Engelhart).
0031-0182/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.palaeo.2013.02.032
a b s t r a c t
a r t i c l e i n f oArticle history:Received 3 July 2012Received in revised form 4 February 2013Accepted 26 February 2013Available online 13 March 2013
Keywords:ForaminiferaPaleoseismologyδ13CBulk geochemistryOregonCascadiaEarthquakeRelative sea level
We assessed the utility of δ13C and bulk geochemistry (total organic content and C:N) to reconstruct relativesea-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 geochemistrydatasets. Foraminiferal samples from the tidal flat and lowmarsh are identified byMiliammina fusca abundancesof >45%, middle and high marsh by M. fusca abundances of b45% and the highest marsh by Trochamminitairregularis abundances >25%. The δ13C values from the groups defined with δ13C/bulk geochemistryanalyses 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 modernforaminiferal and δ13C distributions to a core that contained a stratigraphic contact marking the great Cascadiaearthquake 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 relativesea-level change due to tectonics.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
To evaluate and prepare for the impacts of future great earthquakesalong the Cascadia subduction zone of western North America, it isnecessary to understand the magnitude and recurrence interval of pre-vious earthquakes over thousands of years (e.g., Atwater, 1987;Charland and Priest, 1995; Clague, 1997; Wang and Clark, 1999;Peterson et al., 2000; Frankel et al., 2002; Kelsey et al., 2002; Petersenet al., 2002; Priest et al., 2010). Tidal marsh sediment sequences at es-tuaries along Cascadia coasts archive stratigraphic evidence of Holo-cene great earthquakes (magnitudes 8–9) as records of abruptrelative sea-level (RSL) changes (e.g., Darienzo and Peterson, 1995;Nelson et al., 1996a; Shennan et al., 1998; Clague et al., 2000; Kelseyet al., 2002; Witter et al., 2003; Atwater et al., 2005; Nelson et al.,2006). Microfossil-based sea-level reconstructions have the potentialto produce precise estimates of sudden coastal subsidence or uplift
es, University of Rhode Island,2881, USA. Tel.: +1 401 874
rights reserved.
during great earthquakes (e.g., Guilbault et al., 1995; Hemphill-Haley,1995; Sherrod, 1999; Hughes et al., 2002; Nelson et al., 2008; Hawkeset al., 2011), because of the strong relationship between microfossilspecies distributions and elevation with respect to tide levels (e.g.,Horton and Edwards, 2006).
Tidal-marsh foraminifera have been commonly utilized to recon-struct changes in RSL along tectonically quiescent coasts in Europe(e.g., Horton, 1999; Gehrels et al., 2001; Horton and Edwards, 2005;Edwards, 2006) and eastern North America (e.g., Scott and Medioli,1978; Gehrels et al., 2002, 2004; Leorri et al., 2006; Horton et al.,2009; Kemp et al., 2009a, 2011; Wright et al., 2011). Quantitativeforaminiferal-based reconstructions that use transfer functions (e.g.,Kemp et al., 2011) have a precision of less than ±0.1 m, which hasled to the application of transfer function methods in tectonically ac-tive areas such as the Cascadia margin (Guilbault et al., 1995, 1996;Nelson et al., 2008; Hawkes et al., 2010, 2011). Despite its greater pre-cision, this technique is limited by the site-specific assemblages(Wright et al., 2011) that necessitate collection of multiple localdatasets of modern foraminifera (e.g., Horton and Edwards, 2006;Kemp et al., 2011).
14 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
δ13C and bulk geochemistry (total organic carbon (TOC) and carbonto nitrogen ratios (C:N)) are a potential alternative method forreconstructing past RSL changes (e.g., Tornqvist et al., 2004; Gonzalezand Tornqvist, 2009; Kemp et al., 2010, 2012a). The method is basedon the assumption that δ13C values of bulk sediment should broadly
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Fig. 1. Map of (A) North America showing the location of the Cascadia subduction zone (B)Bay (C) the location of three sites within Siletz Bay that were sampled for foraminifera and δA core (SSV2) was collected from Salishan Spit (D).
reflect its botanical component (e.g., Chmura and Aharon, 1995;Lamb et al., 2006; Gonzalez and Tornqvist, 2009; Kemp et al., 2010)with additional input from particulate and/or dissolved allochthonousmaterial (e.g., Lamb et al., 2006). As with foraminifera, the compositionof plant species communities with different isotopic signatures is
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controlled by the strong elevational and environmental gradientsfound along the transition from freshwater upland to salt marsh andsub-tidal environments (e.g., Chmura et al., 1987; Goni and Thomas,2000). This is particularly evident where communities contain bothC3 and C4 plant species as they have strongly contrasting isotopicsignatures (e.g., Lamb et al., 2006). The majority of salt-marsh plantsin Oregon are C3 but important C4 species include Distichlis spicataand Zostera nana. The application of δ13C in bulk sediments in sea-level reconstructions is in its infancy globally. Although recent worksin the UK (Lloyd and Evans, 2002; Wilson et al., 2005a,b; Lamb et al.,2007; Mackie et al., 2007), Singapore (Bird et al., 2010), US Atlantic(Kemp et al., 2010, 2012a), US Pacific (Hawkes et al., 2011) and USGulf (Tornqvist et al., 2004; Gonzalez and Tornqvist, 2009) coastshave demonstrated their utility.
We compared the distribution of modern foraminifera along salinitygradients with δ13C and bulk geochemistry values in sediment beneathsalt marshes of Siletz Bay, Oregon. We used communities of common,tidal-marsh, vascular plants to define elevation-dependent ecologicalenvironments and compared foraminiferal species assemblage dataand δ13C, TOC and C:N values along environmental gradients to evaluatethe ability of δ13C to reconstruct former sea levels. We then applied bothmethods to a core to reconstruct the amount of coastal subsidenceduring the great earthquake of AD 1700 earthquake at Siletz Bay.
2. Study area
The Siletz Bay estuary is separated from the Pacific Ocean by SalishanSpit (Fig. 1B). The bay formed when the river valley was drowned byrising RSL during the Holocene transgression (Bottom et al., 1979;Peterson et al., 1984). The Bay drains an area of 524 km2 (Seliskar andGallagher, 1983) and contained 1.07–1.46 km2 of salt marsh in theearly 1970s (Eilers, 1975; Jefferson, 1975), with an additional 0.4 km2
reclaimed from previously dyked pastureland by the Siletz Bay NationalWildlife Refuge in 2003. Siletz River flows produce spatially variablesalinity within the estuary with the highest values near the ocean inletin the northwest of the Bay (Gallagher and Kibby, 1980). Salinitypeaks between August and October with minimum values betweenJanuary and March, due to seasonal variations in flow (Oglesby, 1968).Salinity measurements taken in July from open surface water seawardof each site were recorded with values of 22 at Salishan Spit, 16 at SiletzEast, and 11 at Millport Slough.
Siletz Bay has a mixed semidiurnal and diurnal tidal cycle with atidal range (mean lowest low water, MLLW, to mean highest highwater, MHHW) of 2.64 m (Hawkes et al., 2010). Short term (1 yr)tide gauges installed in the bay at Siletz Keys and upriver in MillportSlough showed b7 cm difference in mean high water (MHW) andMHHW elevations relative to North American Vertical Datum (NAVD)88 (Brophy et al., 2011).
We used 13 species of common vascular plants at Siletz Bay to iden-tify tidal environments ranging from tidal flat, to low, middle, and highmarshes, and upland environments (Fig. 2; Table 1). Dominant tidalmarsh species included Gaultheria spp., Potentilla palustris, Juncus spp.,Agrostis spp., Salicornia virginica, Distichlis spicata, Scirpus spp., Carexlyngbyei and Zostera nana, whereas the most common upland taxawere Picea sitchensis, ferns and Conium maculatum.
3. Methods
We collected modern samples from four tidal transects. Two tran-sects at Salishan Spit (SS (A to A′) and SS2 (B to B′)) were 115 and146 m long, respectively, and 3 km from the Bay mouth (Fig. 1Band C). A 123-m-long transect 1.2 km inland of Salishan Spit wasestablished at Siletz East (C to C′), west of U.S. Highway 101 (Fig. 1Band D). The fourth transect was 95 m long at Millport Slough (D toD′), 1.8 km inland of Siletz East (Fig. 1B and E). Transects werepositioned along an elevational gradient to capture the full range of
tidal environments. Salt marsh plants at each sampling station wereidentified with the help of plant guides and from lists of commonspecies found in the Pacific Northwest tidal marshes (Seliskar andGallagher, 1983; Pojar and MacKinnon, 1994; Cooke, 1997). Weascertained the elevation of each sample using a total station, whichwas tied to a local benchmark. The height of the local benchmarkwas obtained using real time kinematic (RTK) satellite navigationand reported relative to NAVD88 (error b 1 cm). Elevations wereconverted to MSL using previously established relationships betweenorthometric and tidal datums (Brophy et al., 2011) to enable theuse of site-specific tidal predictions (e.g., mean high water, MHW)generated for every 3 km of the Oregon coastline (Hawkes et al.,2010).
We collected a sample of 10 cm3 of surface sediment (0–1 cm) ateach station for foraminiferal analysis. The effects of infaunal foraminif-era in Oregon marshes have been shown to be minimal with thehighest concentration of living specimens in the top 1 cm and no livespecimens found at depths greater than 5 cm (Hawkes, 2008;Hawkes et al., 2010). Samples were treated with buffered ethanolafter collection and stained in the field using Rose Bengal to allow dif-ferentiation of live and dead specimens. Only the dead foraminiferaldata were used in the analysis as they most accurately reflect the sub-surface assemblages (Murray, 1982; Horton, 1999; Culver and Horton,2005). Each sample was divided in the laboratory using sieves to isolatethe 63–500 μm fraction. The greater than 500 μm fraction was checkedfor large foraminifera. We used a binocular microscope to count fora-minifera from a known proportion of sample until more than 200dead individuals or all tests were counted. Our taxonomy followsHawkes et al. (2010) with Ammobaculites spp. identified as a singletaxon.
We collected an additional 5 cm3 of surface sediment at each sta-tion for δ13C and bulk geochemistry analyses. Bulk sediment sampleswere prepared for δ13C and total organic carbon and nitrogen followingKemp et al. (2012a). The samples were washed with 5% hydrochloricacid for 24 h before rinsing with deionized water, then dried at 45 °Cand ground to a fine powder using a mortar and pestle. δ13C valueswere obtained using a Costech Elemental Analyzer, coupled on-line toan Optima dual-inlet mass spectrometer. The values were calibratedto the Vienna Pee Dee Belemnite (VPDB) scale using cellulose standardSigma Chemical C-6413 that was included within the runs. Samples %Cand %N were calculated on the same instrument with C:N ratios cali-brated through an acetanilide standard and presented on a weight-to-weight basis. Replicate measurements on well-mixed samplesdiffered b0.2‰.
Foraminiferal and δ13C/bulk geochemistry data were grouped usingthe Partitioning Around Medoids (PAM) method (Kaufman andRousseeuw, 1990; Kemp et al., 2012b) and the ‘cluster’ package inthe computer program R (Maechler et al., 2012). The most appropriatenumber of tidal environments is identified by the highest averagesilhouette width of all environments. We ran the analysis for samplesfrom each of the four transects, as well as for a combined dataset; weshow results for one foraminiferal transect as an example (Fig. 3);data for the remaining transects is in the Supplementary data and thenumber of groups for each analysis is summarized in Table 2. For theforaminiferal data our analyses used percentages with no cutoff valuefor taxa inclusion (Kemp et al., 2012b).
4. Results
4.1. Modern foraminiferal, floral, δ13C, and bulk geochemistry distributions
4.1.1. Salishan Spit Transect 1 (SS)At Salishan Spit Transect 1 (A–A′, Fig. 1D), 12 species were identi-
fied in 24 samples (Figs. 2; 3). The foraminifera Trochamminitairregularis dominated (>65%) the four highest elevation samples,which characterize the highest marsh environment typified by the
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Fig. 2. Elevation profiles of transects at A) Salishan Spit Transect 1, B) Salishan Spit Transect 2, C) Siletz East and D) Millport Slough. Vegetation environments correspond to Table 1.Distribution of dominant foraminifera along each transect in % with only dominant species being shown. SW = P. sitchensis swamp; HHM = highest marsh; HM = high marsh;MM = middle marsh; LM = low marsh; TF = tidal flat.
16 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
plants Gaultheria spp. and Juncus spp. mixed with Picea sitchensis andferns (Table 1). This environment was associated with low δ13Cvalues (−29 to −29.5‰), high TOC (12.2 to 28.8%), and C:N ratiosfrom 14.3 to 16.9 (Fig. 4). Foraminifera species Trochammina inflata(35 to 54%) and Haplophragmoides manilaensis (12 to 18%) character-ized the high marsh with a floral assemblage dominated by Agrostisspp., Juncus spp., Salicornia virginica and Distichlis spicata. δ13C values
Table 1Vascular plant zonations and foraminiferal associations at the three studied sites in Siletz BaHaplophragmoides wilberti; Jm = Jadammina macrescens; Mf = Miliammina fusca; Ti = Tro
Site Wetland environment Dominant vascular plants
Salishan Spit Highest marsh Gaultheria spp., Potentilla paHigh marsh Agrostis spp., Salicornia virgMiddle marsh Distichlis spicata, SalicorniaLow marsh Scirpus spp.Tidal flat Zostera nana
Siletz East High marsh Agrostis spp., Juncus spp., DiLow marsh Carex lyngbyeiTidal flat Unvegetated
Millport Slough Swamp P. sitchensisHigh marsh Potentilla palustris, TriglochiLow marsh Carex lyngbyei
were greater than in the highest marsh (−25.7 to −28.4‰), with re-duced TOC (8.4 to 18.6%) but similar C:N values (11.8 to 13.7).
The Salicornia virginica and Distichlis spicata dominated middlemarsh shows a switch in the dominant species – from Trochamminainflata (37 to 0%) toMiliammina fusca (22 to 99%) –with decreasing el-evation. The elevation of the middle marsh ranged from 1.14 to 0.67 mMSL. The input of C4 plant tissue from D. spicata may be evident in the
y. Bp = Balticammina pseudomacrescens; Hm = Haplophragmoides manilaensis; Hw =chammina inflata; Tr = Trochamminita irregularis.
Foraminifera
lustris, Juncus spp. Picea sitchensis, ferns Trinica, Juncus spp., Distichlis spicata, Potentilla palustris Ti, Hw, Hmvirginica Ti, Jm, Hw, Mf
MfMf
stichlis spicata Ti, Jm, Bp, HwMfMfTr, Hw, Jm, Bp
n maritima, Juncus spp. Tr, Hw, Hm, Bp, MpMf
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Fig. 3. Relative abundance of dead foraminifera at 24 sampling sites on Salishan Spit Transect 1 (SS). The vertical axis is sampling site number reflecting the sequence of collectionalong the transect. The order of the numbers on the axis is dictated by PAM analysis. PAM cluster analysis sub-divides the data into three groups, SS-Ia (gray bars), SS-Ib (black bars)and SS-II (white bars). Silhouette plot for PAM clustering of foraminiferal samples partitioned into three groups. The silhouette plot shows widths between −1 and 1, where valuesclose to −1 indicate that a sample was incorrectly classified and values close to 1 indicate that a sample was assigned to an appropriate group.
17S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
δ13C values (−23.6 to −26.2‰), with a further fall in TOC (4.9 to12.4%) but with similar C:N values (10.6 to 13.7) compared to thehigh marsh.
The lowmarsh, typically covered by Scirpus spp. was characterizedby a near-monospecific Miliammina fusca assemblage (89 to 99%).δ13C values continue to increase (−21.1 to−24.2‰) with greater sa-linity, associated with a fall in TOC (0.3 to 1.5%) and C:N (1.7 to 8.7).The Zostera nana tidal flat was also dominated byM. fusca (83 to 89%)but with the addition of Reophax spp. (5 to 10%). Despite the presenceof the C4 plant Z. nana, δ13C values are similar to those in the lowmarsh (−23.2 to −23.6‰). TOC (1.0 to 1.4%) and C:N ratios (9.0 to9.4) are also comparable to those in the low marsh.
The PAM cluster analysis identified three foraminiferal groups(Fig. 3), which were named following the standard terminology pre-viously used in Oregon (e.g., Hawkes et al., 2010). Group SS-Ia (aver-age silhouette width 0.81) is dominated by Trochamminita irregularis;Group SS-Ib (average silhouette width 0.70) is identified byTrochammina inflata and Group SS-II (average silhouette width 0.80)is dominated byMiliammina fusca. PAM identified two δ13C/bulk geo-chemistry groups. Group SS-G-I had an average silhouette width of0.53 with δ13C value of −27.5 ± 1.4‰, TOC of 14.5 ± 5.6% and C:Nof 13.3 ± 1.5. Group SS-G-II (average silhouette width 0.73) hadδ13C values of −23.2 ± 1.1‰, TOC of 1.7 ±1.5% and C:N of 8.4 ±
Table 2Group inventory for partitioning around medoids (PAM) analysis. For each site, the number ogroups.
Site Number of foraminiferal groups (and
Salishan Spit Transect 1 (SS) 3 (SS-Ia, SS-Ib, SS-II)Salishan Spit Transect 2 (SS2) 2 (SS2-I, SS2-II)Siltz East Transect (SE) 2 (SE-I, SE-II)Millport Slough Transect (MS) 2 (MS-I, MS-II)Combined dataset (SB) 3 (SB-Ia, SB-Ib, SB-II)
2.5. Group SS-G-I is associated with T. inflata and T. irregularis whileSS-G-II is dominated by M. fusca.
4.1.2. Salishan Spit Transect 2 (SS2)At Salishan Spit Transect 2 (B–B′; Fig. 1D), 14 species were identi-
fied in 27 samples (Fig. 2; Supplementary Fig. 1). The three highestelevation samples taken in the transition between the highestmarsh plant communities (Potentilla palustris and Gaultheria spp.)and upland environments (Conium maculatum and ferns) did notcontain any foraminifera. The δ13C are −27.5 to −28.4‰ with TOCranging from 34.6 to 39.6% and C:N ratios of 21.0 to 29.2 (Fig. 4).The highest sample, in a Juncus spp. marsh, had a low concentration(790 per 10 cm3) of foraminifera (SS2-4) with mostly Trochamminitairregularis (59%). Samples from the Agrostis spp., Salicornia virginica,Juncus spp., Distichlis spicata and P. palustris high marsh (SS2-4 toSS2-13) were dominated by Trochammina inflata (maximum 66%)with lesser numbers of Jadammina macrescens (maximum 23%) andHaplophragmoides wilberti (maximum 35%). δ13C values in this envi-ronment ranged from −28.5 to −24.8‰ and are associated withhigh TOC (9.1 to 29.9%) and C:N (11.6 to 19.2) values.
The middle marsh was vegetated with Distichlis spicata andSalicornia virginica and corresponds with increasing Miliamminafusca (2 to 64%) and decreasing Trochammina inflata (4 to 60%) over
f groups and the codes used are listed for the foraminiferal and δ13C/bulk geochemistry
codes) Number of δ13C/bulk geochemistry groups (and codes)
2 (SS-G-I, SS-G-II)2 (SS2-G-I, SS2-G-II)2 (SE-G-I, SE-G-II)2 (MS-G-I, MS-G-II)3 (SB-G-I, SB-G-II, SG-G-III)
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D) Transect MS
00 40 80 120 40 80 120 160 0 40 80 120 0 40 80Distance (m) Distance (m) Distance (m) Distance (m)
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Fig. 4. Elevation profiles of transects at A) Salishan Spit Transect 1, B) Salishan Spit Transect 2, C) Siletz East, and D) Millport Slough. Wetland environments correspond to Table 1. Distri-bution of δ13C, total organic carbon (TOC) and C:N ratios along each transect are shown. SW = P. sitchensis swamp; HHM = highest marsh; HM = high marsh; MM = middle marsh;LM = low marsh; TF = tidal flat.
18 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
an elevation range from 0.83 to 1.15 m MSL. δ13C values were lowerthan the high marsh (−21.3 to −24.6‰), with an associateddecrease in TOC (3.6 to 7.1%) but similar C:N ratios (10.2 to 17.2).This vegetation environment had increasing M. fusca and decreasingT. inflata abundances.
The low marsh (Scirpus spp.) and tidal flat (Zostera nana) weredominated by Miliammina fusca (68 to 92%). δ13C values are similarto the middle marsh (−22.2 to −23.6‰), but with a decrease inTOC (0.7 to 2.1%) and C:N ratios (8.5 to 9.6). Tidal flat samplesincluded Reophax spp. (1–6%) and showed δ13C values similar to thelow marsh (−23.1 to −24.2‰). TOC values (0.8 to 1.9%) and C:Nratios (8.8 to 9.9) showed little change.
PAM identified two foraminiferal groups (Supplementary Fig. 1):Group SS2-I had an average silhouette width of 0.51 and was dominat-ed by Trochammina inflata; and Group SS2-II (average silhouette width0.79) is identified by high abundances of Miliammina fusca. PAM alsoidentified two δ13C/bulk geochemistry groups. Group SS2-G-I had anaverage silhouette width of 0.74 with δ13C value of −28.0 ± 0.5‰,TOC of 35.5 ± 4.2% and C:N of 25.5 ± 4.4. Group SS2-G-II (averagesilhouette width 0.71) had δ13C values of −24.3 ± 2.0‰, TOC of6.2 ± 5.9% and C:N of 11.8 ± 2.8. Group SS2-G-1 samples are absentof foraminifera or dominated by Trochamminita irregularis whileSS2-G-II is dominated by T. inflata and M. fusca.
4.1.3. Siletz East Transect (SE)At Siletz East (C–C′; Fig. 1E), 11 species were identified in 17 samples
(Fig. 2; Supplementary Fig. 2). The highest marsh environment identi-fied at the Salishan Spit transects was absent at Siletz East. The Agrostisspp., Juncus spp. and Distichlis spicata high marsh environments werecharacterized by the foraminifera Trochammina inflata (4 to 30%),Jadammina macrescens (16 to 54%), Balticammina pseudomacrescens(3 to 28%) and Haplophragmoides wilberti (8 to 53%). δ13C values areconsistent with input from C3 vegetation (−25.2 to −26.9‰). TOC(2.1 to 5.6%) and C:N ratios (10.6 to 14.0) are similar to the borderinglow marsh (Fig. 4). The middle marsh environment seen at SalishanSpit is absent at Siletz East. The low marsh dominated by Carex lyngbyeiis associated with increasing Miliammina fusca abundances (54 to 97%)with decreasing elevation (from 0.91 to 0.67 m MSL). δ13C values arelower than for the high marsh (−23.8 to −28.1‰), with a fall in TOC(1.8 to 6.3%) and decreasing C:N ratios (8.4 to 14.0) with decreasingelevation. The unvegetated tidal flat had an almost monospecific assem-blage of M. fusca (82 to 97%). δ13C values were greater than in the lowmarsh (−22.3 to −25.4‰), a trend also seen in TOC (1.4 to 2.9%) andC:N ratios (7.9 to 11.6).
PAM identified two foraminiferal groups (Supplementary Fig. 2):Group SE-I (average silhouette width 0.46) is composed of Trochamminainflata, Jadammina macrescens, Balticammina pseudomacrescens, and
19S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
Haplophragmoides wilberti; Group SE-II (average silhouette width 0.87)is dominated by Miliammina fusca. Similarly, PAM identified two δ13C/bulk geochemistry groups. Group SE-G-I had an average silhouettewidth of 0.70 with δ13C values of −27.7 ± 0.7‰, TOC of 5.4 ± 1.0%and C:N of 13.9 ± 0.2. Group SE-G-II (average silhouette width 0.63)is associated with δ13C values of −24.9 ± 1.1‰, TOC of 2.2 ± 0.7%and C:N of 10.2 ± 1.0. Group SE-G-I is associated with J. macrescens,B. pseudomacrescens and H. wilberti while SE-G-II is dominated byM. fusca and T. inflata.
4.1.4. Millport Slough Transect (MS)At Millport Slough (D–D′; Fig. 1F), 11 species were identified in 11
samples (Fig. 2; Supplementary Fig. 3). The highest elevation sampleon the transect (1.39 m MSL) associated with Conium maculatum didnot contain foraminifera. The Picea sitchensis swamp was associatedwith a mixed assemblage of Trochamminita irregularis (26 to 38%),Haplophragmoides wilberti (2 to 27%), Balticammina pseudomacrescens(14 to 16%) and Jadammina macrescens (14 to 31%). δ13C values werelow (−29.1 to−29.6‰) with high TOC (29.6 to 31.0%) and C:N ratios(20.7 to 21.9) (Fig. 4). The high marsh was vegetated by Potentillapalustris, Triglochin maritima and Juncus spp. and characterized by in-creased abundances of T. irregularis (30 to 61%),Miliammina petilla M.petilla (0 to 18%), Haplophragmoides manilaensis (3 to 24%), H. wilberti(2 to 35%), and B. pseudomacrescens (1 to 24%). δ13C values weregreater than in the P. sitchensis swamp (−29.6 to −30.8‰) butwith decreasing TOC (13.4 to 39.0%) and C:N ratios (14.1 to 28.0).The elevation ranged from 1.27 to 1.30 m MSL. Middle marsh vegeta-tion is absent at this site. The Carex lyngbyei low marsh is dominatedby Miliammina fusca (46 to 93%) with J. macrescens (5 to 20%) and H.wilberti (1 to 17%). δ13C are lower relative to the P. sitchensis swampand high marsh (−27.5 to −28.1‰), a trend also seen in the lowerTOC values (5.4 to 6.4%) and C:N ratios (13.2 to 15.3).
PAM identified two foraminiferal groups (Supplementary Fig. 3):Group MS-I (average silhouette width 0.61) is dominated byTrochamminita irregularis; and Group MS-II (average silhouette width0.57) is composed primarily of Miliammina fusca. PAM also identifiedtwo δ13C/bulk geochemistry groups. Group MS-G-I had an averagesilhouette width of 0.61 with δ13C value of −29.9 ± 0.6‰, TOC of30.2 ± 5.5% and C:N of 21.4 ± 4.0. Group MS-G-II (average silhouettewidth = 0.70) is associated with δ13C values of −28.8 ± 1.1‰, TOCof 9.9 ± 4.7% and C:N of 14.5 ± 0.7. Group MS-G-I is associatedwith Trochamminita irregularis, Balticammina pseudomacrescens andHaplophragmoides wilberti while MS-G-II is dominated by M. fusca,Jadammina macrescens, H. wilberti and T. irregularis.
4.1.5. Combined Siletz Bay datasetWe recorded 14 taxa of foraminifera (12 agglutinated and 2 calcare-
ous) in the dead assemblage of 79 samples from four modern transectsat three sites in Siletz Bay. Foraminifera were absent in four samples, allof which occurred at greater than 1.39 m MSL in areas of upland vege-tation. The assemblages are dominated by agglutinated species includ-ing Balticammina pseudomacrescens, Haplophragmoides manilaensis,Haplophragmoides wilberti, Jadammina macrescens, Miliammina fusca,Trochammina inflata and Trochamminita irregularis (Table 1).
PAM identified three foraminiferal groups in the combined SiletzBay dataset (Fig. 5). Group SB-Ia (average silhouette width 0.44) isdominated by Trochamminita irregularis (Fig. 5). This foraminiferal as-semblage is associated with the highest high marsh environments atSalishan Spit Transects 1 and 2 and the high marsh and Piceasitchensis swamp environments at Millport Slough. Group SB-Ib(average silhouette width 0.47) is dominated by Trochammina inflatawith Haplophragmoides wilberti and Jadammina macrescens presentin all samples. This foraminiferal group is associated with highand middle marsh vegetation. Group SB-II has the highest averagesilhouette width of 0.82 and is dominated by Miliammina fusca andoccurred at all sites.
We measured δ13C, TOC and C:N for 71 samples of bulk sediment(Fig. 4). All δ13C measurements were less than −21.0‰ (range of−21.1 to −30.8‰). As expected, TOC was the lowest in tidal flat envi-ronments and increased in vegetated environments (range of 0.3 to39.0%). C:N values ranged from 1.7 to 28.0.
PAM identified three δ13C/bulk geochemistry groups in the com-bined Siletz Bay dataset (Fig. 6). Group SB-G-I (average silhouettewidth = 0.64) is associated with δ13C of −29.6 ± 0.8‰, TOC of30.0 ± 4.6% and C:N of 20.4 ± 3.7. Group SB-G-II (average silhouettewidth = 0.45) has δ13C of −27.3 ± 1.4‰, TOC of 12.4 ± 4.0% and C:N of 13.6 ± 1.4. Group SB-G-III (average silhouette width = 0.60) ischaracterized by δ13C of−24.1 ± 1.7‰, TOC of 2.5 ± 1.8% and C:N of10.4 ± 2.7.
5. Discussion
5.1. Modern distribution of foraminifera in Siletz Bay
We used the PAM cluster analysis to quantitatively sub-divide 79modern samples of foraminifera from Siletz Bay into three faunalgroups, which reflect the highest high marsh (SB-Ia), high and middlemarsh (SB-Ib), and low marsh and tidal-flat (SB-II) environments.Previous studies of modern foraminifera along Cascadia's coast (Fig. 7)have identified similar foraminiferal assemblage zones (e.g., Jenningsand Nelson, 1992; Guilbault et al., 1996; Hawkes et al., 2010) thoughthere are some noticeable site-specific differences (e.g., Nelson et al.,2008).
Group SB-Ia represents the foraminiferal assemblages found at thehighest elevations in salt marshes and into the transition to theupland environment. The group elevational range extends from 1.18to 1.60 m MSL (1.36 ± 0.15 m). This environment is dominated byTrochamminita irregularis (>25%). This species has previously beenidentified as occupying the high marsh and upland floral environ-ments at Salmon River, South Slough and Coquille River in Oregon(Hawkes et al., 2010) and Tofino, British Columbia (Guilbault et al.,1996). Trochamminita spp. including T. irregularis and Trochamminitasalsa appear to be endemic to Pacific salt marshes having beenfound in South America (e.g., Jennings et al., 1995) and Australasia(e.g., Hayward and Hollis, 1994; Callard et al., 2011) as well asCascadia (e.g., Jennings and Nelson, 1992; Guilbault et al., 1996;Nelson et al., 2008; Hawkes et al., 2010), but not along the Atlanticcoast of North America (e.g., Gehrels, 1994) or in Europe (e.g.,Horton and Edwards, 2006). Haplophragmoides wilberti is also foundsporadically in group SB-Ia. Haplophragmoides spp. is a common occu-pant of the high and middle marshes (e.g., Jennings and Nelson, 1992;Guilbault et al., 1996; Scott et al., 1996; Gehrels and van de Plassche,1999; Patterson et al., 1999; Horton and Edwards, 2006; Kemp et al.,2009b; Hawkes et al., 2010), but it has also been found in similarhighest marsh environments associated with Trochamminita spp. inOregon (Hawkes et al., 2010) and British Columbia (Guilbault et al.,1996). At Siletz River, Trochammina inflata is generally absent in thisenvironment, which is similar to the Salmon River (Hawkes et al.,2010) and Alsea Bay (Nelson et al., 2008) sites, but contrasts withother Cascadia sites (Sabean, 2004; Hawkes et al., 2010).
Group SB-Ib contains foraminiferal assemblages associatedwith highand middle marshes. The group elevational range extends from 0.77 to1.49 m MSL (1.20 ± 0.18 m). The group is dominated by Trochamminainflata with Balticammina pseudomacrescens, Haplophragmoides wilbertiand Jadammina macrescens being significant contributors to theassemblage. T. inflata has been found in the high and middle marshesin studies at Cascadia (Jennings and Nelson, 1992; Nelson andKashima, 1993; Guilbault et al., 1996; Scott et al., 1996; Nelson et al.,2008; Hawkes et al., 2010), but in contrast to our results it is rarelythe dominant species in this assemblage. T. inflata is also commonalong temperate coastlines of eastern North America (e.g., Scott andMedioli, 1978; Culver et al., 1996; Horton and Culver, 2008; Kemp et
SS21SS22SS2-4SS24MS7
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idium spp
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sonian
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PAM Analysis
Silhouette Width
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SB-II
SB-Ib
SB-Ia
% of Dead Assemblage
Fig. 5. Relative abundance of dead foraminifera when combined into a single Siletz Bay dataset. Codes to refer to transect (SS = Salishan Spit Transect 1; SS2 = Salishan SpitTransect 2; SE = Siletz East; MS = Millport Slough) and sample number. PAM cluster analysis sub-divides the data into three groups, SB-Ia (gray bars), SB-Ib (black bars) andSB-II (white bars). Silhouette plot for PAM clustering of foraminiferal samples partitioned into three groups. The silhouette plot shows widths between −1 and 1, where valuesclose to −1 indicate that a sample was incorrectly classified and values close to 1 indicate that a sample was assigned to an appropriate group.
20 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
al., 2009b), Europe (e.g., Horton and Edwards, 2006) and Australasia(e.g., Horton et al., 2003; Southall et al., 2006; Callard et al., 2011). Ithas long been suggested that Jadammina macrescens and/orBalticammina pseudomacrescens (often combined as Trochamminamacrescens) form a dominant or monospecific assemblage at the limitof tidal inundation (Scott and Medioli, 1978, 1980; Edwards et al.,2004; Hayward et al., 2004; Horton and Edwards, 2006). This is in con-trast to their presence in the middle and high marshes at Siletz Bay.
Group SB-II represents the foraminiferal assemblages found in thetidal flat and lowmarsh environments that are always identified fromMHW to below MSL with an unknown lower limit (elevational range−0.43 to 0.91 m MSL (0.32 ± 0.35 m)). This environment is domi-nated by high abundances of Miliammina fusca (>45%), a speciesfound in all Pacific coast studies. In contrast, M. fusca is dominantonly in the low marsh environment along the North American Atlan-tic coast (Wright et al., 2011) and is replaced by calcareous foraminif-era on tidal flats (Kemp et al., 2009b). The M. fusca assemblage is alsoseen in worldwide distributions (e.g., Hayward and Hollis, 1994;
Horton, 1999; Murray and Alve, 1999). Calcareous foraminifera repre-sented by Ammonia parkinsoniana and Elphidium spp. were only pres-ent in low abundances (b10%) in the tidal flats at Siletz Bay. This isconsistent with some previous Cascadia studies (Jennings and Nelson,1992; Guilbault et al., 1996; Shennan et al., 1996; Patterson et al.,2005; Nelson et al., 2008; Hawkes et al., 2010) but higher abundancesof calcareous species have been identified in Netarts Bay (Hunger,1966; Fig. 1). Hawkes et al. (2010) have suggested that the absenceof calcareous species may be due to the low pH of most Oregonshallow subtidal environments.
5.2. δ13C and bulk geochemistry in surface sediments
δ13C and bulk geochemistry analyses have the potential to becomean important method for reconstructing coastal deformation insubduction-zone paleoseismology. Previous research has shown thatthe dominant control on the δ13C values of bulk sediment is the spe-cies of the closest plant communities (e.g., Chmura and Aharon, 1995;
13C (‰)
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-22 -26 -30 0 20 40 0 10 20 30 -0.2 0.2 0.6S
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-III
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-G-I
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-I
Fig. 6. δ13C/bulk geochemistry values when combined into a single Siletz Bay dataset. PAM cluster analysis sub-divides the data into three groups, SB-G-I (gray bars), SB-G-II (blackbars) and SB-G-III (white bars). Silhouette plot for PAM grouping of δ13C/bulk geochemistry samples partitioned into three groups. The silhouette plot shows widths between −1and 1, where values close to −1 indicate that a sample was incorrectly classified and values close to 1 indicate that a sample was assigned to an appropriate group.
21S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
Malamud-Roam and Ingram, 2001; Lamb et al., 2006, 2007), althoughdifferential decomposition may produce sediment with lower δ13Cvalues than local vascular plant tissue (e.g., Buchan et al., 2003;Vane et al., 2003; Lamb et al., 2007). TOC (Fig. 8A and B) demon-strates a pattern of increasing values from tidal flat and low marshto the highest marsh. This is likely due to both a decreasing input ofminerogenic sediment with distance from open water, an increasein the total amount of biomass preservation, due to reduced flushingwith decreasing tidal inundation, and in-situ organic growth (Brain etal., 2011; Kolditz et al., 2012). C:N ratios also show a relationship withelevation (Fig. 8), but are not suitable for reconstructions due to atendency for upland and marsh values to converge (Goni andThomas, 2000; Kemp et al., 2010, 2012a). This may be due to marineinput of carbon from algae, particulate and dissolved organic carbon(Cifuentes, 1991; Lamb et al., 2006) or selective diagenesis of carbonover immobile nitrogen (Chmura et al., 1987; Ember et al., 1987). Thislimitation of C:N ratios has previously been observed at Pacific coastestuaries including San Francisco Bay (e.g., Cloern et al., 2002). Unlikeprevious studies (e.g., Wilson et al., 2005b) C:N alone is not able todistinguish between tidal flat and low marsh sediments; C:N ranges
also overlap for the low marsh and tidal flat group (SB-G-III), andfor the middle and high marsh groups (SB-G-II). Despite these limita-tions, C:N should be used in conjunction with δ13C to understand var-iations in the sediment source contributions that could otherwise leadto confusion between contributions from algae with lower C:N ratiosand plant material with higher C:N ratios (e.g., Lamb et al., 2006).
The vegetation of group SB-G-I consists solely of C3 plants (Potentillapalustris, Gaultheria spp., Juncus spp., Triglochin maritima, Picea sitchensis,Conium maculatum and ferns). The group elevational range extendsfrom 1.18 to 1.60 mMSL (1.30 ± 0.14 m). All sediment samples withinthese environments had δ13C values less than −28.5‰, significantlylower than has been found at other highest high marsh and freshwaterenvironments in North America. Bulk sediment from freshwaterenvironments in San Francisco Bay had δ13C values from −23.3 to−27.2‰ (Cloern et al., 2002), freshwater marshes in Louisianahad an average value of−27.8‰ (Chmura et al., 1987) and four uplandsamples from New Jersey ranged from −25.1 to −26.5‰. Kempet al. (2012a) found δ13C values of −22 to −27‰ in the brackishto upland transition environment in New Jersey. Our values differeven more from those of upland border environments in Massachusetts
TofinoGuilbault (1996)
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Fig. 7. Distribution and elevational ranges of dominant foraminifera from Siletz Bay compared to similar studies at Cascadia (Guilbault et al., 1996; Sabean, 2004; Patterson et al.,2005; Nelson et al., 2008; Hawkes et al., 2010). Aspp = Ammobaculites spp.; Bp = Balticammina pseudomacrescens; Hm = Haplophragmoides manilaensis; Hw = Haplophragmoideswilberti; Hspp = Haplophragmoides spp.; Jm = Jadammina macrescens; Mf = Miliammina fusca; Ti = Trochammina inflata; Tm = Trochammina macrescens; Tr = Trochamminitairregularis; Ts = Trochamminita salsa. Solid line indicates minimal elevational overlap between groups. A dashed line indicates overlap between groups. Elevational ranges areshown in detail for the data presented here. Ranges are presented as box and whisker plots, where the box is the mean ± one standard deviation and the whiskers representthe minimum and maximum elevations in each group.
22 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
(−24.5‰; Middleburg et al., 1997), but results are consistent withthe δ13C values for plants of the highest highmarsh and upland environ-ments at Siletz Bay, which range from−28.3 to−29.6‰ (Table 3). Thevariation between the values reported here and at other North Ameri-can marshes highlights the importance of collecting local bulk sedimentsamples when reconstructing paleoenvironments using δ13C rather thanrelying on previously published values. The δ13C values for SB-G-I areconsistent with those for foraminiferal group SB-Ia (−29.6 ± 0.8‰and−29.5 ± 0.6‰, respectively). TOC values (24.5 to 39.0%) are higherthan found in 6 samples of New Jersey freshwater sediment (b10%;Kemp et al., 2012a), but are consistent with values found at the freshwa-ter/marsh transition (2 to 35%). C:N ratios in SB-G-I are also higher atSiletz Bay (16.9 to 28.0) than in either of these environments in NewJersey (12 to 16; Kemp et al., 2012a).
Group SB-G-II is composed mostly of C3 plants (Agrostis spp.,Juncus spp. and Salicornia virginica) with one C4 plant (Distichlisspicata). The group elevational range extends from 0.16 to 1.60 mMSL (1.19 ± 0.35 m). A number of samples that were classifiedwithin foraminiferal group SB-Ib are not found in group SB-G-II.The effect of this can be seen in the difference between the bulk
sediment δ13C for the foraminiferal (−25.6 ± 2.0‰) and δ13C/bulkgeochemistry (−27.3 ± 1.4‰) groups. The difference is driven bythe species D. spicata. Removing samples consisting mostly of theplant tissue of this species (>50%) in the corresponding foraminiferalgroups results in a δ13C of −26.7 ± 1.8‰, in greater agreement withthe δ13C/bulk geochemistry group average.
Group SB-G-III consists of samples from tidal flats (unvegetatedor sparsely covered with the C4 plant Zostera nana), low marsh (C3
plants Scirpus spp. and/or Carex lyngbyei) and middle marsh (C4
plant Distichlis spicata and C3 plant Salicornia virginica). The groupelevational range extends from −0.43 to 1.24 m MSL (0.48 ±0.44 m). C. lyngbyei plant tissue has a low δ13C value (−28.0‰(Wooller et al., 2007); Table 3). The dominant effect of local vegeta-tion on bulk sediment δ13C values is again seen in this group. Com-pared to an average δ13C value of −24.1 ± 1.7‰, samples notassociated with C. lyngbyei have a lower value of −23.9 ± 1.6‰ incontrast to samples in a dominant C. lyngbyei vegetation environ-ment (−26.6 ± 1.6‰). This is also reflected in greater TOC(2.8 ± 1.4 and 2.5 ± 1.8%) and C:N (11.6 ± 2.0 and 10.3 ± 2.7)values although there is a significant overlap.
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A B
SB-II SB-Ib SB-Ia SB-G-III SB-G-II SB-G-I
Fig. 8. (A). The associated mean ± one standard deviation in δ13C, C:N ratios, total organic content (TOC), and elevations for the modern samples based on the foraminiferal groups.(B) The associated mean ± one standard deviations in δ13C, C:N ratios, total organic content (TOC), and elevations for the modern samples based on the δ13C/bulk geochemistrygroups. Ranges are presented as box and whisker plots, where the box is the mean ± one standard deviation and the whiskers represent the maximum and minimum in eachgroup.
23S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
Table 3Published δ13C values for salt-marsh species found in the marshes of Siletz Bay anddiscussed in this study. The photosynthetic pathway (C3/C4) is identified for eachvascular plant.
Tidal marsh plant species Typical δ13C value(‰)
Reference
Zostera nana/japonica (C4) −12.4 Thayer et al. (1978)Scirpus maritimus (C3) −25.5 Byrne et al. (2001)Carex lyngbyei (C3) −28.0 Wooller et al. (2007)Distichlis spicata (C4) −12.7 Byrne et al. (2001)Salicornia virginica (C3) −27.2 Byrne et al. (2001)Juncus balticus (C3) −28.4 Byrne et al. (2001)Agrostis capilaris/gigantean (C3) −25.99 Wedin et al. (1995)Triglochin maritime (C3) −28.3 Cloern et al. (2002)Potentilla palustris (C3) −29.6 Brooks et al. (1997)Gaultheria shallon/salal (C3) −29.4 Brooks et al. (1997)
24 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
5.3. Tidal-marsh foraminifera and δ13C in reconstructing coseismicrelative sea-level change
Great earthquakes caused by slip on the plate boundary as theJuan de Fuca plate subducts beneath North America present a majorhazard to the Cascadia region (e.g., Clague, 1997; Frankel et al.,2002). When strain from converging plates builds to a point wherethe locked plate boundary ruptures in a great earthquake, the NorthAmerica upper plate responds elastically, flexing downward beneathmost of Cascadia's coast and upward offshore. The sudden subsidenceof coastal regions hundreds of kilometers long is most effectivelypreserved beneath tidal marshes as abrupt stratigraphic contactsbetween the high or middle marsh peat of subsided marshes andthe overlying mud of newly accreted tidal flats (e.g., Nelson et al.,1996a; Atwater and Hemphill-Haley, 1997; Kelsey et al., 2002; Witteret al., 2003; Hawkes et al., 2011). Measureable subsidence is pro-duced by great earthquakes of magnitude 8 or larger, and the amount
57
58
59
60
61
62
Dep
th (
cm)
20
M. p
etilla
Interpretatio
n
T. irregu
laris
20 40 60 80
B. pse
udom
acresc
ens
T. in
flata
H. man
ilaen
sis
H. wilb
erti
20 40 60 80
J. m
acresc
ens
2
M. fus
Abundance (%)
Bur
ied
Mar
sh S
oil
Tsu
nam
i San
din
tert
idal
mud
Fig. 9. Stratigraphy (including lithology and type of contact), foraminiferal abundance, δ13
subsidence across the contact marking the AD 1700 earthquake in the core taken at Salishastructions using each type of data.
of subsidence is roughly proportional to the magnitude of the earth-quake (Nelson et al., 2008; Leonard et al., 2010).
δ13C offers a less labor-intensive, alternative approach, comparedwith microfossil-based methods, to reconstructing the amount ofsubsidence during a great earthquake. To test the utility of the methodwe compared reconstructions of subsidence during the great AD 1700earthquake produced with δ13C (with qualitative control provided byforaminiferal assemblages) with those produced using our foraminifer-al assemblage zones from Siletz Bay (Fig. 9).
At Salishan Spit, we extracted 23 gouge cores to describe the strat-igraphic framework of the marsh. After analysis of these cores, wechose to collect SSV-2, a 7-cm-diameter vibracore taken about 30 mfrom the upper edge of the marsh. This core was chosen because itwas consistent with the overall marsh stratigraphy and was the bestexample of the AD 1700 lithologic boundary. Five foraminiferal andδ13C/bulk geochemistry samples (Fig. 9) were taken across an abrupt(b1 mm) contact at 60 cm between underlying organic sandy silt andan overlying, upward fining, silty sand, overlain in turn, by a silty clay.Unpublished radiocarbon ages and regional correlation to many sim-ilar sites show that the sand was deposited by the tsunami accompa-nying the AD 1700 earthquake (e.g., Atwater et al., 2004; Nelson et al.,1995; Clague et al., 2000; Nelson et al., 2006; Hawkes et al., 2011).The three foraminiferal samples below the contact have high abun-dances of agglutinated foraminifera, dominated by Balticamminapseudomacrescens (60 to 82%) with low to absent Miliammina fusca(0 to 3%) and Trochamminita irregularis (0 to 3%). This fauna indicatesthat the samples formed in the middle/high marsh environment(SB-Ib). δ13C values of −25.7 to −26.2‰, TOC values of 11.0 to11.8%, and C:N ratios of 13.4 to 13.8 place the samples in environmentSB-G-II. The first sample in the silty clay is predominantly M. fusca(59%) suggesting that the sample formed in the low marsh/tidal flatgroup SB-II. The δ13C for this sample increased to −24.6‰ and TOCdecreased to 7.7% indicating group SB-G-III. The C:N ratio (12.6) is in-conclusive for this sample. The magnitude of subsidence using both
0 40 60
ca
-24.5 -25.5 -26.5 0 01 12 2
δ13C (‰) ReconstructedElevation (m MSL)
ReconstructedElevation (m MSL)
0.88 ± 0.39m 0.71 ± 0.56m
Forams δ13C
Abrupt contact inferred to record subsidence in
AD 1700
C and results of semi-quantitative foraminiferal and δ13C reconstructions of coseismicn Spit in Siletz Bay. Calculated subsidence with the error in meters marked on recon-
Table 4Elevational ranges for six environmental groups defined at Siletz Bay on the basis of foraminifera (SB-Ia, SB-Ib and SB-II) and δ13C/bulk geochemistry (SB-G-I, SB-G-II and SB-G-III).MSL = mean sea level.
Group Foraminifera δ13C(‰)
Elevation(m MSL)
SB-Ia Agglutinated foraminifera of which >25% T. irregularis −29.5 ± 0.6 1.36 ± 0.15SB-Ib Agglutinated foraminifera of which b45% M. fusca −25.6 ± 2.0 1.20 ± 0.18SB-II Agglutinated foraminifera of which >45% M. fusca −24.4 ± 1.8 0.32 ± 0.35SB-G-I Agglutinated foraminifera present −29.6 ± 0.8 1.30 ± 0.14SB-G-II Agglutinated foraminifera present −27.3 ± 1.4 1.19 ± 0.35SB-G-III Not required −24.1 ± 1.7 0.48 ± 0.44
25S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
foraminiferal and δ13C methods can be calculated by subtracting thedifference between the center points of the elevations of the forami-niferal and δ13C/bulk geochemistry groups (Table 4) on either sideof the contact. For foraminifera:
Coseismic subsidence¼ SB� Ib and SB� II¼ 1:20m MSL−0:32m MSL¼ 0:88m:
The error is calculated by taking the square root of the sum of halfthe ranges of groups SB-Ib and SB-II:
Error ¼ 0:18m2 þ 0:35m2� �1
.2
¼ �0:39m:
And for δ13C:
Coseismic subsidence¼ SB�G�II and SB�G�III¼ 1:19m MSL−0:48m MSL¼ 0:71m
Error¼ 0:35m2 þ 0:44m2� �1
.2
¼ �0:56m:
Both methods produce estimates of subsidence that overlap,supporting the ability of the δ13C method to give accurate resultswith reasonable errors. Both methods give subsidence values greaterthan the threshold value of 0.5 m suggested by Nelson et al. (1996b)as the minimum needed to attribute subsidence to a great earth-quake. The values are also consistent with subsidence estimates of0.5 to 1.0 m for the AD 1700 earthquakes at Siletz Bay by Darienzoet al. (1994) using qualitative interpretations based on stratigraphicchanges in plant macrofossils and lithology.
6. Conclusions
Cluster analysis applied to modern salt-marsh foraminiferal assem-blages, and δ13C/bulk geochemistry values (TOC and C:N ratio) fromfour transects across three salt marshes with differing salinity regimesat Siletz Bay, Oregon, identifies elevation-dependent environments simi-lar to those observed at other Cascadia sites. The highestmarsh occupies anarrow elevational range and is dominated by Trochamminita irregularis.High and middle marsh environments are dominated by Trochamminainflata with Balticammina pseudomacrescens, Haplophragmoides wilbertiand Jadammina macrescens. Low marsh environments form nearlymonospecific assemblages with Miliammina fusca. Calcareous taxaare sparse and limited to the tidal flat (b10%). The three elevation-dependent environments identified with δ13C, TOC and C:N data broadlycorrespond to those identified for the foraminifera. The highest marsh isdefined by low δ13C (−29.6 ± 0.8‰), high TOC (30 ± 4.6%) and highC:N (20.4 ± 3.7). The high and middle marshes are characterized byδ13C of −27.3 ± 1.4‰, TOC of 12.4 ± 4.0% and C:N of 13.6 ± 1.4. Thelow marsh and tidal flat had the highest δ13C (−24.1 ± 1.7‰), lowest
TOC (2.5 ± 1.8%) and lowest C:N (10.4 ± 2.7) values. Our δ13C valuesare lower than reported for similar environments in North America andhighlight the importance of collecting a local dataset of bulk sedimentsfor δ13C analysis.
The identification of elevation-dependent environments allowsthe use of both foraminifera and δ13C as indicators of former relativesea level that can be used to estimate the amount of coastal subsi-dence during great Cascadia earthquakes. We applied both methodsto a stratigraphic contact recording the AD 1700 earthquake in acore from the Salishan Spit. Foraminifera and δ13C analyses producedsimilar estimates of subsidence (0.88 ± 0.39m and 0.71 ± 0.56m, re-spectively), giving us confidence in this new, semi-quantitative meth-od for reconstructing sea-level change and inferring paleoseismichistories.
Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.palaeo.2013.02.032.
Acknowledgments
This research was supported by an NSF grant (EAR-0842728) toBPH and by the Earthquake Hazards Program of the U.S. GeologicalSurvey. CHV publishes with the permission of the Executive Directorof the British Geological Survey. This paper is a contribution to IGCPProject 588. The Siletz Bay National Wildlife Refuge and the SalishanLeaseholders, Inc. community are thanked for allowing access to thesites. Rich Briggs, Harvey Kelsey and Zebulon Maharrey are thankedfor assistance in the field. Jon Allan, Oregon Department of Geologyand Mineral Industries, provided the use of GPS surveying instru-ments and data processing. David Hill provided the tidal predictionsused in this paper. Two anonymous reviewers are thanked for com-ments that improved the manuscript.
References
Atwater, B.F., 1987. Evidence for Great Holocene earthquakes along the outer coast ofWashington-State. Science 236, 942–944.
Atwater, B.F., Hemphill-Haley, E., 1997. Recurrence intervals for great earthquakes ofthe past 3500 years at northeastern Willapa Bay, Washington. U.S. GeologicalSurvey Professional Paper 1576. (108 pp.).
Atwater, B.F., Tuttle, M., Schweig, E.S., Rubin, C.M., Yamaguchi, D.K., Hemphill-Haley, E.,2004. Earthquake recurrence inferred from paleoseis- mology. In: Gillespie, A.R.,Porter, S.C., Atwater, B.F. (Eds.), The Quaternary period in the United States. Devel-opments in Quaternary Science. Elsevier, New York, pp. 331–350.
Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuji, Y., Ueda, K., Yamaguchi, D.K., 2005.The orphan tsunami of 1700 — Japanese clues to a parent earthquakes in NorthAmerica. U.S. Geological Survey Professional Paper 1707. (133 pp.).
Bird, M.I., Austin, W.E.N., Wurster, C.M., Fifield, L.K., Mojtahid, M., Sargeant, C., 2010.Punctuated eustatic sea-level rise in the early mid-Holocene. Geology 38, 803–806.
Bottom, D., Kreag, B., Ratti, F., Roye, C., Starr, R., 1979. Habitat classification and inven-tory methods for the management of Oregon estuaries. Oregon Department of Fishand Wildlife final estuary inventory project report, pp. 84.
Brain, M.J., Long, A.J., Petley, D.N., Horton, B.P., Allison, R.J., 2011. Compressionbehaviour of minerogenic low energy intertidal sediments. Sedimentary Geology233, 28–41.
Brooks, J.R., Flanagan, L.B., Buchmann, N., Ehleringer, J.R., 1997. Carbon isotope compo-sition of boreal plants: Functional grouping of life forms. Oecologia 110 (3),301–311.
Brophy, L.S., Cornu, C.E., Adamus, P.R., Christy, J.A., Gray, A., Huang, L., MacClellan, M.A.,Doumbia, J.A., Tully, R.L., 2011. New tools for tidal wetland restoration: develop-ment of a reference conditions database and a temperature sensor method for
26 S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
detecting tidal inundation in least-disturbed tidal wetlands of Oregon, USA.Prepared for the Cooperative Institute for Coastal and Estuarine EnvironmentalTechnology (CICEET). 150.
Buchan, A., Newell, S.Y., Butler, M., Biers, E.J., Hollibaugh, J.T., Moran, M.A., 2003. Dy-namics of bacterial and fungal communities on decaying salt marsh grass. Appliedand Environmental Microbiology 69, 6676–6687.
Byrne, R., Ingram, B.L., Starratt, S., Malamud-Roam, F., Collins, J.N., Conrad, M.E., 2001.Carbon-isotope, diatom, and pollen evidence for late holocene salinity change ina brackish marsh in the san francisco estuary. Quaternary Research 55 (1), 66–76.
Callard, S.L., Gehrels, W.R., Morrison, B.V., Grenfell, H.R., 2011. Suitability of salt-marshforaminifera as proxy indicators of sea level in Tasmania. Marine Micropaleontolo-gy 79, 121–131.
Charland, J.W., Priest, G.R., 1995. Inventory of critical and essential facilities vulnerableto earthquake or tsunami hazards on the Oregon coast. In: O.D.o.G.a.M. (Ed.),Industries, p. 52.
Chmura, G.L., Aharon, P., 1995. Stable carbon-isotope signatures of sedimentary carbon incoastal wetlands as indicators of salinity regime. Journal of Coastal Research 11, 124–135.
Chmura, G.L., Aharon, P., Socki, R.A., Abernethy, R., 1987. An inventory of C-13 abun-dances in coastal wetlands of Louisiana, USA — vegetation and sediments.Oecologia 74, 264–271.
Cifuentes, L.A., 1991. Spatial and temporal variations in terrestrially-derived organic-matter from sediments of the Delaware estuary. Estuaries 14, 414–429.
Clague, J.J., 1997. Evidence for large earthquakes at the Cascadia subduction zone.Reviews of Geophysics 35, 439–460.
Clague, J.J., Bobrowsky, P.T., Hutchinson, I., 2000. A review of geological records of largetsunamis at Vancouver Island, British Columbia, and implications for hazard.Quaternary Science Reviews 19, 849–863.
Cloern, J.E., Canuel, E.A., Harris, D., 2002. Stable carbon and nitrogen isotope composi-tion of aquatic and terrestrial plants of the San Francisco Bay estuarine system.Limnology and Oceanography 47, 713–729.
Cooke, S.S., 1997. A Field Guide to the CommonWetland Plants of WesternWashingtonand Northwestern Oregon. Seattle Audubon Society, Seattle, Washington(417 pp.).
Culver, S.J., Horton, B.P., 2005. Infaunal marsh foraminifera from the outer banks, NorthCarolina, USA. Journal of Foraminiferal Research 35, 148–170.
Culver, S.J., Woo, H.J., Oertel, G.F., Buzas, M.A., 1996. Foraminifera of coastal deposition-al environments, Virginia, U.S.A.: distribution and taphonomy. Palaios 11,459–486.
Darienzo, M.E., Peterson, C.D., Clough, C., 1994. Stratigraphic evidence for great subduction-zone earth- quakes at four estuaries in northern Oregon, U.S.A. Journal of Coastal Re-search 10 (4), 850–876.
Darienzo, M.E., Peterson, C.D., 1995. Magnitude and frequency of subduction-zoneearthquakes along the northern Oregon coast in the past 3000 years. OregonGeology 57, 3–12.
Edwards, R.J., 2006. Mid- to late-Holocene relative sea-level change in southwestBritain and the influence of sediment compaction. The Holocene 16, 575–587.
Edwards, R.J., Wright, A., Van de Plassche, O., 2004. Surface distributions of salt-marshforaminifera from Connecticut, USA: modem analogues for high-resolution sealevel studies. Marine Micropaleontology 51, 1–21.
Eilers, H.P., 1975. Plants, Plant Communities, Net Production and Tide Levels: TheEcological Biogeography of the Nehalem salt marshes, Tillamook County, Oregon.Oregon State University, Corvallis (368 pp.).
Ember, L.M., Williams, D.F., Morris, J.T., 1987. Processes that influence carbonisotope variations in salt marsh sediments. Marine Ecology Progress Series 36,33–42.
Frankel, A.D., Petersen, M.D., Mueller, C.S., Haller, K.M., Wheeler, R.L., Leyendecker, E.V.,Wesson, R.L., Harmsen, S.C., Cramer, C.H., Perkins, D.M., Rukstales, K.S., 2002. Doc-umentation for the 2002 update of the national seismic hazard maps. In: U.S.G.(Ed.), Survey (33 pp.).
Gallagher, J.L., Kibby, H.V., 1980. Marsh plants as vectors in trace-metal transport inOregon tidal marshes. American Journal of Botany 67, 1069–1074.
Gehrels,W.R., 1994. Determining relative sea-level change from salt-marsh foraminifera andplant zones on the coast of Maine, USA. Journal of Coastal Research 10, 990–1009.
Gehrels, W.R., van de Plassche, O., 1999. The use of Jadammina macrescens (Brady) andBalticammina pseudomacrescens Bronnimann, Lutze and Whittaker (Protozoa:Foraminiferida) as sea-level indicators. Palaeogeography, Palaeoclimatology,Palaeoecology 149, 89–101.
Gehrels, W.R., Roe, H.M., Charman, D.J., 2001. Foraminifera, testate amoebae anddiatoms as sea-level indicators in UK salt marshes: a quantitative multiproxyapproach. Journal of Quaternary Science 16, 201–220.
Gehrels, W.R., Belknap, D.F., Black, S., Newnham, R.M., 2002. Rapid sea-level rise in theGulf of Maine, USA, since AD 1800. The Holocene 12, 383–389.
Gehrels, W.R., Milne, G.A., Kirby, J.R., Patterson, R.T., Belknap, D.F., 2004. Late Holocenesea-level changes and isostatic crustal movements in Atlantic Canada. QuaternaryInternational 120, 79–89.
Goni, M.A., Thomas, K.A., 2000. Sources and transformations of organic matter insurface soils and sediments from a tidal estuary (north inlet, South Carolina,USA). Estuaries 23, 548–564.
Gonzalez, J.L., Tornqvist, T.E., 2009. A new Late Holocene sea-level record from theMississippi Delta: evidence for a climate/sea level connection? Quaternary ScienceReviews 28, 1737–1749.
Guilbault, J.P., Clague, J.J., Lapointe, M., 1995. Amount of subsidence during a Late Ho-locene earthquake — evidence from fossil tidal marsh foraminifera at Vancouver-Island, west-coast of Canada. Palaeogeography, Palaeoclimatology, Palaeoecology118, 49–71.
Guilbault, J.-P., Clague, J.J., Lapointe, M., 1996. Foraminiferal evidence for the amount ofcoseismic subsidence during a late Holocene earthquake on Vancouver Island,west coast of Canada. Quaternary Science Reviews 15, 913–937.
Hawkes, A.D., 2008. The application of foraminifera to characterize tsunami sediment andquantify coseismic subsidence along the Sumatra and Cascadia subduction zones,Department of Earth and Environmental Science. University of Pennsylvania,Philadelphia (215 pp.).
Hawkes, A.D., Horton, B.P., Nelson, A.R., Hill, D.F., 2010. The application of intertidal fo-raminifera to reconstruct coastal subsidence during the giant Cascadia earthquakeof AD 1700 in Oregon, USA. Quaternary International 221, 116–140.
Hawkes, A.D., Horton, B.P., Nelson, A.R., Vane, C.H., Sawai, Y., 2011. Coastal subsidencein Oregon, USA, during the giant Cascadia earthquake of AD 1700. QuaternaryScience Reviews 30, 364–376.
Hayward, B.W., Hollis, C.J., 1994. Brackish foraminifera in New-Zealand — a taxonomicand ecologic review. Micropaleontology 40, 185–222.
Hayward, B.W., Scott, G.H., Grenfell, H.R., Carter, R., Lipps, J.H., 2004. Techniques forestimation of tidal elevation and confinement (salinity) histories of shelteredharbours and estuaries using benthic foraminifera: examples from New Zealand.The Holocene 14, 218–232.
Hemphill-Haley, E., 1995. Diatom evidence for earthquake-induced subsidence andtsunami 300 years ago in southern coastal Washington. Geological Society ofAmerica Bulletin 107, 367–378.
Horton, B.P., 1999. The distribution of contemporary intertidal foraminifera at CowpenMarsh, Tees estuary, UK: implications for studies of Holocene sea-level changes.Palaeogeography, Palaeoclimatology, Palaeoecology 149, 127–149.
Horton, B.P., Culver, S.J., 2008. Modern intertidal foraminifera of the Outer Banks, NorthCarolina, USA, and their applicability for sea-level studies. Journal of CoastalResearch 24, 1110–1125.
Horton, B.P., Edwards, R.J., 2005. The application of local and regional transfer functionsto the reconstruction of Holocene sea levels, north Norfolk, England. The Holocene15, 216–228.
Horton, B.P., Edwards, R.J., 2006. Quantifying Holocene sea-level change using intertid-al foraminifera: lessons for the British Isles. Cushman Foundation for ForaminiferalResearch Special Publication, 40 (97 pp.).
Horton, B.P., Larcombe, P., Woodroffe, S.A., Whittaker, J.E., Wright, M.R., Wynn, C.,2003. Contemporary foraminiferal distributions of a mangrove environment,Great Barrier Reef coastline, Australia: implications for sea-level reconstructions.Marine Geology 198, 225–243.
Horton, B.P., Peltier, W.R., Culver, S.J., Drummond, R., Engelhart, S.E., Kemp, A.C.,Mallinson, D., Thieler, E.R., Riggs, S.R., Ames, D.V., Thomson, K.H., 2009. Holocenesea-level changes along the North Carolina Coastline and their implications forglacial isostatic adjustment models. Quaternary Science Reviews 28, 1725–1736.
Hughes, J.F., Mathewes, R.W., Clague, J.J., 2002. Use of pollen and vascular plants toestimate coseismic subsidence at a tidal marsh near Tofino, British Columbia.Palaeogeography, Palaeoclimatology, Palaeoecology 185, 145–161.
Hunger, A.A., 1966. Distribution of Foraminifera, Netarts Bay. Oregon State University,Corvallis, Oregon.
Jefferson, C.A., 1975. Plant Communities and Succession in Oregon Coastal SaltMarshes. Oregon State University, Corvallis (192 pp.).
Jennings, A.E., Nelson, A.R., 1992. Foraminiferal assemblage zones in Oregon tidalmarshes — relation to marsh floral zones and sea-level. Journal of ForaminiferalResearch 22, 13–29.
Jennings, A.E., Nelson, A.R., Scott, D.B., Aravena, J.C., 1995. Marsh foraminiferal assem-blages in the Valdivia estuary, south-central Chile, relative to vascular plants andsea-level. Journal of Coastal Research 11, 107–123.
Kaufman, L., Rousseeuw, P.J., 1990. Finding Groups in Data: An Introduction to ClusterAnalysis. Wiley-Interscience, New York (368 pp.).
Kelsey, H.M., Witter, R.C., Hemphill-Haley, E., 2002. Plate-boundary earthquakes andtsunamis of the past 5500 yr, Sixes River estuary, southern Oregon. GeologicalSociety of America Bulletin 114, 298–314.
Kemp, A.C., Horton, B.P., Culver, S.J., Corbett, D.R., van de Plassche, O., Gehrels, W.R.,Douglas, B.C., Parnell, A.C., 2009a. Timing and magnitude of recent acceleratedsea-level rise (North Carolina, United States). Geology 37, 1035–1038.
Kemp, A.C., Horton, B.P., Culver, S.J., 2009b. Distribution of modern salt-marsh forami-nifera in the Albemarle–Pamlico estuarine system of North Carolina, USA: implica-tions for sea-level research. Marine Micropaleontology 72, 222–238.
Kemp, A.C., Vane, C., Horton, B.P., Culver, S.J., 2010. Stable carbon isotopes as potentialsea-level indicators in salt marshes, North Carolina, USA. The Holocene 20,623–636.
Kemp, A.C., Horton, B.P., Donnelly, J.P., Mann, M.E., Vermeer, M., Rahmstorf, S., 2011.Climate related sea-level variations over the past two millennia. Proceedings ofthe National Academy of Sciences 108, 11017–11022.
Kemp, A.C., Vane, C.H., Horton, B.P., Engelhart, S.E., Nikitina, D., 2012a. Application ofstable carbon isotopes for reconstructing salt-marsh floral zones and relative sealevel, New Jersey, USA. Journal of Quaternary Science 27, 404–414.
Kemp, A.C., Horton, B.P., Vann, D.R., Engelhart, S.E., Grand-Pre, C., Vane, C.H., Nikitina,D., Anisfeld, S.C., 2012b. Quantitative vertical zonation of salt-marsh foraminiferafor reconstructing former sea level; an example from New Jersey, USA. QuaternaryScience Reviews 54, 26–39.
Kolditz, K., Dellwig, O., Barkowski, J., Bahlo, R., Leipe, T., Freund, H., Brumsack, H.-J., 2012.Geochemistry of Holocene salt marsh and tidal flat sediments on a barrier island inthe southern North Sea (Langeoog, North-west Germany). Sedimentology 59, 337–355.
Lamb, A.L., Wilson, G.P., Leng, M.J., 2006. A review of coastal palaeoclimate and relativesea-level reconstructions using delta C-13 and C/N ratios in organic material.Earth-Science Reviews 75, 29–57.
27S.E. Engelhart et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 377 (2013) 13–27
Lamb, A.L., Vane, C.H., Wilson, G.P., Rees, J.G., Moss-Hayes, V.L., 2007. Assessing δ13Cand C/N ratios from organic material archived in cores as Holocene sea level andpalaeoenvironmental indicators in the Humber estuary, UK. Marine Geology 244,109–128.
Leonard, L.J., Currie, C.A., Mazzotti, S., Hyndman, R.D., 2010. Rupture area and displace-ment of past Cascadia great earthquakes from coastal coseismic subsidence. Geo-logical Society of America Bulletin 122, 2079–2096.
Leorri, E., Martin, R., McLaughlin, P., 2006. Holocene environmental and parasequencedevelopment of the St. Jones estuary, Delaware (USA): foraminiferal proxies ofnatural climatic and anthropogenic change. Palaeogeography, Palaeoclimatology,Palaeoecology 241, 590–607.
Lloyd, J.M., Evans, J.R., 2002. Contemporary and fossil foraminifera from isolation basinsin northwest Scotland. Journal of Quaternary Science 17, 431–443.
Mackie, E.A.V., Lloyd, J.M., Leng, M., Bentley, M.J., Arrowsmith, C., 2007. Assessment ofdelta C-13 and C/N ratios in bulk organic matter as palaeosalinity indicators inHolocene and Lateglacial isolation basin sediments, northwest Scotland. Journalof Quaternary Science 22, 579–591.
Maechler, M., Rousseeuw, P., Struyf, A., Hubert, M., 2012. cluster: cluster analysis basicsand extensions. R Package Version 1.14.3.
Malamud-Roam, F., Ingram, B.L., 2001. Carbon isotopic compositions of plants andsediments of tide marshes in the San Francisco estuary. Journal of Coastal Research17, 17–29.
Middleburg, J.J., Nieuwenhuize, J., Lubberts, R.K., van de Plassche, O., 1997. Organiccarbon isotope systematics of coastal marshes. Estuarine, Coastal and Shelf Science45, 681–687.
Murray, J.W., 1982. Benthic foraminifera: the variability of living, dead or total assem-blages in the interpretation of palaeoecology. Journal of Micropalaeontology 1,137–140.
Murray, J.W., Alve, E., 1999. Natural dissolution of modern shallow water benthic fora-minifera: taphonomic effects on the palaeoecological record. Palaeogeography,Palaeoclimatology, Palaeoecology 146, 195–209.
Nelson, A.R., Kashima, K., 1993. Diatom zonation in southern Oregon tidal marshesrelative to vascular plants, foraminifera, and sea-level. Journal of Coastal Research9, 673–697.
Nelson, A.R., Atwater, B.F., Bobrowsky, P.T., Bradley, L.A., Clague, J.J., Carver, G.A.,Darienzo, M.E., Grant, W.C., Krueger, H.W., Sparks, R., Stafford, T.W., Stuiver, M.,1995. Radiocarbon evidence for extensive plate-boundary rupture about 300 yearsago at the Cascadia subduction zone. Nature 378, 371–374.
Nelson, A.R., Jennings, A.E., Kashima, K., 1996a. An earthquake history derived fromstratigraphic and microfossil evidence of relative sea-level change at Coos Bay,southern coastal Oregon. Geological Society of America Bulletin 108, 141–154.
Nelson, A.R., Shennan, I., Long, A.J., 1996b. Identifying coseismic subsidence in tidal-wetland stratigraphic sequences at the Cascadia subduction zone of westernNorth America. Journal of Geophysical Research — Solid Earth 101, 6115–6135.
Nelson, A.R., Kelsey, H.M., Witter, R.C., 2006. Great earthquakes of variable magnitudeat the Cascadia subduction zone. Quaternary Research 65, 354–365.
Nelson, A.R., Sawai, Y., Jennings, A.E., Bradley, L.A., Gerson, L., Sherrod, B.L., Sabean, J.,Horton, B.P., 2008. Great-earthquake paleogeodesy and tsunamis of the past2000 years at Alsea Bay, central Oregon coast, USA. Quaternary Science Reviews27, 747–768.
Oglesby, L.C., 1968. Responses of an estuarine population of the polychaete Nereislimnicola to osmotic stress. The Biological Bulletin 134, 118–138.
Patterson, R.T., Guilbault, J.P., Clague, J.J., 1999. Taphonomy of tidal marsh foraminifera:implications of surface sample thickness for high-resolution sea-level studies.Palaeogeography, Palaeoclimatology, Palaeoecology 149, 199–211.
Patterson, R.T., Dalby, A.P., Roe, H.M., Guilbault, J.-P., Hutchinson, I., Clague, J.J., 2005.Relative utility of foraminifera, diatoms and macrophytes as high resolution indi-cators of paleo-sea level in coastal British Columbia, Canada. Quaternary ScienceReviews 24, 2002–2014.
Petersen, M.D., Cramer, C.H., Frankel, A.D., 2002. Simulations of seismic hazard for thePacific Northwest of the United States from earthquakes associated with theCascadia subduction zone. Pure and Applied Geophysics 159, 2147–2168.
Peterson, C., Scheidegger, K., Komar, P., Niem, W., 1984. Sediment composition andhydrography in six high-gradient estuaries of the northwestern United States.Journal of Sedimentary Research 54, 86–97.
Peterson, C.D., Doyle, D.L., Barnett, E.T., 2000. Coastal flooding and beach retreat fromcoseismic subsidence in the central Cascadia margin, USA. Environmental andEngineering Geoscience 6, 255–269.
Pojar, J., MacKinnon, A., 1994. Plants of the Pacific Northwest Coast. British ColumbiaMinistry of Forests and Lone Pine Publishing, Redmond, WA (527 pp.).
Priest, G.R., Goldfinger, C., Wang, K.L., Witter, R.C., Zhang, Y.L., Baptista, A.M., 2010.Confidence levels for tsunami-inundation limits in northern Oregon inferredfrom a 10,000-year history of great earthquakes at the Cascadia subduction zone.Natural Hazards 54, 27–73.
Sabean, J.A.R., 2004. Applications of Foraminifera to Detecting Land Level ChangeAssociated with Great Earthquakes along the West Coast of North America.Simon Fraser University, Burnaby, Department of Earth Sciences.
Scott, D.S., Medioli, F.S., 1978. Vertical zonations of marsh foraminifera as accurateindicators of former sea-levels. Nature 272, 528–531.
Scott, D., Medioli, F., 1980. Quantitative studies of marsh foraminiferal distributions inNova Scotia: implications for sea level studies. Report, 17. Cushman Foundation forForaminiferal Research.
Scott, D.B., Collins, E.S., Duggan, J., Asioli, A., Saito, T., Hasegawa, S., 1996. Pacific rimmarsh foraminiferal distributions: implications for sea-level studies. Journal ofCoastal Research 12, 850–861.
Seliskar, D.M., Gallagher, J.L., 1983. The ecology of tidal marshes of the Pacific North-west coast: a community profile. In: D.o.B.S. (Ed.), U.S. Fish and Wildlife Service,Washington D.C. (65 pp.).
Shennan, I., Long, A.J., Rutherford, M.M., Green, F.M., Innes, J.B., Lloyd, J.M., Zong, Y.,Walker, K.J., 1996. Tidal marsh stratigraphy, sea-level change and large earth-quakes.1. A 5000 year record in Washington, USA. Quaternary Science Reviews15, 1023–1059.
Shennan, I., Long, A.J., Rutherford, M.M., Innes, J.B., Green, F.M., Walker, K.J., 1998. Tidalmarsh stratigraphy, sea-level change and large earthquakes — II: submergenceevents during the last 3500 years at Netarts Bay, Oregon, USA. Quaternary ScienceReviews 17, 365–393.
Sherrod, B.L., 1999. Gradient analysis of diatom assemblages in a Puget Sound saltmarsh: can such assemblages be used for quantitative paleoecological reconstruc-tions? Palaeogeography, Palaeoclimatology, Palaeoecology 149, 213–226.
Southall, K.E., Gehrels, W.R., Hayward, B.C., 2006. Foraminifera in a New Zealand saltmarsh and their suitability as sea-level indicators. Marine Micropaleontology 60,167–179.
Thayer, G.W., Parker, P.L., LaCroix, M.W., Fry, B., 1978. The stable carbon isotope ratio ofsome components of an eelgrass, zostera marina, bed. Oecologia 35 (1), 1–12.
Tornqvist, T.E., Gonzalez, J.L., Newsom, L.A., van der Borg, K., de Jong, A.F.M., Kurnik,C.W., 2004. Deciphering Holocene sea-level history on the US Gulf Coast: a high-resolution record from the Mississippi Delta. Geological Society of America Bulletin116, 1026–1039.
Vane, C.H., Drage, T.C., Snape, C.E., 2003. Biodegredation of Oak (Quercus alba) woodduring growth of the Shiitake mushroom (Lentinula edodes): a molecular approach.Journal of Agricultural and Food Chemistry 51, 947–956.
Wang, Y., Clark, J.L., 1999. Earthquake damage in Oregon, preliminary estimates offuture earthquake losses. In: O.D.o.G.a.M. (Ed.), Industries (59 pp.).
Wedin, D.A., Tieszen, L.L., Dewey, B., Pastor, J., 1995. Carbon isotope dynamics duringgrass decomposition and soil organic matter formation. Ecology 76 (5),1383–1392.
Wilson, G.P., Lamb, A.L., Leng, M.J., Gonzalez, S., Huddart, D., 2005a. Variability oforganic delta C-13 and C/N in the Mersey estuary, UK and its implications forsea-level reconstruction studies. Estuarine, Coastal and Shelf Science 64, 685–698.
Wilson, G.P., Lamb, A.L., Leng, M.J., Gonzalez, S., Huddart, D., 2005b. δ13C and C/N aspotential coastal palaeoenvironmental indicators in the Mersey estuary, UK.Quaternary Science Reviews 24, 2015–2029.
Witter, R.C., Kelsey, H.M., Hemphill-Haley, E., 2003. Great Cascadia earthquakes andtsunamis of the past 6700 years, Coquille River estuary, southern coastal Oregon.Geological Society of America Bulletin 115, 1289–1306.
Wooller, M.J., Zazula, G.D., Edwards, M., Froese, D.G., Boone, R.D., Parker, C., Bennett, B.,2007. Stable carbon isotope compositions of Eastern Beringian grasses and sedges:investigating their potential as paleoenvironmental indicators. Arctic, Antarctic,and Alpine Research 39, 318–331.
Wright, A.J., Edwards, R.J., van de Plassche, O., 2011. Reassessing transfer-function per-formance in sea-level reconstructions based on benthic salt-marsh foraminiferafrom the Atlantic coast of NE North America. Marine Micropaleontology 81, 43–62.
