Marine Micropaleontology 51 (2004) 1 – 21
www.elsevier.com/locate/marmicro
Surface distributions of salt-marsh foraminifera from Connecticut,
USA: modern analogues for high-resolution sea level studies
R.J. Edwards *, A.J. Wright, O. van de Plassche
Department of Earth and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
Received 25 January 2002; received in revised form 1 August 2003; accepted 11 August 2003
Abstract
Salt-marsh foraminifera are routinely used as sea-level indicators since their vertical distribution is closely linked with
elevation relative to the tidal frame. The precise nature of these relationships is variable in time and space, and the accuracy of
sea-level reconstructions depends upon the selection of appropriate modern analogues that reliably reflect past fauna –
environment associations. The marshes of Connecticut, USA, are sites of ongoing research seeking to produce high-resolution
records of sea-level change, yet, little published data regarding their modern foraminiferal distributions exist. This paper
presents new surface foraminiferal data from three Connecticut salt-marshes and evaluates their suitability as modern analogues
for past sea-level changes. The results indicate that significant intra- and inter-site variability between these marshes and those
of neighbouring states exists. As a consequence of this, the extrapolation of fauna – environment relationships developed from
marshes with different hydrographic, physiographic, vegetative or climatic characteristics may produce erroneous
reconstructions, even when adjusted for variations in tidal range. These errors are potentially greatest if single ‘indicator’
species are used since the relative abundance of individual taxa does not vary consistently with elevation, even in high marsh
environments from the same site. Whilst cluster analysis demonstrates that foraminiferal assemblages from Connecticut are
vertically zoned with respect to mean high water (MHW), the composition, elevation and height range of these zones is variable
between sites. This spatial heterogeneity results in reconstructions of relatively low and variable precision that restricts their
utility in high-resolution sea-level research. New studies seeking to distil decimetre-scale changes in relative sea level will need
to employ quantitative methods capable of combining multi-site information to develop fauna – environment relationships that
capture this spatial variability. Reconstructions will be most precise when employing local foraminiferal distributions, but may
require the collection of additional modern analogue samples from other regions when the extant foraminiferal population of a
site differs in composition from its sub-fossil counterpart.
D 2003 Elsevier B.V. All rights reserved.
Keywords: foraminifera; sea-level changes; salt-marsh; holocene; connecticut
1. Introduction
* Corresponding author. Current address: Departments of
Geography and Geology, Trinity College Dublin, Dublin 2, Ireland.
Fax: +353-1-671-3397.
E-mail address: [email protected] (R.J. Edwards).
0377-8398/$ - see front matter D 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.marmicro.2003.08.002
The use of salt-marsh foraminifera as precise
indicators of relative sea-level change has attracted
considerable attention since the pioneering work of
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Scott and Medioli (1978, 1980a). The potential to
relocate former relative sea levels to within F 5 cm
provides an opportunity to investigate relatively
small magnitude (decimetre scale) variations that
are central to research seeking to quantify the
relationships between ocean and climate. However,
this degree of precision is not associated with all
foraminifera species or assemblages. Instead it
relates to a mono-specific assemblage of Jadammina
macrescens, referred to as faunal zone 1A by Scott
and Medioli (1978), which is restricted to the
marsh –upland transition, close to the upper limit
of marine influence. Whilst other assemblages of
foraminifera also exhibit vertical zonation, their
composition and elevation ranges may vary considerably within and between sites, reflecting local
differences in environmental variables such as salinity and climate (Scott and Medioli, 1980a; Scott
and Leckie, 1990; Gehrels, 1994; De Rijk, 1995b).
For this reason, an essential component of any
investigation seeking to produce high-resolution
sea-level reconstructions is the precise and accurate
determination of modern species– environment relationships that are representative of the study area
(Scott and Medioli, 1986).
In this paper, we present new contemporary saltmarsh foraminiferal data from three study areas in
Connecticut, USA (Fig. 1). This region is a locus
for high-resolution sea-level research seeking to
elucidate the relationship between climate and sea
level change during the late Holocene (van de
Plassche, 1991, 2000; Thomas and Varekamp,
1991; Varekamp et al., 1992; Nydick et al., 1995;
van de Plassche et al., 1998). Despite this comparatively long history of research, relatively little has
been published regarding the modern distribution of
salt-marsh foraminifera in Connecticut, and their
relationships with tide levels remain poorly quantified (Gehrels and van de Plassche, 1999). These
data are particularly important given the apparent
absence of assemblages comparable to faunal zone
1A, reported in other New England marshes (Scott
and Leckie, 1990; De Rijk and Troelstra, 1997;
Gehrels and van de Plassche, 1999). This paper
therefore examines the extent to which high marsh
foraminiferal assemblages in Connecticut exhibit
evidence of vertical zonation; the spatial coherence
of these zones in terms of composition and eleva-
tion; and the implications that these results have for
studies seeking to produce precise (decimetre scale)
sea-level reconstructions from the salt-marshes of
Connecticut.
2. Materials and methods
2.1. Sampling methodology
The sampling requirements of surface foraminiferal investigations conducted to complement palaeoenvironmental analysis differ markedly from those
seeking to analyse the taphonomic and ecological
attributes of the foraminifera themselves (De Rijk,
1995a). Since the goal of foraminifera-based sealevel research is the reconstruction of former tide
levels, modern samples were collected along transects encompassing a range of altitudes and vegetation zones most analogous to the environments
encountered in fossil cores. Sampling was concentrated in the vegetated marsh above mean high
water (MHW), since this is the principal environment analysed in sea-level studies (Gehrels and van
de Plassche, 1999). Disturbed areas such as pond
holes, creek margins and low marsh sediments
bioturbated by fiddler crabs were not sampled since
boreholes containing these deposits are not considered reliable indicators of sea-level change. The
majority of salt-marshes in Connecticut have been
ditched (Dreyer and Niering, 1995), and this human
interference has altered their hydrological regime
(Van der Molen, 1997). Where possible, surface
transects were situated away from these ditches
and in areas displaying a well-developed floral
zonation, since these are considered to be more
representative of their ‘natural’, pre-engineered
state.
Surface foraminiferal samples were collected in
vertical intervals of 5 F 1 cm and their altitude
determined by levelling to the nearest geodetic
datum (NGVD 29). Live specimens were stained in
the field using Rose Bengal and stored in ethanol.
On return to the laboratory, samples were washed
through 500- and 63-Am mesh sieves after the
methods described by Scott and Medioli (1980a).
Samples were suspended in approximately 500 ml of
water and sub-divided into eight aliquots using a
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Fig. 1. Site map showing the location of the surface foraminiferal transects and temporary tide gauges.
3
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
rotary wetsplitter following the study by De Rijk
(1995a) which found this to be the most accurate and
time efficient preparation method. All samples were
examined wet under a binocular microscope and
generally over 200 – 300 tests were counted where
possible (Appendix B). In common with other studies, some of the highest marsh samples are associated with smaller counts reflecting low species
abundance and diversity at the upper limit of marine
influence. These assemblages are dominated by only
one or two species and are reliably represented by
low counts. The use of life, death or total foraminiferal assemblages remains a matter of contention
(Scott and Medioli, 1980b; Murray, 1991, 2000;
Horton, 1997; Murray and Bowser, 2000). Here,
dead populations are used to facilitate later comparison with fossil assemblages in accordance with
Horton et al. (1999). It should be noted that dead
individuals contribute at least 90% of the total
number of tests counted at each site.
2.2. Taxonomy
Salt-marsh foraminiferal assemblages are typically dominated by less than 10 benthic species,
reflecting the marginal-marine nature of inter-tidal
environments. A taxonomic list and plates of the
key salt-marsh taxa recovered in our surveys are
presented in Appendix A. The pioneering foraminifera-based investigations of Thomas and Varekamp (1991) and Varekamp et al. (1992), which
underpin many of the subsequent sea-level studies
in Connecticut, use a modified version of the
Nova Scotia vertical zonation, and their taxonomy
follows that of Scott and Medioli (1980a). In this
paper, we follow the taxonomy of De Rijk (1995a),
which differs from that of Scott and Medioli
(1980a) by its separation of individuals formerly
grouped as Trochammina macrescens, into the separate species Balticammina pseudomacrescens and
J. macrescens. Gehrels and van de Plassche (1999)
demonstrate that B. pseudomacrescens and J.
macrescens exhibit different relationships with elevation relative to MHW and that their separation
increases the amount of sea-level information that
may be extracted from fossil foraminiferal assemblages in Maine. The modern distribution of B.
pseudomacrescens in the salt-marshes of Connecti-
cut is poorly understood and one aim of this
study is to address this fundamental lack of knowledge. Similarly, we follow De Rijk (1995a) by
differentiating between Trochammina inflata and
Siphotrochammina lobata, the latter of which is
similar to the microspheric form of Tr. inflata
described by Scott and Medioli (1980a). This
distinction is made to explore whether these forms
display different distributions in Connecticut, and
hence contain additional environmental information.
Ultimately, the taxonomic issues surrounding the
differentiation of genus, species or ecophenotype
do not influence the use of foraminifera as modern
analogues, providing these ‘species’ or forms are
identified consistently.
2.3. Infaunal foraminifera
Sea-level reconstructions based on modern surface distributions of foraminifera implicitly assume
that infaunal populations do not constitute a significant proportion of the total assemblages recovered.
A number of studies have questioned the reliability
of this assumption, reporting the occurrence of
living foraminifera at depths of 30 cm or more in
salt-marshes from Georgia and British Columbia
(Goldstein and Watkins, 1999; Ozarko et al.,
1997). These salt-marsh environments are quite
different from those encountered in New England,
however, where a study by Saffert and Thomas
(1998) indicates that infaunal activity is less significant, particularly in high marsh sediments composed of dense, intertwined root masses and marsh
grasses. At Kelsey marsh in Connecticut, near the
Hammock River transect presented here, Saffert and
Thomas (1998) report that whilst living foraminifera
may be found up to a depth of 30 cm, 90% of the
living individuals occur above 20 cm. More importantly, in the high marsh environments, such as
those considered in this study, species maxima
occur between 0 and 2.5 cm depth, and only 5%
of the total population below 5 cm is living.
To test this result, a 30-cm core was collected
from the high marsh environment adjacent to our
surface transects at Double Beach marsh. The sediment was sliced into 1-cm-thick slices and the
material processed in the same way as the surface
samples. The results are summarised in Fig. 2, and
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
5
Fig. 2. Summary foraminiferal diagram from a 30-cm short core collected in the high marsh at Double Beach. The relative abundance of species
in the death assemblage is show in black. The occurrence of living infaunal foraminifera is shown in grey, expressed as a percentage of the total
count (live + dead).
confirm the pattern identified by Saffert and Thomas (1998). Stained tests contribute 27% of the
topmost sample (0 – 1 cm depth) and fall rapidly
with increasing depth. The life component contributes less than 10% of the assemblage at 2 –3 cm
depth, and falls to between 2% and 3% below this.
2.4. Assemblage groups and tide levels
Here, assemblage zones are based on the results of
unconstrained incremental sum of squares cluster
analysis. Data are screened to remove species conTable 1
Summary tidal characteristics for the study area derived from
permanent NOAA tide gauges and temporary tide gauges installed
at Double Beach and Pattagansett River marshes
Location
The seminal paper by Scott and Medioli (1980a)
visually grouped contemporary salt-marsh foraminifera to define vertical zonations at a number of sites.
More recent work has sought to group assemblages
on statistical grounds which may then be related to
distinct depositional environments (e.g., Patterson,
1990; Jennings and Nelson, 1992; De Rijk, 1995a).
Bridgeport
New Haven
Double Beach
Hammock River
Pattagansett
New London
Altitude (m NGVD)
MHHW
MHW
MTL
1.34
1.24
1.15
0.98
0.76
0.61
1.24
1.14
1.09
0.84
0.61
0.52
0.21
0.19
0.19
0.16
0.14
0.13
MLLW
0.89
0.83
–
–
–
0.33
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
tributing under 2% of any sample, and counts of
less than 40 specimens (Horton et al., 1999), and
analysed via the program Tilia, release 2.0 b.0.5
(Grimm, 1991 – 1993).
The altitude of foraminiferal assemblage zones
relative to NGVD is of less significance in sea-level
reconstruction than their elevation relative to the tidal
frame. The assemblage zones identified via cluster
analysis are therefore plotted relative to MHW at each
site, since this variable is commonly reconstructed in
sea-level investigations (e.g., van de Plassche, 2000).
Long-term tidal data from permanent tide gauges at
New London, New Haven and Bridgeport are used in
conjunction with shorter-term (up to 6 months) records
from temporary tide gauges installed at Double Beach
and Pattagansett marshes (Table 1).
Fig. 3. Summary foraminiferal diagrams showing the relative abundances of individual species comprising the death assemblages at Double
Beach marsh: (a) transect 1; (b) transect 2. Samples are plotted against altitude (NGVD). The number of dead specimens counted, and the
proportion of live specimens expressed as a percentage of the total count (live + dead) are also shown.
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
3. Study sites
Surface foraminiferal samples were taken from
three Connecticut salt-marshes at Double Beach,
Hammock River and Pattagansett River (Fig. 1).
These marshes are, or are close to, locations of sealevel research, and surface sampling was undertaken
to complement these stratigraphic investigations. The
mean tidal range in the area increases westward from
c. 0.8 m near Pattagansett River to c. 1.9 m near
Double Beach (NOAA tide tables). Tidal characteristics for each site are given in Table 1.
All the study sites possess the three main vegetation zones characteristic of Connecticut salt-marshes:
low marsh, high marsh and marsh –upland border
(Redfield, 1972; Dreyer and Niering, 1995). The
dominant vegetation type at each sampling location
is noted in Appendix B. The low marsh zone, which
develops on inter-tidal flats and almost extends up to
MHW, is only represented in the lowermost samples
from Pattagansett River, reflecting the fact that sampling was concentrated in the high marsh zone
(Section 2.1). At the other sites, transects commence
around MHW and are dominated by high marsh
plants like Spartina patens and Spartina alterniflora
(stunted). The high marsh to upland transition varies
7
between sites, primarily reflecting local salinity conditions and the degree of human modification at the
back of the marshes. At Double Beach, the upper
salt-marsh is backed by scrub and Iva frutescens
(transect 1) or grades through Scirpus robustus into
fringing woodland (transect 2). The presence of
sedges and reeds such as Sc. robustus and Phragmites australis are indicative of brackish conditions
where freshwater inputs moderate the marine influence. At Hammock River, the rear of the marsh is
embanked and planted with a line of trees. The
transition from the upper marsh to the bare soil at
the foot of the embankment is associated with a
dense stand of Ph. australis. At Pattangansett River,
the upland transition is associated with I. frutescens,
and in transect 2, patches of dry, sandy soil flanking
a car park.
4. Results
High marsh foraminiferal distributions were collected from a total of five surface transects in three study
areas. These data are used to investigate both intra-and
inter-site variability in modern assemblages and their
distributions. Full counts are tabulated in Appendix B.
Fig. 4. Summary foraminiferal diagrams showing the relative abundances of individual species comprising the death assemblages at Hammock
River marsh. Samples are plotted against altitude (NGVD). The number of dead specimens counted and the proportion of live specimens
expressed as a percentage of the total count (live + dead) are also shown.
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
4.1. Double Beach marsh
Two transects comprising a total of 20 samples
were collected at Double Beach marsh (Fig. 3a– b;
Table B1). The results from both transects are
broadly comparable in terms of the species present.
All of the samples are dominated by the agglutinated species J. macrescens, and this reflects the fact
that sampling was focussed in the high marsh
environment. Whilst the upper portion of transect
1 failed to capture faunal zone 1A of Scott and
Medioli (1980a), it was represented in the top two
samples of transect 2.
A range of other agglutinated species provide
lesser contributions to the total high marsh assemblage. Most notable among these are Tr. inflata and
Si. lobata, which exhibit very similar patterns of
distribution. Previous studies in Connecticut have
Fig. 5. Summary foraminiferal diagrams showing the relative abundances of individual species comprising the death assemblages at Pattagansett
River marsh: (a) transect 1; (b) transect 2. Samples are plotted against altitude (NGVD). The number of dead specimens counted, and the
proportion of live specimens expressed as a percentage of the total count (live + dead) are also shown.
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
not reported Si. lobata, perhaps grouping it with Tr.
inflata, to which it may be related (see Section
2.2).
The slightly greater vertical range of transect 1
(0.49 m) relative to transect 2 (0.35 m) accounts for
the greater diversity of species present in the former.
In particular, species that are reported from middle to
lower marsh environments in neighbouring New
England marshes, such as Arenoparrella mexicana
and Ammotium salsum, are found in the lower
samples.
9
show remarkable consistency between transects,
both in terms of the sequence of change and the
altitudes at which these changes occur. The most
obvious interchange once again is between the M.
fusca and Tr. inflata/Si. lobata assemblages. In
contrast to Hammock River marsh, however, M.
fusca abundances increase with decreasing altitude.
The lowermost samples from transect 1 record an
increase in the diversity of agglutinated species
associated with lower marsh conditions, including
Ammot. salsum, Areno. mexicana and Ammobaculites dilatatus.
4.2. Hammock River marsh
A single surface foraminiferal transect comprising
14 samples was collected at Hammock River marsh
(Fig. 4; Table B2). The occurrence and distribution of
key species is similar to that reported for Double Beach
marsh, with J. macrescens dominant (52% total tests
counted), and lesser contributions provided by Tr.
inflata (13%), Si. lobata (7%), Tiphotrocha comprimata (7%) and Haplophragmoides manilaensis (6%).
The topmost samples show a mixed assemblage of J.
macrescens, H. manilaensis, and Miliammina fusca
similar to that recorded at the top of Double Beach
transect 2.
The slightly greater vertical range sampled at
Hammock River (0.59 m) reveals a clearer succession
of foraminiferal species. Whilst the abundance of J.
macrescens remains high throughout, there is a clear
interchange between declining abundances of M.
fusca and the arrival of Tr. inflata, Si. lobata, and
Ti. comprimata.
4.3. Pattagansett River marsh
Two transects comprising a total of 26 samples
were collected at Pattagansett River marsh (Fig. 5a–
b; Table B3). The results from both transects are
similar, with the larger vertical range of transect 1
(0.7 m) capturing slightly more of the succession
than transect 2. The topmost samples of transect 1
show a virtually monospecific assemblage of J.
macrescens, comparable to faunal zone 1A, whilst
similar altitudes sampled in transect 2 were devoid
of foraminifera.
The distribution of other principal species (Tr.
inflata, Si. lobata, Ti. comprimata and M. fusca)
5. Discussion
The composition of the high marsh death assemblages presented here is broadly comparable to those
of other New England marshes. J. macrescens
dominates all of the assemblages reflecting the fact
that few samples were collected from below MHW.
Tr. inflata is also common throughout the high
marsh zone and its distribution is closely associated
with Si. lobata. This is consistent with the view of
Scott and Medioli (1980a) that Si. lobata is a
microspheric form of Tr. inflata, and suggests that,
in the high marsh zone at least, little additional
environmental information is obtained by sub-dividing these forms.
Only small numbers of B. pseudomacrescens are
recorded in the surveys (rarely contributing more
than 1% of the total assemblage). This apparent
rarity is in stark contrast with distributions reported
from Maine, where B. pseudomacrescens can contribute up to 80% of the assemblage (Gehrels and
van de Plassche, 1999). Further work is necessary to
determine the reasons for these differences in abundance, especially given the proximity and apparent
similarity of the settings. This is of particular importance since fossil assemblages containing large proportions of B. pseudomacrescens are found within
the marsh sediments of Connecticut (Gehrels and
van de Plassche, 1999).
The lowest elevation samples are characterised
by the presence of Areno. mexicana and low
abundances of other agglutinated taxa such as
Ammobaculites or Reophax species. Consequently,
whilst the calcareous component of the life assem-
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
blage is not retained in the death assemblage due to
post-mortem dissolution, agglutinated assemblages
can still be used to distinguish high and low marsh
environments.
The surface distributions of H. manilaenis, M.
fusca and Ti. comprimata exhibit greater spatial
variability reflecting the influence of other environmental variables (e.g., salinity, substrate). The
results from other salt-marsh studies indicate that
the distribution of H. manilaensis is controlled by
local salinity conditions, with it favouring brackish
environments at the rear of marshes or lower
elevation areas associated with freshwater seeps
(Parker and Athearn, 1959; Scott and Medioli,
1980a; Scott and Leckie, 1990; De Rijk, 1995b).
The most notable H. manilaensis dominated assemblage (up to 30%) is recorded at the top of transect
1 from Double Beach and is similar to the low
salinity ‘marsh fringe’ assemblage reported from
Massachusetts by De Rijk (1995b). The absence of
H. manilaensis from the upper samples in transect 2
illustrates the localised influence that freshwater
drainage can exert on the composition of high
marsh foraminiferal assemblages.
The distribution of Ti. comprimata appears to
vary between sites. In Massachusetts, De Rijk and
Troelstra (1997) suggest that it is indicative of
environments above MHW where salinity remains
high. Conversely, Scott and Leckie (1990) state that
it is a good indicator of the transition from low to
high marsh since its abundance decreases markedly
above MHW. In the neighbouring marshes of
Maine, Gehrels (1994) notes peaks in relative abundance of Ti. comprimata between MHW and mean
higher high water (MHHW). The results from Connecticut are consistent with the interpretations of De
Rijk and Troelstra (1997) and Gehrels (1994),
suggesting Ti. comprimata is indicative of environments at or above MHW. Transect 1 from Pattaganssett marsh covers the largest vertical range and
shows the relative abundance of Ti. comprimata
increasing with elevation to a peak between MHW
and MHHW, before falling in the highest marsh
environment. At Hammock River, a fall in the
relative abundance of Ti. comprimata occurs with
the change in vegetation from Sp. patens to Ph.
australis, perhaps reflecting its preference for more
saline conditions.
M. fusca is commonly encountered in low marsh
environments where it may dominate the assemblage
in association with agglutinated taxa such as Ammot.
salsum, and a range of calcareous species (Patterson,
1990; Gehrels, 1994; De Rijk and Troelstra, 1997).
This pattern is clearly exhibited in the transects
from Pattagansett River marsh, where the abundance
of M. fusca increases rapidly below MHW to
dominate the death assemblage (40 –60%). At Double Beach, the lowermost samples of transect 1
around MHW capture a peak in M. fusca (30%).
However, whilst the higher elevation samples of this
transect do not contain significant numbers of M.
fusca ( < 7%), it contributes up to 30% of the death
assemblage at comparable elevations in transect 2.
Similarly, at Hammock River, there is an apparent
increase in abundance to c. 10 – 20% of the death
assemblage with increasing elevation, although M.
fusca is never the dominant species and the lack of
samples from elevations below MHW may account
for this apparently inverse trend in relative abundance. De Rijk and Troelstra (1997) note that at
Barnstable, Massachusetts, whilst M. fusca is dominant in the low marsh, it can also be locally
abundant (up to 20%) in the high marsh above
MHW, where it may be correlated with sandier
substrates or higher flooding frequency.
5.1. Vertical assemblage zones in Connecticut
The foraminiferal death assemblages from each of
the sites described above are grouped by cluster
analysis (see Section 2.4). Fig. 6 presents foraminiferal assemblage zones for each of the study sites,
based on this analysis and plotted relative to MHW.
In the case of Double Beach and Pattagansett, the
assemblage zones are composites of both transects at
each site. In addition, the foraminiferal zones for
Nova Scotia, adapted from Scott and Medioli (1978,
1980a), are included for comparison. The vertical
offset of the various zones reflects inter-site differences in tidal range.
The assemblage zones illustrate that, in contrast
to reports from some sites in New England (e.g., De
Rijk and Troelstra, 1997), foraminiferal assemblages
in Connecticut do exhibit vertical zonation, although
other parameters (e.g., salinity) introduce variability
within and between marshes. Furthermore, the diag-
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
11
Fig. 6. Vertical assemblage zones for each study marsh based on cluster analysis of the foraminiferal death assemblage. Zones are plotted
relative to local mean high water and demonstrate the spatial heterogeneity apparent in modern surface distributions. The Nova Scotia vertical
zonation of Scott and Medioli (1980a) is included for reference.
nostic faunal assemblage zone 1A is recorded at two
of the three study marshes and varies in thickness
from 5 to 10 cm. However, its distribution is
apparently spatially variable within sites as indicated
by the failure of single transects to locate it. It is
therefore possible that additional surveys at Hammock River marsh may reveal its presence.
The variability expressed between these transects
may reflect the contrasting nature of the depositional
environment and substrate encountered at the rear of
these marshes. Both transects that record faunal
assemblage zone 1A have ‘natural’ transitions from
highest marsh into upland. For example, at Double
Beach, the upper portion of transect 2 is characterised by a comparatively moist, vegetated surface
associated with some leaf litter beneath the fringing
marsh woodland. Despite this apparently supra-tidal
setting, a large percentage of living foraminifera are
recorded (20%), and a higher proportion of larger
test sizes are present than compared with other
samples from the high marsh. This environment
contrasts strongly with the upper portion of transect
1, which is characterised by a dry, bare sediment
surface beneath a canopy of I. frutescens. Here, the
living component of the assemblage is very small
(0– 2%). Similarly, at Pattagansett River, transect 1
terminated in shrubs whilst transect 2 was sampled
on dry, loose sandy soil beneath an open canopy of
I. frutescens adjacent to a car park. Finally, the
upper assemblage zone at Hammock River was
recovered from behind a dense stand of Phragmites
backed by a small ditch and bank. Despite this
indicator of lower salinity conditions, H. manilaensis contributes on average only 8% of the total
assemblage.
These results suggest that monospecific J. macrescens assemblages are best developed in areas where
‘natural’ transitions to upland environments are encountered, and that careful sampling is required to
locate suitable modern analogue environments. This is
increasingly difficult since most marsh areas have been
ditched and are backed by embankments, roads, and
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R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
other built structures. The abundance of monospecific
J. macrescens assemblages in fossil samples may
reflect the fact that undisturbed marsh to woodland
transitions were more common and covered much
larger areas than they do today.
5.2. Application in sea-level research
An ideal sea-level indicator will possess a consistent vertical relationship to a defined element of the
tidal frame (termed the indicative meaning). In
reality, most indicators express a range of vertical
relationships (called the indicative range) that
imparts a fundamental limit on the precision to
which past tide levels can be reconstructed. The
Connecticut assemblage zones presented in Fig. 6
demonstrate that individual zones exhibit differing
vertical ranges. For example, the 100% J. macrescens zone has a vertical range between 5 and 10 cm,
whilst the other assemblage zones are typically 20 –
40 cm thick. As a consequence of this type of
variability, the position of a sample relative to the
tidal frame, coupled with the local tidal range, will
determine the precision of the associated reconstruction. Furthermore, similar assemblage zones and
zone boundaries possess different indicative meanings depending on which study site is used as a
reference. This means that the use of vertical
assemblages zones derived from other sites is prone
to error, even if adjustments are made for differences
in tidal range. This is of particular significance given
the spatial variability encountered in surface foraminiferal distributions and the nature of modern
marshes, since it may not be possible to collect a
representative suite of modern analogues from the
same site that fossil material is extracted.
A further problem with the use of assemblage zones
is the low and variable resolution to which changes in
environment can be distinguished. This arises because
changes can only be detected when a transition between assemblage zones occurs. This restricts the
provenance of useful sea-level information to a limited
number of critical thresholds that equate to a small subset of environmental conditions within a salt-marsh
system. The result of this will be at best a punctuated
signal of sea-level change and, where the vertical
ranges of assemblage zones are large and changes in
sea-level small, no record of change at all.
In an attempt to circumvent the problems of low
resolution associated with the use of assemblage
zones, Thomas and Varekamp (1991) employed a
modified version of the vertical zonation reported by
Scott and Medioli (1978, 1980a) to develop marsh
palaeoenvironmental curves that expressed marshsurface elevation relative to the tidal frame. Information on elevation was derived from an index of
flooding frequency, based on the proportion of Tr.
macrescens (or its corollary ‘% other species’). The
resulting reconstructions with a resolution of 5 cm
(Varekamp et al., 1992) have become incorporated in
the sea-level research of the region (Nydick et al.,
1995; van de Plassche et al., 1998; van de Plassche,
2000). The spatial variability apparent in the Connecticut marshes complicates the extrapolation of
zonations from outside the study area and recommends that future sea-level investigation in the
Connecticut region should be based on local modern
analogues. In contrast to some sites in Maine (Gehrels and van de Plassche, 1999), the modern distributions from Connecticut indicate that the
abundance of J. macrescens does not vary uniformly
with elevation, even when sampling is restricted to
high marsh environments above mean high water.
The use of a single foraminifera species as a sealevel indicator is therefore prone to error. A more
reliable approach is to use assemblages of foraminifera that can exploit the varying sensitivities and
tolerances of individual taxa across a range of
elevations.
6. Summary and conclusions
The salt-marshes of Connecticut and its neighbouring states have become prominent in the sealevel literature as the home of high-resolution
reconstructions investigating the relationship between ocean and climate change. Whilst these
studies use salt-marsh foraminifera as sea-level indicators, comparatively little published data regarding
their surface distributions in the modern marshes of
Connecticut exist. These types of data are of particular importance given the apparent lack of vertical zonation recorded in neighbouring salt-marshes
of Massachusetts (De Rijk, 1995b; De Rijk and
Troelstra, 1997).
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
The high marsh surface foraminiferal distributions
from three sites in Connecticut presented here indicate that whilst the vertical zonation concept proposed by Scott and Medioli (1978, 1980a) is
applicable to the marshes of Connecticut, there are
some important limitations that must be taken into
consideration before it can be applied to produce
reliable sea-level reconstructions from fossil material. Comparison of data from these and other sites in
neighbouring areas demonstrates that there is significant intra- and inter-site variability in the occurrence and distribution of individual salt-marsh
foraminiferal species. Individual taxa rarely vary
uniformly with elevation and vertical relationships
with the tidal frame differ within and between sites.
This complicates the use of single indicator species
and means that vertical relationships derived from
marshes with markedly different hydrographic, physiographic, vegetative or climatic characteristics are
potentially erroneous.
This spatial heterogeneity is reflected in local
vertical foraminiferal assemblage zones as differences
in composition, indicative meaning and indicative
range. This compounds the problems of limited and
variable precision inherent in the assemblage zone
approach, which means that reconstructions are restricted to sediments representing a sub-set of environmental conditions and are associated with errors of
varying magnitude.
Whilst the heterogeneity described above suggests
that local fauna – environment relationships are to be
preferred, the disturbance of salt-marshes by human
activity means that it may not be possible to collect a
full range of modern analogues from every study
marsh. Furthermore, environmental changes at a site
may produce extant populations that differ in composition to sub-fossil assemblages. In such instances, it
may be necessary to collect appropriate modern analogues from other marshes or regions, but this must be
done in a way that accounts for the spatial variability
outlined above.
The problems associated with using assemblage
zones can be circumvented by adopting an approach
that still considers assemblages as a whole, but is
capable of discerning more subtle variations in the
13
abundance of individual species. The use of foraminiferal transfer functions offers one means of achieving this since they assign ecological optima and
tolerances to individual species, but produce reconstructions based on assemblages as a whole (Guilbault et al., 1996; Horton et al., 2000; Edwards and
Horton, 2000; Gehrels, 2000). In addition, they can
combine data from a number of marshes to ensure
that a wide range of modern analogues can be
collected, whilst quantifying the variability within
these assemblages. In this way, complementary sites
can be selected to combine desirable attributes such
as a long stratigraphic sequence indicative of high
marsh deposition, and a relatively pristine, unaltered
modern salt-marsh.
Gehrels (2000) successfully applied a foraminiferal transfer function to salt-marsh assemblages
from Maine and demonstrated its reliability and
utility in resolving decadal-scale sea-level changes.
Differences in the occurrence and distribution of
foraminiferal species between Maine and Connecticut (e.g., B. pseudomacrescens) mean that the
application of this transfer function in Connecticut
is prone to error unless local assemblages are
included in the data used to derive fauna – environment relationships (termed a ‘training set’). The
new foraminiferal data presented here form the basis
of such a modern training set which, in combination
with other data from Connecticut, is suitable for the
derivation of a transfer function for tide level
reconstruction in this area.
Acknowledgements
The manuscript was prepared at Trinity College
Dublin and was facilitated by a Trinity award. We
thank Wilfried Goossen (Vrije Universiteit) for his
assistance in the field. Thanks are also due to Ben
Horton (Durham University) for the helpful comments
and discussion. This research is a contribution to the
project ‘‘Coastal Records’’, currently funded by the
Vrije Universiteit Amsterdam. The manuscript was
significantly improved by the thoughtful comments of
two anonymous reviewers.
14
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Appendix A . Systematic taxonomy
Ammot. salsum (Cushman and Brönnimann)
Ammobaculites salsus Cushman and Brönnimann, 1948, p. 16, pl. 3, figs. 7 – 9.
Ammot. salsum (Cushman and Brönnimann), Scott and Medioli, 1980a, p. 35, pl. 1, figs. 11 – 13.
Areno. mexicana (Kornfeld)
Plate 1 : Figs. 1 – 2.
Tr. inflata (Montague) var. mexicana Kornfeld, 1931, p. 86, pl. 13, fig. 5.
Areno. mexicana (Kornfeld), Andersen, 1951, p. 31, figs. 1a – c.
Areno. mexicana (Kornfeld), Scott and Medioli, 1980a, p. 35, pl. 1, figs. 8 – 11.
B. pseudomacrescens Brönnimann, Lutze and Whittaker
Tr. macrescens Lutze, 1968, pp. 25 – 26, tafel 1, fig. 9.
Tr. inflata (Montagu) var. macrescens Scott, 1976, p. 320, pl. 1, figs. 4 – 7.
Tr. macrescens macrescens Scott et al., 1990, p. 733, pl. 1, figs. 1a – b.
B. pseudomacrescens Brönnimann et al., 1989, p. 169, pl. 1 – 3.
B. pseudomacrescens (Brönnimann, Lutze and Whittaker), Gehrels and van de Plassche, 1999, p. 98, pl. 1,
figs. 6 – 10.
J. macrescens (Brady)
Plate 1: Figs. 3 – 4.
Tr. inflata (Montagu) var. macrescens Brady, 1870, p. 290, pl. 11, fig. 5a – c.
Jadammina polystoma Barnstein and Brand, 1938, p. 381, figs. 1a – c, 2a – l; Parker and Athearn, 1959, p. 341,
pl. 50, figs. 21 – 22, 27.
Tr. macrescens Brady, Phleger and Walton, 1950, p. 281, pl. 2, figs. 6 – 9; Parker and Athearn, 1959, p. 341,
pl. 50, figs. 23 – 25.
Trochammina macrescens polystoma Scott et al., 1990, p. 737, pl. 1, fig. 2a – c.
J. macrescens (Brady), Murray, 1971, p. 41, pl. 13, figs. 1 – 5; Brönnimann and Whittaker, 1984, p. 305,
figs. 1 – 21; Gehrels and van de Plassche, 1999, p. 98, pl. 1, figs. 1 – 5.
H. manilaensis (Anderson)
Plate 1: Figs. 5 – 6.
H. manilaensis (Anderson, 1953, p. 22), pl. 4, figs. 8a – b.
Haplophragmoides bonplandi (Todd and Brönnimann), Scott and Medioli, 1980a, p. 40, pl. 2, figs. 4 – 5.
H. manilaensis (Anderson), Thomas and Varekamp, 1991, p. 155; De Rijk, 1995a, p. 29, pl. I, figs. 1 – 8.
M. fusca (Brady)
Plate 1: Fig. 7.
Quinqueloculina fusca Brady, in Brady and Robertson, 1870, p. 47, pl. 11, figs. 2 – 3.
M. fusca (Brady), Phleger and Walton, 1950, p. 280, pl. 1, figs. 19a – b; Scott and Medioli, 1980a, pp. 40 – 41,
pl. 2, figs. 1 – 3.
Polysaccammina ipohalina Scott
Po. ipohalina Scott, 1976, p. 318, pl. 2, figs. 1 – 4.
Po. ipohalina Scott, Scott and Medioli, 1980a, p. 43, pl. 2, figs. 8 – 11.
Pseudothurammina limnetis (Scott and Medioli)
Plate 1: Fig. 8.
Thurammina ? limnetis Scott and Medioli, 1980a, p. 43, pl. 1, figs. 1 – 3.
Ps. limnetis (Scott and Medioli), Scott et al., 1981, p. 126.
Reophax species
Genus Rheophax Montfort, 1808
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Appendix A (continued)
Si. lobata Saunders
Plate 1: Figs. 9 – 10.
Si. lobata Saunders, 1957, pp. 9 – 10, pl. 3, figs. 1 – 2; Brönnimann et al., 1992, p. 31, pl. 4, figs. 1 – 2;
De Rijk, 1995a, p. 33, pl. III, figs. 9, 11 – 13.
Textularia earlandi Parker
Plate 1: Fig. 11.
Te. earlandi Parker, 1952, p. 458 (footnote).
Te. earlandi Parker, Scott et al., 1990, p. 732.
Ti. comprimata (Cushman and Brönnimann)
Plate 1: Figs. 12 – 13.
Trochammina comprimata Cushman and Brönnimann, 1948, p. 41, pl. 8, figs. 1 – 3.
Ti. comprimata (Cushman and Brönnimann), Scott and Medioli, 1980a, p. 44, pl. 5, figs. 1 – 3.
Tr. inflata (Montagu)
Plate 1: Figs. 14 – 15.
Nautilus inflatus Montagu, 1808, p. 81, pl. 18, fig. 3.
Tr. inflata (Montagu), Phleger and Walton, 1950, p. 280, pl. 2, figs. 1 – 3.
Tr. inflata (Montagu), De Rijk, 1995a, p. 31, pl. 2, figs. 1 – 3.
Trochammina ochracea (Williamson, 1858)
Rotalina ochracea Williamson, 1858, p. 55, pl. 4, fig. 112, pl. 5, fig. 113.
Tr. ochracea (Williamson), Cushman, 1920, p. 75, pl. 15, fig. 3.
15
16
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Plate 1. Scale bars equivalent to 100 Am. (1). Areno. mexicana, dorsal view (Double Beach marsh, surface). (2) Areno. mexicana, aperture view
(Double Beach marsh, surface). (3) J. macrescens, ventral view (Double Beach marsh, surface). (4) J. macrescens, dorsal view (Double Beach
marsh, surface). (5) H. manilaensis, aperture view (Double Beach marsh, surface). (6) H. manilaensis, side view (Double Beach marsh, surface).
(7) M. fusca, side view (Pattagansett River marsh, surface). (8) Ps. limnetes (Double Beach marsh, surface). (9) Si. lobata, dorsal view (Double
Beach marsh, surface). (10) Si. lobata, ventral view (Double Beach marsh, surface). (11) Te. earlandi (Pattagansett River marsh, surface). (12)
Ti. comprimata, ventral view (Pattagansett River marsh, surface). (13) Ti. comprimatai, dorsal view (Pattagansett River marsh, surface). (14) Tr.
inflata, dorsal view (Double Beach marsh, surface). (15) Tr. inflata, ventral view (Double Beach marsh, surface).
Appendix B. Foraminiferal counts
Table B1
Foraminiferal death assemblages from Double Beach marsh
Notes
Altitude
Ammot. Areno.
B.
J.
H.
M.
Ps.
Si.
Te.
Ti.
Tr.
Not Calcareous Dead
(m NGVD) salsum mexicana pseudomacrescens macrescens manilaensis fusca limnetis lobata earlandi comprimata inflata ID
tests
counted
1
1
1
1
1
1
1
DB1-11
DB1-10
DB1-9
DB1-8
DB1-7
DB1-6
DB1-5
1.57
1.54
1.47
1.42
1.37
1.32
1.27
1
7
10
84
1
1
DB1-4
DB1-3
1.22
1.18
31
8
1
DB1-2
1
DB1-1
2
2
2
2
2
2
2
2
2
DB2-27
DB2-26
DB2-25
DB2-24
DB2-23
DB2-22
DB2-21
DB2-20
DB2-19
I. frutescens
I. frutescens
I. frutescens
Scirpus sp.
Scirpus sp.
Scirpus sp.
Juncus
gerardii
Sp. patens
Sp.
alterniflora
(stunted)
Sp.
alterniflora
(stunted)
Sp.
alterniflora
(stunted)
Woodland
Woodland
Wood fringe
Scirpus sp.
Scirpus sp.
Scirpus sp.
Scirpus sp.
Scirpus sp.
Sp. patens
1.12
1.08
1.63
1.58
1.53
1.48
1.43
1.38
1.33
1.28
1.28
1
1
50
113
105
366
339
414
1099
28
43
28
84
19
1
8
6
11
2
11
8
9
13
249
209
1
7
7
108
55
4
509
50
1
2
75
166
141
171
262
140
129
123
254
1
1
1
1
58
68
21
9
6
79
120
43
35
38
15
2
1
8
3
2
7
3
2
5
7
16
93
40
44
258
5
65
2
10
88
271
279
123
477
2
8
1
91
185
240
832
693
609
2016
1
3
44
29
6
4
11
6
81
46
7
2
5
6
443
318
3
2
17
2
2
190
20
6
217
3
13
823
16
41
28
67
2
17
9
4
33
9
7
15
79
1
1
4
1
5
1
1
75
166
157
253
385
296
293
231
462
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Transect Sample
Unidentified specimens refer to deformed or small (juvenile?) tests.
17
18
Table B2
Foraminiferal death assemblages from Hammock River marsh
Notes
Altitude
Ammot. Areno.
B.
J.
H.
M.
Po.
P.
Si.
Te.
Ti.
Tr.
Tr.
Not Dead
(m NGVD) salsum mexicana pseudomacrescens macrescens manilaensis fusca ipohalina limnetis lobata earlandi comprimata inflata ochracea ID tests
counted
HRM-1
Fringing
Woodland
Fringing
Woodland
Fringing
Woodland
Bare
Bare
Bare
Ph. australis
Ph. australis
Sc. robustus
Sp. patens
Sp. patens
Sp. patens
Sp.
alterniflora
(stunted)
Sp.
alterniflora
(stunted)
1.42
10
1.37
54
1.29
44
1.25
1.19
1.13
1.09
1.06
1.04
1.02
0.97
0.92
0.87
HRM-2
HRM-3
HRM-4
HRM-5
HRM-6
HRM-7
HRM-8
HRM-9
HRM-10
HRM-11
HRM-12
HRM-13
HRM-14
0.83
4
1
58
1
6
9
2
32
Unidentified specimens refer to deformed or small (juvenile?) tests.
2
2
14
12
6
72
1
7
7
59
47
43
67
100
76
90
32
85
100
188
3
5
5
14
25
29
9
18
14
13
5
12
19
2
3
5
2
3
65
75
96
140
140
226
176
132
207
368
133
12
4
266
11
19
1
1
7
7
2
1
1
2
1
1
1
17
35
2
11
35
38
21
1
1
1
1
1
9
23
15
12
18
44
2
6
34
47
20
29
66
17
45
2
2
2
1
1
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Sample
Table B3
Foraminiferal death assemblages from Pattagansett River marsh
Notes
Altitude
Ammob. Ammot. Areno.
B.
J.
H.
M.
Po.
Reophax S.
Te.
Ti.
Tr.
Not ID Calcareous Dead
(m NGVD) dilatatus salsum mexicana pseudomacrescens macrescens manilaensis fusca ipohalina sp.
lobata earlandi comprimata inflata
tests
counted
1
1
1
1
1
1
1
1
1
1
1
1
PAT1-3
PAT1-4
PAT1-5
PAT1-6
PAT1-7
PAT1-8
PAT1-9
PAT1-10
PAT1-11
PAT1-12
PAT1-13
PAT1-14
1.05
1.00
0.95
0.93
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
1
PAT1-15
1
PAT1-16
1
PAT1-17
1
PAT1-18
2
2
2
2
2
PAT2-18
PAT2-17
PAT2-16
PAT2-15
PAT2-14
2
2
2
2
2
PAT2-13
PAT2-12
PAT2-11
PAT2-10
PAT2-9
I. frutescens
I. frutescens
I. frutescens
I. frutescens
I. frutescens
I. frutescens
I. frutescens
Sp. patens
Sp. patens
Sp. patens
Sp. patens
Sp. alterniflora
(stunted)
Sp. alterniflora
(stunted)
Sp. alterniflora
(tall)
Sp. alterniflora
(tall)
Sp. alterniflora
(tall)
I. frutescens
I. frutescens
I. frutescens
I. frutescens
Distichlis
spicata
Sp. patens
Sp. patens
Sp. patens
Sp. patens
Sp. patens
2
4
6
3
1
9
9
87
57
117
61
72
72
57
143
123
113
147
57
0.5
19
2
23
147
0.45
35
16
23
77
7
6
41
19
36
110
9
7
8
44
41
146
4
23
0.40
0.35
4
1
2
1
1
0.99
0.94
0.89
0.85
0.80
0.75
0.69
0.65
0.60
0.55
1
2
3
1
5
7
7
3
10
46
56
33
51
50
3
1
29
170
440
261
177
119
64
45
190
46
15
13
1
23
5
21
14
58
2
1
5
16
48
1
12
291
155
272
601
13
8
3
11
20
9
30
20
5
8
166
56
35
59
79
1
4
20
19
13
19
31
251
144
218
377
1
275
87
130
56
146
1
1
0
7
18
7
4
2
24
49
21
241
1
2
2
3
2
9
3
5
3
2
4
25
1
31
115
214
1
2
5
42
11
29
22
23
54
44
1
2
1
2
1
1
90
59
153
245
565
404
272
359
292
268
479
456
228
10
200
1
3
250
342
49
548
307
508
1031
3
1
2
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
Transect Sample
490
186
228
251
478
Unidentified specimens refer to deformed or small (juvenile?) tests.
19
20
R.J. Edwards et al. / Marine Micropaleontology 51 (2004) 1–21
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