THE ROLE OF BACKBARRIER INFILLING IN THE
FORMATION OF BARRIER ISLAND SYSTEMS
CHRISTOPHER J. HEIN1, DUNCAN M. FITZGERALD2, EMILY A. CARRUTHERS3,
BYRON D. STONE4, ALLEN M. GONTZ5
1.
2.
3.
4.
5.
Department of Earth Sciences, Boston University, 675 Commonwealth Ave., Boston,
MA 02215, USA. [email protected]
Department of Earth Sciences, Boston University, 675 Commonwealth Ave., Boston,
MA 02215, USA. [email protected]
Woods Hole Oceanographic Institution, MS #22 Clark 259, Woods Hole, MA 02543,
USA. [email protected]
U.S. Geological Survey, 12201 Sunrise Valley Drive Mail Stop 926A, Reston, VA
20192, USA. [email protected]
Department of Environmental, Earth, and Ocean Sciences, University of
Massachusetts, Boston, 100 Morrissey Blvd., Boston, MA 02125, USA.
[email protected]
Abstract: Barrier islands develop through a variety of processes, including spit
accretion, barrier elongation, and inlet filling. New geophysical and
sedimentological data provide a means of documenting the presence of a paleoinlet within a barrier lithosome in the western Gulf of Maine, illuminating the
process of backbarrier infilling and its effect on barrier and tidal inlet
morphodynamics. The transport of sediment into the backbarrier through tidal
inlets as well as sediment contribution from nearby rivers led to bay infilling,
formation of tidal flats and marshes, and a vast reduction in the bay tidal prism.
Using existing marsh stratigraphy and high resolution imaging of a paleo inlet, this
study investigates the effects of this diminishing tidal prism and inlet closure
process. Chronostratigraphic reconstructions and digital backstripping of the
backbarrier explain rates and timing of infilling and eventual conversion of an
open water lagoon to the modern high marsh and tidal creek system.
Introduction
Traditional barrier island formation theories address the roles of changes in sea
level, wave climate, and / or sediment supply in the initiation of barrier
formation, followed by further development through processes of spit accretion,
barrier elongation, and inlet breaching. Contrarily, this study presents new
geophysical and sedimentological data collected along a barrier system in the
northeastern United States as a means of documenting a previously
unrecognized process of barrier evolution: backbarrier infilling resulting in tidal
prism reduction and the closure of early stage tidal inlets.
The Plum Island barrier system is located along a paraglacial, mixed-energy,
tide-dominated (range: 2.7 m) coastline in the western Gulf of Maine (Fig. 1). It
is part of the longest barrier island chain in Massachusetts (approximately 34 km
long), backed primarily by marsh and tidal creeks that often enlarge to small
bays near the inlet openings (Smith and FitzGerald, 1994). Barriers in this
region are backed by primarily tidal rivers that have some freshwater influx
from nearby streams. The only true estuary is the mouth of the Merrimack
River, a system that has its headwaters in the White Mountains of New
Hampshire and a catchment of approximately 13,000 km2. Sediment discharged
from the mouth of the Merrimack ranges in size from fine to coarse sand and
granules. These sediments are subsequently reworked by the southeasterly
longshore current formed as a result of strong storm waves associated with
Northeasters.
Following an isostatically-induced sea-level highstand coincident with ice front
retreat at approximately 16 ka (note: all ages in this manuscript are calibrated
radiocarbon ages), this region experienced rapid isostatic rebound resulting in a 45 m lowstand at 13-14 ka (Oldale et al., 1983; Oldale et al., 1993). The
subsequent Holocene transgression progressed relatively rapidly and
episodically for the first 7,000 years. At approximately 6 ka, sea-level rise
slowed to near modern rates (Oldale et al., 1993). The shoreline reached its
modern position by approximately 3 - 4 ka. Since that time, the barriers of the
Merrimack Embayment have been aggrading, elongating, and prograding as
additional sediments have been delivered from the Merrimack River.
A
B
C
Figure 1: GPR transects and sediment core locations. GPR lines (both 100 and 200 MHz lines)
shown as thin blue lines. Core locations given as circles (green: vibracores; red: Geoprobe cores;
yellow: auger drill cores). A) Satellite image location map of Plum Island. B) Overview of data
collected along Plum Island. C) Central Plum Island (red box in [B]), overlain on Lidar data
(Valentine and Hopkinson, 2005).
Although an expansive body of work has been devoted to the general
development Plum Island and adjacent barrier islands (Chute and Nichols, 1941;
Rhodes, 1973; McIntire and Morgan, 1964; Oldale et al., 1983; Edwards, 1988;
Boothroyd and FitzGerald, 1989; FitzGerald et al., 1993), no detailed studies
have focused on the mid- to late- Holocene development of Plum Island, the
largest barrier in the chain. This study presents a new, high resolution model,
based on extensive geophysical surveys and detailed coring. Furthermore, it uses
this evolutionary model to investigate the driving factors behind the formation
of this barrier system.
Methods
Plum Island barrier stratigraphy was determined through the collection of 15 km
of ground-penetrating radar (GPR) data (Fig. 2) using a Geophysical Survey
Systems Inc (GSSI) SIR-2000 with a 200 MHz antenna (7 - 9 m depth
penetration) and a Mala Pro-Ex with a 100 MHz antenna (16 – 20 m depth
penetration). These data were post-processed (site-specific data filtering,
variable-velocity migration, gain control) and time-depth converted using a
combination of Radan (GSSI), RadExplorer (DECO-Geophysical Co. Ltd.), and
GPR-Slice (Geophysical Archaeometry Laboratory) software packages.
A series of seven vibracores (max 4 m depth), 12 direct push cores (max 16 m,
using a Geoprobe Model 54DT machine), and 11 auger drill cores (max 38 m,
using a truck-mounted B2 auger drill rig) were used to ground truth GPR data
and determine the stratigraphic framework. (Fig. 2). Sediment samples from the
cores were analyzed using combined wet / dry sieve techniques described by
Folk and Ward (1957). Mineralogical classifications (via hand-picking) were
completed for a series of randomized samples. Sedimentological descriptions
were used to sub-divide cores into facies. Additionally, 12 mollusk, wood, and
peat samples were selected from cores for radiocarbon analysis. As no mollusk
samples were found articulated and in growth position, individuals were
identified for dating based on quality of preservation and likelihood of prior
reworking. Results of radiocarbon analysis, calibrated using Calib 6.0.1 (Stuiver
and Reimer, 1993), with IntCal09 (Reimer et al., 2009) for mixed and terrestrial
samples and Marine09 (Reimer et al., 2009, corrected to a regional-averaged ΔR
of 92 ± 59 years) for mollusk samples. Samples were analyzed at either Beta
Analytic Inc (Miami, FL, USA) or the National Ocean Sciences Accelerator
Mass Spectrometry Facility (NOSAMS; Woods Hole, MA, USA). All dates in
text are reported as 1-sigma calibrated ages before present.
In addition to the 30 sediment cores collected for this study, a complimentary
database of 179 cores was compiled from various studies in the Merrimack
Embayment (McIntire and Morgan, 1963; McCormick, 1969; Hartwell, 1970;
Rhodes, 1973; Som, 1990) and the Massachusetts Water Resources Authority
database. Based on published descriptions, these cores were sub-divided by
facies (barrier, marsh, tidal flat, backbarrier sediment, glaciomarine clay, till,
and bedrock). Core elevations (referenced to mean low water) were extracted
from 2005 LIDAR data (Valentine and Hopkinson, 2005) and 2003 Mass GIS
Digital Terrain Model (DTM) data. Modern tidal creek and inlet boundaries
were manually added to this database using ArcGIS, georeferenced NOAA
charts, and orthophotos.
From these data, facies surfaces were gridded using Surfer 9 (Golden Software).
Gridding was accomplished through linear variogram kriging methods using a 2
km search sensitivity to produce 10,000 m2 square grid resolution. Grids were
clipped to backbarrier boundaries established as the upland extent of the modern
saltwater wetland areas on the west, the lateral mid-line of the barriers on the
east, and to the southern and northern extents of backbarrier marshes behind
Castle Neck and Salisbury Beach, respectively. Three-dimensional digital
geologic maps (DGMs) were exported to a GIS platform for analysis.
Figure 2: GPR profiles with graphic core logs collected in central Plum Island. Colors of exterior
boxes correspond to colors of lines showing profile locations in Fig. 1C. Width of units in graphic
core logs proportional to grain size (smaller = finer); color also denotes grain size (gray: silt and
clay; beige: fine sand; brown: medium sand; yellow: coarse sand and gravel; black: organic-rich
layers). (A) Southward prograding spit system and northern extension of Paleo-Parker Inlet. Note
thickening of spit sequence (yellow highlighted layers) overlying sub-horizontal, sub-parallel
reflectors of backbarrier / spit platform (brown layers; composed of fine to medium sand). (B)
Primary inlet sequence (blue layers), truncating spit platform (brown layers) and underlying shallow
spit sequence (yellow layers). (C) Southerly extent of inlet system showing rapid progradation of
spit (yellow layers) over shoaled and closed inlet (blue layers).
Results
The Plum Island barrier sequence is underlain by at least 15 m of glaciomarine
clay (Presumpscot formation, deposited during the post-glacial highstand of sea
level; Bloom, 1963), composed of laminated, highly compacted and dewatered,
very fine sand to fine clay, with some fine gravel (dropstones). The uppermost
section is nonuniform and typically composed of green to brown, oxidized clay
with some pockets of organic-rich gytcha, all interpreted as evidence of
subaerial erosion during regression and the late Pleistocene lowstand (14 ka). In
most locations, this unit is unconformably overlain by 12 – 15 m of nearly
homogeneous, massive, fine and moderately well-sorted sand and silt deposits
interpreted as backbarrier sediment. This sediment is dominated by quartz but
often with large amounts of mica and occasional minor organic material. In GPR
profiles, this layer consists of weak, horizontal to sub-horizontal reflectors, with
little discernable pattern and many small-scale truncations of individual
reflectors (Fig. 2). A 4 – 5 m thick barrier lithesome overlies these backbarrier
sediments. This unit consists of a series of sub-parallel sigmoid oblique
reflectors, composed of quartz-rich medium- to coarse- sand and fine gravel
with occasional centimeter to decimeter thick heavy mineral concentrations.
These units are predominantly southerly dipping, with smaller packets of
northward dipping reflectors. Cross-shore profiles reveal a seaward component
to these reflectors, with rare, less than 20 m wide, sections of landward dipping
packets. Strongly resembling the modern beach environment, this unit represents
the southerly migrating and seaward prograding spit sequence that
predominantly formed the island (Fig. 2a). Landward- and northward- dipping
sections are interpreted as small bars associated with the recurved extent of the
spit. These depositional processes are evident at the southern end of the barrier,
which is influenced by modern spit accretion around nearby glacial till deposits.
The Paleo-Parker Inlet
Along a 300 m long section of central Plum Island, the repetitive southwarddipping GPR reflectors of the southerly prograding spit are interrupted by a
complex sequence of conformable sets of southerly dipping reflectors
punctuated by sharp truncation surfaces, cut and fill features and smaller packets
of northerly dipping reflectors (Fig. 2). This sequence is interpreted as the
remnants of a paleo-inlet (termed the “paleo-Parker Inlet”). This entire sequence
is between 5 and 6 m thick and shoals to the south. Cores indicate that it consists
of fine to medium sand with repetitive interbedded coarse sand units, marking
the high energy depositional events associated with spit accretion and
displacement of the inlet southward. Driven by the same northeast storms that
forced the progadation of the spit system, the shoaling inlet migrated rapidly to
the south.
Together, these features capture events of inlet migration, ebb-delta breaching,
onshore bar migration, channel shoaling, and inlet infilling associated with the
migration and eventual closing of the paleo-Parker Inlet. Radiocarbon analysis
of organic matter collected within a coarse sand / granule unit at the base of the
inlet sequence produced a date of 3600 ± 40 cal yr BP (Fig. 2b), corresponding
to a sea level of 3 m below modern (see calibrated sea level curve, Fig. 4).
Backbarrier Reconstructions
DGMs were produced for the marsh surface, the backbarrier sediment surface,
the backbarrier “base” (glaciomarine, till, or bedrock surfaces), and of the
backbarrier at various times (see discussion); examples are shown in Fig. 3.
Subtraction of these various facies allowed for the calculation of the volume of
backbarrier sediment, estimated at 850 x 106 m3. This represents approximately
ten times the sediment volume of Plum Island and is about 65% of the volume
of the lowstand paleodelta located offshore of Plum Island (1.3 x 109 m3; Oldale
et al., 1983).
Figure 3: Digital Geologic Models shown both in three-dimensional perspective views and overlain
on color orthophotos. Color scales on all images is the same to highlight changes between layers. All
elevations with respect to mean low water. A) Surface of backbarrier reconstructed by interpolation
from 209 cores and channel and boundary control points (BCP). B) Surface of backbarrier
sediments, after removal of barrier and marsh units, reconstructed by interpolation from 140 cores
and channel and BCP. C) Surface underlying backbarrier sediments, composed of either
glaciomarine, till, or bedrock, reconstructed by interpolation from 65 cores and channel and BCP.
D) Backstripped surface at 3.6 ka (see Discussion for details).
Discussion
The multi-stage development of the Plum Island barrier system in a regime of
variable-rate sea-level rise over the last 6 ka involved periods of barrier
migration, spit elongation, inlet closure, and progradation. Early in its
development, the barrier was likely composed of several discrete islands situated
offshore of modern Plum Island. Several of the river systems that currently feed
the modern backbarrier (Parker and Ipswich Rivers) extended across the shallow
shelf (Hein et al., 2007). By about 3.6 ka, a proto-barrier had formed in the
present position of Plum Island. At the center of this barrier an active inlet
channel was maintained by tidal flows into a largely open backbarrier system.
This paleo-Parker Inlet underwent a complex evolutionary history as recorded in
the sedimentary record, including thalweg migration, ebb-delta breaching,
onshore bar migration, channel shoaling, and eventual closure of the inlet (Fig.
5). The top of this 4 -5 m thick sequence is located at 2 m below modern sea
level, confirming the approximate age of this sequence at 3.6 ka (Fig. 4). As
mapped using GPR and sediment core data, remnants of this inlet cover an area
of 1300 m2 under Plum Island, approximately 40% of the size of the modern
Parker Inlet at the southern end of Plum Island and within 75% of the modern
Merrimack and Essex Inlets (Table 1).
Figure 4: Calibrated Holocene sea level curve for northern Massachusetts based on published data,
as noted in figure, and new dates from this study. Vertical and temporal errors are given by heights
and widths of data rectangles. Standard vertical errors of ± 1 m given to ages of all possibly
reworked material from Plum Island (green boxes). Ages are calibrated 1-sigma ranges.
Backbarrier Infilling as a Driver of Barrier Formation
Tidal inlets are maintained in barrier systems by the regular tidal fluxes between
the backbarrier and open ocean. To a first-order approximation, and absent any
landward barrier migration or additional inorganic sediment supply, the gradual
rise in sea level over the past 3.6 ka (Fig. 4) experienced in northeast
Massachusetts would have tended to increase tidal prisms as additional upland
areas are flooded. This larger tidal prism would necessitate larger, or additional
tidal inlets in the barrier system. However, the discovery of a paleo-inlet within
the Plum Island lithosome suggests that the opposite occurred; and that tidal
prism has decreased over time to its present size (32 x 106 m3; Vallino and
Hopkinson, 1998). One likely possibility for this decrease is the sediment
infilling of backbarrier regions.
Figure 5: Evolutionary model for the formation of Plum Island. Note that B-E are within red box
shown in A and F. (A) Transgressive Migration of Sand Shoals: regressive and lowstand deposits
reworked onshore during transgression; sands pinned to glacial deposits as transgression proceeds;
proto-barrier develops from continued sediment input. (B) Southerly Migration of Parker Inlet:
northeast storms produce southerly long shore transport; islands elongate by spit migration; PaleoParker Inlet occupies Parker River channel and begins southerly migration; active around 3600 cal yr
BP. (C) Ebb Tidal Delta Breaching: inlet deflected to north, truncating southerly prograding spit
and platform; inlet narrows, deepens; backbarrier filling begins. (D) Closure of Inlet: inlet shoals and
narrows due to reduced tidal prism; southerly spit progradation; increased backbarrier infilling. (E)
Rapid Southerly Spit Progradation: Paleo-Parker Inlet closes completely; spit progrades south,
overtopping inlet fill and intertidal shoals. (F) Barrier Stabilization: Plum Island progrades; Parker
River joins Rowley and Ipswich Rivers as a single estuary with one inlet (Parker) at the southern end
of Plum Island, stabilized between two drumlins.
Table 1. Cross-sectional areas of the three modern and one relict inlet of the Plum Island barrier
system. Cross-sectional areas of modern inlets determined from analysis of bathymetric data.
Equivalent tidal prisms (TP) calculated from regression equation (A = 5.37 x 10-6 TP1.07) comparing
minimum cross sectional areas below mean sea level (A) to spring or diurnal tidal prisms for inlets
with one or zero jetties (Jarrett, 1976).
Inlet
X-C Area, m2
Equivalent TP, m3
Merrimack Inlet
1900
2.55 x 107
Hubbard, 1971
Parker Inlet
2500
3.29 x 107
FitzGerald et al., 2002
Essex Inlet
1720
2.32 x 107
FitzGerald et al., 2002
Paleo-Parker Inlet
1300
1.80 x 107
This study
X-C Area Data Source
Backbarrier Backstripping
It can be assumed that the entire backbarrier sediment sequence was deposited
during the Holocene marine transgression. Published (McIntire and Morgan,
1964) and unpublished (this study) marsh accretion rates (average: 0.12 cm/yr)
and long-term estimates of backbarrier sediment accretion rates (0.28 cm/yr)
determined from dates collected within this unit were used to “backstrip” the
backbarrier unit. This method assumes that these rates were roughly constant
through time and performs the backstripping using the following formulas:
If Mo-BBo=0; BB1=BBar*T1
(1)
If Mo-BBo>3; BB1=BBo
(2)
If Mo-BBo<3; (T1-(Mo-BBo)*Mar)*BBar
(3)
where at a given location Mo is the elevation of modern marsh; M1 is the marsh
level at time T1 (3.6 ka); BBo is the elevation of modern backbarrier sediment;
BBo is the elevation of backbarrier sediment at time T1; BBar is the mean
backbarrier sediment accretion rate; and Mar is the mean marsh accretion rate.
If no marsh is currently at a given location (for instance in tidal creeks), it is
assumed that marsh never existed there and only backbarrier accretion rates are
used in the backstripping (Eq. 2). Conversely, this method assumes that marsh
growth could only have commenced once mid-Holocene sea-level rise slowed
enough to allow marsh accretion to keep up with rising sea level. Implicit in this
notion is the assumption that the backbarrier was infilled to a point where marsh
colonization could be initiated, a process intimately tied to the closure of the
paleo-Parker Inlet. Therefore, the earliest date for the initiation of marsh growth
is given as 3.6 ka, around the same time as inlet closure. This is factored into
backstripping calculations: if marsh / peat thicknesses at a given location are
greater than or equal to 3 m (approximate rise in sea level since 3.6 ka), then all
marsh is stripped from that location and the top of the backbarrier sediment is
used as the surface for the reconstruction (Eq. 3). The resulting reconstruction
approximates the surface of the Plum Island backbarrier at 3.6 ka, the time at
which the paleo-Parker Inlet was active (Fig. 3d).
Paleo-Tidal Prism Calculation
The backstripped backbarrier DGMs (Fig. 3d) were used in the determination of
backbarrier tidal prism (the difference in water volume in the backbarrier
between mean low and high tides). To account for errors, paleo-surfaces were
adjusted by ± 0.5 m at each location and tidal prism calculations were adjusted
based on normalization of tidal prisms calculated using the reconstructed
modern backbarrier surface to known modern tidal prism (Table 2).
Table 2. Results of paleo-tidal prism calculations using reconstructed backbarrier DGMs. Equivalent
tidal inlet cross-sectional area determined from Eq. 4. Tidal prisms and equivalent cross sectional
area of the combined modern inlets in this system (Merrimack, Parker, and Essex Inlets) also given.
System
X-Sect Area, m2
Equivalent TP, m3
Combined Modern Inlets
6700
88 x 106
Reconstructed Paleo-Backbarrier
13,100 ± 1200
155 x 106 ± 11 x 106
Residual
5300
67 x 106
The Backbarrier – Inlet Tidal Prism Disparity
The inlet cross sectional area corresponding to the paleo-tidal prism calculated
from reconstructed backbarrier surfaces at 3.6 ka (13,100 m2) is nearly twice as
large as the combined cross sectional areas of the three modern inlets (6700 m2);
the resulting residual inlet cross sectional area (5300 m2; Table 2) is of the same
order of magnitude as the combined modern inlets. Approximately ¼ of the
residual can be accounted for by the presence of an additional inlet in the Plum
Island barrier system: the paleo-Parker Inlet had a cross sectional area of 1300
m2 and therefore, at its maximum, transmitted 18 x 106 m3 of flow each tidal
cycle, leaving a ~50 x 106 m3 disparity between the tidal prisms calculated from
the cross sectional areas of the inlets (three modern and one extinct) and the
reconstructed backbarrier paleo-tidal prism. First, implicit in the calculation of
the combined cross sectional areas of the three inlets that still exist in this
system is the assumption that the modern inlets had similar form and cross
sectional areas at time when paleo-Parker Inlet was active. While these inlets are
often pinned to, and bottomed by, shallow till (i.e. Parker Inlet; FitzGerald et al.,
1993), it is very likely that may have changed in form over the past 3600 years.
A second possible explanation for the disparity is related to preservation
potential of the paleo-Parker Inlet. The active nature of this inlet suggests that it
may have re-worked much of its own sedimentary and geophysical signature,
and therefore the full extent of the paleo-inlet was not determined through the
methods discussed here. Finally, discovery of one paleo-inlet in the Plum Island
system does not discourage the possibility of others; rather, it suggests quite the
opposite. However, GPR signal attenuation adjacent to salt water marshes
constrained the search for additional inlet systems along much of Plum Island.
Conclusions
This study reveals the importance of backbarrier infilling in the development of
the Plum Island barrier system. The paleo-Parker Inlet could only have existed if
the barrier system had a large enough tidal prism to maintain an additional
channel through which tidal flows would be transmitted. Eventually, it was the
import of sediment into the backbarrier through these tidal inlets, as well as
minor sediment contribution from nearby rivers, that led to the formation of tidal
flats and marshes, a vast reduction in the bay tidal prism, and the eventual
shoaling and closing of the paleo-Parker Inlet. This connected two previously
disparate sections of Plum Island, allowing for the further elongation of the spit
system, and the transition to a progradational regime. Notwithstanding
disparities between expected and determined paleo-tidal prisms, this study
presents evidence for barrier island formation in direct response to infilling of
the backbarrier and reduction of tidal prism. Significant conclusions include:
1. Plum Island developed in its modern location by processes of onshore
sediment migration, southerly spit accretion, and progradation. A paleo-inlet
system in the center of the island shows evidence for channel migration, ebbdelta breaching, onshore bar migration, channel shoaling and inlet infilling.
2. The paleo-Parker Inlet had a maximum cross-sectional area of 1300 m2 and
was active at 3.6 ka. Discovery of this feature suggests that the paleo-tidal
prism of this system was once large enough to require the presence of an
additional inlet. Import of sediment into the backbarrier led to bay infilling,
the formation of tidal flats and marshes, and a vast reduction in the bay tidal
prism. The result was shoaling and closure of the inlet.
3. Using a series of core logs collected along the barriers, marshes, and tidal
channels of the barrier system, digital geologic models were created to
reconstruct individual stratigraphic facies and then, using average marsh and
backbarrier sediment accumulation rates, to “backstrip” sediment to various
time periods. The resulting reconstructions allowed for the determination of
paleo-tidal prism at the time that the paleo-Parker Inlet was active.
4. A disparity exists between tidal prisms determined from the backbarrier
reconstructions (155 x 106 ± 11 x 106 m3) and the combined modern inlets
(88 x 106 m3) and paleo-Parker Inlet (18 x 106 m3). Likely reasons are the
existence of additional undiscovered paleo-inlets within the Plum Island
lithosome and errors inherent in the methods of backbarrier reconstruction.
Acknowledgements
This study was funded by the US Minerals Management Service, the US
Geological Survey State Map Program, the Boston University Undergraduate
Research Opportunities Program, the American Association of Petroleum
Geologists Grants-in-Aid program, the Clare Booth Luce Summer Research
Fellowship Program, and the National Science Foundation Graduate Research
Fellowship Program. Mary Ellison, Nicholas Cohn, Rachel Scudder, Carol
Wilson, Christine Harrington, Brittany Schwartz, Susana Costas, and Jeff Grey
are acknowledged for their contributions in the field and lab.
References
Bloom, A.L. (1963). “Late-Pleistocene fluctuations of sea level and post-glacial
crustal rebound in coastal Maine,” Amer. Journal of Science, 261, 862-879.
Boothroyd, J.C. and FitzGerald, D.M. (1989). “Coastal geology of the
Merrimack Embayment, SE New Hampshire, NE Massachusetts,” SEPM
Eastern Section Field Trip Guide, June 2-4, 1989.
Chute, N. E. and Nichols, R. L. (1941). “The geology of the coast of
northeastern Massachusetts,” Mass. Dept. Public Works - U. S. Geological
Survey Cooperative Geology Project, 7, 48.
Donnelly, J.P. (2006). “A revised late Holocene sea-level record for northern
Massachusetts, USA,” Journal of Coastal Research, 22, 1051-1061.
Edwards, G.B. (1988). “Late Quaternary geology of northeastern Massachusetts
and Merrimack Embayment, western Gulf of Maine,” M.Sc. Thesis, Boston
Univ., Boston, MA, 337 p.
FitzGerald, D.M., van Heteren, S., and Rosen, P.S. (1993). “Distribution,
morphology, evolution, and stratigraphy of barriers along the New England
Coast,” Tech. Report No. 16, Spring 1993.
FitzGerald, D.M., Buynevich, I.V., Davis, R.A., and Fenster, M.S. (2002). “New
England tidal inlets with special reference to riverine-associated systems,”
Geomorphology, 48(1), 179-208.
Folk, R.L. and Ward, W.C (1957). “Brazos River bar: a study in the significance
of grain size parameters,” Journal of Sedimentary Petrology, 27, 3-26.
Hartwell, A.D. (1970). “Hydrography and Holocene sedimentation of the
Merrimack River Estuary, MA,” Contrib. No. 5-CRG, Univ. Massachusetts.
Hein, C.J., FitzGerald, D., and Barnhardt, W. (2007). “Holocene reworking of a
sand sheet in the Merrimack Embayment, Western Gulf of Maine,” Journal
of Coastal Research, SI 50, 863-867.
Hubbard, D.K. (1971). “Tidal inlet morphology and hydrodynamics of
Merrimack Inlet, Massachusetts,” M.Sc. Thesis, Univ. South Carolina,
Columbia, SC, 144 p.
Jarrett, J.T. (1976). “Tidal prism-inlet area relationships,” GITI Report No. 3,
U.S. Army Corps of Engineers, Vicksburg, MS,”54 p.
Keene, H.W. (1971). “Post glacial submergence and salt marsh evolution in
New Hampshire,” Maritime Sediments, 7, 64-68.
Lyon, C.J., and Harrison, W. (1960). “Rates of submergence of coastal New
England and Acadia,” Science, 132(3422), 295–296.
Massachusetts Water Resources Authority, GBase - Data base of highway and
bridge borings constructed by the Executive Office of Transportation.
McCormick, C.L. (1969). “Holocene stratigraphy of the marshes at Plum Island,
Massachusetts,” Ph.D. Thesis, U. Massachusetts, 104 p.
McIntire, W.G. and Morgan, J.P. (1963). “Recent geomorphic history of Plum
Island, Massachusetts, and adjacent coasts,” Louisiana State Univ., Coastal
Studies Series, no. 8, 44 p.
Oldale, R.N., Wommack, L.E., and Whitney, A.B. (1983). “Evidence for a
postglacial low relative sea-level stand in the drowned delta of the
Merrimack River, western Gulf of Maine,” Quat. Res., 19(3), 325-336.
Oldale, R.N., Colman, S.M., and Jones, G.A. (1993). “Radiocarbon ages from
two submerged strandline features in the western Gulf of Maine and a sealevel curve for the northeastern Massachusetts Coastal Region,” Quat. Res.,
40(1), 38-45.
Reimer, P.J., et al. (2009). “IntCal09 and Marine09 radiocarbon age calibration
curves, 0–50,000 years cal BP.,” Radiocarbon 51(4), 1111–50.
Rhodes, E.G. (1973). “Pleistocene-Holocene Sediments Interpreted by Seismic
Refraction and Wash-Bore Sampling, Plum Island-Castle Neck,
Massachusetts,” Tech. Mem. 40, U. S. Army Corps of Engineers, Coastal
Engineering Research Center, Vicksburg, MS.
Smith, J.B., and FitzGerald, D.M. (1994). “Sediment transport patterns at the
Essex River Inlet ebb tidal delta, Massachusetts, U.S.A.,” Journal of
Coastal Research, 10, 752-774.
Som, M.R. (1990). “Stratigraphy and the evolution of a backbarrier region along
a glaciated coast of New England: Castle Neck-Essex Bay, MA,” M.Sc.
Thesis, Boston University, 184 p.
Stuiver, M. and Reimer, P.J. (1993). “Extended 14C data base and revised
CALIB 3.0 14C age calibration program,” Radiocarbon, 35, 215-230.
Valentine, V. and Hopkinson Jr., C.S. (2005). “NCALM LIDAR: Plum Island,
Massachusetts, USA: 18-19 April 2005,” Elevation data and products
produced by NSF-Supported National Center for Airborne Laser Mapping
(NCALM) for Plum Island Ecosystems Long Term Ecological Research
(PIE-LTER) Project. The Ecosystems Center, MBL, Woods Hole, MA.
Vallino, J.J. and Hopkinson Jr., C.S. (1998). “Estimation of dispersion and
characteristic mixing times in Plum Island Sound estuary,” Estuarine
Coastal and Shelf Science, 46, 333-350.