HEIN AND STONE A5-1

ICE, WATER, AND WIND:

A SOURCE-TO-SINK VIEW OF THE GLACIAL, PARAGLACIAL AND COASTAL SEDIMENTS AND

PROCESSES THAT HAVE SHAPED NORTHEASTERN MASSACHUSETTS

by

Christopher J. Hein1, Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346,

Gloucester Point, VA 23062

Byron D. Stone2, Eastern Geology and Paleoclimate Science Center, U.S. Geological Survey, 101 Pitkin St.,

East Hartford, CT 06108

Email addresses: 1hein@vims.edu,

2bdstone@usgs.gov

INTRODUCTION

Modern geologic maps have revealed the detailed extent of glacial, proglacial-meltwater, paraglacial, and

postglacial deposits across the Merrimack Embayment area of northeastern Massachusetts (Sammel, 1963; Oldale,

1964; Cuppels, 1969; Stone et al., 2006; Hein et al., 2013). Recent offshore mapping studies have located critical

evidence of submerged coastal features, which track the level and age of the late Wisconsinan postglacial marine

regression and latest transgression (Oldale and Wommack, 1987; Oldale et al., 1993; Barnhardt et al., 2009; Hein et

al., 2012, 2013, 2014). This trip will focus on the glacial, proglacial, paraglacial, and postglacial coastal deposits

associated with the regressive and transgressive marine cycles following the retreat of the Laurentide Ice Sheet from

northeastern Massachusetts. Relative sea level during deglaciation of this region reached a maximum of about 31 m

above the present level. Glacial, fluvial and coastal processes resulted in the shaping of drumlins, deposition of

glacial deltas and draped glaciomarine clay, and development of regressive shoreline features and fluvial terraces, all

of which dominate the modern onshore landscape. Many of these deposits have been mapped continuously across

the modern shoreline (Hein et. al., 2013) and into the submerged environment offshore of the barrier islands.

Detailed mapping and stratigraphic analysis extend beyond the 13,000-year-old lowstand shoreline located 45 m

below modern mean sea level (MSL). Reworking of these glacial and post-glacial sedimentary deposits by coastal

processes during the most recent and ongoing marine transgression has culminated in construction of the massive

barriers, beaches, marshes and dunes of the modern coastal zone. This trip will trace the shoreline from its highstand

position at Haverhill, Massachusetts, down the Merrimack River valley, and out to Plum Island, tracking the various

processes and deposits responsible for building the modern landscape. We will discuss how Quaternary glacial and

marine geologists can come together to map continuous surficial geology across the modern shoreline.

PHYSICAL SETTING

Physiography of the lower Merrimack Valley / Merrimack Embayment This field trip covers a region in the lower Merrimack River valley downstream from Haverhill, Massachusetts,

to its mouth in the area known as the Merrimack Embayment, which extends from Cape Ann to north of the New

Hampshire state line (Figs. 1, 2, 3). The Merrimack River basin, 13,000 km2 in area, heads in the White Mountains

of New Hampshire and extends 180 km to the ocean (Fig. 2a). It drains areas dominated by granitic plutons and

other crystalline rocks that have been eroded to produce quartzose, sandy glacial deposits (Fig. 2b). The lower part

of the river flows through coarse, sandy glacial deltas that formed along the retreating ice front in the glaciomarine

highstand sea and in subsequent glacial lakes up valley (Stone et al., 2006). In its coastal reach, the Merrimack

largely flows over till and bedrock before draining into a mixed-energy, tide-dominated, inlet-influenced (FitzGerald

and van Heteren, 1999) embayment in the western Gulf of Maine. The Merrimack Embayment coastal barrier

system consists of a 34-km long series of barriers, tidal inlets, estuaries and backbarrier sand flats, channels and

marshes (Fig. 3). This is the longest such barrier system in the Gulf of Maine. Individual barriers (Seabrook Beach,

Salisbury Beach, Plum Island, Castle Neck and Coffins Beach) are 2–13 km long, generally less than 1 km wide and

are backed primarily by marsh and tidal creeks that typically expand to small bays near inlets (Smith and FitzGerald,

1994). Barriers contain abundant, vegetated parabolic dunes that reach as much as 20 m in elevation. These are best

developed along central and southern Plum Island and Castle Neck, reflecting abundant quartz sand associated with

high rates of longshore transport.

A5-2 HEIN AND STONE

Figure 1. Simplified surficial geologic map and field trip stop locations 1-9 (circled numbers); AP-assembly point.

White labels are geologic map units: d-drumlins and thick till, ld-glaciolacustine deltaic deposit, md-glaciomarine

deltaic deposits, mc-glaciomarine clay deposits, r-regressive deposits, b-post-glacial beach and dune deposits (data

from Stone et al., 2006). Detailed Holocene coastal deposits are shown in Fig. 3.

Bedrock geology and physiography

The broad physiographic features of this area are related to the resistance of the complexly deformed,

metamorphosed bedrock units (Zen, 1983), which have reacted variably to chemical and physical erosive processes

that shaped the bedrock surface during the late Tertiary and Quaternary periods. The local bedrock falls into several

lithotectonic terranes (Hibbard et al., 2006): (1) Avalonia, extending north from Cape Cod, is dominated by

Ediacaran granitoid rocks but intruded by Silurian Cape Ann Granite (Thompson and Ramezani, 2008) near the

mouth of the Merrimack River; (2) the Ganderian Nashoba belt, comprising metamorphosed island arc assemblages

and Ordovician to Devonian granites, that was welded onto North America during the Paleozoic (Hepburn et al., this

volume); and (3) the Merrimack trough composed of Upper Ordovician to Silurian marine clastic rocks and younger

Paleozoic plutons. North of the Clinton-Newbury fault (located 1.3 km south of the mouth of the Merrimack River),

the New Hampshire–Maine Sequence is composed largely of Silurian metasedimentary turbiditic rocks (Berwick

and Eliot Formations) in the western upland area, and Silurian intrusive igneous rocks of the Newburyport Complex

HEIN AND STONE A5-3

along the river and adjacent uplands (Stop 3). Offshore, high-resolution bathymetry shows the submerged outcrop

pattern of these granitic rocks to the east (Hein et al., 2013). South of the fault, the regional Avalon Belt includes

Silurian and Devonian mafic metasedimentary rocks of the Newbury Basin, which underlies the central eastern

lowland of the embayment. These contain red siltstone and sandstone that compose till-stone marker lithologies in

local drumlins and till of Plum Island (STOP 5; Fig. 3). Red sedimentary rocks are bordered by hydrothermally

altered Precambrian granodiorite to the south (Dennen, 1991). Silurian granite and local Devonian-Silurian felsic

volcanics also are included in the Avalon Belt in the map area. A sloping seafloor plain extends eastward from the

central lowland to depths below 85 m west and northwest of Jeffrey’s Ledge, which is a glacially modified

submerged platform composed of coastal plain strata topped by thick glacial deposits.

Across the eastern area, bedrock hills lying below the glaciomarine highstand level (28–32 m) are covered by

only patchy thin till or thin glaciomarine silt-clay, the result of coastal erosion during the postglacial marine

regression. Similar features extend offshore on the ocean bottom. The rock outcrops contain linear and orthogonal

topographic patterns that reflect steeply dipping joint sets, faults, sheeting joints, foliation, and bedding, all of which

facet and shape the extent of outcrops. Structural controls related to Palaeozoic tectonism also have shaped the

coastal and nearshore regions of the western Gulf of Maine. Fault and fold patterns control the configuration of

individual coastal compartments, and the gradients of the coastal lowland and proximal continental shelf control

accommodation available for backbarrier and offshore deposits. Major rivers, such as the Merrimack, drain to the

south-southeast, generally across the structural grain of bedrock, except locally where erosion of weaker rocks by

both fluvial and glacial scouring controls local strike-aligned reaches.

Thick till deposits in drumlins stand in bold relief 20–50 m above the surrounding bedrock surface (Fig. 1). The

highest points of the landscape are underlain by thick till in drumlins: Powwow Hill, Amesbury (101 m); Prospect

Hill, Georgetown (81 m); and Turkey Hill, Ipswich (77 m). In the valleys of the uplands, and across the central

lowland of the area, glaciodeltaic deposits, glaciomarine silt-clay, and recent alluvial, swamp, marsh, and coastal

sediments form a fairly continuous blanket deposit further obscuring relief on top of the bedrock surface. The lower

Merrimack River flows in a narrow, rock-lined reach, below the base of drumlins, incised through glacial sand and

clay deposits. The Parker, Egypt, Rowley, and Ipswich rivers, which drain into the Plum Island Estuary (backbarrier

of Plum Island) similarly are incised into the surficial deposits lowland. The extensive coastal spit and tidal marsh

deposits of Salisbury Beach, Plum Island, Castle Neck, and Coffins and Wingaersheek Beach (Fig. 3) are products

of the late Holocene marine transgression to present sea level. These are pinned to bedrock promontories and high

glacial till deposits in drumlins. Tidal inlets typically are situated in drowned bedrock-controlled river valleys.

Figure 2. Maps of the

Merrimack River drainage

basin (modified from Hein

et al., 2014). (a) Extent of

the Merrimack River

drainage basin. (b) The

distribution of plutons and

sandy glacial deposits in the

Merrimack River drainage

basin (modified from

FitzGerald et al., 2005).

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PREVIOUS WORK

The earliest surficial geologic mapping studies in the Merrimack Embayment quickly followed publication of

the first U.S. Geological Survey 15’ topographic maps in the 1880’s (Shaler, 1889). J.W. Goldthwait (in Antevs,

1922) summarized decades of previous work on the glaciomarine and glacial-lake features of the region in his map

of the recession of the last ice sheet from New England and New York. Detailed geologic mapping in the region

showed the extent of glacial, meltwater, and postglacial deposits (Sammel, 1963; Oldale, 1964; Cuppels, 1969).

These maps differentiated glaciomarine deltas and fans from other glacial-lake deltaic deposits at higher altitudes in

the Merrimack River valley (Koteff, 1976; Koteff and Stone, 2000; Stone et. al, 2006). Regressive marine features

were recognized in later mapping studies of the Merrimack area (Stone and Peper, 1982). Although sparse,

macrofossils were recovered from glaciomarine clay in the Danvers brick pits (Sears, 1906), in the Ipswich

quadrangle (Sammel, 1963), and in sandy beds beneath diamict sediment in Gloucester (Tarr and Woodworth,

1903). The rich assemblage of shells at West Lynn, Massachusetts, provided two radiocarbon dates from the same

shell (Kaye and Barghoorn, 1964) having calibrated ages of 17,410 ± 62 and 16,410 ± 489 (Calib 6.1; Stuiver and

Reimer, 1993), based on standard marine correction of 400 yrs. They could be 600 years younger if further

correction for old marine carbon is warranted. Offshore, dated macrofossils have placed ages on the marine clay

(Birch, 1990), beaches and spits (Oldale and O’Hara, 1980; Oldale et al., 1983; Oldale, 1985; Oldale et al., 1993),

and the post-glacial marine lowstand delta (Oldale et. al., 1993). Correlative deposits in sediment cores (Birch,

1990) have a maximum calibrated age of 16,330 ± 400.

In the Merrimack Embayment, Goldthwait’s 1922 crustal uplift isobases show tilted glaciomarine features

rising linearly from altitudes of 15 m just south of Eastern Point, Gloucester (Cape Ann), to 30 m just north of

Amesbury. The upward-tilt direction of these features is toward N45oW, having a slope of 0.37 m/km. Goldthwait

extended the high glaciomarine inundation through the extensive delta deposits clogging the lower Merrimack

valley to Manchester, New Hampshire. The slope of his marine limit increases to 0.92 m/km in the area of

southeastern New Hampshire along the same direction of tilt. I.B. Crosby and R.J. Lougee (1934) revisited the field

localities of Shaler, Tarr, Goldthwait, Woodworth, Horner, and others, and leveled the altitudes of 39 shoreline

features. From these points they derived an upward tilt direction of N27.5oW, similar to the results of Horner (1929).

Their plot of delta surfaces from Gloucester to Salisbury has a slope of 0.40 m/km, increasing sharply at the New

Hampshire state line. Crosby and Lougee carefully discussed the effects of timing and rates of crustal tilting and

Figure 3. Merrimack Embayment

barrier chain and marine lowstand

delta. (Modified from Hein et al.,

2012). Lowstand shoreline and delta

locations are derived from Hein et

al. (2013).

HEIN AND STONE A5-5

relative sea-level (RSL) rise on plots of tilted marine deltas. They presented diagrams of tilted and curved lines of

the marine limit based on different combinations of these variables. They envisioned the probable stability of the

crust during deglaciation of the region, known from studies of tilted glacial-lake shorelines, and attributed the

increase in tilt of the glaciomarine shoreline to RSL rise. Similar results were obtained by Stone and Peper (1982),

Koteff et.al. (1993). Stone et. al. (2004) reanalyzed the older and some new data for the Merrimack Embayment and

constructed a new RSL curve based on the concepts of Kaye and Barghorn (1964): 1) global eustatic sea-level

changes (Bard et al., 1996), 2) local field evidence of delayed crustal rebound tilt (Stone and Peper, 1982, Koteff et

al., 1993), 3) calibrated radiocarbon ages, and 4) constraining ages from the New England varve chronology (Ridge,

2004). This locally constrained model presents a time interval 11–15 ka during which RSL varied only 10 m, from

-30 to -40 m. This interval is a product of the RSL calculation using eustatic sea-level rise and a simple half-life

rebound tilt function.

Following on the studies of McIntire and Morgan (1964), Oldale et al. (1983) presented an initial empirical

post-glacial RSL curve based on their discovery of a lowstand paleo-delta offshore of the Merrimack River. Oldale

et al. (1993) and Hein et al. (2012, 2013) later refined these curves with the incorporation of new data from the

shallow shelf of the Merrimack Embayment and from the marshes and estuarine sediments of Plum Island. A recent

comparison of RSL reconstructions for northern Massachusetts and coastal Maine (Fig. 4; Hein et al., 2014)

demonstrates notable differences likely derived from the dearth of data in northern Massachusetts between 13.5 and

8 ka. In the absence of additional data, incorporation of the approach of Stone et al. (2004), supported by dated

curves in Maine (Barnhardt et al., 1995, Kelley et al., 2010, 2013) (see Fig. 4), may offer some significant

improvement on this section of the curve and demonstrate more consistent trends across the western Gulf of Maine.

Figure 4. Comparison of Late Pleistocene and Holocene sea-level changes in northern Massachusetts and Maine.

Northern Massachusetts RSL data are from Hein et al. (2012). Coastal Maine RSL data are from Kelley et al.

(2010). Rheologic-eustatic curve derived from Stone et al. (2004).

A5-6 HEIN AND STONE

Early studies of the Merrimack Embayment barrier-island chain developed hypotheses regarding its formation

based on sediment-core data and morphological considerations (Chute and Nichols, 1941; Rhodes, 1973; McIntire

and Morgan, 1964; Boothroyd and FitzGerald, 1989). Later, offshore mapping studies located submerged marine

and coastal deposits, which locate the level and age of the postglacial marine regression and latest transgression

(Oldale, 1985; Oldale et al., 1993). For example, geophysical studies of the nearshore zone of the Merrimack

Embayment revealed the existence of a lowstand paleodelta located approximately 6–7 km offshore and trending

parallel to the present coast (Oldale et al., 1983; Edwards and Oldale, 1986; Edwards, 1988; Barnhardt et al., 2009;

Hein et al., 2013). Together, the results of these coastal and nearshore mapping studies further constrained theories

for the formation of these barrier systems, which place various sedimentological units in their chronostratigraphic

context and treat the evolution of the barrier system with respect to a varying RSL (McIntire and Morgan, 1964;

FitzGerald et al., 1994, Hein et. al, 2013). In these models, shoreline and deltaic sediments were deposited on the

shoreface, directly overlying eroded glacial and glaciomarine deposits, during post-glacial, rebound-induced RSL

fall. Following maximum RSL lowering, coastal processes during the RSL transgression reworked these formerly

stranded deposits into beaches. Stratigraphic units beneath Plum Island show that an initial barrier formed at 6.3 ka

and migrated landward to its present location, which it reached about 3 ka.

QUATERNARY STRATIGRAPHIC FRAMEWORK

Sedimentary deposits in the lower Merrimack Valley and the Merrimack Embayment have mixed glacial,

proglacial, paraglacial and nonglacial origins. Recent surficial mapping efforts by Stone et al. (2006), Barnhardt et

al. (2009) and Hein et al. (2013) show the distribution of bedrock outcrops, Illinoisan and Late Wisconsin glacial

deposits, deposits related to marine highstand, regression and transgression, and post-glacial (on land) and post

transgression (coastal zone, offshore) deposits. Mappable units shown in the field trip map and stratigraphic

successions in exposures and seismic profiles (Hein et al., 2013) provide relative stratigraphic order among deposits

in relation to glacial to nonglacial origins from about 17 ka to present. Fig. 5 is presented here in order to facilitate

discussion of the Middle-Late Quaternary history of the field trip area. Selective age and event annotations shown

on the diagram are derived from the regional array of radiocarbon dates (Kaye and Barghoorn, 1964; McIntire and

Morgan, 1964; Redfield, 1967; Keene, 1971; Oldale et al., 1983; Stone and Borns, 1986; Collins, 1989; Oldale et al.,

1993; Stone et. al., 2004; Donnelly, 2006; Kirwan et al., 2011; Hein et. al., 2012, 2013), the regional varve

chronology (Ridge et al., 2012), regional Be dates (Balco et al., 2009), and the presently known relative physical

stratigraphy of glacial ice lobes (Stone et. al., 2004), glacial lakes and synglacial sea ice-margin positions.

Drumlins and till: Products of Illinoian and Wisconsinan glacial flow (Glacial Period) The dominant glacial deposit throughout the lower Merrimack Valley and Merrimack Embayment is sandy till

of late Wisconsinan age, which drapes the bedrock surface and the surface of numerous drumlin landforms, which

coincide with our present map unit (Stone et al., 2006) of thick till (Fig. 1). Drumlins in northeastern Massachusetts,

like nearly all drumlins in southern New England, contain a core of compact Illinoisan till, smoothed by glacial

movements during the last two glaciations (Schafer and Hartshorn, 1965; Stone, 1989; Newman et al., 1993; Stone

et al., 2004). Drumlins in the field trip area typically are elliptical in plan, varying in length from 0.35 km to 1.65

km, and 0.2–0.8 km in width. Vertical heights of the summit point above the closed contour at the drumlin base and

vary from < 15 m to 54 m. These are likely constraining values for the possible maximum thickness of till within the

drumlins. The position of the summit point of drumlin axes is variable; the group is about equally divided between

hills with crests in the stoss side and those with crests in the lee side. Some clustered drumlins are welded in

composite forms in which individual drumlin crests are aligned in downstream, transverse, and en echelon oblique

directions. The orientation of long axes of drumlins in the Merrimack Embayment describes a fan distribution from

south-southeast trends in the southern and western parts of the area, to mixed trends that include strong easterly

directions in the eastern part. The easterly trend probably is present in drumlins that are submerged along the coast

(Sammel, 1963). Several such clusters of drumlins are identified offshore to a depth of at least 70 m, extending up to

the present-day shoreline in southern Plum Island (Hein et al., 2013; STOP 5) and western Castle Neck. Many

drumlins in the coastal zone have undergone two post-glacial marine regression-transgression cycles, resulting in

extensive erosion and their occurrence on the shelf as rubble lag, visible at low tide at STOP 5.

Till stratigraphy in the drumlins consists of two tills, known regionally as the lower (older) Illinoisan till in the

core, and the upper (younger) late Wisconsinan till at the surface (Fig. 6). At STOP 5 the superposed stratigraphy

consists of a nonweathered lower till that extends down to the bedrock surface. This unit is characteristically

HEIN AND STONE A5-7

compact, clayey silty sand with only 5–10 % gravel-sized rock particles. The volumetric content of stones larger

than 5 cm in drumlin till is probably about 5 %. Boulders larger than 1 m are rare in large excavations. The drumlin-

till matrix (particles less than 2 mm in diameter) contains 22–55 weight % silt and clay. The proportion of clay (3.9

microns particle size) is 6–24 %. Very coarse and coarse sand make up < 10% of the till matrix (Crosby, 1891; as

derived from data from Boston Harbor).

Figure 5. Schematic diagram of the pattern of sedimentation in the lower Merrimack River Valley and the

Merrimack Embayment coastal zone during and following glaciation. Modified from Hein et al. (2014).

Figure 6. Drumlin till stratigraphy and

weathered zone in lower till.

The top of the lower till is characterized by an oxidized zone, typically 3–9 m thick. Weathering effects are

progressive upward through this zone: amount of leaching increases, pH values decline, dissolution of garnets

increases, color values of matrix stain increase, degree and darkness of iron-manganese stain on joint faces increase,

blocky structure increases and is more densely developed, and illuviated clay on vertical joints increases. Laboratory

data showing alteration of clay minerals and iron-bearing minerals further define the weathering gradient. The

weathered zone is the upper part of the C horizon of a probable well-developed soil. The depth and degree of this

weathering zone indicate a long or intense period of weathering, probably during the Sangamon and succeeding

early Wisconsin time prior to advance of the last ice sheet. The base of the weathered zone is subparallel to the

surface of the landform, indicating soil genesis after glacial smoothing by Illinoian ice. The late Wisconsinan till

deposits on drumlins are thin and overlie the truncated weathering profile in the drumlin till, indicating that erosion

A5-8 HEIN AND STONE

and shaping of the drumlins by the last ice sheet did little to reshape many of these drumlin forms. The strong

easterly ice-flow directions, confirmed by fresh bedrock striations, were similar during deglaciation of the last two

ice sheets. Offshore drumlins (Barnhardt et al., 2009; Hein et al., 2013) are identified based on their shape, size,

orientations, occurrence in groups, bathymetric and backscatter characteristics and seismic characteristics. One

offshore reveals that the Holocene transgression nearly eroded the entire drumlin core till, leaving the lower extent

outlined by an apparent ramp of eroded till, probably the upper till with boulders.

Overlying Illinoian drumlin tills is a thin upper till composed of nonsorted, nonstratified matrix of sand, some

silt, and little clay, containing scattered gravel clasts and few large boulders. It is loose to moderately compact,

generally sandy and commonly stony. This is predominantly till of the last (late Wisconsinan) glaciation. Two till

facies are present in some places: a looser, coarser-grained ablation facies, melted out from supraglacial position;

and an underlying, more compact, finer-grained lodgement facies deposited subglacially. Both ablation and

lodgement facies are sandy and stony, and are derived from coarse-grained crystalline rocks. Subsurface till overlies

fresh, nonweathered bedrock and locally weathered rock.

Late Wisconsinan glaciomarine deposits (Proglacial Period)

Coarse- and fine-grained Late Wisconsinan meltwater deposits blanket the lowland in the eastern part of the

field trip area, disconformably onlapping older bedrock, drumlins and till deposits. They are nearly ubiquitous

offshore and are prominent along the coast and extend up the Merrimack River Valley to Haverhill, MA (Fig. 1).

Glaciomarine delta deposits. Glaciomarine deltas in the Merrimack Embayment and river valley are typical

glaciodeltaic morphosequences, characterized by ice-contact slopes on their northerly proximal sides, and lobate

distal foreslopes on their distal sides which merge tangentially with marine-bottom plains (Fig. 7b; STOP 4). Fluvial

beds at the surface and underlying foreset strata have been observed in almost all of these deposits during the past

100 years, so that their identification as ice-marginal glaciomarine deltas is consistent with our present

understanding of the marine inundation. The surface of each delta is a gently sloping glaciofluvial plain, underlain

by delta-topset fluvial sand and gravel, and punctuated by kettle depressions in the proximal part of most deposits.

Deltaic deposits vary from 700–1700 m in width, and 200–2000 m in length. In some examples, ice-channel ridge

deposits extend north in a series of irregular linear forms. Local relief along the ice-contact backslope of these deltas

varies from 8 m to 20 m. Recessional ice-margin position line symbols show the trend of ice-contact slopes

generally to the northeast, but some are deflected around buttressing bedrock and drumlin hills in pocket basins.

Aligned deltas and recessional ice-margin lines in Newburyport-Amesbury and up the Merrimack valley indicate

recession of the ice margin toward the northwest. The positions and sizes of individual ice-marginal deltas in the

Merrimack Valley demonstrate the successive positions and sizes of local depositional basins uncovered by wasting

ice masses during systematic retreat of the stagnant ice zone in this lowland. Ice-contact deltas have distal plain

elevations that reach up to 33 m in Salisbury. The general rise of these surfaces permits their differentiation from

higher glacial-lake deposits along the western part of the area and further southwest along the western margin of the

glaciomarine incursion (Cuppels, 1969; Oldale, 1964; Stone and Peper, 1982).

A generalized diagram of the internal structure of these deltaic deposits is shown in Fig. 7a. The contact at the

base of topset strata and underlying inclined foresets is inferred to be coincident with sea level at the time of delta

deposition. The level probably represents low-tide level, based on observations of modern glaciofluvial distributary

channel scour-and fill processes during low-tide cycles. Topset deposits consist of glaciofluvial sedimentary facies

Figure 7. Glaciomarine delta stratigraphy. (a) Generalized

model of an ice-contact glaciomarine delta. (b)

Glaciomarine delta at Ipswich, MA; topset-foreset contact

and collapse faults behind Harold Nielson.

a

b

HEIN AND STONE A5-9

in horizontally stratified, alternating beds of planar- or cross-bedded gravel and sand. Gravel clasts are well rounded

to subrounded; gravel clasts commonly are imbricated. The sand matrix in gravel beds is poorly sorted, medium to

coarse sand. Individual sets of gravel planar beds or sets of cross beds are less than 1.5 m thick. All beds are

bounded by erosional contacts; individual beds or sets of beds extend laterally as much as 15 m. In the general

model, foreset strata show a progradational sequence from the proximal surface of the delta, but an upward

aggradational sequence from marine fan to upper delta foresets also is possible (J.C. Boothroyd, pers. comm., 1992).

Delta foreset beds have variable dips (15°–40°) and are grouped in disconformable sets, commonly 2–10 m thick.

Sets of foreset beds are planar tabular in proximal parts of deltas and trough-shaped in distal parts. Foreset strata

contain planar, cross bedded, and ripple-laminated beds. Total thickness of foreset beds varies from 2 to > 15 m.

Foreset facies generally intertongue with bottomset beds beneath the distal parts of each delta. Bottomset strata are

subhorizontally layered and contain alternating sets of ripple and planar laminations composed of medium to fine

sand, silt, and clay. Bottomset beds are grouped in conformable flat-lying sets or in disconformable trough-fill sets

that dip less than 10°. Bottomset beds commonly extend gradationally from the lobate depositional front of the delta

to the marine-bottom deposits.

Glaciomarine fan deposits. Glaciomarine fans are ice-marginal morphosequences, smaller than nearby glacial

deltas, and characterized by ice-contact slopes on their northerly proximal sides, and lobate distal foreslopes on their

distal sides which merge tangentially with marine-bottom plains. These deposits do not attain the local level of the

projected general rise of the deltas. Surfaces of fans are variable. Some show an irregular hummocky surface

underlain by sandy and silty sediments. Others have a gently sloping surface plain, underlain by fluvial or marine

littoral sand and gravel that disconformably overlies sandy and silty beds. Fan surfaces do not contain kettles or

sharp ice-contact slopes or ice-channel feeder deposits. Some fans have bedrock outcrops that protrude through the

deposits, indicating anchoring of the deposits around a local bedrock core or glacial-margin grounding point. Fan

deposits vary from 200–1100 m in width and 100–500 m in length. Local relief along the ice-contact backslopes of

these fans varies from 6–10 m. Recessional ice-margin position line symbols show the trend of ice-contact slopes

generally to the northeast. Aligned fans and recessional ice-margin lines in Ipswich indicate recession of the ice

margin toward the northwest.

Glaciomarine-bottom deposits. Finer-grained marine-bottom sand, silty sand, and silt-clay deposits form an

extensive blanket across the area, onlapping the slopes of the older ice-contact deposits. Glaciomarine-bottom

deposits extend continuously offshore (Oldale and Wommack, 1977) where they overlie till and older deposits on

the bottom of the Gulf of Maine. They extend under Plum Island and its associated backbarrier marshes and are

found up to the highstand shoreline in the Merrimack River Valley (+ 33 m), but are discontinuous on land. For

example, this unit does not extend beneath the regressive terrace deposits at the Plum Island Airport (STOP 4).

Marine-bottom deposits are reportedly 18–23 m thick over the deepest parts of the underlying bedrock surface. This

deposit is known locally and throughout New Hampshire and Maine as the Presumpscot Formation (Bloom, 1963;

Thompson and Borns, 1985) and in the Massachusetts Bay area as the Boston Blue Clay (Kaye, 1961) (see trip B5).

This unit ranges in thickness from a thin (< 1 m) drape to > 30 m (McIntire and Morgan, 1964; Rhodes, 1973; Stone

et al., 2006; Barnhardt et al., 2009). It is composed of Lower (glacier-grounding-line proximal) and Upper

(grounding-line distal) glaciomarine units (Belknap and Shipp, 1991). Its strongly micaceous composition suggests

derivation from glacial erosion of metamorphic rocks (Kelley, 1989). Fine to very-fine sand, massive and laminated,

is commonly present at the surface and grades downward into interbedded very-fine sand, silt, and silty clay. Lower

silty clay and clay is massive and thinly laminated (Sammel, 1963; Oldale, 1964; Stone et al., 2006). Thin to thick

(< 10 cm to > 1 m) lenses and beds of fine sand occur as interbedded units within the silty clay. Thin beds in these

sandy units are planar or ripple-laminated, with silty draped laminae over ripples. Solitary pebble and cobble

dropstones reveal the presence of glacial, coastal, or river ice during deposition of most of the unit. In cores, the

uppermost section of tends to be oxidized, as result of subaerial exposure following deposition (Hein et al., 2012).

Late Wisconsinan fluvial deposits (Early Paraglacial Period) River terrace deposits. Postglacial stream terrace deposits along the Merrimack River and smaller rivers are

present at altitudes below the glaciomarine deltas and marine coastal deposits. Terrace segments are discontinuous

and merge downstream with extensive plains at 10–15 m altitudes near the mouths of the rivers. These deposits

disconformably overlie finer marine-bottom deposits. They are composed of fluvial sand and gravel facies, and

pebbly sand facies (Stone et al., 2004, 2005), 1–5 m thick. Along the south side of the mouth of the Merrimack

River, these deposits are subaerially exposed within 5 m of MSL and have provided a flat morphology onto which

the Plum Island Airport was constructed (STOP 4).

A5-10 HEIN AND STONE

River channel cut-and-fill deposits. Fluvial cut-and-fill deposits have been mapped by Hein et al. (2012,

2013) as dendritic structures offshore of the Rowley and Parker rivers, several kilometers south of the Merrimack

River. The absence of evidence of these features offshore of the mouth of the Merrimack River can likely be

attributed to the coarse grain sizes, rather than non-deposition. This unit is composed of sorted and stratified medium

to coarse sands with local gravel-rich and mud-rich layers. Buried fluvial channel deposits extend under northern

Plum Island and southern Salisbury Beach; they are also found under central Plum Island, extending in a dendritic

channel pattern offshore. Under central Plum Island, ground-penetrating radar (GPR) profiles reveal that this unit is

eroded into underlying Glaciomarine silt-and-clay deposits at depths of 11–13 m below MSL (Fig. 8; STOP 7). A

sediment core revealed that this unit is composed of a 5-cm thick layer of mixed coarse sand to large pebbles with

interstitial fine sand overlain by a 25-cm thick sequence of small, sub-angular pebbles in a matrix of very coarse

sand and granules that fines upward to medium sand. Buried sections of this unit were deposited dominantly by

fluvial systems at lower stands of sea level, though locally with some tidal influence. More recent, late Holocene

through 19th

century paleo-channel deposits, < 1 to ~3 m thick, underlie the active channel of the Merrimack River,

southern Salisbury Beach (Costas and FitzGerald, 2011) and northern Plum Island (Nichols, 1942; STOP 8).

Late Wisconsinan marine and coastal deposits (Early Paraglacial Period and Paraglacial Sand Maxima)

Discontinuous, disparate regressive, sand and gravel coastal deposits (barrier beaches, spits, regressive fluvial

deltas) have been identified between the highstand shoreline (+ 33 m) and modern MSL throughout the field trip

area. These continue discontinuously offshore.

Marine beach and spit deposits. These regressive deposits are composed of sand or sand and gravel, and

underlie morphologic features that are similar to the size and shape of modern coastal beaches, spits, and tombolos.

These deposits are smaller and thinner than nearby glaciodeltaic or fan deposits. They characteristically extend as

overlapping sedimentary bodies onto the sides of glaciomarine deposits or drumlin hills that were islands in the

postglacial Merrimack Embayment. In some locations, these deposits extend along the base of steep wave-cut

slopes. In most cases, the surfaces of these coastal deposits are 1–2 m higher than the distal surfaces of local

glaciomarine deltas. Pebbly sand forms a narrow ridge that slopes from 6–19 m beneath High Road south of Rolfe

Lane, and which are inferred to be a river-mouth bar or eroded delta. Other sandy deposits at 15–19 m above MSL at

Newbury Old Town and south of the Parker River are local beach and spit deposits. Coarse sand deposits also

compose the barrier ridge at 12–21 m above MSL beneath Lafayette Road. These deposits were formed by coastal

processes (waves, tides, wind) during falling RSL following highstand. These deposits are distinguished from

regressive-transgressive shoreline deposits in that they have not been modified by the subsequent transgression.

Figure 8. Raw and

interpreted shore-

parallel GPR profile

collected across river

channel cut-and-fill

deposits associated with

the lowstand Parker

River channel. Data

collected with a Mala

Pro-Ex GPR with a 100

MHz antenna. TWTT:

two-way travel time.

Solid vertical white

lines in upper image

indicate locations of

cores. Dashed lines

indicate unit boundary

designations shown in

lower image. Modified

from Hein et al. (2012).

HEIN AND STONE A5-11

Regressive-transgressive shoreline deposits. This subaqueous unit in the Merrimack Embayment is composed

of a continuous, 4–15-m thick deposit of unknown sediment type, capped by surficial lag of medium-coarse sand

and granules, which generate high backscatter in sidescan-sonar data. Deposits are directly overlie glaciomarine silt-

and-clay deposits and are discontinuously capped by finer Holocene deposits. Along its seaward extent, it extends

along and partially overlies proximal sections of the lowstand paleodelta. The surface of the unit is fully exposed in

an 8–10-km wide (perpendicular to the shore) and 16-km long tract east of the modern Merrimack River (Barnhardt

et al., 2009). This mostly transparent unit exhibits little structure in seismic sections.

Lowstand paleodelta. Initial geophysical investigations of the shallow shelf of the Merrimack Embayment

(Oldale et al., 1983, Edwards, 1988) revealed the extent of the submerged Merrimack River lowstand delta located

6–7 km offshore and trending parallel to the present coast. The seaward-prograding lowstand delta foresets are well

imaged in seismic reflection transects (Oldale et al., 1983; Barnhardt et al., 2009; Hein et al., 2013; Fig. 9). This unit

can be divided into three sub-sections in seismic profiles (Fig. 9): 1) the proximal section contains medium to

coarse sand in high-angle delta foreset strata that appear as intermediate angle (5–10o), concave-up, seaward-dipping

foresets in seismic profiles; 2) the intermediate unit contains fine, well-sorted sand and silt in gradually seaward-

shallowing delta-foreset strata; 3) the distal subunit is dominated by gently-sloping delta bottomset beds that directly

overlie glaciomarine clay and silt (Barnhardt et al. 2009; Hein et al., 2013).

Figure 9. Seismic-reflection profile across the Merrimack Embayment (see Fig. 3 for location) collected using an

EdgeTech Geo-Star FSSB system and a SB-0512i towfish (Barnhardt et al., 2009). A constant seismic velocity of

1500 m/s through both water and sediment was used to convert travel time to depth.

Holocene marine deposits (Middle to Late Paraglacial periods) Offshore marine deposits. In depths > 40 m, the seafloor is dominated by fine sand to clay with variable

textures. Shallower sections (ca. 40–50-m depth) grade into the seaward edge of the foreset beds of the lowstand

paleodelta and are sand-dominated with minor silt and clay (< 10%); intermediate sections (ca. 50–70-m depth) are

mud-dominated with significant (> 10%) sand fractions; the finest fractions contain > 95% silt and clay and are

generally found offshore of the 70-m depth contour and grade downward into the upper, distal sections of the

glaciomarine silt-and-clay deposits. This unit is finely laminated in high-resolution seismic data. Its thickness

increases in a seaward direction, exceeding 20 m in deep basins beyond the seaward edge of the paleodelta. Locally,

as a talus apron surrounding subaqueous exposures of bedrock and eroded till, coarse-grained marine deposits

dominate. These are predominantly composed of shell-rich sand, but locally contain significant (> 25%) lithic

gravel. This minor unit is interpreted as an erosional lag deposit from bedrock and boulders exposed on the sea floor.

Nearshore marine transgressive deposits. The shallow (< 45 m) sea floor of the Merrimack Embayment is

discontinuously overlain by transgressive sand sheet deposits composed of relatively well-sorted fine to medium

sand with minor quantities of silt and gravel (Barnhardt et al., 2009). This unit ranges in thickness from < 1 m to ca.

9–10 m. The thickest deposits are located along the shoreface and offshore of southern Plum Island and Castle Neck

(Barnhardt et al., 2009). They extend from approximately the postglacial lowstand shoreline to mean low water,

where they grade laterally into barrier and beach deposits.

Holocene barrier system deposits (Middle and Late Paraglacial and Post-paraglacial periods) The modern barrier systems of the Merrimack Embayment are very similar to those found along coastlines

throughout the world (Fig. 10). Each is bounded by tidal inlets with associated ebb and flood tidal deltas,

backbarriers with marshes, tidal flats and tidal channels, active shorefaces, and dunes of varying heights and degrees

of vegetation. The units comprising these systems remain active, undergoing reworking by modern coastal processes

(wind, waves, tides, storms). Although traditionally lumped as “coastal deposits” in surficial geologic maps, they are

split here based on detailed study of their sedimentological and stratigraphic characteristics and relationships to their

bounding combined onshore and offshore geologic units.

A5-12 HEIN AND STONE

Figure 10. Idealized barrier-

island cross section, extending

from the backbarrier, dominated

by lagoonal, estuarine and/or

salt-marsh deposits, across the

barrier island and into the

nearshore zone and shallow

shelf.

Freshwater Marsh Deposits. At the contact between the modern barrier system and upland areas, as well as

locally preserved at the base of the barrier-island sequence is freshwater marsh deposits. These are composed of

fine-grained organic matter, and fibric and hemic peat that contains minor amounts of stratified and poorly sorted

sand, silt, and clay in poorly drained areas. Most deposits are < 3 m thick and generally overlie glacial sediment or

bedrock. In west-central Plum Island, this habitat has been artificially created by the emplacement of dikes across

the estuarine sediments in the late 1940s. Freshwater marsh deposits also are commonly found at depth, underlying

younger salt-marsh deposits; the contact between freshwater marsh and salt-marsh deposits marks the leading edge

of the late Holocene transgression.

Estuarine deposits. This expansive deposit underlies the entire “Great Marsh” system behind the Merrimack

Embayment barriers and extends under each of the barriers and likely into the shallow nearshore zone, where it is

covered by active beachface and sand sheet deposits. This unit is composed of largely massive, moderately well-

sorted fine sand and silt, dominated by quartz but locally containing > 10% muscovite mica and traces of organic

materials. This unit dominantly contains weak, horizontal to sub-horizontal (< 2o dip), discontinuous reflections in

GPR profiles, with little discernable pattern. Chaotic reflections are also common, as are small-scale (< 1 m,

horizontally) truncations of individual clinoforms. Locally, reflections pinch out laterally and are generally

indistinct, indicating a fairly homogeneous composition of fine sand-sized sediment with minimal internal structure.

However, sets of sigmoid-shaped radar-reflection sets are often visible in upper sections of this unit and correspond

to medium to coarse sand. These are interpreted as former migrating estuarine tidal channels. This unit generally

overlies glaciomarine silt-and-clay deposits and is as much as 20 m thick. It comprises backbarrier lagoonal

sediments, tidal-channel sequences, and flood-tidal deltas.

Salt-marsh deposits. Estuarine sediments are discontinuously overlain by salt-marsh deposits composed of

fine-grained organic matter, and fibric and hemic peat interbedded with fine sand, silt and clay. Sediments are

typically greater than 30% organic and 1–6 m thick. In the major estuaries (Plum Island Sound and the Merrimack

River Estuary), salt-marsh deposits overlie estuarine and/or freshwater marsh deposits. These deposits are generally

found in environments of low wave energy in backbarrier areas.

Tidal inlet channel deposits. Located in the primary inlet channels and proximal backbarrier channels at each

of the inlet systems in the Merrimack Embayment, this unit is composed of thinly-laminated medium to coarse sand

interbedded with coarse sand, medium sand, fine sand, organic laminae and thin lenses of heavy minerals. The base

of this unit is generally composed of coarse sand and granules, reflecting the strong tidal flows transferred through

these inlets. These deposits are deposited by the daily and storm tidal currents that exchange water and sediment

between estuarine water bodies and the coastal ocean. Modern inlet channel deposits receive only minor fluvial

sediments from small local rivers draining into estuarine environments and then through inlets during ebbing tides

(e.g., the Parker, Ipswich, and Rowley Rivers that drain through the modern Parker Inlet channel at the southern end

of Plum Island). Under central Plum Island, GPR profiles reveal a relict tidal inlet at a depth of 2–7 m below MSL

(the “paleo-Parker Inlet”; Hein et al., 2012) in the form of a U-shaped channel that can be divided into two

complexes: a 3.5-m thick northern section dominated by southerly dipping reflections; and a southern complex of

variable thickness (Fig. 11; STOP 6).

Ebb-tidal-delta deposits. Offshore of the primary inlet channels are ebb-tidal deltas, composed of medium to

coarse sand with minor gravel, often with active surface bedforms and exhibiting herringbone ripple stratification

HEIN AND STONE A5-13

and relict bedforms in cross section. This unit ranges from < 1 m to about 4 m thick and are actively reworked by

tidal and wave-generated currents and smoothed by wave action along the seaward edge.

Beachface deposits. Modern beach deposits are deposited along the shoreline by coastal processes (waves and

currents) throughout the tidal cycle. The beachface is defined as the area between mean low water and the dune toe.

It is composed of moderately-sorted, fine to very-coarse sand, which is commonly flat-laminated. Coarser layers

locally contain some granules and fine pebbles; finer layers contain very-fine sand and traces of silt. Beachface

deposits are generally < 5 m thick and overlie inactive estuarine and saltmarsh deposits. Beachface deposits extend

under each of the barrier islands. In the landward 10 % of most barriers they are dominated by storm overwash

sediments, whereas the remaining 90% of the barrier beachfaces grew through seaward progradation and spit

elongation (Dougherty et al. 2004; Hein et al., 2012). Alongshore textural variability is generally controlled by the

texture and proximity of sediment sources (i.e., estuary mouth, eroding glacial deposits).

Dune deposits. Sand dunes in the Merrimack Embayment are composed of mobile, well-sorted, fine and very-

fine sand. The seaward edge of dunes (the “dune toe”) is usually unvegetated and grades from beachface deposits,

with the contact noted as the change in slope of the upper beach face above the storm high-tide line, which marks

the toe of the dune. On the landward side of the unit, dune deposits are underlain by inactive estuarine and marsh

deposits; on the seaward side they are underlain by beach deposits. Internal GPR reflections are commonly chaotic

in nature. This unit is 1–10 m thick. Dune deposits are formed from eolian processes and may be vegetated with

beach grass, beach pea, beach plum shrubs, coastal pine-oak-maple-cherry forest, or may be unvegetated.

Figure 11. Buried inlet sequence at Plum Island, as imaged in GPR profiles. Modified from Hein et al. (2013, 2014).

Profile was collected with a GSSI SIR-2000 with a 200 MHz antenna. Profile will be observed in detail at STOP 6.

QUATERNARY HISTORY OF THE LOWER MERRIMACK VALLEY AND THE MERRIMACK

EMBAYMENT: INSIGHTS FROM SEAMLESS ONSHORE-OFFSHORE SURFICIAL MAPPING

The coastal zone represents the boundary between land, sea and air. It also marks the traditional contact

between marine and terrestrial geological investigations. Through careful study of this transition zone, surficial

geologic units can be seamlessly mapped across these environments (Fig. 12), thereby providing insights into the

overall development of the marine and terrestrial landscapes that would be impossible through traditional,

disciplinary study.

A5-14 HEIN AND STONE

Figure 12. Stratigraphic cross sections of the Merrimack Embayment (see Fig. 3 for locations). (a) Shore-normal

cross section. Eastern half is based on seismic-reflection data (Fig. 9), ground-truthed with surficial sediment

samples and one offshore vibracore. (b) Shore-parallel cross section across four barriers in Merrimack Embayment.

Note: vertical exaggeration of (b) is twice the vertical exaggeration of (a). Modified from Hein et al. (2013, 2014).

A source-to-sink summary of the post-glacial history of the lower Merrimack River Valley and the

Merrimack Embayment Multiple Quaternary glaciations resulted in significant erosion (tens of meters) of coastal plain sediments and

bedrock across the Gulf of Maine, and in extensive scouring of bedrock-controlled fluvial valleys on land. Physical

and chemical weathering of intrusive granitic (with minor gabbro and granodiorities) plutons common to inland

regions throughout the Gulf of Maine, as well as glacial excavation of saprolite, generated much of the sand-rich

sediment that was later reworked into glacial and paraglacial deposits (Hanson and Caldwell 1990; Thompson et al.,

1989; FitzGerald et al., 2005). Ice sheets of the most recent glaciations, the Illinoian and Wisconsinan, left behind

non-stratified glacigenic sediments (drumlins and thin till) throughout the Gulf of Maine and in adjacent New

England. Contemporaneously, meltwater streams drove the accumulation of extensive, quartz-feldspar-rich,

stratified ice-contact sediments throughout the region, both under and in front of the ice sheet. The distribution of

sandy eskers, outwash plains and fans, and coarse sandy ice-marginal deltas reflect the ice-sheet extent and

recession (FitzGerald et al., 2005).

Upper Quaternary glaciation drove complex Late Pleistocene and Holocene RSL changes (Fig. 4) which

resulted from the combined forcings of global eustatic sea-level rise and regional glacio- and hydro-isostatic

adjustments. These set the stage for the redistribution of glacially generated sediment across the across the lower

Merrimack River Valley and the Merrimack Embayment. The resulting stratigraphic units reflect the erosion,

reworking, transport and deposition sediment during and after glaciation. This occurred over multiple periods, each

marked by the deposition of distinct sedimentary units and the formation and modification of specific landforms

(Fig. 5; Hein et al., 2014).

Deglaciation and sea-level highstand (Glacial and Proglacial periods). The Laurentide Ice Sheet of the

Wisconsinan glaciation reached its maximum extent in southern New England between 27 and 23 ka (Balco et al.,

2002; Rittenour et. al., 2012; Stone, 2012). While near its maximum extent, the mass of the Laurentide Ice Sheet

depressed the lithosphere across southern New England. The ice sheet receded northward as climate warmed, exiting

HEIN AND STONE A5-15

present-day Massachusetts by ca 17–16 ka (Borns et al., 2004). Eustatic sea level rose rapidly during this period,

submerging isostatically depressed areas immediately upon their deglaciation in a tidewater setting (Bloom, 1963).

As such, for the period of retreat through the western Gulf of Maine, sediment carried by meltwater streams was

immediately modified by waves and currents. Glaciomarine deposits consist of bedded gravel, sand, and mud

deposited either under the ice sheet (e.g., eskers) or at the front of the retreating ice sheet by meltwater streams

(glaciomarine deltas; grounding-line fans; glaciomarine silt-and-clay).

Isostatic rebound, sea-level fall and lowstand (Early Paraglacial Period). The maximum marine limit was

reached at 31–33 m above modern MSL in northern Massachusetts (Fig. 4) (Stone and Peper, 1982; Oldale et al.,

1983; Ridge, 2004; Stone et al., 2004). It is identified by an ice-contact marine delta at + 30 m in the lower

Merrimack River valley, estimated to be about 16,000 years old. Rapid crustal rebound coincident with deglaciation

resulted in RSL fall and attendant forced shoreline regression. River mouths and channels followed the regressing

shoreline and coastal and fluvial processes modified and redistributed sediments across the open Merrimack

Embayment that developed on the emergent glaciomarine plain. This resulted in the deposition of coarse sand to

gravel as fluvial channel-fill deposits which have been mapped under modern barriers and extending onto the

shallow shelf (Hein et al., 2012, 2013). Upstream, falling base level forced fluvial downcutting and the stranding of

river terrace deposits (alternating layers of gravel and sand, STOP 9, 9A) above modern RSL. Simultaneously,

regressive shoreline sediments were deposited by waves, currents and wind action (Stone et al., 2006).

Discontinuous, disparate remnants of regressive beaches and spits and fluvial terraces have been identified between

the highstand and modern coastlines along much of Gulf of Maine and lower Merrimack Valley (Retelle and

Weddle, 2001; Stone et al., 2006). Off the mouth of the Merrimack River, abundant coarse sediment produced a 10-

km wide deposit that parallels the shore for 16-km and is 4 to 15-m thick (Barnhardt et al., 2009). The exact nature

and origin of this “regressive-transgressive” shoreline deposit remains unknown. It is the subject of intense debate,

even among the authors of this guide (CJH & BDS), who variously argue that it is either a fully regressive, late

Pleistocene fluvial unit, minimally modified in the surface < 1 m by coastal processes during the Holocene

transgressive (CJH), or a chiefly transgressive unit, overlying coarse fluvial beds in local tributary channels to the

low delta, and composed of sandy sediments from the Merrimack River and the erosion of upper beds of the

lowstand paleodelta (BDS).

Continued isostatic rebound resulted in rapid RSL fall as regional uplift outpaced eustatic sea-level rise. By 13–

14 ka, RSL stabilized as rebound decelerated and temporarily matched the rate of eustatic sea-level rise. This

produced a relative marine lowstand at ca. -41 m below MSL (as estimated from the change in slope of the drowned

paleodelta foresets) (Oldale et al., 1993; Hein et al., 2012) or in two calculated lows at ca. 12 and 14.5 ka (Stone et.

al., 2004) (Fig. 4). Deceleration and subsequent cessation of RSL fall led to the deposition of a lowstand delta at the

mouth of the Merrimack River (Oldale et al., 1983). This occurred during a period of large-scale delivery to the

coast of sediments derived from glacial and primary paraglacial deposits within the Merrimack River valley (the

Paraglacial Sand Maxima) (Hein et al., 2014). The resulting lowstand delta is the seaward extent, and significantly-

finer component, of the regressive-transgressive shoreline deposits. It is 20 km long, 4–7 km wide, up to 20 m in

thickness, and lies beneath 41–50 m of water (Oldale et al., 1993). The delta contains ca. 1.3 billion m3 (Oldale et

al., 1983) of fine to coarse, bedded sand and silt deposits.

Late Pleistocene and early Holocene rapid sea-level rise (Middle Paraglacial Period). Following the

lowstand, RSL likely rose rapidly in the Merrimack Embayment, leading to erosion of regressive shoreline and

lowstand deposits. Seismic profiles across Merrimack lowstand paleodelta delta demonstrates the presence of a

smooth, gently-dipping erosional surface that truncates the upper parts of delta foresets, indicating deep scouring

during the early transgression (Oldale et al., 1983). The resulting transgressive unconformity was discontinuously

overlain by transgressive sand sheet deposits composed of relatively well-sorted fine to medium sand with minor

quantities of silt and gravel (Barnhardt et al., 2009). This broad time-transgressive sand sheet formed both from

direct contributions from local rivers (predominantly the Merrimack River) and as a product of the reworking and

winnowing of older transgressive, regressive, and lowstand deposits during the Holocene marine transgression. It

likely also contains smaller contributions from remnants of either past barriers or intertidal to supratidal sand shoals

deposited along the shoreline during the transgression. In its modern form, this unit undergoes varying degrees of

reworking in relation to proximity to the modern shoreline. Along the shoreface, this unit demonstrates significant

textural diversity over short spatial (< 100 m) and temporal (< 1 year) scales and is actively reworked by both tidal

currents and storm waves. Further offshore, this unit is likely only impacted by rare, high energy events

(dominantly, northeast storms). Here, this unit is dominated by low-amplitude (0.3–3.5 m), long-wavelength (150–

A5-16 HEIN AND STONE

900 m) bedforms that demonstrate a variety of orientations. These indicate reworking of the upper portion of the unit

during high-energy events (Hein et al., 2007).

Middle to late Holocene slow sea-level rise (Late Paraglacial Period). Sea-level rise in the Merrimack

Embayment gradually slowed to 0.6 ± 0.1 m/yr by 4–5 ka (Fig. 4). Continuing, but slowed, marine transgression

drove sediments from coastal and river sources farther onshore to the locations of modern barrier systems. Thin and

mobile protobarriers were pinned to contemporaneous emerged drumlins and bedrock outcrops proximal to modern

barrier positions by 4 ka (Hein et al., 2012). There is little evidence of overwash following this original pinning

phase. Abundant GPR profiles collected along Salisbury Beach and Plum Island reveal few overwash deposits along

the proximal landward side of the barriers (Costas and FitzGerald, 2011; Hein et al., 2012). Although preserved

washovers are somewhat more prevalent along the Crane Beach section of Castle Neck (Dougherty et al., 2004),

evidence of progradation, aggradation and spit elongation generally dominate (greater than 90%) barrier widths

(Hein et al., 2012).

Freshwater marsh deposits, composed of organic matter and peat that contains minor amounts of stratified and

poorly sorted sand, silt, and clay, formed at the leading edge of the transgression (e.g., McIntire and Morgan, 1964).

This was followed by the deposition of massive, moderately well-sorted fine sand and silt. These estuarine deposits

comprise backbarrier lagoonal sediments, tidal channel sequences and flood tidal deltas. This unit was generally

sourced from offshore deposits (regressive fluvial shorelines and deltas) and moved onshore by wave and tidal

processes during the landward migration of proto-barrier systems. Finer sediment was transported by tidal currents

to the backbarrier through inlets and additional sediment was likely derived from upland deposits (e.g., bluff

erosion, small streams with local drainages, etc.). Coarser units were generally deposited by overwash and inlet

breaching during the landward migration of the barrier system; finer sediments were transported by tidal forces to

the backbarrier through inlets and were reworked by tidal and locally-wind-generated waves and currents (Hein et

al., 2012). Within these estuarine deposits are tidal channel-fills, deposited by migrating backbarrier tidal channels

and tidal inlets. One such inlet-fill sequence (the “paleo-Parker Inlet”) was identified under central Plum Island

(STOP 6), highlighting the role played by backbarrier infilling and tidal-inlet closure in barrier formation: inlet

closure was driven by the reduction of bay tidal prism over time by backbarrier sedimentation and was closely

followed by the rapid expansion of backbarrier marshes and the aggradation, elongation and progradation of the

barriers themselves (Hein et al., 2011, 2012).

Fresh and brackish marsh deposits initially formed at the leading edge of the transgression (McIntire and

Morgan, 1964). The cause and timing of subsequent salt-marsh expansion in Merrimack Embayment estuaries has

been attributed to a late-Holocene decrease in the rate of RSL rise. Most observations suggest a rapid transition from

barren tidal flats to well-developed high marsh around or after 4 ka (Oldale, 1989; FitzGerald et al., 1994).

The Merrimack Embayment in the Anthropocene Unlike many barrier islands throughout the world, the Merrimack River barriers, including Plum Island, are

generally stable. They remain progradational and, except locally (i.e., the southern tip of Plum Island), show few

signs of retreat and migration. However, these systems remain dynamic, responding to the coastal processes of wind,

waves, storms and tides. This is especially the case proximal to tidal inlets, where complex river / inlet / tidal-delta

interactions create highly dynamic depositional settings. Although most of the barriers of the Merrimack

Embayment remain in semi-natural states, both Seabrook Beach and northern Plum Island are developed. The final

stops of this field trip will be on the beaches of northern Plum Island, within the town of Newbury, and is thus the

focus of the history of Anthropocene modifications.

Plum Island was first settled as pasture land in the early-1600s (Waters, 1918). The island was sub-divided

between the towns of Newbury (2/5), Ipswich (2/5) and Rowley (1/5) in 1649 (Toppan, 1905) and by the late 19th

century had become a popular tourist destination featuring several large hotels and private homes. The PRNWR was

established across parts of the island and its backbarrier in 1942, followed more recently by the Sandy Point State

Reservation (Mass. Department of Conservation and Recreation). Today, the northern 1/3 of PI is shared by the

towns of Newbury and Newburyport. Located immediately seaward of the harbor of Newburyport and downstream

of the important mill towns of Lawrence, Lowell and Haverhill, the entrance to the Merrimack River at the northern

end of Plum Island quickly became a critical pathway for commercial and, later, recreational boating. However,

driven by processes of southerly longshore transport, spit elongation and ebb-delta breaching, the Merrimack River

Inlet at that time actively migrated across the area currently covered by southern Salisbury Beach and northern Plum

HEIN AND STONE A5-17

Island (Figs. 13, 14). This caused not only periods of severe erosion and accretion along proximal sections of these

barriers. Following a significant ebb-delta breaching event in the mid-1800s, a large sediment bar welded onto the

northern end of Plum Island, forming the landward-most piece of the eastern “fork” of northern Plum Island, and

abandoning the former river channel in what is today known as “The Basin”, an estuarine lowland between the east

and west forks of the northern section of the island (Fig. 15; FitzGerald, 1993). The US Army Corps of Engineers

(USACE) initiated a series of public works projects at the mouth of the river in the 1880s to stabilize the Merrimack

River Inlet in its new configuration for navigation purposes (Fig. 15). These included the construction of North and

South Federal Jetties, the latter of which was lengthened in the late 1960s.

The inlet stabilized by these jetties is periodically dredged by the USACE. The fate of the spoils has varied over

time, including dumping both offshore or directly on the beach face as beach nourishment. Several groins were also

installed along the northern sector of Plum Island around this same time. This section of the barrier is now densely

populated (ca. 1200 homes and > 100 roads), but has experienced long-term erosion at rates of ca. 0.2 m/yr

(averaged from 1850–2000) and nearly 0.5 m/yr in the past 30 years (EOEEA, 2010). Over longer timescales,

shoreline retreat is not a steady state, or a storm- or season-linked process, but includes variability over small areas

and varying timeframes; this variability is central to understanding the overall sediment dynamics of the barrier. For

example, abundant evidence indicates the existence of a decadal-scale cycle of erosion and accretion along northern

Plum Island. Refraction of northeast storm waves around the ebb-tidal delta seaward of the Merrimack River jetties

causes a reversal of net longshore transport, driving sediment north across the developed portion of the shoreline and

“leaking” sand back into the inlet through degraded sections of the jetty. While this reversal has created a broad

accretional deposit adjacent to the inlet, it is at the expense of beach to the south. Superimposed on the local

transport system are smaller-scale variations in refraction and wave energy along the shore which appear to

correspond to shifting bars on the ebb-delta platform. Shifting of these shoals creates specific erosion hotspots that,

when active, can focus severe erosion on a small portion of the developed barrier, while leaving other areas stable or

accretionary (EOEEA, 2010). These hotspots can last months to years in an aperiodic pattern.

Beginning in the late 1950s and early 1960s, a range of beach structures, including groins and riprap seawalls

were constructed as a result of this cyclic erosion; many have been lost to erosion since then. Recent erosion-

mitigation techniques have included the installation of “geotubes” (2008), hay bales and coir rolls (2009, 2010),

beach nourishment (2010), and, most recently, controversial citizen-led programs of beach-scraping (2011, 2012),

the construction of rip-rap revetments (2013) and artificial nourishment (2013–2014). Nonetheless, severe erosion

persists, exposing groins and revetments from earlier periods of erosion, and threatening residential and commercial

properties along the shoreline with every high-energy event. The variability in the timescales and patterns of beach

erosion at Plum Island has contributed to the lack of any unified understanding, policy, or response to erosion when

it does threaten structures. This is compounded by generation-long (multi-decadal) cycles of accretion, which

contribute to a belief in holding ground during erosion cycles until the accretion area moves down the beach again.

Figure 13. Northeastern section of the map of the Town of

Newbury by Philander Anderson, 1831. Note the absence of

the northern section of Plum Island and the southerly

extension of Salisbury Beach.

A5-18 HEIN AND STONE

Figure 14. Ground-penetrating radar section collected with a Mala Pro-Ex GPR with a 100 MHz antenna across

southern end of The Basin, the early 19th

century channel of the Merrimack River. Time-depth conversion uses a

depth-averaged radar velocity of 8.5 cm/ns and ground-truthed with sediment core (Geoprobe core PIG26). Note

eastward-dipping reflections signifying eastward migration of the river / inlet. This former channel was abandoned

as the river breached the ebb-tidal delta to the north, truncating southern Salisbury Beach.

Figure 15. Changes at the mouth of the Merrimack River prior to and following construction of the jetties. Modified

from the The Daily News of Newburyport, as derived from Nichols (1942) and earlier USACE maps.

Glacial and paraglacial sediment sources and coastal sediment sinks of the Merrimack Embayment Previous studies have identified a number of likely sediment sources that contributed the Merrimack

Embayment barrier system. Based on their experience studying the development of the Boston Harbor Islands,

Chute and Nichols (1941) proposed that the barriers in the Merrimack Embayment formed relatively recently, from

the in situ erosion and reworking of drumlins during the latest stages of the modern transgression. Although the

modern shoreline is dotted with subaerial drumlins and nearshore boulder lag deposits from eroded drumlins, the

possible sediment contributions from these features is dwarfed by even conservative estimates of the sediment found

comprising the barriers (~75 x 106 m

3; Table 1).

Paraglacial sedimentary deposits on the shallow shelf (regressive-transgressive shoreline deposits, lowstand

delta) provide a second possible source for the Merrimack Embayment barriers. Derived largely from primary

glacial and proglacial deposits upstream in the Merrimack River Valley, these shelf deposits serve as both long-term

and temporary sediment sinks in the system. For example, seismic records show that the upper portion of the

paleodelta foresets are truncated (Fig. 9), indicating that the surface of the delta was reworked during the early

Holocene transgression (Oldale et al., 1983; Barnhardt et al., 2009). FitzGerald et al. (1993) present a four-stage

evolution for the system in which sediments of the upper paleodelta were eroded during the early transgression,

reworked onshore as an expansive sand sheet, and pinned to drumlins and shallow till and bedrock between 5 and 4

HEIN AND STONE A5-19

ka. While much of this general evolution is accepted, shallow vibracores through the paleodelta foresets (Edwards,

1988) show that delta is composed of fine sand to silt, as opposed to the barrier which is dominated by fine to coarse

sand. Recent studies have identified the coarse grained (sand to gravel) regressive-transgressive shoreline deposits as

a secondary source for the sediments comprising the barrier system. This unit represents, at least to some degree, a

lag deposit of the most recent transgression. Sediments eroded from this unit were a likely source for sediments that

formed the Holocene shelf sand sheet and barrier systems (Hein et al., 2007; Barnhardt et al., 2009; Hein et al.,

2013, 2014).

Table 1: Sediment reservoirs associated with the Plum Island barrier system.

System Type Name Est. Sediment Volume Data Sources / References

Barrier Beaches Plum Island 2.95E+07 Hein et al., 2012

Castle Neck 2.10E+07 Dougherty et al., 2004

Coffins Beach 8.50E+06 McKinlay, 1996

Salisbury Beach 6.80E+06 Costas and FitzGerald, 2011

Seabrook Beach 3.64E+06 Costas and FitzGerald, 2011

Hampton Beach 3.42E+06 Estimated

Backbarriers Plum Island, Castle Neck &

Salisbury Beach backbarriers 8.50E+08 Hein et al., 2011

Tidal Deltas Merrimack River ETD 1.20E+07 Hubbard, 1971

Parker / Ipswich ETD 2.43E+07 FitzGerald, et al., 2002

Essex River ETD 1.04E+07 FitzGerald et al, 2002

Annisquam River ETD 8.58E+06 FitzGerald, unpublished

Essex River FTD & Sand Shoals 9.40E+06 Rhodes, 1973

Nearshore

Holocene

Reservoirs

Mobile Sand Sheet 1.21E+08 Barnhardt et al., 2009

Unmapped Nearshore Sand

Sheet 1.36E+08 Estimated

Shallow Shelf

Pleistocene

Reservoirs

Lowstand Paleodelta 1.30E+09 Oldale et al., 1983

Regressive / Transgressive

“Braidplain Delta” undetermined N/A

A final source of sediments for the Merrimack Embayment barriers is the rivers draining into the coastal zone.

Three small rivers currently discharge into the backbarrier of Plum Island: the Ipswich River (drainage area [A]: 402

km2; annual freshwater discharge [Q]: 0.56 km

2), the Parker River (A: 167 km

2; Q: 0.033 km

2) and the Rowley

River (A: 36 km2; Q: negligible [tidal]) (Sammel, 1967; Simcox, 1992). Although these may have contributed some

inorganic sediment to the development of the backbarrier marsh system in the past (e.g., Kirwan et al., 2011),

modern flow is dominated by tidal fluxes and sediment exports are minimal. The only estuary in this system with

significant freshwater discharge is the Merrimack River, which has an average discharge of 6.5 km3/yr and total

suspended sediment load of 0.2 Mt/yr (Milliman and Farnsworth, 2012). Dredging operations from the Merrimack

River Inlet over a 62 year period removed 2.6 x 106 m

3 of sand and gravel, suggesting an average annual deposition

rate of 4.16 x 104 m

3/yr since the mid-1900s (Hein et al., 2012), a time of reduced sand and gravel supply as

compared to earlier in the Holocene (Fig. 5). This sediment ranges in size from fine to coarse sand and granules.

Southerly- and ebb-oriented bedforms within the ebb-tidal-delta complex seaward of the jetties indicate southerly

migration, corroborating sedimentologic evidence of a southerly-fining trend across the ebb delta, and a general

trend of increasing textural and mineralogical maturity to the south, away from the Merrimack River. This trend

reflects winnowing and differential transportation of finer sand grains by wave action (FitzGerald, 1993; FitzGerald

et al., 2002) and demonstrates the dominance of southerly longshore currents and the continued contribution of

sediment to the Merrimack Embayment barrier system by the Merrimack River. These recent findings suggest that it

is likely that the barriers of the Merrimack Embayment formed from a combination of the truncation of paleodelta

forsets, winnowing of the regressive-transgressive shoreline deposits, and a continual fluvial source (Hein et al.,

2012).

The magnitudes of changes in the relative contributions from each of the major sediment sources (fluvial

erosion and reworking of upstream glacial and paraglacial deposits; erosion and reworking of shallow shelf and

A5-20 HEIN AND STONE

nearshore glacial and paraglacial deposits by coastal processes during RSL rise) over time are currently unknown

(Fig. 16). Detailed mapping and sampling of the shallow shelf offshore of the Merrimack Embayment (Barnhardt et

al., 2009; Hein et al., 2013) has revealed the existence of several large bedform fields formed by coastal “set-up”

during intense extratropical cyclones that regularly affect the coast (Hein et al., 2007). The result is a medium-term

(101 to 10

10 yrs) sand-circulation gyre that may actively exchange sediment with the barrier system (Hein et al.,

2007). However, the rates and net-mass fluxes between the barrier and nearshore, and how these fluxes will be

affected by climate change (SLR, changes in storminess), remain unknown. Thus, there is an enhanced reliance on

new sediment inputs from local rivers for continued barrier stability. The Merrimack River, the ultimate sediment

source for all post-glacial subaerial and subaqueous deposits in the Merrimack Embayment, has undergone extensive

anthropogenic modifications which have decreased the sediment supply from the river in recent centuries. Major

dams were constructed along the river in the 19th

century, most notably at Lowell (1820s) and Lawrence (1847).

Additionally, large river-dredging projects below Lowell were carried out beginning in the 1870s as part of an effort

to create a navigable waterway on the Merrimack River from Newburyport to Lowell (Bradlee, 1920). While major

dredging of the river in recent decades has been centered at the mouth of the Merrimack under the aegis of the

USACE, hydraulic changes to river’s channel and sediment loading are a product of the many historic alterations to

the land and streams within the Merrimack Valley. This, combined with the natural stabilization of slope, terrace

and floodplain deposits, and the river channel, by bedrock knickpoints and vegetation cover, has greatly reduced

fluvial sediment supply to the Merrimack Embayment over time.

Figure 16. Conceptual model

of the spatial and temporal

scales of the factors

influencing sediment supply

to the Merrimack

Embayment.

SOURCES AND ACKNOWLEGEMENTS

Portions of this text were derived and edited from Stone et al. (2004), Stone et al. (2006), Hein et al. (2012)

Hein et al. (2013) and Hein et al. (2014). The authors wish to thank the following landowners and organizations for

permission to observe geologic features on their properties: farm gravel pit Haverhill, Plum Island Airport, and

Nancy Pau and Matt Poole of the Parker River National Wildlife Refuge. Editor Meg Thompson solicited this trip

and remained supportive during the final editing stages.

HEIN AND STONE A5-21

FIELD TRIP ROAD LOG

This trip will leave from the MARKET BASKET parking lot in the HAVERHILL PLAZA SHOPPING

CENTER, 285 Lincoln Ave, Haverhill, MA at 8:15am. Directions are given from Wellesley College to the meeting

location. Road Log is listed in cumulative miles, beginning at STOP 1. Times are cumulative within direction sets.

Street addresses and GPS coordinates are included in each STOP and DRIVEBY locality. Future users of this road

log are reminded that all STOPS are on private or publically administered property; it is the responsibility of future

visitors to request permission from the land owners to visit these locales. Maps used in trip stop locations for STOPS

1-6 are the USGS 7.5-minute, 1:25,000-scale topographic quadrangles. For STOPS 7 and 8, map is from NOAA

Chart 13282, Newburyport Harbor and Plum Island Sound. Black asterisks on maps show stop locations.

Roads on this trip are paved and in good condition, with the exception of the road to and from STOP 6, which is

a dirt road through the Parker River National Wildlife Refuge (PRNWR). There is also limited parking at STOPS 6

and 7. Thus, STOP 5 will be a brief stop in a large parking lot just beyond the entrance to the PRNWR, on our way

south to STOPS 6 and 7. At STOP 5, we will combine into as few vehicles as possible, leaving others behind.

Restroom facilities are also located at STOP 5. We will return to STOP 5 for our final stop, STOP 8.

Mileage Time Directions (Wellesley College to Haverhill Plaza Shopping Center [Meeting Place])

00.0 0 min (UTM 19N: 310343 E, 4684951 N) Start at Wellesley Science Center Parking Lot.

00.6 5 min Make left on Washington St. from Wellesley College

01.2 8 min Turn right onto MA-16 E / Washington St.

04.4 15 min Make slight right to merge onto I-95 N / MA-128 N toward Portsmouth, NH

44.7 55 min Follow I-95 N (do NOT follow signs for 128N). Take exit 54B from I-95 to MA-133 W

toward Georgetown

51.1 1 hr, 12 min Follow MA-133W and MA-97N onto Groveland St. in Haverhill, MA; cross over

Merrimack River

51.2 1 hr, 13 min Make second left after the bridge (immediately after Gulf station) onto Lincoln Ave.

51.3 1 hr, 14 min Make left into Haverhill Plaza Shopping Center (UTM 19N: 333272 E, 4736621 N)

Mileage Time Directions (Haverhill Plaza Shopping Center [Meeting Place] to STOP 1)

00.0 0 min Start (8:15am) at Haverhill Plaza Shopping Center (UTM 19N: 333272 E, 4736621 N)

00.1 1 min Make right onto Lincoln Ave.

00.2 2 min Turn left (west) onto Groveland St.

00.7 4 min Turn right (NE) onto East Broadway

01.5 7 min Turn left onto Eves Way

01.5 8 min Turn right onto Seven Sister Rd.

01.6 9 min Arrive at STOP 1, at 78 Seven Sister Rd.

A5-22 HEIN AND STONE

STOP 1: SEVEN SISTER DRUMLIN (30 MINUTES) – start at 8:30am

(UTM 19N: 333718 E, 4737621 N)

Figure 17. Topographic map showing the location of STOP 1.

This stop is along the Seven Sister Rd. in a new(ish) housing development built atop the Seven Sister Drumlin.

Note the similarities in the subaerial forms of the drumlins proximal to STOP 1 and those along the coast, proximal

to STOP 6 (Fig. 18). The stratigraphically lower Illinoisan till is exposed in the cores of both hills. Typical of the

area (Weddle et al., 1989) the lower till has a dark gray (5Y 3.5-5/1) clayey silt matrix of low plasticity and medium

dry strength, small medium-coarse sand component, and scattered pebbles and few small cobbled-size gravel clasts.

Principal axes of elongate gravel clasts show a northwesterly preferred direction of shallow dip. The oxidized zone

of the lower till is exposed beneath sandy till of the mixed-till zone at the top of the small drumlin. Effects of

weathering can be seen to increase upward in the oxidized zone above a transitional contact with underlying gray

till. Color values of matrix stain increase from olive-olive gray (5Y4-5/2-3) at the base to olive brown 2.5Y 4-5/3-5).

Oxidized halos in matrix surrounding individual garnet grains can be seen at the top. The degree and darkness of

iron-manganese stain on joint faces increase. Blocky structure increases and is more densely developed along

horizontal and vertical joints. The extent of the excavation in the small drumlin reveals that the base of the

weathered zone is subparallel to the surface of the landform, indicating prolonged or intense soil genesis after till

deposition and glacial smoothing in the Illinoisan. The mixed zone of weathered and fresh lower till fragments

within a sandier Late Wisconsin till matrix is present in the upper 2 m of the excavation. Soils developed in the

surface till and mixed-till zone since late Wisconsinan deglaciation are inceptisols, characterized by B-horizons that

contain < 20 percent illuviated clay, and weakly modified clay mineralogy. Typically, Canton and Charlton soils

series develop in the surface tills, and the Paxton soil develops in the thin mixed-till zone on drumlins (Fuller and

Holtz, 1981).

HEIN AND STONE A5-23

Figure 18. LiDAR maps of drumlin patches. (a) LiDAR imagery from vicinity of Seven Sister Hill drumlin (STOP

1), from 2011 MassGIS LiDAR imagery database. Elevations range from +80 m (light shades) to -1 m (Merrimack

River; dark shades). (b) LiDAR imagery from vicinity of South Plum drumlin at the southern tip of Plum Island

(STOP 6). Data from the Plum Island Ecosystems Long-Term Ecological Research project (Valentine and

Hopkinson, 2005). Elevations range from +40 m (Plover Hill; light shades) to -2 m (water; dark shades).

Mileage Time Directions (STOP 1 to STOP 2)

01.6 0 min Start at STOP 1. Head back out Seven Sister Rd.

01.6 1 min Make a left onto Eves Way

01.6 2 min Make a left (northeast) onto East Broadway

04.5 8 min Make hard left onto Country Bridge Rd.

04.5 9 min Arrive at STOP 2; park alone side of road.

A5-24 HEIN AND STONE

STOP 2: KIMBALL HILL FARM PIT (60 MINUTES) – start at 9:30am

(UTM 19N: 334794 E, 4740280 N)

Figure 19. Topographic map of drumlins, glaciomarine deltas, terrace, and alluvial flood plain deposits at STOP 2.

The topographic map of the area (Fig. 19) shows flat delta topset plains at 30 m altitude of at least four ice-

marginal glaciomarine deltas. These extend continuously from Rocks Village to Kimball Hill thick till deposits and

two other thick-till hills to south of Millvale Reservoir. Either previous pits south of Greenwood cemetery or the

active pit on Country Bridge Road will be STOP 1, depending on pit conditions and landowner permissions. We

hope to see field examples of features shown in Fig. 7. Numerous other glaciomarine deltas are at this altitude down

valley to Newburyport. Thus, all deltas here are aligned more or less with the crustal-uplift isobases of Goldthwait

(in Antevs, 1922), Koteff et. al. (1995), who use some topset/foreset data from these pits, and Stone et. al. (2004).

Note the wide stream terrace deposit at 12 m altitude, and the wide alluvial flood plain at 3 m altitude south of

Kimball Hill. As you drive to the next stop, note how the river is deeply incised into the glacial deposits, and is not

bordered by a wide flood plain. The river here has been transgressed by the sea. The river is tidal and part of the

estuary.

DRIVE BY: The route to STOP 2 takes you along a textbook example (BDS) of the erosional contact between the

glaciomarine deltaic deposits in Newburyport and the highest regressive post-glacial river-terrace deposit that

resulted from crustal uplift and tilting. This scarp contact can easily be seen along Ferry Road at the 80-ft surface

and High Rd, at the 50 ft surface.

Mileage Time Directions (STOP 2 to STOP 3)

04.5 0 min Start at STOP 2. Return along Country Bridge Rd. towards East Broadway

04.6 1 min Turn left onto East Broadway; continue onto East Main St.

05.1 3 min Turn left onto River Rd. and follow road along Merrimack River (to your right)

08.2 8 min Turn right onto Pleasant Valley Rd. ; turns into Merrimac St. (13.1 mi) (stay right)

13.5 14 min Take first right onto Main St.; road turns into Evans Pl. and then back to Main St.

14.1 19 min Cross Merrimack River on Main St.; turns into Spofford St.

14.3 20 min At traffic circle, go straight to stay on Spofford St.

14.4 21 min Make a slight left onto Ferry Rd.

14.6 22 min Merge onto High St. / MA Rt. 113

15.2 25 min Turn right onto Toppans Ln.; turns into Hale St.

15.9 30 min Turn left down road to Little River Hale St. Stop; park along road

HEIN AND STONE A5-25

STOP 3: LITTLE RIVER HALE STREET GLACIOMARINE OUTCROP (30 MINUTES) – start at 11:00am

(UTM 19N: 344215 E, 4740517 N)

Figure 20. LiDAR map of bedrock outcrops and areas of shallow bedrock exposed above the top of eroded

glaciomarine clay of the Presumpscott Formation. (a) Location of Stop 3 (symbol) on topographic map, 3 m contour

interval. (b) LiDAR imagery from 2011 MassGIS LiDAR imagery database.

At this stop you can evaluate the control by rock fractures of outcrop size, shape, and relief of relatively

homogeneous intrusive rocks of the Silurian Newburyport Complex (SOngd) granodiorites of the New Hampshire-

Maine sequence. The outcrops, shown by lighter shades of gray in the LiDAR data (Fig. 20), are clustered, showing

orthogonal topographic expression. In marine high-resolution bathymetric surveys to the east, similar contrasting

shades, shapes, and bathymetric expression also reveal mappable outcrops and areas of shallow rock surrounded by

eroded till or glaciomarine clay of the Presumpscot Formation.

Mileage Time Directions (STOP 3 to STOP 4)

15.9 0 min Start at STOP 3. Return to Hale St. and make right

16.3 2 min Continue on Hale St. back onto Toppans Ln.

16.6 4 min Make right onto High St.

18.4 11 min Make left onto Rolfes Ln.; turns into Ocean Ave.

18.8 13 min Make right onto Water St. at end of Ocean Ave.; Pass entrance to PRNWR Visitor’s

Center; Water St. becomes Plum Island Turnpike

19.3 15 min Arrive at Plum Island Airport (STOP 4) parking lot on right. Park in lot.

A5-26 HEIN AND STONE

STOP 4: PLUM ISLAND AIRPORT FLUVIAL TERRACE (60 MINUTES, including lunch) – start at 11:45am

(UTM 19N: 349444 E, 4739823 N)

Figure 21. Topographic map of the regressive deposits and recent back-bay marsh at Stop 4.

The Plum Island Airport and our USGS drilling site are located on a very low flat plain, which straddles the 3 m

contour and dips very slightly to the east. This plain is considered to be the lowest regressive river terrace along the

Merrimack River. Take time to view the extent of the plain and its relief above the river (Figs. 1, 21). The corehole

revealed about 19 ft of medium to coarse sand with some pebbles in the upper part, and cobble gravel at the base.

This fluvial sequence overlies fine, nonoxidized sand with some silt to a total depth of 52 ft. We did not encounter

organic sediments or fine back-bay deposits that underlie the coastal marsh to the east. Thus, the low terrace sits

disconformably on slightly older Pleistocene deposits related to the post-glacial marine regression. The topography

and position of Stop 4 (Fig. 21) show why drilling operations were challenged in these low-lying deposits. Extreme

heaving of sand into the core barrel stopped us at 52 ft. Proximity and permeability of regressive marine deposits to

the west provide a direct path for ground water flow from the water-table mound to the drill site.

Mileage Time Directions (STOP 4 to STOP 5)

19.3 0 min Start at STOP 4. Make right (east) onto Plum Island Turnpike from airport parking lot.

Cross over Plum Island River via Plum Island Turnpike

20.7 5 min Turn right onto Sunset Dr.

21.2 7 min Go through entrance to Parker River National Wildlife Refuge (PRNWR) (no fee

required if with field trip group); road becomes Refuge Rd.

21.3 8 min Make left into large parking lot (Parking Lot #1) of PRNWR (STOP #5/8)

HEIN AND STONE A5-27

STOP 5: PRNWR PARKING LOT #1 (5 MINUTES)

(UTM 19N: 352078 E, 4739076 N)

Figure 22. Topographic / bathymetric map of northern Plum Island showing the location of PRNWR Parking Lot #1

(STOP 5).

This is a brief stop for use of the restrooms and to consolidate into as few vehicles as possible (there is limited

parking at STOPS 6 and 7). Extra vehicles can be left in parking lot, which is the location of the final stop (STOP 8)

of trip. Trip will leave PRNWR Lot #1 to continue to STOP 6 at 1:00pm. The drive to STOP 6 will be partially

along a flat, dirt road. Please plan accordingly.

Mileage Time Directions (STOP 5 to STOP 6)

21.3 0 min Start at STOP 5 in as few vehicles as possible. Make left onto Refuge Rd.

27.6 20 min Drive (slowly!) to Sandy Point State Reservation at southern tip of Plum Island. Note that

road becomes dirt at 3.5 miles along route. Arrive at STOP 6 (small dirt parking lot on

left) and carefully find parking. Additional parking is available along road to right,

another 0.2 miles down. If needed, walk back to STOP 6 from overflow parking lot.

A5-28 HEIN AND STONE

STOP 6: SANDY POINT DRUMLIN (30 MINUTES) – start at 1:20pm

(UTM 19N: 354797 E, 4729596 N)

Figure 23. Topographic / bathymetric map of southern Plum Island showing the location of STOP 5, at Sandy Point

State Park. Parking is just north of South Plum drumlin.

The southern tip of Plum Island is occupied by a lone drumlin (South Plum) which rises above the relatively flat

topography in front of you when driving south. South Plum is one of a patch of drumlins, including Cross Farm Hill

ca. 1.5 km to the north and the drumlins that make up Plover Hill and Little Neck on the mainland (west) side (in

Ipswich, MA) and Castle Hill across the Parker River Inlet on Castle Neck / Crane’s Beach (Fig. 19b). Stage Island

is composed of till, but its origin is unknown. These comparatively erosion-resistant drumlins serve as “pinning

points” for the barrier systems, reducing wave energy through refraction. At lower stages of RSL, these drumlins

also served to route local fluvial systems, such as the Ipswich River. The lowstand river channel was later re-

occupied by the Parker River Inlet that separates Plum Island and Castle Neck.

Walking east from the parking lot to the beach, you will encounter two boulder fields which are fully exposed at

low tide. These are lag deposits from drumlins that have been eroded in recent centuries and which likely served as

earlier pinning points for southern Plum Island before it migrated landward to its present location. Additional lag

deposits from former drumlins in this cluster are found offshore to depths of 35–40 m. These were eroded by waves

and tides as the shoreline transgressed across that area during the early Holocene. Finer sediments were eroded out,

possibly contributing some small volume of sand to the developing barrier / backbarrier systems of the Merrimack

Embayment (it is noted that these drumlins contain little sand), and gravel lags were left behind on the modern

seafloor.

Evidence of the ongoing landward migration of southern Plum Island is also evident in peat deposits which

occasionally outcrop along the low- and mid-tide beach in this location. These peats are several meters thick and are

remnants of marsh systems that once lived behind Plum Island, when it was positioned further offshore. The ages of

these peats are currently unknown but are under investigation (Hein, unpub.).

To the south of the drumlin is Sandy Point, the active recurve of the Plum Island spit. Up to 60 % of Plum

Island formed through spit elongation (Hein et al., 2012), a process that continues at the southern end of Plum Island

today. Much of Sandy Point is a spit platform building into the Parker River Inlet. However, the position of this inlet

is stabilized by the South Plum and Castle Hill drumlins and cannot migrate further south to accommodate further

HEIN AND STONE A5-29

elongation of Plum Island. If time and tide permit, the sands of Sandy Point are commonly formed into some of the

most spectacular intertidal bedforms in the northeast. These were a major focus of a 1989 SEPM coastal geology

field trip (Boothroyd and FitzGerald, 1989).

Mileage Time Directions (STOP 6 to STOP 7)

27.6 0 min Start at STOP 6. Head back north along dirt Refuge Rd.

31.6 15 min Drive (slowly!) along Refuge Rd. to PRNWR Sub-Station (STOP 7). Make left into lot.

Additional parking is available in small lot 0.15 mi south of STOP 7 lot (before arriving

at STOP 7).

A5-30 HEIN AND STONE

STOP 7: PRNWR SUBSTATION (45 MINUTES) – start at 2:05pm

(UTM 19N: 352323 E, 4735390 N)

Figure 24. Topographic / bathymetric map of central Plum Island showing the location of STOP 6.

At this stop you are standing at the PRNWR sub-station. Underneath your feet lies barrier washover sands,

nearly 20 m of backbarrier sediments, and at least 15 m of glaciomarine silt-and-clay. These units are captured in a

sediment core which we will open at this location to see how middle Holocene transgressive barrier deposits lie

unconformably on 17,000-year-old glaciomarine deposits, which are the same as those seen exposed at STOP 3.

Had you been here 7000–13,000 years ago, you would have been standing along the north bank of the Parker

River (seen heading to the west from the Plum Island River to your west), which at that time extended its course due

east out onto an exposed plain of glaciomarine clay and regressive shoreline deposits. Though small, this river

helped to feed the growth of the lowstand paleodelta, located in 40 m of water, ca. 7 km offshore of Plum Island.

Fluvial cut-and-fill structures can be imaged in seismic and GPR data both offshore of this location and under this

section of Plum Island (Fig. 9). By 3600 years ago, the lower Parker River had become fully tidal and developed in

this location into a nearly 700-m wide tidal inlet, the paleo-Parker Inlet (Fig. 11). We will look in detail at GPR and

sediment-core data from this buried inlet sequence. Over the course of hundreds of years, this inlet migrated,

underwent ebb-delta breaching, shoaled and, by ca. 2000 years ago, closure (Hein et al., 2012). This final step

resulted in the continued elongation of Plum Island, driven by dominant southerly sediment transport.

As in much of Plum Island, remnants of overwash fans can be seen along the western edge of the island in this

location (these are largely covered south of the substation by freshwater marsh formed by the construction of dikes

by the PRNWR). Overwash makes up only the western ca. 10 % of this island. The other 90 % of its width was built

through progradation (seaward-building) (Hein et al., 2012). Plum Island owes this unusual feature to the fact that it

has an ample source of sediment from the Merrimack River through which to continue to widen and build vertically.

Mileage Time Directions (STOP 7 to STOP 8)

31.6 0 min Go back out to Refuge Rd. and turn left (north)

33.9 10 min Continue (slowly!) along Refuge Rd. to PRNWR Parking Lot #1 (STOP 5/8). Make right

into lot. Ample parking is available.

HEIN AND STONE A5-31

STOP 8: PRNWR PARKING LOT #1 (60 MINUTES) – start at 3:00pm

(UTM 19N: 352078 E, 4739076 N)

Figure 25. Topographic / bathymetric map of northern Plum Island showing the location of PRNWR Parking Lot #1

(STOP 5). From here, we will walk to the beach and north to Center Island (east of end of Plum Island Turnpike).

A 200 m walk east of the parking lot across aeolian sand dunes brings you to the beach at the northern end of

the PRNWR. From here you can see Cape Ann to the south and, on a clear day, Boar’s Head to the north. These

bedrock promontories mark the boundaries of the Merrimack Embayment. Offshore to a depth of ca. 60 m, sitting

atop glacial till and post-glacial glaciomarine silt-and-clay, is an enormous volume (likely more than 2 billion m3;

Table 1) of gravel, sand and silt that compose the late Pleistocene and Holocene regressive-transgressive braidplain

delta, lowstand paleodelta, and sand sheet. The latter of these remains mobile and likely includes remnants of former

barrier islands that existed during lower stages of sea level as well as sediments that have continued to be fed from

erosion of sandy glacial deposits and bedrock upstream in the Merrimack River basin. Through erosion and

reworking during the most recent marine transgression (13 ka to present), each of these paraglacial units has fed the

development of the wide, long Plum Island barrier system with its high, well-developed dunes over which you just

walked to arrive at the beach. The Merrimack Embayment barrier, backbarrier and shallow shelf system is

enormous, and owes its entire existence to the sandy deposits left behind by the Laurentide Ice Sheet and the

Merrimack River, which transported those sediments to the coast for reworking by waves, tides and wind.

A shallow cross-shore trench through the beach and the vertical scraping of the dune toe illuminate the

processes by which waves, winds and storms rework sediment along and across the Plum Island beach and dunes.

A5-32 HEIN AND STONE

Cross bedding in the dune face demonstrates the act of winds to move sand from the beach, over the foredunes, and

into the large, well-vegetated dunes on Plum Island. Multiple “heavy mineral” layers are evident in the profile.

Though of similar grain size to the surrounding sediments, these layers are composed dominantly of red garnet.

Some say this is where “Plum” Island got its name; others attribute it to plum bushes in the vegetated dunes. This

garnet has a higher density than quartz sands and is therefore requires higher wave energy to move. It becomes

concentrated along the beach face during storms and then buried during quieter times. These heavy-mineral layers

thus mark old storm events. They are also responsible for most of the radar reflections visible in GPR lines.

Looking north again, one can see the south jetty of the Merrimack River Inlet. Constructed in the 1880s,

lengthened several times throughout the 20th

century, and reinforced and heightened as recently as Spring 2014,

these jetties serve to stabilize the mouth of the Merrimack River. Without these jetties, the entire “north fork” of

Plum Island (the section of island east of The Basin, the former channel of the Merrimack River) would not exist.

Nor would most of the hundreds of homes that populate the northern 1/3 of Plum Island. Prior to the installation of

the jetties, the Merrimack River mouth would migrate alongshore by several kilometers, nearly as far south as where

you now stand.

However, the fight to control the coastal system of Plum Island continues. Walking north from the path over the

dunes, you will pass out of the PRNWR and into the town of Newbury. A series of shore-normal groins extend from

the dunes out into the surf zone. Mostly built in the 1970s during a former period of severe erosion, these had been

fully covered by sand as the northern section of Plum Island prograded and accreted. As recently as 2007, their

existence had been forgotten. However, the return of the “erosion hot spot”, driven by wave refraction around the

Merrimack River Inlet ebb-tidal delta and its associated bars, at Center Island (the eastern end of Plum Island

Turnpike) in 2007–2008 exposed the northern-most groin. Several homes were lost to erosion during this time (Fig.

26a). Southerly migration of this hot-spot has now exposed two additional groins and greatly intensified erosion

along Annapolis Way, causing additional homes to fall into the Gulf of Maine (Fallon et al., submitted). The

response by residents has been swift . . . and not always to the letter of the law. A group of homeowners starting a

program of “beach-scraping” in 2012 and 2013, followed by the emplacement of a rip-rap revetment in the form of

large boulders in front of their homes in 2013, and most recently, nourishment of the beach. While this has

undoubtedly saved many homes, it has also changed the nature of the beach forever. Or has it? The exposure of an

earlier (1970s?) revetment wall under what appeared only years ago to have been natural dunes suggests that the

erosion that appears so devastating today is in fact cyclical, returning once every 25–30 years. Perhaps, residents just

need to wait this cycle out and their homes can be save for another generation, or at least until the forces of

accelerated RSL rise and enhanced storminess overcome the natural inlet-sediment cycles.

Figure 26. Photos of recent erosion on Plum Island. (a) Erosion north of Center Island in February, 2009 (image

courtesy of the Boston Globe, 9 February 2009). (b) High tide along Annapolis Way, 17 December 2013 (image

courtesy of G. Cliffords, Plum Island Resident). Note groin (dating to 1970s) in foreground and rip-rap revetment

along eroded dune line (installed in spring 2013). Although this section of beach used to look like the beach in the

PRNWR as recently as 2008, little beach remains today at high tide.

HEIN AND STONE A5-33

END OF TRIP (4:00pm)

RETURN TRIP TO WELLESLEY COLLEGE

Return to Wellesley College, approximately 1 hour, 15 min (without traffic) for Welcome Reception and

registration (at The College Club at Wellesley College), starting at 5:00pm.

Mileage Time Directions (STOP 8 to Wellesley College)

33.9 0 min Start at STOP 5/8, PRNWR Parking Lot #; make right onto Refuge Rd and leave through

PRNWR entrance gate

34.5 2 min Make left onto Plum Island Turnpike; becomes Water St.

36.4 5 min Make left onto Ocean Ave.; becomes Rolfes Ln.; cross over High Rd. (Rt. 1A); road

becomes Hanover St.

38.1 12 min Go straight at light at Rt 1 (Newburyport Turnpike); road becomes Middle Rd.

38.5 13 min Turn right onto Highfield Rd.

39.2 14 min Turn left onto Scotland Rd.

41.3 16 min Turn left to merge onto I-95 S

85.5 58 min Follow I-95 S. Take exit 21B-22 from I-95 S for Grove St. toward MA-16 W / Wellesley;

Take exit 21B on the left toward MA-16 W / Wellesley

89.4 1 hr, 5 min Merge onto Quinobequin Rd.

89.6 1 hr, 6 min Turn right onto MA-16 W / Washington St.

92.7 1 hr, 10 min Turn left onto Washington St.

93.4 1 hr, 15 min Arrive at The College Club at Wellesley College, 727 Washington St., Wellesley, MA

A5-34 HEIN AND STONE

REFERENCES

Antevs, E., 1922, The recession of the last ice sheet in New England: American Geographical Society Research

Series, no. 11, 120 p.

Balco, G., Stone, J.O.H., Porter, S.C., and Caffee, M.W., 2002, Cosmogenic-nuclide ages for New England coastal

moraines, Martha’s Vineyard and Cape Cod, Massachusetts, USA: Quaternary Science Reviews, v. 21, p.

2127–2135.

Balco, G., Briner, J., Finkel, R.C., Rayburn, J.A., Ridge, J.C., and Schaefer, J.M., 2009, Regional beryllium-10

production rate calibration for late-glacial northeastern North America: Quaternary Geochronology, v. 4, p. 93–

107.

Barnhardt, W.A., Gehrels, W.R., Belknap, D.F., and Kelley, J.T., 1995, Late Quaternary relative sea-level change in

the Western Gulf of Maine: Evidence for a migrating glacial forebulge: Geology, v. 23, p. 317–320.

Barnhardt, W., Andrews, B., Ackerman, S., Baldwin, W., and Hein, C., 2009. High Resolution Geologic Mapping of

the Inner Continental Shelf: Cape Ann to Salisbury Beach Massachusetts. U.S. Geological Survey Open-File

Report OFR-07-1373: US Department of Interior, Reston, VA, 50 p.

Bard, E., Hamelin, B., Arnold, M., Montaggioni, L., Cabioch, G., Faure, G., and Rougerie, F., 1996, Deglacial sea-

level record from Tahiti corals and the timing of global meltwater discharge: Nature, v. 382, p. 241–244.

Belknap, D.F., and Shipp, R.C., 1991, Seismic stratigraphy of glacial-marine units, Maine inner shelf, in Anderson,

J.B. and Ashley, G.M., eds., Glacial-Marine Sedimentation: Paleoclimatic Significance: Geological Society of

America Special Paper 261, p. 137–157.

Birch, F.S., 1990, Radiocarbon dates of Quaternary sedimentary deposits on the inner continental shelf of New

Hampshire: Northeastern Geology, v. 12, p. 218–230.

Bloom, A.L., and Stuiver, M., 1963, Submergence of the Connecticut coast: Science, v. 139, p. 332–334.

Boothroyd, J.C., and FitzGerald, D.M., 1989, Coastal Geology of the Merrimack Embayment, SEPM Eastern Field

Trip Guide, 43 p.

Borns, W.H., Jr., Doner, L.A., Dorion, C.C., Jacobson, G.L., Jr., Kaplan, M.R., Kreutz, K.J., Lowell, T.V.,

Thompson, W.B., and Weddle, T.K., 2004, The deglaciation of Maine, USA: Developments in Quaternary

Sciences, v. 2, p. 89–109.

Bradlee, F.B.C., 1920, Some account of steam navigation in New England: Essex Institute, Salem, MA, 153 p.

Chute, N.E., and Nichols, R.L., 1941, The geology of the coast of northeastern Massachusetts: Massachusetts

Department of Public Works / United States Geological Survey Cooperative Geology Project, Bulletin 7: US

Department of Interior, Reston, VA, 48 p.

Collins, D.W., 1989, Biostratigraphy of post-glacial sediments, Gosport Harbor, Isles of Shoals, New Hampshire:

M.Sc. Thesis, University of New Hampshire, Durham, NH.

Costas, S., and FitzGerald, D., 2011, Sedimentary architecture of a spit-end (Salisbury Beach, Massachusetts): The

imprints of sea-level rise and inlet dynamics: Marine Geology, v. 284, p. 203–216.

Crosby, W.O., 1891, Composition of the till or boulder clay: Boston: Society of Natural History Proceedings, v. 25,

p. 115–140.

Crosby, I.B., and Lougee, R.J., 1934, Glacial marginal shores and the marine limit in Massachusetts: Geological

Society of America Bulletin, v. 45, p. 441–462.

Cuppels, N.P., 1969, Surficial geology of the Georgetown quadrangle, Massachusetts: U.S. Geological Survey

Geologic Quadrangle Map GQ-850, US Department of Interior, Reston, VA, 1:24,000 scale, one sheet.

Dennen, W.H., 1991, Bedrock geologic map of the Ipswich quadrangle, Essex Co., Massachusetts: U.S. Geological

Survey Map I-1698, map scale 1:24,000, one sheet.

Donnelly, J.P., 2006, A revised late Holocene sea-level record for northern Massachusetts, USA: Journal of Coastal

Research, v. 22, p. 1051–1061.

Dougherty, A.J., FitzGerald, D.M., and Buynevich, I.V., 2004, Evidence for storm-dominated early progradation of

Castle Neck barrier, Massachusetts, USA: Marine Geology, v. 210, p. 123–134.

Edwards, G.B., 1988, Late Quaternary geology of northeastern Massachusetts and Merrimack Embayment, western

Gulf of Maine: M.Sc. Thesis, Boston University, Boston, MA, 337 p.

Edwards, G.B., and Oldale, R.N., 1986, Evidence for Holocene erosional shoreface retreat in a linear ridge system

offshore Merrimack River, Massachusetts: Geological Society of America Abstracts with Programs, v. 18, p.

14.

EOEEA (Executive Office of Energy and Environmental Affairs), 2010, Beach Scraping Report,

http://www.townofnewbury.org/pages/EOEEA%20Beach%20Scraping%20Workgroup%20Report.pdf

HEIN AND STONE A5-35

Fallon, A.R., Hein, C.J., and Rosen, P.S., submitted abstract, Cyclical shoreline erosion: The impact of a jettied river

mouth on the downdrift barrier island: Coastal Sediments 2015 (San Diego, CA, May, 2015).

FitzGerald, D.M., and van Heteren, S., 1999, Classification of paraglacial barrier systems: coastal New England,

USA: Sedimentology, v. 46, p. 1083–1108.

FitzGerald, D.M., 1993, Origin and stability of multiple tidal inlets in Massachusetts, in Aubrey, D.G., and Giese,

G.S., eds., Formation and Evolution of Multiple Tidal Inlets: Coastal and Estuarine Studies Series, American

Geophysical Union, Washington, D.C., p. 1–61.

FitzGerald, D.M., Rosen, P.S., and van Heteren, S., 1994, New England Barriers, in Davis, R.A. ed, Geology of

Holocene Barrier Island Systems: Springer-Verlag, Berlin, p. 305–394.

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, v. 48, p. 179–208.

FitzGerald, D.M., Buynevich, I.V., Fenster, M.S., Kelley, J.T., and Belknap, D.F., 2005, Coarse-grained sediment

transport in northern New England Estuaries: A synthesis, in FitzGerald, D.M. and Knight, J., eds., High

Resolution Morphodynamics and Sedimentary Evolution of Estuaries: Springer, New York, p. 195–214.

Fuller, D.C., and Holtz, C.F., 1981, Soil survey of Essex County, Massachusetts, northern part: U.S Department of

Agriculture, Soil Conservation Service, 194 p.

Hanson, L. S., and Caldwell, D.W., 1990, The geomorphology of the mountainous regions in north-central Maine, in

Marvinney, R.G., and Tucker, R.D., eds., Geologic structure and stratigraphy of Maine: C.T. Jackson volume 1,

Maine Geological Survey, Augusta, Maine, 40 p.

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, Special Issue 50, p. 863–867.

Hein, C.J., FitzGerald, D., Stone, B.D., Carruthers, E.A., and Gontz, A.M., 2011, The role of backbarrier infilling in

the formation of barrier island systems, in Kraus, N.C., and Rosati, J.D., eds., Coastal Sediments ’11:

Proceedings of the 8th International Symposium on Coastal Engineering and Science of Coastal Sediment

Processes, 2–6 May 2011, Miami, FL.

Hein, C.J., FitzGerald, D.M., Carruthers, E.A., Stone, B.D., Barnhardt, W.A., and Gontz, A.M., 2012, Refining the

model of barrier island formation along a paraglacial coast in the Gulf of Maine: Marine Geology, v. 307–310,

p. 40-57.

Hein, C.J., FitzGerald, D.M., Barnhardt, W.A., and Stone, B.D., 2013, Onshore-offshore surficial geologic map of

the Newburyport East and northern half of the Ipswich Quadrangles, Massachusetts: Massachusetts Geological

Survey, Geologic Map GM 13-01, 1:24,000 scale, three sheets.

Hein, C.J., FitzGerald, D.M., Buynevich, I.V., van Heteren, S., and Kelley, J.T., 2014, Evolution of paraglacial

coasts in response to changes in fluvial sediment supply: Geological Society, London, Special Publication 388,

doi: 10.1144/SP388.15.

Hepburn, J.C., Kuiper, Y., Buchanan, J.W and Kay, A., Evolution of the Nashoba terrane, an early Paleozoic

Ganderian arc remnant in eastern Massachusetts: p. B3-1 to B3-20, this volume.

Hibbard, J. P., van Staal, C. R., Rankin, D. W., and Williams, H., 2006, Lithotectonic map of the Appalachian

Orogen, Canada-United States of America: Geological Survey of Canada Map 2096A, 1:1,500,000 scale, 1

sheet.

Hubbard, D.K., 1971, Tidal inlet morphology and hydrodynamics of Merrimack Inlet, Massachusetts: M.S. Thesis,

University of South Carolina, Columbia, SC, 144 p.

Horner, N.G., 1929, Late glacial marine limit in Massachusetts: American Journal of Science, v. 17, p. 123–145.

Kaye, C.A., 1961, Pleistocene stratigraphy of Boston, Massachusetts: U.S. Geological Survey Professional Paper,

424-B, US Department of Interior, Reston, VA, p. 73–76.

Kaye, C.A., and Barghoorn, E.S., 1964, Late Quaternary sea-level change and crustal rise at Boston, Massachusetts,

with a note on the autocompaction of peat: Geological Society of America Bulletin, v. 75, p. 63–80.

Keene, H.W., 1971, Post glacial submergence and salt marsh evolution in New Hampshire: Maritime Sediments, v.

7, p. 64–68.

Kelley, J.T., 1989, A preliminary mineralogical analysis of glaciomarine mud from the western margin of the Gulf

of Maine: Northeastern Geology, v. 11, p. 141–150.

Kelley, J.T., Belknap, D.F. and Claesson, S.H., 2010, Drowned coastal deposits with associated archaeological

remains from a sea-level "slowstand": Northwestern Gulf of Maine, USA: Geology, v. 38, p. 695–698.

Kelley, J.T., Belknap, D.F. Kelley, A.R., and Claesson, S.H., 2013, A model for drowned terrestrial habitats with

associated archeological remains in the northwestern Gulf of Maine, USA: Marine Geology, v. 338, p. 1–16.

A5-36 HEIN AND STONE

Kirwan, M.L., Murray, A.B., Donnelly, J.P., and Corbett, D.R., 2011, Rapid wetland expansion during European

settlement and its implication for marsh survival under modern sediment delivery rates: Geology, v. 39, p. 507–

510.

Koteff, C., 1976, Surficial Geologic Map of the Nashua North quadrangle, Hillsborough and Rockingham Counties,

New Hampshire: U.S. Geological Survey, Map GQ-1290, US Department of Interior, Reston, VA, 1:24,000

scale, one sheet.

Koteff, C., and Stone, B.D., 2000, Surficial geologic map of the Manchester South quadrangle, Hillsborough and

Rockingham Counties, New Hampshire: New Hampshire Department of Environmental Services, Open-File

Report Geo-144, 1:24,000 scale, one sheet.

Koteff, C., Robinson, G.R., Goldsmith, R., and Thompson, W.B., 1993, Delayed postglacial uplift and synglacial

sea levels in coastal central New England: Quaternary Research, v. 40, p. 46–54.

McIntire, W.G., and Morgan, J.P., 1964, Recent geomorphic history of Plum Island, Massachusetts, and adjacent

coasts: Louisiana State University Press, Baton Rouge, 57 p.

McKinlay, P.A., 1996, Bedrock controls on the evolution and stratigraphy of Coffins Beach, Gloucester,

Massachusetts: M.Sc. Thesis, Boston University, Boston, MA, 147 p.

Milliman, J.D., and Farnsworth, K.L., 2011, River discharge to the coastal ocean: Cambridge University Press,

Cambridge, 384 p.

Newman, W.A., Mickelson, D.M., Berg, R.C., Rendigs, R.D., Oldale, R.N., and Bailey, R.H., 1993, Pleistocene

geology of the Boston Basin and its adjacent surroundings: Geological Society of America, Field Trip

Guidebook for the United States: 1993 Boston GSA, p. U1–U24.

Nichols, R.L., 1942, Shoreline changes on Plum Island, Massachusetts: American Journal of Science, v. 240, p.

349–355.

Oldale, R.N., 1964, Surficial geology of the Salem quadrangle, Massachusetts: U.S. Geological Survey Geologic

Quadrangle map GQ-271, US Department of Interior, Reston, VA, 1:24,000 scale, one sheet.

Oldale, R.N., 1985, A drowned Holocene barrier spit off Cape Ann, Massachusetts: Geology, v. 13, p. 375–377.

Oldale, R.N., 1989, Timing and mechanisms for the deposition of the glaciomarine mud in and around the Gulf of

Maine: a discussion of alternative models, in Tucker, R.D., and Marvinney, R.G., eds., Studies in Maine

Geology Volume 5: Quaternary Geology: Maine Geological Survey, Augusta, p. 1–10.

Oldale, R.N., and O'Hara, C.J., 1980, New radiocarbon dates from the inner continental shelf off southeastern

Massachusetts and a local sea-level-rise curve for the past 12,000 yr: Geology, v. 8, p. 102–106.

Oldale, R.N. and Wommack, L.E., 1987, Maps and seismic profiles showing geology of the inner continental shelf,

Cape Ann, Massachusetts to New Hampshire: U.S. Geological Survey Miscellaneous Field Studies Map MF-

1892, US Department of Interior, Reston, VA, 1:125,000 scale, three sheets.

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: Quaternary Research, v. 19, p. 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 sea-level curve for the northeastern Massachusetts coastal region: Quaternary

Research, v. 40, p. 38–45.

Redfield, A.C., 1967, Ontogeny of a salt marsh, in Lauff, G.H., ed, Estuaries: American Association for the

Advancement of Science, Washington, D.C., p. 108–114.

Retelle, M.J., and Weddle, T.K., 2001, Deglaciation and relative sea-level chronology, Casco Bay Lowland and

lower Androscoggin River valley, Maine, in Weddle, T.K., and Retelle, M.J., eds., Deglacial History and

Relative Sea-Level Changes, Northern New England and Adjacent Canada: Geological Society of America

Special Papers, v. 351, p. 191–214.

Rhodes, E.G., 1973, Pleistocene-Holocene sediments interpreted by seismic refraction and wash-bore sampling,

Plum Island-Castle Neck, Massachusetts: US Army Corps of Engineers Technical Memorandum 40, U.S. Army

Corps of Engineers, Coastal Engineering Research Center, Vicksburg, MS, 75 p.

Ridge, J.C., 2004, The Quaternary glaciations of western New England with correlations to surrounding areas, in

Ehlers, J., and Gibbard, P.L., eds., Quaternary Glaciations, Extent and Chronology Part II: North America:

Elsevier, Amsterdam, p. 169–199.

Ridge, J.C., Blaco, G., Bayless, R.L., Beck, C.C., Carter, L.B., Dean, J.L., Voytek, E.B., and Wei, J.H., 2012, The

new North American Varve Chronology: A precise record of southeastern Laurentide Ice Sheet deglaciation and

climate, 18.2-12.5 kyr BP, and correlations with Greenland ice core records: American Journal of Science, v.

312, p. 685–722.

HEIN AND STONE A5-37

Rittenour, T., Stone, B.D., and Mahan, S.A., 2012, Application of OSL dating to glacial deposits in southern

Massachusetts: Refining the chronology and addressing questions related to solar resetting in glacial

environments: Geological Society of America Abstracts with Programs, v. 44, p. 86.

Sammel, E.A., 1963, Surficial geology of the Ipswich Quadrangle, Massachusetts: U.S. Geological Survey

Geological Quadrangle Map GQ-0189, US Department of Interior, Reston, VA, 1:24,000 scale, one sheet.

Sammel, E.A., 1967, Water Resources of the Parker and Rowley River Basins, Massachusetts, U.S. Geological

Survey Hydrologic Investigations Atlas HA-247, US Department of Interior, Reston, VA, 1:24,000 scale, one

sheet.

Schafer, J.P., and Hartshorn, J.H., 1965, The Quaternary of New England, in Wright, H.E., Jr., and Frey, D.G., eds.,

The Quaternary of the United States: Princeton University Press, Princeton, N. J., p. 113–128.

Sears, J.H., 1905, The physical geography, geology, mineralogy and paleontology of Essex County: The Essex

Institute, Salem, Massachusetts, 1:62,500 scale, 416 p.

Shaler, N.S., 1889, The geology of Cape Ann, Massachusetts: U.S. Geological Survey 9th Annual Report: US

Department of Interior, Reston, VA, p. 529–611.

Shride, A.F., 1976, Stratigraphy and correlation of the Newbury volcanic complex, northeastern Massachusetts, in

Page, L.R., ed., Contributions to the Stratigraphy of New England: Geological Society of America Memoir

148, p. 147–177.

Simcox, A.C., 1992, Water resources of Massachusetts. U.S. Geological Survey Water-Resources Investigations

Report 90–4122: US Department of Interior, Reston, VA, 94 p.

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, v. 10, p. 752–774.

Stone, B.D., 1989, in Weddle, T.K., Stone, B.D., Thompson, W.B., Retelle, M.J., Caldwell, D.W., and Clinch, J.M.,

Illinoian and late Wisconsinan tills in eastern New England: A transect from northeastern Massachusetts to

west-central Maine, with a section on till stratigraphy of southern New England by B.D. Stone, in Berry, A.W.,

Jr., ed, New England Intercollegiate Geological Conference, 81st Annual Meeting, guidebook for field trips in

southern and west-central Maine: Farmington, Maine, University of Maine, p. 25–85.

Stone, B.D., 2012, Contrasts in Early and Late Pleistocene glacial records in northeastern U.S.A. resulting from

topographic relief, climate change, and crustal depression: Geological Society of America Abstracts with

Programs, v. 44, p. 86.

Stone, B.D., and Borns, H.W., Jr., 1986, Pleistocene glacial and interglacial stratigraphy of New England, Long

Island, and adjacent Georges Bank and Gulf of Maine, in Sibrava, V., Bowen, D.Q., and Richmond, G.M., eds.,

Quaternary Glaciations in the Northern Hemisphere: Pergamon Press, Oxford, p. 39–52.

Stone, B.D., and Peper, J.D., 1982, Topographic control of the deglaciation of eastern Massachusetts: ice lobation

and marine incursion, in Larson, G.J., and Stone, B.D., eds., Late Wisconsinan glaciation of New England:

Kendall/Hunt, Dubuque, IA, p. 150–170.

Stone, B.D., Stone, J.R., and McWeeney, L.J., 2004, Where the glacier met the sea: Late Quaternary geology of the

northeast coast of Massachusetts from Cape Ann to Salisbury, in Hanson, L., ed, New England Intercollegiate

Geological Conference, 85th Annual Meeting: Salem, Massachusetts, Salem State College, Trip B-3, 25 p.

Stone, B.D., Stone, J.R., and DiGiacomo-Cohen, M.L., 2006, Surficial Geologic Map of the Salem-Newburyport

East-Wilmington-Rockport Quadrangle Area in Northeast Massachusetts, U.S. Geological Survey Open-File

Report, 2006-1260-B Reston, VA: US Department of Interior.

Stone, J.R, Schafer, J.P, London, E.H., DiGiacomo-Cohen, Mary, Lewis, R.S., and Thompson, W.B., 2005,

Quaternary geologic map of Connecticut and Long Island Sound Basin: U.S. Geological Survey Miscellaneous

Investigations Map I-2784. US Department of Interior, Reston, VA., 1:24,000 scale, 1 sheet, 76 p.

Stuiver, M., and Reimer, P.J., 1993, Extended 14C data base and revised CALIB 3.0 14C age calibration program:

Radiocarbon, v. 35, p. 215–230.

Tarr, R.S., and Woodworth, J.B., 1903, Postglacial and interglacial (?) changes of level and Cape Ann,

Massachusetts, with a note on the elevated beaches: Bulletin of the Museum of Comparative Zoology of

Harvard College, 15 p.

Thompson, M.D., and Borns, H.W. Jr., 1985, Surficial Geologic Map of Maine: Maine Geological Survey, Augusta.

1:500,000 scale, one sheet.

Thompson, M.D., and Ramezani, J., 2008, Refined ages of Paleozoic plutons as constraints on Avalonian accretion

SE New England: Geological Society of America Abstracts with Programs, v. 40, p. 14.

Thompson, W.B., Crossen, K.J., Borns, H.W., Jr., and Andersen, B.G., 1989, Glaciomarine deltas of Maine and

their relation to late Pleistocene–Holocene crustal movements, in Andersen, W.A., and Borns, H.W., Jr., eds.,

A5-38 HEIN AND STONE

Neotectonics of Maine: Studies in Seismicity, Crustal Warping, and Sea-Level Change: Maine Geological

Survey, Augusta, Bulletin 40, p. 43–67.

Toppan, R.N., 1905, Edward Rawson: Transactions of the Colonial Society of Massachusetts, v. 7, p. 280–294.

Valentine, V., and Hopkinson, C.S. Jr., 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. Final version.

Woods Hole, MA: The Ecosystems Center, MBL.

Waters, T.F., 1918, Plum Island: Ipswich, Mass, Publications of the Ipswich Historical Society. XXII: Ipswich

Historical Society, Ipswich, MA, 64 p.

Weddle, T.K., Stone, B.D., Thompson, W.B., Retelle, M.J., Caldwell, D.W., and Clinch, J.M., 1989, Illinoian and

Late Wisconsinan Tills in Eastern New England: a Transect from Northeastern Massachusetts to West-Central

Maine, in Berry, A.W., Jr., ed, New England Intercollegiate Geological Conference, Guidebook for Field Trips

in Southern and West-central Maine, Trip A-2, 25 p.

Zen, E-an, Goldsmith, R., Ratcliffe, N.M., Robinson, P., and Stanley, R.S., compilers, 1983, Bedrock geologic map

of Massachusetts: U.S. Geological Survey, Reston, VA, 1:250,000 scale, 3 sheets.