The 106th meeting of the
New England Intercollegiate Geological Conference
October 10-12, 2014
Wellesley College, Wellesley, Massachusetts
The 106th meeting of the New England Intercollegiate Geological October 10, 11
& 12 at Wellesley College, Wellesley, MA
organized by Meg Thompson and David Hawkins, Wellesley College
Schedule of Events
Friday October 10th
Field Trips
(see list of field trips for specific meeting times and places)
Welcome Reception
5:00 PM
The College Club at Wellesley College
hors d'oeuvres & cash bar
(directions and additional details coming soon)
Saturday, October 11th
Field Trips
(see list of field trips for specific meeting times and places)
Cocktail Hour and Banquet
6:00pm
The College Club at Wellesley College
cash bar & buffet dinner
poster-session-style spaces will be available for displaying maps
(directions and additional details coming soon)
Sunday, October 12th
Field Trips
(see list of field trips for specific meeting times and places)
See p. 13 for lodging and camping suggestions
October 12th
Field Trips (see list of field trips for specific meeting times and places) See p. 13
for lodging and camping suggestions
LIST OF FIELD TRIPS
Please doublecheck your trip for updated logistics!
2014 Trip List p. 2
Many trips in the following list have assembly points other than Wellesley College,
and details for these can be found in the final section of each trip blurb. Trips
leaving from the College will assemble in the parking lot east of the Science
Center in down-loadable pdf map. The single exception is Trip B6 (see blurb
below).
Friday—October 10
Trip A1. BEDROCK QUARRIES OF EASTERN MASSACHUSETTS. Leaders: Carl A.
Francis and Mark Van Baalen
Description: This trip focuses on the mineralogy, petrology, and history of three very different
bedrock quarries of Eastern Massachusetts. The first stop is the historic Quincy Railroad Quarry,
one of several quarries in close proximity to each other. The peralkaline rock here is the Early
Devonian Quincy Granite, containing sodic pyroxenes and amphiboles. The Quincy Granite has
traditionally been associated with the Peabody Granite and the Cape Ann Granite (Zartman &
Marvin, 1971), but these have now been dated as Upper Devonian and Middle Silurian,
respectively (Thompson & Ramezani, 2008). See also Trip A-4, this guidebook. This rock is
extremely hard and resistant to weathering, which has made it useful for building stone used at
the Bunker Hill Monument and other historic structures. This quarry is also the site of the first
railroad in the United States, opened in 1826 and used to transport granite from the quarry to
Boston Harbor. A portion of the railroad remains. Today the quarry is also much favored by rock
climbers. The second stop is the Fletcher granite quarry in Westford, in continuous operation for
150 years. The peraluminous rock here is the Devonian Chelmsford Granite, recently remapped
by Walsh et al. (2013). At this locality we will see an operating granite quarry and its highly
automated finishing mill. The minerals here include both muscovite and biotite, as well as
aluminous accessory minerals such as garnet and tourmaline. Chelmsford Granite is also highly
sought after for use as curbstones, fence posts, and the like. The final stop is the historic Bolton
Quarry, used from the early 1700s for production of lime for plaster and mortar. A portion of the
old lime kiln remains. Minerals here include scapolite, forsterite (“boltonite”), and diopside, all
formed through contact metamorphism. The calc-silicate bedrock here, part of the Nashoba
Block, is probably Cambrian but may be as young as mid-Ordovician. Contact metamorphism
occurred as a result of an unnamed Devonian (?) intrusion (Kopera, 2005).
Starting point and other logistics: Assembly will be at parking lot east of the Wellesley
College Science Center, 8:30 a.m., and the trip will end at the same place. Van pooling
is encouraged.
Group size limited to 50. Participants should bring lunch and all-weather clothing.
Trip A2. AGES IN THE RYE COMPLEX, COASTAL, NH: A DEFORMATIONAL
HISTORY SLOWLY REVEALED.
Leaders: Wally Bothner, Patrick Kane, Erin Stoesz, Kristin Sorota, Jo Laird, Art Hussey,
Chris Hepburn, Mick Kunk, Mike Dorais and Bob Wintsch
Description: The Rye Complex occupies coastal New Hampshire and a bit of southwestern
Maine. It represents an enigmatic slice between 1) the well-documented Avalonian basement of
northeastern Massachusetts and an offshore extension of the Nashoba block, and 2) the SiluroDevonian cover rocks of the Merrimack and Central Maine belts. New U/Pb ages of detrital
zircons from the metasedimentary rocks, geochemistry and U/Pb zircon ages of intrusive bodies,
and 40/39Ar cooling ages from variably strained phases of the Rye indicate multiple
deformational, metamorphic and magmatic events spanning the entire Paleozoic and Mesozoic!
2014 Trip List p. 3
However, correlation with rocks of the Nashoba to the south, parts of the Casco Bay sequence to
the north, and exposed basement to the west remain elusive. We look forward to discussing
these results and possible regional ties on the outcrops!
Starting point and other logistics: 9am at Hampton Park and Drive (19T 348295E
4757520N), I-95 to Hampton Exit from North or South, then to Exit 13 eastbound on Rt
101 towards the town of Hampton, NH follow Timber Swamp Rd to parking lot.
https://www.google.com/maps/place/Hampton+Park+and+Ride/@42.955153,70.859469,17z/data=!3m1!4b1!4m2!3m1!1s0x89e2e8f8a8056f4d:0xaf7d3c5a34085693
Trip A3.THE EASTERN MERRIMACK TERRANE IN
MASSACHUSETTS: REVISITING METAMORPHISM, DEFORMATION AND
PLUTONISM
Trip leaders: Joe Kopera and Greg Walsh
Description: This trip will reexamine the Nashua and Rockingham sub-belts of the Merrimack
Terrane in light of recent NCGMP-sponsored geologic mapping, structural analysis, metamorphic
petrology, and geochronology. The first half of the day will focus on spectacular fold-fabric
relationships and low-grade metamorphic assemblages in metaturbidites that typify the belts,
including the famous chiastolite schist of the Worcester formation. The second half of the day will
be spent examining phases of the Ayer-Chelmsford pluton and their intrusive relations to the
Berwick formation.
Starting point and other logistics: 8:30 AM at Walmart Plaza in Leominster, MA at
Junction of Rts 117 and 190 (42.493185, -71.729052) - This is approximately a 50
minute drive from Wellesley College going against rush hour traffic, so please plan
accordingly. We strongly encourage participants to carpool and consolidate into highclearance vehicles. The trip will involve driving on rutted woods-roads that require high
clearance. The last stop will be in Tyngsborough, MA, approx. 45 minutes northeast of
the starting point and 1 hour north of Wellesley with Boston's rush-hour traffic between.
Vehicles will be returning to the starting point.
Please bring a packed lunch, as we will be eating on the outcrop. Bathroom facilities will
not be available for most of the trip.
Abundant overnight accommodations and camping areas exist nearby.
Trip A4. THE CAPE ANN PLUTONIC SUITE: CLASSIC STOPS FOR TEACHING
PETROLOGY ALONG THE NORTH SHORE
Leaders: John B. Brady, John T. Cheney, Jahandar Ramezani and Margaret D. Thompson
Description: This trip will visit class-accessible localities from Marblehead to Rockport selected
mostly from previous NEIGC trips led by Toulmin (1964), Dennin (1976), and Hon et al. (1993)
where units have recently been constrained by reliable U-Pb isotopic dates. The goal of the trip
is to view and discuss the rocks in the context of using them to teach concepts in igneous
petrology. Come on this trip if you would like to see typical North Shore igneous rocks, if you
would like to discuss their origin, and/or if you would like to discuss teaching petrology in the field.
Starting Point and other logistics: The trip will assemble at 8:30 am in the parking lot
of the Square One Mall, 1201 Broadway, Saugus, MA 01906. The Square One Mall is
2014 Trip List p. 4
on Route 1 (and Route 129), 4 miles south of I-95. Look for the outcrops in the mall
parking lot NE of Macys. Bring your lunch.
Trip A5. ICE, WATER, AND WIND: A SOURCE-TO-SINK VIEW OF THE GLACIAL,
PARAGLACIAL AND COASTAL SEDIMENTS AND PROCESSES THAT HAVE
SHAPED NORTHEAST MASSACHUSETTS
Leaders: Chris Hein and Byron Stone
Description: This trip will focus on the sedimentary deposits associated with the transgressive
and regressive cycles following the retreat of the Laurentide Ice Sheet from northeastern
Massachusetts. Sea level in this region reached a maximum of ca. 32 m above present as the ice
sheet retreated. Glacial, fluvial and coastal processes resulted in the deposition of drumlins,
glacial deltas, draping glaciomarine clay, and regressive shorelines and fluvial terraces which
dominate the modern onshore landscape. Many of these deposits have been mapped
continuously across the modern shoreline and into the subaqueous environment offshore of the
barrier islands of the Merrimack Embayment and beyond the 13,000-year-old lowstand shoreline
located 45 m below modern sea level. Reworking of these glacial and post-glacial deposits by
coastal processes during the most recent (and, in some places, ongoing) marine transgression
has allowed for the building of the barriers, beaches, marshes and dunes of the modern coastal
zone. This trip will trace the shoreline from its highstand position up the Merrimack River Valley
and down to Plum Island, tracking the various processes and deposits responsible for building the
modern landscape, and discussing how glacial and marine geologists can come together to map
continuous surficial geology across the modern shoreline.
Starting Point and other logistics: This trip will leave trip will leave at 8:15 AM from
an assembly point in front of the Market Basket in Haverhill Plaza Shopping Center, 285
Lincoln Ave, Haverhill, MA. Participants are encouraged to bring a bagged lunch since
the trip will continue past the lunch hour. Excellent restaurants for a late lunch will be
pointed out at the end of the trip for any who want to sample the local Newburyport
cuisine before leaving!
For those who may be driving from Wellesley, directions to Haverill Plaza can be found
on p. A5-23 of the field trip guide. This drive will take 1hr 15 minutes.
Saturday—October 11
Trip B1. QUATERNARY GEOLOGY OF THE BOSTON AREA: GLACIAL EVENTS
FROM LAKE CHARLES TO LAKE ABERJONA
Leader: Byron Stone
Description: During this trip we will review the new detailed geologic maps of the Boston area
and briefly discuss the revisions of the history of glacial Lake Charles. We travel through
Needham to Newton and will visit historical sites in this lake, including eskers, the famous delta at
Newtonville, and erosional features that were created during the emptying of the lake along the
lower Charles River reach to the glaciomarine sea. After learning of low-frequency seismic
methods to detect depth to bedrock beneath drumlins, we turn to the gravel at the top of Mt.
Auburn Cemetery where we will discuss the fairly simple geology of the Boston basin, and pay
our respects to Professor Agassiz there. At the Fresh Pond moraine we will see a core from the
lake (?) clay to the north, which leads to discussion of the marine-lake-marine-lake history of the
lower Aberjona valley.
2014 Trip List p. 5
Starting Point and other logistics: This trip will begin at 7:45 AM in the parking lot
east of the Science Center at Wellesley College (link to campus map at beginning of this
announcement). Bring lunch.
Trip B2. Conglomerate in and around the Boston Basin, Massachusetts: U-Pb
geochronology, stratigraphy and Avalonian tectonic setting.
Leader: Meg Thompson
Description: Conglomerate in Boston, Massachusetts was named more than a century ago for
exposures in the Roxbury district of the city, and since then other conglomerates across the
region have all been lumped under this heading. Systematic attention to clast assemblages and
especially the availability of U-Pb zircon age constraints for units in and around the Boston Basin,
however, reveal new distinctions within the Roxbury itself, as well as the presence of pre-Roxbury
conglomerate. This trip will proceed stratigraphically from basement on the south side of the
Boston Basin through Roxbury Conglomerate and associated Brighton igneous units within the
Basin. Locations to be visited will highlight recently completed age constraints showing that
conglomerate lying unconformably on 609.5 Ma Dedham Granite is part of the 597-593 Ma LynnMattapan Volcanic Complex and demonstrating a 595-585 Ma age range for the Roxbury proper.
Discussion throughout the day will emphasize implications of the new age constraints for
Avalonian tectonics both in and beyond southeastern New England.
Starting point and other logistics: Trip will leave at 8AM from parking lot east of the
Wellesley College Science Center. Car/van pooling strongly encouraged for better
chance of keeping together en route though Boston & suburbs. Spare vehicles can stay
at Wellesley where we will return at the end of the day.
Limited to 50 people. Bring lunch.
Trip B3. EVOLUTION OF THE NASHOBA TERRANE, AN EARLY PALEOZOIC
GANDERIAN ARC REMNANT IN EASTERN MASSACHUSETTS
Leaders: J. Christopher Hepburn, Yvette Kuiper, John Wesley Buchanan and Andrew
Kay
Description: The Nashoba terrane is a fault-bounded, tectonized and highly metamorphosed
early Paleozoic arc/backarc complex that lies between lower grade Avalonian rocks to the east
and Merrimack belt metasediments to the west. This terrane forms the trailing edge of Ganderia
in SE New England. During the excursion we will include recent radiogenic dating, geochemistry
and Sm/Nd isotopic analyses in our discussions as these have helped to identify the Ganderian
nature of the rocks and allow them to be related to other Ganderian arcs in the northern
Appalachians. The trip is designed to be a general introduction to the stratigraphy,
metamorphism, structure and plutonic rocks of the terrane. We will include visits to the early
Paleozoic metamorphosed rocks that make up the tectonostratigraphy of the terrane as well as
younger plutonic rocks that intruded during the approach of Avalonia in the mid-Paleozoic.
Starting point and other logistics: Meet in the parking lot east of the Wellesley
College Science Center at 8am where we will carpool as much as possible. Please
bring lunch; we will picnic at the outcrop.
Trip B4. DIKE SWARMS OF CAPE ANN, MASSACHUSETTS
Leader: Marty Ross
2014 Trip List p. 6
Description: This trip will emphasize the field characteristics of selected dikes within the swarms
on Cape Ann. In addition to the usual fine-to-medium-grained aphyric dolerites, other types to be
seen include coarsely plagioclase-phyric dolerites, a dike in which felsic and mafic magma have
mingled, a thick aplite dike intruded along an older rhyolite dike, a pyroxene trachyte dike, diorite
dikes intruded into mobile granite magma, and large dike segments containing large purple
plagioclase xenocrysts and xenocryst clusters.
Starting point and other logistics: 9:00 AM at Sunoco Station service area on Route
128 just north of Exit 19. First Stop will be Rafe’s Chasm Park, Magnolia, Gloucester.
Trip B5. ALLEGHANIAN METAMORPHISM OF THE SOUTHERN NARRAGANSETT
BASIN, RI: HINGED BURIAL AND EXHUMATION.
Leaders: Daniel Fetherston, Daniel Murray, and Robert Wintsch
Description: The Pennsylvanian Rhode Island Formation (RIF) preserves in detail the effects of
the Alleghanian orogeny on southeastern New England. This trip will revisit classic locales along
the southern RI coast, where new metamorphic and geochronologic data will be presented that
tightly constrain models for the burial, deformation & regional metamorphism, and exhumation of
the Narragansett Basin. Stops include chlorite to sillimanite grade metasedimentary rocks, as
well as the contact of the RIF with the Narragansett Pier Granite. The start and end of this trip
are the same as those for the Carter et al trip on Sunday. Moreover, both trips will lunch at the
locale where the contact between the Pennsylvanian cover and the Pre-Alleghanian basement
occur.
Starting point and other logistics: 9AM at commuter parking lot at intersection of
Route 1A and 138. Allow 1.5 hours, to go from Wellesley College to the starting point of
the trip. We will consolidate vehicles at the start, and the trip will finish here at 4PM.
The trip is suitable for all vehicles, and will entail less than ~40 miles of driving. The
stops will be primarily on shoreline outcrops, and waterproof shoes with good grip are
needed. Bring lunch, as there will be opportunities to purchase food only at the start in a
convenience store.
Group size limited to 50.
Trip B6. GROUNDWATER CONTAMINATION IN WELLESLEY AND NORWELL,
MASSACHUSETTS: LOCATION OF SOURCES AND PROTECTION OF PUBLIC
WATER SUPPLIES.
Leaders: Jim Besancon, Rudi Hon, Peter Dillon, David Beutel, and Bianca Bello
Description: We will visit three contaminant sources on the Wellesley College campus: the
Paintshop Pond lead and chromium paint pigment site (remediated), the Alumnae Valley coal tar
site (being remediated), and the sodium chloride sources affecting campus drinking water,
demonstrating some of the field sampling and analysis methods used to trace their origin. We will
then proceed to Norwell, Massachusetts where a small (10 square miles) drainage basin supplies
most of the town water supply. If current trends continue, drinking water chloride content will
reach EPA Secondary Maximum Contaminant Drinking Water limits within the next decade.
Eleven new Geoprobe wells and cores, piezometer nests, long duration high frequency logging of
surface and groundwater levels and specific conductivity, and extensive chemical analysis all
help distinguish between several potential salt contaminant sources. We will examine the main
production well, and visit several field measurement sites along Third Herring Brook. We will tour
2014 Trip List p. 7
the Norwell water treatment plant which produces most of the town supply. This trip is
especially appropriate for students.
Starting point and other logistics: This is the one trip originating at Wellesley that will
not assemble in the Science Center Parking lot. Instead head west on Route 135 past
the West Entry to the College and turn left on drive immediately past the Keohane
Sports Center shown in the campus map. Follow drive on left around to (unmarked)
parking lot west of the Distribution Center. We will depart at 8:30 for walk to first stop
(on campus)
Group size limited to forty. Participants should bring lunch and all-weather clothing.
Trip B7. THE SEISMIC, HISTORIC AND GEOLOGIC RECORD OF EARTHQUAKES
IN NEW ENGLAND
Leaders: Katrin Monecke, John E. Ebel, Iglika Atanassova (with contributions from
Charlotte Benishek, Michaela Fendrock, Emma Howey, Diana Lee, Rosalie Sharp)
Description: The USGS National Seismic Hazard Map indicates an increased seismic hazard for
northeastern Massachusetts and southeastern New Hampshire, which is largely determined by
the occurrence of two damaging historical earthquakes, the A.D. 1727 Newbury, MA, magnitude
M=5.6 and the A.D. 1755 Cape Ann, MA, M=5.9 earthquakes. This trip will start at the Weston
Observatory that operates the New England Seismic Network. Here we will discuss the recent
seismicity in New England and how it relates to the historically reported earthquakes. Then we
will visit the Bloody Bluff Fault Zone in Minute Man Park, Lexington, MA, as well as other major
faults in the Newbury area to get an idea about the regional tectonic setting and possible sources
of the 1727 earthquake. Numerous historical accounts of liquefaction exist for the epicentral
region of the 1727 earthquake and were identified in trenches during paleoseismic studies in the
Newbury area in the early 1990s. We will visit some of these locations (now largely obscured due
to development) and analyze the liquefaction potential of exposed quaternary sediments in this
area. In addition, we will present preliminary results from recent paleoseismic studies of lake
sediments in northeastern Massachusetts. A number of historic houses built in the late 17 th
century exist in the Newbury area and if time allows, we will evaluate the potential structural
damage to these historic sites.
Starting Point and other logistics: 8:00 am at Weston Observatory, 381 Concord
Road, Weston, MA 02493-1340 (for directions see:
http://www.bc.edu/content/bc/research/westonobservatory/about/directions.html). Please
bring lunch and water and dress accordingly to the weather. Trip limit: 20
Sunday—October 12
Trip C1. Bedrock Geology of Boston Harbor: Cambridge Argillite and associated
diabase sills and debris flows.
Leaders: Peter J. Thompson, Joe Kopera, Marty Ross. Dick Bailey, Meg Thompson
Description: The focus of this trip will be the Cambridge Argillite, including the latest thinking on
internal stratigraphy and depositional setting, relations to the rest of the Boston Bay Group, new
data on diabase sills and dikes, and structure beneath Boston Harbor, based on recent mapping
of the Hull 7 ½′ Quadrangle and reports on the geology of sewage tunnels: the Inter-Island
Tunnel and the Outflow Tunnel. The trip will start in the morning with a traverse in Squantum to
view multiple debris flows within the Cambridge. (The cost of this early part of the trip is included
in the conference registration). We will then go by boat to Calf Island, the largest of the Brewster
2014 Trip List p. 8
Islands north of Boston Light. The boat trip is limited to 24 people in addition to trip leaders, and
the cost will be $45 per person. If weather conditions preclude landing on Calf, alternate stops
will be arranged on the mainland and your money will be refunded.
Starting Point and other logistics: Meet at 8:30AM at the American Legion parking
lot, Squantum Head, Quincy, to the left before the bridge to Moon Island. (We must
schedule this early in order to catch the low tide). Bring lunch.
2014 Trip List p. 9
Trip C2. BEDROCK GEOLOGY AND GEOMORPHOLOGY OF THE BREAKHEART
AND LYNN WOODS RESERVATIONS: WHAT THEY REVEAL AND WHAT STILL
NEEDS TO BE EXPLORED.
Leaders: Lindley Hanson and Rory McFadden
Description: This trip focuses on the geology of the Lynn Woods and Breakheart reservations, where we
will use contact relationships viewed in outcrops and in glacial erratics, and new U-Pb age data to
evaluate magmatic, stratigraphic and tectonic relationships of rocks within the Boston-Avalon Terrane
north of the Northern Border Fault. New data indicate that at some locations, rocks previously mapped as
Lynn Volcanics are most likely Middlesex Fells Volcanics. We will also investigate contact relationships
between the Neoproterozoic Westboro Formation and the Middlesex Fells in the Breakheart Reservation,
and investigate the nature of the Walden Pond Fault that delineates the northern portion of Burrill Hill
structural block in Lynn Woods. Lunch will be at the Saugus Iron works where we will stop for a brief tour.
Starting Point and other logistics: Meeting place is the Walden Pond entrance to Lynn Woods:
Lat 42.493283° Long -70.977386°. Meeting Time 8:00. Bring comfortable walking
Trip C3. CLIMATE CHANGE COMES TO THE SOUTH SHORE OF RHODE ISLAND:
EROSION, INUNDATION, MIGRATION
Leaders: Jon Boothroyd, Bryan Oakley, Scott Rasmussen, Janet Freedman, Stephen
McCandless, Matthew Dowling, Robert Hollis
Description: The trip will focus on coastal hazards and human response to same along the
southern shore zone (barriers and headlands) of Rhode Island from Narragansett Pier to
Westerly. Hazards include frontal erosion from storm waves, storm-surge inundation (now and
future), and barrier migration under conditions of present, and accelerated, sea-level rise. We will
examine some changes from Superstorm Sandy, including interesting coastal-zone management
issues (beach and foredune replenishment for instance).
Starting Point and other logistics: Remote start. We will assemble in the south
parking lot at Narragansett Town Beach (Stop 1) at 8:30 am.
Consolidate if you can at Wellesley (northbound people). We can also leave cars at Stop
1. Number of vehicles will indicate individual stop locations; we cannot fit a large number
of vehicles at some locations.
Bring lunch.
2014 Trip List p. 10
Trip C4. STRUCTURAL HISTORY OF THE NASHOBA TERRANE - MERRIMACK
BELT BOUNDARY ZONE, EASTERN MASSACHUSETTS
Leaders: Yvette D. Kuiper, J. Wesley Buchanan, Robert Charnock, J. Christopher
Hepburn, Joseph P. Kopera
Description: The Nashoba terrane is an early Paleozoic arc-backarc complex with Ganderian
affinity, while the adjacent Merrimack belt to the northwest consists of Silurian metasedimentary
rocks, likely derived from both Ganderian and Laurentian sources. The Nashoba terrane was
metamorphosed under upper amphibolite conditions while the Merrimack terrane adjacent to the
Nashoba terrane only reached greenschist facies conditions. Both are strongly deformed, but the
deformation styles are different and the ages of deformation may not be the same. While
deformation in the Nashoba terrane is predominantly consistent with Acadian and Neoacadian
ages, deformation in the Merrimack belt may be predominantly Alleghanian. We will compare and
contrast structures in the partially migmatized rocks of the northwestern Nashoba terrane with
those in the Merrimack belt, and the (proto)mylonitic and cataclastic rocks along the ClintonNewbury fault zone between them. The relative and absolute timing of structures across the fault
zone and the potential relationships between them will be discussed.
Starting Point and other logistics: Meet in the parking lot east of the Wellesley
College Science Center, at 8 AM where we will carpool as much as possible. Please
bring lunch; we will picnic at the outcrop.
Trip C5. ALLEGHANIAN DEFORMATION OF CAMBRIAN METASEDIMENTARY
ROCKS IN SOUTHERN NARRAGANSETT BAY, RI: IS THERE EVIDENCE FOR PREALLEGHANIAN TECTONISM?
Leaders: Matthew Carter, Daniel Murray, and Sharon Mosher
Description: The southern half of Conanicut Island RI includes the most complete and well
exposed occurrences of Cambrian-aged Avalonian metasedimentary rocks in the USA. This trip
will focus on recent fieldwork carried out by Matthew Carter that provides new insights into
Avalonian and Alleghanian orogenesis in southeastern New England, and which can be used to
test the assertion that all of the penetrative deformation recorded in the Cambrian rocks can be
attributed to Alleghanian tectonism, as seen in the contiguous Pennsylvanian rocks of the
Narragansett Basin.
In the spirit of NEIGC this field guide will also prove of use to a diverse audience, that includes
not only geologists familiar with the tectonic evolution of the Appalachian orogeny, but also STEM
educators, from middle school through college, who wish to incorporate these superb examples
of geologic features into their courses. James Sammons has prepared a supplement to the trip
guide that provides strategies for incorporation of the Beavertail geology into field and classroom
activities suitable for middle and high school.
Starting Point and other logistics: 9AM at commuter parking lot at intersection of
Route 1A and 138. Allow 1.5 hours for trip to starting point from Wellesley College. We
will consolidate vehicles at the start, and the trip will finish here at 3PM. The trip is
suitable for all vehicles, and will entail less than 20 miles.
The stops will be on shoreline outcrops, and appropriate shoes are needed. Bring lunch,
as there will be opportunities to purchase food only at the start in a convenience store.
All stops are “hammer free”, and sampling of fossiliferous rocks is not permitted.
2014 Trip List p. 11
Trip C6. GEOMORPHIC RESPONSE TO THE REMOVAL OF THE MERRIMACK
VILLAGE DAM ON THE SOUHEGAN RIVER, NEW HAMPSHIRE: RESULTS FROM
SIX YEARS OF MONITORING
Leaders: Noah P. Snyder and Mathias J. Collins
Description: Removing the Merrimack Village Dam on the lower Souhegan River in southern
New Hampshire in August 2008 provided a field-scale experiment in river response to a major
change in sediment flux and base level. We began monitoring the study area in August 2007,
surveying a series of eight permanent cross sections within the impoundment and four
downstream between the dam and the confluence with the Merrimack River. We also surveyed
the longitudinal profile through the 1-km study reach, measured bed grain size, and photographed
the site from ground-level stations. We conducted nine repeat surveys from 2008 to 2014, with
the greatest frequency soon after dam removal.
The dam removal resulted in a near-instantaneous 3.9-m drop in base level in the impoundment.
The river incised rapidly through the impounded sand and removed over 50% of it within two
months. This added sediment load resulted in up to 3.2 m of deposition in the downstream reach.
After the initial, rapid phase of channel adjustment, ongoing erosion of impoundment sediment
depended primarily on flood events that could access sediment stored outside of the newly
developed, active channel. This process was modulated by the recruitment of large wood from
terraces through bank erosion, which subsequently armored banks. By 2012, less than 20% of
the impounded sand remained.
After an introduction at the former dam site, the fieldtrip will spend the morning looking at the
impoundment and the early afternoon in the downstream reach. We will see evidence for rapid
geomorphic adjustment, sedimentary structures in the remaining impounded sediment and active
channel, and historical artifacts and structures. We will also discuss the role of vegetation
changes and large wood in the impoundment and adjacent wetland in the ongoing geomorphic
evolution of the site. The trip will end around 2 pm, allowing time for participants to begin the
journey home.
Starting Point and other logistics: 9 AM at the Merrimack town park on the east side
of Rt. 3 in Merrimack, NH (across from the fire station; 42°51'44"N, 71°29'34"W). This
site has plenty of parking; it is 55 minutes from the Wellesley College campus, and 2
miles from exit 11 on the Everett Turnpike in southern New Hampshire.