GEOLOGY OF THE FREDERICTON

WHITEHEAD
GEOLOGY OF THE FREDERICTON-MACTAQUAC DAM AREA
by
James Whitehead, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3
INTRODUCTION
This trip will introduce the participants to the princip al lithologies present in the Fredericton area . These
include: locally graptolite-bearing, complexly folded Silurian meta-wackes and slates of the Kingsclear Group;
Mississippian McKinley Formation red beds; several Mississippian-Pennsylvanian basaltic flows with rubbly tops
and their possible feeder dike, and; overlying Pennsylvanian Boss Point Formation quartz-conglomerates. Features
of regional significance include an angular unconformity present at the Mactaquac Dam which represents the level of
post-Acadian Orogeny erosion in the area, and the Fredericton Fault which is the shallower-level equivalent of the
Norumbega Fault Zone that is present south-west of the U.S. border. Participants will be taken on a tour of the
Mactaquac Dam, which has recently achieved infamy owing to deterioration of concrete in the water-intake and
spillway areas as a result of alkali-aggregate reactions. This could potentially halve the expected life of the dam.
GEOLOGIC OVERVIEW
The simplified geology of New Brunswick comprises a series of belts, zones and subzones that are part of the
NE-SW Appalachian trend (Figure 1). These include, from southeast to northwest, the Precambrian to Cambrian
rocks of the Avalon Zone (a.k.a. the Avalon Terrane; Williams and Hatcher, 1982), the St. Croix Subzone of the
Gande r Zone, the S ilurian wacke s and slates of the Fredericto n Troug h, the Ordo vician Sed imentary roc ks and Late
Figure 1 - Location map showing the area depicted in Figure 2. Inset map of the
province showing the b oundaries of the tectonostratigrap hic regions.
Abbreviations: AZ - Avalon Zone; CC - Carboniferous Cover of the Maritime
Basin; FT - Fredericto n Troug h; MSZ - Miramich i Subzon e; MB - Matape dia
Basin; SCSZ - St. Croix Subzone.
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Silurian to D evonian p lutons of the M iramichi Sub zone (also within the Gan der Zone ), and the O rdovician to
Devonian Matapedia Ba sin (Fyffe, 1982). These were developed during several tectonic episodes, including the
Ordovician to Silurian Taconian orogeny and the Devonian Acadian orogeny. Syn- and post-orogenic intrusions are
abundant, particularly in the Miramichi Subzone and in the St. George area in the south-west of the province (Figure
1). Central and eastern New Brunswick are unconformably overlain by Carboniferous successor deposits that
comprise part of the Maritimes Basin. These Carboniferous cover rocks are also preserved in P.E.I., Cape Breton
and parts of northern Nova Scotia (Fyffe and Barr, 1986).
METAMORPHIC AND SEDIMENTARY ROCKS
Silurian rocks in the Fredericton region consist of the Burtts Corner beds of the Kingsclear Group (Figures 1 and
2). They comprise thin- to thick-bedded, non-calcareous meta-wackes and interbedded slates (Wake, 1984).
Graptolites from the Cyrtograptus linarssoni to Monograptus nilsonni Zones are present in the Burtts Corner beds
near Hayesville and near Woolastock (Stop 7), and constrain the beds to a Wenlockian to upper Ludlovian age
(Fyffe, 1995 ).
Although these rocks were intensely folded during the Acadian Orogeny and weakly metamorphosed to a subgreenschist grade, this event has not significantly destroyed their sedime ntary features. These features are best
Figure 2 - Detailed location map showing stops. Abbreviations: F’ton - Fredericton
center; MSR - Mazerolle Settlement Road; RRQ - Royal Road quarry; TCH Trans-Canada Highway; UNB - University of New Brunswick; WB Woolastock Bridge.
preserved where folding-induced layer-parallel shear and penetrative slaty cleavage development are at a minimum.
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Sedimentary features include: tool marks (Stop 3) and flute casts (Stops 4 and 8) whose orientations differ
significantly betwe en beds; gr aded units (S top 4); sma ll bed scou rs (Stop 13 ), and; cross-b edded laminations.
The Siluria n units are interp reted to hav e been de posited o n the continen tal rise region o f a middle P aleozoic
ocean, which closed during the Acadian Orogeny (Berry and Osberg, 1989). Erosional horizons and the development
of large scale flute casts are consistent with instabilities on the continental rise having generated these turb idite units.
Carboniferous sedimentary units present in the Fredericton area belong to the Mabou, Cumberland and Pictou
groups (va n de Po ll, 1995; va n de Po ll and others, 1 995) an d were prin cipally depo sited during N amurian to
Westphalian times (during a period that brackets the Mississippian-Pennsylvanian boundary) (Figure 3). Red
conglom erates, brec cio-conglo merates, sand stones and siltstones of the M cKinley Fo rmation (M abou G roup) loc ally
rest unconformably on the Lower Paleozoic Silurian turbidites at the Mactaquac Dam (Stop 4) and along the new
Trans-Canada Highway (Stop 11). At the basal conglomerate, angular clasts of the Silurian Kingsclear Group are
commo n. Rapid c hanges in wa ter velocity are d emonstrate d by a wide variation in gra in sizes and er osional ba ses to
the coarses t-grained be ds. The M abou G roup has b een com pared to th at of contem porary alluv ial fan depo sits
deposited in areas of low relief (van de Poll, 1995).
Overlying the basalt flows in the Carlisle Road quarry on the north side of the Saint John River at Fredericton
(Stop 1) are highly mature, buff-colored quartz conglomerates that belong to the Boss Point Formation (Cumberland
Group ). Veining o f jasper is pre sent at this location . The upp ermost flow( s) in the Carlisle R oad qua rry is
Figure 3 - Stratigraphy of selected locations in the Fredericton area. Stratigraphic units after van de Poll and
others ( 1995) and Keighley (1996). Abbreviations: Fm. - Formation; Mnt - Mountain; RB - red
bed units, as in Figure 4; Rd - Road; Sil - Silurian, and; Stn - Station.
discontinuous, which may reflect its original lateral extent, or may indicate so me erosion of the upp ermost flow(s)
prior to the deposition of the Boss Point Formation. The Boss Point Formation is not exposed in the Royal Road
quarry, thou gh is present 4 00 m (36 0 yds) to the N E of the qua rry along a hyd ro line cut.
The bulk of the Ca rboniferous sedimentary ro cks in the Fredericton area are buff-colored sandstones,
conglomerates with minor red siltstones of the Westphalian Pictou Group. These mature sandstones are dominated
by moderate- to well-rounded quartz clasts, though granitoid clasts, presumably derived from the erosion of
Devon ian plutons, an d slate clasts also occur loca lly. The sand stones com monly con tain plant leave s, Calamites
stems and fossilized trees which are indicative of an increasingly humid climate. This contrasts with the Lower
Carbon iferous arid clim ate during wh ich extensive e vaporite d eposits form ed in the south of New B runswick and in
Nova Scotia. Paleomagnetic studies of Namurian Mabou Group basalt flows (see below) indicate a paleolatitude of
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WHITEHEAD
36°N at that time (Seguin and Fyffe, 1986).
Thick units o f interbedd ed red siltston es have be en used to su bdivide the Pictou G roup into up to eight cyclic
sandstone-siltstone units (van de Poll, 1995). Such a marker siltstone unit can be seen on the north-bound lane of the
new Trans-Canada Highway, 16 km southwest of Fredericton (see road log, 82.1 km, 51.3 miles). If this red siltstone
is a laterally extensive marker, it divides cyclic sequence I to the southwest, from cyclic sequence II underlying the
city of Fredericton, or subdivide s sequence I into uppe r (1b) and lower (1 a) sub-units.
IGNEOUS ROCKS
Igneous ro cks in the vicinity of F redericton are restricted to several C arbonifero us alkalic basa lt flows and its
possible fee der dike o n the north side of the Saint Jo hn River. E xposures within the eastern -most outcro p of the Late
Silurian-Ear ly Devonia n Pokiok granitoid ba tholith are pre sent -27 km (16.9 miles) to the west of the city (Figure
1).
The basalts comprise sparse plagioclase phenocrysts (up to 2mm in diameter) with a groundmass comprising
sub-millimeter-sized andesine to labradorite which is enclosed subophitically in clinopyroxene (Wo 46 En 36 Fs 18),
iddingsite-chlorite replacements of olivine (Fo 47-48). Minor c onstituents includ e interstitial analcim e, calcite, apa tite
and Fe-T i oxides (Fyffe a nd Barr , 1986).
Their major- and trace-element chemistries are consistent with a continental intraplate origin (Fyffe and Barr,
1986). Although they have not been dated by radiometric dating techniques, upper-Mississippian spores have been
identified from a core sample of the underlying McKinley Formation red beds (Barss, 1983) (Figure 3). The flows
are therefore upper Mississippian to lower
Pennsylvanian (Namurian) in age.
Crustal exten sion during the Early
Carboniferous gen erated mantle melts, whose
erupted equivalents decreased in quantity through
the rest of the Carboniferous as the extension
waned. Inc reasing fractio nation of the m antle melts
coupled with decreasing amounts of source melting
controlled their geochemical evolution from
initially basic alkalic basalts in the late Visean and
Namuria n to peralka lic rhyolites in the late
Westphalian (Fyffe and Barr, 1986).
Two discrete, 30°NE-dipping flows are
separated by a red arg illaceous to ar enaceou s unit
from 3 to 4 m (10-13') thick in the old city quarry
on Royal Road. A second, larger quarry on the
Carlisle Ro ad (Stop 1) is curiously un reported in
the literature (Figure 4). This location exposes three
stratigraphic levels of flows, the lower two of which
are separa ted by a unit o f interbedd ed hema titic
argillite and arenite 1 to 4 m thick. The lower two
laterally-extensive flows extend with uniform
thicknesses ac ross the 15 0 m width o f the quarry.
The uppermost volcanic unit appears to have
divided into at least two, possibly three flows,
separated by clastic basaltic rubble (aa). Although
the duration of the volcanism is unknown, it is clear
that periods of active effusion were interspersed
with volcanic-q uiescent per iods in which c lasts
from the rubbly tops of the flows were incorporated
into overlying red beds. The lateral continuity of
Figure 4 - B edrock g eology of the Carlisle Ro ad quarry. K ey: B the red beds in the Carlisle Road quarry and the
- baked contact; J - Jasper veining in the Boss Point Fm; H - presence of basaltic intrac lasts within this unit
clearly indicate that the red be ds are not m erely a
specularite (hematite)-calcite slickenfibers in excavated
local raft of red sedimentary rock entrained by the
basalt blocks; RB - red beds (McKinley Fm); * - curved
flow (cf., Laughlin, 1960).
jointing patterns indicative of the toes of two lava flows.
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The tops of the flows are rubbly and more highly vesiculated than lower parts. The flows are typically massive,
though flow-parallel jointing and margin-orthogonal columnar jointing are heterogeneously developed. Near the
entrance to the uppermost Royal Road quarry and in the northwest wall of the Carlisle Road quarry, curvature of the
flow-parallel jointing mimics the pattern expected in the toe of a lava flow. The closure direction of the curvature
provide s a crude ind ication of the p rovenanc e direction o f the lava flow (Fig ure 5). On this basis, the flow (la va unit
2; Figure 4) in the Carlisle R oad qua rry came fro m the south, an d the Roya l Road lav a flowed fro m the west.
A 30°east-dipping, columnar jointed basalt dike occurs at Currie Mountain (formerly Clarke’s Hill) (Stop 2). It
intrudes and bakes horizontally-bedded
McKinley Formation (Mabou Group)
red siltstones and sandstones. Rounded
void spaces in the siltstone suggest that
the sediment was not lithified during
intrusion of the dike and that heat
conducted from the dike caused pore
water to boil. This, coupled with the
geochemical similarities between the
dike and flows, and the presence of
McKinley-type red-beds between lavas
in both quarries indicates that the dike
and flows are broadly
contemporan eous.
It has been suggested that the
Figure 5 - Basalt in the Carlisle Road quarry, exhibiting curved cooling
Currie Mou ntain dike feeds the flows 5
joints that define the original morphology of the advancing lava flow, km to the northeast in the Royal Road
which indicate a northerly flow direction. Note the dog in the
quarry (Bailey, 1910). The new
foreground for scale.
exposure s in the Carlisle R oad qua rry,
located less th an one kilom eter (0.5
mile) to the north of Currie Mountain, provides a closer tie between the flows and the potential feeder dike than
existed between the dike and the lavas in the Royal Road quarry. The flow directions in both quarries, based on the
curved jo inting patterns se en in the basa lts, are also con sistent with having b een derive d from the C urrie Mo untain
area.
STRUCTURE
Several episodes of deformation can be distinguished in the Silurian rocks. The principal folds in the region are
upright, generally high amplitude folds that plunge shallowly to the NE or SW. They typically possess tight hinge
zones with straight limbs (approaching a chevron fold morphology; Stop 9) though locally, lower amplitude open
folds are present (Stop 10). Modification of these folds by limb faulting as the interlimb angle decreases is common,
especially where the psammite beds are of non-uniform thickness. Steeply plunging slickensides along the bedding
surfaces sugg est folding by flex ural slip. The pelites posse ss a well-develo ped axial p lanar slaty cleava ge, with little
or no cleavage in the wack e beds. The clea vage develope d during the Late Silurian, conco mitant with the earliest
phases of the intrusion of the Pokiok batholith (Caron, 1996).
A later set of sm all-scale chevro n folds with nea r-horizontal a xial surfaces are locally presen t. These pr obably
correlate with the second generation folds identified by Fyffe (1995) in the Flume Ridge Formation south of the
Fredericton Fault. Conjugate sets of kink folds are also present in the Burtts Corner beds, and probably post-date the
recumbent chevron folds if the folding age relationship deduced south of the Fredericton Fault (Fyffe, 1995) can be
extrapolated to this area.
The Fredericton Fault is the northern, shallow-level equivalent of the mid- to upper-crustal Norumbega Shear
Zone exposed south of the U.S.-Canada border (Hubb ard and others, 1995). Seismic reflection surveys in Maine
indicate the fault penetrates the Moho (Doll and others, 1996).
Although it has been assigned the distinction of a major terrane boundary (Keppie, 1985), the similarities of the
Silurian Burtts Corner beds and the Flume Ridge Formation to the north and south of the fault in New Brunswick
suggest continuity, though the fault may still have accommodated significant transcurrent motion (Fyffe, 1995).
Rotation of slaty cleavage in the Kingsclear Group near the Fredericton Fault indicates a dextral-transcurrent motion
(Fyffe, 1988 ). Although p ost-Devo nian move ment is not exte nsive (W ones, 198 0), post-Ca rbonifero us motion is
indicated by the truncation of Carboniferous beds in the Fredericton area (Figures 1 and 2). Extensive specularite-
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WHITEHEAD
calcite slickenfibres along joints in the vicinity of the fault in the Royal Road quarry possess shallow plunges and
may indicate continued post-Carboniferous strike-slip motion. Along the new Trans-Canada Highway at Stop 14,
normally near-horizontal Pictou Group sandstones and conglomerates are increasingly tilted with proximity to the
Fredericto n Fault until they are locally overtur ned. Th e Frederic ton Fault is now here expo sed, though is located to
within 10 m (30‘) along road-cuts along the new Trans-Canada Highway (Whitehead and Park, 2001) (Stop 13).
Although four post-Famennian (Late Devonian) periods of deformation are discernible in the Canadian
Appala chians, the first is thoug ht to have be en restricted to Nova S cotia and so uthern Ne w Brunsw ick (van de P oll
and others, 1995), while the second, although regional, cannot be clearly discerned in the Fredericton area.
Subsidence following the sec ond period o f deformation allowed o nlap of the Carbonifero us sediments to its greatest
extent on the underlying bedrock. Deformation inducing the gentle tilting of the Carboniferous strata in the
Fredericto n area is believ ed to have occurred between E arly Permia n and Late Triassic time s because E arly Triassic
red beds on P.E.I. are tilted, and an angular unconformity exists between mid-Carboniferous and Triassic strata in the
Bay of Fu ndy region ( van de P oll, 1983 ). This perio d also gene rated the reg ional synclines su ch as the M arysville
basin (Figure 1) and the Moncton Basin (van de Poll and others, 1995). The fourth, post- Triassic period of
deformation canno t be distinguished in the Fredericton are a owing to a lack of preserve d Triassic sedimentary roc ks.
MACTAQUAC DAM
The Mactaquac Dam is located at the confluence of the Saint John and Mactaquac rivers. Mactaquac in the local
indigenou s Maliseet la nguage, trans lates as ‘big bra nch’ alluding to this meeting of the waterways. Sin ce its
construction in 1968, the dam has been the largest hydroelectric plant in the Maritimes, with a generating capacity of
600 megawatts of power.
The structu re is of comp osite design: the water intakes a nd spillways we re construc ted of massiv e concrete while
the main section of the dam comprises a core of various grades of sieved tills and crushed Silurian metagreywackes
and slates, derived almost entirely from the excavated region where the intake channels and spillways are now
located (Watson, 1970). This main section, known as a rockfill dam, was chosen over a wholly concrete dam owing
to the ease with which the rockfill could be placed on top of surficial deposits present in the river valley without
requiring their complete removal, thereby expediting the construction time by approximately one year over that
anticipated for a wholly concrete structure. Additional bedrock widening of the channel would also have been
necessary for a concrete dam should additional faults have been discovered during excavation (Watson, 1970).
Surficial deposits in the area comprise: up to 30 m (100') of permeable silts, sands and gravels that comprise an
artesian layer; an overlying 20 m (65') of imp ermeable tills, including a lowe r, stiff brown till and a n upper gr ay till
with considerably lower yield strength; a discontinuous unit of estuarine clay up to 16 m (53') thick deposited during
flooding o f the river valley at the end of the last gla ciation, prior to significant isostatic readjustm ent and; a
discontinuous layer of alluvium up to 7 m (23') thick. Assessments of the yield strengths of these layers indicated that
the alluvium, estuarine clays and weak gray till were incapable of bearing the load of the rockfill dam, and were
consequently removed. The removal of these overlying units temporarily released the pressure within the basal
artesian layer, whose pore water pressures had to be reduced via piping in order to prevent rupture of the overlying
brown till until the m ain mass of the rockfill was introd uced.
The elevated wa ters behind the dam extend some 97 km (6 0 miles) upstream and floo ded numerou s settlements.
Historically significant buildings were relocated to the Kings Landing Historic Settlement which is the province’s #2
tourist attraction, located 14 km (9 miles) upstream of the dam. The additional crustal load provided by the headpond waters may have resulted in local subsidence, though absolute ground elevations were not established during
the local surveying prior to dam construction to allow for a present day comparison. Glacial striae that are offset
vertically along joints may have been generated by loading-related subsidence or by isostatic rebound following the
last glaciation.
The concrete sections of the dam are suffering from alkali-aggregate reaction damage (AAR). AAR decay
involves a reaction between the cement and aggrega te clasts that contain fine-grained quartz (Dem erchant and others,
2000) and results in volume expansion and cracking, which can affect the operation of equipment in the structure.
Despite an original expected lifespan of one hundred years, a NB Power Commission engineering report contracted
in 1999 estimated the remaining lifespan to be 15-30 years, should the AAR-related decay continue at the current
rate (Seguin, 2000). Remedial action is currently underway to reduce the effects of the AAR damage.
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WHITEHEAD
ACKNOW LEDGEMENTS
Thanks are extended to Adrian Park for providing companionship and expertise during transects along the new
Trans-Canada Highway, and to Les Fyffe and Ron Pickerill for providing useful feedback on an earlier version on
the manuscript. Logistical support provided by the DNRE Minerals and Mines Branch for one of the preliminary
excursions is gratefully acknowledged.
ROAD LOG
The assembly point is in the parking lot of the Holiday Inn at Mactaquac, 9.00 am, 22nd September, 2001.
Participants will be asked to consolidate into as few vehicles as possible as parking is severely limited at a number of
the stops. B ring lunch with yo u, as we will have no opp ortunity to stop for supplies.
km (mile)
0.0 (0.0)
8.1 (5.0)
15.0 (9.4)
15.5 (9.7)
15.7 (9.8)
Turn left at the exit to Holiday Inn Mactaquac and cross the dam. Take the first right, Route 105
east, towards Fredericton.
Route 104 will join from the left. Continue east on Route 105.
Turn left at C arlisle Cross R oad. At the T -junction with C arlisle Road , turn left.
The entrance to the Carlisle Road quarry is immediately opposite civic address 139. Take the right
hand (low er) track into the quarry.
STOP 1: Drive into the quarry. There are three layers of lava exposed. The lower two are present
in the lowest excavated bench and are separated by a hematitic siltstone-sandstone bed 1 to 4 m (3
to 13') thick. The flow tops are rubbly and rip-up clasts of basalt are incorporated into the lower
parts of the overlying beds. The base of the volcanic unit 2 (Figure 4) has baked <10 cm (4") of the
underlying red beds. The upper part of volcanic unit 2 is extremely rubbly, resembling aa lava.
Internal shearing of the lavas are defined by attenuated vesicles and shrinkage joints parallel to the
cooling surface. These jo ints are curved at two localities (Figure 4) and define the toe of two flows,
that advanc ed from the south.
Fracturing o f the basalt as it adv anced o ver wet red siltsto nes, has resulted in injections of silt
veins into the flow at the northern end of the quarry. A third flow(s) overlies the lava and lava
rubble of v olcanic unit 2 in the northern end of the q uarry. The upperm ost flow(s) was p artially
eroded prior to the deposition of the overlying B oss Point Forma tion mature quartz conglo merates.
Jasper veining is present in the Boss Point Formation.
Return to vehicles and proceed to the quarry entrance.
15.9 (9.9)
Exiting the quarry, turn left on Carlisle Rd. Take the first right, onto Carlisle Cross Road again.
Turn right a t the bottom . Drive 1.2 km to Curr ie Mou ntain.
17.6 (11.0)
STOP 2: The exposure adjacent to civic address 1122 is the largest exposure on Currie Mountain.
Take care when cutting across the oncoming traffic into the parking lane adjacent to the river. The
contact between a basaltic dike and the adjacent McKinley Formation is present at the western end
of the exposure. The dike dips 30° towards 114° (east) and the intruded hematitic siltstones and
sandstones are horizontal. Columnar jointing orthogonal to the cooling surface is well developed
within -10 m (30 ') of the contact. E xposures along the ba se of Currie M ountain indic ate that this
dike is greater than 200 m (650') wide. A fissile iron-reduced contact zone is developed in the
McKinley Formation within 10 cm (4") of the dike contact. Voids in the sediment may be related
to boiling of pore water during intrusion.
On leaving, the exposure, continue back to the Mactaquac head pond, turn left towards Edmunston
and re-cross the dam. Immediately after crossing, turn into the parking lot that overlooks the dam.
30.9 (19.3)
STOP 3: View of the dam. On foot, take the path at the rear of the parking lot into a small quarry
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on the right. Weakly metamorphosed, steeply dipping Silurian beds belong to the Burtts Corner
beds of the Kingsclear Group . The exp osure is pred ominantly ps ammite with m inor pelitic
intercalations. Tool marks and small current-eddy pits 1 to 10 cm wide indicate that the beds are
inverted. T he anastom osing fissility of the pelites , generated by layer-para llel slip during their
folding, masks any cleavage. Both limbs of a tight, upright anticlinal synform can be seen, though
the core is disrupted (a common feature, owing to competence contrasts between the pelite and
psammite layers).
Continue a long the track . Winsco nsinan basa l till is present and co mprises a p oorly sorted , matrix
supporte d surficial unit up to 2 m (7') thick. T he clasts, which ra nge from sub -angular to unu sually
rounded for a till, comprise locally derived psammite and pelite, granodiorite and alkali granites
derived fro m the Pok iok Batho lith to the southwe st, buff-colored sandstone s which are p robably
derived fro m erosion of the Carb oniferous P ictou Gro up, as well as m inor rhyolite an d basalt.
Striated, glacially polished Silurian bedrock exhibits striae sets oriented 108° and 142°. The 142°
set overprints the earlier 108° set, though likely has no regional significance. Down-flow plucking
indicates an ice-flow direction up-slope, towards E-SE.
40.0 (25.0)
41.5 (25.9)
41.7 (26.1)
Leaving the p arking lot, turn righ t and cross the dam.
Turn right (e ast) onto Ro ute 105 a gain.
Turn right onto Powerhouse Road and keep left at the fork in the road at the bend.
42.4 (26.4)
STOP 4: Park opposite the first red exposure. Please pull completely off the road, as large trucks
frequent this route. This exposure comprises McKinley Formation red beds. These include a basal
unit of hematitic fissile siltstone that contains buff-colored calcareous concretions that extend
downwards from the upper limit of the bed for tens of centimeters (>6"). These may represent
concretio ns nucleated around ro ots in a caliche-typ e environm ent. The up per layers of the possible
paleosol were eroded during the deposition of the overlying 2 m (7') thick breccio-conglomerate.
The breccio-conglomerate bed sharply grades upwards into a coarse sandstone unit. Several
laterally discon tinuous sand stone-cong lomerate laye rs are prese nt.
Walk over the grassed area towards the river. The uphill extremity of the first exposure on the
north side of the road is McKinley Formation breccio-conglomerate. This is underlain by Silurian
Burtts Corner beds. The former extent of the Acadian angular unconformity exposure was hidden
under the gr assed area during land scaping follo wing constru ction of the da m.
Return to ca rs and drive to the parking lot at the bottom of the hill.
42.9 (26.8)
The Burtts Corner beds opposite the Mactaquac Fish Culture Station sign include at least four
identifiable pa ckets of fine-grain ed, well-sorted psammite g rading upw ards to fissile pe lite, with
large flute casts defining the base of each packet. The beds dip steeply (76°) to the west, though
are not inverted as seen at STOP 3.
42.9 26.8)
STOP 5: Tour o f the Macta quac D am, prov ided by staff of the facility.
Drive back up the hill, turn left at the junction with Route 105, then take the first right (signposted
Mactaquac North, Route 105).
44.3 (27.7)
STOP 6: After 300 m (330 yds), pull off the road to the picnic area by the waters edge for
LUN CH.
Re-cross the dam and pass the Ho liday Inn.
46.5 (29.1)
56.9 (35.6)
Take Route 102 (inaccurately signposted Route 2 at the time of writing) towards Edmundston.
Note the folds in the Burtts Corner beds on the left (east) side of the road. These were generated
during the Acadian Orogeny, as a result of the collision of the Meguma Terrane with the
Laurentian margin in the Devonian.
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WHITEHEAD
65.2 (40.8)
STOP 7: Pull completely off the road. Take care crossing to the oxidized iron-stained area of the
exposure. The staining belies the presence of pyrite which is spatially associated with the
graptolite-bearing organic-rich horizon. Graptolite localities are rare, owing to the pervasive
Acadian cleavage in many exposures and destruction by layer-parallel slip during folding.
Consequently, please DO NOT HAMM ER THE EXPOS URE. Collecting can be done from the
copious samples in the scree. Monoserial- and biserial-stiped graptolites are common, as are
curved Cyrtograptus sp.
Continue south and slow at the picnic sign. Park before the sign.
67.3 (42.1)
STOP 8: Classic overturned flute casts are present in this exposure (Figure 6). The timing of enechelon quartz veining seen at the southern end of the flute cast occurrence is moot. They may be
the consequence o f Acadian or later Carb oniferous earth movem ents.
Continue so uth along R oute 102 . After crossing the first inlet of the M actaquac headpo nd, pull to
the side of the ro ad by the first large exposure encounter ed.
67.8 (42.4)
STOP 9: Splendid Acadian
fold closures can be observed
on the eastern rock face
(Burtts Corner beds). Three
synforms and three antiforms
can be clearly identified.
These are steep-upright folds
with straight limbs and tight
closures. They verge to the
south. The northern limbs are
slightly overturned, as
indicated by flute casts in the
northern-central part of the
exposure. Pelite com prises a
larger fraction of the exposure
than hitherto encountered (2030%), which may account for Figure 6 - Flute casts in the Burtts Corner beds
the developmen t of these
similar folds without excessive accommodation structures (e.g., faults).
68.5 (42.8)
70.2 (43.9)
Continue south. Cross the Woolastock Bridge.
Follow the signs for Route 3, take the left hand fork in the road on the bend, and follow the signs
for St. Steph en and E dmunds ton.
At the first opp ortunity, follow the sign for Rou te 2 toward s Fredericto n.
Turn left onto Route 2 towards Fredericton (east).
70.8 (44.3)
71.3 (44.6)
73.6 (46.0)
STOP 10: 2.3 km (1.4 miles) along Route 2 pull off the road, as far away from the moving lanes as
possible. T AKE CARE , this is a dangero usly busy road and stopp ing here is not stric tly allowed. A
classic ope n antiform is pr esent here, in co ntrast to the tight fold s observed elsewhere in the Burtts
Corner beds. A synform with a pinched hinge is present at the eastern end of the exposure. Way-up
structures include: truncated foresets in cross-bed s, small scour hollows and larger flute casts.
Layer-parallel shear has opened en-echelon shear veins oriented perpendicular to bedding in the
psammite o n the eastern lim b of the larges t antiform. Pyrite is commo n along fractu res and in
asymmetric sheared lenses parallel to So. Unconformable McKinley Formation red beds can be
seen in the adjacent exposure (STOP 11).
74.2 (46.4)
STOP 11: McKinley For mation red beds a re exposed on the west side of the road. The y comprise
hematitic, clast supported conglomerates with intercalations of red sandstone. The sandstones are
locally entrained as clasts up to 30 cm (1') long by successive conglomerate layers, suggesting that
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WHITEHEAD
they were partly indurated prior to reworking. The clast load is dominated by psammites derived
by erosion of the underlying Silurian units, though limonitic buff-colored sandstones also occur.
Locally, sand stone layers are discontinuo us owing to tru ncation by su ccessive co nglomera te flows.
This outcrop of Carboniferous strata to the west of the Fredericton Fault (Figure 1), was identified
as early as 1936 by A .C. Freeze (Freeze, 1 936), without the assistance of new ro ad cut exposures!
75.0 (46.9)
Continue north along Route 2. Note the change in lithology at kilometer 75 (mile 46.9).
78.2 (48.9)
STOP 12: These gray shales, buff-colored sandstones and conglomerates belong to the Pictou
Group , which is the do minant bed rock stratigrap hic unit under the city of Fred ericton. He re, a
lower meter (3') of gray shale has been mobilized by loading owing to the weight of the overlying
beds. These overlying units include quartz-chert-conglomerates with rip-up clasts of the underlying
gray shale. Preservation of these soft clasts in the conglomerates indicates that they were
incorporated as the velo city of the current decreased. Ero sive scours into the gray shale are also
present. Overlying cross-bedded sandstones locally exhibit full sets of cross-beds, while many top
sets have be en remov ed by the ero sion that prec eded the d eposition o f subsequen t sets. In this
outcrop, the paleocurrent indicated by cross-beds was to the north-east. Fossil plants include
several logs, inte rnal casts of stem s from the arb orescent ho rsetail Calamites, and other
unidentifiable fragmented plant rem ains.
81.2 (50.8)
A thick sequence of red siltstones are present here, further north along Route 2. Red bed units have
been used as marker horizons that help subdivide the Pictou Group (van de Poll, 1995). Although
the reliability of these units as regional stratigraphic markers is questionable and depends on the
paleoenvironmental interpretation assigned to them (van de Poll, 1995), this red siltstone unit may
subdivide the lower P ictou Gro up cyclic seq uence I from the overlying cyc lic sequence 2.
84.4 (52.8)
88.6 (55.4)
Continue north and cross Mazerolle Settlement Road.
The bedding in the sandstone steepens with proximity to the Fredericton Fault, and here dips at 80°
or more.
Burtts Co rner beds are here exp osed on th e NW side of the Fre dericton F ault.
89.8 (56.1)
89.9 (56.2)
STOP 13: This stop is reached by continuing north until Deerwood Drive. Park before the overpass, well off the road. Features present include: a synformal fold closure; tool marks; unidentified
depressions on bedding planes up to 4 cm (2") wide with raised central peaks; scours on bedding
surfaces and cross-bedd ed laminated mud stones.
97.1 (60.7)
From ST OP 13 continue no rth until Exit 28 9, Hanw ell Road. T ake the exit. At the junction with
Hanwell Road , turn right towards the traffic lights. Cross into the left hand lane prior to the lights,
signposted Route 2 to wards Ed mundston . Follow the sign s for Edm undston (i.e., turn left again
after the signal lights).
You cross the Fredericton Fault from the opposite direction, immediately before the Deerwood
Drive overpass.
104.6 (65.4)
106.8 (66.8)
STOP 14: Pull into the weighbridge siding along the Highway. 20 m (70') to the south of the
southern end of the excavated area, Pictou Group sandstones and conglomerates are encountered.
The Fredericton Fault has again been crossed. The Carboniferous beds dip at 85°towards the north,
rather than near-horizontal further from the fault, owing to fault-related deformation.
110.8 (69.3)
119.9 (74.9)
126.9 (79.3)
To return to the Holiday Inn at Mactaquac or Fredericton continue to the Mazerolle Settlement
Road e xit, then follow the sig ns for Kingsc lear along R oute 640 .
At the junctio n with Route 102, turn rig ht.
Take exit 274 for the Holiday Inn at Mactaquac, and continue on Route 102 for Fredericton.
A1-10
WHITEHEAD
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