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Catastrophic tidal expansion in the Bay of Fundy,

Canada1

John Shaw, Carl L. Amos, David A. Greenberg, Charles T. OReilly,

D. Russell Parrott, and Eric Patton

Abstract: Tidal models for the Bay of Fundy, Canada site of the highest recorded modern tide show that tidal am-

plification began in the early Holocene and by ca. 5000 BP the range was almost 80% of the present range. Empirical

data consisting of 146 sea-level index points and other observations appear to contradict model results. Aggregated relative

sea-level data for Chignecto Bay and Minas Basin show that rapid tidal expansion began ca. 3400 BP. However, if we sep-

arate these two geographically separate data sets, evidence for this rapid late-Holocene tidal expansion is confined to

Minas Basin. We explain this singularity by positing a barrier at the mouth of Minas Basin, at the Minas Passage, that de-

layed tidal expansion. With the rapid breakdown of this barrier and near-instantaneous tidal expansion, water temperature

dropped, tidal currents and turbidity increased, and the form of the inner estuary was changed from lagoonalmesotidal to

macrotidal. We argue that the catastrophic breakdown of the barrier is related in the aboriginal legend of Glooscap, show-

ing that aboriginal peoples observed the rapid environmental changes and preserved an oral record for 3400 years.

Resume : Les modeles pour les marees dans la baie de Fundy, Canada lieu des plus fortes mare es enregistrees dans les

temps modernes montrent que lamplification des marees a debute a lHolocene precoce et que vers 5000 ans avant le

present, letendue des marees etait denviron 80 % de letendue actuelle. Des donnees empiriques comportant 146 points

indiquant le niveau de la mer et dautres observations semblent contredire les resultats du modele. Les donnees agregees

pour le niveau relatif de la mer pour la baie Chignecto et le bassin Minas montrent quune rapide extension des mare es a

debute vers 3400 ans avant le present. Toutefois, si nous separons ces deux ensembles de donnees geographiquement dis-

tinctes, les preuves pour cette expansion rapide des marees a lHolocene tardif se limitent au bassin Minas. Nous expli-

quons cette singularite en positionnant une barriere a lembouchure du bassin Minas, au passage Minas, retardant ainsi

lexpansion des marees. Avec la destruction rapide de cette barriere et lexpansion presque instantanee des marees, la tem-

perature de leau a chute, les courants de maree et la turbidite ont augmente et la forme de lestuaire interne a change de

lagunaireme sotidal a macrotidal. Nous postulons que la destruction catastrophique de la barriere soit reliee a la legende

autochtone de Glooscap, montrant que les peuples autochtones ont observe les changements environnementaux rapides et

en ont conserve une tradition orale depuis 3400 ans.

[Traduit par la Redaction]

Introduction

The Bay of Fundy (Fig. 1) is home to the Worlds largestrecorded tides (16.3 m) (Canadian Hydrographic Service2006). The extreme tides near the head of the bay are a re-cent phenomenon, however, and the range was relativelysmall in the early Holocene. Various authors have linked

the increasing tidal range to relative sea-level changes.Amos and Zaitlins (19841985) relative sea-level curve forthe upper Bay of Fundy Chignecto Bay region showed rel-

ative sea-level falling from a high of +48 m ca. 13 500 BPto a low of 25 m ca. 7000 BP and rising thereafter. Theyshowed a mesotidal period during the lowstand and macro-tidal conditions beginning just before 4000 BP.

Tidal modeling shows how tidal range expanded duringthe Holocene in both the Bay of Fundy and the adjacentGulf of Maine. The definitive modeling study by Scott andGreenberg (1983) demonstrated that tidal amplitudes in theBay of Fundy increased more rapidly from 7000 to4000 years ago than from 4000 years ago to the present andtidal amplitudes were linearly related to changes in waterdepth on Georges Bank (Fig. 1). Similar results were ob-tained by Gehrels et al. (1995) who concluded that M 2 tidalranges in the Gulf of Maine Bay of Fundy (as a percent-age of the present range) were 54%59% at 7000 BP, 73%at 5000 BP, 78% at 4000 BP, 85% at 3000 BP, 94% at 2000

BP, and 98% at 1000 BP.However, empirical data contradict these modeling re-

sults. Bleakney and Davis (1983) showed that a bed of oys-ters (Crassostrea virginica) in growth position in the lower

Received 9 December 2009. Accepted 11 May 2010. Publishedon the NRC Research Press Web site at cjes.nrc.ca on 7 August2010.

Paper handled by Associate Editor S. Bentley.

J. Shaw,2 D.R. Parrott, and E. Patton. Geological Survey ofCanada (Atlantic), Bedford Institute of Oceanography,Dartmouth, NS B2Y 4A2, Canada.C.L. Amos. National Oceanography Centre, The Centre forCoastal Processes, Engineering and Management, EmpressDock, Southampton, Hampshire, SO14 3ZH, UK.D.A. Greenberg and C.T. OReilly. Canadian HydrographicService, Bedford Institute of Oceanography, Dartmouth, NSB2Y 4A2, Canada.

1Earth Sciences Sector (ESS) Contribution 20090423.2Corresponding author (e-mail: [email protected]).

1079

Can. J. Earth Sci. 47: 10791091 (2010) doi:10.1139/E10-046 Published by NRC Research Press


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intertidal zone of Minas Basin, upper Bay of Fundy (inset ofFig. 1) was dated at 3800 BP. The oyster bed was 0.3 m be-low rooted trees that had died, fallen over and been buriedby sediments several hundred years previously (p. 3). Thissuggests that tidal range was restricted to less than severalmetres at that time. The authors interpreted the evidence ofoysters and other material entombed in the same deposit asindicative of water temperatures >20 8C in summer, salinity

of 20%25%, and low energy. The oysters died owing to anevent that buried them under a thick layer of clay, depositedfrom suspension. Thus, while the modeled tidal range was*80% of the modern range at ca. 4000 BP, empirical dataappear to suggest a range less than several metres at thattime. In the light of this seeming contradiction betweenmodels and observations, the goals of this paper are

By using empirical palaeoenvironmental data, argue thattidal expansion was considerably delayed in Minas Basin,relative to other areas at the head of the Bay of Fundy.

To explain this delay by hypothesizing that a natural bar-rier beach extended across Minas Passage (Fig. 1), theentrance to Minas Basin, such that tidal range was con-

strained in the mid-Holocene. Propose the hypothesis that the barrier was destroyed in a

few hundred years, tidal expansion to macrotidal condi-tions was thus near-instantaneous, and this event is re-corded in legends of the Mikmaq people, specificallythe legend of Glooscap.

Study area

The Bay of Fundy (Fig. 1) is a body of water bounded bya line from the southwestern tip of Nova Scotia to Maine.The bay generally shallows northwards. The Bay of Fundyhas the Worlds largest recorded tides (16.3 m; Canadian

Hydrographic Service 2006) the estimate for the maxi-mum possible is 17 m (OReilly et al. 2003, 2005). The

magnitudes of the tides decrease towards the mouth of thebay, and the range on German Bank (Fig. 1), south of the

Bay of Fundy, is only *1 m. The period and relative mag-nitude of the tidal wave are controlled by astronomical forc-ing such as the perigeeapogee and springneap lunar

cycles, as well as the 18.6-year nodal cycle. The magnitude

of the extreme tides is due to near resonance of the Bay ofFundy Gulf of Maine with the oceanic semi-diurnal tideheavily influenced by basin geometry and bottom friction.

In the northeast, the Bay of Fundy narrows and dividesinto two arms: Chignecto Bay and Minas Basin. Chignecto

Bay (inset of Fig. 1) shallows and narrows landwards andterminates in a series of estuaries that have been infilled bysalt marshes fronted by extensive mud flats. The majority of

salt marshes were dyked beginning in the late 1600s and re-main dyked today. As demonstrated by Noordjik and Pronk

(1981), Shaw and Ceman (1999), and others, the saltmarshes are largely inorganic but contain layers of highlyorganic sediment, which have been interpreted as having

formed during regressive episodes, when the rate of relativesea-level rise slackened (Grant 1985, 1989; Shaw and Ce-

man 1999). Near the low tide level, tree stumps in growthpositions and beds of leaves are exposed in some areas, no-

tably at Fort Beausejour (Grant 1970), Fort Lawrence (Har-rison and Lyon 1963), and Grand Pre.

Minas Basin (inset of Fig. 1) lies east of Minas Passage;farther east it is known as Cobequid Bay. The latter containselongate sand bars and sand flats (Dalrymple and Zaitlin

1994) characteristic of a tide-dominated estuary (Dalrympleet al. 1992). Salt marshes occur in many areas and are most

extensive in the southwest part of Minas Basin, the Wolf-ville Grand Pre area. Minas Passage is notable for tidal

Fig. 1. Location of the Bay of Fundy, Canada. Sable Island is visible on the extreme eastern part of the Scotian Shelf. Inset map shows

locations of 14C dating sites. (1) Aulac, Tantramar Marsh, Sunken Island, Fort Beausejour, and Fort Lawrence (Chignecto Bay); (2) Amherst

Point (Chignecto Bay); (3) Marys Point, N.B.; (4) Blomidon (Minas Basin); (5) Kingsport and Grand Pre (Minas Basin); (6) Avon River

(Minas Basin); (7) Salmon River (Minas Basin); and (8) Masstown, Minas Basin. The hook of land just north of site 4 is Cape Split.

1080 Can. J. Earth Sci. Vol. 47, 2010

Published by NRC Research Press


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currents that approach 15 km/h at times. The volume ofwater passing here in a single high tide has been estimatedas greater than the combined flow of all the Worlds rivers.The anatomy of the channel was described in the report byHuntec Ltd. (1966), who termed it the Minas PassageScour Trench (see also Swift and Borns 1967). Recent, un-published multibeam sonar surveys show that it attains a

maximum depth of 170 m below chart datum (approximatelowest tidal level) just north of Cape Split.

Methodology

Empirical data on water-level changes

We use a suite of 148 radiocarbon dates (Table 1), themajority previously published, to determine a chronology ofhigh and low water thresholds over the past 5000 radiocar-bon years in the upper Bay of Fundy. These dates havebeen collected over a long period of time and, therefore,vary in quality. In many instances, it is not clear how theelevation data were obtained, and furthermore, the relation-ship between tidal levels and geodetic datum is not well

known in much of the bay. Generally speaking, a verticalerror of 0.3 m was used, but in a few cases 1.0 m wasused. The samples that were dated comprise salt-marsh peatthat accumulated in the upper quarter of the tidal range,freshwater peat that accumulated above the highest tidal lev-els; oysters (C. virginica) that accumulated below lower lowwater (LLW) level (Morris 1973) (although they may occurintertidally (J.T. Kelly, personal communication, 2010));ribbed mussels (Geukensia demissa) that accumulated inter-tidally in Spartina marshes; sublittoral piddock clams (Zir- faea crispata) that also occur intertidally (Bleakney et al.1980); and one sample of Mya arenaria, an intertidal bi-valve (Morris 1973).

The majority of samples are from salt marshes. The bota-

nical datum, defined by high salt marsh plants, is approxi-mately equated with higher high water large tides(HHWLT). At Amherst Point, the present high salt marsh is7.6 m above the CGVD28 datum (Shaw and Ceman 1999).Mean sea level (MSL) is 0.2 m above this datum, andHHWLT is 7.8 m above. The dates are from a wide rangeof dating laboratories, many of which no longer function,and most predate the advent of accelerator mass spectrome-try (AMS) dating. Some of the samples from the AmherstPoint series were dated using AMS, as were two samplesfrom Blomidon.

The radiocarbon dates are reported as conventional dates,i.e., d13C = 25%. Calibration was performed on a group ofdates from Minas Basin to better constrain tidal range at ca.4000 BP. The calibration was performed using Calib601,with a Delta R value of 90, ascertained from the marine res-ervoir database at Queens University of Belfast, NorthernIreland (Stuiver et al. 2005).

Multibeam mapping and other geophysical data

The Minas Passage area (inset of Fig. 1) was mapped in2007 by the Canadian Coast Guard Ship (CCGS) Matthew,equipped with a Simrad EM-710 multibeam sonar, andlaunches equipped with the Simrad EM-3002 system. Thesurveys were undertaken by the Canadian HydrographicService and Natural Resources Canada. During the surveys,

the Matthew collected 3.5 kHz sub-bottom profiler data us-ing a hull-mounted Knudsen sounder. The sounder data(SEGY format) were processed to remove noise and con-verted to JPEG2000 format. They were then viewed usingPhotoshop with a JPG2000 plug in. We also had access todata collected during earlier surveys such as sub-bottom pro-filer data collected in 1966 (Huntec Ltd. 1966).

Tidal modeling

When Scott and Greenberg (1983) modeled changes in ti-dal range in the Bay of Fundy Gulf of Maine, they alteredbathymetry within several adjoining blocks to compensatefor postglacial sea-level changes. Not only have models be-come more sophisticated in subsequent years (Greenberg etal. 2005), but they can now use realistic palaeotopographyas input. We used palaeotopography adjusted for relativesea-level changes by Shaw et al. (2002). These grids haddepth values spaced *860 m apart and were sampled tocreate the mesh used for the tidal model. We used palaeoto-pography for 13, 12, 11, 10, 8, and 6 ka BP (radiocarbonyears).

Results

Radiocarbon dating of sea-level index points

The 148 radiocarbon samples (Table 1) are from two sep-arate regions in the upper Bay of Fundy: upper ChignectoBay (111 samples) and Minas Basin (37 samples).

Chignecto Bay Amherst Point

The salt marshes at the head of Chignecto Bay contain or-ganic-rich layers that Grant (1985, 1989) associated with rel-ative sea-level lowerings of several decimetres, which hethought might be tidal or steric rather than crustal or geoidalin origin. Work at Amherst Point by Shaw and Ceman(1999) was an attempt to understand the significance ofthese layers. They published a series of 56 dates on samplescollected from a salt-marsh section that has been eroded bymigrations of the Maccan River. The dates range back to3220 BP. Most samples are bulk dates collected from or-ganic-rich layers at the site, some are AMS dates on plantmacrofossils from organic-rich layers, and some are AMSdates on basal macrofossil samples. Two of the samples inthe series were freshwater peat, and the remainder formedin high-to-low salt marsh settings. Shaw and Ceman (1999)showed that the majority of dates in this swarm were oflittle use in tightly constraining the path of marsh aggrada-tion and hence water-level rise. The bulk dates were com-

monly*

600 years too old because of recycling of oldercarbon in the salt marsh. A relatively small group of basalmacrofossil dates constrained the rise of higher high water(HHW), as depicted in Fig. 2. Another four dates here areon samples from the base of the eroding salt-marsh cliff;collected by D.R. Grant (Lowden et al. 1971), they rangefrom 1800 to 2960 BP.

Chignecto Bay Aulac

This short series includes dates on four samples collectedusing an Eijkelkamp auger on the salt marsh at Aulac,close to the site at which Chalmers (1895) reported 80 feet(1 foot = 0.3048 m) of salt marsh overlying turf and

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Table 1. Radiocarbon dates.

LocationAge (radiocarbonyears BP) Lab No. Material

Elevation (metresgeodetic datum) References

Amherst Point 31555 Beta-65697 SMP 6.3670 Shaw and Ceman 1999












Amherst Point 280070 Beta-65709 FWP 0.3860 Shaw and Ceman 1999

Amherst Point 312070 Beta-65701 FWP 0.3060 Shaw and Ceman 1999


















Amherst Point 246060 Beta-68911 SMP 2.7970 Shaw and Ceman 1999Amherst Point 239060 Beta-68912 SMP 2.5720 Shaw and Ceman 1999


Amherst Point 159050 TO-4391 SMP 6.0910 Shaw and Ceman 1999











Amherst Point 219050 Beta-88460 SMP 1.4910 Shaw and Ceman 1999Amherst Point 184060 Beta-88461 SMP 3.6040 Shaw and Ceman 1999










Kingsport 2355180 GX-6812 SMP 1.6000 Scott and Greenberg 1983




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Table 1 (continued).





Beausejour 1335130 GX-8141 SMP 3.6000 Scott and Greenberg 1983




Marys Point 2225160 GX-8146 SMP 2.5000 Scott and Greenberg 1983




Aulac 250060 Beta-65696 SMP 1.7000 This paper




Sunken Island 38050 Beta-118902 FWP 6.7500 This paper

Evangeline 331025 DAL-362 M 5.0000 Bleakney and Davis 1983

Evangeline 3615100 DAL-296 O 5.0000 Bleakney and Davis 1983

Evangeline 372060 GSC-3043 O 5.0000 Bleakney and Davis 1983

Evangeline 375060 GSC-2598 O 5.0000 Bleakney and Davis 1983

Evangeline 380080 GSC-3040 M 5.0000 Bleakney and Davis 1983

Blomidon 38070 DAL-360 Z 6.3000 J.S. Bleakney, personal communication, 1980






Evangeline 367535 DAl-361 T 4.5000 Bleakney and Davis 1983

Evangeline 4115235 Isotopes inc. T 4.5000 Bleakney and Davis 1983

Evangeline 447060 GSC-3105 T 4.5000 Bleakney and Davis 1983

Evangeline 4455130 Isotopes inc. T 4.3000 Bleakney and Davis 1983

Grand Pre 3820100 Isotopes Inc. T 4.2000 Harrison and Lyon 1963

Grand Pre 3530150 Isotopes Inc. T 0.6000 Harrison and Lyon 1963Grand Pre 3100100 Isotopes Inc. T 1.5000 Harrison and Lyon 1963

Blomidon 57040 Beta-182469 Z 6.6000 This paper

Blomidon 74040 Beta-182470 Z 6.6000 This paper

Fort Lawrence 297080 Isotopes Inc. T 1.7000 Harrison and Lyon 1963




Grand Pre 4450110 Isotopes Inc. T 4.7000 Harrison and Lyon 1963

Beausejour 1790130 GSC-1030 M 1.7000 Grant 1975

Beausejour 3520140 GSC-975 T 1.6000 Grant 1975

Beausejour 4010130 GSC-930 T 3.7000 Grant 1975

Beausejour 2200110 GX-5830 SMP 6.5000 This paper, C.L. Amos


Beausejour 1620160 GX-5832 SMP 5.6000 This paper, C.L. AmosBeausejour 675125 GX-5833 SMP 5.4000 This paper, C.L. Amos








Beausejour 2925.135 GX-5841 SMP 3.4000 This paper, C.L. Amos

Salmon? 3425150 GX-5842 SMP 4.5000 This paper, C.L. Amos

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bog. The dates are from organic layers in the salt marshand are 1240 60 BP at 3.20 m below the marsh surface(Beta-74550), 2230 60 BP at 5.05 m (Beta-74551),

2100 60 BP at 5.72 m (Beta-65695), and 2500 60 BPat 5.85 m (Beta-65696). Based on work at nearby AmherstPoint (Shaw and Ceman 1999), these highly organic layers

would have formed at the highest salt-marsh level. A fifthsample, dated 380 50 BP (Beta-118902), was freshwater

peat from a short auger hole at Sunken Island, an enig-matic inlier of freshwater marsh surrounded by salt marshnear Aulac. The sample was from a depth of 0.8 m below

the bog surface and was overlain by a 0.3 m thick layer ofsalt-marsh clay.

Chignecto Bay Tantramar Marsh series

These dates, in the range of 1303770 BP, are part of a

series of 16 dates published in the thesis by Noordijk andPronk (1981). The dated samples were from boreholes onthe Tantramar Marsh, the large salt marsh in the vicinity of

Aulac (Fig. 1). They are bulk dates, unadjusted for compac-tion. We used 13 of the original 16 dates: two dates weremodern, and a third had insufficient organics for dating.

The dates are from organic layers in the salt marsh sedi-ments described by Grant (1985, 1989).

Chignecto Bay Fort Beausejour and Marys Point

Several authors have published dates from the Fort Beau-sejour area (Fig. 1), where submerged forests are exposed at

low tide. The environmental setting was illustrated by Grant

(1970, 1975) who showed the location of three GeologicalSurvey of Canada (GSC) dates, two of which were on sam-ples from tree stumps rooted in till near the modern low tide

Table 1 (concluded).



Salmon? 4045165 GX-5843 SMP 5.0000 This paper, C.L. Amos

Beausejour II 110080 Que-900 SMP 2.8300 Noordijk and Pronk 1981

Beausejour III 298090 Que-901 SMP 3.4000 Noordijk and Pronk 1981

Beausejour IV 296090 Que-902 SMP 4.4200 Noordijk and Pronk 1981

Beausejour V 377090 Que-903 SMP 4.5000 Noordijk and Pronk 1981

Nappan II 13080 Que-904 SMP 5.7700 Noordijk and Pronk 1981

Nappan III 32070 Que-905 SMP 5.5700 Noordijk and Pronk 1981

Nappan IV 88060 Que-906 SMP 5.1200 Noordijk and Pronk 1981

NappanRailway

168080 Que-907 SMP 2.0700 Noordijk and Pronk 1981

Amherst I 1100110 Que-908 SMP 2.5200 Noordijk and Pronk 1981

Amherst III 1300110 Que-910 SMP 1.0400 Noordijk and Pronk 1981

Tantramar II 700100 Que-912 SMP 3.5900 Noordijk and Pronk 1981

UpperSackville


Beausejour Is-land


Amherst Point 1800130 GSC-1076 SMP 3.9900 Noordijk and Pronk 1981

Amherst Point 1910130 GSC-1079 SMP 3.2300 Lowden et al. 1971Amherst Point 2750150 GSC-1073 SMP 0.9400 Lowden et al. 1971

Amherst Point 2960130 GSC-1075 SMP 0.2800 Lowden et al. 1971

Sackville 640130 GSC-602 T 5.6000 T. Pronk, personal communication, 2003

Amherst marsh 1000140 GSC-1032 SMP 4.3000 T. Pronk, personal communication, 2003

Tidal dam 3430110 S3238 T 1.5000 T. Pronk, personal communication, 2003

Tidal dam 3290100 S3241 T 0.6000 T. Pronk, personal communication, 2003

Amherst 5300150 S3 T 6.5000 T. Pronk, personal communication, 2003

Masstown 116070 Beta-65697 SMP 6.6000 Dalrymple and Zaitlin 1994












Note: SMP, salt marsh peat and macrofossils; FWP, freshwater peat; M, mussels; O, oysters (Crassostrea virginica); T, tree; Z, boring clam (Zirfeaacrispata).




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level (3520 140 and 4010 130 BP); the third date at thissite was on Mya arenaria shells at around the mid-tide level

(1790 130 BP). Scott and Greenberg (1983) published fourdates on the salt-marsh sediments at Fort Beausejour, rangingback to 3800 160 BP for the deepest sample. In the same

paper, they published a further four dates from Marys Point(Fig. 1), New Brunswick, on the west side of upperChignecto Bay, where the deepest sample (*10 m below

present HHW) was dated at 3640 180 BP. A series of 12dates was collected by one of the present authors, C.L. Amos.

Chignecto Bay Fort Lawrence

Drowned forests similar to those at Fort Beausejour alsooccur at adjacent Fort Lawrence (Fig. 1; Dawson 1856;Goldthwait 1924; Johnson 1925). Harrison and Lyon (1963)cited four dates from Fort Lawrence, ranging in age from2970 to 3655 BP. The lowest (and oldest) stump was de-scribed as being 10.2 feet below the mean tide level (MTL).In an earlier paper (Lyon and Harrison 1960), the stumpswere described as white pine (Pinus strobus); it was thought based on dating of just two of the stumps that the sub-

Fig. 2. Combined paleoindicator data from Chignecto Bay and Minas Basin, with lines indicating mean higher high water (top), mean sea

level (dashed, middle), and mean lower low water (bottom).

Fig. 3. Paleoindicator data from Chignecto Bay only, with line showing mean higher high water.

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mergence rate indicated was at least three times greater than

the average rate of postglacial rise of sea level as deter-mined from data presented by Shepard and Suess (1956).The high water level was believed to have increased at arate of 4.4m/1000 years. However, in the later paper (Har-rison and Lyon 1963), in which all four stumps were dated,a more complex sea-level history was proposed, with rapidsubmergence from 3700 to 3300 BP.

Chignecto Bay Miscellaneous

This is a series of five dates from various settings re-ported by T. Pronk (personal communication, 2003). Fourof the dates are on trees and range from 640 to 5300 BP.The fifth date is on freshwater peat (1000 BP). Two of the

dates were from the GSC laboratory, Ottawa, Ont.; the labo-ratory used for the remainder is uncertain.

Minas Basin Grand Pre

W. Harrison and C.J. Lyon dated four in situ stumps ofwhite pine (P. strobus) at Grand Pre (Fig. 1), at elevationsdown to 4.6 m below mean tide level and reported the re-sults in two papers. The dates, from the Cambridge IsotopesInc. Laboratory, Andover, Mass., range from 3100 to 4450BP. In the earlier paper (Lyon and Harrison 1960), thestumps were described as white pine (P. strobus). As atFort Lawrence (mentioned earlier), it was thought that thesubmergence rate indicated was greater than the averagerate of postglacial rise of sea level and the high water levelwas believed to have increased at a rate of 46.2 m/1000 years. However, in the later paper (Harrison and Lyon1963), a more complex sea-level history was again pro-posed, with rapid submergence from ca. 3800 to ca. 3400BP.

A suite of nine dates from Grand Pre was published byBleakney and Davis (1983). Four of these are on trees at*1.8 m above chart datum and range from 3675 to 4455BP. Two of the trees were birch and a third was hemlock

(J.S. Bleakney, personal communication, 2006). Three datesare from a flat bed of American oysters ( C. virginica) at anelevation of 1.5 m above chart datum and fall in the range36153750 BP. Two dates on ribbed mussels (G. demissa)at an elevation similar to that of the oysters are 3310 and3800 BP. The elevation range for all these dates isfrom 4.3 to 5.0 m, and the total age range is *1400 years.These samples from a small area are critical because theystrongly constrain tidal range. The trees are supratidal, theribbed mussels intertidal (they are found in tidal marshesrich in Spartina alterniflora), and the oysters are subtidal. Arelatively small tidal range is evident. Commenting on thestate of preservation of the oysters, Bleakney and Davis

Fig. 4. Palaeoindicator data from Minas Basin alone, also indicating mean higher high water (top), mean sea level (middle), and mean lower

low water (bottom).

Fig. 5. Modeling results showing changes in tidal amplitude at five

locations in the study area.




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(1983) noted that they were in growth position and had been

rapidly embedded in silt, which caused their deaths.The radiocarbon dates from this area were calibrated to

confirm that deductions as to a small tidal range are correct.One sigma calibrated ages for the five tree samples at 4.2

to 4.5 m span the range of 39305282 BP. Correspondingdates on oysters at 5.0 m span the range of 32513855 BP.

Minas Basin Blomidon

Bleakney et al. (1980) published a date of 865 100 BP

Fig. 6. Top: Physiography of Minas Passage based on multibeam bathymetry; bottom: interpretation. White arrow on top image indicates

position of a bedrock ridge extending northwest from Cape Split.

Shaw et al. 1087



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(DAL-318) on a boring clam (also known as the piddockclam) Z. crispata extracted from a burrow near the lowest

tide level on the intertidal Triassic sandstone platform atBlomidon (Fig. 1). Five other DAL-dates range from 200 to865 BP (J.S. Bleakney, personal communication, 1980). Theoldest dates in the series somewhat constrain the fall of thelow water level that will be discussed later. In situ boringclams collected in 2005 by the first author at the site of theBleakney series are dated 570 40 BP (Beta-182649) and740 40 BP (Beta-182470).

Minas Basin Masstown

This is a collection of 12 dates extending back to 2240 70 BP, on samples collected by Dalrymple and Zaitlin(1994) at Masstown (Fig. 1) on the shores on Minas Basin.The depths used in this study have been taken from their

fig. 15, and a vertical error of 1 m has been applied. Asfar as can be determined, these are bulk dates on organic-rich mud in a sequence of marsh sediments behind the mod-ern dyke. As at Amherst Point (Shaw and Ceman 1999) andindeed, throughout the Tantramar marshes (Noordijk andPronk 1981), organic-rich layers are embedded in organic-poor mud.

Minas Basin Kingsport and Salmon River

Three dates on salt-marsh sediment at Kingsport (Fig. 1)were published by Scott and Greenberg (1983) while thetwo dates on salt marsh sediments from Salmon River(Fig. 1) were obtained by C.L. Amos.

Sea-level trends

Trends based on the combined data set

The sea-level data are plotted in three ways: combineddata from Chignecto Bay and Minas Basin (Fig. 2),Chignecto Bay data only (Fig. 3), and Minas Basin dataonly (Fig. 4). In all three figures, we have delineated prob-able levels for HHW, MSL, and LLW. In the combined dataset (Fig. 2), the critical data are dates on oysters in growthposition, ribbed mussels, salt marsh, and trees all within anarrow vertical interval, suggestive of a relatively small tidalrange. It appears, therefore, that if the data for both areas areaggregated, we appear to observe rapid tidal expansion after

ca. 3400 BP. This observation appears to disagree with pub-lished rates of tidal expansion based on models.

Trends based on Chignecto Bay data alone

Considering the data for Chignecto Bay alone (Fig. 3),where oysters and ribbed mussels have not been found nordated, we are forced to draw a very different curve of

HHW. Based on 111 dates, the HHW level increases frombefore 4000 BP, and there is no evidence for a small tidalrange at that time. These data would agree with the pub-lished tidal models.

Trends based on Minas Basin data

The history of water levels in Minas Basin (Fig. 4) differsfrom that of Chignecto Bay and is divisible into threephases. In the first phase (pre-3400 BP), MSL was risingfrom the early postglacial lowstand of 25 m. The positionof HHWLT is defined by salt-marsh deposits and the pres-ence of a well-developed forest of oak and white pine 1 mabove the marsh surface. The juxtaposition of these synopticpaleoindicators precludes large springneap variations. Low-

est low water extremes are constrained by oysters (C. virgin-ica) and ribbed mussels (G. demissa) in life positions 2 mbelow the salt-marsh deposits. The tidal range was probably


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extending west from Cape Split. However, the ridge lies*40 m relative to chart datum so could not have formed abarrier during the sea-level lowstand; nor do we believe thatit may have stood at a higher elevation and was eroded bystrong tidal currents.

It is more likely that the barrier consisted of a sand andgravel spit, a type of coastal landform commonly found in

Atlantic Canada, wherever significant accumulations of gla-cigenic material are exposed to wave action (Carter et al.1989; Shaw et al. 1990; Shaw and Forbes 1992; Forbes etal. 1995). Commonly spits comprise subaerial gravel beachridges, sometimes overlain by coastal dunes, built on suba-queous spit platforms. Some contain huge volumes of sedi-ment, such as Flat Island spit, in Newfoundland (Shaw andForbes 1992). This structure is 12 km long and comprises aspit platform up to 50 m thick, with subaerial gravel beachridges and small areas of sand dunes. It is located adjacentto large glacigenic sediment sources.

Swift and Borns (1967) described and mapped the copiousglacial outwash deposits that occur along the north shore ofMinas Basin and coined the term Five Islands Formation.

The glaciers stood just inland of the modern coast here some14 000 years ago. Relative sea level was dropping rapidly asthe ice retreated, so that the glacial deposits were incised bystreams and formed lowstand deltas (Swift and Borns1967,fig. 13; Wightman 1980). The formation is most extensiveat Parrsboro, located at the mouth of one of the largest val-leys crossing the Cobequid Highlands, and subbottom profil-ing established that the formation extends well below sealevel here (Swift and Borns 1967, fig. 12). These authorsalso claimed that a graded outwash plain extended acrossMinas Basin and reiterated the idea that Annapolis Valleywas a spillway or marine strait, in which case Minas Pas-sage must have been clogged by drift or ice.

We suggest that as relative sea level dropped, as was por-trayed in Swift and Bornss cartoon (Swift and Borns 1967,fig. 13), deltaic deposits resulting from stream incision werethe sediment source for a large sand and gravel spit that ex-tended across the bay to Blomidon, where a tidal channelmaintained the connection between Minas Basin and therest of the Bay of Fundy (Fig. 7). The barriers orientationwould have resulted from dominant sediment longshoretransport from the east, where the maximum fetch was50 km. In addition, as Swift and Borns (1967) and Wight-man (1980) showed, the Five Islands Formation occuredwest of Parrsboro, eastward littoral transport from that areaalso contributed. The eastern counterpart to the Parrsborobarrier was located at Bass River, eastern Cobequid Bay,

where Dalrymple and Zaitlin (1994) provided compellingseismic evidence of a structure of comparable magnitude,together with a flood-tidal delta inferred from subbottomprofiler data.

There are examples in Atlantic Canada of similar config-urations, with barriers sourced at one side of an embaymentthat extend to a rocky coast at the other, with the inlet lo-cated under cliffs. The barrier at Terrenceville Newfound-land (Shaw and Frobel 1992) is a good example. There isno obvious evidence of the barrier in Fig. 6, however.Where the barrier formerly stood, intense tidal scour and re-moval of*4.4 km3 of sediment has created the Minas Pas-sage Scour Trench (Huntec Ltd. 1966), which extends to

170 m below chart datum. Much of the eroded material waslikely glaciomarine mud and thus dispersed away from thelocale. Radiocarbon dates from the salt marshes of the re-gion are nearly all


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how Glooscap, wanting to take a bath, ordered Beaver tobuild a dam across the mouth of the bay to hold the oceanwater so that there would be lots of water for his bath. Bea-ver did as Glooscap asked, but Whale was unhappy becausenow the water did not flow as before. Why has the waterstopped? Whale cried. Glooscap hearing him and not want-ing Whale to be upset told Beaver to break the dam and re-

lease the water. Beaver liked the dam he had made, so hewas slow to begin taking it apart. Whale became impatientbecause he wanted the water as it was before and he startedusing his great tail to break the dam apart. This caused thewater to flow back and forth with such force that it contin-ues so until this day. This interpretation of the legend isfound on various web sites, but with no reference to thesource. Rand (1894) merely notes that Minas Basin was hisGlooscaps beaver pond, and it was there that he cut openthe beaver dam. A useful source for this legend is Beck(1972), who states that:

It came to pass in those days that the beavers had built adam across from Utkoguncheek or Cape Blomidon, to the

opposite shore, and thereby made a pond that filled allthe valley of Annapolis. [p. 112.]

Beck was advancing the possibility that these legendswere folk memories of the former existence of the Pleisto-cene giant beaver Castoroides ohioensis. She went on to de-scribe how Glooscap broke the beaver dam:

And when the dam was cut from where it joined theshore there was a mighty rush of many waters, so that itswung round to the westward, yet it did not break fromthe other shore. Therefore the end of it lodged with agreat split therein where the flood had found a freecourse, and the hole may be seen there still, even to thisday, and may be seen by all who of those who pass upthe bay; and this point, or Cape Split, is called by theMicmacs Pleegun, which being interpreted, means theopening of a beaver dam. [p. 112.]

We would argue that this oral legend attests to the de-struction of a barrier across Minas Passage, an event thatwas observed by First Nations peoples *3400 years ago.

Conclusions

(1) A suite of 148 radiocarbon dates from upper Bay ofFundy, Canada, appears to show a small tidal range until3400 BP, followed by rapid expansion. This conflicts

with results from previously published tidal models, anda new model results that utilizes topography adjusted forpostglacial relative sea-level changes. The models agreethat tidal expansion started much earlier.

(2) When the data are divided into two sets ChigenctoBay and Minas Basin, then the Chignecto Bay data agreewith the tidal models, and the Minas Basin data areanomalous.

(3) The existence of a large spit that extended across MinasPassage, separating Minas Basin from the Bay of Fundyand maintaining a low tidal range is supported by (1) thepresence of the copious glacigenic deposits at Parrsboro,which, by analogy with numerous sites elsewhere in

Atlantic Canada, acted as a sediments source; (2) com-pelling published geophysical evidence for a barrier ofcomparable magnitude at the east end of Minas Basin;and (3) tentative evidence for a fall in HHW in NewEngland at the time of barrier destruction, as predictedby tidal modeling.

(4) The absence of physical remains of the spit is explained

by the development of the 170 m deep Minas PassageScour Channel.

(5) An oral record of the destruction of the barrier exists inMiKmaq legends of Glooscap. This means that aborigi-nal peoples observed an event 3400 BP and preserved arecord of the event in their oral tradition.

Acknowledgements

We thank Brian Todd for material in Fig. 6 and ShermanBleakney for useful discussions. Roger Lewis and GeraldGloaden provided information on the Glooscap legend. Wealso thank Brian Todd and Bob Taylor for internal reviewsof the paper and are especially grateful to external reviewers

Robert Dalrymple and Joseph Kelley.

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