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Home , Kaministiquia, Kaministiquia River, Lake Agassiz, Lake Minong, Lake Ojibway

J Paleolimnol DOI 10.1007/s10933-010-9461-1

ORIGINAL PAPER

An 8,900-year-old forest drowned by Superior: hydrological and paleoecological implications

M. Boyd • J. T. Teller • Z. Yang • L. Kingsmill • C. Shultis

Received: 28 January 2010 / Accepted: 13 August 2010 Ó Springer Science+Business Media B.V. 2010

Abstract Exposures along the lower with the Houghton phase forced the ancestral Kami- River (near , , ) provide nistiquia River to downcut. By *9,100 cal (*8,100) insight into early lake level fluctuations and BP, older channels eroded into subaqueous underflow paleoenvironmental conditions in the northwestern fan deposits in the Thunder Bay area near Fort basin. These exposures show at least William Historical Park (FWHP) were abandoned two large paleochannels which were downcut into and colonized by a Picea-Abies-Larix forest. Based offshore sediments, and were later filled with [2m on stratigraphic data corrected for differential iso- of sand, *3 m of rhythmically laminated silt and static rebound, the lake was below the Sault Ste. clay, and *6 m of interbedded silt and sand. Buried Marie bedrock sill between at least 9,100 cal (8,100) by the rhythmically laminated silty clay unit is a well- and 8,900 cal (8,000) BP. Shortly after 8,900 cal BP, preserved organic deposit with abundant plant the lake quickly rose and buried in situ lowland macrofossils from terrestrial and emergent taxa, vegetation at FWHP with varved sediments. We including several upright tree trunks. Three AMS argue that this transgression was due to overflow radiocarbon ages were obtained on wood and conifer from glacial Agassiz or Ojibway associated cones from this deposit: 8,135 ± 25 (9,130–9,010 with the retreat of the Laurentide from the cal), 8,010 ± 25 (9,010–8,780 cal), and 7,990 ± 20 Nakina and/or the Cochrane surge margins (8,990–8,770 cal) BP. This sequence records an early in the Lowlands. A continued rise in postglacial high-water phase, followed by the Hough- lake level after 6,420 ± 20 (7,400 cal) BP at FWHP ton lowstand, and reflooding of the lower Kaminis- may record uplift of the North Bay outlet above the tiquia River Valley. The drop in lake level associated Sault Ste. Marie bedrock sill and the onset of the Nipissing transgression in the Lake Superior basin. M. Boyd (&) Department of Anthropology, Lakehead University, Keywords Lake Superior Houghton low-water 955 Oliver Rd, Thunder Bay, ON P7B 5E1, Canada phase Boreal forest Plant macrofossils e-mail: [email protected] Paleohydrology Holocene paleoecology J. T. Teller Z. Yang Department of Geological Sciences, University of , , MB, Canada Introduction

L. Kingsmill C. Shultis Department of Anthropology, Lakehead University, The geology of the Superior basin yields crucial Thunder Bay, ON, Canada insight into the history of meltwater drainage from 123 J Paleolimnol the interior of to the Atlantic Ocean. of the lake level drop associated with the Houghton Until *9,000 cal (8,000) BP when discharge was phase. diverted through the Hudson Bay Lowlands (Dyke In 2006, sedimentary exposures were discovered and Prest 1987; Teller and Mahnic 1988; Bajc et al. along the lower (near Thunder 1997; Breckenridge et al. 2004), catastrophic out- Bay, Ontario) which provide chronological control bursts from over the continental divide over the Houghton lowstand phase and a subsequent flowed directly into the Superior basin, leaving transgression. These sections expose at least two sedimentary and geomorphic records of these events large (*250-m-wide) channels which were cut into (Teller and Mahnic 1988; Breckenridge 2007). underflow fan deposits and, later, were filled with Downstream in the North Atlantic Ocean, some of varved silt and clay. Importantly, the varved unit is these freshwater outbursts may have forced abrupt underlain by an extensive organic deposit containing climate change through disruption of thermohaline plant macrofossils and in situ trees—the remains of a circulation (Broecker et al. 1989; Teller et al. 2002; forest that was drowned and buried by a rise in lake Leverington and Teller 2003; Yu et al. 2010). Despite level. Elsewhere in the Upper , buried its importance and possible connection to wider forests have provided key insight into lake level environmental events in the Northern Hemisphere, fluctuations, glacial chronology, and paleovegetation many aspects of the postglacial geological history of composition during the Holocene (Lowell et al. 1999; the Superior basin remain poorly understood. To a Pregitzer et al. 2000; Lewis et al. 2005; Hunter et al. large extent, this is the result of uncertainties in the 2006; Schneider et al. 2009). In the present study, we chronology of major lake level fluctuations shortly report the first buried forest from the north shore of after deglaciation, as well as the exact location of the Lake Superior and one of only a small number of (LIS) margin which helped similar deposits known across the . control overflow from glacial Lakes Agassiz and Based on stratigraphy, plant macrofossil content, and Ojibway. In many parts of the basin, radiocarbon radiocarbon ages, we reconstruct the history of early dates on early postglacial beaches and other paleo- lake level fluctuations following the final retreat of lake level indicators are few, unreliable, or compli- the LIS from the Thunder Bay area. These data cated by reworking of older organics (Yu et al. 2010). provide new insight into the paleohydrology of the In general, the early postglacial history of the Superior basin during, and immediately following, Superior basin is marked by significant changes in the Houghton low-water phase *9,000 cal ([8,000) lake level which occurred in response to differential BP, while also providing an outstanding ‘snapshot’ of isostatic rebound, meltwater inflow, and outlet ero- local early mid-Holocene paleovegetation. sion among other factors. The focus of this paper is on the Houghton phase, a period of low-water level in the Lake Superior basin *9,000 cal (8,000) BP that Early postglacial lake level fluctuations followed an earlier deep-water proglacial period (the in the Superior basin Minong phase; Farrand and Drexler 1985; Fisher and Whitman 1999; Yu et al. 2010). The Houghton phase Between *11,000 and 6,000 cal (*9,650 and 5,200) is important because it coincided in time with the BP, three major phases have been recognized in the diversion of Agassiz meltwater away from the Lake Superior basin: an initial highstand (Minong), Superior basin into the Hudson Bay Lowlands, and followed by a regression during the Houghton phase, the onset of a dramatically reduced hydrological and subsequent transgression (Nipissing phase). budget. In the and Huron basins, reduction Events after *6,000 cal (5,200) BP, which are only of meltwater inflow coupled with climate change in briefly outlined here, are discussed in other publica- the early mid-Holocene may have forced these lakes tions (Booth et al. 2002; Johnston et al. 2007). to fall below the level of their outlets and become The Minong phase was the last period when ice- hydrologically closed (Lewis et al. 2007, 2008). marginal lakes occupied the Superior basin, and Details about these events in the Superior basin began when the LIS re-advanced southward into the during this time, however, are unclear because little basin, reaching the northern Upper Peninsula of information exists on the exact timing and magnitude Michigan by 11,500 cal (10,000) BP (Drexler et al. 123 J Paleolimnol

Fig. 1 Modern digital elevation model (DEM) of study area Table 1. A Pic River spillway channel; B Sault Ste. Marie showing location of Fort William Historical Park (white dot), outlet. Dashed lines on inset map are isobases (Teller and and in the northwestern Lake Superior basin (Thunder Thorleifson 1983) Bay area). Numbers refer to radiocarbon dates and sites listed in

1983; Lowell et al. 1999). This advance (Marquette) Minong phase lake level was controlled by a morainal briefly divided the basin into two lakes, Duluth and sill crossing from Nadoway Point (Michigan) to Minong (Farrand and Drexler 1985). In the Thunder Gross Cap (Ontario) at the eastern end of the basin Bay area, the Marks and Dog Lake moraines (Fig. 1) (Farrand and Drexler 1985; Yu et al. 2010). Near may represent the position of the LIS during this time Thunder Bay, the elevation of the Minong level is (Clayton 1983; Drexler et al. 1983; Teller and *230 m asl (47 m above the modern water plane). A Thorleifson 1983). As the ice margin retreated from conventional radiocarbon age of 9,380 ± 150 the Keweenaw Peninsula (largest peninsula on the (*10,500 cal) BP (Table 1) was obtained on wood south shore [Fig. 1, inset]) *10,500 cal (9,300) BP, from the base of the Minong beach at Rosslyn (Dyck Lakes Minong and Duluth coalesced. Elevation of the et al. 1966), roughly 6 km upstream of the study area.

123 123

Table 1 Radiocarbon ages and other relevant data associated with early postglacial sites in the Thunder Bay area. Radiocarbon years were calibrated using the IntCal04 terrestrial dataset (Reimer et al. 2004), with the 2r range and means shown. Location of sites and dates are shown in Fig. 1 Site name Lab 14C years BP Calibrated 2r range Material dated Context Modern Latitude Longitude Reference number and mean (cal BP) elevation (N) (W) (m asl)

1 Rosslyn Pit GSC-287 9,380 ± 150 11,094–10,248 (10,671) Wood Base of Minong beach 227 48°21.80 89°27.30 Dyck et al. (1966) 2 Cummins Pond TO-547 9,260 ± 170 11,092–9,948 (10,500) Conifer wood Basal sand (Minong 230 48°24.30 89°20.90 Julig et al. beach) (1990) 3 Old Fort William UCIAMS- 8,135 ± 25 9,127–9,009 (9,070) Wood Tree in life position 186 48°20.70 89°21.10 This study 26800 extending into silty clay 4 Boyd Cut ETH-31437 8,070 ± 70 9,046–8,658 (8,850) Charcoal Base of interlaminated 199 48°20.40 89°21.50 Loope (2006) clayey silt and sand 5 Old Fort William UCIAMS- 8,010 ± 25 9,005–8,776 (8,891) Picea sp. cone Located at base of silty 186 48°20.70 89°21.10 This study 26801 clay in organic laminae 6 Boyd Cut ETH-31438 7,995 ± 65 9,014–8,641 (8,828) Charcoal Base of interlaminated 199 48°20.40 89°21.50 Loope (2006) clayey silt and sand 7 Upstream UCIAMS- 7,990 ± 20 8,994–8,774 (8,884) Pinus Located at base of silty 186 48°20.50 89°21.20 This study paleochannel 61732 banksiana cone clay in organic laminae 8 Old Fort William UCIAMS- 7,970 ± 30 8,993–8,659 (8,826) Wood Log in silty clay *2.5 m 189 48°20.70 89°21.10 This study 26802 above base of unit 9 Old Fort William UCIAMS- 6,420 ± 20 7,421–7,291 (7,356) Scirpus sp. In upper organic deposit 195 48°20.70 89°21.10 This study 61733 achenes 10 Surprise Lake BETA- 8,170 ± 40 9,010–9,260 (9,135) Betula leaves Lake isolation 187 48°20.10 88°49.30 Yu et al. 230960 and scales (2010) 11 Little Harbor ETH-32328 8,365 ± 100 9,090–9,540 (9,315) Betula leaves Lake isolation 183 46°49.20 85°21.70 Yu et al. and twigs (2010) Paleolimnol J J Paleolimnol

This date is in line with other chronological estimates drawdown after this time (Breckenridge et al. 2004; for the Minong phase in the Superior basin (Drexler Lewis et al. 2007, 2008). et al. 1983; Julig et al. 1990; Fisher and Whitman At the end of the Houghton phase, the lake level 1999), and indicates that final deglaciation of the began to rise in response to differential isostatic Thunder Bay area was completed less than rebound of the North Bay outlet that carried overflow 1,000 years after the Marquette re-advance had to the drainage system (Lewis and reached its maximum on the Upper Peninsula of Anderson 1989; Booth et al. 2002; Lewis et al. 2007). Michigan. This is recorded by the Nipissing transgression which During the Minong phase (*10,500 cal [*9,300] culminated 6,800–5,700 cal (*5,950 and 5,000) BP BP), meltwater from Agassiz was with the Nipissing I highstand (Lewis 1970; Fisher and diverted into the Superior basin through a series of Whitman 1999; Booth et al. 2002). Continued uplift of outlets located on the western side of Lake the North Bay outlet made it inactive by 5,500 cal (Teller and Thorleifson 1983; Teller and Mahnic (4,800) BP, transferring control to the Port Huron and 1988; Leverington and Teller 2003; Breckenridge Chicago outlets (Lewis 1969; Lewis and Anderson et al. 2004, 2010). This event may have been due to a 1989; Booth et al. 2002). A second high-water phase, re-advance of the LIS which closed the Clearwater- Nipissing II, dates to between 4,600 and 4,400 cal Athabaska spillway in and diverted (4,100–4,000) BP, and the drop in lake level following Agassiz overflow to its eastern outlet (Teller and these two highstands may be due to erosion of the Port Boyd 2006). Increased flow via the Nipigon basin Huron outlet (located at the southern end of Lake may have briefly raised the level of (by Huron; Booth et al. 2002; Johnston et al. 2007). By at hydraulic damming at the outlet [Tinkler and Peng- least 1,200 cal (1,300) BP, the Sault Ste. Marie (SSM) elly 1995]); in , this event initiated the outlet rebounded above the elevation of the Port Huron early Mattawa highstand (Lewis and Anderson 1989; outlet and Lake Superior became separated from Lakes Lewis et al. 2007). The exact sequence of events in Michigan and Huron (Johnston et al. 2007). the Superior basin between *10,300 and 9,000 cal (*9,150 and 8,000) BP is unclear, although several fluctuations in lake level may have occurred during Materials and methods this time in response to changes in Agassiz outflow, differential isostatic round, the location of the LIS The focus of this study is a 1 km section along the margin, or a combination of these factors (Farrand lower Kaministiquia River across from Fort William 1960; Saarnisto 1974; Slattery et al. 2007; Breckenridge Historical Park (FWHP). Along this stretch of the et al. 2010; Yu et al. 2010). river, cutbanks are upwards of 14 m high and expose Between *9,400 and 9,000 cal (*8,400 and multiple fine-grained sedimentary units deposited [8,000) BP, multiple sites from the Superior basin following the retreat of the LIS from the Marks record a significant drop in lake level (Farrand and moraine (Fig. 1). At FWHP, the elevation at river Drexler 1985; Fisher and Whitman 1999; Saarnisto level is roughly 4 m above the present (183 m) water 1974; Yu et al. 2010). The initiation of this phase, the plane of Lake Superior. As a result of its low ‘‘Houghton Low’’, has been attributed to erosion of elevation, the lower Kaministiquia Valley would the sill at Nadoway Point (Prest 1970; Saarnisto have been highly sensitive to past fluctuations in lake 1974; Farrand and Drexler 1985; Fisher and Whitman level. These fluctuations are largely recorded, and 1999; Yu et al. 2010). Yu et al. (2010) propose that mediated, by fluvial sedimentary processes operating the large volume of freshwater released into the within the valley, and can be seen in episodes of North Atlantic Ocean by this event triggered the channel downcutting and aggradation. 9,300 (8,300) cal BP cold event, which is widely recorded across the Northern Hemisphere. Addition- Paleotopographic reconstructions ally, diversion of Lake Agassiz overflow away from the Superior basin by *8,000 (*9,000 cal) BP would Three paleotopographic time slices (10,400, 8,900, have dramatically changed the hydrological budget and 7,400 cal [9,250, 8,000 and 6,500] BP) were and made the lake more prone to climate-induced generated using GIS software. Modern digital 123 J Paleolimnol elevation data (90 m resolution) was obtained from Chronological control was established by AMS the USGS Seamless Data Distribution System radiocarbon dating of hand-picked, terrestrial, ma- (http://seamless.usgs.gov/index.php). Lake Superior crofossils or wood from in situ trees (Table 1). bathymetric data (1 km resolution) was downloaded Samples selected for radiocarbon dating were sub- from The Lake Superior Decision Support Project mitted to the Keck Carbon Cycle AMS Facility (Natural Resources Research Institute, University of (UCIAMS). Radiocarbon ages were calibrated using Duluth) website (http://www.nrri.umn. Calib (version 6.0) and the Reimer et al. (2004) edu/lsgis/databases.htm). After the downloaded data IntCal04 terrestrial dataset. These dates and their were imported into ArcGIS, the bathymetric data locations, as well as conversions to calibrated ages, were resampled to get 90 m resolution data, and then are presented in Table 1. One-number calibrated the DEM mosaics for the terrestrial and lake portions ages, when given, represent the mean of the 2r of the Superior basin were merged using ArcGIS calibrated range. Spatial Analyst. Isostatic rebound for three time points (based on dates and elevations at #2, 5 and 9 in Plant macrofossils Table 1) was calculated using an empirical model developed by Lewis and Thorleifson (2003), starting A total of 14 bulk samples from Unit D were with isobase lines shown in Teller and Thorleifson collected at 5 m horizontal intervals across the 70 m- (1983). The isostatic rebound values of isobase lines long exposure at OFW. In the lab, 100 cc subsamples were then interpolated and a rebound surface was were deflocculated in 5% sodium hexametaphosphate generated for the three time periods using ArcGIS 3D for 24 h and gently washed through a column of Analyst. Finally, three paleotopographic maps were screens (Beaudoin 2007). The remaining material generated by subtracting isostatic rebound values for was then air-dried for 48 h before being examined the three time slices from the modern DEM mosaic. under a stereomicroscope. Plant macrofossil identifi- Comparison with the isobases drawn by Farrand and cations used comparative collections in addition to Drexler (1985) on the Minong and Washburn beaches keys in Le´vesque et al. (1988) and other sources. In in the Superior basin shows a close match in this paper, we present a summary of initial macro- trend and value with those in our paleotopographic fossil recoveries from the 8,900 cal (8,000) BP reconstructions. organic unit (Unit D). Detailed discussion of the full paleoecological dataset from the OFW site will be Stratigraphy and AMS radiocarbon dating presented in a subsequent paper.

Exposed sediments along the Kaministiquia River in the Thunder Bay region near Fort William Historical Results Park (FWHP) were described and sampled over four successive field seasons. The majority of this work, Fluvial sequence (Units F and G) however, focused on one section, named the ‘‘Old Fort William’’ (OFW) site, where in situ buried trees The lower part of the sedimentary sequence exposed in were first observed in 2006 (Fig. 1). cuts along the lower Kaministiquia River Valley Six slab samples were collected from the rhythmi- generally consists of [12 m of massive to horizon- cally laminated unit and underlying organic deposit for tally- or cross-laminated, well-sorted fine sand to sandy thin-section preparation. These samples were desic- silt (Unit F; Fig. 2). This unit exhibits no obvious cated in a vacuum oven for 7 days and impregnated vertical trends in grain size, bed thickness, or other under low vacuum pressure using a low viscosity Spurr sedimentary characteristics within the sequence. resin kit composed of nonenyl succinic anhydride, Within Unit F there are units (10–25 cm thick) of silty vinylcyclohexene dioxide, diglycidyl ether of poly- rhythmites and interbedded (often ripple-laminated) propylene glycol, and 2-dimethylaminoethanol. The sand (Fig. 2). Climbing ripples are commonly ratios of these chemicals used to produce the resin, the observed in sandy units within Unit F, and zones of embedding technique, and other procedures followed a convoluted laminae/beds are occasionally visible. This standard recipe for lake sediments (Myrbo 2005). unit is also described by Loope (2006: 28–32), who 123 J Paleolimnol

Fig. 2 Photo (looking towards the south) of Old Fort William (OFW) cutbank site showing *8,900 cal BP organic deposit (Unit D), western paleochannel margin, major lithologic units, and composite stratigraphic column (left) observed rhythmic beds of clayey silt and sand in a 4 m Basal sediments within the paleochannel at the interval at the Boyd Cut (located 700 m upstream OFW site consist of \0.5–2.0? m of massive to of the OFW paleochannel). Approximately 1.2 km laminated fine to medium sand in the sample area upstream of FWHP, the basal contact of this unit is (Unit E; Fig. 2). Asymmetrical ripples (including exposed above river level and is sharply underlain by climbing ripples) are common throughout. This sandy 50? cm of weakly imbricated, rounded, gravel and unit can be traced laterally along the bottom of both coarse sand (Unit G). channels, forming the contact with Unit F (Fig. 2). Along the higher channel margin, laminae were Paleochannel sequence (Units A–E) deposited parallel to the contact between Units E and F, and at least one example of a lateral accretion/point In the FWHP study area, two large paleochannels bar deposit (composed of fine to coarse sandy (*250 m wide, *12 m deep) are exposed in cross- laminae that dip towards the channel thalweg) was section across a continuous series of cutbanks on the observed. In the paleochannel farthest upstream in the southern side of the Kaministiquia River. Both FWHP study area, massive to weakly bedded coarse channels are incised into, and truncate, Unit F sand and gravel were observed mid-channel in the (Fig. 2), and dip below the modern river level same stratigraphic position as Unit E. (\186 m in this area). The infill sequence within Above Unit E, several sets of thin (mm-scale), both channels is similar and consists, in general, of a horizontally-bedded, organic laminae were observed fining-upward sequence of sand and laminated silty in both paleochannels. This distinct, peaty, organic clay separated by a thin and nearly-continuous deposit (Unit D)is*10 cm thick and consists of well organic (peat) deposit (Unit D). A more detailed preserved plant macrofossils; in the field, bryophyte description of this sedimentary sequence follows. mats, conifer needles, conifer and alder cones, as well

123 J Paleolimnol as in situ tree trunks (between 3 and 17 cm diameter), All in situ trees observed in Unit D have stems that were observed in this unit over three successive field extend upwards (up to 1 m) into the overlying silt and seasons (Fig. 3). Although discontinuous in places, clay of Unit C. Three AMS radiocarbon dates were this thin peat deposit was traced over almost 200 m. obtained from this unit on hand-picked, terrestrial In the centre of both channels, Unit D dips below the macrofossils (Table 1). One of these dates modern river level. Closer to the channel margins, it (7,990 ± 20 BP, UCIAMS-61732) was obtained on can be traced laterally along the margin to an a jack pine (Pinus banksiana) cone recovered from elevation roughly 11 m above the modern river the basal organic zone in the upstream paleochannel, (Fig. 2). The thin organic laminae of Unit D gener- while the other two dates (UCIAMS-26800 and ally show little evidence of post-depositional distur- 26801) were obtained from an 18-cm-diameter tree bance, although convolutions and other structures stem in life position (8,135 ± 25 BP) and spruce indicative of loading or post-depositional reworking (Picea sp.) cone (8,010 ± 25 BP) recovered from the were observed in one small (*1 m) horizontal zone. same stratigraphic unit at the OFW site (Table 1). Woody debris, frequently alternating with zones This indicates that the basal organics (Unit D) likely dominated by moss litter, is common in Unit D and were contemporaneous in both paleochannels much of this wood material consists of small to exposed at FWHP. The combined 1-r range for all medium, well-preserved, roots which are oriented three basal radiocarbon ages is 8,780–9,089 cal BP parallel to the bedding plane. Significant root pene- (mean = 8,935 cal BP). However, based on the tration into the underlying sterile sand of Unit E was radiocarbon date for the in situ tree (UCIAMS- not observed along the length of this deposit. In at 26800, 8,135 ± 25 [*9,070 cal] BP), and allowing least one example, roots oriented in this manner were some time for growth (36 tree rings counted in one connected to an upright (3-cm-diameter) tree stem log), organic accumulation in Unit D probably began indicating that much, if not all, of this material is in no later than *9,100 cal (*8,100) BP. Loope its original (life) position (Fig. 3). (2006) reports two radiocarbon ages on charcoal

Fig. 3 Photos of the 8,900 cal BP organic deposit: a in situ b spruce (Picea) cone associated with bryophyte (moss) litter; tree (3 cm diameter) with preserved bark on lower portion of and c thin section showing contact between Units C and D stem extending upwards into varved sediment (Unit C), and (1 mm scale bar located in lower right corner) horizontal roots within *8,900 cal BP organic deposit (Unit D); 123 J Paleolimnol

Table 2 List of plant and from the base of an interlaminated silty clay and sand Trees and shrubs unit at the Boyd Cut: 8,070 ± 70 BP (ETH-31437) other macroremains recov- ered from *8,900 cal Abies balsamea needles and 7,995 ± 65 BP (ETH-31438; Table 1). We (8,000) BP peat deposit Abies balsamea seeds observe that the organic bed dated by Loope (2006) (Unit D), OFW site Abies balsamea twigs correlates stratigraphically with the peat deposit near Larix laricina needles the bottom of the OFW and upstream paleochannels. Larix laricina seeds Plant macroremains are abundant in Unit D; seeds Larix laricina twigs and other debris from a variety of terrestrial, aquatic Larix laricina cones and emergent, and bryophyte taxa were commonly Picea needles recovered in the sieved fractions from nearly all Picea seeds samples at the OFW site (Table 2). In general, Picea twigs macroremains from conifer species were the most Picea glauca cone Pinus abundant, with Abies balsamea (fir), Larix laricina needles Pinus seeds (tamarack), and Picea glauca (white spruce) being Pinus banksiana cone the most common taxa identified. Occasional Pinus Alnus crispa nutlets (pine) needles were also recovered in addition to a Arctostaphylos uva-ursi seeds jack pine cone from the same deposit at the upstream Betula papyrifera nutlets site. In addition to these trees, macroremains from Betula papyrifera fruit scales Betula papyrifera (paper birch), Alnus crispa (green Rubus idaeus seeds alder) were common, and occasional seeds from Aquatics and emergents Arctostaphylos uva-ursi (kinnikinnick), and Rubus Nymphaeaceae seeds idaeus (raspberry) were found in some of the Scirpus americanus achenes samples. Several emergent taxa were also identified, Carex sp. (trigonous) achene including Scirpus americanus (bulrush), and Carex Bryophytes sp. (sedge). In some samples, mosses were very Pleurozium schreberi abundant although only two species have been Dicranum polysetum identified: Pleurozium schreberi, and Dicranum Bryozoans polysetum (Table 2). Cristatella mucedo statoblasts Conformably overlying Unit D is a *2.75-m- Plumatella sp. statoblasts Cladocera thick deposit of predominantly silt and clay (Unit C) Daphnia sp. ephippia which is overlain by silty clay containing thin sandy Fungi ripple- to horizontally-laminated units (Unit B; Cenococcum geophilum Fig. 2). In thin sections obtained from the contact sclerotia between Unit C and the underlying organic deposit we observed: small-scale convolutions and other deformations of the laminae in the main zone of present, and these coarser laminae are more common organic accumulation, and small-scale rip-ups and towards the top of this unit. The rhythmically occasional fine sand at the contact with Unit C laminated sediments of Unit C are interpreted as (Fig. 3c). In general, Unit C is composed of silty clay varves due primarily to their uniformity and repeti- to clayey silt with faint to distinct light–dark couplets tiveness; the sandy laminae which are occasionally (rhythmites) that are common throughout. These observed in this sequence may have been deposited couplets vary in thickness from *1 to 2 mm (per by sediment gravity flows and/or suspension settling couplet) to 2 cm. Analysis of thin sections indicates of eolian sand. The normally-graded zone which that each couplet contains a thin (\1 mm) clay occurs between the clay (winter) and coarse silt lamina, one or more overlying normally graded silt (summer) laminae in each couplet may represent laminae of variable thickness, and a zone above this density underflow currents associated with the spring which is dominated by coarse silt sized particles melt. Occasional bivalve (up to 7 cm diameter) and embedded in a finer clayey matrix. Occasional very gastropod shells occur throughout this unit. Within fine to fine sand laminae and couplets are also the lower *1–2 m of Unit C, occasional logs are 123 J Paleolimnol visible; the largest of these is 30 cm in diameter and fluvial sand (Unit E); (3) local channel abandonment is oriented horizontally. Other than the in situ trees and colonization of the channel by a spruce-fir- extending upward from Unit D (see above), all logs tamarack forest (Unit D); (4) rapid reflooding of the observed in Unit C were redeposited. One of these lower Kaministiquia River valley and onset of a deep horizontal logs, deposited *2.5 m from the base of water, low-energy, depositional environment with Unit C, yielded a radiocarbon age of 7,970 ± 30 high sediment flux (Unit C); (5) episodic fluvial and (8,990–8,660 cal) BP (UCIAMS-26802). Based on lacustrine sedimentation and deposition of Units B extrapolation from zones where light–dark couplets are and A; and (6) incision of the modern Kaministiquia distinct (average sedimentation rate = 0.74 cm/year), River to its present elevation. we estimate that Unit C at the OFW site represents Unit F records a period of rapid sedimentation in a roughly 200 years of deposition. For the same unit in subaqueous underflow fan environment. Evidence for the upstream paleochannel we counted an average of this is the presence of climbing ripples, loading 192 couplets (range = 182–203) directly from the structures, overall fine grain size with occasional silty outcrop. The upper contact with Unit B is generally rhythmites, lack of fossils, and similarity with wavy and erosional in appearance. underflow fan sequences described elsewhere (Klassen Unit B is distinguished from the underlying unit by 1983; Sun 1993; Boyd 2007). Presence of an the presence of multiple fine to very fine sand beds underlying, coarse, gravel deposit (Unit G) indicates with massive to faintly laminated silty clay (Fig. 2). that deposition of Unit F was preceded by a higher- In places, laminae form couplets. The sandy beds are energy fluvial event. Due to the position of the FWHP commonly laminated and contain ripples and climb- sequence inside the Marks moraine and absence of ing ripples, and thicken (from 13 to 100 cm) and till in the exposed sequence, these sediments must coarsen upward. In three of the sand beds, fibrous/ have been deposited after the Marquette re-advance woody organics are present. reached its maximum *11,500 cal (9,900) BP (Dyck Unit A is massive to poorly laminated sandy silt with et al. 1966; Drexler et al. 1983; Julig et al. 1990; a soil developed in the upper part (Fig. 2). Approxi- Lowell et al. 1999; Lowell et al. 2009). With the mately 2 m below surface, a zone of organic laminae retreat of the Superior Lobe, proglacial lakes that had (5–15 cm thick in total) is visible. Individual organic been impounded between the Marks moraine and laminae are *1–5 mm thick and alternate with silt continental divide to the west would have drained laminae that are about the same thickness. Plant rapidly to the east through the Kaministiquia River macrofossils recovered from this organic zone are valley (Loope 2006). sediments are dominantly sedge (Carex sp.) and bulrush (Scirpus sp.) extensive west of this moraine, and these deposits seeds, suggesting a shallow pond environment with have been attributed to a string of short-lived ice- emergent vegetation. Several of the Carex achenes still marginal lakes (e.g., glacial Lakes O’Connor, Baldy, had their fragile perigynium attached, indicating little Kaministiquia; Zoltai 1963; Teller and Thorleifson or no postdepositional reworking and redeposition of 1983; Phillips and Fralick 1994). The thick sequence macroremains. Scirpus seeds sieved from this lami- exposed in the study area indicates that a large nated organic deposit yielded an average age of amount of sediment was rapidly deposited in the 6,420 ± 20 (7,400 cal) BP (UCIAMS-61733). lower Kaministiquia River valley following deglaci- ation, and meltwater discharge from one or more proglacial lakes west of the study area, plus meltwa- Interpretations ter from the retreating LIS, are the likely sources of this sediment. Consequently, we suggest that Unit F Sedimentary exposures in the FWHP study area records a period of underflow fan construction in document the following series of events: (1) deposi- Lake Minong, the precursor to Lake Superior, that tion of gravel (Unit G) and a sandy subaqueous occurred sometime after ice retreated (*11,000 cal underflow fan (Units F) following retreat of the (9,650) BP) but before 9,100 cal (8,100) BP (the Superior Lobe from the Marks moraine; (2) erosion oldest age of basal organics at OFW). of channels into these sediments when the level of The paleochannels at FWHP, which are incised Lake Superior fell, and partial infilling of channels by into subaqueous underflow fan deposits to below the 123 J Paleolimnol modern river level, record a significant drop in the channel abandonment, as well as elsewhere in the base level of the lake. Radiocarbon ages on plant basin (Yu et al. 2010), represents the regression of macrofossils inside the channel indicate that low Lake Superior during the Houghton phase. This event water levels were established no later than 9,100 cal was due to rapid erosion of the Nadoway morainal (8,100) BP. In general, development of the organic sill near Sault Ste. Marie (Yu et al. 2010). Yu et al. deposit (Unit D) may reflect a substantial decrease in (2010) concluded that this level was 45 m below the discharge through the channel, which allowed vege- Nadoway barrier. Because both paleochannels in the tation to colonize a previously active alluvial surface. FWHP study area dip below the modern river level, By 8,900 cal (8,000) BP, this vegetation was a mix of we infer that the relative lake level at this time lay at coniferous (boreal) forest and wetland elements. or below the modern water plane (B183 m asl). Yu Spruce (Picea), tamarack (Larix) and fir (Abies) et al. (2010; Fig. 3) report similar results from lake formed the dominant tree cover along with some cores collected at Little Harbor, Michigan and Lake boreal deciduous tree species such as paper birch Surprise, Ontario; these sites, which today lie (Betula papyrifera) and green alder (Alnus crispa). between 183 and 187 m asl, were isolated beginning The paucity of pine macroremains suggests that pine between 9,100 and 9,400 cal (8,170 and 8,370) BP trees did not grow in the wetter channel bottom; (Table 1), as lake level dropped *45 m below the instead, jackpine (Pinus banksiana) was probably overflow channel/sill and previous level of the lake confined to drier upland zones in the local area (Julig (Yu et al. 2010). Significantly, when corrected for 1984). differential isostatic rebound, one of these sites (Little In the channel at OFW, ground cover was domi- Harbor) was disconnected from Lake Supe- nated by mosses (especially Pleurozium schreberi and rior *10 m below the elevation of the SSM bedrock Dicranum polysetum), in addition to occasional low sill between 9,200 and 9,400 cal (8,400) BP (Yu et al. shrubs such as kinnikinnick (Arctostaphylos uva-ursi) 2010: Fig. 3). Our isostatic rebound model also and raspberry (Rubus idaeus). Presence of wetland shows that overflow across the sill at SSM could taxa such as sedges and bulrush may imply occasional not yet have occurred at 8,900 cal (8,000) BP above-ground water levels in the channel bottom or (Fig. 4c, d). By interpolating between isobases 6 presence of discrete wetland habitats. and 7 in Fig. 4c, d, where isobase 7 is 100 km north The absence of carbonized wood, needles or other of isobase 6 and is 32 m higher at this time, it can be charred plant macroremains indicates that fire fre- seen that SSM lies *30 km south (on isobase 6.5) of quencies were locally very low between *9,100 and the isobase that extends through FWHP, which lies 8,900 cal (*8,100 and 8,000) BP. This agrees with on isobase 6.8. This means that their difference in the ecology of Pleurozium schreberi and Dicranum elevation was 30/100 9 32 = 9.6 m. So, when the polysetum; in the boreal forest today, these moss organics at OFW were flooded, the floor of the species are dominant in mature forests (80–120 year) overflow channel at SSM still lay almost 10 m above with little or no fire disturbance (Boudreault et al. that. This was confirmed by more detailed processing 2002). Abies balsamea, the most abundant conifer of DEM data of Fig. 4d in the channel (not shown). inside the channel (based on total number of macro- Thus, we suggest that the level of Lake Superior had fossils), is also a late-successional, fire-intolerant, dropped below the elevation of the SSM bedrock sill species that is commonly associated with Picea between at least 9,100 and 8,900 cal (8,100 and glauca (white spruce), tamarack (Larix laricina) 8,000) BP. In the Michigan, Huron, and Georgian and Pleurozium and Dicranum in lowland areas of Bay basins, Lewis et al. (2008) describe a closed-lake the boreal forest (Uchytil 1991). Low fire frequencies phase between 8,770 and 8,300 cal (*7,900 and during the period of peat accumulation at OFW may 7,500) BP which they attribute to high rates of have been due to climate or, more likely, topography. evaporation and decreased hydrological inputs asso- It is reasonable that the relatively moist alluvial ciated with early mid-Holocene climate change and surface would have inhibited local wildfires, enabling the northward retreat of the LIS. In the Superior late successional species to dominate in this setting. basin, early postglacial paleoclimatic records are The drop in lake level before 9,100 cal (8,100) BP, either too few or too coarse to compare with the recorded at FWHP by fluvial downcutting and local timing of the Houghton Low. However, in southern 123 J Paleolimnol

Fig. 4 Paleotopography of the Thunder Bay and Sault Ste. for the Thunder Bay area are shown in (c) and can be correlated Marie areas, with inset maps showing the Lake Superior basin, to the outlet channel at Sault Ste. Marie shown in (d). Dates at: 10,400 cal (9,250) BP (a ? b); 8,900 cal (8,000) BP and their locations used to control the DEM paleotopography (c ? d); and 7,400 cal (6,500) BP (e ? f), calculated from model are shown, and include the Cummins site (10,400 cal modern DEM topography adjusted for differential isostatic BP; Julig et al. 1990; #2 in Table 1), and select dates from the rebound at the times shown as described in the text. Isobases OFW section (#5 and 9 in Table 1) 123 J Paleolimnol

Minnesota, the time-transgressive nature of mid- (represented by the rhythmically laminated silt and Holocene aridification, and its broad overlap in time clay of Unit C) occurred rapidly, with no intervening with the Houghton low-water phase, is indicated by nearshore facies. Scenario #2 is unlikely because the the rapid eastward movement of the -forest ice margin was well north of the SSM outlet by this border between 10,000 and 8,000 cal (8,900 and time (Dyke 2004). We rule out #3 because the timing 7,200) BP (Williams et al. 2009). The shift to more of this transgression in FWHP occurred during one of arid climatic conditions, in combination with diver- the driest intervals in the Holocene (Bartlein et al. sion of meltwater into the Hudson Bay Lowlands 1998; Lewis et al. 2008; Williams et al. 2009). (Dyke and Prest 1987; Teller and Mahnic 1988;Bajc Instead, we suggest that the rise in water level that et al. 1997; Breckenridge et al. 2004), may have occurred shortly after 8,900 cal (8,000) BP was due produced a negative hydrological budget within the to a renewed influx of meltwater, possibly from Superior basin and drawdown of the lake below the Lakes Ojibway and/or Agassiz or directly from the elevation of the SSM bedrock sill by *9,100 cal LIS, which raised the level of Lake Superior for at (*8,100) BP. least 200 years. The rhythmically laminated (varved) fine-grained Supporting evidence for a late influx of water from sediment of Unit C that overlies the organic zone of Lakes Ojibway and/or Agassiz comes from: Unit D records the onset of a subsequent deep water lake phase in the lower Kaministiquia River valley. We (1) Glaciodeltaic deposits at the mouth of the Black argue that the transition from a subaerial, terrestrial, River valley, *15 m above the Houghton low- environment during the period of peat formation to a water level, which date to 8,070 ± 180 deep water depositional environment occurred rapidly, (*9,000 cal) BP (Bajc et al. 1997: 689). and very shortly after 8,900 cal (8,000) BP. This is (2) Glaciofluvial sediments with paleoflow direc- based on: (1) presence of in situ trees with intact bark tions toward the southwest in the Mullet Outlet- that extend up to at least 1 m into the overlying varves; Pic River lowland, which links the Superior (2) presence of well-preserved organics with minimal basin with the Hudson Bay Lowland. These reworking; and (3) fine-grained sediment (silt/clay) sediments record meltwater overflow into the immediately above the basal peat with no evidence of Superior basin following the retreat of the LIS intervening nearshore deposits. Based on varve counts, from the Nakina II moraine (Slattery et al. Unit C represents at least 200 years of continuous 2007); this moraine formed *9,200 cal (8,200) lacustrine deposition. Importantly, a sustained rise in BP (Teller and Thorleifson 1983; Teller et al. relative lake level beginning *8,900 cal (*8,000) 1996; Dyke 2004). The subsequent retreat of the BP is also observed at other sites in the Superior basin ice margin from this moraine after 9,200 cal (Yu et al. 2010). In the Thunder Bay region, this is most (8,200) BP would have allowed overflow from clearly seen at Surprise Lake, Ontario (#10 in Fig. 1 Lakes Agassiz or Ojibway to be directed into and Table 1), where re-connection with Lake Superior the Pic River and into a post-Minong phase of began sometime between 8,730 and 9,010 cal (8,010 ± the Superior basin (Slattery et al. 2007: 344). 40) BP, and lasted until *1,840 cal (1,900 ± 65) BP (3) Instability of the southern margin of the LIS in the (Yu et al. 2010). Hudson Bay Lowlands, with frequent surges into An increase in lake level shortly after 8,900 cal glacial after 9,000 cal (*8,000) (8,000) BP may have occurred due to: (1) isostatic BP (Dyke and Dredge 1989). These surges, rebound at the outlet; (2) damming the outlet by a including the Cochrane readvances (Prest 1970; glacial readvance; (3) climate change; or (4) an Dyke and Dredge 1989), are important because increase in meltwater flux entering the lake. We rule they may have raised the level of Lake Agassiz- out #1 because lake transgressions due to isostatic Ojibway and caused meltwater to overflow into rebound are gradual, occurring often over hundreds the Superior basin at the end of the Houghton or thousands of years as is the case for the Nipissing Low. The Pic River, which is situated in an area rise (Booth et al. 2002; Fisher and Whitman 1999; of low topography across the continental Lewis 1969, 1970). As argued above, the switch to a divide (Fig. 1), could have served as a conduit deep water depositional environment at FWHP for meltwater discharge into the Superior basin 123 J Paleolimnol

during this time. Significantly, ostracodes from isobases in Fig. 4c, d), would have uplifted FWHP at a lakes Huron and Michigan record negative, and faster rate, causing downcutting of the Kaministiquia abrupt, oxygen isotopic excursions that are dated River and emergence of the region from the lake. to about 8,900 cal (8,000) BP (Rea et al. 1994; Moore et al. 2000; Breckenridge and Johnson 2009). Because this change occurs at almost the Conclusions same time as the reflooding of the lower Kami- nistiquia River valley, it is possible that overflow Profound environmental and hydrological changes from the same source was responsible for both. occurred in the Lake Superior basin in the first three millennia following deglaciation. One of the most AMS dating of Unit A indicates that rising lake level significant events during this time period was the large and sediment accumulation continued until sometime drop in lake level during the Houghton phase. Multiple after 7,400 cal BP. This subsequent rise in lake level at sites in the Superior basin, including the one reported in FWHP probably records the Nipissing transgression, this paper, indicate that the level of the lake was no which was due to differential uplift of the North Bay higher than the SSM bedrock sill between [9,100 and outlet (Lewis and Anderson 1989; Booth et al. 2002; 8,900 cal ([8,100 and 8,000) BP, and was therefore Lewis et al. 2007). This event slowly raised the water hydrologically closed during this time. By 9,100 cal level in the Superior basin above the SSM bedrock sill (8,140) BP, abandoned river channels near FWHP until Lake Superior was confluent with Lakes Mich- were colonized by a lowland boreal plant association. igan and Huron (Lewis and Anderson 1989; Lewis In this protected setting, fire-intolerant, late-succes- et al. 2007). Comparison of uplift histories at North sional conifer species (e.g., Abies balsamea) domi- Bay and Sault Ste. Marie indicates that the North Bay nated the overstory in association with common boreal outlet was lifted above the previous outlet at SSM deciduous trees and shrubs (Betula papyrifera, Rubus beginning *7,400 cal (6,400) BP (Lewis and Ander- idaeus, Arctostaphylos uva-ursi), emergent (Carex sp., son 1989: Figure 7c); our paleotopographic recon- Scirpus americanus), and bryophyte (Pleurozium structions also suggest that the water level was above schreberi, Dicranum polysetum) taxa. Shortly after the SSM bedrock sill by the time that Unit A was being 8,900 cal (8,000) BP, the lake level rapidly rose, deposited (beginning *7,400 cal (*6,400) BP; drowning and burying lowland vegetation in the lower Fig. 4f). Continued uplift of the North Bay outlet, in Kaministiquia River valley in a deep-water deposi- combination with a wetter climate (Lewis et al. 2008), tional environment. We suggest that this rapid trans- would have resulted in a slow transgression at FWHP gression was due to overflow from glacial Lake to the Nipissing level until the outlet switched to Agassiz-Ojibway, perhaps related to surging of the Chicago/Port Huron. In the Thunder Bay region, the margin of the LIS in the Hudson Bay Lowlands, which Nipissing level is represented by a prominent wave-cut routed water into the Superior basin through one or scarp *210 m asl (Julig et al. 1990), 27 m above the more spillway channels on the northern side of the lake. modern water plane and 24 m above Unit D at FWHP. A continued rise in lake level and sedimentation Sometime after 7,400 cal (6,400) BP, however, the after *7,400 cal (6,400) BP likely records the begin- modern Kaministiquia River downcut to its present ning of the Nipissing transgression, when the North elevation. We suggest that this was due to the overall Bay outlet was differentially lifted above the SSM decline in lake level that occurred at the end of the bedrock sill. The subsequent entrenchment of the Nipissing highstand, in combination with differential Kaministiquia River to its modern elevation (after isostatic rebound. Following the Nipissing high water 7,400 cal (6,400) BP) was probably initiated by the phases (*6,800 and 4,400 cal [*5,950 and 3,950] basin-wide drop in water level that occurred at the end BP), the lake level in the Superior basin dropped of the Nipissing highstand in combination with differ- gradually due, perhaps, to erosion of the overflow ential isostatic rebound. outlet at Port Huron (Booth et al. 2002; Johnston et al. 2007). In addition to an absolute drop in lake level, Acknowledgments Funding for this study was provided differential isostatic rebound between FWHP and the through the Social Sciences and Humanities Research outlets at Port Huron and, later, Sault Ste. Marie (see Council (MB), Canada Foundation for Innovation (MB), and

123 J Paleolimnol a Discovery Grant from the Natural Sciences and Engineering Drexler CW, Farrand WR, Hughes JD (1983) Correlation of Research Council of Canada (JTT). We are also grateful to: glacial lakes in the Superior Basin with eastern discharge Trevor Mellors for assistance in the field in 2006; Alice Telka events from Lake Agassiz. In: Teller JT, Clayton L (eds) for radiocarbon sample collection and submission; Amy Myrbo Glacial Lake Agassiz. Special paper 26, Geol Assoc Can, and Kamil Zaniewski for their help with epoxy impregnation of pp 309–330 lake sediments; Anne Hammond for thin section preparation; Dyck WJ, Lowdon JA, Fyles JG, Blake WJ (1966) Geological and Shi-Yong Yu for supplying corrected elevations for lake survey of Canada radiocarbon dates. Geol Surv Can Paper level indicator sites in the Superior basin. 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