J Paleolimnol DOI 10.1007/s10933-010-9461-1 ORIGINAL PAPER An 8,900-year-old forest drowned by Lake 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 Kaministiquia with the Houghton phase forced the ancestral Kami- River (near Thunder Bay, Ontario, Canada) provide nistiquia River to downcut. By *9,100 cal (*8,100) insight into early Holocene 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 Lake Superior 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 Lakes Agassiz or Ojibway associated cones from this deposit: 8,135 ± 25 (9,130–9,010 with the retreat of the Laurentide Ice Sheet from the cal), 8,010 ± 25 (9,010–8,780 cal), and 7,990 ± 20 Nakina moraine and/or the Cochrane surge margins (8,990–8,770 cal) BP. This sequence records an early in the Hudson Bay 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 Á Houghton low-water 955 Oliver Rd, Thunder Bay, ON P7B 5E1, Canada phase Á Boreal forest Á Plant macrofossils Á e-mail: [email protected] Paleohydrology Á Holocene paleoecology J. T. Teller Á Z. Yang Department of Geological Sciences, University of Manitoba, Winnipeg, MB, Canada Introduction L. Kingsmill Á 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 North America 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 Kaministiquia River (near Thunder 1997; Breckenridge et al. 2004), catastrophic out- Bay, Ontario) which provide chronological control bursts from Lake Agassiz 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 Great Lakes, 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 Laurentide Ice Sheet (LIS) margin which helped similar deposits known across the Great Lakes basin. 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 Michigan 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 moraines 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.