J Paleolimnol
DOI 10.1007/s10933-010-9447-z
ORIGINAL PAPER
A late Lake Minong transgression in the Lake Superior
basin as documented by sediments from Fenton Lake,
Ontario
Andy Breckenridge • Thomas V. Lowell
Timothy G. Fisher • Shiyong Yu
•
Received: 21 April 2009 / Accepted: 2 June 2010
Ó Springer Science+Business Media B.V. 2010
Abstract The evolution of the early Great Lakes was
driven by changing ice sheet geometry, meltwater
influx, variable climate, and isostatic rebound. Unfortunately none of these factors are fully understood.
Sediment cores from Fenton Lake and other sites in the
Lake Superior basin have been used to document
constantly falling water levels in glacial Lake Minong
between 9,000 and 10,600 cal (8.1–9.5 ka) BP. Over
three meters of previously unrecovered sediment from
Fenton Lake detail a more complex lake level history
than formerly realized, and consists of an early
regression, transgression, and final regression. The
initial regression is documented by a transition
from gray, clayey silt to black sapropelic silt. The
A. Breckenridge (&)
Department of Geology, Mercyhurst College,
501 E. 38th St, Erie, PA 16546, USA
e-mail: abreckenridge@mercyhurst.edu
T. V. Lowell
Department of Geology, University of Cincinnati,
Cincinnati, OH 45221, USA
e-mail: thomas.lowell@uc.edu
T. G. Fisher
Department of Environmental Science, The University
of Toledo, Toledo, OH 43606, USA
e-mail: timothy.fisher@utoledo.edu
S. Yu
Department of Earth and Environmental Sciences, Tulane
University, New Orleans, LA 70118, USA
e-mail: syu2@tulane.edu
transgression is recorded by an abrupt return to gray
sand and silt, and dates between 9,000 and 9,500 cal
(8.1–8.6 ka) BP. The transgression could be the result
of increased discharge from Lake Agassiz overflow or
the Laurentide Ice Sheet, and hydraulic damming at the
Lake Minong outlet. Alternatively ice advance in
northern Ontario may have blocked an unrecognized
low level northern outlet to glacial Lake Ojibway,
which switched Lake Minong overflow back to the
Lake Huron basin and raised lake levels. Multiple sites
in the Lake Huron and Michigan basins suggest
increased meltwater discharges occurred around the
time of the transgression in Lake Minong, suggesting a
possible linkage. The final regression in Fenton Lake is
documented by a return to black sapropelic silt, which
coincides with varve cessation in the Superior basin
when Lake Agassiz overflow and glacial meltwater was
diverted to glacial Lake Ojibway in northern Ontario.
Keywords Lake Superior Lake Minong Lake levels Lake Agassiz Paleohydrology
Introduction
Glacial Lake Minong and Fenton Lake
Glacial Lake Minong was the last lake in the Superior
basin that received glacial sediments from the
retreating Laurentide Ice Sheet (LIS). The paleogeography at the inception of Lake Minong is poorly
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J Paleolimnol
constrained, but the lake formed after 11,500 cal
(10.0 ka) BP in the eastern Superior basin following
drawdown from a Lake Algonquin level, a highstand
that connected the Superior, Huron and Michigan
basins (Farrand and Drexler 1985) (Fig. 1a). During
the early phase of Lake Minong, a separate pro–
glacial lake (Lake Duluth) also existed in the western
Superior basin. During ice margin retreat, Lake
Minong expanded and eventually coalesced with
Lake Duluth (Fig. 1b). At later stages, Lake Minong
was not a pro-glacial lake, but continued to receive
meltwater (Fig. 1c). By around 9,000 cal (8.1 ka) BP,
the ice margin retreated north of the Hudson Bay
drainage divide, and LIS runoff diverted to glacial
Lake Ojibway, ending Lake Minong (Fig. 1d) (Bajc
et al. 1997; Breckenridge et al. 2004).
The Lake Minong lake level history is complicated by multiple factors including: (1) inadequately
understood crustal rebound of the region from the
unloading of glacial ice, (2) poorly constrained ice
margin recessional positions, (3) uncertain rates of
outlet sill incision, and (4) a suspected highly variable
discharge at the outlet. Until recently, the only outlet
for Lake Minong was believed to have been the St.
Mary’s River. The sill, which was initially based in
glacial drift, has been referred to as the Nadoway
Fig. 1 a–d General late glacial history of Lake Minong, the
Great Lakes basin, and Lake Agassiz. SMR is the St. Mary’s
River outlet. Multiple sources were used for these
reconstructions, most notably: Lewis and Anderson (1989),
Lewis et al. (1994), and Dyke et al. (2003)
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J Paleolimnol
barrier (Farrand and Drexler 1985). North of the
isobase passing through the outlet, relative lake levels
were presumed to have constantly lowered due to
crustal rebound and incision of the outlet sill. Falling
Lake Minong water levels resulted in the emergence of
small lake basins, such as Fenton Lake on the eastern
side of Lake Superior (Figs. 2, 3a) (Saarnisto 1975).
When regressing Lake Minong waters fell below the
local sills in these small lake basins, sediments
changed from clays or silts typical of oligotrophic
lakes, to more organic-rich sediments (a sapropel)
typical of small, mesotrophic to eutrophic temperate
lakes on non-calcareous bedrock. Modern sediment
studies support this interpretation. Lake Superior
sediments have \4% total organic carbon (TOC) and
the organic carbon is primarily allochthonous (Thomas and Dell 1978; Johnson et al. 1982; Mothersill
1985). Small temperate lakes generally have [10%
TOC and the organic matter is primarily autochthonous (e.g. Dean 1999). Saarnisto (1975) radiocarbon
dated organic-rich muds at the transitions between
these two lithofacies within Fenton Lake and several
adjacent sites to establish the timing of emergence and
assign ages to falling Lake Minong lake levels. Since
this study, multiple lines of evidence suggest a
potential for one or more transgressions, and therefore
we returned to Fenton Lake to test this hypothesis.
Fig. 2 Topographic map for the lake sites studied by Saarnisto
(1975). Core locations are numbered and referenced in Table 1
and Figs. 3 and 6b. The Fenton Lake core site is number 7. The
Minong I (dashed) and Dorion (dotted) lake levels from Fig. 3
are traced
A short review of the Lake Minong lake level history is
helpful to understand why transgressions may have
occurred.
Lake Minong lake levels
Reconstruction of Lake Minong water levels are
primarily based on raised shoreline features and
graded fluvial terraces. Connected features determine
past ‘water planes’ or lake levels (Fig. 3) (Lawson
1893; Stanley 1932; Sharp 1953; Farrand 1960; Bajc
1986). Former water planes have been differentially
uplifted, and rise to the northeast where ice was
thickest. Lewis et al. (2005) used dated shorelines and
studies of crustal response following ice sheet unloading to estimate uplift decrease as a function of time.
Regional uplift rates are highest to the northeast, and
uplift rates decrease exponentially with time. Seven
lines of equal uplift (isobases) are drawn across the
Superior basin at approximately 100 km spacing in
Fig. 3a based on Lewis et al. (2005). The elevations of
all mapped Lake Minong shoreline features in the
Lake Superior basin are drawn relative to these
isobases in Fig. 3b (Farrand 1960; Cowan 1985; Bajc
1986; Phillips and Fralick 1994; Slattery et al. 2007).
Several discrete water planes are associated with
Lake Minong (Farrand 1960). The terminology is
confusing because the Minong I level (the highest
level) is just one of several designated water planes for
glacial Lake Minong. At least 8 separate Lake Minong
levels have been identified: the Minong I–III, PostMinong I–IV, and the Houghton (Farrand 1960). The
Houghton is the lowest level, which was controlled by
a bedrock sill on the St. Mary’s River outlet (Farrand
1960). The Post-Minong IV level is well developed
near Dorion, Ontario, and named the Dorion. Note that
lake levels above the Minong I have been mapped in
the western Lake Superior basin that relate to glacial
Lake Duluth. The Nipissing level (Fig. 3) is a midHolocene transgression in the upper Great Lakes
resulting from uplift of the North Bay outlet in the
Lake Huron basin, which reached a maximum level by
4,500 cal (*4.0 ka) BP (Thompson and Baedke
1997). This transgression drowned Lake Minong
strandlines in western Lake Superior (Farrand 1960).
For most of the basin, discrete Lake Minong lake
levels are an abstraction, because in a rebounding basin
stable water levels only occur near an outlet or on the
same isobase (see Larsen 1987). Water levels fall on
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J Paleolimnol
Fig. 3 Lake Minong (and Nipissing level) shoreline features.
a White dots mark Lake Minong and Nipissing features from
Farrand (1960) and Bajc (1986), as well as the delta associated
with the Nakina moraine by Slattery et al. (2007). The numbers
(italicized) are radiocarbon dated sites that constrain lake levels,
which are listed in Table 1. Isobases numbered 0–6 are spaced at
approximately 100-km intervals and are based on a rebound
model (Lewis et al. 2005). Using these isobases, the analysis by
Lewis et al. (2005), and ArcGIS (ArcView 9.3), the modern
topography was adjusted for 10,200 cal BP and 5700 cal BP to
plot the extent of the Minong (black line) and Nipissing (white
line) water levels. The Minong shoreline assumes the outlet sill
was at a modern elevation of 750 ft/229 m asl at the St. Mary’s
River outlet (the Sheguiandah level of Cowan 1985), and the
Nipissing level assumes a modern elevation 650 ft/198 m asl at
the St. Mary’s River headwaters. Note that the northern Minong
shoreline was fronted by an ice margin, therefore the projected
Minong shoreline is farther north than the mapped lake extent
(white dots). The Nakina moraine deltas associated with Lake
Minong by Slattery et al. (2007) may have been within Lake
123
Minong, or they may have formed in a pro-glacial lake
that drained into Lake Minong. Elevation data combines 90 m
SRTM data (http://www.seamless.usgs.gov) with the Great
Lakes bathymetric data set (http://www.ngdc.noaa.gov/mgg/
greatlakes/). b Projected elevations of shoreline features that
correspond to the white dots in Fig. 3a, radiocarbon dated lake
sites (triangles with superscript site numbers, Table 1), and other
sites (abbreviations) relative to the isobases in Fig. 3a. The
shoreline features are primarily from Farrand (1960) (black
diamonds) and Bajc (1986) (grey squares). All dates are in calibrated years before present. Related sites are identified with
abbreviations noted in Fig. 3a. The Minong, Dorion, and
Nipissing lake levels are calculated after Lewis et al. (2005). The
topographical profile over the White Otter River drainage divide
(Fig. 3a) is provided. The Minong and the highest post-Minong
lake levels project above this drainage divide, but younger Lake
Minong water levels do not. If the ice margin retreated north
of the drainage divide before sufficient down-cutting of the
St. Mary’s River sill, Lake Minong would have over topped the
drainage divide, and flowed into the Lake Ojibway basin
J Paleolimnol
isobases north of an outlet and rise south of an outlet.
The Lewis et al. (2005) model provides estimates for
rates of change at any time period. At 10,500 cal
(9.3 ka) BP lake levels were falling at a rate of
*2.5 cm/yr in the northeast (isobase no. 6, Fig. 3a),
but rising at a rate of *2 cm/yr in the southwest
(isobase no. 1, Fig. 3a). In addition to these changes,
during a 1,500 year period in Lake Minong (ending
around 9,000 cal BP), the Nadoway barrier was
downcut *45 m to bedrock (Cowan 1985), equivalent
to lake levels dropping basinwide by *3 cm/yr.
Episodic downcutting of the Nadoway barrier due
to glacial Lake Agassiz flooding has been proposed
(Farrand and Drexler 1985). Lake Agassiz was a
massive pro-glacial lake (Fig. 1) that drained eastward
into Lake Minong through a series of successively
lower outlets via the Lake Nipigon basin between
9,000–10,600 cal (8.1–9.4 ka) BP (Figs. 1 and 3a)
(Teller and Thorleifson 1983; Leverington and Teller
2003; Breckenridge 2007). The opening of each outlet
is proposed to have released catastrophic floods,
perhaps up to 8,000 km3 of water in 1–3 years
(Leverington and Teller 2003). There is physical
evidence of these floods, including boulder strewn
outlet channels that empty into the Lake Superior
basin. Discharges are estimated to have been as high as
100,000 m3/s (Teller and Thorleifson 1983). There are
thick glacial varves in Lake Superior sediment cores
that must relate to anomalously high sediment
influxes, possibly Lake Agassiz discharge (Teller
and Mahnic 1988; Breckenridge 2007). In Lake Huron
and Michigan basin sediments, an abrupt decrease
in the d18O composition of benthic ostracodes is
explained by increased meltwater or Lake Agassiz
discharge (Colman et al. 1994; Rea et al. 1994). This
event occurred between 9,000 and 9,400 cal
(8.1–8.4 ka) BP (Breckenridge and Johnson 2009).
There is the undated glaciofluvial delta in the Killala
valley that documents an 18 m Lake Minong transgression thought to relate to Lake Agassiz flooding
(Fig. 3) (Phillips and Fralick 1994). Finally, there are
beach gravels within silt and clay varves in the Black
River valley that may relate to significant water level
fluctuations (Bajc 1986). Numerical models suggest
large discharges ([100,000 m3/s) could cause hydraulic damming at the St. Mary’s River outlet and
temporarily raise lake levels (Tinkler and Pengelly
1995). In summary, large Lake Agassiz floods probably spilled into Lake Minong, and the floods had the
potential to raise lake levels. They may have also
caused rapid sill downcutting, lowering lake levels
(Farrand and Drexler 1985).
There is an alternative explanation for an observed
Lake Minong transgression; the Lake Minong outlet
may not have always been the St. Mary’s River. This
hypothesis is based entirely on d18O records from
Lake Superior and Lake Huron sediments. The d18O
composition of Lake Minong water was similar to
meltwater, which is too low to explain the coeval d18O
composition of water in the Lake Huron basin, which
was similar to present-day (Rea et al. 1994; Breckenridge and Johnson 2009). One hypothesis is that
overflow from Lake Minong diverted away from the
Lake Huron basin via a divide at the headwaters of the
Pic-White Otter River on the north side of the Lake
Superior basin (Fig. 3) (Breckenridge and Johnson
2009). A diversion to a lower elevation northern outlet
(Pic-White Otter) would create a basinwide regression. Subsequent uplift of the northern outlet would
create a basinwide transgression.
Field work within the Pic River valley and tributaries has documented paleoflow directions in glaciofluvial deposits that are exclusively down-valley,
towards Lake Superior (Bajc 1986). These include
radiocarbon dated sediments associated with the
Dorion level that date near the end of Lake Minong
at 9,000 cal BP (8,070 ± 180 BP, Table 1: 13b) (Bajc
et al. 1997). Dates on the Lake Huron d18O record
suggest an active northern outlet between 9,400 and
10,000 cal (8.4–8.9 ka) BP, when the d18O values of
lake water were close to modern (Rea et al. 1994). If
there was a northern Lake Minong outlet, the
sediments dated to 9,000 cal (8.1 ka) BP near the
Pic River require an undocumented ice readvance over
the drainage divide to restore southern flow. Note that
the Lake Minong glacial varve sediment record within
Lake Superior is continuous (Breckenridge 2007), so
even if a northern outlet for Lake Minong opened,
Lake Minong always received Lake Agassiz and LIS
meltwater and sediments via the Lake Nipigon inlets.
Fenton Lake was isolated from Lake Minong at
9,000 cal (8.1 ka) BP, and this was the only record
studied by Saarnisto (1975) that documents emergence from Lake Minong after 9700 cal (8.8 ka) BP.
Crozier Lake was isolated after 9,700 cal BP too, but
isolation of Crozier Lake post-dates Lake Minong.
For this reason none of the other sites could record an
initial regression and subsequent transgression from
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Table 1 Radiocarbon dates associated with Lake Minong lake
levels. Sites are numbered and mapped in Figs. 2 and 3. Most
dates are also referenced in Fig. 5b. The radiocarbon dates are
calibrated using Calib 5.0 (Stuiver and Reimer 1993), using the
intcal04.14c calibration dataset (Reimer et al. 2004). The
extreme 2r calibrated ages before present are provided along
with the median probability age
Site no.: site
Lat. N. &
Long. W
Lab. no. &
date
Material dated and stratigraphy
1: Antoine Lake
47 53.8
Hel-398
84 50.5
8,830 ± 200
Bulk sediment, above Lake
Minong clay
10,397
2: Alfies Lake
47 52.8
84 52.1
GSC-1851
Bulk sediment, above Lake
9,210 ± 100 Minong clay
3a: Beaver Lake
86 20.5
WW-1362
43 34.0
8,320 ± 60
3b: Beaver Lake
86 20.5
WW-1356
43 34.0
8,360 ± 70
3c: Beaver Lake
3d: Beaver Lake
4: Blackington
Lake
5: Crozier Lake
86 20.5
WW-1363
43 34.0
8,520 ± 60
86 20.5
WW-1361
43 34.0
9,480 ± 60
47 53.8
Hel-399
Peat, between rhythmites
Reference
9,476
9,900
Saarnisto 1975
10,204
10,651
10,390
Saarnisto 1975
9,136
9,340
Fisher and Whitman
1999
9,370
Fisher and Whitman
1999
9,510
Fisher and Whitman
1999
10,750
Fisher and Whitman
1999
9,700
Saarnisto 1975
8,400
Saarnisto 1975
9,139
9,521
Peat, between rhythmites
9,427
9,596
Wood, in sand below rhythmites 10,572
11,079
84 50.3
47 54.1
Hel-396
84 49.2
7,590 ± 180
Bulk sediment, above clay
9,004
10,403
8011
8,970
10,440
Julig et al. 1990
9,010
Saarnisto 1975
84 52.8
10,645
Bulk sediment, above L. Minong 8,563
8,100 ± 180 sediment
9,467
7b: Fenton Lake
47 51.35
OS-64682
9,540
This study
84 52.73
8,570 ± 45
8: Jock Lake
48 47.6
Hel-402
10,190
Saarnisto 1975
10,430
Saarnisto 1975
10,670
Flakne 2003
6,340
Saarnisto 1975
10,630
Zoltai 1965
7a: Fenton Lake
9: Last Lake
10: Lily Lake
11: Roller Lake
12: Rosslyn Pit
13a: Rous Delta
89 20.9
47 51.3
TO-547
Med.
Prob.
9,468
Gyttja, above rhythmites
Bulk sediment, above Lake
8,640 ± 280 Minong clay
6: Cummings Pond 48 24.3
2r Cal
BP
Wood, above basal sand
10,248
9,260 ± 70
Hel-400
Pine wood, in gray silt Lake
Minong silt
86 27.9
Bulk sediment, above Lake
9,060 ± 200 Minong clay
47 55.7
GSC-1719
89 5.4
9,220 ± 180
47 55.7
AA-12529
89 5.4
9,420 ± 90
47 54.5
GSC-1731
84 49.3
5540 ± 150
48 21.8
GSC-287
89 27.3
9,380 ± 150
86 2.7
WAT-1508
9,478
9,624
9,563
10,691
Bulk sediment, above Lake
Minong clay
11,079
9,905
Bulk, from gyttja above gray
clay
11,086
Bulk sediment, above L.
Superior sediment
6,660
Wood, at contact between sand
& clay
11,094
10,402
5,955
10,248
Wood, bottomset of glaciofluvial
8,310 ± 200 delta
WAT-1,623 Wood, overlain by sands
8,070 ± 180 associated w/Rous Delta
8,648
9,260
Bajc et al. 1997
9,678
8,543
8,970
Bajc et al. 1997
14: Lake St. Croix 46 22.9
ETH-31000
10,429
10,660
91 46.8
9,420 ± 75
Lowell and Fi Fisher,
unpublished
13b: Black River
cutbank
123
48 42.1
48 44.2
85 58.7
Wood, in basal sand/silt
rhythmites
9,442
11,070
J Paleolimnol
the opening and closing of a northern outlet, which
would have occurred between 9400 and 10,000 cal
(8.4–8.9 ka) BP. The motivation for our work was to
test this hypothesis by re-coring Fenton Lake to
determine whether or not there was evidence for an
undocumented regression and transgression in the
sediment.
pre-treated with hydrogen peroxide to remove organic
matter. Eight pollen samples from the top 2.2 m were
prepared following standard techniques (Faegri and
Iverson 1989). All pollen samples have counts over
250 grains. The overlapping sections from Fen05-A
and Fen05-B were correlated visually and with the
MSCL data to create composite profiles for the TOC,
pollen, and grain size data.
Methods
Results
Two Livingston square-rod piston cores with overlapping sections that prevent stratigraphic gaps were
recovered in February of 2005 from the southern
basin of Fenton Lake (z = 14.6 m, 47.8558°N,
-84.8788°W) (Fig. 2). These cores are designated
Fen05-A and Fen05-B. The sediment core from
Saarnisto (1975) is designated Fen67. Successive
sections were driven, recovered, and extruded with a
hydraulic motor, which aided the recovery of dense
sediment. The shallowest core (Fen05-B) begins at
19.5 m below the ice surface. In comparison, core
Fen67 begins at 19.9 m, and water depth was 14.4 m.
The cores were logged at the Limnological
Research Center in Minneapolis with a Geotek MultiSensor Core Logger (MSCL). The MSCL measures
whole core, volume magnetic susceptibility and wet
bulk density via gamma ray attenuation. The cores
were split into working and archive halves and
photographed with a flatbed DMT CoreScanÒ digital
core scanner. Archive halves are stored at the National
Lacustrine Core Repository in Minneapolis. Sediment
lithologic descriptions are based primarily on smear
slide analyses using classifications by Schnurrenberger
et al. (2003). Grayscale intensity was calculated from
digital images with Image J image analysis software
after calibrating grayscale colors using Adobe Photoshop and a Gregtag-Macbeth Mini ColorCheckerÒ
card included with each core scan. Total organic
carbon (TOC) and grain size analyses were completed
at a 10 cm sampling interval. TOC data are from losson-ignition (LOI) at 5508 C using a LOI:TOC ratio of
2.13:1 (Dean 1974). The LOI data provide a direct
comparison to data obtained by Saarnisto (1975). Grain
size analyses (0.4–2,000 lm) were completed via laser
diffraction using a LS320 Beckman-Coulter size
analyzer. Samples were disaggregated with a sodium
hexametaphosphate solution in a shaker and sonicated
for 90 s prior to analysis. Samples with[5% LOI were
The TOC profile from cores Fen05-A/B matches the
TOC profile from core Fen67 if the depths are
adjusted by 30 cm (Fig. 4). Data from core Fen67 are
lowered by 30 cm to match cores Fen05-A/B. An
additional 3.5 m of sediment was recovered below
the inorganic clay in which core Fen67 terminates.
The stratigraphy is broken into 5 lithofacies, referred
to as units 1, 2, 3, 4, and 5 (Figs. 4, 5). Unit 4 is
further subdivided into sub-units 4a, 4b, and 4c. The
elevation of Fenton Lake requires lake levels higher
than the Dorion level in Lake Minong to deposit the
inorganic gray clay silt into which Fen67 terminates
(sub-unit 4b). Below these sediments is a dark,
organic-rich unit ([4% TOC) uncharacteristic of
Lake Superior sediments (unit 3). Unit 3 must have
resulted from initial emergence and isolation of
Fenton Lake from Lake Minong.
The base of the core (unit 1) is characterized by light
gray (2.5YR 5/1–7/1) calcareous sand/silt rhythmites
(Fig. 5e). These are Lake Minong glaciolacustrine
rhythmites, but probably not glacial varves (annual
rhythmites) because the thickness patterns of the
couplets are irregular. The coarsest-grained layers are
well-sorted fine-grained sands. The finer-grained laminae are clayey silts. These may be ice proximal
glaciolacustrine sediments, but ice proximal rhythmites from the open lake have regular thickness
patterns and the coarse-grained layers are not so well
sorted (Breckenridge 2007). This site was close to
shore (\500 m) and water depths were never more than
60 m, even in the earliest phases of Lake Minong
(Fig. 2), therefore the Fenton Lake site is much
different than the sediment records from the deeper
basin. Perhaps the differences are explained by coastal
currents or waves.
There is an abrupt transition to mottled gray
(2.5YR 4/1) clayey silt (unit 2) (Fig. 5d). This unit
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J Paleolimnol
19.5
% TOC
0
4
8
Selected pollen
Volume magnetic susceptibility
(×10-6, SI units)
12
10
% Clay
40 30 20 10
100 340
% Picea % Pinus % Betula
0
60
0 20 0 20
0 20
Lithofacies &
Interpretation
20.5
9.01
4a 4: Gray clayey silt,
4b 4b, between sandier
subunits, 4a & 4c.
Lake Minong
4c
9.54
14C
dates (cal ka BP)
5: Black sapropelic
clayey silt.
isolation from
Lake Minong
21.5
3: Black sapropelic
clayey silt.
isolation from
Lake Minong
22.5
2: Gray clayey silt
with iron sulfide
laminae. Laminated
above and generally
mottled near base.
Lake Minong
23.5
Depth from ice surface (m)
Fig. 4 Stratigraphic data
for Fenton Lake, including
core Fen67 (dashed lines)
and cores Fen05-A/B (solid
lines). The original depth
for core Fen67 is lowered
by 30-cm to match the data
from cores Fen05-A/B. The
raw grayscale and magnetic
susceptibility data are
provided for every section
from the two overlapping
cores (Fen05-A/B), but the
grain size, pollen, and TOC
data is presented as a
composite profile based on
the correlated cores.
Radiocarbon dates (7a and
7b, Table 1) are noted on
the depth scale (left side)
24.5
1: Gray calcareous
clayey silt
rhythmically
laminated with well
sorted, quartzose
sand.
Lake Minong
255 100
(white)
10
Grayscale
gradually darkens upsection (2.5YR 5/1), and TOC
increases as grain size and magnetic susceptibility
decreases. Clay content is high and these sediments
are similar to modern nearshore Lake Superior
sediments (Thomas and Dell 1978; Mothersill
1985). As water levels fell from the Minong to the
Dorion level, the Fenton Lake site became a bay on
Lake Minong with a restricted inlet to the southwest
(Fig. 2). The increasing organic carbon and decreasing grain size in unit 2 are explained by falling lake
levels and a narrowing inlet.
The transition to unit 3, a black (5Y 2.5/1) to dark
olive gray (5Y 3/2) sapropelic silt, is evident by a rise
in TOC and a decrease in clay content (Fig. 5c). The
rise in organic carbon occurs over *10 cm. The high
organic content precludes the possibility that these
sediments were deposited in Lake Minong, and
therefore they must be from an isolated lake. There
are discontinuous *0.67-mm scale light/dark
123
1
(black)
8
7
6
5
4
3
Grain size (φmean)
laminations within unit 3 (see base of Fig. 5c). These
are alternating laminae of dark, organic-rich sediments and gray clayey silt, and may be bioclastic
varves. If these couplets are annual, unit 3 represents
*500 years of deposition. This sediment accumulation rate is similar to the average post-glacial
accumulation rates calculated for unit 5.
The transition to unit 4 is abrupt (Fig. 5b). Unit 4
has a complex stratigraphy. The base and top (subunits 4a and 4c) are poorly sorted gray sands with
plant macrofossils, including terrestrial plant material. Sub-unit 4b consists of gray clayey silt that is
lithologically similar to unit 2. Pine wood within subunit 4b was radiocarbon dated by accelerator mass
spectrometry to 9540 cal BP (8,570 ± 45 14C yr BP,
Table 1: 7b). The transition to unit 5 is also sharp and
marked by more organic material and sand (sub-unit
4c) (Fig. 5a). Unit 5 is lithologically identical to unit
3, although the light/dark couplets are less apparent.
J Paleolimnol
Fig. 5 Core images of the five lithostratigraphic units. a Fen05-B, secton 2, 10–30 cm. b Fen05-B, section 2, 54–74 cm. c Fen05-B,
section 2, 79–99 cm. d Fen05-B, section 4, 40–60 cm. e Fen05-B, section 6, 20–50 cm
The base of unit 5 was dated to around 9,010 cal BP
(8,100 ± 180 yr BP, Table 1: 7a) (Saarnisto 1975).
This radiocarbon date is on bulk sediment, and if the
sediment included aquatic plants that incorporated
dissolved carbonate leached from calcareous drift, the
dates may be too old. However, with the exception of
the date from Last Lake, the bulk sediment dates
from Saarnisto (1975) appear to be consistent with
radiocarbon dates on macrofossils from elsewhere in
the basin (Julig et al. 1990; Bajc et al. 1997; Fisher
and Whitman 1999).
The pollen across units 5, 4, 3, and 2 were
analyzed to test the idea that unit 4 was simply reeroded, older glaciolacustrine sediment (from units 1
and 2). Qualitatively, overlapping pollen analyses
from cores Fen05-A/B match core Fen67 very well.
The Picea data appear very similar. Pinus abundance
is overestimated and Betula abundance is underestimated in our analysis, but the trends are identical.
The key feature is that the six pollen samples are
unique within unit 4 compared to older glaciolacustrine sediments, and show a consistent trend downsection. If unit 4 were re-eroded Lake Minong clay,
the pollen signature should have higher Picea
concentrations than sediment below and be more
homogenized. We conclude that unit 4 is not purely
reworked glaciolacustrine sediment, but must have
been deposited in glacial Lake Minong following a
transgression, which happened at 9,540 cal (8.6 ka)
BP or some time thereafter. The radiocarbon dated
123
J Paleolimnol
wood may be reworked, therefore this date is
considered a maximum age for the transgression.
Discussion
As outlined in the introduction, the regression (documented by the transition to unit 3) and subsequent
transgression (documented by the transition to unit 4)
was predicted (Breckenridge and Johnson 2009). The
hypothesis was that ice retreat north of the drainage
divide opened an isostatically depressed northern
outlet at the headwaters of the White Otter River, a
tributary of the Pic River, which lowered lake levels
below the sill at the St. Mary’s River, and caused a
basinwide regression. A subsequent ice readvance
blocked the outlet, created the glaciofluvial sediments
that record down valley paleoflow directions in the Pic
River valley and tributaries (Bajc 1986), and caused
lake level rise and a transgression.
Despite evidence for a transgression at Fenton Lake,
there are multiple unresolved problems with the
northern outlet hypothesis. The reference isobases
across the proposed drainage divide calculated by
Lewis et al. (2005) do not depress the northern outlet
enough to cause isolation of Fenton Lake when the
outlet is opened. The isobases would need to be shifted
by several 10’s of kilometers (M. Lewis, personal
communication). The Lewis et al. (2005) estimates
could be incorrect because there are few control points
on the most northern isobases, or maybe there is
significant sedimentation on the valley floor that postdates drainage. A second problem is that field work in
the Pic River valley documents only southerly paleoflow directions (Bajc 1986). A third problem is that the
sedimentological transition between units 2 and 3 (the
regression) is gradual. Unit 2 is characterized by slowly
increasing TOC concentrations and decreasing clay,
which is best explained by decreasing lake levels and
local restriction of the connection with Lake Minong.
The transition to unit 3 (the initial isolation horizon) is
not abrupt as would be expected from a rapid drop in
lake level when an ice dam on the northern outlet was
breached, but instead appears to be part of a continuum
of gradually falling lake levels. Perhaps the ice dam
breach occurred only after Fenton Lake was isolated, or
there was a drift covered sill across the outlet that was
gradually downcut (in a manner perhaps similar to the
Nadoway barrier).
123
An alternative explanation for the transgression
(the transition from unit 3 to 4) is increased discharge
from Lake Agassiz and/or glacial meltwater caused
lake level rise due to hydraulic damming at the St.
Mary’s River outlet. As explained earlier there is
widespread evidence of high discharges of glacial
meltwater or Lake Agassiz overflow from 9,000 to
9,500 cal (8.1–8.5 ka) BP (Fig. 6a). Several radiocarbon dated sediment records in the Lake Huron
basin document episodic lake level rises that can only
be explained by hydraulic resistance at the Lake
Huron basin outlet (Lewis and Anderson 1989; Lewis
et al. 1994, 2005). In the southern Michigan basin,
the Olson Forest Bed was drowned by rising lake
levels (Chrzastowski et al. 1991; Miller et al. 2000).
The oxygen isotope records from sediments in Lakes
Huron and Michigan document an abrupt decrease in
d18O, which is due to the influx of glacially derived
meltwater (Colman et al. 1994; Rea et al. 1994). If
the transgression recorded at Fenton Lake is from
meltwater or Lake Agassiz floods, the floods must
have persisted for at least several decades in order to
deposit sub-unit 4b (a 20-cm thick silty clay bed). If
the cause was Lake Agassiz drawdown, flooding
lasted much longer than the 1–3 year prediction of
Teller and Leverington (2004).
Both hypotheses to explain the deposition of unit
4b: (1) basinwide flooding from hydraulic damming at
the St. Mary’s River outlet, and (2) a basinwide
transgression from closure or uplift of a northern
outlet, are reasonable and can be tested. The timing of
the transgression at Fenton Lake is close to the timing
suggested for flooding in the Lake Huron and Michigan basins, but the flooding hypothesis lacks a good
mechanism for maintaining high discharges for a
prolonged period. The northern outlet hypothesis lacks
supporting evidence of sufficient crustal depression of
the drainage divide at the headwaters of the White
Otter River, and a subsequent unrecognized ice readvance must cross the drainage divide at some point.
Future modeling efforts should be able to detail the
range of discharges that would be required to produce
both the d18O records and lake level data. Hopefully
these models can shed light on potential mechanisms
for the abrupt changes in discharge and/or lake level
that occurred around 9,400 cal (8.4 ka) BP.
A summary relative lake level curve (Fig. 6b) is
constructed by projecting all radiocarbon dates associated with Minong lake levels to the Fenton Lake isobase
J Paleolimnol
Fig. 6 a Evidence for floods in the Great Lakes basin.
Triangles are dates on emergence of lakes and bogs, squares
are tree stumps, circles are reworked material and likely flood
deposits (2r distributions shown). Radiocarbon dates from the
Lake Huron basin are numbered according to Table 1 from
Lewis et al. (2005). The thick varve event in Lake Superior
lasts 36 years but has a 200 year age uncertainty (Breckenridge
et al. 2004). Radiocarbon dates from the Olson Forest Bed are
labeled O:1 (Miller et al. 2000) and O:2 (Chrzastowski et al.
1991). The d18O data are from Rea et al. (1994) for Lake Huron
and Colman et al. (1994) for Lake Michigan, but the ages are
from Breckenridge and Johnson (2009). The dates for when
Lake Agassiz may have begun draining into Lake Minong are
labeled A:1 (Mann et al. 1997), A:2 (Teller et al. 2000), and
A:3 (Fisher 2003). b A relative lake level curve for Lake
Minong at Fenton Lake determined from radiocarbon dates
(with 1r and 2r error bars). Elevations for all sites are
projected according to Lewis et al. (2005) equations 7 and 8,
using the calibrated radiocarbon dates, and adjusting elevations
to the Fenton Lake isobase. The grey dashed lines are
calculated lake levels based on isostatic rebound alone (no
sill downcutting). The dashed black line is the interpolated
Lake Minong lake level history at Fenton Lake assuming there
was never an ice free northern outlet. The corresponding
Fenton Lake lithofacies (Fig. 4) are based on the core
sedimentology and interpretation
using equations 7 and 8 from Lewis et al. (2005). The
Minong lake level history at Fenton Lake is interpolated
with a black dashed line. Gray dashed lines predict lake
levels from isostatic rebound alone (no downcutting).
The lithofacies (1–5) from Fenton Lake correspond to
the interpolated Minong lake levels.
123
J Paleolimnol
The transgression in the Killala valley (Phillips and
Fralick 1994) is much older and at a higher elevation
(Minong level) than the Fenton Lake transgression.
This transgression may be from the initial Lake
Agassiz floods to Lake Minong (see Fig. 6a). Emergence of the lakes studied by Saarnisto (1975) [Jock
Lake (8), Antoine Lake (1), and Blackington Lake (4)]
are explained by a combination of isostatic uplift and
gradual sill downcutting at the St. Mary’s River outlet.
Date 7b is the wood from the transgression layer (unit
4) in Fenton Lake. If this age is correct, and unit 3
represents a 500 year period of isolation from Lake
Minong, then Fenton Lake was isolated by 10,000 cal
(8.9 ka) BP, but this timing is earlier than the isolation
of both Antoine (1) and Blackington (4) which are at
higher elevations. Instead a transgressive event at
around 9,300 cal (8.3 ka) BP is interpreted, which is
younger than the radiocarbon date within unit 4
(Fig. 6b). The 9,300 cal (8.3 ka) BP date is more
consistent with evidence from the Lake Huron and
Michigan basins for flooding (Fig. 6a) and the radiocarbon dated wood in Fenton is interpreted to be
re-worked from flooding of the local basin. The
transgression correlates spatially and temporally with
the glaciofluvial delta in the Black River valley (13b)
(Bajc et al. 1997). If the organic-rich sands from
subunits 4a and 4c are from rapid lake level rise and
local flooding, unit 4 may represent two floods during
a period of high Minong lake levels. The Lake
Michigan d18O record details two meltwater events,
and at Beaver Lake, a peat deposit is located stratigraphically between rhythmically laminated sand and
clay from Lake Minong (Fisher and Whitman 1999).
By around 9,000 cal BP lake levels dropped in Fenton
Lake, which may directly correlate to the loss of
glacial meltwater that is recognized throughout the
Superior basin by the abrupt cessation of glacial
varves (Breckenridge et al. 2004). This period marks
the diversion of all Lake Agassiz overflow and glacial
meltwater to glacial Lake Ojibway in the present
Hudson Bay watershed.
dates to before 10,200 cal (9.0 ka) BP. The younger
transgression recorded at Fenton Lake occurred
between 9,000 and 9,500 cal (8.1–8.5 ka) BP. Fenton
Lake was isolated from Lake Minong for a period of
perhaps 500 years prior to the transgression. The
basinwide lake level rise required to flood Fenton Lake
was at least 12 m. The cause of the transgression is
uncertain. If a lower elevation northern outlet for Lake
Minong at the headwaters of the White Otter River
was opened by the retreat of the LIS, a subsequent ice
advance, or ongoing uplift, closed the outlet and
caused the transgression. This hypothesis is appealing
because the diversion of Lake Minong overflow away
from the Lake Huron basin, and subsequent redirection back to the Huron basin, explains the d18O values
between 9,400 and 10,000 cal (8.4–8.9 ka) BP from
western Lake Huron that suggest an absence of
glacially derived water (Rea et al. 1994; Breckenridge
and Johnson 2009). However, published rebound
models do not support a reconstruction where Fenton
Lake is isolated with the opening of this northern
outlet, and there is no field evidence to support the
existence of this outlet.
Alternatively, high discharges ([100,000 m3/s)
and hydraulic damming at the St. Mary’s River outlet
to the Lake Huron basin could explain lake level rises
in Lake Minong. Numerous records from the Lake
Huron basin suggest high discharges raised lake
levels at about this time (Lewis and Anderson 1989;
Lewis et al. 2005). There is also a series of 36
anomalously thick varves dated to around 9,100 cal
(8.1 ka) BP in Lake Superior sediments that correspond to high Lake Agassiz or glacial meltwater
discharge (Breckenridge 2007). Models show that
large flood discharges had the potential to temporarily raise lake levels by many meters (Tinkler and
Pengelly 1995). The Fenton Lake transgression lasted
long enough to deposit 20 cm of clayey silt in the
small Fenton Lake basin. The transgression ends by
9,000 cal (8.1 ka) BP when lake levels abruptly fell.
The timing is consistent with evidence from the upper
Great Lakes of an abrupt cessation of meltwater
(Breckenridge et al. 2004; Lewis et al. 2007).
Conclusions
The Fenton Lake sediment record documents the
second of at least two basinwide transgressions
in glacial Lake Minong. An older transgression
documented by Phillips and Fralick (1994) probably
123
Acknowledgments Access to Fenton Lake, which lies within
Lake Superior Provincial Park, was graciously provided by the
Ontario Ministry of Natural Resources and Lake Superior
Provincial Park. Joshua Michaels, Henry Loope, and Colby
Smith assisted with fieldwork. Anders Noren and Kristina Brady
assisted with the initial core logging at the Limnological
J Paleolimnol
Research Center, Department of Geology and Geophysics,
University of Minnesota-Twin Cities. Jeff Illingworth,
Mercyhurst Archaeology Institute, helped with identification of
the radiocarbon dated wood. Reviews by Mike Lewis, Andy
Bajc, and an anonymous reviewer significantly improved this
manuscript.
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