CANADIAN LANDFORM EXAMPLES - 32
WISCONSINAN REFUGIAL LANDSCAPES,
EASTERN BAFFIN ISLAND, NORTHWEST
TERRlTORl ES
Alexander P. Wolfe
LaboratoireJacques-Rousseau, Departernentde geographie,
Universite de Montreal, C.P. 61 28 Centre-Ville, Montreal, Quebec,
Canada H3C 317 (e-mail: [email protected])
Geomorphologists, geologists, and ecologists alike have
long been interested in the occurrence of regions that
escaped Wisconsinan glaciation, whether partially or
wholly. This is because such areas offer rare (in the
Canadian context) glimpses of landscapes having evolved
over significantly longer time frames than those
deglaciated following the late Wisconsinan. The study of
such areas has implications for long-term rates of weathering and denudation, pleniglacial biological refugia and
the loci ofsubsequentspeciesexpansions, and research in
Quaternary paleoecology and paleoclimatology. O n
Cumberland Peninsula, eastern Baffin Island, despite a
complex glacial history that juxtaposes the influences of
cirque glaciation, local ice caps, and the Baffin sector of
the Laurentide Ice Sheet, certain areas nonethelessappear
to have escaped glacial modification throughout the last
glacial cycle. An example near the hamlet of Pangnirtung
(66" 16' N, 65" 45'w) serves to illustrate the development
of these ancient landscapes.
Geological Framework
Eastern Baffin Island i s the northeastern margin of the
Canadian Shield. Along the east coast, a variety of
Precambrian rocks form a structural high that descends
westward into a cratonic basin within Foxe Basin, which
is largely infilled by thick sequences of Paleozoic sedimentary rocks. In the area under consideration, dominant
lithologies are Archean granites, granite gneisses, and
quartz monzonites. The region's physiographic evolution
owes much to extensive Cretaceous to Tertiary tectonism
that resulted in block faultingat several distinct scales. For
example, Meta Incognita, Hall, and Cumberland peninsulas each represent horsts separated by Frobisher Bay
and Cumberland Sound grabens. At the same time, the
geometery of many fiords on the island's east coast
suggests at least partial structural control (Dyke et al.
1982; Dowdeswell and Andrews 1985).
Morphostratigraphic Context
O f the three stadia1 advances of the Laurentide Ice Sheet
over Cumberland Peninsula during Foxe Glaciation (Andrews 1980), the most extensive i s also the oldest (> 70 ka
BP), based on the mapping of discrete moraine systems and
the application ofweathering criteria to the relativedating
of associated deposits (Dyke et al. 1982). The oldest of
these events constructed the Duval moraines (Dyke
1979), at which time outlet glaciers preferentially exploited major valleys and fiords, probably overdeepening
the latter. Sills near the mouths of many fiords may well
represent marine counterparts of early Foxe moraines
(Gilbert 1985) because, during subsequent advances of
Laurentide ice (middle and late Foxe), terrestrial glaciers
did not reach fiord mouths, but rather terminated closer to
fiord heads or remained landfast. Although very large
volumes of late Foxe ice may have been evacuated
through Cumberland Sound (Jennings 1993, Figure l),
there i s no evidence for a coeval widespread event on
land.
Therefore, the preservation of landscapes of pre-Foxe
age arises if three conditions are met: (1) being situated
above the highest Foxe marine limit; (2) occurring
morphostratigraphically beyond Duval or equivalent
moraines of early Foxe age; and (3) not having been
affected by expansions of local cirque glaciers. This last
The Canadian Geographer/ Le Ceographe canadien 40, no 1 (1996) 81-87
0 / 1996 Canadian Association of Geographers / L'Association canadienne des geographes
82 Canadian Landform Examples
I
lTop legend
@
Glacial limits of Jennings (1993) with isochrones in ka EP.
Right legend
Y
3
C
Early Foxe (Duval Stade) moraine A 1
Middle foxe moraine
NL
Duval ice flow direction
TI
Cirque
UL
Alpine glacier or perenniol snowpack
Amorok Loke (848 m osl)
Nauyak Loke (743 m asl)
Tulugak Loke (754 m asl)
Ukalik Loke (545 m asl)
condition is of particular importance, since many areas
satisfying ( 2 )are also above the local glaciation level and
thus presently support cirque glaciers (Figure 2). Miller
(1976) has shown that many such glaciers were more
extensive in the Neoglacial (including the Little Ice Age)
than at any time since the early Foxe. Lichen-kill zones
and ice-cored moraines reliably delimit these anomalous
cirque glacier advances, so that surfaces beyond these
Neoglacial limits, with the advanced weathering features
described below, can securely be categorized as preFoxe.
landforms of Prolonged Subaerial Weathering
In the study area, Duval moraine is a prominent feature
where it i s preserved intact (Figure2); in many areas only
fragments remain, as a result of colluvial processes and
rock glacierization. In the floors of valleys tributary to
Pangnirtung Fiord, thick sequences of massive to laminated sandy lacustrineand deltaic sediments are accumulated, especially near the coast. Presumably, during retreat up-valley of smaller tributary valley glaciers from
their early to middle Foxe maximum positions, a major
trunk glacier remained in the fiord, impounding lakes of
considerable size. In the Kolik Valley, this glaciolacustrine fill is deeply dissected by the Kolik River, providing
exposures over more than 10 km.
Above the Duval moraines, bedrock is more frequently
exposed. Quartz veins are typically raised up to 5 cm
above the surface of preferentially weathered host rocks
(Figure 3 (a) and (b)). Vascular plants are fewer and less
diverse, but lichen cover increases. Very large single or
Figure 2
National Air Photo Library trimetrigon images 1213 ~ ~ 2 (top)
2 2 and ~ 3 2 6 ~ - 2 1(bottom),
6
showing the field area. Legend as follows: A = Amarok Lake;
= Nauyak Lake; T = Tulugak Lake; u = Ukalik Lake; fm = late Foxe moraine; fpr = late Foxe protalus rampart; npr = Neoglacial protalus rampart.
Note how the moraines in front of the small glacier above Nauyak Lake are only about 800 rn in front of the present ice margin. This glacier’s present
mass balance appears to be negative. Reproduced with the permission of Energy, Mines and Resources Canada, @Her Majesty the Queen in Right of
Canada 1948, 1949.
N
The Canadian Geographer / Le Geographe canadien 40, no 1 (1 996)
Canadian Landform Examples 83
The Canadian Geographer / Le Geographe canadien 40, no 1 (1996)
84 Canadian Landform Examples
merged thalli ofRhizocarpongeographicumarecommon
(c). On exposed bedrock surfaces, pitting i s widespread
and frequently advanced. Resulting macropits may be
cleansed by rain, snowmelt, or wind, although in more
protected sites the pits may retain a grus-like accumulation of polymineralic grains, dominated by quartz (d).
True grussification of bedrock is also present, resulting in
thedevelopment ofjoint-like structures between blocksof
disaggregating bedrock (e). The same processes of rock
disarticulation function at a larger scale, producing tors
up to 4 m in height, with individual constituent blocks
having 1-5 rn-long axes (0.Ventifactsoccur on some tors,
which typically occupy highly exposed ridges, so that the
effect of wind erosion may have reduced their vertical
development somewhat.
However, in the same area, up to 1000 m asl, perched
boulders and faceted bedrock surfaces indicate former
glaciation (Figure 3 (g) and (h)). Materials surrounding
these landforms are an amalgamated residuum of grus,
old tills, and erratics, themselves grussified, and redistributed aeolian deposits. Given the elevation of these glacial
features and the unlikelihood that they originated from
cirques, the explanation that best reconciles these data i s
that all of Cumberland Peninsula, and probably all of
Baffin Island, were glaciated at some time prior to Foxe
Glaciation, but, subsequently, many upland areas remained ice-free during Foxe glacial events. The emplacement of high erratics at a site so near the coast implies a
former ice mass impinging well onto the Continental
Shelf, for which there is directly corresponding marine
geophysical evidence 30-60 km off the coast of northern
Cumberland Peninsula (Gilbert 1982). This reconstruction is further supported by the Baffin Bay paleoceanographic record, which reveals light isotopic (6l80)
meltwater spikes within oxygen isotope stages 6 (-125195 ka BP) and 8 (-250-295 ka BP) (Aksu 1985). These
features of the isotopic record could reflect the waning of
pre-Foxe icecover that may havecoveredtheentire island
during either or both isotopic stages.
It is recognizedthat weatheringcriteria alone should be
used only cautiously to delimit the extent of former
glaciation (Sugden and Watts 1977; Gangloff 1983). In
the present study area, the weathering regime is potentially quite variable over short distances, for the same
lithologies. For example, around the hamlet of Pangnirtung, well within the Duval glacial limit, tor-like fea-
tures are as well developed as on the pre-Foxe surfaces
described above. In these cases, accelerated rates of tor
formation are probably a function of coastal proximity
and enhanced salt weathering.
Of Paleonunataks and Ancient Cirques
A nunatak is ‘a rocky summit or mountain range that
stands above a surrounding ice sheet in an area that is
currently being glaciated’ (Allaby 1994, 273). The evidence presented here suggests that the pre-Foxeterrain of
Cumberland Peninsula existed as a series of paleonunataks during the early to middle Foxe, as this i s the
only time for which the morainic evidence (Dyke et al.
1982, Figure 1(b))issufficienttostatewith confidencethat
ice fully encircled the uplands. During the late Foxe, the
possibility of paleonunataks also exists, if indeed ice
positions were much more advanced than initially
mapped by Dyke (1979), as suggested by some recent
studies (Davis et al. 1993; Jennings 1993). However, in
areas such as the Kolik Valley, there i s no geomorphic
evidence for the presence of late Foxe glacier ice. Further,
a date of 7580 f 140 (AA-1 004) from basal, ice-proximal
sediments in a core from Tasikutaaq Lake suggests a late
Foxe glacial terminus near the head of this lake and icefree conditions in the lower Kolik Valley (Lemmen et al.
1988). On these grounds, the pre-Foxe uplands were
doubtfully paleonunataks sensu strict0 during late Foxe
Glaciation, as they had been during previous glacial
events.
A remaining enigma i s the age of the cirques that occur
on the upland and their relationship to the inferred
event(s) of contiguous pre-Foxe glaciation. Considerable
alpine glacial erosion is manifested by the four lake
basins, supporting tarns presently 15-50 m deep, within
or down-valley of the cirques (figures 1 and 2). Possibly
these basins were formed by vestigial ice masses following retreat of the ice sheet that once inundated the entire
area. Alternately, the cirques may predate extensive preFoxe glaciation, with upland regions having provided the
loci of ice-sheet inception, as cirque glaciers progressively coalesced. In this hypothesis, the preservation of
cirque morphology, despite the subsequent passage of
ice, can be reconciled by the locally thin and cold-based
character of the ice sheet in areas of high relief (cf. Watts
1979).
Figure 3
Geomorphic features of the pre-Foxe uplands. Quartz vein relief resulting from differential weathering (A and 5); merged thalli of Rhizocarpon
geographicurn (C); macropit (D); intense grussification of gneiss (E); incipient tor development (F); glacial erratic with 2 rn long axis, ca. 800 m as1 (C);
glacially faceted bedrock amid shallow weathered till and erratics (H; dashed line indicates sense of ice flow, presumed westward into Kolik Valley;
qz = quartz veins).
The Canadian Geographer/ Le Gagraphe canadien 40, no 1 (1996)
Canadian Landform Examples 85
The Canadian Geographer / Le Geographe canadien 40, no 1 (1996)
86 Canadian Landform Examples
Table 1
Pre-Holocene Radiocarbon Dates from Lakes in the Study Area
Location
Lake name
(UTMC)
Depth in
core (cm)
Tulugak Lake
Ukalik Lake
Amarok Lake
Amarok Lake
Amarok Lake
Amarok Lake
~17753
ti7652
~17655
~17655
~17655
~17655
90-91
102-1 03
60-69
1 1 1-1 13
112-1 13
110-1 17
Lab no
~*3242
TO-3241
CAMS-T 2256
CAMS^ 1340
TC-3243
csc-5497
Age
36120i340
37 990 i 410
1 7 3 3 0 i 1200
18730i90
20 110 f 340
> 38000
NOTES:Dates from TO (Isotrace, University of Toronto) and CAMS
(Lawrence
Livermore National Laboratories, California) are AMS (accelerator mass
spectrometry) determinations on bryophyte remains, whereas the csc
(Geological SurveyofCanada, Ottawa)date is aconventionaldetermination
on bulk sediment. All dates are uncalibrated radiocarbon years before
present, corrected by convention to 6°C = -25.00% PDB.
Direct Evidence of a Refugium
In the course of lake sediment studies (Wolfe 1994a,
1994b), several radiocarbon dates (Table 1) add support
to the inferences based on morphostratigraphicrelations
and weathering criteria. These dates, with the exception
of csc-5497, were determined on small quantities (i.e.,
<50 mg) of preserved bryophytes recovered from silty
sediments that underlie a cover of Holocene gyttja. The
possibility that some of these mosses are redepositedfrom
older sediments is not ruled out. However, in the absence
of any local carbonate lithologies or calcareous till, it i s
unlikely that chemical contamination has resulted in
spuriously old apparent ages. Therefore, the results indicate that the dated mosses were extant on the uplands
between 17 and 38 ka BP. The 101-1 03 cm interval of the
Ukalik Lake core i s particularly rich in macrofossils
(which dated 37 990 2 41 0, Table 1) and was therefore
examined in greater detail. With the exception of a
single, poorly preserved lsoetes megaspore, no aquatic
macrofossils were found, indicating unproductive limnological conditions. Although abundant, all other
macrofossils are restricted to leaves and stems of the
bryophytes Warnstorfia exannulataand Polytrichum spp.
The physically degraded state of these fragments suggests
that they were wind-blown to the lake (cf. Glaser 1981).
The absence of terrestrial vascular plant macrofossils
suggests a very sparse tundra, although there were sufficient moist enclaves for the above mosses to have flourished. However, an exploratory pollen analysis of adjacent silty sedimentsfromwithin thesame lithological unit
(98-99 cm) reveals that many elements of the area’s
modern vegetation were present on the landscape in the
late Wisconsinan. These plants include typical compoThe Canadian Geographer/ Le Ceographe canadien 40, no 1 (1996)
nents of herbaceous tundra (Cyperaceae, Poaceae,
Caryophyllaceae, and some Ericaceae), coupled to shrub
willow. Exotic (tree) pollen is rare (< So/,), implying little
long-distance atmospheric transport from source areas
south of the Laurentide Ice Sheet. The existence of
pleniglacial refugial plant populations on the pre-Foxe
terrain is therefore evidenced by the paleobotanical data,
despite likely harsh prevailing climatic conditions.
Synthesis and Implications for Quaternary Research
The presence of Wisconsinan refugial landscapes on
eastern Baffin Island can be attributed primarily to two
factors. First i s the restricted extent of late Wisconsinan
glaciation throughoutthe Canadian Arctic. This i s thought
to have resulted from extreme high-latitude aridity imposed by the Laurentide Ice Sheet to the south, which
effectively served as a topographic barrier to the passage
of moisture-bearingair masses advected from the North
Atlantic (Miller and Dyke 1974; England and Bradley
1978). Thus, the asynchrony of glacial maxima between
the Arctic and temperate regions of North America can be
accounted for in causative terms.
For example, the extensive Cockburn moraines constructed on eastern Baffin Island between 8 and 9 ka BP
and representing the late Foxe maximum (Miller and
Dyke 1974; Andrews 1989) were most likely a response
to warmer and moister conditions in the early Holocene
(Miller and De Vernal 1992), a period during which the
southern Laurentide Ice Sheet had already waned considerably and continued to do so uninterrupted. By this time,
the decreased elevation of the ice sheet’s profile facilitated the entry of cyclones to the Eastern Arctic, resulting
in increased precipitation and glacier expansion.
Secondly, bedrockconfiguration is critical to theoccurrences of refugial landscapes. Fiords, of structural origin,
served as interdigitating outlets for large volumes of
Laurentide ice, thereby leaving the intervening uplands
ice-free, with the exception of cirque glaciers influenced
by local topocl imatic conditions.
These ancient landscapes are in no way restricted to the
area described in this paper. Other portions of Baffin
Island (see, for example, England and Andrews 1973;
Nelson 1981) appear to have broadly similar Quaternary
glacial histories. In each of these regions, critically selected lake basins may archive very long paleoenvironmental records. Because of an often incomplete
stratigraphy of glacial events, an uncertain geochronological infrastructure, and the inherently lagged glaciological response to climate forcing, these basins may offer
the sole repositories of information pertaining to mean-
Canadian Landform Examples 87
ingful land-ocean correlations over, potentially, the last
glacial-interglacial cycle.
Acknowledgments
Alayn Larouche and Nicole Morasse (Laboratoire Jacques-Rousseau,
Universitede Montreal) provided, respectively, themacrofossil and pollen
analyses. The research was supported by NSERC grants to R. Gilbert and
awards to the author. Comments by P.J.H. Richard and P. Gangloff
(Universite de Montreal), as well as journal reviewers, have led to many
improvements.
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