Paleogeography and paleoenvironments of southwestern Baffin Island (Nunavut, Canada):
post-glacial isostatic uplift and isolation of Nettilling Lake from marine influence
Biljana Narancic¹ (biljana.narancic.1@ulaval.ca), Reinhard Pienitz¹, Pierre Francus², Bernhard Chapligin3 and Hanno Meyer3
1 Geography Department, Centre for Northern Studies (CEN) Laval University, Quebec, Canada; 2 Institut National de la Recherche, Eau-Terre-Environnement, Quebec, Canada; 3 Alfred Wegener Institute (AWI) for Polar and Marine Research, Potsdam, Germany.
Ni4-7
Ni2-B
RESULTS OF MULTIPROXY SEDIMENT CORE ANALYSIS
Upper facies (0-16cm )
GENERAL CONTEXT AND STUDY OBJECTIVES Here we present a pioneer study with respect to ecosystemic postglacial succession that has never been completed before in this remote region of the Canadian Arctic.
This multiproxy study will generate new paleolimnological and paleoenvironmental data by reconstructing the history of postglacial isostatic uplift and isolation of the lake basin from marine influence.
It will provide further evidence for the usefulness of multiproxy analysis (biological and geochemical indicators) in reconstructing sea-level changes and land-uplift in formally glaciated landscapes.
The paleolimnological record from the study will enable ice-sheet modelers to accurately reconstruct the past and better predict the future contribution of polar ice sheets to global sea-level change.
Core Ni4-7
Diatoms (Lagoon)
0
5
10
15
20
25
30
35
40
45
50 Age (cal yr BP) Depth (cm)
X-RayOptical image
5275
5779
6053
6510
0163 24864 Ca/Ti Si/Ti 0.15 0.75 1.35
Biogenic silica Carbonates
Cl 0.00250.0050.00750.010.0125 0
Salinity
1000 !"#$%&#'(%)*+, LOI (%)
1.2 3.6 6.0 8.4 10.8 -4 41220281 10 100
Magnetic suseptibility
04080 120 I Marine littoral Cluster analysis Zones Paleoenvironment
II Brackish interdital IIIb Freshwater IIIc Freshwater
IIIa Freshwater
1224364860 Water content (%)
Relative abundance (%)
Polyhalobous Mesohalobous Oligohalobous Halophobous
Rhabdonema minutumPlagiogramma staurophorumGrammatophora oceanicaGrammatophora arcuataCocconeis scutellum var . parva
Opephora marinaEhrenbergiulva ganulosaDiatomella minutumEllebeckia arenariaTabularia fasciculataPinnularia quadratareaAchnanthes cf. delicatula
var . hauckiana
Opephora olseniiLicmophora sp.1
Caloneis bacillumNavicula digitoradiataAmphora cf. copulata Pseudostaurosira brevistriataStaurosirella pinnata Staurosira construens
var . venter
Staurosira construens Amphora pediculaAchnanthes minutissimaDenticula cf. tenuis
0 1 2 0 0
0 0 1 200
0 1 20 0 10 20 300 1 2000 100 100 100 1 2000 1 2000 100 100 100 100 100 100 100 100 100 1 2000 01 20 30 40 50 60 70 80 901 20 30 40 50 600 01 20 30 40 50 600 0000 100 1 2
Chironomids ( Lagoon)
Taxa inclus (Walker 1995) Cricocopus Orthocladius Chironomus Procladius Psectrocladius Cricotopus
Coryn oneura
Stichtochir onom
us
P araki
eff eriella
fen nica
-type
Psectrocl ad ius so
rdid ellu
s-gro up
T anyta
rsus sp.
Micropsectra r adialis-type
T anyt
arsus with s pur
Microsp ectra
sp.
Oliver dia O rth
ocladius Corynocera olive
ri-type
Ta nyt ars
us without s pur
Chiro nomin
i sp.
P aratanyt
arsus
Micro psectra in
si gnilo
bus -typ
e
Het erotr
isso cl adi
us grimsha
wi-typ e
Procl adius
Coryn oce
ra am bigua
-typ e
Para cla dius
Chiro nom
us an thra
cin us-type
C lad
ota nytarsus
S erg
entia Zalutsch
ia sp . B
Ab isko
myia Hetero
trissocla dius m
arcid us-ty
pe
H eterot
risso cla dius
sub pi losu
s-ty pe
Limn ophyes
H eterotriss
ocl adius ma
eaeri -typ
e
H eterot
riss ocl ad ius sp
.
Prota nyp
us
Ch iron
omi d salinity tolerance
015 30 45 60 75 0 20 0 0 015 015 0 20 0 015 0 0 015 30 015 0 0 0 0 0 0 20 40 60 015 0 0 0 0 0 0 0 0 015 015 0 015 30 45 60 75 0 5 10
°C
Chironomid-inferred August air temperature Shifts in the composition of fossil
diatom assemblages document the marine-brackish-freshwater transition.
Fossil chironomid larvae started to appear in the lake only after basin isolation and the establishment of freshwater conditons.
Paleosalinity and paleoproductivity changes are reflected in the sediment core geochemistry, as shown by shifts in Ca/Ti, Si/Ti and Cl profiles that coincide with the diatom-inferred basin isolation.
Relative abundance (%)
BIOLOGICAL INDICATORS PHYSICAL AND GEOCHEMICAL INDICATORS
Marine inference Productivity inferences
Isolation of lake basin end of postglacial marin influence
METHODS
A multi-proxy paleolimnological approach is used to study the sedimentary records preserved in Nettilling Lake.
Physical properties:
- LOI and magnetic susceptibility Chemical properties:
- Relative concentration of chemical elements by high resolution micro-fluorescence (µ-XRF) core scanner
- Isotope analysis Biological properties:
- Chironomid, diatom and foraminifer assemblage analyses
Two sampling areas were chosen based on the hypothesis that post-glacial marine transgression and the establishment of the freshwater lake would be preserved in the sediment records from the extreme opposite (west-east) parts of Nettilling Lake.
!"#$%&#'(%)*+,
-50 50 150250350
0 4 8 12 16
LOI %
Water content % Magnetic suseptibility
162432404856 1 10 100 1000
-8 0 8 16 24
Depth (cm)
X-RayOptical image
Redox layer Forams rich layers
Salinity
0.000 0.001 0.002 0.003 0.004 Cl/kcps
0 1 2 3 4
Ca/Fe
0.0 0.1 0.2 0.3
Mn/kcps
1 35 7 911
Fe/kcps
0.0 0.2 0.4 0.6
Mn/Ti
0 8 16 24 32
Fe/Ti
0.00 0.03 0.06 0.09 0.12 Mn/Fe
IV Freshwater Cluster analysis
I Marine intertidal II Brackish intertidal
0 50 150
III Brackish-Freshwater 0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
PHYSICAL AND GEOCHEMICAL INDICATORS
0.1 0.2 0.3 0.4
Si/Ti
0 2 4 68 10
Ca/Ti
0.07 0.08 0.10 0.11 0.12 0.13 Si/K
0.0000 0.0002 0.0004 0.0006 Ca/K Productivity inferences Marine inferences
Isolation of lake basin end of postglacial marin influence
Age (cal yr BP)
2523
5410
5051
4118
Shifts in Ca/Ti, Si/Ti, and Cl reflect the end of marine influence and the establishment of the brackish-freshwater conditions.
Diatom fraction used > 10 µm Difference in fractination factor between fresh and marine layer confirms the marine influence in the Nettilling Lake basin.
CONCLUSION
Glacio-isostatic submergence of the Earth crust moved the Foxe-Basin coastline inland by hundreds of km for much of the Holocene.
Glacio-isostatic rebound resulted in the formation of a meromictic saline lake system.
Sea water trapped in the lake during the isolation process was preserved in a dense saline and anoxic hypolimnion that lasted for several hundred years.
Nettilling Lake basin remained under marine influence until the Mid-Holocene (5000 yr cal. BP), followed by freshening and fluvial processes that supplied sediment and fresh water until the present-day.
Precise radiocarbon dating of the transitional zone in the Ni2-B sediment core will allow to refine the history of post-glacial sea extent and duration of glacio-isostatic uplift.
Studies of the diatom assemblages from the Ni2-B sediment core will further refine our interpretations of changes in diatom species in response to the effects of decreasing salinity in the lake.
diatoms21,24‰
diatoms22,92‰
diatoms27,31‰
water-17,53‰
High Mn/Fe rations indicate strong anoxic conditions in the lower water columne during saline to freshwater transition.
The clear difference in geochemistry of upper facies compared with lower facies:
1. Higher Ca peaks area in the low marine facies are indicative of endogenic calcite precipitation in the postglacial sea 2. Shifts in sediment source from carbonate terrain to Precambrian granites/gneiss terrain
Lower facies (70-82cm)
GEOCHEMICAL INDICATORS
Core Ni2-B
Core Ni2-B Core Ni2-B
BIOLOGICAL INDICATORS
Dept h (c
m) Troch
am mina
sp.
Polymorphinidae unidentified For
ams
Polychaete mo uth parts
Hydroz oa tubes
Spicules (st raight and simpl
e)
Tin tinnopsis riodelapla
tensis
Chiro nomids
Difflugia oblonga Difflugia oblonga "glans"
Centropyxis acu
leata
Centropyxis c onstricta
?Pontigulasi a com
pressa
Paleozoic Echinoderms & Bryoz oas
| | | | | | | | | | | | | |
33 X X X
43 X X X X X X
53 X X X X X
61 X X X X X
68 X X X X
77 X X X X X X X
brackish
marine/brackish freshwater
Thecamoebae Foraminifers
In this diagram, we present 63-1000 µm fractions.
We found fossil fragments from paleozoic carbonate terrain at 77 cm core depth. This confirms the shift in sediment source from carbonate terrain to Precambrian granites/gneiss terrain.
