Geological Survey of Denmark and Greenland Bulletin 13, 2007
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Review of Survey activities 2006, 33-36 |
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The western margin of the Greenland craton has been much
less stable in the Phanerozoic than previously thought. This
new insight has come from close integration of independent
data sets: geomorphological analysis of large-scale landscapes,
apatite fission track analysis (AFTA), onshore and offshore
stratigraphy and analysis of onshore fault and fracture sys -
tems. Each data set records specific and unique parts of the
event chronology and is equally important to establish a con-
sistent model. A key area for understanding the Mesozoic-
Cenozoic landscape evolution and into the present is the
uplifted part of the Nuussuaq Basin, where remnants of pla-
nation surfaces cut across the Cretaceous to Eocene sedimen-
tary and volcanic rocks. Our integrated analysis concluded
that the West Greenland mountains were formed by late
Neogene tectonic uplift (Fig. 1) and also provided new
insight into early Phanerozoic development. To understand
our model, we present the different methods and the results
that can be deduced from them.
less stable in the Phanerozoic than previously thought. This
new insight has come from close integration of independent
data sets: geomorphological analysis of large-scale landscapes,
apatite fission track analysis (AFTA), onshore and offshore
stratigraphy and analysis of onshore fault and fracture sys -
tems. Each data set records specific and unique parts of the
event chronology and is equally important to establish a con-
sistent model. A key area for understanding the Mesozoic-
Cenozoic landscape evolution and into the present is the
uplifted part of the Nuussuaq Basin, where remnants of pla-
nation surfaces cut across the Cretaceous to Eocene sedimen-
tary and volcanic rocks. Our integrated analysis concluded
that the West Greenland mountains were formed by late
Neogene tectonic uplift (Fig. 1) and also provided new
insight into early Phanerozoic development. To understand
our model, we present the different methods and the results
that can be deduced from them.
Basic concepts
The mapping of volcanic and sedimentary successions within
the Nuussuaq Basin is crucial for understanding the late
Mesozoic-Palaeogene landscape development (e.g. Dam et al .
1998; Chalmers et al . 1999; Dalhoff et al . 2003). Especially
important for the landscape analysis is the availability of maps
showing vertical geological sections (Pedersen et al . 2006).
Exploration for hydrocarbons has resulted in many seismic
data, and several deep wells have been drilled both onshore
and offshore (e.g. Chalmers et al . 1999; Piasecki 2003).
the Nuussuaq Basin is crucial for understanding the late
Mesozoic-Palaeogene landscape development (e.g. Dam et al .
1998; Chalmers et al . 1999; Dalhoff et al . 2003). Especially
important for the landscape analysis is the availability of maps
showing vertical geological sections (Pedersen et al . 2006).
Exploration for hydrocarbons has resulted in many seismic
data, and several deep wells have been drilled both onshore
and offshore (e.g. Chalmers et al . 1999; Piasecki 2003).
Landscape analysis aims at setting up a relative tectonic
event chronology through identification and mapping of
both extensive baselevel governed surfaces and re-exposed
surfaces. These palaeosurfaces, formed by erosion in climates
or tectonic settings different from the present, cut across
bedrock of different ages and can be arranged in chronologi-
cal order based on (1) stratigraphical relationships with cover
rocks, (2) geometrical relationships between different palaeo-
surfaces, and (3) analysis of the detailed forms of the large-
scale landscapes, reflecting climatic-driven formation processes.
The baselevel is fundamental, as lowering of baselevel (an
uplift event) causes valley incision and initiation of surface
both extensive baselevel governed surfaces and re-exposed
surfaces. These palaeosurfaces, formed by erosion in climates
or tectonic settings different from the present, cut across
bedrock of different ages and can be arranged in chronologi-
cal order based on (1) stratigraphical relationships with cover
rocks, (2) geometrical relationships between different palaeo-
surfaces, and (3) analysis of the detailed forms of the large-
scale landscapes, reflecting climatic-driven formation processes.
The baselevel is fundamental, as lowering of baselevel (an
uplift event) causes valley incision and initiation of surface
formation while raising baselevel (subsidence) causes palaeo-
surfaces to be preserved below cover rocks (Bonow 2005;
Bonow et al . 2006a, b).
surfaces to be preserved below cover rocks (Bonow 2005;
Bonow et al . 2006a, b).
AFTA is a method for defining the temperature history of
rock samples, based on analysis of radiation damage features
(`fission tracks') produced by spontaneous fission of
(`fission tracks') produced by spontaneous fission of
238
U
atoms within apatite crystals. Tracks are produced continu-
© GEUS, 2007.
Geological Survey of Denmark and Greenland Bulletin
13, 33-36. Available at:
www.geus.dk/publications/bull
33
A multi-disciplinary study of Phanerozoic landscape
development in West Greenland
development in West Greenland
Johan M. Bonow, Peter Japsen, Paul F. Green, Robert W. Wilson, James A. Chalmers,
Knud Erik S. Klint, Jeroen A.M. van Gool, Karna Lidmar-Bergström and Asger Ken Pedersen
Fig. 1.
Left
: Study area with Precambrian basement and cover rocks that
are crucial for determining the relative age of palaeosurfaces. The rose
diagram summarises the regional lineament patterns, based on field
mapping in the framed area (cf. Wilson
et al
. 2006). The relationship
between lineaments onshore and offshore allows for a relative event
chronology; colouring refers to timing (cf. Fig. 3). Position of GRO#3
well indicated.
ES
, etch surface of Late Mesozoic - Paleocene age. Note
its position close to cover rocks. Modified from Bonow
et al
. (2006a).
Right
: Topography. A regionally developed Oligo cene-Miocene plana-
tion surface was differentially uplifted on separate tectonic blocks in the
Neogene. Today it is close to the summit level and has been tilted in dif-
ferent directions.
ously over geological time, but are shortened at a rate that
depends on the prevailing temperature, until at temperatures
higher than c . 120°C tracks are totally erased (`annealing').
Fission track age and track length data provide the basis for
estimating the time at which a sample began to cool from a
palaeo-thermal maximum as well as the magnitude of the
maximum palaeotemperature. Cooling can be interpreted as
either change of heat-flow within the crust or erosion of over-
lying rocks (e.g. Green et al . 2002).
depends on the prevailing temperature, until at temperatures
higher than c . 120°C tracks are totally erased (`annealing').
Fission track age and track length data provide the basis for
estimating the time at which a sample began to cool from a
palaeo-thermal maximum as well as the magnitude of the
maximum palaeotemperature. Cooling can be interpreted as
either change of heat-flow within the crust or erosion of over-
lying rocks (e.g. Green et al . 2002).
Structural analysis of faults and fracture systems aims to
establish a relative chronology of tectonic movements that
have changed the stress field, as a change will lead to the for-
mation of a new set of faults and possibly the reactivation of
older ones. Structural analysis of the area between Nuussuaq
and Sisimiut forms the basis for a regional model, explaining
different tectonic movements through time (Wilson et al . 2006).
have changed the stress field, as a change will lead to the for-
mation of a new set of faults and possibly the reactivation of
older ones. Structural analysis of the area between Nuussuaq
and Sisimiut forms the basis for a regional model, explaining
different tectonic movements through time (Wilson et al . 2006).
Key results
Geology
. The Cretaceous-Palaeogene sedimentary and vol-
canic successions within the Nuussuaq Basin record deep
incision of valleys in the Maastrichtian and early Paleocene
(e.g. Dam et al . 1998), subsidence during volcanism, and
deposition of marine sediments within the volcanic succes-
sion now at high elevation (Piasecki et al . 1992), which are
evidence that both uplift and subsidence of kilometre scale
took place during and after rifting (Chalmers et al . 1999).
During the Palaeogene the basalts offshore (and probably
onshore, Japsen et al . 2006a) became buried below sedi-
ments. Seismic sections west of Nuussuaq show that Palaeo-
gene and younger sequences have been tilted seawards and
truncated at a late date (Chalmers 2000).
canic successions within the Nuussuaq Basin record deep
incision of valleys in the Maastrichtian and early Paleocene
(e.g. Dam et al . 1998), subsidence during volcanism, and
deposition of marine sediments within the volcanic succes-
sion now at high elevation (Piasecki et al . 1992), which are
evidence that both uplift and subsidence of kilometre scale
took place during and after rifting (Chalmers et al . 1999).
During the Palaeogene the basalts offshore (and probably
onshore, Japsen et al . 2006a) became buried below sedi-
ments. Seismic sections west of Nuussuaq show that Palaeo-
gene and younger sequences have been tilted seawards and
truncated at a late date (Chalmers 2000).
34
Fig. 2. Views of the etch surface (ES) and the upper and lower planation surfaces (UPS and LPS) formed in basement rocks.
A
: The re-exposed ES at
Fortunebay, southern Disko. The white line shows the approximate border between Paleocene basalt and gneiss. Area location in Fig. 1. Photo location
in B.
B
: 3D model of the Fortunebay area. Note the Oligocene-Miocene planation surface at high elevation across the basalt. Modified from Bonow (2005).
C
: The stripped ES at Nassuttooq. Location in Fig 1.
D
: The Oligocene-Miocene UPS east of Sukkertoppen Iskappe cuts across Precambrian basement.
Location in E.
E
: 3D model showing the well-preserved UPS east of Sukkertoppen Iskappe. Red frame indicates position of map in F.
F
: Map show-
ing UPS and LPS. Hill complexes rising above the UPS may be part of a sub-Ordovician peneplain. Modified from Bonow
et al
. (2006a).
Geomorphology
. Three different palaeosurfaces in the Pre -
cam brian basement have been identified in West Greenland,
viz. a surface formed by deep weathering and stripping of the
weathering mantle (etch surface, ES), and an upper and lower
planation surface (UPS and LPS; Bonow 2005; Bonow et al .
2006a, b). The ES is characterised by distinct hills (Fig. 2A)
and re ceived its final shape in part prior to the deposition of
Upper Cretaceous deltaic sediments and in part prior to the
extrusion of Palaeogene basalts (Fig. 2B). The ES can mainly
be identified at low elevations and close to cover rocks (Figs
1, 2C). The UPS has low relative relief compared to the ES
(Fig. 2D) and must be younger as it cuts across both mid-
Eocene basalts and the etch surface. The UPS forms the sum-
mits of differentially tilted, fault-bounded tectonic blocks. A
planation surface cannot be formed as an inclined plain
because any tilt would cause valleys to incise and the relief to
rejuvenate towards the baselevel (Bonow et al . 2006b, fig. 6).
The LPS was formed in response to lowered baselevel (uplift)
and became incised into the UPS (Fig. 2E). Furthermore,
summits of distinct hill complexes above the UPS (Fig. 2F)
viz. a surface formed by deep weathering and stripping of the
weathering mantle (etch surface, ES), and an upper and lower
planation surface (UPS and LPS; Bonow 2005; Bonow et al .
2006a, b). The ES is characterised by distinct hills (Fig. 2A)
and re ceived its final shape in part prior to the deposition of
Upper Cretaceous deltaic sediments and in part prior to the
extrusion of Palaeogene basalts (Fig. 2B). The ES can mainly
be identified at low elevations and close to cover rocks (Figs
1, 2C). The UPS has low relative relief compared to the ES
(Fig. 2D) and must be younger as it cuts across both mid-
Eocene basalts and the etch surface. The UPS forms the sum-
mits of differentially tilted, fault-bounded tectonic blocks. A
planation surface cannot be formed as an inclined plain
because any tilt would cause valleys to incise and the relief to
rejuvenate towards the baselevel (Bonow et al . 2006b, fig. 6).
The LPS was formed in response to lowered baselevel (uplift)
and became incised into the UPS (Fig. 2E). Furthermore,
summits of distinct hill complexes above the UPS (Fig. 2F)
may relate to a sub-Ordovician palaeosurface because rem-
nants of Lower Palaeozoic rocks suggest that West Greenland
may have had a long-lasting Palaeozoic cover (Bonow et al .
2006a). Consequently, erosion of Precambrian basement
rocks has been limited since the early Palaeozoic, but this does
not ex
nants of Lower Palaeozoic rocks suggest that West Greenland
may have had a long-lasting Palaeozoic cover (Bonow et al .
2006a). Consequently, erosion of Precambrian basement
rocks has been limited since the early Palaeozoic, but this does
not ex
clude deposition and subsequent removal of thick
sequences of Phanerozoic cover rock as indicated by AFTA
data.
data.
Thermochronology
. AFTA data from Cretaceous sedimen-
tary rocks define three major Cenozoic cooling episodes, while
basement samples define major Triassic and Jurassic cooling
episodes (related to rifting?), and also earlier (Palaeo zoic)
episodes (Table 1). The deepest samples in the 3 km deep
GRO#3 well on Nuussuaq are totally annealed (Fig. 1; Japsen
et al . 2005). The progressive development of fission tracks
can therefore be followed through the sedimentary section,
giving a rare opportunity to resolve the details of the late Ceno -
zoic cooling history. Oligocene cooling involved both exhu -
mation and a decrease in basal heat flow, while Miocene and
Pliocene cooling episodes were dominantly related to exhu -
mation. The two latest cooling events constrain the cooling
events into the present.
basement samples define major Triassic and Jurassic cooling
episodes (related to rifting?), and also earlier (Palaeo zoic)
episodes (Table 1). The deepest samples in the 3 km deep
GRO#3 well on Nuussuaq are totally annealed (Fig. 1; Japsen
et al . 2005). The progressive development of fission tracks
can therefore be followed through the sedimentary section,
giving a rare opportunity to resolve the details of the late Ceno -
zoic cooling history. Oligocene cooling involved both exhu -
mation and a decrease in basal heat flow, while Miocene and
Pliocene cooling episodes were dominantly related to exhu -
mation. The two latest cooling events constrain the cooling
events into the present.
Faults and fractures.
Analysis of regional lineament trends
shows five main systems that fit a two-stage model (Wilson
et
al . 2006). A system of N-S- and NNW-SSE-trending nor-
mal faults reflects the fault patterns in the Davis Strait during
the Late Cretaceous to Paleocene. This system was over-
printed and reactivated by strike-slip faults associated with a
later NNE-SSW-trending sinistral wrench system that re -
flects the development of the Ungava transform system dur-
ing the Eocene.
al . 2006). A system of N-S- and NNW-SSE-trending nor-
mal faults reflects the fault patterns in the Davis Strait during
the Late Cretaceous to Paleocene. This system was over-
printed and reactivated by strike-slip faults associated with a
later NNE-SSW-trending sinistral wrench system that re -
flects the development of the Ungava transform system dur-
ing the Eocene.
35
Fig. 3. Event chronology for central West Greenland based on data from the separate disciplines. Integration of these data sets shows that the western
margin of the Greenland craton has been less stable than previously thought. Shaded intervals indicate the proven age of geological units, onshore
and offshore, and the estimated time required for formation of palaeosurfaces. Horizontal arrows indicate extensional reactivation and opening of ver-
tical fault and fracture systems. The associated intervals indicated by stippled lines illustrate the probable geological age range and uncertainties in dat-
ing palaeo-surfaces.
ES
, etch surfaces;
UPS
, upper planation surface;
LPS
, lower planation surface. Data from Piasecki
et al
. (1992); Dam
et al
. (1998);
Chalmers
et al
. (1999); Chalmers (2000); Dalhoff
et al
. (2003); Piasecki (2003); Bonow (2005); Japsen
et al
. (2005, 2006a); Bonow
et al
. (2006a, b, c);
Pedersen
et al
. (2006) and Wilson
et al
. (2006).
The model and future implementation
Our model shows where in time independent constrained
data exist and time-frames for uncertainties and lack of data
(Fig. 3). The model shows that each discipline has long peri-
ods of no data, but when combined only few periods have no
data representation at all. In particular, landscape analysis and
AFTA data complement each other, because palaeosurfaces
show that rock was exposed at the landsurface, whereas AFTA
data indicate when and by how much a palaeosurface has been
buried. This approach shows that the present summits were
buried below up to 1 km of rocks prior to Eocene-Oligocene
uplift, and that the UPS formed during the Oligocene-
Miocene due to stable baselevel conditions. Similarly, uplift
in the late Miocene resulted in valley incision (the LPS) and
tilting of the UPS. Final uplift in the ?Pliocene resulted in the
present-day mountains. Late uplift reactivated and opened
the fault and fracture systems, thus facilitating both weather-
ing and the development of a coastal escarpment (Bonow et
al . 2006c). Our model is also used in ongoing uplift studies in
South-West Greenland (Japsen et al . 2006b).
data exist and time-frames for uncertainties and lack of data
(Fig. 3). The model shows that each discipline has long peri-
ods of no data, but when combined only few periods have no
data representation at all. In particular, landscape analysis and
AFTA data complement each other, because palaeosurfaces
show that rock was exposed at the landsurface, whereas AFTA
data indicate when and by how much a palaeosurface has been
buried. This approach shows that the present summits were
buried below up to 1 km of rocks prior to Eocene-Oligocene
uplift, and that the UPS formed during the Oligocene-
Miocene due to stable baselevel conditions. Similarly, uplift
in the late Miocene resulted in valley incision (the LPS) and
tilting of the UPS. Final uplift in the ?Pliocene resulted in the
present-day mountains. Late uplift reactivated and opened
the fault and fracture systems, thus facilitating both weather-
ing and the development of a coastal escarpment (Bonow et
al . 2006c). Our model is also used in ongoing uplift studies in
South-West Greenland (Japsen et al . 2006b).
The integration of data from geomorphology, thermo
-
chrono logy, geology and fault/fracture patterns to show that
the present landscape of West Greenland is the result of tec-
tonic movements throughout the Phanerozoic with signifi-
cant movements also in the Neogene and even into the
present (Fig. 3). The approach presented here may be applied
to understand landscape development along other passive
continental margins.
the present landscape of West Greenland is the result of tec-
tonic movements throughout the Phanerozoic with signifi-
cant movements also in the Neogene and even into the
present (Fig. 3). The approach presented here may be applied
to understand landscape development along other passive
continental margins.
Acknowledgements
This work was supported by the Carlsberg Foundation, the Bureau of
Minerals and Petroleum, the Danish Natural Science Research Council,
the Swedish Research Council, Arktisk Station, Stiftelsen Margit Althins
stipendiefond, Svenska Sällskapet för Antropologi och Geografi and
John Söderbergs stiftelse.
Minerals and Petroleum, the Danish Natural Science Research Council,
the Swedish Research Council, Arktisk Station, Stiftelsen Margit Althins
stipendiefond, Svenska Sällskapet för Antropologi och Geografi and
John Söderbergs stiftelse.
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Authors' addresses
J.M.B., P.J., J.A.C., K.E.S.K. & J.A.M.v.G.,
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail:
jbon@geus.dk
P.F.G.,
Geotrack International, 37 Melville Road, Brunswick West, Victoria 3055, Australia.
R.W.W.,
Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham, DH1 3LE, UK.
K.L.-B.,
Department of Physical Geography and Quaternary Geology, Stockholm University, SE-106 91 Stockholm, Sweden.
A.K.P.,
Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark.
36
