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Tectonic evolution of southern Baffin Bay and Davis Strait: Results from a seismic refraction transect between Canada and Greenland

April 2012
Journal of Geophysical Research Atmospheres 117(B4):B04107

April 2012
117(B4):B04107

DOI:10.1029/2011JB009110

Authors:

Thomas Funck

Geological Survey of Denmark and Greenland

Karsten Gohl

Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research

Volkmar Damm

Bundesanstalt für Geowissenschaften und Rohstoffe

Ingo Heyde

Bundesanstalt für Geowissenschaften und Rohstoffe

Wide-angle reflection/refraction seismic data were acquired on a 450-km-long transect in southern Baffin Bay extending from Baffin Island to Greenland. Dense air gun shots were recorded on 22 ocean bottom seismometers. A P wave velocity model was developed from forward and inverse modeling of the observed travel times. Beneath the Baffin Island shelf, a three-layered continental crust is observed with velocities of 5.5 to 6.9km/s. Typical for transform margins, there is a sharp transition between continental and oceanic crust. Off Baffin Island, 7-km-thick oceanic crust is interpreted to lie in a major transform fault identified on the gravity map. Beneath the deep Baffin Bay basin, 9-km-thick oceanic crust is encountered but thins to 6km within an assumed fracture zone. The thicker than normal oceanic crust indicates an ample magma supply, possibly related to melt extracted from a mantle plume. Seaward of the Greenland continental crust, 20-km-thick igneous crust (6.3 to 7.3km/s) is encountered in a 25-km-wide zone interpreted as a leaky transform fault that can be correlated southward through Davis Strait. The igneous crust is bounded by a 20-km wide basin to the west, underlain by 4-km-thick crust of unknown affinity. This structure is probably associated with transform movements. A high-velocity lower crustal layer (7.1km/s) of 8km thickness is indicated beneath the Greenland crust and can be correlated into the adjacent thick igneous crust. Both the thick igneous and Greenland crust are covered by up to 4km of Paleogene volcanics (5.2 to 5.7km/s).

Location map of line 600 (full name: AWI20080600) of the MSM09/3 expedition. The red lines mark the shot locations along lines 600 and 500. White circles indicate the location of ocean bottom seismometers (OBS) on line 600, gray circles mark OBS with no data. The OBS station numbers are annotated (red annotations refer to OBS that are shown in Figures 4–8). Blue lines indicate segments of line 600 along which coincident seismic reflection data were collected [Gohl et al., 2009]. The bathymetry (GEBCO 08 grid) is plotted with solid lines; the contour interval is 200 m.

…

Comparison of velocity-depth functions from line 600 with average oceanic crust. The gray area shows the range of typical oceanic crust encountered in the Atlantic Ocean with a crustal age between 59 and 127 Ma [White et al., 1992]. The color lines show the velocities from line 600; the position (km) refers to the distance along the velocity model (Figure 9).

…

Comparison of velocity functions from within the Ungava fault zone. Simplified models from NUGGET line 1 (between 200 and 230 km) [Funck et al., 2006] and line 600 (between 380 and 395 km, this study). For location of the lines see Figure 1. Note that velocities below a depth of 12 km are not well resolved for this segment of line 600. Abbreviation HVLC is high-velocity lower crust.

…

(top) Part of record section of OBS 625 (hydrophone component) displayed with a reduction velocity of 5.4 km/s. The horizontal scale is distance along the velocity model. (middle) The same record shown together with calculated travel times (red lines) for some selected phases. (bottom ) The corresponding velocity model (same color scheme as in Figure 9) with the raypaths of the selected phases. The red triangle marks the position of the OBS. For phase names see also Table 1. Abbreviations are LVZ, low-velocity zone; MCB mid-crustal boundary.

…

(top) Part of record section of OBS 620 (hydrophone component) displayed with a reduction velocity of 5.9 km/s. The horizontal scale is distance along the velocity model. Yellow arrows indicate the zone where the weak P 2 phase can be correlated. (middle) The same record shown together with calculated travel times (red lines) for some selected phases. (bottom) The corresponding velocity model (same color scheme as in Figure 9) with the raypaths of the selected phases. The red triangle marks the position of the OBS. For phase names see also Table 1.

…

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Tectonic evolution of southern Baffin Bay and Davis Strait:

Results from a seismic refraction transect between Canada

and Greenland

Thomas Funck,

Karsten Gohl,

Volkmar Damm,

and Ingo Heyde

Received 19 December 2011; revised 2 March 2012; accepted 8 March 2012; published 26 April 2012.

[1]Wide-angle reflection/refraction seismic data were acquired on a 450-km-long

transect in southern Baffin Bay extending from Baffin Island to Greenland. Dense air

gun shots were recorded on 22 ocean bottom seismometers. A Pwave velocity model

was developed from forward and inverse modeling of the observed travel times.

Beneath the Baffin Island shelf, a three-layered continental crust is observed with

velocities of 5.5 to 6.9 km/s. Typical for transform margins, there is a sharp transition

between continental and oceanic crust. Off Baffin Island, 7-km-thick oceanic crust is

interpreted to lie in a major transform fault identified on the gravity map. Beneath the

deep Baffin Bay basin, 9-km-thick oceanic crust is encountered but thins to 6 km within

an assumed fracture zone. The thicker than normal oceanic crust indicates an ample

magma supply, possibly related to melt extracted from a mantle plume. Seaward of the

Greenland continental crust, 20-km-thick igneous crust (6.3 to 7.3 km/s) is

encountered in a 25-km-wide zone interpreted as a leaky transform fault that can be

correlated southward through Davis Strait. The igneous crust is bounded by a 20-km

wide basin to the west, underlain by 4-km-thick crust of unknown affinity. This

structure is probably associated with transform movements. A high-velocity lower

crustal layer (7.1 km/s) of 8 km thickness is indicated beneath the Greenland crust and

can be correlated into the adjacent thick igneous crust. Both the thick igneous and

Greenland crust are covered by up to 4 km of Paleogene volcanics (5.2 to 5.7 km/s).

Citation: Funck, T., K. Gohl, V. Damm, and I. Heyde (2012), Tectonic evolution of southern Baffin Bay and Davis Strait:

Results from a seismic refraction transect between Canada and Greenland, J. Geophys. Res.,117, B04107,

doi:10.1029/2011JB009110.

1. Introduction

[2] The separation between Greenland and Canada has

remained largely unsolved because of an insufficient

understanding of the crustal nature in Baffin Bay and Davis

Strait and the tectonic relationship of both areas to the

Labrador Sea. In order to address this problem, the German

research vessel Maria S. Merian carried out a geophysical

survey in Davis Strait and southern Baffin Bay (Figures 1

and 2). The expedition was a component of the lead proj-

ect “Plate Tectonics and Polar Gateways in the Earth Sys-

tem (PLATES and GATES)”of the International Polar Year

(IPY 2007/08). The overall objective of the cruise was the

tectonic and sedimentary reconstruction of the opening of

Davis Strait and southern Baffin Bay. The study of this

paper covers the tectonic development and architecture of

the southern Baffin Bay and its transition to Davis Strait,

while the spreading history of southern and central Baffin

Bay is described in Suckro et al. [2012].

[3] No modern seismic refraction data are available for

southern Baffin Bay. Older sonobuoy profiles are interpreted

to indicate the presence of oceanic crust [Keen and Barrett,

1972]. However, the obtained velocity functions show a

substantial scatter and are not always compatible with

average oceanic crust [White et al., 1992]. Furthermore, no

linear magnetic anomalies typical for seafloor spreading

could be identified in Baffin Bay yet [Chalmers and

Pulvertaft, 2001]. The new data set will allow the nature of

the crust in southern Baffin Bay to be determined, whether it

consists of oceanic crust or of unroofed and partially ser-

pentinized mantle as suggested for northern Baffin Bay

[Reid and Jackson, 1997]. Despite the lack of unequivocal

evidence for oceanic crust in Baffin Bay, a prominent

gravity low in the center of the bay is interpreted as the

location of the extinct spreading axis [Whittaker et al.,

1997]. Other north-south striking anomalies are interpreted

as the expression of transform faults [Whittaker et al., 1997;

Chalmers and Pulvertaft, 2001]. The seismic refraction

Geological Survey of Denmark and Greenland, Copenhagen, Denmark.

Alfred Wegener Institute for Polar and Marine Research, Bremerhaven,

Germany.

Federal Institute for Geosciences and Natural Resources, Hanover,

Germany.

Published in 2012 by the American Geophysical Union.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, B04107, doi:10.1029/2011JB009110, 2012

B04107 1of24

component of the project was designed to map the crustal

character and thickness in Baffin Bay, and to check for the

seismic expression of the gravity lows. This will set the stage

for the discussion of the tectonic development of the area.

[4] Paleogene volcanism in the Davis Strait and southern

Baffin Bay is associated with a mantle plume [Storey et al.,

1998]. The seismic refraction data will provide information

on the distribution and volume of this volcanism, both near

the surface and as underplated layers at deep-crustal levels.

This will also allow the interaction between the plume and

the transform-rifted margin in the Davis Strait [Funck et al.,

2007] to be investigated.

2. Geological Setting

2.1. General Setting

[5] Davis Strait is a bathymetric high between Baffin

Island to the west and Greenland to the east that separates

Labrador Sea from Baffin Bay (Figure 1). The oldest

undisputed seafloor spreading magnetic anomaly in the

Labrador Sea is magnetic chron 27n (62.0–61.7 Ma using

the time scale of Gradstein et al. [2005]) [Chalmers and

Laursen, 1995]. Other authors suggest that seafloor spread-

ing started during magnetic chron 33 (84–73.6 Ma) [Roest

and Srivastava, 1989] or between magnetic chrons 29 and

31 (71.0–64.4 Ma) [Chian et al., 1995a]. A reorientation of

the spreading axis took place during magnetic chron 24r

(56.7–53.8 Ma), at the same time that seafloor spreading

initiated between Greenland and Europe. Spreading in the

Labrador Sea ceased by magnetic chron 13 (34.8–33.3 Ma)

[Srivastava, 1978]. The continental stretching and rifting in

the Labrador Sea and Davis Strait occurred over an extended

period of time as indicated by dyke swarms in West

Greenland. Based on the ages of these dykes, Larsen et al.

[2009] identified several phases of tectonomagmatic activ-

ity: initial stretching from the Late Triassic to Late Jurassic

(223 to 150 Ma), stretching and thinning in the Late Jurassic

(150 Ma), further stretching and thinning in the Early Cre-

taceous (140 to 133 Ma) followed by Paleogene thinning

and break-up (63 to 50 Ma).

[6] Baffin Bay is the northwest extension of the Labrador

Sea spreading system. The transform margin in Davis Strait

that links these two areas is characterized by the Ungava

transform fault, a name that was first introduced by Kerr

[1967]. Later, the term Ungava fault zone (UFZ) became

more commonly used (Figure 2). The position of the UFZ is

taken to be along the SE side of a line of positive gravity

anomalies. Davis Strait and the northern Labrador Sea are

bounded by volcanic margins [Keen et al., 2012; Gerlings

et al., 2009; Funck et al., 2007; Chalmers, 1997].

Onshore, Palaeogene volcanics crop out on either side of the

strait in a short narrow belt near Cape Dyer on Baffin Island

and in a wider zone in the Disko-Svartenhuk area of West

Greenland (Figure 2). Storey et al. [1998] identified two main

pulses of volcanism in West Greenland: one between 60.7

and 59.4 Ma and one between 54.8 and 53.6 Ma. The first

pulse is probably related to the arrival of the Iceland plume

beneath Greenland [Lawver and Müller, 1994; Storey et al.,

1998]. However, the assumed plume position at that time is

based on models and not on direct observations. Larsen and

Saunders [1998] explain the almost simultaneous volcanism

from 62 to 60 Ma in West Greenland [Storey et al., 1998],

East Greenland [Larsen and Saunders, 1998], and on the

British Isles [Pearson et al., 1996] by rapid lateral flow of a

small plume head that impinged on the continental litho-

sphere. Continental break-up of East Greenland from NW

Europe occurred at 56 Ma [Larsen and Saunders, 1998] and

caused a reorientation of the spreading axis in the Labrador

Sea [Srivastava, 1978]. Storey et al. [1998] suggested that the

Figure 1. Bathymetric map Baffin Bay and Labrador Sea.

Data source: General Bathymetric Chart of the Oceans

(GEBCO) 08 grid (http://www.gebco.net). Seismic refrac-

tion lines of the Maria S. Merian cruise MSM09/3 are

shown in red [Gohl et al., 2009]. Solid lines indicate pub-

lished seismic refraction lines in Baffin Bay and Davis Strait

as well as selected profiles in the Labrador Sea (lines 91–1

and 91–3[Jackson and Reid, 1994]; lines 91–2 and 91–4

[Reid and Jackson, 1997]; line 2001–3[Funck et al.,

2006]; line GR89-WA [Gohl and Smithson, 1993]; line

NUGGET 1 [Funck et al., 2007]; line NUGGET 2

[Gerlings et al., 2009]; line 88R2 [Chian and Louden,

1994]; line 90R1[ Chian et al., 1995b]). Dashed lines mark

the location of sonobuoy lines [Keen and Barrett, 1972;

Srivastava et al., 1982]. Abbreviations are FB, Foxe Basin;

LS, Lancaster Sound; NS, Nares Strait.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

2of24

second pulse of volcanism in West Greenland could be

related to this reorientation of the spreading axis, during

which remnants of the plume could have generated melts

along the UFZ. Volcanic layers, lava flows and seaward

dipping reflectors (SDR) are mapped in large areas of Davis

Strait [Skaarup et al., 2006; Chalmers and Laursen, 1995;

Chalmers, 1997]. In addition, volcanic rocks were drilled in a

number of wells (Hekja O-71 and Gjoa G-37 [Klose et al.,

1982]; Ralegh N-18 (BASIN database, Geological Survey

of Canada, Dartmouth, Nova Scotia, Canada); Hellefisk-1

Figure 2. Geologic map of the southern Baffin Bay, the Davis Strait region and the northernmost Lab-

rador Sea [after Chalmers and Oakey, 2007]. Red lines indicate the location of the MSM09/3 seismic

refraction lines (AWI20080[500/600/700]) with white circles showing the position of ocean bottom seism-

ometers (OBS) along line 600. The station number of every 5th OBS is labeled. Well locations are indi-

cated by yellow circles. The blue line marks the location of NUGGET line 1 [Funck et al., 2007].

Abbreviation SDR is seaward dipping reflections.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

3of24

and Nukik-2 [Rolle, 1985]). Laser Argon dating of basaltic

rocks from the Gjoa well (Figure 2) yielded ages of 59.5 Ma

[Williamson et al., 2001], which relates those rock samples to

the first pulse of volcanism.

[7] Baffin Bay forms a sedimentary basin that extends

from Davis Strait in the south to Nares Strait in the north.

The sediment thickness is up to 12 km in northern Baffin

Bay [Reid and Jackson, 1997]. The nature of the crust in

Baffin Bay is disputed. Keen et al. [1974] provide evidence

that the Baffin Bay crust was created by seafloor spreading,

which is supported by velocity models that are compatible

with oceanic crust [Keen and Barrett, 1972]. In contrast,

Reid and Jackson [1997] interpret their velocity model as

evidence for serpentinised mantle in northern Baffin Bay in

support for amagmatic continental rifting and separation.

Serpentinised mantle is often observed in ocean-continent

transition zones of non-volcanic continental margins [e.g.,

Funck et al., 2003, 2004] or at ultra-slow spreading ridges

[Jokat et al., 2003]. Chalmers and Pulvertaft [2001] point

out that there are no unequivocal magnetic anomalies in

Baffin Bay that can be related to seafloor spreading.

Absence of these anomalies could be related to oblique

spreading or to a blanketing effect of up to 12 km of sedi-

ments. The position of the extinct spreading axis and of the

transform faults in Figure 2 is determined from gravity and

magnetic anomaly maps [Chalmers and Pulvertaft, 2001;

Chalmers and Oakey, 2007].

2.2. Previous Geophysical Studies

[8] The coverage by refraction and regional deep seis-

mic reflection data is variable along the ocean basins west

of Greenland. The most detailed picture is available for the

Labrador Sea, where a number of refraction profiles define

the non-volcanic nature of the conjugate continental mar-

gins of Labrador and SW Greenland [e.g., Chian and

Louden, 1994; Chian et al., 1995b]. In addition, long

regional seismic reflection lines were acquired by the Federal

Institute for Geosciences and Natural Resources (BGR), the

Geological Survey of Canada (GSC) and LITHOPROBE

[e.g., Chalmers and Laursen, 1995; Chian et al., 1995a;

Hall et al., 2002].

[9] In the Baffin Bay, modern seismic refraction lines with

ocean bottom seismometers are limited to the entrance of the

Nares Strait [Jackson and Reid, 1994; Reid and Jackson,

1997], where Reid and Jackson [1997] interpret velocities

of 6.8 km/s as indication for serpentinized mantle rather than

oceanic crust. The remainder of the Baffin Bay is only

covered by short sonobuoy profiles (Figure 1), which show

velocities compatible with oceanic crust [Keen and Barrett,

1972].

[10] In the Davis Strait, two lines from the NUGGET

experiment [Funck et al., 2007; Gerlings et al., 2009] and a

line along the Greenland coast [Gohl and Smithson, 1993]

provide some information on the crustal structure in that

region (Figure 1). NUGGET line 1 shows that southern

Davis Strait is underlain by thinned continental crust with

the exception of an area around the UFZ, where crust of an

oceanic affinity was observed [Funck et al., 2007]. The

oceanic crust is associated with pronounced gravity and

magnetic anomalies that can be correlated through Davis

Strait. This suggests that the UFZ acted as a leaky transform

fault during phases of transtension. The 7 to 12-km-thick

continental crust on NUGGET line 1 is underlain by a

5 km thick high-velocity zone (HVZ) that Funck et al.

[2007] associate with southward flow of plume material

along lithospheric thin spots beneath the Davis Strait region,

similar to a model suggested earlier by Nielsen et al. [2002].

[11] While Funck et al. [2007] found no evidence for a

HVZ beneath the thicker continental crust close to Greenland,

Gohl and Smithson [1993] identified an up to 8-km-thick

HVZ at the base of the Greenlandic crust, where the Moho

depth varies between 30 to 42 km. Gohl and Smithson

[1993] interpret the HVZ to be associated with hot spot

magmatism in the Davis Strait and Baffin Bay region. This

magmatism is also observed along NUGGET line 2

(Figure 1), which extends from southern Davis Strait into

northern Labrador Sea. Here, Gerlings et al. [2009]

observed a 12-km-thick oceanic crust that is overlain by

an up to 2-km-thick sequence of Palaeogene basalts. This is

in the area of BGR line 77–6, where Chalmers and Laursen

[1995] identified seaward-dipping reflections that are

indicative of volcanic-style margins. Keen et al. [2012] also

report seaward-dipping reflectors off Labrador. However,

the volcanism is limited to the northern part of Labrador

Sea. Farther south, the continental margins have a non-

volcanic character with serpentinised mantle in the continent-

ocean transition zone [Chian et al., 1995b].

3. Wide-Angle Seismic Experiment

3.1. Data Acquisition and Processing

[12] Geophysical data were collected in September and

October 2008 onboard the German research vessel Maria

S. Merian [Gohl et al., 2009] including the three seis-

mic refraction lines AWI20080500, AWI20080600 and

AWI20080700. For simplicity, these lines are subsequently

referred to as lines 500, 600, and 700 (Figures 1 and 2).

This paper presents the results from line 600, a 450-km-

long transect (Figure 3) from the shelf off Baffin Island,

across the southern Baffin Bay and onto the shelf off West

Greenland. Close to the southeastern termination of line

600, the location of the 3201-m-deep Hellefisk-1 well was

crossed. Results from the crossing line 500 can be found in

the work of Suckro et al. [2012]. Figure 2 shows the loca-

tion of line 600 in a geological context. The characterization

of basement types is primarily based on seismic reflection

data, potential field data and plate reconstructions since

seismic refraction data are scarce in this area (see 2.2 Pre-

vious Geophysical Studies).

[13] A total of 25 ocean bottom seismometers (OBS) were

deployed at equal distances along the line (18.4 km spacing).

The instruments were provided by IFM-GEOMAR (Kiel,

Germany) and were equipped with a three-component 4.5-Hz

seismometer and a hydrophone [Gohl et al., 2009]. The

seismic source consisted of 16 G. Guns

ranging in size

from 1.1 to 4 L (70 to 250 in

) with a total volume of 50 L

(3100 in

) operated at a pressure of 145 bar. In addition, two

Bolt guns with a volume of 32 L (1953 in

) each were used at

a pressure of 80 bar (1160 psi). The shot interval was one

minute, which resulted in an average shot spacing of 156 m at

a variable ship speed of 4 to 5 knots. For navigation, the

ship’s Global Positioning System (GPS) system was used

with an accuracy of 10–20 m [Gohl et al., 2009].

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

4of24

[14] The shots were simultaneously recorded by a

3450-m-long digital streamer (SEAL system by Sercel) with

276 channels. The purpose of the coincident seismic

reflection line was to assist the velocity modeling of

the seismic refraction data by providing detailed informa-

tion on the geometry of the basement and sedimentary

layers.

[15] During the shooting of line 600, the vessel encoun-

tered an area with active fishing at the seaward limit of the

Greenland shelf. This happened at night during a heavy

snow storm with a visibility well below 50 m. For this rea-

son, the streamer had to be recovered and the ship detoured

to the north (Figure 3). This resulted in a kink in the line

with shots being offset by up to 23 km from the deployed

positions of OBS 616, 617 and 618. As discussed later, the

resolution of the velocity model is reduced in this zone.

[16] After recovery of the OBS, the data were dumped to

disk, corrected for OBS clock drift, converted to SEG-Y

format, and debiased. Travel time picks of the direct wave

were used to recalculate the position of the instruments at the

seafloor using a least squares method and velocity-depth

profiles for the water column obtained from CTD (conduc-

tivity, temperature, depth) measurements. Shot-receiver

ranges were calculated from the new OBS locations. Record

sections are displayed with a band-pass filter from 8 to

24 Hz (Figures 4–8). Deconvolution improved the recogni-

tion of seismic phases to some extent but was less successful

in the shallow water where the large Bolt guns produced

significant reverberations. Trace amplitudes in the record

sections are weighted by their distance to the OBS to

increase amplitudes for large offsets.

3.2. Methodology

[17] The goal of the analysis of the seismic refraction data

was to obtain a two-dimensional velocity model for the

sediments, volcanics, crust, and uppermost mantle. Line 600

was shot along a great circle arc with the exception of the

off-line shots due to fishing vessels. This arc forms the

baseline for the model with the origin (x = 0 km) defined by

the northwestern-most shot.

[18] The Pwave velocity model was developed using the

program RAYINVR [Zelt and Smith, 1992; Zelt and

Figure 3. Location map of line 600 (full name: AWI20080600) of the MSM09/3 expedition. The red

lines mark the shot locations along lines 600 and 500. White circles indicate the location of ocean bottom

seismometers (OBS) on line 600, gray circles mark OBS with no data. The OBS station numbers are anno-

tated (red annotations refer to OBS that are shown in Figures 4–8). Blue lines indicate segments of line

600 along which coincident seismic reflection data were collected [Gohl et al., 2009]. The bathymetry

(GEBCO 08 grid) is plotted with solid lines; the contour interval is 200 m.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

5of24

Forsyth, 1994], which allows both for forward and inverse

modeling. Initially, a forward model was developed from top

to bottom (seafloor to mantle) by fitting the observed travel

times. Layer boundaries within the sediments and the base-

ment geometry were taken from the coincident seismic

reflection record whenever the data quality allowed for this.

However, the low fold of the seismic reflection data, the

location of the seabed multiple, and the gap in the reflection

data due to the deviation around fishing vessels, prevent a

clear definition of the basement along most portions of line

600. After the development of the initial forward model, both

layer boundaries and velocities within layers were optimized

by using the inversion algorithm in RAYINVR. Gravity data

were used to help defining the deep structures at the edges of

the line without ray coverage (see section 4.3).

3.3. Seismic Data

[19] Three of the 25 OBS had technical problems, which

prevented the recording of data (OBS 605, 606 and 621).

Most records exhibit a high signal-to-noise ratio that allow

for the identification of seismic phases down to the mantle

(mantle refraction P

) as for example on OBS 609 (Figure 4).

The Moho reflection (P

P) can be recognized on most

records, in particular for OBS’s on crust with oceanic affinity

(Figure 4) but also in the continental domain (Figure 5). Most

instruments between OBS 604 and 619 show a prominent

refraction that is approximately horizontal when plotted with

Figure 4. Seismic record, raypaths and travel times for OBS 609. (top) Record section of hydrophone

component with calculated travel times (red lines), (middle) calculated travel time (black lines) with

observed travel times (red lines), and (bottom) raypaths through the velocity model (same color scheme

as in Figure 9). The uncertainty of the observed travel times is given by the height of the vertical bars.

Travel times are displayed with a reduction velocity of 6.8 km/s. The horizontal scale is distance along

the velocity model. A red triangle marks the OBS position. For phase names see also Table 1.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

6of24

a reduction velocity of 6.8 km/s (e.g., Figure 4). This indi-

cates the presence of a crustal layer with a velocity around

6.8 km/s, which is very typical for layer 3 in oceanic crust

[White et al., 1992].

[20] Three important record sections are discussed here in

more detail. OBS 625 (Figure 6) at the SE end of line 600

shows a high-amplitude mid-crustal reflection (P

P). Such

mid-crustal reflections are generally not observed in oceanic

crust as there is a rather smooth transition from the upper to

lower crustal velocities [cf. White et al., 1992]. In contrast,

mid-crustal reflections are very typical for continental crust

[Mooney and Brocher, 1987; Funck and Louden, 1999;

Funck et al., 2000b, 2003]. Hence, this reflection is regarded

as an indication for the presence of continental crust at this

part of the line. Further evidence is provided by the observed

velocities (see section 4.1).

[21] A second feature to be discussed for OBS 625

(Figure 6) is the occurrence of a low-velocity zone that is

revealed by a time delay (“jump”) in the first arrivals some

30 km to the NW of the OBS (at a distance of 417 km). At

this distance, the refraction within the volcanic layer (labeled

and inferred from correlation with the Hellefisk-1 well)

disappears and some 200 ms later another refraction (P

within the upper crust) becomes the new first arrival. Such a

time delay can only be generated by a layer between the

volcanic layer and the upper crust with a velocity lower than

in the volcanic layer. Velocities within such a low-velocity

zone (LVZ) cannot be constrained due to the lack of

refractions (see also section 4.2).

[22] One OBS that was very difficult to model was OBS

620 (Figure 7). This was due to a very complex geometry

close to that OBS with a deep basin that caused problems

with phase identification. A strong reflection at a distance of

Figure 5. Seismic record, raypaths and travel times for OBS 624 (hydrophone component). For details

see caption for Figure 4. For phase names see also Table 1. Abbreviations are HVZ, high-velocity zone;

L2, oceanic layer 2; LVZ, low-velocity zone.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

7of24

330 to 335 km was initially thought to be the Moho reflec-

tion P

P. However, later it was determined to be a reflection

from the base of the basin. The most important phase on this

record is the P

refraction - a phase that is very difficult to

spot due to its low amplitude. The velocity (5.5 km/s) is

similar to that observed in the upper crust between 317 and

330 km. However, using a velocity of 5.5 km/s for the entire

basin cannot explain the time delay for deep crustal phases

Figure 6. (top) Part of record section of OBS 625 (hydro-

phone component) displayed with a reduction velocity of

5.4 km/s. The horizontal scale is distance along the velocity

model. (middle) The same record shown together with calcu-

lated travel times (red lines) for some selected phases. (bot-

tom) The corresponding velocity model (same color

scheme as in Figure 9) with the raypaths of the selected

phases. The red triangle marks the position of the OBS.

For phase names see also Table 1. Abbreviations are LVZ,

low-velocity zone; MCB mid-crustal boundary.

Figure 7. (top) Part of record section of OBS 620 (hydro-

phone component) displayed with a reduction velocity of

5.9 km/s. The horizontal scale is distance along the velocity

model. Yellow arrows indicate the zone where the weak P

phase can be correlated. (middle) The same record shown

together with calculated travel times (red lines) for some

selected phases. (bottom) The corresponding velocity model

(same color scheme as in Figure 9) with the raypaths of the

selected phases. The red triangle marks the position of the

OBS. For phase names see also Table 1.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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observed on instruments farther to the SE. This is why

velocities <5.5 km/s had to be used for the basin. To match

the observed P

phase at OBS 620 (Figure 7), a thin layer

with a velocity of 5.5 km/s was introduced at the top of the

basin. Overall, the raypaths were very sensitive to even

slight changes in the basin like velocities, steepness of the

flanks, and thickness of the top layer. This made it difficult

to obtain an acceptable fit for all the observed seismic

phases.

[23] OBS 604 (Figure 8) is located at the position where

an abrupt lateral change in the crustal velocities had to be

introduced. To the southeast, an oceanic velocity structure is

encountered with the P

and P

refractions. Crustal refrac-

tions in the northwest (P

and P

) arrive earlier due to the

shallowing of the basement. The phase velocity of the P

refraction is higher than that of the P

phase in oceanic layer

3. However, this apparent higher velocity is also related to

the northwestward shallowing of the basement. The actual

modeled velocity in the mid-crustal layer through which the

is propagating, is only 6.1 km/s. This compares to

6.8 km/s in oceanic layer 3. The change from oceanic to

continental crust around 60 km is also indicated by the

presence of a mid-crustal reflection (P

P) to the northwest

that is not observed to the southeast.

[24] Off Greenland, the P

Pphase (Figure 5) marks the

top of a high-velocity lower crustal layer. In order to obtain a

visible P

Preflection, velocities have to increase from the

constrained 6.8 km/s at the base of the lower crust to

values >7.0 km/s below. As there are no refractions within

the high-velocity zone, there are no direct constraints on its

Figure 8. Seismic record, raypaths and travel times for OBS 604 (hydrophone component). For details

see caption for Figure 4. For phase names see also Table 1. Abbreviations are L2, oceanic layer 2;

L3, oceanic layer 3; MC, mid-crustal layer; UC, upper crust.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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velocity. However, the presence of high velocities as

deduced from the P

Preflections is consistent with the

better constrained results from NUGGET line 1 in southern

Davis Strait [Funck et al., 2007].

4. Results

[25] Below, the Pwave velocity model for line 600 is

presented. First, the model is described followed by a

detailed account of the model resolution and uncertainties.

Finally, two-dimensional gravity modeling is employed to

check for consistency of the velocity model with the

observed gravity data.

4.1. Velocity Model

[26] The Pwave velocity model for line 600 is shown in

Figure 9. Although some interpretation of the observed

velocity structure is given here, a more detailed account can

be found in the next section (section 5). The upper part of the

model consists of a series of sediment layers. In the central

part of the line in the deep basin of Baffin Bay, velocities

within the sedimentary layers vary from 1.6 to 4.2 km/s and

the total thickness reaches 6 km. However, the velocities of

1.6 km/s close to the seafloor are not constrained by any

refractions. In the NW beneath the Baffin Island shelf, the

lowermost sediment layer is modeled with a velocity of 4.3

to 4.4 km/s. On the Greenland side velocities are not as high;

sediments above the volcanic basement reach a velocity of

3.8 km/s. However, the maximum sediment thickness on

line 600 is slightly higher off Greenland than off Baffin

Island with values of 6 and 5 km, respectively.

[27] Volcanic rocks were drilled in the lower section of the

Hellefisk-1 well. The velocity model (Figure 9) shows

velocities of 5.2 to 5.7 km/s that are consistent with a vol-

canic layer with a maximum layer thickness of 4 km. This

thickness is quite variable as the volcanic sequence consists

of two mounded structures. The minimum thickness is as

little as 1 km. To the northwest, the layer pinches out at

365 km. Between 333 and 357 km another layer appears

with velocities of 4.7 to 4.9 km/s (poorly constrained) and a

thickness of 5 km. This layer forms a basin. At the SE end of

the line, a low-velocity zone (LVZ) is observed beneath the

basalts. The modeled velocity is 4.1 km/s within the LVZ,

but it should be emphasized here that the velocity within the

LVZ is not constrained due to the absence of refractions;

even the depth of the top of the LVZ is undefined. However,

the seismic reflection data indicate the disappearance of

high-amplitude reflections at that depth level. The velocity

in this layer is <5.6 km/s but the composition remains

unclear (basalts or non-volcanic sediments). Other, local

LVZs are observed within the sedimentary column.

[28] The crust shows large lateral variations both in

velocity and thickness (Figure 9). Between 0 and 60 km, the

crust is modeled with three layers with velocities of 5.5–

5.9 km/s in the upper crust, 6.1 to 6.3 km/s at mid-crustal

levels and 6.6 to 6.9 km/s within the lower crust. This

velocity distribution and the occurrence of mid-crustal

reflections are consistent with continental crust [Mooney and

Brocher, 1987]. Rough basement topography with three

basement highs and a seaward shallowing of the Moho

indicates that the crust has been faulted and thinned. The

Moho depth is only constrained between 40 and 60 km

where it shallows from 15 to 13 km. The landward deepen-

ing of the Moho between 0 and 40 km is inferred from the

gravity modeling (see section 4.3.).

[29] As discussed in section 3.3, a rather abrupt velocity

change occurs at 60 km. Between 60 and 333 km, the crust

is divided into an upper and lower crustal layer interpreted

as oceanic layers 2 and 3 (Figure 9). Velocities within layer

3 are fairly constant and around 6.8 km/s at the top and 7.0

to 7.2 km/s at the base as is typical for oceanic crust [White

et al., 1992]. Layer 2 velocities can be divided laterally into

three segments: between 60 and 135 km velocities range

from 5.5 to 6.0 km/s, between 135 and 227 km there is an

increase to 6.1 to 6.5 km/s, and between 227 and 333 km

velocities decrease again to 5.5 to 6.0 km/s. The thickness

of layer 2 is generally around 2 km, but locally exceeds

3 km. The total oceanic crustal thickness varies from 5 to

9 km and the Moho discontinuity is located at depths

between 13 and 16 km. The previously discussed basin

between 333 and 357 km is partly covered by a thin layer

with a velocity of 5.5 km/s, which is similar to the adjacent

oceanic layer 2. The exact thickness of this layer, which is

assumed to be basaltic, is not determined seismically. The

model shows a termination of this layer at 352 km as there

was no seismic evidence for a continuation to the SE.

[30] Crustal velocities beneath the basin (333 to 357 km)

are not constrained seismically. However, reflections from

the base of the basin and from the Moho give a thickness

estimate of 4 km for the crust in this zone (Figure 9). Farther

to the SE, the crust thickens substantially; the Moho deepens

from 15 km beneath the basin to 26 km between 380 and

400 km. In this zone, two crustal layers can be distinguished

with velocities of 6.3 to 6.6 km/s and 6.8 to 7.3 km/s in the

upper and lower layer, respectively. This crust is interpreted

as thick igneous crust. Farther to the SE toward Greenland,

crustal velocities decrease and this, together with the obser-

vations of mid-crustal reflections, suggest a continental

character of the crust. In the upper continental crust, veloc-

ities range from 5.8 to 6.2 km/s while the lower crust exhi-

bits velocities from 6.5 to 6.8 km/s. The upper crust is

between 3 and 4 km thick, while the lower crustal thickness

decreases from 10 km in the NW to 6 km in the SE. Beneath

the continental crust, another layer was introduced into the

model to explain a set of reflections (P

P). These phases

originate from a depth level that is shallower than the Moho

in the zone that is adjacent to the thick igneous crust. This

observation was accommodated by continuing the high

velocities of the igneous crust beneath the continental crust

and is interpreted as magmatic underplating. Velocities in

this high-velocity zone (HVZ) are not constrained due the

lack of refractions from this layer. However, the velocity

change in the model from 6.8 km/s at the base of the lower

continental crust to 7.1 km/s at the top of the HVZ yields in

an impedance contrast that is sufficient to create detectable

reflections. Funck et al. [2007] found a similar and well-

resolved underplated layer in the southern Davis Strait,

where the velocity was 7.4 km/s. This gives an idea of the

possible range of velocities in the HVZ. Mantle velocities

within the oceanic domain were modeled between 7.8 and

7.9 km/s. Beneath the continental crust off Baffin Island,

mantle velocities of 8.0 km/s were used in the model.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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Figure 9. (top) Magnetic anomalies, (middle) Pwave velocities with interpretation, and (bottom) diag-

onal values of the resolution matrix of the Pwave velocity model along line 600. Data source for the mag-

netic data: Verhoef et al. [1996]. The outer parts of the velocity model and of the resolution matrix with no

ray coverage are shown in white, velocities are specified in km/s, the velocity contour interval is 0.1 km/s.

Red circles show the location of OBS’s that were used for the modeling, the black circles refer to non-

functional OBS’s. The location of the Hellefisk-1 well and the cross-point with refraction line 500 are indi-

cated by a red and blue line, respectively. Abbreviations are BAS, basalts/volcanic rocks; FZ, fault zone;

MCB, mid-crustal boundary; L2, oceanic layer 2; LC, lower crust; LVZ, low-velocity zone; MC, mid-

crustal layer; MCB, mid-crustal boundary; UC, upper crust.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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4.2. Model Resolution and Uncertainty

[31] To assess the resolution and uncertainty of the

velocity model, a formal error analysis for individual phases

is given next to plots showing the ray coverage. In addition,

the values of the diagonal of the resolution matrix for the

velocity nodes are calculated. The resolution matrix is a

good indicator that distinguishes between poor and well

resolved parts of a model. Ideally, values of the resolution

matrix are 1 but values >0.5 indicate reasonably well

resolved model parameters [Lutter and Nowack, 1990].

[32] The formal error analysis for individual phases on line

600 is summarized in Table 1. The normalized c

is based

on assigned pick uncertainties of 40–200 ms depending on

the quality of each individual travel time pick. Pick uncer-

tainties are graphically indicated in Figure 10. The model is

generally well constrained with a total RMS misfit of 80 ms

between calculated and picked travel times. This is close to

the average travel time uncertainty of 83 ms. The normalized

of 0.68 is below the optimum value of 1 when travel

times are fitted within the given pick uncertainty. This could

indicate that either the model was fit to noise in the data or

the pick uncertainties were overestimated.

[33] The diagonal values of the resolution matrix of the

velocity nodes are shown in a gridded version in Figure 9

and show a close correlation with the ray coverage

(Figure 10). That is, areas with good and reversed ray cov-

erage are characterized by high resolution values. Within the

sedimentary column, velocities are generally well resolved,

although there are some exceptions. In the area where the

ship deviated from the track line (ca. 265 to 335 km), there

are zones with reduced resolution that are caused by lack of

observations (absence of close offset shots) or by complex-

ities associated with the three-dimensionality introduced by

the off-line shots. During the modeling, large lateral varia-

tions were avoided within that area. In this zone, the

observed seismic phases are generally consistent with the

velocities in the adjacent areas with online shots. However,

an offset in time is often noticed, which indicates a change in

the sedimentary thickness perpendicular to the line. In these

cases, the offset was accepted because no consistent two-

dimensional model could be found that would explain all the

observations within this zone. Thus, the velocity model is

representative for the location of the OBS rather than for the

off-line shot locations. Phases that displayed these problems

were not included in the error analysis. Another zone with

poor resolution is within the sediments on the Baffin Island

shelf between 0 and 30 km, where low-velocity zones occur

and where not all raypaths are reversed.

[34] The low-velocity zone beneath the basalts at the

southeastern end of the profile is not well resolved. How-

ever, this is the nature of low-velocity zones in which no

refractions can be observed which would allow for a direct

determination of the velocity. The existence of the low-

velocity zone is well constrained as seen by the characteristic

delay of refractions (Figure 6). Similar, the low resolution in

the basin between 333 and 357 km is related to the com-

plexities in the velocity structure there. The data cannot be

explained without a basin at that location that is covered by a

thin layer with a higher velocity than in the underlying

sediments. The reduced resolution reflects the uncertainty of

the thickness of the overlying layer and the velocity within

the basin.

[35] Velocities within the oceanic crust are well resolved

(Figure 9), but as before, the resolution decreases in the

region where the ship deviated from the line during the

shooting. Nevertheless, some P

rays sampled the lower

crust in this region and are consistent with layer 3 velocities

farther to the NW. Also the few P

observations are con-

sistent with layer 2 velocities outside this zone. However, no

or P

Pphases are observed between 280 and 335 km,

which could determine the Moho depth. As mentioned

above, velocities within low-velocities zones cannot be

resolved and a resolution value of 0.3 in the basin around

340 km indicates uncertainty in the velocities there. Reduced

resolution within the crust close to the outer limit of the

model coincides with a decrease of the number of reversed

raypaths in these areas. The lower crust around 390 km has

well resolved velocities at the top (resolution values of 0.7–

0.8), but at the bottom and within the adjacent HVZ,

velocities are only poorly resolved. Mantle velocities display

resolution values up to 0.9 in areas where P

phases are

observed. The plot with the ray coverage (Figure 10) also

indicates the segments of layer boundaries that are con-

strained by wide-angle reflections.

[36] Absolute errors of the model can be estimated by

perturbation of single nodes (velocity and boundary nodes)

in the model and examination of the sensitivity of the travel

times to these perturbations. Such a test was performed

within the basin between 333 to 357 km (Figure 9). It was

found that velocities that deviate 0.4 km/s from the mod-

eled 4.7 to 4.9 km/s can still explain most of the travel time

observations, although it becomes increasingly difficult to fit

all observations once the velocities are varied by more

than 0.2 km/s.

[37] Line 600 offers another opportunity to check the

accuracy of the velocity model since the line crosses

the Hellefisk-1 well. Figure 11 shows a comparison of

the velocity model with the sonic log from the well

(obtained from GEUS data repository). To reduce the scatter

in the sonic log data, a median filter with a filter length of

20 m was used. It should also be noted that the log data

were not used to adjust the velocity model; only the wide-

angle reflections and refractions as well as the coincident

seismic reflection data were used for the modeling. There is

Table 1. Number of Observations, n, RMS Misfit Between

Calculated and Picked Travel Times, t

rms

, and Normalized c

for Individual Phases on Line 600

Phase nt

rms

(s) c

Direct wave 1735 0.026 0.379

(all sediment refractions) 3129 0.045 0.354

P(all sediment reflections) 1337 0.096 1.683

(refraction in basalt) 585 0.048 0.441

P(reflection base basalt) 45 0.046 0.214

(refraction in oceanic layer 2) 1532 0.132 0.913

(refraction in oceanic layer 3) 3518 0.068 0.575

(refraction in upper crust) 747 0.066 0.724

P(reflection base upper crust) 102 0.045 0.372

(refraction in mid-crustal layer) 882 0.090 0.859

P(reflection base mid-crustal layer) 255 0.094 0.521

(refraction in lower crust) 30 0.035 0.197

P(Moho reflection) 1670 0.077 0.619

(refraction in mantle) 2177 0.113 0.876

All phases 17744 0.080 0.683

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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Figure 10

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

13 of 24

a general agreement between the two velocity curves but

there are also deviations. For example, the velocity model

has different velocity gradients within layers, since the

refractions primarily constrain velocities at the top of each

layer. The layer at a depth of 1500 m and a sonic velocity of

4.5 km/s is completely missing in the velocity model

because no refractions could be detected in the seismic data

and, hence, such a layer is not required by the data. By

missing this layer and having too low a velocity gradient in

the underlying layer, the average velocity down to basement

was underestimated. Thus, the top of the volcanic unit

(velocities >5 km/s) is modeled 400 m too deep. However,

in two-way travel time, the velocity model still fits the

travel time to the top of the volcanic layer as can be seen

when compared with the coincident seismic reflection data

(Figure 12). Velocities within the basalts compare fairly

well (around 5.5 km/s). In summary, the comparison shows

that the refraction data are unable to resolve the detailed

velocity structure within the sediments but still match the

long-wavelength features. It can also be seen that the

absolute depth error of layer boundaries at the basement

level is on the order of 400 to 500 m.

4.3. Gravity Modeling

[38] Gravity modeling can provide additional constraints

on velocity models, in particular in areas where the

Figure 10. Ray coverage along line 600 obtained from “point to point”(shot to OBS) ray-tracing for all travel time picks

used for the modeling (only phases below basement are shown). The figure is divided into four panels for different depth

levels. The lower part of each panel shows the layer boundaries of the velocity model together with the raypaths; the upper

part visualizes the calculated travel times (solid lines) and the associated travel time picks (vertical bars with a height

corresponding to the estimated pick uncertainty). Not every travel time pick and ray is plotted, a distance of 2 km between

picks is used to keep the plot readable. Triangles mark the positions of the OBS’s. For phase names see also Table 1. Abbre-

viations are HVZ, high-velocity zone; L2, oceanic layer 2; L3, oceanic layer 3; LC, lower crust; MC, mid-crustal layer; UC,

upper crust.

Figure 11. Comparison of the sonic log velocities from the

well Hellefisk-1 (GEUS database) with the velocities

obtained from the modeling of the seismic refraction data

along line 600.

Figure 12. Part of seismic reflection record on line

BGR08–315 around the Hellefisk-1 well. The well location

is marked by a blue line. (top) Migrated seismic record,

and (bottom) the same record shown together with velocity

model (Figure 9) converted to two-way travel time. Trian-

gles indicated the location of OBS 624 and 625. Abbrevia-

tion LVZ is low-velocity zone.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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Figure 13. Gravity modeling along line 600. (top) Models A through C explore the Moho geometry at

the outer limits of the model with no constraints from the seismic refraction data (compare with ray-

coverage in Figure 10). (bottom) Models A, D and E test for lateral variations of the density in the mantle

and within the basin around 350 km. The observed gravity is the free-air gravity measured during the

MSM09/3 expedition. The shaded area indicates the range of gravity values in a 20-km-wide zone to

either side of line 600 (extracted from DTU10 1-min grid [Andersen, 2010]). All densities in the model

are given in kg m

3

. For details see text. Abbreviations are HVZ, high-velocity zone; L2, oceanic layer 2;

LC, lower crust; MC, mid-crustal layer; UC, upper crust.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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Figure 14. Free-air gravity map with interpretation of crustal character along line 600 and along other

available seismic refraction lines. Shading by artificial illumination from the east. Data source: Satellite

altimetry, DTU10 1-min grid [Andersen, 2010]. Blue lines refer to the MSM09/3 seismic refraction lines

(AWI20080[500/600/700]) [Gohl et al., 2009]; pink lines show the location of other seismic refraction

experiments: GR89-WA [Gohl and Smithson, 1993], NUGGET 1 [Funck et al., 2007], and NUGGET 2

[Gerlings et al., 2009]; dashed pink lines indicate sonobuoy experiments: C1 to C10, B1 and D1 [Keen

and Barrett, 1972], D3 [Srivastava et al., 1982]. The distribution of crustal domains and structural ele-

ments is indicated by black and gray lines. White circles mark the location of OBS on line 600. Yellow

circles indicate the positions of wells (for well names compare with Figure 2). Abbreviation UFZ is

Ungava fault zone.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

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velocities are poorly resolved. In addition, gravity modeling

can be used to verify how consistent the velocity model is

with the gravity data. Gravity values are derived from the

KSS31M sea gravimeter that was installed on the vessel

Maria S. Merian. In this study, two-dimensional gravity

modeling was performed along line 600 using the algorithm

of Talwani et al. [1959]). The observed gravity in the

models (Figure 13) are free-air gravity anomalies measured

along the main line, i.e., not along the local deviation during

the shooting. Densities were obtained from conversion of the

Pwave velocities (Figure 9) using the curve shown by

Ludwig et al. [1970], which is approximated by

r¼2:83v4þ70:4v3598v2þ2230v700

where ris the density in kg/m

and vis the Pwave velocity

in km/s. Densities of 1.03 and 3.30 g/cm

were used for the

seawater and the mantle, respectively. There is no fixed ref-

erence gravity value. Instead, a reference is calculated from

minimizing the misfit between observed and calculated grav-

ity. Some caution has to be applied in the two-dimensional

modeling approach as some gravity anomalies terminate very

close to line 600 (Figure 14). Figure 13 illustrates that the

gravity variations can be up to 70 mgal in a 20-km-wide

zone to either side of line 600. Hence, the modeling and

discussion focuses on general trends in the gravity data.

[39] In the starting model (Model A; Figure 13, top), the

Moho is continued horizontally to the outer boundaries

where there is no ray coverage. At the NW end of the line

(between 0 and 40 km) the Moho depth was kept at 15 km.

This depth is not compatible with the gravity data as the

observed and calculated gravity deviate by up to 190 mgal.

To compensate for that, the Moho depth was increased to

30 km at that end of the line (model B) and this resulted in a

greatly reduced misfit. Full thickness continental crust

beneath Baffin Island is likely to be >30 km if one uses the

measurements in the nearby Precambrian crust in northern

Labrador as an indicator for the thickness [Funck and

Louden, 1998, 1999; Funck et al., 2000a]. Receiver func-

tions on southern Baffin Island also indicate a crustal

thickness of >40 km [Darbyshire, 2003]. However, the NW

extension of line 600 runs for another 100 km on the shelf

(Figure 2) where the crustal thickness is less than onshore.

[40] At the SE end of the line, a decrease of Moho depth

by 4 km (model C) can reduce the misfit, although the cal-

culated gravity is still too low. Further shallowing of the

Moho in that area, however, started to affect the overall

shape of the calculated gravity and was therefore not pur-

sued. Instead, the mantle density was increased from 3300 to

3350 kg m

3

at the SE end of the line (model D; Figure 13,

bottom), assuming that the lithosphere beneath the conti-

nental crust might be colder and denser than in the oceanic

domain. However, this assumption is questionable as this

zone is affected by the mantle plume as indicated by the

HVZ beneath the continental crust that is interpreted as

magmatic underplating. Decreasing the mantle density

beneath the oceanic crust has a similar effect. This could be

explained by high degrees of melting that strip out the

magnesium and iron, which leaves a low-density restite

behind. In any case, a lateral density change in the mantle

greatly reduces the misfit between observed and calculated

gravity in the southeast. Alternatively, a density increase in

the HVZ can produce a similar effect as a lateral density

variation within the mantle. When the density of the conti-

nental mantle beneath Baffin Island is increased to

3350 kg m

3

as well, the Moho there has to be adjusted to a

depth of 31 to 32 km to keep the fit with the observed

gravity. Between 70 and 110 km, the pressure at the base of

the model decreases by 10 MPa. This indicates some iso-

static imbalance that is evidenced by the flat Moho in this

zone while the basement shallows toward Baffin Island. This

imbalance can be compensated for by a gradual landward

increase of the density in the mantle. Such a lateral density

increase would be compatible with a cooling of the litho-

sphere from the oceanic crust into the region that is inter-

preted as transform fault [Chalmers and Pulvertaft, 2001].

At the same time, such a density increase would reduce the

misfit between observed and calculated gravity in this

region.

[41] In a last modeling step, the misfit in the area of the

basin at 340 km was investigated. As mentioned above,

velocities within the basin are not well resolved and the

velocity uncertainty may be up to 0.2 to 0.4 km/s. To obtain

a good fit, the density had to be reduced from 2510 to

2310 kg m

3

(model E; Figure 13, bottom). Although this

decreases the misfit in the area of the basin, it seems unlikely

that the density within the basin is that low. A reduction by

200 kg m

3

compared to the empirical formula by Ludwig

et al. [1970] corresponds to a velocity decrease from 4.8

to 3.1 km/s. This is far too low to explain the observed

travel times in the seismic refraction data. In addition, both

density and velocity would be lower than in the overlying

sedimentary layers. Alternatively, the sedimentary basin

could be deeper than the model indicates, as the seismic

constraints on this are not very strong. However, the crust

underneath the basin is already rather thin (4 km).

[42] In summary, even with some density adjustments,

there is no perfect fit to the observed gravity data. Many of

the deviations are likely due to three-dimensional effects that

cannot be treated properly in a two-dimensional model. One

example is the 4-km-deep sedimentary basin around 20 km

(Figure 13) that is required to model the observed delays of

crustal phases in that zone. The basin has a pronounced

signature in the calculated gravity, but cannot be seen in the

observed gravity. This indicates that the basin has to be a

local feature that violates the assumption of two-dimensionality

in the gravity model. Figure 14 shows a free-air gravity map

of the study area. The map indicates that most features cross

line 600 at an oblique angle. The most prominent departure

from two-dimensionality occurs around the pronounced

gravity high around OBS 621. This high can be correlated

southward all the way through the Davis Strait but dis-

appears just to the north of the line.

5. Discussion and Interpretation

[43] In section 4.1, the model for line 600 was presented

with a description of the velocity distribution in the sedi-

ments, the crust, and the mantle. In addition, a first inter-

pretation of the crustal structure was given. However, a more

thorough discussion of the model is necessary and is pre-

sented in this section. The model is discussed in context of

the regional geology as well as compared to studies in sim-

ilar tectonic and geologic settings. The discussion starts in

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

17 of 24

the NW of the profile off Baffin Island and then moves

toward the SE following the segmentation of the crust indi-

cated in Figure 9.

5.1. Continental Crust (0–60 km)

[44] The segment between 0 and 60 km is interpreted as

continental crust (Figure 9). The velocity structure is divided

into three layers with velocities that are not typical of oce-

anic crust [White et al., 1992]. In addition, the occurrence of

mid-crustal reflections is a strong indicator for continental

crust [Mooney and Brocher, 1987]. Velocities of 5.5 to 6.3

and 6.6 to 6.9 km/s for the upper and lower crust, respec-

tively, compare well with the range of velocities found

elsewhere in West Greenland and Eastern Canada along the

shores of the Labrador Sea and the Baffin Bay. For this

comparison, the mid-crustal layer is considered as part of the

upper crust. The Archean Nain Province in Labrador, where

Funck and Louden [1998] report velocities of 5.8 to 6.5 and

6.6 to 6.9 km/s in the upper and lower crust, respectively, is

very close to the study area. In the Nain Province, the

uppermost crust was interpreted to have a gneissic compo-

sition based on Pwave velocities and a Poisson’s ratio of

0.20 to 0.24. To the SE of Baffin Island along NUGGET line

1, upper and lower crustal velocities of 5.8 to 6.1 and 6.4 to

6.6 km/s were reported [Funck et al., 2007]. However, upper

crustal velocities there are only poorly resolved. Farther to

the east on that line (off Greenland), upper crustal velocities

were as low as 5.4 km/s. This is very close to the observed

5.5 km/s on line 600. Funck et al. [2007] suggested a

granitic composition of the upper crust on NUGGET line 1.

Intense faulting on line 600 as indicated by the rough base-

ment topography between 0 and 60 km, may result in a

reduction of the Pwave velocity. Laboratory measurements

of rock samples measured at pressures compatible with mid-

crustal levels (300–500 MPa) indicate Pwave velocities of

6.07 0.22 km/s for granite [Holbrook et al., 1992], which

is higher than what is observed on line 600. However, on a

seismic refraction line off SW Greenland, Chian et al.

[1995b] reported upper crustal velocities of 5.4 km/s in an

area that is characterized by widespread granitic intrusions.

[45] One other interesting aspect of the continental crust at

the NW end of line 600 is the abrupt transition to oceanic

crust at around 60 km (Figure 9), without any indication for

a transitional crust. Transitional crust at non-volcanic con-

tinental margins is often characterized by velocities that

differ from the adjacent normal continental and oceanic crust

and that are often difficult to interpret. The lack of such a

transition zone is interpreted to be related to the location of

line 600, which is parallel to the assumed extinct spreading

axis [Chalmers and Pulvertaft, 2001; Chalmers and Oakey,

2007] (Figure 2). The boundary from continental to oce-

anic crust crosses a N-S striking gravity low (Figure 14) that

is interpreted as transform margin [Chalmers and Pulvertaft,

2001]. Crustal thinning across transform margins is charac-

terized by a thinning of the crust over short distance. One

well-studied transform margin is the margin off Ghana in the

Equatorial Atlantic. Edwards et al. [1997] show that the

continental crust thins from 23 to 4 km over a distance of

only 20 km when initial oceanic crust is encountered. Such a

thinning is comparable to the one observed on line 600,

although it is only constrained by gravity modeling. Another

example for rapid thinning of the continental crust with no

transition zone can be found at the transform margin south of

Svalbard [Breivik et al., 2003] or off South Africa where the

transition occurs over a 50-km-wide zone [Parsiegla et al.,

2009].

[46] The thickness of the continental crust at the transition

to the oceanic crust is 7 km (Figure 9). This value is com-

patible with the 8 km found at the seaward limit of the Baffin

Island crust on NUGGET line 1 [Funck et al., 2007]. There

are no seismic refraction data on Baffin Island to determine

the thickness of the unstretched crust. However, receiver

functions indicate a crustal thickness between 40 and 45 km

beneath southern Baffin Island [Darbyshire, 2003]. This

would indicate a stretching factor of six.

5.2. Oceanic Crust (60–333 km)

[47] The zone between 60 and 333 km is interpreted as

oceanic crust but displays both lateral thickness and velocity

variations. Velocity variations are restricted to the upper

crustal layer (oceanic layer 2). Figure 15 shows a compari-

son with average oceanic crust in the North Atlantic with a

crustal age between 59 and 127 Ma as compiled by White

et al. [1992]. The comparison shows that the layer 2

velocities of 6.1 to 6.5 km/s between 135 and 227 km are

slightly higher than average. Otherwise the velocities fall

well into the range of typical oceanic crust both in terms of

the absolute velocities and velocity gradients. With respect to

crustal thickness, the values on line 600 are typically 6 km or

9 km, which are either slightly lower or slightly higher when

Figure 15. Comparison of velocity-depth functions from

line 600 with average oceanic crust. The gray area shows

the range of typical oceanic crust encountered in the Atlantic

Ocean with a crustal age between 59 and 127 Ma [White

et al., 1992]. The color lines show the velocities from line

600; the position (km) refers to the distance along the

velocity model (Figure 9).

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

18 of 24

compared with average crust. White et al. [1992] found a

global average thickness of 7.1 0.8 km.

[48] Figure 9 shows that the lateral velocity variations in

layer 2 correlate with changes in the observed magnetic

anomalies. The zone with the higher velocities (6.1–

6.5 km/s) displays positive anomalies, while the lower

velocities (5.5–6.0 km/s) are generally associated with neg-

ative magnetic anomalies. Changes of magnetic polarity in

oceanic crust mirror the reversals of the Earth’s magnetic

field over time and, hence, the lateral changes observed

along line 600 could indicate that the segments of oceanic

crust have a different age. However, there is currently no

consensus that there are seafloor-spreading magnetic

anomalies in Baffin Bay (Figure 16). Nevertheless, the

positive magnetic anomalies between OBS 609 and 612

show up as a linear feature that is parallel with the spreading

axis, which is itself parallel to line 600. The location of the

spreading axis is assumed to coincide with a gravity low

[Whittaker et al., 1997] (Figure 14), which is seismically

confirmed by Suckro et al. [2012]. If the magnetic anomaly

between OBS 609 and 612 is indeed related to seafloor-

spreading, it may correspond to polarity chron 21n (45.3 to

47.2 Ma) as this was the last clear spreading anomaly in the

Labrador Sea [Roest and Srivastava, 1989] and has a similar

distance to the extinct spreading axis. The southwestern and

northeastern limitation of the magnetic anomaly fits with the

location of a transform fault and an assumed fracture zone

(cf. Figure 14).

[49] On the free-air gravity map (Figure 14), the extinct

spreading axis in Baffin Bay stands out as a gravity low

parallel to line 600. In addition, another gravity low can be

seen that continues northward from the extinct spreading

axis, roughly between OBS 604 and 608. This gravity low

correlates with a proposed transform fault along which the

spreading axis is displaced to the north [Chalmers and

Oakey, 2007] (Figure 2). It is in this zone that the oceanic

crustal thickness is reduced to 6 km. A second zone with

reduced crustal thickness is observed near OBS 612

(Figure 9). Northward of this zone, the spreading axis shows

a minor displacement (Figure 14) interpreted as the location

of a fracture zone [Chalmers and Oakey, 2007] (Figure 2).

There is no clear signal in the gravity that would connect the

displacement in the spreading axis with the zone of reduced

crustal thickness on line 600. However, such a trend would

be consistent with the northward orientation of the transform

fault in the west and the UFZ in the east. Variations in the

thickness of oceanic crust can have various reasons. In the

study region, thickness variations may for example relate to

the variable nature of volcanic activity in the Davis Strait

region. The crust in transform faults and fracture zones is

often anomalously thin and the observed velocities can

deviate from normal oceanic crust [Detrick et al., 1993].

Detrick et al. [1993] show that the crust in North Atlantic

fracture zones is frequently quite thin (<1–2 km thick) and is

characterized by low Pwave velocities and the absence of a

normal seismic layer 3. These anomalies are explained by a

reduced magma supply at the end of spreading segments. In

contrast, the velocity structure within the transform fault and

the assumed fracture zone on line 600 is much closer to

normal oceanic crust even though it is thinner than the local

average. This probably relates to the influence of the Iceland

plume that provided ample magma supply in southern Baffin

Bay. This extra magma supply generated the 9-km-thick

oceanic crust along the line, some 2 km thicker than average

oceanic crust. Although the thickness decreases by 3 km

within the transform fault and the assumed fracture zone, the

resulting thickness of 6 km is still close to normal oceanic

crust.

[50]Storey et al. [1998] identified two main pulses of

volcanism in West Greenland: one between 60.7 and

59.4 Ma and one between 54.8 and 53.6 Ma. On line 600,

the distance to the extinct spreading axis is only 40 km and

an oceanic crustal thickness of 9 km is observed, indicating

that the plume must have influenced the region well after

53.6 Ma to create the thicker than normal oceanic crust.

While the age of the oceanic crust along line 600 is not

known, some estimates can be made. Srivastava and Keen

[1995], in an interpretation of a seismic reflection line

across the extinct spreading axis in the Labrador Sea, assume

a half-spreading rate of 3 mm/yr between magnetic anoma-

lies 18 and 13. At anomaly 13 (~33 Ma), Greenland and

North America are thought to have moved as a single plate.

Under the assumption that these parameters are applicable to

the Baffin Bay as well, a 40 km distance to the axis at a half-

spreading rate of 3 mm/yr would translate to 13 million

years prior to the cessation of spreading. This yields an age

estimate of 46 Ma for the oceanic crust on line 600, some 7

millions of years after the last main pulse of volcanism

sampled onshore West Greenland.

[51] The area between 285 and 335 km is seismically

poorly resolved due to the deviation from the line. However,

the most convincing fit to the observed travel times was

achieved with a velocity structure that is compatible with

oceanic crust. This zone is within the area that Gregersen

and Bidstrup [2008] define as the Aasiaat Basin and

Aasiaat Structural Trend. Some deep reflections in this zone

are interpreted to have an Early to mid-Cretaceous age

[Gregersen and Bidstrup, 2008] but lack a direct well con-

trol. With that age, the sediments would post-date the initi-

ation of seafloor spreading and the underlying basement

should be of continental character. This would contradict our

interpretation as oceanic crust. In contrast, G. Oakey and

J. Chalmers (A new model for the Paleogene motion of

Greenland relative to North America: Plate reconstructions

of the Davis Strait and Nares Strait regions between

Canada and Greenland, submitted to Journal of Geophysi-

cal Research, 2012) infer from plate reconstructions that

the Aasiaat Basin is most likely underlain by Paleocene

oceanic crust.

5.3. Transition Zone (333–400 km)

[52] The region between 333 and 400 km is named tran-

sition zone because its seismic character is different from

both the adjacent 9-km-thick oceanic crust to the NW and

the continental crust to the SE (Figure 9). The transition zone

is divided into two very distinct segments. The area that is

labeled leaky transform fault is characterized by 20-km-thick

igneous crust, while the basin to the NW is underlain by only

4-km-thick crust of unknown nature.

5.3.1. Leaky Transform Fault

[53] The 20-km-thick igneous crust between 375 and

400 km lies within the area referred to as Ungava fault zone

(UFZ) –a transform fault system that links the spreading axis

in the northern Labrador Sea to that in the southern Baffin

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

19 of 24

Figure 16. Magnetic anomaly map. Shading by artificial illumination from the southeast. Data source:

Verhoef et al. [1996] and Oakey [2001]. Blue lines refer to the MSM09/3 seismic refraction lines

(AWI20080[500/600/700]) [Gohl et al., 2009]; thin solid lines show the location of other seismic refrac-

tion experiments: GR89-WA [Gohl and Smithson, 1993], NUGGET 1 [Funck et al., 2007], and NUGGET

2[Gerlings et al., 2009]; dashed lines indicate sonobuoy experiments: C1 to C10, B1 and D1 [Keen and

Barrett, 1972], D3 [Srivastava et al., 1982]. The bold dashed lines indicate the location of the extinct

spreading axis (taken from the gravity low shown in Figure 14). White circles mark the location of

OBS on line 600 (every 5th station number is annotated). Yellow circles indicate the positions of wells.

The outline of the leaky transform fault is taken from the gravity data (Figure 14).

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

20 of 24

Bay. Storey et al. [1998] suggested that the Davis Strait went

through transtensional phases that created gaps between the

Canadian and Greenlandic continental crust. These gaps

were then filled with melt that formed thick igneous crust. In

this sense the UFZ acted as a leaky transform fault. Storey

et al. [1998] link the Early Eocene volcanism in West

Greenland to net extension on the UFZ, caused by a change

in plate kinematics as the North Atlantic opened at

55 Ma. Funck et al. [2007] identified 16-km-thick igne-

ous crust within the UFZ in southern Davis Strait on

NUGGET Line 1. They favor a Paleocene age of the UFZ

based on radiometric dates of the basalts (59.5 Ma)

[Williamson et al., 2001] in the nearby Gjoa G-37 well.

[54] The igneous crust within the UFZ correlates with a

gravity high that can be correlated through the entire Davis

Strait (Figures 14). With the addition of this study, the oce-

anic or igneous character of this gravity high is confirmed at

both ends (line 600 and NUGGET line 1) and there can be

little doubt that this feature is composed of igneous crust

along its entire length. In addition, the UFZ stands out as a

prominent feature on the magnetic map (Figure 16),

although the correlation is not as good as in the gravity data.

In particular, the northern part of the UFZ appears less

continuous in the magnetic data.

[55] Comparison of the velocity models of the UFZ in the

north (line 600) and in the south (NUGGET line 1) indicates

some lateral changes (Figure 17). In general, the crustal

velocities on these two lines are very similar and any dif-

ferences are close to the limit of seismic resolution. More

significant seems to be the division into a distinct HVZ on

NUGGET line 1 that is overlain by two crustal layers that

are similar to normal oceanic crust with a total thickness of

8 km. The distinct HVZ could indicate a multiphase devel-

opment. First, transtension or extension between Greenland

and Canada produced a gap that was filled with new igneous

crust with a velocity structure similar to normal oceanic

crust. Afterwards, this new crust, as well as the adjacent

thinned continental crust, was magmatically underplated,

creating the HVZ. This magmatic underplating is consistent

with geodynamic models [e.g., Nielsen et al., 2002] that

suggest southward flow of plume material through Davis

Strait along lithospheric thin spots. In the north, no such

division into an upper and lower unit could be detected.

However, the zone where thick igneous crust is observed is

much narrower on line 600 than on NUGGET line 1 (30 km

versus 60 km width). The detection of a potentially weak

reflection within the igneous crust from the top of a HVZ

would be significantly more difficult in such a narrow zone.

The thickness decrease of the igneous crust from north to

south seems to be compatible with the previously mentioned

southward channelling of plume material through Davis

Strait. Including the overlying basalts, the igneous thickness

is 23 km in the north compared to 17 km in the south. The

volcanism also extends into the Baffin Bay, where wide-

spread Paleogene basalts are observed off Disko and Svar-

tenhuk (Figure 2). A volcanic margin extends as far north as

the northern end of line 500 where there is indication for a

high-velocity lower crustal layer [Suckro et al., 2012].

5.3.2. Basin/Transform Fault

[56] Between 333 and 357 km, the velocity model

(Figure 9) indicates the presence of a 5-km-deep basin. As

discussed earlier, velocities within the basin are poorly

resolved but are probably within 0.2 km/s of the modeled

4.7 to 4.9 km/s. The crust immediately below the basin was

not sampled by refracted waves and, hence, the velocities are

unknown.

[57] There are two possible explanations for the basin.

Either this segment is a thin sliver of stranded continental

crust left between the leaky transform fault and the oceanic

crust or it is a transform fault, possibly associated with the

UFZ. If the basin is located on continental crust, the infill

could contain Cretaceous or older sediments. However, as

the igneous crust of the leaky transform fault can be corre-

lated directly to the SE flank of the basin, it appears more

likely that the bulk of the infill consists of volcanic material,

possibly interbedded with some non-volcanic sediments.

The velocities of 4.7 to 4.9 km/s can be easily explained with

volcanic rocks. Sonic log measurements in the Lopra-1

borehole on the Faroe Islands show velocities between 3.3

and 6.6 km/s in the volcanic sequence, which consists of

basalts and hyaloclastites [Christie et al., 2006].

[58] On the free-air gravity map (Figure 14), the basin

shows up as a north-south striking linear feature bordered by

two gravity highs. The western gravity high (around OBS

618 or at 320 km in Figure 13) follows the shelf break

northward into the Baffin Bay with a variable amplitude.

Watts [1988] note that such a free-air gravity high near the

Figure 17. Comparison of velocity functions from within

the Ungava fault zone. Simplified models from NUGGET

line 1 (between 200 and 230 km) [Funck et al., 2006] and

line 600 (between 380 and 395 km, this study). For location

of the lines see Figure 1. Note that velocities below a depth

of 12 km are not well resolved for this segment of line 600.

Abbreviation HVLC is high-velocity lower crust.

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

21 of 24

continental shelf break is typical for Atlantic continental

margins.

[59] Seafloor spreading in a north-south direction requires

a transform fault between the oceanic crust in the southern-

most Baffin Bay and the continental crust observed at the SE

end of line 600. Based on the gravity signature, the leaky

transform fault disappears just to the north of line 600

(Figure 14). Hence, the basin could easily form this trans-

form fault if extended northward up to the extinct spreading

axis. The interpretation as a transform fault can also explain

the low crustal thickness of 4 km as is commonly observed

in fracture zones and transform faults and discussed above

[Detrick et al., 1993]. In this context it is interesting to note

that a similar basin was observed on NUGGET line 1, where

the leaky transform fault (UFZ) is bounded by a graben

structure to the west [Funck et al., 2007]. Although the

velocity structure within the graben is not very well

resolved, the model for NUGGET line 1 indicates a volcanic

fill (velocities of 5.4 km/s) and the crust is potentially only

3 to 4 km thick (not including the underlying HVZ)

[Funck et al., 2007]. However, the 5.4-km/s layer could

also represent oceanic layer 2, in which case the crust

would be 7 km thick; but still thinner than the crust within

the UFZ. In summary, the UFZ seems to be bounded by a

narrow zone with thinned crust to the west. However,

more work is needed to determine if this feature is con-

tinuous through Davis Strait.

5.4. Underplated Continental Crust (400–450 km)

[60] Finally, the continental crust at the SE end of line 600

is discussed. Velocities in the upper and lower crust between

400 and 450 km are well-resolved (Figure 9) and are very

distinct from the oceanic and igneous crust observed else-

where along the line. Hence, there is little doubt that this

crust has a continental character with velocities of 5.9 to

6.2 km/s and 6.5 to 6.8 km/s in the upper and lower layer,

respectively. Further evidence for a continental affinity

comes from the observed mid-crustal reflections. While the

lower crustal velocities are comparable to the ones found off

Baffin Island, upper crustal velocities off Greenland are

slightly lower than off Baffin Island. However, the NW and

SE ends of line 600 are not conjugate. In a plate recon-

struction [Skaarup et al., 2006], the SE end of line 600

would move southward to a position some 100 to 200 km to

the north of NUGGET line 1 (for location see Figure 1).

Hence, the Baffin Island continental crust on NUGGET line

1 would come close to the continental crust off Greenland on

line 600. Indeed, velocities on NUGGET line 1 are 5.8 to

6.1 km/s and 6.4 to 6.6 km/s in the upper and lower crust,

respectively [Funck et al., 2007], close to the values found

off Greenland on line 600 (Figure 9).

[61] The crust at the SE end of line 600 has a continental

affinity but was later modified by the Iceland plume that

created the basaltic layer at the top (as drilled in the Helle-

fisk-1 well) and the HVZ at the base of the crust. The HVZ is

interpreted as magmatic underplating. A similar layer is

observed on NUGGET line 1 beneath the thinned portions of

the continental crust but disappears to the east where the

Greenlandic continental crust thickens [Funck et al., 2007].

This observation was interpreted by Funck et al. [2007] to be

consistent with the channelling model of Sleep [1997] and

Nielsen et al. [2002]. In this model, buoyant plume material

ponds at the base of the lithosphere and then flows laterally

and preferentially along thin lithosphere. With a thickness

between 9 and 13 km (not including the volcanics and the

HVZ), the continental crust around the Hellefisk-1 well can

be considered as thinned when compared with full-thickness

continental crust in this area. Gohl and Smithson [1993]

report a thickness of up to 40 km on a line in Davis Strait

close to the coast of Greenland (for location see Figure 14).

6. Conclusions

[62] The data from line 600 provide new insight into the

crustal affinity and geodynamic evolution in the southern

Baffin Bay. The central part of the line is characterized by

oceanic crust that is divided into several segments based on

crustal thickness and on velocities within layer 2 (Figure 9).

In the NW near Baffin Island, the line crosses a transform

margin with a sharp transition from continental into oceanic

crust. The oceanic crust at this transition is 6 to 7-km thick,

which is approximately the same as normal oceanic crust

(7 km) [White et al., 1992]. However, it is thinner than along

most of the remainder of the line. Thus, the segment is

interpreted to be part of the transform fault that can be cor-

related northward in the gravity data (Figure 14). An offset

in the extinct spreading axis correlates with another segment

of thinned oceanic crust (6 km) that is assumed to lie within

an oceanic fracture zone. Similar to the transform fault in the

west, this assumed fracture zone cuts the spreading axis at an

oblique angle, which is further confirmation for oblique

seafloor spreading in Baffin Bay as suggested by Chalmers

and Pulvertaft [2001].

[63] A third zone with a reduced crustal thickness (4 km)

is interpreted as a transform fault with a probable oceanic

composition that separates oceanic crust in the southern

Baffin Bay from 20-km-thick igneous crust and continental

crust farther landward. The igneous crust coincides with a

gravity high that can be correlated through the Davis Strait

and into the Labrador Sea, where similar igneous crust is

observed on NUGGET line 1 [Funck et al., 2007]. This

igneous crust is thought to form a leaky transform fault

(Ungava fault zone) where material from the Paleogene

Iceland plume filled the gaps that developed during phases

of transtension. The plume also created the high-velocity

zone beneath the continental crust on the Greenland side of

the line. Based on its distance to the extinct spreading axis

(40 km), the oceanic crust on line 600 may have an

approximate age of 46 Ma. Given that the oceanic crust here

is thicker than the global average (9 km outside the fracture

zones and transform faults compared to 7 km for typical or

average crust), the plume seems to have influenced the

spreading system for a long time after the initial impact of

the plume. This impact is thought to coincide with the first

major volcanic pulse in West Greenland at around 60.7 to

59.4 Ma [Storey et al., 1998]. The thicker than normal oce-

anic crust in the southern Baffin Bay is in contrast to

northern Baffin Bay, where Reid and Jackson [1997] find

serpentinized mantle indicative of a low magma supply.

Hence, somewhere in Baffin Bay, a transition from volcanic

to non-volcanic continental margins is expected. This would

be similar to what is observed in the Labrador Sea [Keen

et al., 2012].

FUNCK ET AL.: SEISMIC REFRACTION SOUTHERN BAFFIN BAY B04107B04107

22 of 24

[64] The continental crust at the SE end of the line is

overlain by volcanic rocks that were drilled in the Hellefisk-1

well. The velocity model indicates a maximum thickness of

4 km for the basalts. A low-velocity zone observed beneath

some of these basalts may indicate the presence of older

sediments deposited prior to the Paleocene volcanics.

However, as there are no velocity constraints at all for this

LVZ, the layer may also represent basalts with a lower

velocity.

[65]Acknowledgments. We thank all personnel onboard the RV

Maria S. Merian who helped to collect the seismic data. We are grateful

to Jim Chalmers and Gordon Oakey who made their geological map avail-

able in digital format. John Hopper read an earlier version of the manu-

script. Reviews by Charlotte Keen, Keith Louden, and the Associate

Editor greatly improved the manuscript. Funding for the cruise was pro-

vided by Deutsche Forschungsgemeinschaft. Various parts of the project

were funded by AWI, BGR, and GEUS with support by the Danish

National Research Council. IfM-Geomar provided ocean bottom seis-

mometers through an EU grant (contract RITA-CT-2004-505322). Support

for the data analysis was provided by Capricorn Greenland, Dong E&P

Grønland A/S, ExxonMobil, and Husky Energy. The paper is published

with the permission of the Geological Survey of Denmark and Greenland.

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Rifting and evolution of the Labrador-Baffin Seaway

Chapter

Full-text available

Aug 2022

The Northeast Canada Rifted Margin Composite Tectono-Sedimentary Element, Baffin Bay, Davis Strait, and Labrador Sea

Article

Full-text available

Feb 2023

The Northeast Canada Rifted Margin (NCRM) Composite Tectono-Sedimentary Element (CTSE) developed during a long and complex history that produced two tectono-sedimentary elements (TSEs): (1) the pre-rift TSE of pre-Cretaceous age; and (2) the syn-rift TSE of Early Cretaceous-Paleocene age. The pre-rift TSE includes the oldest and most poorly known offshore sedimentary accumulations which mainly evolved in a cratonic setting. In contrast, Cretaceous-lower Paleocene sedimentary basins of the syn-rift TSE are known from several wells, seismic data, outcrops, and seabed samples, and their extent and distribution are mapped in most parts of the margin. The syn-rift TSE is the most prospective part of the margin and hydrocarbon shows have been documented in some wells and offshore seeps studies. This review provides insights into the Paleozoic-Cenozoic evolution of the NE Canada rifted margin in the Labrador Sea, Davis Strait, and Baffin Bay. In this context, we discuss structural inheritance and rift development, and account for confirmed and potential hydrocarbon systems and plays.

Stratigraphy of western Baffin Bay: a review of existing knowledge and some new insights

Chapter

Full-text available

Aug 2022

Sedimentary basins within the Labrador-Baffin Seaway are the product of rifting between Greenland and the paleo-North American Plate. Rifting started in the Early Cretaceous, with seafloor spreading initiated in the Paleocene and ending near the Eocene-Oligocene boundary. A change in the spreading direction in the latest Paleocene resulted in transform offsets in the Davis Strait and along fracture zones in Baffin Bay, with deformation in northern Baffin Bay during the Eurekan Orogeny. Since the stratigraphy of western Baffin Bay is poorly constrained, analogues are used from the well studied Labrador and West Greenland margins and exposures on nearby Bylot Island. The generally northwest-trending basement structures are infilled with Cretaceous strata, which are overlain by a seaward-thickening wedge of post-rift Paleocene to Middle Miocene sedimentary rocks. Finally, a thick Middle Miocene and younger interval blankets the deep water and oceanic crust, with clinoforms locally developed on the shelf.

Stratigraphy of the West Greenland margin

Chapter

Full-text available

Aug 2022

The chapter describes the stratigraphy and geological evolution of West Greenland continental margin, including the tectonostratigraphy, the seismic stratigraphy, the lithostratigraphy, and the biostratigraphy, with ties to all offshore wells on the margin, and with descriptions from selected onshore wells and outcrops.

Wide-angle seismic transect reveals the crustal structure of(f) southern Sri Lanka

Article

Full-text available

Apr 2022
TECTONOPHYSICS

We present results derived from a seismic refraction experiment and gravity measurements about the crustal structure of southern Sri Lanka and the adjacent Indian Ocean. A P-wave velocity model was derived using forward modelling of the observed travel times along a 509 km long, N-S trending profile at 81°E longitude. Our results show that the continental crust below southern Sri Lanka is up to 38 km thick. A ~ 65 km wide transition zone, which thins seawards to ~7 km thickness, divides stretched continental from oceanic crust. The adjacent, 4.7 to 7 km thick normal oceanic crust is covered by up to 4 km thick sediments. The oceanic crust is characterized by intra-crustal reflections and displays P-wave velocity variations, especially in oceanic layer 2, along our profile. In the central part of the profile, the uppermost mantle layer is characterized by normal P-wave mantle velocities of 8.0–8.1 km/s. At the southern end of the profile, unusual low upper mantle seismic velocities, ranging from 7.5 to 7.6 km/s only, characterize the uppermost mantle layer. These low upper mantle velocities are probably caused by partially serpentinized upper mantle. At even greater depths the upper mantle layer is characterized by velocities of 8.3 km/s on average. The type of margin along our profile is difficult to identify, since it is characterized by features typical for different types of margins.

The Davis Strait proto-microcontinent: The role of plate tectonic reorganization in continental cleaving

Article

May 2024
GONDWANA RES

The orogenic bridge theory: towards a predictive tool for past and future plate tectonics

Article

Full-text available

Apr 2024

Wegener's Continental Drift Theory has laid the foundations of modern plate tectonics. However, despite decades of work and studies around the globe, modern plate tectonics still does not explain all the datasets acquired up to now and is well overdue for a major update. We propose a new theory, the orogenic bridge theory, which partly builds on the Continental Drift Theory and modern plate tectonics and reconciles them with the idea put forward by a competing theory, the Land Bridge Theory (or Isthmian Links). The orogenic bridge theory states that the style of continental rifting is directly controlled by preexisting orogenic structures. On the one hand, preexisting orogens trending parallel to an opening rift facilitate breakup and rift propagation and control the strike and geometry of rift-related structures. This endmember has already been broadly studied worldwide. On the other hand, orogens oriented orthogonal (or highly oblique) to the opening rift will act as strong barriers forcing the rift to step, therefore delaying or impeding breakup and rift propagation and localizing the formation of major-offset transform faults. In the present contribution, we review the evidence in favor of a correlation between rift-orthogonal orogens and major transforms and discuss some of the main implications of the orogenic bridge theory.

Radial Miscible Viscous Fingering of Icelandic Mantle Plume

Thesis

Jun 2022

Patricia Galbraith-Olive

The Icelandic plume, a major convective upwelling, has had a considerable influence on the geological evolution of the North Atlantic region. Direct manifestations of this major convective upwelling include positive residual depth anomalies and long wavelength free-air gravity anomalies, both of which reach from Baffin Island to Norway and from Newfoundland to Svalbard. Signifi cant shear wave velocity anomalies, observed in full-waveform tomographic models between 100 km and 200 km depth, show the Icelandic plume has a complex, irregular planform. These anomalies suggest about fi ve horizontal fi ngers radiate away from the central plume conduit. The best imaged fingers lie beneath the British Isles, southern Scandinavia and Greenland, extending ~1,000 km from the Icelandic plume. It is proposed that these radial miscible fi ngers develop due to the Saffman-Taylor instability, a fluid dynamical phenomenon which occurs when a less viscous fluid is injected into a more viscous fluid. Mobility ratio (i.e. the ratio of fluid viscosities), Peclet number (i.e. the ratio of advective and diffusive transport rates) and thickness of the horizontal layer into which the fluid is injected, together control the presence of fi ngering due to the Saffman-Taylor instability. Estimates for the Icelandic plume suggest the mobility ratio is at least 15, the Peclet number is ~ 2 x 10⁴, and the asthenospheric channel thickness is 100 ± 50 km. Appropriately scaled laboratory experiments play a key role in developing a quantitative understanding of the spatial and temporal evolution of mantle plume planforms. My results prove that the presence or absence of radial miscible fi ngering due to the Saffman-Taylor instability is controlled by changes in mobility ratio, Peclet number and horizontal layer thickness. At large horizontal thicknesses, gravity has an increasingly important influence and acts to damp the production of radial viscous miscible fi ngers. Observed values from the Icelandic plume suggest the fluid dynamics may be more complex than the Saffman-Taylor instability alone. Additional processes, such as interaction with the base of the lithospheric plate, along with the Saffman-Taylor instability, may be the origin of the fi ngers.

Lithostratigraphy, geology and geochemistry of the Tertiary volcanic rocks on Svartenhuk Halvø and adjoining areas, West Greenland

Article

Full-text available

Oct 2022

The Palaeogene volcanic succession in the northern part of the Nuussuaq Basin in West Greenland comprises three formations: the Vaigat and Svartenhuk Formations of Paleocene age (61–58 Ma) and the Naqerloq Formation of Eocene age (57–54 Ma). In this study, we formalise and describe the volcanic stratigraphy on Svartenhuk Halvø and the areas with lavas that flowed across the basin boundary onto the adjoining basement areas in the north and east. The Vaigat Formation comprises three members. The Kakilisaat and Nerutusoq Members are of minor volume and consist of, respectively, crustally contaminated basalts and chemically enriched basalts with relatively high contents of incompatible trace elements. They are overlain by the voluminous Nunavik Member of tholeiitic picrites (MgO ≥12 wt%) and subordinate magnesian basalts. The oldest volcanic deposits are commonly foreset-bedded hyaloclastites, and the overlying subaerial lavas are mainly thin, grey, crumbling flows. Eruption sites were mainly within the basin, with depocentres in the south and hyaloclastite and lava transport directions towards the north. Thicknesses vary from up to at least 2000 m in the south to ≥380 m in the northernmost exposures close to 72°N. The Svartenhuk Formation comprises four members. The lowest, Kuugaartorfik Member, is up to 100 m thick and consists partly of quartzofeldspathic and partly volcanogenic sediments; it is restricted to northern Svartenhuk Halvø and the Innerit peninsula. The overlying volcanic Tunuarsuk, Nuuit and Skalø Members are voluminous and widespread, with a combined thickness of up to 1800 m. They consist of tholeiitic basalts with similar chemical compositions but with correlatable stratigraphic variation patterns. The Tunuarsuk Member consists of interspersed flow groups of thin, grey flows and massive, brown flows; the Nuuit Member comprises mainly massive brown flows, and the Skalø Member is dominated by light grey flows. The Svartenhuk Formation oversteps the Vaigat Formation on the basement in the north and east. In these distal areas the Tunuarsuk and Nuuit Members constitute the major volumes, and preserved thicknesses are up to 1400 m. In northern and eastern Svartenhuk Halvø and also farther to the north and east, foreset-bedded hyaloclastites indicate transport directions towards the north and possibly east from eruption sites within the basin. The Naqerloq Formation comprises one member, the Arfertuarsuk Member, consisting of flows of brown basalt with relatively enriched chemistry and a single trachyte flow. The member is only found in western Svartenhuk Halvø and on Skalø, where it conformably overlies the older lavas with up to 350 m thickness preserved after erosion. Dykes of all three formations are present. The distribution of dykes of the Naqerloq Formation suggests that this originally extended much farther east. Picrites and basalts of the Vaigat and Svartenhuk Formations are geochemically related; the picritic lavas represent erupted primitive magmas, whereas the basaltic lavas represent fractionated melts formed in deep magma chambers. The melts formed from a geochemically depleted but heterogeneous mantle; in addition melts from enriched sources were occasionally incorporated. The enriched basalts of the Naqerloq Formation arose from another mantle source. Low contents of V, Cu and Ni in some crustally contaminated lavas indicate that accumulation of these elements may be present at depth.

Introduction and summary

Chapter

Full-text available

Aug 2022

The papers contained in this bulletin provide a comprehensive summary and updated understanding of the onshore geology and evolution of Baffin Island, the Labrador-Baffin Seaway, and surrounding onshore regions. This introductory paper summarizes and links the geological and tectonic events that took place to develop the craton and subsequent Proterozoic to Cenozoic sedimentary basins. Specifically, the Precambrian and Paleozoic geology of Baffin Island and localized occurrences underlying the adjacent Labrador-Baffin Seaway, the Mesozoic to Cenozoic stratigraphy and rift history that records the opening and evolution of the Labrador-Baffin Seaway, the seismicity of the region, as well as both the mineral (Baffin Island) and hydrocarbon (onshore and offshore) resource potential are discussed.

The seismic velocity structure of the deep continental crust

Article

Full-text available

Jan 1992
Dev Geotectonics

The seismic velocity structure of the deep continental crust.

Chapter

Full-text available

Jan 1992
Dev Geotectonics

Borehole seismic studies of a volcanic succession from the Lopra-1/1A borehole in the Faroe Islands, northern North Atlantic

Article

Full-text available

Jul 2006

Extruded basalt flows overlying sedimentary sequences present a challenge to hydrocarbon exploration using reflection seismic techniques. The Lopra-1/1A re-entry well on the Faroese island of Suduroy allowed us to study the seismic characteristics of a thick sequence of basalt flows from well logs and borehole seismic recordings. Data acquired during the deepening operation in 1996 are presented here. The re-entry well found that the seismic event at 2340 m, prognosed from the pre-drill Vertical Seismic Profile (VSP) as a decrease in impedance, was not base basalt and the deepened well remained within the lower series basalts. Nonetheless, compressional and shear sonic logs and a density log were recorded over the full open hole interval. These allowed a firm tie to be made with the reflected wavefield from a new VSP. The sonic logs show a compressional to shear wavespeed ratio of 1.84 which is almost constant with depth. Sonic compressional wavespeeds are 3% higher than seismic velocities, suggesting dispersion in the basalt flows. Azimuthal anisotropy was weakly indicated by the shear sonic log but its orientation is consistent with the directions of mapped master joints in the vicinity of the well. The VSP downgoing compressional wavelet shows good persistence, retaining a dominant period of 28 ms at 3510 m depth. Average vertical velocity is 5248 m/s, higher than previously reported. Attenuation can largely be modelled by geometrical spreading and scattering loss, consistent with other studies. Within the piled flows, the effective Q from scattering is about 35. Elastic layered medium modelling shows some hope that a mode-converted shear wave may be observed at moderate offsets. Like its predecessor, the 1996 VSP indicates a decrease in impedance below the final depth of the well. However, it is unlikely to be basement or sediment and is probably an event within the volcanic sequence.

Southern African continental margin: Dynamic processes of a transform margin

Article

Full-text available

Mar 2009
GEOCHEM GEOPHY GEOSY

Dynamic processes at sheared margins associated with the formation of sedimentary basins and marginal ridges are poorly understood. The southern African margin provides an excellent opportunity to investigate the deep crustal structure of a transform margin and to characterize processes acting at these margins by studying the Agulhas-Falkland Fracture Zone, the Outeniqua Basin, and the Diaz Marginal Ridge. To do this, we present the results of the combined seismic land-sea experiments of the Agulhas-Karoo Geoscience Transect. Detailed velocity-depth models show crustal thicknesses varying from ˜42 km beneath the Cape Fold Belt to ˜28 km beneath the shelf. The Agulhas-Falkland Fracture Zone is embedded in a 50 km wide transitional zone between continental and oceanic crust. The oceanic crust farther south exhibits relatively low average crustal velocities (˜6.0 km/s), which can possibly be attributed to transform-ridge intersection processes and the thermal effects of the adjacent continental crust during its formation. Crustal stretching factors derived from the velocity-depth models imply that extension in the Outeniqua Basin acted on regional as well as more local scales. We highlight evidence for two episodes of crustal stretching. The first, with a stretching factor β of 1.6, is interpreted to have influenced the entire Outeniqua Basin. The stresses possibly originated from the beginning breakup between Africa and Antarctica (˜169-155 Ma). The second episode can be associated with a transtensional component of the shear motion along the Agulhas-Falkland Transform from ˜136 Ma. This episode caused additional crustal stretching with β = 1.3 and is established to only have affected the southern parts of the basin. Crustal velocities directly beneath the Outeniqua Basin are consistent with the interpretation of Cape Supergroup rocks underlying most parts of the basin and the Diaz Marginal Ridge. We propose that the formation of this ridge can be either attributed to a transpressional episode along the Agulhas-Falkland Transform or, more likely, to thermal uplift accompanying the passage of a spreading ridge to the south.

The crustal structure of southern Baffin Bay: Implications from a seismic refraction experiment

Article

Full-text available

Jul 2012

Baffin Bay represents the northern extension of the extinct rift system in the Labrador Sea. While the extent of oceanic crust and magnetic spreading anomalies are well constrained in the Labrador Sea, no magnetic spreading anomalies have yet been identified in Baffin Bay. Thus, the nature and evolution of the Baffin Bay crust remain uncertain. To clearly characterize the crust in southern Baffin Bay, 42 ocean bottom seismographs were deployed along a 710-km-long seismic refraction line, from Baffin Island to Greenland. Multichannel seismic reflection, gravity and magnetic anomaly data were recorded along the same transect. Using forward modelling and inversion of observed traveltimes from dense airgun shots, a P-wave velocity model was obtained. The detailed morphology of the basement was constrained using the seismic reflection data. A 2-D density model supports and complements the P-wave modelling. Sediments of up to 6 km in thickness with P-wave velocities of 1.8-4.0 km s-1 are imaged in the centre of Baffin Bay. Oceanic crust underlies at least 305 km of the profile. The oceanic crust is 7.5 km thick on average and is modelled as three layers. Oceanic layer 2 ranges in P-wave velocity from 4.8 to 6.4 km s-1 and is divided into basalts and dykes. Oceanic layer 3 displays P-wave velocities of 6.4-7.2 km s-1. The Greenland continental crust is up to 25 km thick along the line and divided into an upper, middle and lower crust with P-wave velocities from 5.3 to 7.0 km s-1. The upper and middle continental crust thin over a 120-km-wide continent-ocean transition zone. We classify this margin as a volcanic continental margin as seaward dipping reflectors are imaged from the seismic reflection data and mafic intrusions in the lower crust can be inferred from the seismic refraction data. The profile did not reach continental crust on the Baffin Island margin, which implies a transition zone of 150 km length at most. The new information on the extent of oceanic crust is used with published poles of rotation to develop a new kinematic model of the evolution of oceanic crust in southern Baffin Bay.

Baffin Bay: Small ocean basin formed by sea-floor spreading

Article

Jan 1974
AAPG BULL

Petroleum exploration offshore southern Baffin Island, northern Labrador Sea, Canada

Article

Jan 1982

A refraction seismic transect from Greenland To Ellesmere Island, Canada: The crustal structure in southern Nares Strait

Article

Jan 2004
Polarforschung

A refraction and wide-angle reflection seismic study was carried out in southern Nares Strait (northernmost Baffin Bay) on a 378 km long profile running from Pituffik/Thule Air Base on Greenland into Makinson Inlet on Ellesmere Island, Canada. Eight ocean bottom seismometers and eight land stations were deployed to record the airgun shots along the line. A crustal velocity model was developed by forward and inverse modeling techniques. The Proterozoic Thule Basin can be correlated across Nares Strait as a continuous structure with a total thickness of 4-5 km. The basin is divided into three units. The upper unit has velocities of 4.5-5.0 km s-1 and a Poisson's ratio (σ) of 0.30, indicating a high content of carbonates. The middle unit is characterized by high velocities (6.1 km s-1) and a Poisson's ratio of 0.28. This unit is interpreted to correlate with the basaltic sills found in the Cape Combermere formation. The lower unit is a low-velocity zone and, hence, its velocities are unconstrained. The underlying crust is divided into three layers, upper crust (6.0-6.2 km s-1, σ = 0.25), middle crust (6.1-6.3 km s-1, a = 0.26) and lower crust (6.7-6.9 km s-1, σ = 0.26). These properties are consistent with a granitic/gneissic composition in the upper/middle crust and with granulites in the lower crust. Moho depth on either side of Nares Strait is 36 km, with some shallowing to 33 km in a 100 km wide zone. The Moho shallowing is related to local uplift at the Carey Islands just to the south of the line based on correlation with the gravity data. With only minor lateral changes of crustal velocities and Moho depth across southern Nares Strait, the eastern Archean/Proterozoic part of Ellesmere Island appears to be part of the same plate as Greenland with Thule Basin as intracratonic feature. No structures consistent with a strike-slip boundary could be resolved in southern Nares Strait.

A geologic Time Scale 2004

Article

Mar 2005

A successor to A Geologic Time Scale 1989 (Cambridge, 1990), this volume introduces the theory and methodology behind the construction of the new time scale, before presenting the scale itself in extensive detail. An international team of over forty stratigraphic experts develops the most up-to-date international stratigraphic framework for the Precambrian and Phanerozoic eras. A large wallchart (not available for eBook) summarizing the time scale at the back of the book completes this invaluable reference for researchers and students.

The Geologic Time Scale 2012

Book

Jan 2004

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Tectonic evolution of southern Baffin Bay and Davis Strait: Results from a seismic refraction transect between Canada and Greenland

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