Geological Development

Pre-rift

The coastal areas flanking Labrador Sea are dominated by Archaean and Lower Proterozoic igneous and metamorphic rocks. Scattered outcrops of Lower Paleozoic deposits exist on the Canadian side. Ordivician carbonates are known from Baffin Island and the Labrador Shelf.

Following the deposition of Lower Paleozoic carbonates there is no evidence of sedimentation or rifting in the West Greenland region during Devonian to Jurassic times. The nearest outcrops of these sediments are in the Sverdrup Basin of northern Canada and in the Jeanne D’arc Basin offshore Newfoundland.

Early rift phase

During the earliest Cretaceous the margins of Canada and West Greenland were subjected to rifting and several riftbasins were created on the shelves along the Labrador Sea and the Davis Strait.

On seismic data offshore South-West Greenland the Cretaceous sedimentary package is up to 6 sec. thick, roughly corresponding to 9 km of sediments. Well data and interpretation of seismic data from the continental shelves flanking the Labrador Sea indicate that sedimentation began in Barremian-Aptian, and that an important unconformity occurs at the base of a Cenomanian/Turonian-Mastrichtian mudstone unit. During the earliest phase of rifting Barremian-Albian fluvio-deltaic and shallow marine sediments (Atane Fm. onshore West Greenland and L. Bjarni Fm. on the Labrador Shelf) were deposited in the rift basins.

Mid Cretaceous inter rift period

During Albian differential subsidence decreased and was replaced by a more uniform subsidence caused by a thermal contraction of the continental crust. During the earliest Late Cretaceous (end of Cenomian or early Turonian) the structural highs along the sedimentary basins became less pronounced. Initial non-marine sediments are followed by dark marine mudstones, and a distinct Tertiary/Upper Maastrichtian unconformity is present.

Late Cretaceous-Early Paleocene rift

A late phase of extension is interpreted in southern West Greenland (Chalmers et al., 1993) and in the Baffin Bay area (Hamann & Whittaker, 1994). As documented in outcrops in West Greenland pronounced rifting has taken place in Late Maastrichtian and again after extrusion of Upper Paleocene basalts (Rosenkrantz & Pulvertaft, 1969; Dam & Sønderholm, 1994).

On the Canadian side of Baffin Bay there are unconformities between the Lower Tertiary and underlying Cretaceous both at Cape Dyer (Burden & Langille, 1991) and the Eclipse Trough (Miall et al., 1980). In the Southern West Greenland shelf area the second phase of rifting is believed to have taken place largely in the Early Paleocene, whereas in Melville Bay renewed rifting may have begun in the Late Cretaceous (fig.4 & 8).

End of late rift phase -drift phase

Towards the end of the rift phase strike-slip movements affected the area leading to the development of anticlines in synrift sequences. These movements occurred near the end of the first phase of sea floor spreading in the Labrador Sea (anomaly 24R; Late Paleocene) and followed the extrusion of the West Greenland Plateau basalts.

The crests of anticlines were eroded prior to the deposition of post-rift, drift-phase sediments. The anticlines are widely scattered and difficult to correlate between the widespaced seismic lines.

In the Central West Greenland and at Cape Dyer the sedimentary sections are overlain by very thick picritic and basaltic lavas. The volcanism started in Late Danian, corresponding to sea floor spreading anomaly 27R (Piasecki et al., 1992), which is when the earliest oceanic crust is thought to have been formed in the Labrador Sea (Chalmers, 1991; Chalmers & Laursen, 1995). The youngest basalts known are believed to be Late Paleocene, corresponding to anomaly 25N. 

Drift phase

Rifting and volcanisem were followed by a relatively quiet period of thermal subsidence, with less active extensional faulting gradually dying out towards the end of this drift phase. This period of faulting was controlled by strike-slip movements related to the oblique spreading of Baffin Bay. The direction of sea floor spreading in Baffin Bay and the Labrador Sea was roughly NNE-SSW.

Early Eocene marine and delta front deposits are known to have transgressed the southern part of the area and are described from Hellefisk-1 (Rolle, 1985). Deposition following the latest phase of rifting is interpreted from seismic data to have taken place in a series of restricted basins, controlled by extension or strike-slip movements. Evidence for strike-slip movements along faults can be seen on seismic lines north of Hellefisk-1. Here two major but narrow grabens extend north-south and NNE-SSW, the latter continuing into the Itilli Fault Zone onshore Nuussuaq. Shale diapirs and folds trending NW-SE seen immediately north and south of plateau basalts were also formed during this period.

Post-drift and late uplift

Both the seismic data offshore West Greenland and exposed sections onshore West Greenland indicate that there was a period of late uplift and erosion. The timing of this episode appears to be post thermal subsidence of the continental shelf. There is also evidence from the Labrador Sea and south-east Baffin Island that a high relief was established in the onshore areas in the Late Oligocene, and that uplift was renewed in Late Miocene (Trettin, 1991). An indication of minimum post-Paleocene uplift onshore West Greenland is provided by occurrence of Early Paleocene marine mudstones at about 1000 m above sea level. The western half of the offshore area, however, does not appear to have been affected by this uplift and is now at the maximum depth of burial

A third major regional unconformaty is of Lower Oligocene age. This is interpreted in both the Labrador Sea and Baffin Bay to represent the end of the sea floor spreading.

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