The southern West Greenland continental margin: rifting history, basin development, and petroleum potential

Abstract

The development of the continental margin of West Greenland is closely related to the processes that led to the opening of the Labrador Sea. The opening of the Labrador Sea began in the Early Paleocene (anomaly 27N), and not in the Late Cretaceous as previously supposed. Modelling of magnetic data and new interpretation of seismic data indicate that a large area previously regarded as underlain by oceanic crust is in fact underlain by block-faulted continental crust overlain by syn- and post-rift sedimentary sequences. The ocean–continent transition is now placed 100–150 km southwest of the foot of the continental slope instead of at the foot of this slope. Rifting in the Labrador Sea area began, however, in the Early Cretaceous. The earliest sediments are the syn-rift lower and upper members of the Bjarni Formation on the Labrador shelf and their likely equivalents, the pre- to syn-rift Kitsissut and Appat sequences on the Greenland margin. The age of these units is Barremian (or older) to Albian. The units are overlain by widespread mudstone-dominated units, the Markland Formation of the Labrador shelf and the Kangeq Sequence on the Greenland margin. The former is Cenomanian–Danian in age. By analogy the base of the Kangeq Sequence is probably Cenomanian (or Turonian), while the top is known from well ties to be at the Cretaceous–Tertiary boundary. Rifting was subdued during deposition of these mudstone units. Rifting was renewed in the Early Paleocene, and mudstones, siltstones and very fine sandstones were deposited. With the initiation of sea-floor spreading there was considerable igneous activity at the ocean–continent transition, as well as in the onshore area where picrites followed by plagioclase-porphyritic basalts were erupted. After the end of the Paleocene there was little rifting in the region, but compressional structures were formed locally as a response to transpression related to strike-slip movements that transferred plate motion from the Labrador Sea to Baffin Bay. A marked Early Oligocene unconformity separates the syn-drift Paleocene–Eocene succession from the post-drift middle Oligocene–Quaternary sediments. Sediments deposited since the Paleocene are dominated by sands. The main hydrocarbon play types offshore West Greenland are related to tilted fault blocks. Source rocks are anticipated near the base of the Kangeq Sequence, which is also the seal, and reservoirs are sandstones in the Appat and Kitsissut sequences. These two sequences were not reached by any of the exploration wells drilled in the 1970s.