ABSTRACT

Stratigraphic data from exploratory wells on the Labrador Shelf permit an integrated interpretation to be made of two important subsurface features of the Labrador margin revealed by multichannel reflection seismic surveys. Firstly, a strong reflector buried deep beneath the slope and rise off northern Labrador is interpreted to represent an unconformity correlative with the Early Cretaceous unconformity beneath the continental shelf to the south. Secondly, a tentative Late Miocene age has been determined for a buried erosional surface represented by irregular seismic reflectors on the Labrador Shelf.

These interpretations conflict with existing plate-tectonic models of the Labrador Sea region. The unconformity beneath the slope and rise off northern Labrador indicates that continental crust extends into a region that previously has been defined as oceanic on the basis of magnetic, gravity, and refraction seismic measurements interpreted in a plate-tectonic mode. The Late Miocene erosional surface on the shelf serves as a marker to illustrate the style of subsidence of the Labrador continental margin in Late Cenozoic time; it is apparent that this subsidence has not proceeded as predicted by conventional plate-tectonic models.

These conflicts pose such questions concerning basic precepts of plate-tectonic theory as the source of linear magnetic anomalies on the seafloor, and the validity of refraction seismic criteria as a basis for defining crust as continental or oceanic. As the Labrador Sea is considered a 'typical' ocean, the problems with plate-tectonic models in this region may exist in other oceanic areas. For the Labrador margin, these conflicts with plate-tectonic models have important implications regarding the occurrence and extent of 'basement' rocks with potential for trapping or generating hydrocarbons.