Abstract

Labrador Basin is an immense structural and topographic trough with a broad, deep oceanic basement floor of Late Cretaceous to middle Tertiary age. The basin floor is separated from high-standing North American and Greenland continental domains of old Precambrian crystalline rocks by the cratonic monocline, a narrow zone of variably extended, rifted, subsided cratonic basement.

Brittle, upper lithospheric extension of the cratonic monocline was achieved across an articulated array of large and small basement normal faults. Some of these faults may have been reactivated Precambrian-age faults of other dynamic origin. The cratonic monocline contains unconnected, fault-bounded wedges of Lower Cretaceous and lower Upper Cretaceous, syn-rift terrigenous clastics, and some basalt.

A very thick, post-rift, seaward-prograding, continental terrace prism of Upper Cretaceous and Cenozoic terrigenous clastics oversteps the cratonic monocline in both landward and seaward directions. The terrace prism is divisible into two parts: an Upper Cretaceous - Upper Eocene megasequence deposited during active sea-floor generation in central Labrador Basin; and an Oligocene - Quaternary megasequence deposited after ocean floor spreading. The dominantly fine grained clastics of the drift-phase megasequence were probably derived from widespread erosion of central Canada. Much coarser clastics of the upper part of the post-drift megasequence were eroded from basement rocks of the Labrador margin during and following robust late Tertiary coastal uplift.

Some segments of the shelf extended slightly in middle and late Tertiary, prompting detachment and structural adjustment within the terrace prism cover rocks.