The Mesozoic-Cenozoic History Of The Northeastern Margin Of North America
Authors: Wade John A. 
Published: October 2008

Late Triassic-Early Jurassic continental clastics and evaporites were deposited in northeast- southwest trending taphrogenic basins over an Early Paleozoic basement of deformed metasedimentary and plutonic rocks. These extend from the eastern Grand Banks to Georges Bank, with similar facies occurring in southern Portugal and western Morocco. Following the initiation of seafloor spreading between the African and the European North American continental plates, a normal marine regime was established and along the northwestern margin of the developing Atlantic Ocean a thick shelf edge carbonate bank developed simultaneously with back bank clastics and deeper water shales. A tectonic pulse, associated with the separation of the European Plate from the North American Plate in the Late Jurassic-Early Cretaceous, resulted in the uplift of a large salient southeast of Newfoundland. At the same time a regional regression resulted in the deposition of a series of deltaic complexes along the northeastern margin of North America, one of the largest of which is in the Scotian Basin. During the Late Cretaceous eustatic rise of sea level, a thick transgressive clastic wedge was deposited along the margin. The transgression culminated in the Campanian-Maas-trichtian with widespread deposition of coccolith chalk. Following this a predominately regressive cycle deposited-an upward coarsening, prograding clastic sequence which constructed the present day continental shelves.

Several small oil and gas discoveries nave been made in the Upper Jurassic to Upper Cretaceous clastic wedge in the vicinity of Sable Island. In most of these, trapping appears to be related to salt-tectonics. Geochemistry indicates a general thermal immaturity of the section penetrated but raises the possibility of hydrocarbon source from deeper untested beds.

INTRODUCTION

The purpose of this paper is to review the geologic history of the continental margin basins of Atlantic Canada, and to describe the stratigraphy and structure of the Mesozoic and Cenozoic formations they contain. The portion of the Atlantic continental margin described encompasses an area of approximately 600,000 square kilometres. It extends from about the equidistance line between Canada and the United States, which crosses the northeastern part of Georges Bank, to approximately 48°N east of Newfoundland and from the edge of coastal plain rocks to the upper continental rise (Figure 1). Basic data for the study are from two main sources. Firstly some 18000 km of reflection seismic profiles which were used to provide a regional structural framework, establish sediment distribution patterns, timing of tectonic events, etc. Secondly, well history reports from some 100 exploratory wells and the study of ditch cuttings and cores from selected wells were used to provide stratigraphic detail.

REGIONAL GEOLOGY

Tectonic Elements

The tectonic subdivisions of the Atlantic continental margin were described by Wade (1974) and Jansa and Wade (1975) and have been modified only slightly since that time. Briefly the Mesozoic/Cenozoic sedimentary basins of eastern Canada on lap the southern flank of the Appalachian Orogen. The tectonic elements are delineated by basin fill and basement configuration (Figure 2).