Abstract

The Petrel Limestone is a consistent geological and geophysical marker unit of Cretaceous age which is present in the Grand Banks area, south of Newfoundland, on the eastern North American continental shelf.

The Petrel Limestone most commonly consists of microcrystalline limestone of an apparent outer-shelf environment of deposition. It is locally more than 400 ft. (122 m) thick. The limestone overlies the marginal to shallow marine “Eider Unit” sands or locally the “Heron Limestone” and is overlain by an unnamed marine shale section.

As determined by high magnifications provided by the scanning electron microscope, the primary constituent of the limestone is coccolith plates derived from the exoskeletons of calcareous algae. While wireline logs commonly indicate the presence of substantial porosity in this limestone unit, examination by binocular microscope indicates nearly an entire lack of visual porosity. Analogy is drawn with the Danian “chalk” reservoirs of the North Sea which derive productive capacity primarily from fracturing within a similar limestone sequence and it is suggested that the Petrel Limestone could provide potential for hydrocarbon accumulation.